Wet compression versus dry compression in heat pumps working with pure refrigerants or non-azeotropic mixtures for different heating applications
- Vorster, Paul Philip Jacobus
- Authors: Vorster, Paul Philip Jacobus
- Date: 2012-09-12
- Subjects: Heat pumps , Refrigerants
- Type: Thesis
- Identifier: uj:10256 , http://hdl.handle.net/10210/7627
- Description: M.Ing. , Wet compression versus dry compression in heat pumps working with pure refrigerants or nonazeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 nonazeotropic binary mixtures at different concentrations are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants were analysed for three different heating applications found in practice: the heating of swimming pool water, heating air for interior space heating, and the heating of water for domestic use. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better heating COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves, consistently produce higher heating COP's when wet compression is used. However, their heating capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the few exceptions that do exist, some manage to produce very high COPh's while retaining competitive heating capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered
- Full Text:
- Authors: Vorster, Paul Philip Jacobus
- Date: 2012-09-12
- Subjects: Heat pumps , Refrigerants
- Type: Thesis
- Identifier: uj:10256 , http://hdl.handle.net/10210/7627
- Description: M.Ing. , Wet compression versus dry compression in heat pumps working with pure refrigerants or nonazeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 nonazeotropic binary mixtures at different concentrations are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants were analysed for three different heating applications found in practice: the heating of swimming pool water, heating air for interior space heating, and the heating of water for domestic use. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better heating COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves, consistently produce higher heating COP's when wet compression is used. However, their heating capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the few exceptions that do exist, some manage to produce very high COPh's while retaining competitive heating capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered
- Full Text:
The design, optimization and experimental verification of an accumulator heat exchanger
- Authors: Van der Vyver, Stefanus
- Date: 2012-09-11
- Subjects: Heat exchangers - Design
- Type: Mini-Dissertation
- Identifier: uj:10059 , http://hdl.handle.net/10210/7447
- Description: M.Ing. , In spite of recent developments on accumulator heat exchangers for small air conditioning systems, no models exist that can be used for their design. In this paper a simple design methodology is presented that can be used for the design of an accumulator heat exchanger. An accumulator heat exchanger was designed and built using the refrigerant R134a. The application was for a transport refrigeration system using the refrigerant R134a. The accumulator heat exchanger was tested experimentally and compared to a similar system without an accumulator heat exchanger. Based on the experimental results, it was concluded that the design methodology was accurate (since the actual heat transfer rates were within 10% of the calculated values) and that the use of an accumulator heat exchanger improves refrigeration capacity and energy efficiency.
- Full Text:
- Authors: Van der Vyver, Stefanus
- Date: 2012-09-11
- Subjects: Heat exchangers - Design
- Type: Mini-Dissertation
- Identifier: uj:10059 , http://hdl.handle.net/10210/7447
- Description: M.Ing. , In spite of recent developments on accumulator heat exchangers for small air conditioning systems, no models exist that can be used for their design. In this paper a simple design methodology is presented that can be used for the design of an accumulator heat exchanger. An accumulator heat exchanger was designed and built using the refrigerant R134a. The application was for a transport refrigeration system using the refrigerant R134a. The accumulator heat exchanger was tested experimentally and compared to a similar system without an accumulator heat exchanger. Based on the experimental results, it was concluded that the design methodology was accurate (since the actual heat transfer rates were within 10% of the calculated values) and that the use of an accumulator heat exchanger improves refrigeration capacity and energy efficiency.
- Full Text:
Hot water consumption in South Africa
- Authors: Muya, T.M.
- Date: 2012-09-10
- Subjects: Hot-water supply -- South Africa , Water consumption -- South Africa , Water use -- South Africa
- Type: Thesis
- Identifier: uj:9864 , http://hdl.handle.net/10210/7265
- Description: M.Ing. , A one-year investigation on hot water consumption was conducted in South African developed and developing communities of Johannesburg to determine the personal and household average daily consumption of hot water as well as the average hourly (in summer and in winter) and monthly patterns. The motivation for this research project was to provide to engineers and water heaters manufacturers reliable experimental data on hot water consumption from various categories of dwellings. The existing sources of information in South Africa being extremely limited and results of estimations. The necessary information was collected from hourly and monthly measurements taken by monitoring hot water systems in different dwellings including, houses (300 units), traditional houses (90 units), shacks (200 units), apartments (123 units), townhouses (90 units). For the purpose of this study, the selected (not statistically) dwellings were classified into three categories, which are: high-density dwellings representing the developing communities, medium-density and low-density dwellings which represent the developed communities. The results of measurements show that, in general, people living in developed communities (low-density dwellings) use at least 1.4 times more hot water than those of developing communities (high-density dwellings). The patterns of hot water consumption have been determined for monthly and hourly consumption. The former is divided in four sections: summer weekdays, winter weekdays, summer weekends and winter weekends. The differences between sections are the specific times of peaks and the consumption. The results of this study should be of great assistance to engineers and water heaters designers in analysing existing systems for performance improvement, and in sizing more efficient and suitable systems to South African use.
- Full Text:
- Authors: Muya, T.M.
- Date: 2012-09-10
- Subjects: Hot-water supply -- South Africa , Water consumption -- South Africa , Water use -- South Africa
- Type: Thesis
- Identifier: uj:9864 , http://hdl.handle.net/10210/7265
- Description: M.Ing. , A one-year investigation on hot water consumption was conducted in South African developed and developing communities of Johannesburg to determine the personal and household average daily consumption of hot water as well as the average hourly (in summer and in winter) and monthly patterns. The motivation for this research project was to provide to engineers and water heaters manufacturers reliable experimental data on hot water consumption from various categories of dwellings. The existing sources of information in South Africa being extremely limited and results of estimations. The necessary information was collected from hourly and monthly measurements taken by monitoring hot water systems in different dwellings including, houses (300 units), traditional houses (90 units), shacks (200 units), apartments (123 units), townhouses (90 units). For the purpose of this study, the selected (not statistically) dwellings were classified into three categories, which are: high-density dwellings representing the developing communities, medium-density and low-density dwellings which represent the developed communities. The results of measurements show that, in general, people living in developed communities (low-density dwellings) use at least 1.4 times more hot water than those of developing communities (high-density dwellings). The patterns of hot water consumption have been determined for monthly and hourly consumption. The former is divided in four sections: summer weekdays, winter weekdays, summer weekends and winter weekends. The differences between sections are the specific times of peaks and the consumption. The results of this study should be of great assistance to engineers and water heaters designers in analysing existing systems for performance improvement, and in sizing more efficient and suitable systems to South African use.
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Optimal control versus conventional control strategies for ice-based thermal storage
- Authors: Maluleke, Archibald
- Date: 2012-09-10
- Subjects: Heat storage devices -- Automatic control
- Type: Thesis
- Identifier: uj:9905 , http://hdl.handle.net/10210/7304
- Description: M.Ing. , Ice storage systems are used to store thermal energy in the form of ice build-up inside storage tanks. During off peak hours, the chiller is used to charge up the storage tank until it is full. During on peak hours, the storage is discharged to meet a certain fraction of the building cooling load. The control strategy employed determines the extent to which the storage compensates the chiller and visa versa. Given the way in which electricity rates are structured, ice storage systems become an effective energy management strategy. The objective of the study is to compare energy savings derived by using conventional control strategies versus optimal control. Conventional control strategies can be classified as chiller priority control, constant proportion control and storage priority control. In chiller priority control, the chiller meets the cooling load subject to a pre-set limit not being exceeded. Should the limit be exceeded, the remaining cooling load (at each time horizon) is compensated for by the storage. In constant proportion control, both the storage and chiller meets a constant proportion of the cooling load. Storage priority control attempts to discharge as much of the storage as possible, such that at the end of the planning horizon, the ice build up in the storage tank is just depleted. Optimal control employs dynamic programming to ensure that the integrated cost of energy, during the entire planning horizon, is minimal. A steady state ice storage plant model for analysing the performance of the control strategies is presented. The model computes the inlet and outlet temperatures into the various components of the air-conditioning plant, being the air-handling units, heat exchanger, ice storage tanks and chiller. The maximal possible discharge and charging rate at each time period (for the different control strategies) is determined using the model. Given the state of charge of the ice storage tank at each time period, it is then possible to calculate chiller power consumption. The power consumed by fans, fan coil units and pumps (in the air-conditioning plant) has not been calculated in the present analysis, however, the model can easily be extended to include such calculations. The ice storage plant model, enabled simulations of the different control strategies to be carried out over building cooling load profiles for summer and winter. Based on a 24-hour planning horizon, optimal control is found to be optimal and the only consistently performing strategy for all seasons. For the 5000 kWh ice storage plant investigated, optimal control yielded 25% energy savings in June and 12% in January, amounting to a potential of R 11 000 per month. Chiller priority control was near optimal in January but consumed 25% more energy than the base case (without storage) in June. Constant proportion control was optimal in January but poorer in June. Storage priority control is found to be optimal in June but the lowest performer in January. The drawback of optimal control and storage priority control, however, is that they require prediction of future cooling loads. The variance when using auto-regressive neural network to predict the load is expected to be in the region of 2% and thus considered acceptable. Chiller priority control and constant proportion control are instantaneous and simple to implement hence their popularity.
- Full Text:
- Authors: Maluleke, Archibald
- Date: 2012-09-10
- Subjects: Heat storage devices -- Automatic control
- Type: Thesis
- Identifier: uj:9905 , http://hdl.handle.net/10210/7304
- Description: M.Ing. , Ice storage systems are used to store thermal energy in the form of ice build-up inside storage tanks. During off peak hours, the chiller is used to charge up the storage tank until it is full. During on peak hours, the storage is discharged to meet a certain fraction of the building cooling load. The control strategy employed determines the extent to which the storage compensates the chiller and visa versa. Given the way in which electricity rates are structured, ice storage systems become an effective energy management strategy. The objective of the study is to compare energy savings derived by using conventional control strategies versus optimal control. Conventional control strategies can be classified as chiller priority control, constant proportion control and storage priority control. In chiller priority control, the chiller meets the cooling load subject to a pre-set limit not being exceeded. Should the limit be exceeded, the remaining cooling load (at each time horizon) is compensated for by the storage. In constant proportion control, both the storage and chiller meets a constant proportion of the cooling load. Storage priority control attempts to discharge as much of the storage as possible, such that at the end of the planning horizon, the ice build up in the storage tank is just depleted. Optimal control employs dynamic programming to ensure that the integrated cost of energy, during the entire planning horizon, is minimal. A steady state ice storage plant model for analysing the performance of the control strategies is presented. The model computes the inlet and outlet temperatures into the various components of the air-conditioning plant, being the air-handling units, heat exchanger, ice storage tanks and chiller. The maximal possible discharge and charging rate at each time period (for the different control strategies) is determined using the model. Given the state of charge of the ice storage tank at each time period, it is then possible to calculate chiller power consumption. The power consumed by fans, fan coil units and pumps (in the air-conditioning plant) has not been calculated in the present analysis, however, the model can easily be extended to include such calculations. The ice storage plant model, enabled simulations of the different control strategies to be carried out over building cooling load profiles for summer and winter. Based on a 24-hour planning horizon, optimal control is found to be optimal and the only consistently performing strategy for all seasons. For the 5000 kWh ice storage plant investigated, optimal control yielded 25% energy savings in June and 12% in January, amounting to a potential of R 11 000 per month. Chiller priority control was near optimal in January but consumed 25% more energy than the base case (without storage) in June. Constant proportion control was optimal in January but poorer in June. Storage priority control is found to be optimal in June but the lowest performer in January. The drawback of optimal control and storage priority control, however, is that they require prediction of future cooling loads. The variance when using auto-regressive neural network to predict the load is expected to be in the region of 2% and thus considered acceptable. Chiller priority control and constant proportion control are instantaneous and simple to implement hence their popularity.
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Heat transfer coefficients in concentric annuli
- Authors: Dirker, Jaco
- Date: 2012-09-05
- Subjects: Nusselt number , Heat -- Transmission
- Type: Thesis
- Identifier: uj:9597 , http://hdl.handle.net/10210/7019
- Description: M.Ing , The geometric shape of a passage's cross-section has an effect on its convective heat transfer capabilities. For concentric annuli, as cross section, the diameter ratio of the annular space plays an important role. The purpose of this investigation was to find a . correlation that will accurately predict heat transfer coefficients at the inner wall of smooth concentric annuli for the flow of water. Experiments were conducted on water under turbulent flow conditions for a wide range of diameter ratios. The Wilson plot method was used to determine the heat transfer coefficients from which a correlation was developed that could be used to predict the heat transfer coefficients. It was found that the correlation predicted Nusselt numbers accurately within 3% of measured values for diameter ratios between a = 1.7 and a = 5.1 and a Reynolds numbers range of 4 000 to 30 000.
- Full Text:
- Authors: Dirker, Jaco
- Date: 2012-09-05
- Subjects: Nusselt number , Heat -- Transmission
- Type: Thesis
- Identifier: uj:9597 , http://hdl.handle.net/10210/7019
- Description: M.Ing , The geometric shape of a passage's cross-section has an effect on its convective heat transfer capabilities. For concentric annuli, as cross section, the diameter ratio of the annular space plays an important role. The purpose of this investigation was to find a . correlation that will accurately predict heat transfer coefficients at the inner wall of smooth concentric annuli for the flow of water. Experiments were conducted on water under turbulent flow conditions for a wide range of diameter ratios. The Wilson plot method was used to determine the heat transfer coefficients from which a correlation was developed that could be used to predict the heat transfer coefficients. It was found that the correlation predicted Nusselt numbers accurately within 3% of measured values for diameter ratios between a = 1.7 and a = 5.1 and a Reynolds numbers range of 4 000 to 30 000.
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A steady-state model for the high-pressure side of a unitary air-conditioning unit
- Authors: Petit, Pascale Jacqueline
- Date: 2012-08-27
- Subjects: Air conditioning - Mathematical models
- Type: Thesis
- Identifier: uj:3184 , http://hdl.handle.net/10210/6599
- Description: M.Ing. , A steady-state model was developed to predict the performance of the highpressure side' of vapour-compression air-conditioning systems. The model consists of two segments; the compressor model and condenser model. The compressor model consists of a single empirical equation, for reciprocating compressors, operating with R-22, and having a cooling capacity from 2.6 to 3.5 kW. An important advantage of the approach is that the compressor performance indexes are based on operating conditions. The condenser model displays an exact method to determine physical dimensions of heat exchangers, and a simple, accurate manner to calculate the heat transfer variables. The correctness of the condensing temperature is obtained by an iterative procedure, using terms from both the compressor and condenser studies. The feasibility of the proposed model is demonstrated via a comparison with experimental data and a simulation study. Results indicate a good correlation between the mathematical model and its counterparts.
- Full Text:
- Authors: Petit, Pascale Jacqueline
- Date: 2012-08-27
- Subjects: Air conditioning - Mathematical models
- Type: Thesis
- Identifier: uj:3184 , http://hdl.handle.net/10210/6599
- Description: M.Ing. , A steady-state model was developed to predict the performance of the highpressure side' of vapour-compression air-conditioning systems. The model consists of two segments; the compressor model and condenser model. The compressor model consists of a single empirical equation, for reciprocating compressors, operating with R-22, and having a cooling capacity from 2.6 to 3.5 kW. An important advantage of the approach is that the compressor performance indexes are based on operating conditions. The condenser model displays an exact method to determine physical dimensions of heat exchangers, and a simple, accurate manner to calculate the heat transfer variables. The correctness of the condensing temperature is obtained by an iterative procedure, using terms from both the compressor and condenser studies. The feasibility of the proposed model is demonstrated via a comparison with experimental data and a simulation study. Results indicate a good correlation between the mathematical model and its counterparts.
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Average boiling heat transfer and pressure drop coefficients of R22/R142b in a helixaly coiled water heated tube-in-tube heat exchange
- Authors: Bukasa, Jean-Pierre M.
- Date: 2012-08-20
- Subjects: Heat exchangers -- Fluid dynamics , Heat -- Transmission , Refrigerants
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/371889 , uj:2734 , http://hdl.handle.net/10210/6175
- Description: M.Ing. , The two-phase heat transfer and pressure drop coefficients of pure R22, the mixtures 80% R22/20% R142b and 60% R22/40% R142b within a helix coiled tube-in-tube heat exchanger are presented in this study. Experimental data was presented in the form of average heat transfer coefficient and two-phase friction factor. Comparison of the experimental heat transfer coefficient with the predicted values obtained from the Jung, Murata and Thome methods confirms a good accuracy of these methods although they were developed for the straight tube-in-tube heat exchanger. The predicted two-phase friction factor values obtained from the Martinelli correlation deviates more than 50% from the experimental results for the three working fluids. This confirms that the Martinelli method is not accurate enough for the helix coiled tube-in-tube heat exchanger.
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- Authors: Bukasa, Jean-Pierre M.
- Date: 2012-08-20
- Subjects: Heat exchangers -- Fluid dynamics , Heat -- Transmission , Refrigerants
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/371889 , uj:2734 , http://hdl.handle.net/10210/6175
- Description: M.Ing. , The two-phase heat transfer and pressure drop coefficients of pure R22, the mixtures 80% R22/20% R142b and 60% R22/40% R142b within a helix coiled tube-in-tube heat exchanger are presented in this study. Experimental data was presented in the form of average heat transfer coefficient and two-phase friction factor. Comparison of the experimental heat transfer coefficient with the predicted values obtained from the Jung, Murata and Thome methods confirms a good accuracy of these methods although they were developed for the straight tube-in-tube heat exchanger. The predicted two-phase friction factor values obtained from the Martinelli correlation deviates more than 50% from the experimental results for the three working fluids. This confirms that the Martinelli method is not accurate enough for the helix coiled tube-in-tube heat exchanger.
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Condensation heat transfer and pressure drop coefficients of R22/R142b in a water cooled helicaly coiled tube-in-tube heat exchanger.
- Authors: Kebonte, Shiko A.
- Date: 2012-08-20
- Subjects: Heat exchangers - Fluid dynamics , Heat - Transmission , Refrigerants , Condensation
- Type: Thesis
- Identifier: uj:2741 , http://hdl.handle.net/10210/6181
- Description: M.Ing. , Heat transfer and pressure drop characteristics during in-tube condensation of nonazeotropic mixtures of R22/R142b in a smooth helically coiled copper tube with an inside diameter of 8.11 mm are investigated. The experimental results are compared with prediction from correlation. The coefficient of performance of.the heat pump built and used for experiments has been studied. The mass flux of the refrigerant was varied during the course of the experiments. At similar mass flow rate of fluids, the average heat transfer coefficients for mixtures were lower than those for pure refrigerant R22 used as reference for comparison. Also, the heat transfer coefficients of all the refrigerants increased with increasing mass flux.
- Full Text:
- Authors: Kebonte, Shiko A.
- Date: 2012-08-20
- Subjects: Heat exchangers - Fluid dynamics , Heat - Transmission , Refrigerants , Condensation
- Type: Thesis
- Identifier: uj:2741 , http://hdl.handle.net/10210/6181
- Description: M.Ing. , Heat transfer and pressure drop characteristics during in-tube condensation of nonazeotropic mixtures of R22/R142b in a smooth helically coiled copper tube with an inside diameter of 8.11 mm are investigated. The experimental results are compared with prediction from correlation. The coefficient of performance of.the heat pump built and used for experiments has been studied. The mass flux of the refrigerant was varied during the course of the experiments. At similar mass flow rate of fluids, the average heat transfer coefficients for mixtures were lower than those for pure refrigerant R22 used as reference for comparison. Also, the heat transfer coefficients of all the refrigerants increased with increasing mass flux.
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Wet compression versus dry compression in refrigeration cycles working with pure or non-azeotropic refrigerant mixtures for air-conditioners
- Authors: Swanepoel, Wayne
- Date: 2012-08-17
- Subjects: Air conditioning , Refrigerants
- Type: Thesis
- Identifier: uj:2652 , http://hdl.handle.net/10210/6097
- Description: M.Ing. , Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.
- Full Text:
- Authors: Swanepoel, Wayne
- Date: 2012-08-17
- Subjects: Air conditioning , Refrigerants
- Type: Thesis
- Identifier: uj:2652 , http://hdl.handle.net/10210/6097
- Description: M.Ing. , Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.
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Evaluation of a permanent magnet to decrease scale formation in a tube
- Authors: Da Veiga, Reinaldo
- Date: 2012-08-15
- Subjects: Descaling , Incrustations , Water- Purification
- Type: Thesis
- Identifier: uj:9354 , http://hdl.handle.net/10210/5793
- Description: M.Ing. , Fouling and more specifically scaling is one of the most discussed and not yet well understood problems facing engineers. Scale formation which has enormous economic and environmental consequences does not only influence heat transfer characteristics and pressure drop through tubes, but influence the volumetric flow rate as well. To solve this problem Physical Water Treatment (PWT) devices have been developed which reportedly reduce scale formation. The efficiency of PWT devices is a controversial subject and many contradictions exits in the claimed effect. Researchers have been trying to prove the efficiency of PWT devices but in most cases the results are typically characterised by low reproducibility. An experimental measuring technique is thus required to measure scale formation and the influence PWT devices has on scaling. This technique must also produce reproducible results to clarify the questions surrounding PWT devices. This thesis is an experimental investigation in which an experimental setup and measuring technique is developed. It is used to evaluate a permanent magnet for the decrease of scale formation in tubes. The volumetric flow rate is used as the indicator of scale formation, which relies on the basic principle that the friction pressure drop increases if scaling takes place. The volumetric flow rate is monitored by measuring the time necessary to fill a container of known volume. The test section consists of three soft drawn copper tubes in which water with a velocity of ± 2 m/s flows. One of the tubes is used to evaluate the PWT device and the other two tubes are used as a control. The water temperature is kept at 53°C. The experiments are done in five phases in which the PWT device is placed onto one of the tubes in phase four and removed in phase five. It follows from the results obtained that a very sensitive experimental setup was designed and built which can be used to evaluate the efficiency of PWT devices. It follows from the variation in time necessary to fill the container in phase four and five that a clear conclusion can not be made. More experiments must be done in which reproducible results are obtained.
- Full Text:
- Authors: Da Veiga, Reinaldo
- Date: 2012-08-15
- Subjects: Descaling , Incrustations , Water- Purification
- Type: Thesis
- Identifier: uj:9354 , http://hdl.handle.net/10210/5793
- Description: M.Ing. , Fouling and more specifically scaling is one of the most discussed and not yet well understood problems facing engineers. Scale formation which has enormous economic and environmental consequences does not only influence heat transfer characteristics and pressure drop through tubes, but influence the volumetric flow rate as well. To solve this problem Physical Water Treatment (PWT) devices have been developed which reportedly reduce scale formation. The efficiency of PWT devices is a controversial subject and many contradictions exits in the claimed effect. Researchers have been trying to prove the efficiency of PWT devices but in most cases the results are typically characterised by low reproducibility. An experimental measuring technique is thus required to measure scale formation and the influence PWT devices has on scaling. This technique must also produce reproducible results to clarify the questions surrounding PWT devices. This thesis is an experimental investigation in which an experimental setup and measuring technique is developed. It is used to evaluate a permanent magnet for the decrease of scale formation in tubes. The volumetric flow rate is used as the indicator of scale formation, which relies on the basic principle that the friction pressure drop increases if scaling takes place. The volumetric flow rate is monitored by measuring the time necessary to fill a container of known volume. The test section consists of three soft drawn copper tubes in which water with a velocity of ± 2 m/s flows. One of the tubes is used to evaluate the PWT device and the other two tubes are used as a control. The water temperature is kept at 53°C. The experiments are done in five phases in which the PWT device is placed onto one of the tubes in phase four and removed in phase five. It follows from the results obtained that a very sensitive experimental setup was designed and built which can be used to evaluate the efficiency of PWT devices. It follows from the variation in time necessary to fill the container in phase four and five that a clear conclusion can not be made. More experiments must be done in which reproducible results are obtained.
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A performance comparison between an air-source and a ground-source reversible heat pump
- De Swardt, Christiaan Alexander
- Authors: De Swardt, Christiaan Alexander
- Date: 2011-11-23
- Subjects: Heat pumps
- Type: Thesis
- Identifier: uj:1722 , http://hdl.handle.net/10210/4072
- Description: M.Ing. , In this study the performance of a reversible ground-source heat pump, coupled to a municipal water reticulation system, is compared experimentally and with simulations with a conventional air-source heat pump for space cooling and heating. A typical municipal water reticulation system comprises hundreds of kilometres of pipes designed in loops that will ensure adequate circulation of the water. This results in a substantial heat exchanger with great potential. Indirect heat transfer occurs between the refrigerant and ground via the municipal water reticulation system that acts as the water-to-ground heat exchanger. The experimental and simulated comparisons of the ground-source system to the air-source system are conducted in both the cooling and heating cycles. Climatalogical statistics are used to calculate the capacities and coefficients of performance of the ground-source and air-source heat pumps. Results obtained from measurements and simulations indicate that the utilisation of municipal water reticulation systems as a heat source/sink is a viable method of optimising energy usage in the air-conditioning industry, especially when used in the heating mode.
- Full Text:
- Authors: De Swardt, Christiaan Alexander
- Date: 2011-11-23
- Subjects: Heat pumps
- Type: Thesis
- Identifier: uj:1722 , http://hdl.handle.net/10210/4072
- Description: M.Ing. , In this study the performance of a reversible ground-source heat pump, coupled to a municipal water reticulation system, is compared experimentally and with simulations with a conventional air-source heat pump for space cooling and heating. A typical municipal water reticulation system comprises hundreds of kilometres of pipes designed in loops that will ensure adequate circulation of the water. This results in a substantial heat exchanger with great potential. Indirect heat transfer occurs between the refrigerant and ground via the municipal water reticulation system that acts as the water-to-ground heat exchanger. The experimental and simulated comparisons of the ground-source system to the air-source system are conducted in both the cooling and heating cycles. Climatalogical statistics are used to calculate the capacities and coefficients of performance of the ground-source and air-source heat pumps. Results obtained from measurements and simulations indicate that the utilisation of municipal water reticulation systems as a heat source/sink is a viable method of optimising energy usage in the air-conditioning industry, especially when used in the heating mode.
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Heat transfer and pressure drop characteristics of angled spiralling tape inserts in a heat exchanger annulus
- Authors: Coetzee, Hennie
- Date: 2011-11-21
- Subjects: Heat exchangers , Heat transmission
- Type: Thesis
- Identifier: uj:1716 , http://hdl.handle.net/10210/4059
- Description: M.Ing. , There are different types of heat transfer enhancement techniques that can be used, but some of these techniques are expensive and cannot be afforded by small manufacturing firms. An easy and affordable technique considered in this paper has an angled spiralling tape inserted into the annulus of a tube-in-tube heat exchanger. The purpose of this paper was to determine the single phase heat transfer and pressure drop characteristics in the annulus. Experimental measurements were taken on four set-ups; a normal tube-in-tube heat exchanger used as a reference and three heat exchangers with different angled spiralling tape inserts. From the results correlations were developed that can be used to predict the heat transfer and pressure drop characteristics. It was concluded that the angled spiralling tape inserts resulted in an increase in the heat transfer and pressure drop characteristics as can be expected.
- Full Text:
- Authors: Coetzee, Hennie
- Date: 2011-11-21
- Subjects: Heat exchangers , Heat transmission
- Type: Thesis
- Identifier: uj:1716 , http://hdl.handle.net/10210/4059
- Description: M.Ing. , There are different types of heat transfer enhancement techniques that can be used, but some of these techniques are expensive and cannot be afforded by small manufacturing firms. An easy and affordable technique considered in this paper has an angled spiralling tape inserted into the annulus of a tube-in-tube heat exchanger. The purpose of this paper was to determine the single phase heat transfer and pressure drop characteristics in the annulus. Experimental measurements were taken on four set-ups; a normal tube-in-tube heat exchanger used as a reference and three heat exchangers with different angled spiralling tape inserts. From the results correlations were developed that can be used to predict the heat transfer and pressure drop characteristics. It was concluded that the angled spiralling tape inserts resulted in an increase in the heat transfer and pressure drop characteristics as can be expected.
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Heat transfer performance during condensation inside spiralled micro-fin tubes
- Authors: Bukasa, Jean-Pierre Muenja
- Date: 2011-11-21
- Subjects: Heat transmission , Heat exchangers , Condensation
- Type: Thesis
- Identifier: uj:1713 , http://hdl.handle.net/10210/4056
- Description: D.Ing. , Many studies have been conducted in order to establish the respective influence of geometric parameters such as fins number, fin shape (apex angle), spiral angle, fin height, fin pitch etc. on the condensation heat transfer performance of the spiralled micro-fin tubes. However, the effect of the spiral angle could not be clearly established in those investigations, because other geometric parameters affecting the heat transfer performance such as fin height, fin thickness, apex angle were also varied. The influence of the spiral angle on the heat transfer performance during condensation inside spiralled micro-fin tubes having all other geometric parameters the same was experimentally investigated in this study. A new experimental-based predictive correlation was developed for practical design of this specific class of micro-fin tubes. Tests were conducted for condensation of R22, R134a and R407c inside a smooth and three micro-fin tubes having spiral angles of 10, 18 and 37 degrees. Experimental results indicated a heat transfer augmentation due to heat transfer area increase. As the spiral angle was increased, the heat transfer area increased causing a substantial heat transfer augmentation. Condensation inside the 10° spiralled micro-fins produced a heat transfer augmentation of about 170% for a heat transfer area increase of 1.87 when compared to condensation in ~he correspondent smooth tube while the 18° spiralled " micro-fins produced an augmentation of 180% for a heat transfer area increase of 1.94. The 37° spiralled micro-fins produced the highest enhancement of 220% for a heat transfer area increase of 2.13. Additional heat transfer augmentation was produced by: (a) the turbulence in the condensate film due to the presence of spiralled micro-fins (stronger effect at lower mass velocities and vapor qualities) and (b) the effect of surface tension forces (at higher vapor qualities). The proposed new correlation predicted the majority of experimental results of the present study within a deviation zone of ± 20 percent.
- Full Text:
- Authors: Bukasa, Jean-Pierre Muenja
- Date: 2011-11-21
- Subjects: Heat transmission , Heat exchangers , Condensation
- Type: Thesis
- Identifier: uj:1713 , http://hdl.handle.net/10210/4056
- Description: D.Ing. , Many studies have been conducted in order to establish the respective influence of geometric parameters such as fins number, fin shape (apex angle), spiral angle, fin height, fin pitch etc. on the condensation heat transfer performance of the spiralled micro-fin tubes. However, the effect of the spiral angle could not be clearly established in those investigations, because other geometric parameters affecting the heat transfer performance such as fin height, fin thickness, apex angle were also varied. The influence of the spiral angle on the heat transfer performance during condensation inside spiralled micro-fin tubes having all other geometric parameters the same was experimentally investigated in this study. A new experimental-based predictive correlation was developed for practical design of this specific class of micro-fin tubes. Tests were conducted for condensation of R22, R134a and R407c inside a smooth and three micro-fin tubes having spiral angles of 10, 18 and 37 degrees. Experimental results indicated a heat transfer augmentation due to heat transfer area increase. As the spiral angle was increased, the heat transfer area increased causing a substantial heat transfer augmentation. Condensation inside the 10° spiralled micro-fins produced a heat transfer augmentation of about 170% for a heat transfer area increase of 1.87 when compared to condensation in ~he correspondent smooth tube while the 18° spiralled " micro-fins produced an augmentation of 180% for a heat transfer area increase of 1.94. The 37° spiralled micro-fins produced the highest enhancement of 220% for a heat transfer area increase of 2.13. Additional heat transfer augmentation was produced by: (a) the turbulence in the condensate film due to the presence of spiralled micro-fins (stronger effect at lower mass velocities and vapor qualities) and (b) the effect of surface tension forces (at higher vapor qualities). The proposed new correlation predicted the majority of experimental results of the present study within a deviation zone of ± 20 percent.
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The development of an experimental heat transfer enhancement in tube-in-tube heat exchangers
- Authors: Coetzee, S.
- Date: 2011-11-21
- Subjects: Heat exchangers , Heat transmission
- Type: Thesis
- Identifier: uj:1702 , http://hdl.handle.net/10210/4046
- Description: M.Ing. , Heat transfer enhancement is currently a very popular field of research in heat transfer engineering. Before an investigation of this nature can be performed a suitable experimental set-up is needed to perform the experimental work. The object of this study was to develop such an experimental set-up to be used in determining the heat transfer and pressure drop characteristics of the refrigerant condensing in the inner tube of a tube-in-tube heat exchanger, with water flowing in the annulus. The experimental set-up was built and experiments were conducted with water flowing in the inner tube and annulus. From these readings heat transfer correlations were derived for the water flowing in the inner tube as well as the annulus by using the modified Wilson plot technique.
- Full Text:
- Authors: Coetzee, S.
- Date: 2011-11-21
- Subjects: Heat exchangers , Heat transmission
- Type: Thesis
- Identifier: uj:1702 , http://hdl.handle.net/10210/4046
- Description: M.Ing. , Heat transfer enhancement is currently a very popular field of research in heat transfer engineering. Before an investigation of this nature can be performed a suitable experimental set-up is needed to perform the experimental work. The object of this study was to develop such an experimental set-up to be used in determining the heat transfer and pressure drop characteristics of the refrigerant condensing in the inner tube of a tube-in-tube heat exchanger, with water flowing in the annulus. The experimental set-up was built and experiments were conducted with water flowing in the inner tube and annulus. From these readings heat transfer correlations were derived for the water flowing in the inner tube as well as the annulus by using the modified Wilson plot technique.
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Characteristics of a semicircular heat exchanger used in a water heated condenser pump
- Authors: Da Veiga, Willem Richter
- Date: 2009-02-26T12:17:42Z
- Subjects: Heat exchangers , Heat pumps , Heat transmission , Nusselt number
- Type: Thesis
- Identifier: uj:8151 , http://hdl.handle.net/10210/2158
- Description: D.Ing. , According to literature 6% of South Africa’s primary energy consumption could be saved if heat pumps were used to their full technical potential. Although there is world-wide interest in the use of heat pumps and considerable effort has been expended on heat-pump research, heat pumps are not commonly used in South Africa. The objective of this thesis is to determine the possibility of a combined evaporator or condenser with a normal pump. This will reduce cost and space of a normal heat pump and make heat pumps economically more competitive against resistance element geysers. In order to investigate this combination research is done on semicircular heat exchangers, since this is the primary geometry of the heating channels in the condenser pump. Analyses is done experimentally on a standard 28.58 mm hard drawn copper tube, cut trough the middle, with a 1.6 mm copper plate in between to obtain a semicircular heat exchanger. Turbulent flow is investigated with the flat side of the semicircular heat exchanger being horizontal or vertical, a spiralled and a s-shape semicircular heat exchanger. In each case the heat transfer coefficient is determined with the use of the Wilson plot technique. It is found that there is a significant increase in Nusselt number for semicircular heat exchangers above a normal tube-in-tube heat exchanger but the pressure loss coefficient increase with an equal amount.
- Full Text:
- Authors: Da Veiga, Willem Richter
- Date: 2009-02-26T12:17:42Z
- Subjects: Heat exchangers , Heat pumps , Heat transmission , Nusselt number
- Type: Thesis
- Identifier: uj:8151 , http://hdl.handle.net/10210/2158
- Description: D.Ing. , According to literature 6% of South Africa’s primary energy consumption could be saved if heat pumps were used to their full technical potential. Although there is world-wide interest in the use of heat pumps and considerable effort has been expended on heat-pump research, heat pumps are not commonly used in South Africa. The objective of this thesis is to determine the possibility of a combined evaporator or condenser with a normal pump. This will reduce cost and space of a normal heat pump and make heat pumps economically more competitive against resistance element geysers. In order to investigate this combination research is done on semicircular heat exchangers, since this is the primary geometry of the heating channels in the condenser pump. Analyses is done experimentally on a standard 28.58 mm hard drawn copper tube, cut trough the middle, with a 1.6 mm copper plate in between to obtain a semicircular heat exchanger. Turbulent flow is investigated with the flat side of the semicircular heat exchanger being horizontal or vertical, a spiralled and a s-shape semicircular heat exchanger. In each case the heat transfer coefficient is determined with the use of the Wilson plot technique. It is found that there is a significant increase in Nusselt number for semicircular heat exchangers above a normal tube-in-tube heat exchanger but the pressure loss coefficient increase with an equal amount.
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Uncertainty analysis of heat exchangers
- Authors: Coblentz, Liora Chana
- Date: 2009-02-26T12:17:05Z
- Subjects: Heat exchangers , Heat transmission , Uncertainty analysis
- Type: Thesis
- Identifier: uj:8149 , http://hdl.handle.net/10210/2156
- Description: M.Ing. , Experiments are being conducted with regard to heat exchange systems. However, there are errors and uncertainties attached to each system. Journals, which publish articles concerning heat transfer experiments, require an estimate of this uncertainty. These uncertainties must be calculated in order to determine how valid a set of results is. The uncertainty describes to what level one may rely on a set of experimental results and conclusions. The uncertainty was calculated by the formulation of an uncertainty equation with the use of various statistical methods. Adjustments or modifications had to be made to the present uncertainty equations in order to calculate the uncertainty in heat transfer systems. Uncertainty based on a general uncertainty equation by Schultz and Cole (1979) enabled the derivation of the equations to calculate the necessary uncertainty factor for heat transfer systems. Implementation of the equations in various experimental set-ups was achieved. The uncertainty equations yielded results that seemed consistent with the subjective view of the experimenter. Therefore, the equations were considered valid.
- Full Text:
- Authors: Coblentz, Liora Chana
- Date: 2009-02-26T12:17:05Z
- Subjects: Heat exchangers , Heat transmission , Uncertainty analysis
- Type: Thesis
- Identifier: uj:8149 , http://hdl.handle.net/10210/2156
- Description: M.Ing. , Experiments are being conducted with regard to heat exchange systems. However, there are errors and uncertainties attached to each system. Journals, which publish articles concerning heat transfer experiments, require an estimate of this uncertainty. These uncertainties must be calculated in order to determine how valid a set of results is. The uncertainty describes to what level one may rely on a set of experimental results and conclusions. The uncertainty was calculated by the formulation of an uncertainty equation with the use of various statistical methods. Adjustments or modifications had to be made to the present uncertainty equations in order to calculate the uncertainty in heat transfer systems. Uncertainty based on a general uncertainty equation by Schultz and Cole (1979) enabled the derivation of the equations to calculate the necessary uncertainty factor for heat transfer systems. Implementation of the equations in various experimental set-ups was achieved. The uncertainty equations yielded results that seemed consistent with the subjective view of the experimenter. Therefore, the equations were considered valid.
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Heat transfer characteristics of a fractal heat exchanger
- Authors: Van der Vyver, Hilde
- Date: 2009-01-22T05:37:25Z
- Subjects: Heat exchangers , Heat transmission , Nusselt number , Fluid dynamics , Fractals
- Type: Thesis
- Identifier: uj:14816 , http://hdl.handle.net/10210/1941
- Description: D.Ing.
- Full Text:
- Authors: Van der Vyver, Hilde
- Date: 2009-01-22T05:37:25Z
- Subjects: Heat exchangers , Heat transmission , Nusselt number , Fluid dynamics , Fractals
- Type: Thesis
- Identifier: uj:14816 , http://hdl.handle.net/10210/1941
- Description: D.Ing.
- Full Text:
Condensing coefficients of the refrigerant mixture R-22/R-142b in smooth tubes and during enhanced heat transfer configurations
- Authors: Smit, Floris Jakobus
- Date: 2009-01-22T05:36:38Z
- Subjects: Refrigerants , Condensation , Heat transmission
- Type: Thesis
- Identifier: uj:14812 , http://hdl.handle.net/10210/1938
- Description: D.Ing. , The heating of water with hot-water heat pumps is extremely energy-efficient. With the refrigerant R-22 hot water temperatures of 60° C to 65° C are possible. However, these temperatures are low in comparison with the temperatures obtained from other methods of water heating, for instance electrical geysers. Should higher water temperatures be obtained, the applications of hot-water heat pumps will increase. This is possible by using a zeotropic refrigerant mixture as working fluid. A R-22 and R-142b zeotropic refrigerant mixture shows exceptional potential in achieving hot water temperatures. The condensing coefficients need to be predicted correctly to optimize the condenser design. Unfortunately, there is a lack of detailed literature available on condensing coefficients for the recommended mass fractions of R-22 with R-142b at condensing temperatures of 60° C or more. Micro-fin tubes perform outstanding in enhancing heat transfer and are widely used to save energy. Unfortunately, there is also a lack of detailed literature on condensing coefficient at the recommended mass fractions of R-22/R-142b refrigerant mixtures condensing in micro-fins, twisted tapes and high fins at temperatures of 60° C or more. In this study condensing coefficients of R-22 and the zeotropic refrigerant mixture R-22 with R-142b were obtained in smooth tubes at mass fractions of 90%/10%, 80%/20%, 70%/30%, 60%/40%, 50%/50%. The experimental data were used to evaluate some of the methods that are commonly used to predict condensing coefficients. Experiments were also conducted at the same zeotropic mass fractions, to compare three different methods of heat transfer enhancement to that of the smooth tubes namely: micro-fins, twisted tapes and high fins. All measurements were conducted at an isobaric inlet pressure of 2.43 MPa. The test sections consisted of a series of eight tubes with lengths of 1 603 mm. The smooth tubes had an inner diameter of 8.11 mm. With the R-22/R-142b zeotropic refrigerant mixture condensing in smooth tubes, it was observed in the sight glasses that a predominantly stratified wavy flow regime exists at low mass fluxes, from 40 kg/m2s to 350 kg/m2s. The refrigerant mass fraction decreased the condensing coefficient by up to a third on average from 100% R-22 to a 50%/50% mixture of R-22 with R142b. A predominantly annular flow regime was observed at mass fluxes of 350 kg/m2s and more. At this flow regime the condensing coefficients were not strongly influenced by the refrigerant mass fraction, decreasing only by 7% as the refrigerant mass fraction changed from 100% R-22 to a 50%/50% mixture of R-22 with R142b. When the experimental data were compared with three methods that are commonly used to predict condensing coefficients it was found that the flow pattern correlation of Dobson and Chato (1998) gave the best predictions for R-22. The Silver (1964) and Bell and Ghaly (1964) method gave the best predictions for the R-22/R-142b mixtures. When the three heat transfer enhancement methods were compared with smooth tubes it was found that micro-fins were more suitable as an enhancement method than twisted tubes or high fins. It was also found that the condensing coefficients and pressure drops decrease as the mass fractions of R-142b increases.
- Full Text:
- Authors: Smit, Floris Jakobus
- Date: 2009-01-22T05:36:38Z
- Subjects: Refrigerants , Condensation , Heat transmission
- Type: Thesis
- Identifier: uj:14812 , http://hdl.handle.net/10210/1938
- Description: D.Ing. , The heating of water with hot-water heat pumps is extremely energy-efficient. With the refrigerant R-22 hot water temperatures of 60° C to 65° C are possible. However, these temperatures are low in comparison with the temperatures obtained from other methods of water heating, for instance electrical geysers. Should higher water temperatures be obtained, the applications of hot-water heat pumps will increase. This is possible by using a zeotropic refrigerant mixture as working fluid. A R-22 and R-142b zeotropic refrigerant mixture shows exceptional potential in achieving hot water temperatures. The condensing coefficients need to be predicted correctly to optimize the condenser design. Unfortunately, there is a lack of detailed literature available on condensing coefficients for the recommended mass fractions of R-22 with R-142b at condensing temperatures of 60° C or more. Micro-fin tubes perform outstanding in enhancing heat transfer and are widely used to save energy. Unfortunately, there is also a lack of detailed literature on condensing coefficient at the recommended mass fractions of R-22/R-142b refrigerant mixtures condensing in micro-fins, twisted tapes and high fins at temperatures of 60° C or more. In this study condensing coefficients of R-22 and the zeotropic refrigerant mixture R-22 with R-142b were obtained in smooth tubes at mass fractions of 90%/10%, 80%/20%, 70%/30%, 60%/40%, 50%/50%. The experimental data were used to evaluate some of the methods that are commonly used to predict condensing coefficients. Experiments were also conducted at the same zeotropic mass fractions, to compare three different methods of heat transfer enhancement to that of the smooth tubes namely: micro-fins, twisted tapes and high fins. All measurements were conducted at an isobaric inlet pressure of 2.43 MPa. The test sections consisted of a series of eight tubes with lengths of 1 603 mm. The smooth tubes had an inner diameter of 8.11 mm. With the R-22/R-142b zeotropic refrigerant mixture condensing in smooth tubes, it was observed in the sight glasses that a predominantly stratified wavy flow regime exists at low mass fluxes, from 40 kg/m2s to 350 kg/m2s. The refrigerant mass fraction decreased the condensing coefficient by up to a third on average from 100% R-22 to a 50%/50% mixture of R-22 with R142b. A predominantly annular flow regime was observed at mass fluxes of 350 kg/m2s and more. At this flow regime the condensing coefficients were not strongly influenced by the refrigerant mass fraction, decreasing only by 7% as the refrigerant mass fraction changed from 100% R-22 to a 50%/50% mixture of R-22 with R142b. When the experimental data were compared with three methods that are commonly used to predict condensing coefficients it was found that the flow pattern correlation of Dobson and Chato (1998) gave the best predictions for R-22. The Silver (1964) and Bell and Ghaly (1964) method gave the best predictions for the R-22/R-142b mixtures. When the three heat transfer enhancement methods were compared with smooth tubes it was found that micro-fins were more suitable as an enhancement method than twisted tubes or high fins. It was also found that the condensing coefficients and pressure drops decrease as the mass fractions of R-142b increases.
- Full Text:
Development of a calcium carbonate scale formation experimental set-up for the evaluation of physical water treatment devices
- Authors: Da Veiga, Reinaldo
- Date: 2008-11-19T06:20:56Z
- Subjects: Water purification , Fouling , Descaling , Incrustations , Heat exchangers incrustations , Flow meters
- Type: Thesis
- Identifier: uj:14735 , http://hdl.handle.net/10210/1740
- Description: D.Ing.
- Full Text:
- Authors: Da Veiga, Reinaldo
- Date: 2008-11-19T06:20:56Z
- Subjects: Water purification , Fouling , Descaling , Incrustations , Heat exchangers incrustations , Flow meters
- Type: Thesis
- Identifier: uj:14735 , http://hdl.handle.net/10210/1740
- Description: D.Ing.
- Full Text:
The Economic viability of a microturbine cogeneration system
- Authors: Denys, Nele
- Date: 2008-11-18T08:57:55Z
- Subjects: Cogeneration of electric power and heat
- Type: Thesis
- Identifier: uj:14722 , http://hdl.handle.net/10210/1727
- Description: M.Ing. , Currently, electrical resistance heaters are used to produce most of the hot water in South Africa. Increasing electricity tariffs make these devices very expensive. This study investigates the economic savings potential of using a cogeneration system made of microturbines, heat pumps and heat exchangers. Specifically the heating of water for large residential units is investigated. Different economic parameters are used to compare microturbine heat pump systems with electrical resistance heaters, natural gas boilers and heat pumps. For 27 main centres in South Africa, the amount of hot water is determined where a cogeneration system is economically more viable than other types of water heaters. It has been concluded that the most important influence factor is the electricity tariff. The higher the electricity tariff in a city, the smaller the number of domestic consumers where a cogeneration system becomes viable.
- Full Text:
- Authors: Denys, Nele
- Date: 2008-11-18T08:57:55Z
- Subjects: Cogeneration of electric power and heat
- Type: Thesis
- Identifier: uj:14722 , http://hdl.handle.net/10210/1727
- Description: M.Ing. , Currently, electrical resistance heaters are used to produce most of the hot water in South Africa. Increasing electricity tariffs make these devices very expensive. This study investigates the economic savings potential of using a cogeneration system made of microturbines, heat pumps and heat exchangers. Specifically the heating of water for large residential units is investigated. Different economic parameters are used to compare microturbine heat pump systems with electrical resistance heaters, natural gas boilers and heat pumps. For 27 main centres in South Africa, the amount of hot water is determined where a cogeneration system is economically more viable than other types of water heaters. It has been concluded that the most important influence factor is the electricity tariff. The higher the electricity tariff in a city, the smaller the number of domestic consumers where a cogeneration system becomes viable.
- Full Text:
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