The performance of a municipality water reticulation ground-coupled reversible heat pump
- Authors: Oerder, Stacy-Ann
- Date: 2014-02-10
- Subjects: Heat pumps , Air conditioning , Heat exchangers
- Type: Thesis
- Identifier: uj:3728 , http://hdl.handle.net/10210/9108
- Description: M.Ing. (Mechanical Engineering) , A reversible ground source heat pump, coupled to a municipality water reticulation system, is investigated as an alternative to conventional air source systems for space heating and cooling. The investigation was executed through the development of analytical models that were used for the design of a ground-coupled reversible heat pump and a conventional, also reversible air source system. The models were verified with experimental measurements. The results of the models and measurements indicate that ground source systems are a cost effective alternative.
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- Authors: Oerder, Stacy-Ann
- Date: 2014-02-10
- Subjects: Heat pumps , Air conditioning , Heat exchangers
- Type: Thesis
- Identifier: uj:3728 , http://hdl.handle.net/10210/9108
- Description: M.Ing. (Mechanical Engineering) , A reversible ground source heat pump, coupled to a municipality water reticulation system, is investigated as an alternative to conventional air source systems for space heating and cooling. The investigation was executed through the development of analytical models that were used for the design of a ground-coupled reversible heat pump and a conventional, also reversible air source system. The models were verified with experimental measurements. The results of the models and measurements indicate that ground source systems are a cost effective alternative.
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Modelling and design of a latent heat thermal storage system with reference to solar absorption refrigeration
- Authors: Kantole, Joseph Basakayi
- Date: 2012-10-24
- Subjects: Solar thermal energy , Heat storage , Heat exchangers
- Type: Thesis
- Identifier: uj:10417 , http://hdl.handle.net/10210/7883
- Description: M.Ing. , The research in this thesis focuses on the theoretical thermal modelling and design of a Latent Heat Storage system (LHS) for an absorption refrigeration machine. A shell-and-tube latent heat storage exchanger retaining any excess solar thermal energy is selected. Here, solar thermal energy supplied by a collector is transferred to and stored by the LHS. During low insolation, stored thermal energy is transferred by a Heat Transfer Fluid (HTF) into the generator, a component of an Ammonia Absorption Refrigerator (AAAR), to ensure efficiency of the cooling cycle. The shell-and-tube LHS contains Phase Change Material (PCM) which fills space outside the tube heat exchangers. The HTF flowing through the tubes exchanges thermal energy with the PCM. The selection of a suitable PCM for a LHS is based on several factors. A primary criterion for an efficient, reliable storage unit is the correct melting point of the PCM at a desired operating temperature of the heating application. An analytical model describing both the freezing process in the PCM and increased HTF temperature in the tube heat exchangers is investigated. The model is developed using energy balance equations. It is solved in terms of dimensionless parameters. The thermal resistance of the tube heat exchangers is considered for this model. From the result of the analytical model, the design approach to size the LHS is provided and the different steps are given in order to determine the volume, mass, number of tube heat exchangers, inner and outer radius of the tube heat exchangers and other parameters of the LHS. The dimensions of LHS are given as a function of a storage period, PCM properties, HTF properties, inner and outer radius of the tube heat exchangers, material of construction of the tube heat exchangers and the nature of load on the heating process. Simulations from the analytical model developed are provided for the output thermal parameters of the storage system. These thermal parameters of the shell-and-tube latent exchanger are given in terms of the HTF outlet temperature, the front solidification of the PCM and the heat transfer rate during the solidification process of the PCM. A case study to demonstrate the application of the design approach with respect to the size shell-and-tube latent heat exchanger is provided.The integration of the tube heat exchangers thermal conductivity in the modelling of the LHS resulted in an increase of 2% in mass of the storage material compared to an analytical model neglecting the thermal conductivity of the tube heat exchangers. The results of the model developed compared well with the results obtained from other analytical models at similar operating conditions.
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- Authors: Kantole, Joseph Basakayi
- Date: 2012-10-24
- Subjects: Solar thermal energy , Heat storage , Heat exchangers
- Type: Thesis
- Identifier: uj:10417 , http://hdl.handle.net/10210/7883
- Description: M.Ing. , The research in this thesis focuses on the theoretical thermal modelling and design of a Latent Heat Storage system (LHS) for an absorption refrigeration machine. A shell-and-tube latent heat storage exchanger retaining any excess solar thermal energy is selected. Here, solar thermal energy supplied by a collector is transferred to and stored by the LHS. During low insolation, stored thermal energy is transferred by a Heat Transfer Fluid (HTF) into the generator, a component of an Ammonia Absorption Refrigerator (AAAR), to ensure efficiency of the cooling cycle. The shell-and-tube LHS contains Phase Change Material (PCM) which fills space outside the tube heat exchangers. The HTF flowing through the tubes exchanges thermal energy with the PCM. The selection of a suitable PCM for a LHS is based on several factors. A primary criterion for an efficient, reliable storage unit is the correct melting point of the PCM at a desired operating temperature of the heating application. An analytical model describing both the freezing process in the PCM and increased HTF temperature in the tube heat exchangers is investigated. The model is developed using energy balance equations. It is solved in terms of dimensionless parameters. The thermal resistance of the tube heat exchangers is considered for this model. From the result of the analytical model, the design approach to size the LHS is provided and the different steps are given in order to determine the volume, mass, number of tube heat exchangers, inner and outer radius of the tube heat exchangers and other parameters of the LHS. The dimensions of LHS are given as a function of a storage period, PCM properties, HTF properties, inner and outer radius of the tube heat exchangers, material of construction of the tube heat exchangers and the nature of load on the heating process. Simulations from the analytical model developed are provided for the output thermal parameters of the storage system. These thermal parameters of the shell-and-tube latent exchanger are given in terms of the HTF outlet temperature, the front solidification of the PCM and the heat transfer rate during the solidification process of the PCM. A case study to demonstrate the application of the design approach with respect to the size shell-and-tube latent heat exchanger is provided.The integration of the tube heat exchangers thermal conductivity in the modelling of the LHS resulted in an increase of 2% in mass of the storage material compared to an analytical model neglecting the thermal conductivity of the tube heat exchangers. The results of the model developed compared well with the results obtained from other analytical models at similar operating conditions.
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Characterisation of a plate heat exchanger under superheat conditions
- Authors: Schröder, Lukas Herman
- Date: 2012-09-05
- Subjects: Heat exchangers
- Type: Thesis
- Identifier: uj:3561 , http://hdl.handle.net/10210/6945
- Description: M.Ing. , The objective of this study is to analytically evaluate the heat transfer and area requirements of a plate heat exchanger, in which the refrigerant exits the heat exchanger as a saturated vapour; a superheated vapour, under variable inlet conditions, through application of the experimental results obtained by Yan and Lin (1999) on the evaporation heat transfer and pressure drop of refrigerant R134a in a plate heat exchanger. Through the analytical evaluation it will firstly be shown that for the instance in which the refrigerant enters the heat exchanger at different inlet qualities and exits the heat exchanger as a saturated vapour that the amount of heat transferred and area requirement reduces as the inlet quality of the refrigerant increases. Secondly, when the refrigerant enters the heat exchanger as a saturated vapour and exits at different values of superheated vapour that the amount of heat transferred from the water to the refrigerant increases as the amount by which the refrigerant is superheated increases, combined with an increased area requirement in order to realise a certain amount of heat transfer. All evaluations are conducted at fixed mass flow rates. Through comparison of the two evaluations it will be shown that the area requirement in the superheated region is significantly larger than in the evaporation region of the heat exchanger whilst obtaining significantly less heat transfer.
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- Authors: Schröder, Lukas Herman
- Date: 2012-09-05
- Subjects: Heat exchangers
- Type: Thesis
- Identifier: uj:3561 , http://hdl.handle.net/10210/6945
- Description: M.Ing. , The objective of this study is to analytically evaluate the heat transfer and area requirements of a plate heat exchanger, in which the refrigerant exits the heat exchanger as a saturated vapour; a superheated vapour, under variable inlet conditions, through application of the experimental results obtained by Yan and Lin (1999) on the evaporation heat transfer and pressure drop of refrigerant R134a in a plate heat exchanger. Through the analytical evaluation it will firstly be shown that for the instance in which the refrigerant enters the heat exchanger at different inlet qualities and exits the heat exchanger as a saturated vapour that the amount of heat transferred and area requirement reduces as the inlet quality of the refrigerant increases. Secondly, when the refrigerant enters the heat exchanger as a saturated vapour and exits at different values of superheated vapour that the amount of heat transferred from the water to the refrigerant increases as the amount by which the refrigerant is superheated increases, combined with an increased area requirement in order to realise a certain amount of heat transfer. All evaluations are conducted at fixed mass flow rates. Through comparison of the two evaluations it will be shown that the area requirement in the superheated region is significantly larger than in the evaporation region of the heat exchanger whilst obtaining significantly less heat transfer.
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Direct contact brine-air heat exchanger characteristics
- Authors: Kotze, Christo
- Date: 2012-08-27
- Subjects: Heat -- Transmission , Heat exchangers , Gold mines and mining -- Cooling
- Type: Thesis
- Identifier: uj:3203 , http://hdl.handle.net/10210/6616
- Description: M.Ing. , Gold ore deposits are depleted near the surface of the earth and the remaining deposits are located at great depths of over 3000m. Geothermal energy will cause the ventilation air temperature to increase above 50°C, and therefore it must be cooled to an effective working temperature. The cost of providing acceptable air temperatures to the workers in the mine plays an important role in the feasibility of whether to proceed with a mining project. At present the air in South African gold mines is cooled by a number of processes including bulk air coolers and direct contact spray chambers. In all of the above mentioned processes large quantities of water need to be pumped into the mine where it is used as the cooling fluid to reduce the air temperature. One of the recent developments for cooling the ventilation air uses ice, produced on surface in large quantities and transported underground in conventional plastic piping. It is regarded as the most effective system for creating chilled cooling water. To create an even more effective process, the properties of a new coolant will be investigated. In the new process, ice is transported into the mine and then mixed with a brine solution. The presence of the salt in the brine creates a freezing point depression and an endothermic chemical reaction causing the temperature of the mixture to decrease well below zero degrees Celsius. This chilled brine solution will be used instead of water to decrease the temperature of the ventilation air. The aim of the project is to conduct an analytical and experimental evaluation by using ice and brine as the coolant. In the experimental investigation the coolant is pumped over a flat, multi-plate heat transfer surface where the air flow is maintained at a constant rate. This simplifies the mathematical modeling and gives useful relationships between the experimental results and the theoretical results.
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- Authors: Kotze, Christo
- Date: 2012-08-27
- Subjects: Heat -- Transmission , Heat exchangers , Gold mines and mining -- Cooling
- Type: Thesis
- Identifier: uj:3203 , http://hdl.handle.net/10210/6616
- Description: M.Ing. , Gold ore deposits are depleted near the surface of the earth and the remaining deposits are located at great depths of over 3000m. Geothermal energy will cause the ventilation air temperature to increase above 50°C, and therefore it must be cooled to an effective working temperature. The cost of providing acceptable air temperatures to the workers in the mine plays an important role in the feasibility of whether to proceed with a mining project. At present the air in South African gold mines is cooled by a number of processes including bulk air coolers and direct contact spray chambers. In all of the above mentioned processes large quantities of water need to be pumped into the mine where it is used as the cooling fluid to reduce the air temperature. One of the recent developments for cooling the ventilation air uses ice, produced on surface in large quantities and transported underground in conventional plastic piping. It is regarded as the most effective system for creating chilled cooling water. To create an even more effective process, the properties of a new coolant will be investigated. In the new process, ice is transported into the mine and then mixed with a brine solution. The presence of the salt in the brine creates a freezing point depression and an endothermic chemical reaction causing the temperature of the mixture to decrease well below zero degrees Celsius. This chilled brine solution will be used instead of water to decrease the temperature of the ventilation air. The aim of the project is to conduct an analytical and experimental evaluation by using ice and brine as the coolant. In the experimental investigation the coolant is pumped over a flat, multi-plate heat transfer surface where the air flow is maintained at a constant rate. This simplifies the mathematical modeling and gives useful relationships between the experimental results and the theoretical results.
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Design methodology and experimental verification used to optimize liquid overfeeding effects achieved with heat exchanger accumulators
- Authors: Wood, Craig Willoughby
- Date: 2012-08-22
- Subjects: Heat exchangers , Heat exchangers - Design
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/380535 , uj:2951 , http://hdl.handle.net/10210/6378
- Description: M.Ing. , This study involves the mathematical modeling and experimental verification of a heat exchanger accumulator. The study was initiated with a literature survey which, according to the author, revealed that there was no published material that described how heat exchanger accumulators are designed to ensure that they are correctly sized according to the operating system and conditions. The heat exchange process that takes place within the heat accumulator was studied and a mathematical model of a heat exchanger accumulator developed. This model was used to develop a universal design procedure that correctly sized the heat exchanger accumulator according to various requirements identified by the author. The model was then verified by conducting experimental tests and it was concluded that the model could be used to design heat exchanger accumulators.
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- Authors: Wood, Craig Willoughby
- Date: 2012-08-22
- Subjects: Heat exchangers , Heat exchangers - Design
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/380535 , uj:2951 , http://hdl.handle.net/10210/6378
- Description: M.Ing. , This study involves the mathematical modeling and experimental verification of a heat exchanger accumulator. The study was initiated with a literature survey which, according to the author, revealed that there was no published material that described how heat exchanger accumulators are designed to ensure that they are correctly sized according to the operating system and conditions. The heat exchange process that takes place within the heat accumulator was studied and a mathematical model of a heat exchanger accumulator developed. This model was used to develop a universal design procedure that correctly sized the heat exchanger accumulator according to various requirements identified by the author. The model was then verified by conducting experimental tests and it was concluded that the model could be used to design heat exchanger accumulators.
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Effect of nozzle loads on the stress distribution inside unpartitioned plug type headerboxes
- Authors: Nel, Hugh-Jean
- Date: 2012-06-11
- Subjects: Nozzles , Heat exchangers , Fluid dynamics , Stress concentration
- Type: Thesis
- Identifier: uj:8762 , http://hdl.handle.net/10210/5113
- Description: M.Ing. , Dry air cooled heat exchangers form a vital part of industrial heat transfer systems, especially in countries where the supply and availability of clean cooling water is limited. Headerboxes are rectangular pressure vessels that act as the inlet distribution and outlet collection devices. As rectangular pressure vessels, headerboxes are subject to design codes such as ASME (ASME Section VIII, Division 1, 2007). Unfortunately ASME (ASME Section VIII, Division 1, 2007) offers no guidance on how to allow for the effect of external loads applied to the headerbox through the vessel’s nozzles. This creates a difficult situation, since vessel designers are mandated by ASME to consider the effects of nozzle loads by American Petroleum Institute standard 661 (API, 2006). The aim of this project was therefore to develop a closed form design methodology that accurately predicts the stresses inside a headerbox that is subject to external loadings as well as internal pressure. After extensive research it was decided that the only viable approach would be to extend ASME’s rigid frame theory. This was done, and a new set of equations describing the stress distribution inside a headerbox were derived. These equations were then tested using 2D Finite Element Analysis (FEA) to determine whether they represented the reality of the 2D model they described. It was found that the equations were accurate enough in 2D and the next step was to test the model experimentally and using full 3D FEA. A local manufacturer of air cooled heat exchangers was approached and they helped design an experimental specimen and agreed to fund its construction. Unfortunately, due to time constraints, it was not possible to build and test the specimen experimentally. The specimen geometry was then analysed using the Abaqus (Dassault Systѐmes Simulia Corp., 2010) FEA package. The 3D FEA analysis considered several different load cases. After carefully analysing the results it was seen that the rigid frame model could make useful qualitative statements about the effects of the nozzle loads, but it performed poorly as a quantitative prediction method. However, since the effects of the nozzle loads are generally quite small it is possible that, with appropriate safety factors, the rigid frame model could be used as a conservative design methodology. The usefulness of a commonly used empirical guideline was also examined. This project is far from conclusive and much more work is required to fully examine the usefulness of rigid frame theory. That being said, this project has made important steps towards a more complete understanding of rectangular pressure vessels and has shown possible ways forward.
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- Authors: Nel, Hugh-Jean
- Date: 2012-06-11
- Subjects: Nozzles , Heat exchangers , Fluid dynamics , Stress concentration
- Type: Thesis
- Identifier: uj:8762 , http://hdl.handle.net/10210/5113
- Description: M.Ing. , Dry air cooled heat exchangers form a vital part of industrial heat transfer systems, especially in countries where the supply and availability of clean cooling water is limited. Headerboxes are rectangular pressure vessels that act as the inlet distribution and outlet collection devices. As rectangular pressure vessels, headerboxes are subject to design codes such as ASME (ASME Section VIII, Division 1, 2007). Unfortunately ASME (ASME Section VIII, Division 1, 2007) offers no guidance on how to allow for the effect of external loads applied to the headerbox through the vessel’s nozzles. This creates a difficult situation, since vessel designers are mandated by ASME to consider the effects of nozzle loads by American Petroleum Institute standard 661 (API, 2006). The aim of this project was therefore to develop a closed form design methodology that accurately predicts the stresses inside a headerbox that is subject to external loadings as well as internal pressure. After extensive research it was decided that the only viable approach would be to extend ASME’s rigid frame theory. This was done, and a new set of equations describing the stress distribution inside a headerbox were derived. These equations were then tested using 2D Finite Element Analysis (FEA) to determine whether they represented the reality of the 2D model they described. It was found that the equations were accurate enough in 2D and the next step was to test the model experimentally and using full 3D FEA. A local manufacturer of air cooled heat exchangers was approached and they helped design an experimental specimen and agreed to fund its construction. Unfortunately, due to time constraints, it was not possible to build and test the specimen experimentally. The specimen geometry was then analysed using the Abaqus (Dassault Systѐmes Simulia Corp., 2010) FEA package. The 3D FEA analysis considered several different load cases. After carefully analysing the results it was seen that the rigid frame model could make useful qualitative statements about the effects of the nozzle loads, but it performed poorly as a quantitative prediction method. However, since the effects of the nozzle loads are generally quite small it is possible that, with appropriate safety factors, the rigid frame model could be used as a conservative design methodology. The usefulness of a commonly used empirical guideline was also examined. This project is far from conclusive and much more work is required to fully examine the usefulness of rigid frame theory. That being said, this project has made important steps towards a more complete understanding of rectangular pressure vessels and has shown possible ways forward.
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Comparison between CFD analysis and experimental work on heat exchangers
- Authors: Krüger, E.
- Date: 2012-03-26
- Subjects: Heat exchangers , Fluid dynamics
- Type: Thesis
- Identifier: uj:2188 , http://hdl.handle.net/10210/4568
- Description: M.Ing. , There are two advantages of enhanced heat transfer. Firstly a decrease in the heat exchanger size and secondly an increase in the heat transfer coefficient. A method of increasing the heat transfer coefficient is to insert spiralled wires in the annulus of a tube-in-tube heat exchanger. It was decided to investigate this method further and therefore the objectives of the investigation are twofold. First to determine what the optimum spiral angle of the wires is, and secondly what mechanism causes the enhanced heat transfer. Specifically to determine if it is an increase in the turbulence or an increase in the flow rotation. A numerical model that was experimentally verified was used to do the investigation. It was concluded from the numerical results that for optimum heat transfer, the spiral angle of the wires should be 30°. It was also found that the mechanism for enhanced heat transfer is an increase in the rotation of the flow in the annulus.
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- Authors: Krüger, E.
- Date: 2012-03-26
- Subjects: Heat exchangers , Fluid dynamics
- Type: Thesis
- Identifier: uj:2188 , http://hdl.handle.net/10210/4568
- Description: M.Ing. , There are two advantages of enhanced heat transfer. Firstly a decrease in the heat exchanger size and secondly an increase in the heat transfer coefficient. A method of increasing the heat transfer coefficient is to insert spiralled wires in the annulus of a tube-in-tube heat exchanger. It was decided to investigate this method further and therefore the objectives of the investigation are twofold. First to determine what the optimum spiral angle of the wires is, and secondly what mechanism causes the enhanced heat transfer. Specifically to determine if it is an increase in the turbulence or an increase in the flow rotation. A numerical model that was experimentally verified was used to do the investigation. It was concluded from the numerical results that for optimum heat transfer, the spiral angle of the wires should be 30°. It was also found that the mechanism for enhanced heat transfer is an increase in the rotation of the flow in the annulus.
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Design of a temperature controllable demand water heater
- Authors: Duff, Craig Andrew
- Date: 2012
- Subjects: Renewable energy sources , Hot-water supply , Solar energy , Heat exchangers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/256890 , uj:26975
- Description: Abstract: The purpose of this study is to investigate ways to reduce the wastage of electricity and water during domestic hot water applications. Contemporary electric water heaters do not use water and electricity in an efficient manner due to their methods of operation, the placement of the water heater unit away from the point‐of‐use and the lack of direct user‐control. The aim of this study is to consider the feasibility of decentralising water heating to the point‐of‐use by combining a compact heating chamber with the tap, providing scope for the user to be in direct control of the water heating system. This study is necessary in order to support the development of products that improve the efficient use of essential resources, in this case electricity and water. The method used to study the feasibility of user‐controlled decentralised water heating is laboratory‐based experimentation, for which a compact heating chamber and user‐operated controls are designed. This study uses mixed‐methods research to measure both the heating chamber and the user‐control simultaneously. The experimental findings confirm that it is possible to heat flowing water in a compact heating chamber and the user is able to directly control the water heating system. These findings support further research and development of the user‐controlled point‐of‐use water heating concept as a method to save electricity and water. Further research and development should aim to determine to what extent this concept saves water and electricity when compared to existing water heating systems. , M.Tech. (Industrial Design)
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- Authors: Duff, Craig Andrew
- Date: 2012
- Subjects: Renewable energy sources , Hot-water supply , Solar energy , Heat exchangers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/256890 , uj:26975
- Description: Abstract: The purpose of this study is to investigate ways to reduce the wastage of electricity and water during domestic hot water applications. Contemporary electric water heaters do not use water and electricity in an efficient manner due to their methods of operation, the placement of the water heater unit away from the point‐of‐use and the lack of direct user‐control. The aim of this study is to consider the feasibility of decentralising water heating to the point‐of‐use by combining a compact heating chamber with the tap, providing scope for the user to be in direct control of the water heating system. This study is necessary in order to support the development of products that improve the efficient use of essential resources, in this case electricity and water. The method used to study the feasibility of user‐controlled decentralised water heating is laboratory‐based experimentation, for which a compact heating chamber and user‐operated controls are designed. This study uses mixed‐methods research to measure both the heating chamber and the user‐control simultaneously. The experimental findings confirm that it is possible to heat flowing water in a compact heating chamber and the user is able to directly control the water heating system. These findings support further research and development of the user‐controlled point‐of‐use water heating concept as a method to save electricity and water. Further research and development should aim to determine to what extent this concept saves water and electricity when compared to existing water heating systems. , M.Tech. (Industrial Design)
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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.
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- 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.
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- 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.
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- 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.
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- 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.
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- 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.
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A unified prediction method for smooth and micro-fin tube condensation performance
- Authors: Liebenberg, Leon
- Date: 2009-01-22T05:36:54Z
- Subjects: Heat transmission , Heat exchangers , Condensation , Refrigerants
- Type: Thesis
- Identifier: uj:14813 , http://hdl.handle.net/10210/1939
- Description: D.Ing.
- Full Text:
- Authors: Liebenberg, Leon
- Date: 2009-01-22T05:36:54Z
- Subjects: Heat transmission , Heat exchangers , Condensation , Refrigerants
- Type: Thesis
- Identifier: uj:14813 , http://hdl.handle.net/10210/1939
- Description: D.Ing.
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The influence of annular tube contact in a helical-wound tube-in-tube heat exchanger
- Authors: Louw, Willie I.
- Date: 2009-01-20T07:06:01Z
- Subjects: Heat exchangers
- Type: Thesis
- Identifier: uj:14808 , http://hdl.handle.net/10210/1934
- Description: M.Ing. , Tube-in-tube heat exchangers have wide industrial application. From fields as diverse as food and beverage to automotive industries these devices are used extensive to enable heat exchange. In many cases they are manufactured by coiling two tubes placed one within the other. This method often results in the tubes not sharing the same centre line and in some cases annular contact occurs. Comparison of such heat exchangers to aligned (concentric) devices was done experimentally to quantify the influence annular contact has on the heat exchange capabilities. By comparison of the Nusselt numbers calculated for each vessel in each experiment, it was concluded that annular contact diminishes the capability of a counterflow tube-in-tube heat exchanger to transfer energy from a hot to a cold fluid. This effect becomes more profound at higher Reynolds and Prandtl numbers respectively.
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- Authors: Louw, Willie I.
- Date: 2009-01-20T07:06:01Z
- Subjects: Heat exchangers
- Type: Thesis
- Identifier: uj:14808 , http://hdl.handle.net/10210/1934
- Description: M.Ing. , Tube-in-tube heat exchangers have wide industrial application. From fields as diverse as food and beverage to automotive industries these devices are used extensive to enable heat exchange. In many cases they are manufactured by coiling two tubes placed one within the other. This method often results in the tubes not sharing the same centre line and in some cases annular contact occurs. Comparison of such heat exchangers to aligned (concentric) devices was done experimentally to quantify the influence annular contact has on the heat exchange capabilities. By comparison of the Nusselt numbers calculated for each vessel in each experiment, it was concluded that annular contact diminishes the capability of a counterflow tube-in-tube heat exchanger to transfer energy from a hot to a cold fluid. This effect becomes more profound at higher Reynolds and Prandtl numbers respectively.
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Flow patterns during refrigerant condensation in smooth and enhanced tubes
- Authors: Owaga, Denis
- Date: 2009-01-20T07:05:17Z
- Subjects: Refrigerants , Condensation , Heat transmission , Heat exchangers
- Type: Thesis
- Identifier: uj:14806 , http://hdl.handle.net/10210/1931
- Description: M.Ing. , The Montreal Protocol led to the phasing-out of ozone layer depleting refrigerants and replacing them with more environmentally friendly refrigerants, which in many cases caused heat transfer degradation in heat exchanger equipment. To make up for the heat transfer degradation, there was a need for the application of heat transfer enhancement techniques. One such technique is the use of micro-fin tubes as opposed to traditional smooth tubes. The purpose of this study is to develop a flow regime map for the condensation of R-22, R-407C and R-134a in a herringbone micro-fin tube. It was perceived that with the knowledge of flow patterns inside the tube and especially the annular-to-intermittent transition, it is possible to perform improved analyses of the heat transfer and pressure drop characteristics. Experimental and analytical work was performed to investigate the flow regimes during condensation of the refrigerants in smooth, helical micro-fin and herringbone micro-fin tubes at an average saturation temperature of 40oC, with mass fluxes ranging from 300 to 800 kg/m2s. Condensation occurred in tube-in-tube type condensers with cooling water flowing in the annulus and the refrigerant in the inner tubes. The condensers consisted of eight sub-sections to allow for the acquisition of sectional heat transfer and pressure data. Various criteria were considered in order to generate flow regime maps. The Thome flow regime transition criterion was used and complemented with visually-observed and photographic imaging, as well as the objective power spectral density distributions of the pressure signals of the condensing refrigerants. The observed flow regimes were mainly annular flow and intermittent flow. Stratified-wavy flow was observed at low mass fluxes and low vapour qualities. There were notable similarities in the flow pattern between the smooth and micro-fin tubes. However, the experimental results show that the transition from annular to intermittent flow regimes occurred at average vapour quality values of 0.26, 0.29 and 0.48 for the herringbone micro-fin, the helical micro-fin and smooth tubes respectively. The combined analyses assisted in adapting the helical micro-fin tube condensing flow pattern map, to ensure its application in accurately predicting herringbone micro-fin tube condensation. The new transition criterion effectively predicts the delay in transition from annular to intermittent flow for all three refrigerants, condensing in the herringbone micro-fin tube.
- Full Text:
- Authors: Owaga, Denis
- Date: 2009-01-20T07:05:17Z
- Subjects: Refrigerants , Condensation , Heat transmission , Heat exchangers
- Type: Thesis
- Identifier: uj:14806 , http://hdl.handle.net/10210/1931
- Description: M.Ing. , The Montreal Protocol led to the phasing-out of ozone layer depleting refrigerants and replacing them with more environmentally friendly refrigerants, which in many cases caused heat transfer degradation in heat exchanger equipment. To make up for the heat transfer degradation, there was a need for the application of heat transfer enhancement techniques. One such technique is the use of micro-fin tubes as opposed to traditional smooth tubes. The purpose of this study is to develop a flow regime map for the condensation of R-22, R-407C and R-134a in a herringbone micro-fin tube. It was perceived that with the knowledge of flow patterns inside the tube and especially the annular-to-intermittent transition, it is possible to perform improved analyses of the heat transfer and pressure drop characteristics. Experimental and analytical work was performed to investigate the flow regimes during condensation of the refrigerants in smooth, helical micro-fin and herringbone micro-fin tubes at an average saturation temperature of 40oC, with mass fluxes ranging from 300 to 800 kg/m2s. Condensation occurred in tube-in-tube type condensers with cooling water flowing in the annulus and the refrigerant in the inner tubes. The condensers consisted of eight sub-sections to allow for the acquisition of sectional heat transfer and pressure data. Various criteria were considered in order to generate flow regime maps. The Thome flow regime transition criterion was used and complemented with visually-observed and photographic imaging, as well as the objective power spectral density distributions of the pressure signals of the condensing refrigerants. The observed flow regimes were mainly annular flow and intermittent flow. Stratified-wavy flow was observed at low mass fluxes and low vapour qualities. There were notable similarities in the flow pattern between the smooth and micro-fin tubes. However, the experimental results show that the transition from annular to intermittent flow regimes occurred at average vapour quality values of 0.26, 0.29 and 0.48 for the herringbone micro-fin, the helical micro-fin and smooth tubes respectively. The combined analyses assisted in adapting the helical micro-fin tube condensing flow pattern map, to ensure its application in accurately predicting herringbone micro-fin tube condensation. The new transition criterion effectively predicts the delay in transition from annular to intermittent flow for all three refrigerants, condensing in the herringbone micro-fin tube.
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Pressure loss at the tubular inlet section of a low temperature differential heat exchanger
- Authors: Bijkersma, Jan
- Date: 2008-07-18T13:40:52Z
- Subjects: Heat exchangers , Pressure , Fluid dynamics , Condensers (vapors and gases)
- Type: Thesis
- Identifier: uj:7322 , http://hdl.handle.net/10210/805
- Description: When water vapour condenses at a sub-atmospheric pressure, the pressure drop may be a significant fraction of the absolute pressure. Furthermore the pressure drop in a condenser passage also reduces the absolute vapour temperature and therefore affects the heat transfer capacity of a condenser. For a tubular heat exchanger the pressure loss in the heat exchanger tubes can be minimized by the use of contoured or rounded inlet sections at the inlets of the tubes instead of using a sudden contracting inlet section or a protruding inlet section for the tubes. The pressure loss characteristics of different inlet sections to the tubes were obtained through a literature survey of the pressure loss coefficients. The pressure loss at the inlet sections were also investigated with computational fluid dynamics, using the Star-CD software system. The flow regimes for which the pressure loss was investigated were for the laminar incompressible and turbulent incompressible flow regimes. The inlet sections investigated were a sudden contraction and two rounded inlet sections with a rounding radius of 52% and 105% of the tube diameter respectively. The computational fluid dynamics results of the laminar flow simulations revealed that the pressure loss coefficients of the sudden contraction and rounded inlet sections were very similar. The pressure loss coefficient of the sudden contraction inlet sections only being 3 to 6% higher than the rounded inlet sections. This is due to the dominant effect of viscosity in the laminar flow regime. The viscosity reduces the extent of flow contraction occurring since transverse momentum is damped by the viscous dissipation. The dominant pressure loss mechanism in the laminar flow regime is hydrodynamic flow development. With hydrodynamic flow development the flow velocity profile changes from a uniform velocity profile before the inlet section into a pointed parabolic profile downstream in the tube. The turbulent flow simulation results revealed that the pressure loss coefficients of the rounded inlet sections investigated in this study were very similar. The pressure loss coefficient of the sudden contracting inlet section was higher than the rounded inlet sections’ pressure loss coefficient. The results indicated that rounded tubular inlet sections would be of limited value in the laminar flow regime; it would however be beneficial in the turbulent flow regime. , Prof.J.P. Meyer Prof. L. Pretorius
- Full Text:
- Authors: Bijkersma, Jan
- Date: 2008-07-18T13:40:52Z
- Subjects: Heat exchangers , Pressure , Fluid dynamics , Condensers (vapors and gases)
- Type: Thesis
- Identifier: uj:7322 , http://hdl.handle.net/10210/805
- Description: When water vapour condenses at a sub-atmospheric pressure, the pressure drop may be a significant fraction of the absolute pressure. Furthermore the pressure drop in a condenser passage also reduces the absolute vapour temperature and therefore affects the heat transfer capacity of a condenser. For a tubular heat exchanger the pressure loss in the heat exchanger tubes can be minimized by the use of contoured or rounded inlet sections at the inlets of the tubes instead of using a sudden contracting inlet section or a protruding inlet section for the tubes. The pressure loss characteristics of different inlet sections to the tubes were obtained through a literature survey of the pressure loss coefficients. The pressure loss at the inlet sections were also investigated with computational fluid dynamics, using the Star-CD software system. The flow regimes for which the pressure loss was investigated were for the laminar incompressible and turbulent incompressible flow regimes. The inlet sections investigated were a sudden contraction and two rounded inlet sections with a rounding radius of 52% and 105% of the tube diameter respectively. The computational fluid dynamics results of the laminar flow simulations revealed that the pressure loss coefficients of the sudden contraction and rounded inlet sections were very similar. The pressure loss coefficient of the sudden contraction inlet sections only being 3 to 6% higher than the rounded inlet sections. This is due to the dominant effect of viscosity in the laminar flow regime. The viscosity reduces the extent of flow contraction occurring since transverse momentum is damped by the viscous dissipation. The dominant pressure loss mechanism in the laminar flow regime is hydrodynamic flow development. With hydrodynamic flow development the flow velocity profile changes from a uniform velocity profile before the inlet section into a pointed parabolic profile downstream in the tube. The turbulent flow simulation results revealed that the pressure loss coefficients of the rounded inlet sections investigated in this study were very similar. The pressure loss coefficient of the sudden contracting inlet section was higher than the rounded inlet sections’ pressure loss coefficient. The results indicated that rounded tubular inlet sections would be of limited value in the laminar flow regime; it would however be beneficial in the turbulent flow regime. , Prof.J.P. Meyer Prof. L. Pretorius
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