Effective borehole thermal resistance of a single u-tube ground heat exchanger
- Authors: Liao, Quan , Zhou, Chao , Cui, Wenzhi , Jen, Tien-Chien
- Date: 2012
- Subjects: Ground-source heat pumps
- Type: Article
- Identifier: uj:5271 , ISSN 1040-7782 , http://hdl.handle.net/10210/14940
- Description: A ground-source heat pump (GSHP) uses the earth as a heat source or heat sink to extract or reject the thermal energy. Since the annual temperature fluctuation of soil under the ground is relatively small, the GSHP system has been recognized as one of the most energy-efficient systems for space heating and cooling in residential and commercial buildings. In a GSHP system, one of the most important components is the ground-coupled heat exchanger, through which thermal energy is exchanged between heat carrier fluid (i.e., water or water-antifreeze fluid) and soil. Since the ground heat exchanger is responsible for a major portion of the initial cost of the GSHP system, and the efficiency of this system depends on the performance of a ground heat exchanger, careful design of the ground heat exchanger is crucial for successful application of the GSHP system [1].
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New correlation for thermal resistance of vertical single u-tube ground heat exchanger
- Authors: Liao, Quan , Zhou, Chao , Cui, Wenzhi , Jen, Tien-Chien
- Date: 2012
- Subjects: Ground-source heat pumps
- Type: Article
- Identifier: uj:5283 , http://hdl.handle.net/10210/14952
- Description: Ground-source heat pump (GSHP) uses the earth as a heat source or heat sink to extract or reject the thermal energy. Since the annual temperature fluctuation of soil under the ground is relatively small, the GSHP system has been recognized as one of the most energy efficient systems for space heating and cooling in residential and commercial buildings. In a GSHP system, one of the most important components is the ground-coupled heat exchanger through which the thermal energy is exchanged between heat carrier fluid (i.e., water or water-antifreeze fluid) and soil. Since the ground heat exchanger is responsible for a major part of the initial cost of GSHP system and the efficiency of this system depends on the performance of ground heat exchanger, a careful design of ground heat exchanger is crucial for a successful application of GSHP system [1].
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An experiment study of flow pattern and pressure drop for flow boiling inside microfinned helically coiled tube
- Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Liao, Quan , Chen, Qinghua
- Date: 2008
- Subjects: Flow boiling , Pressure drop , Helically coiled tubes , Microfin tubes , Flow patterns , Finned tubes
- Type: Article
- Identifier: uj:5278 , http://hdl.handle.net/10210/14947
- Description: In this paper, flow patterns and their transitions for refrigerant R134a boiling in a microfinned helically coiled tube are experimentally observed and analyzed. All the flow patterns occurred in the test can be divided into three dominant regimes, i.e., stratified-wavy flow, intermittent flow and annular flow. Experimental data are plotted in two kinds of flow maps, i.e., Taitel and Dukler flow map and mass flux versus vapor quality flow map. The transitions between various flow regimes and the differences from that in smooth straight tube have also been discussed. Martinelli parameter can be used to indicate the transition from intermittent flow to annular flow. The transition from stratified-wavy flow to annular or intermittent flow is identified in the vapor quality versus mass flux flow map. The flow regime is always in stratified-wavy flow for a mass flux less than 100 kg/m2 s. The two-phase frictional pressure drop characteristics in the test tube are also experimentally studied. The two-phase frictional multiplier data can be well correlated by Lockhart–Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations are proposed, and show a good agreement with the respective experimental data.
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Heat transfer performance in 3D internally finned heat pipe
- Authors: Liao, Quan , Jen, Tien-Chien , Chen, Qing-hua , Li, Longjian , Cui, Wenzhi
- Date: 2007
- Subjects: Heat pipes , Heat transfer , Finned tubes
- Type: Article
- Identifier: uj:5276 , http://hdl.handle.net/10210/14945
- Description: An experimental study of heat transfer performance in 3D internally finned steel-water heat pipe was carried out in this project. All the main parameters that can significantly influence the heat transfer performance of heat pipe, such as working temperature, heat flux, inclination angle, working fluid fill ratio (defined by the evaporation volume), have been examined. Within the experimental conditions (working temperature 40 C–95 C, heat flux 5.0 kw/m2–40 kw/m2, inclination angle 2–90 ), the evaporation and condensation heat transfer coefficients in 3D internally finned heat pipe are found to be increased by 50–100% and 100–200%, respectively, as compared to the smooth gravity-assisted heat pipe under the same conditions. Therefore, it is concluded that the special structures of 3D-fins on the inner wall can significantly reduce the internal thermal resistance of heat pipe and then greatly enhance its heat transfer performance.
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A heat transfer correlation of flow boiling in micro-finned helically coiled tube
- Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Chen, Qinghua , Liao, Quan
- Date: 2006
- Subjects: Convective boiling , Heat transfer , Helically coiled tubes , Nucleate boiling
- Type: Article
- Identifier: uj:5275 , http://hdl.handle.net/10210/14944
- Description: Two main mechanisms, nucleate boiling and convective boiling, are widely accepted for in-tube flow boiling. Since the active nuclei on the heated wall are dominant for nucleate boiling and flow pattern governs the convective boiling, the heat transfer coefficient is strongly influenced by the wall heat flux, mass flux and vapor quality, respectively. In practical industrial applications, for example, the evaporators in refrigeration, forced convective evaporation is the dominant process and high heat transfer efficiency can be obtained under smaller temperature difference between wall and liquid. Therefore, it is of importance to develop a correlation of convective boiling heat transfer with a good accuracy. In this paper, a new kind of micro-finned helically coiled tube was developed and the flow boiling heat transfer characteristics were experimentally studied with R134a. Based on the analysis of the mechanisms of flow boiling, heat transfer correlations of the specific micro-finned helically coiled tubes are obtained.
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Heat transfer and pressure drop experimental correlations for air-water bubbly flow
- Authors: Cui, Wenzhi , Li, Longjian , Chen, Qinghua , Liao, Quan , Jen, Tien-Chien
- Date: 2006
- Subjects: Bubbly flow , Gas-liquid flow , Heat transfer , Pressure drop
- Type: Article
- Identifier: uj:5268 , http://hdl.handle.net/10210/14937
- Description: In this paper, a novel air–water bubbly flow heat transfer experiment is performed to investigate the characteristics of pressure drop of airflow and heat transfer between water and tubes for its potential application in evaporative cooling. The attempts to reduce the pressure drop while maintaining higher heat transfer coefficient have been achieved by decreasing the bubble layer thickness through the water pump circulation. Pressure drops of air passing through the sieve plate and the bubbling layer are measured for different height of bubble layer, hole–plate area ratio of the sieve plate and the superficial air velocity. Experimental data show that the increase of bubble layer height and air velocity both increase the pressure drop while the effect of the hole–plate area ratio of the sieve plate on the heat transfer coefficient is relatively sophisticated. A pressure drop correlation including the effects of all the tested parameters is proposed, which has a mean absolute deviation of 14.5% to that of the experimental data. Heat transfer coefficients of the water and the outside tube wall are measured and the effects of superficial air velocity, heat flux and bubble layer height are also examined. Through a dimensional analysis, a heat transfer correlation with a mean absolute deviation of 9.7% is obtained based on experimental data.
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The acceleration of charged nano-particles in gas stream of supersonic de-laval-type nozzle coupled with static electric field
- Authors: Jen, Tien-Chien , Pan, Liang-Ming , Li, Longjian , Chen, Qing-hua , Cui, Wenzhi
- Date: 2006
- Subjects: Static electric potential , Bow shock , Electrostatic-force-assisted cold gas dynamic spray , Cold gas dynamic spraying , Nano-particles
- Type: Article
- Identifier: uj:5269 , http://hdl.handle.net/10210/14938
- Description: This paper presents a numerical analysis of an innovative method for nano-scale particle deposition, called Electrostatic-forceassisted cold gas dynamic spray (ECGDS). The transport characteristics of nano-scale charged particles in supersonic gas stream coupled with electrostatic field are simulated. Outside the nozzle, there exists bow shock near the substrate, which causes steep pressure increase across the shock. When the gas flow penetrates the bow shock and approaches to the substrate, the carrier gas speed decreases to nearly zero. In this study, electrostatic force is used to assist the charged particle to achieve high velocity upon impact of the substrate. The effect of electrostatic field to the velocity distribution of charged particles is investigated. It is found that smaller particles have the higher impact velocities on substrate. The higher particle charge densities can lead to higher particle impact velocities; and the closer the particles approach to the substrate, the stronger the electrostatic forces act on particles. For nano-scale particles the particle density (i.e. different materials) almost has no influence on the velocity profile.
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Heat transfer augmentation in 3D internally finned and micro-finned helical tube
- Authors: Li, Longjian , Cui, Wenzhi , Liao, Quan , Mingdao, Xin , Jen, Tien-Chien , Chen, Qinghua
- Date: 2005
- Subjects: Helical tubes , Finned tubes , Heat transfer
- Type: Journal
- Identifier: uj:5263 , http://hdl.handle.net/10210/14932
- Description: Experiments are performed to investigate the single-phase flow and flow-boiling heat transfer augmentation in 3D internally finned and micro-finned helical tubes. The tests for single-phase flow heat transfer augmentation are carried out in helical tubes with a curvature of 0.0663 and a length of 1.15 m, and the examined range of the Reynolds number varies from 1000 to 8500. Within the applied range of Reynolds number, compared with the smooth helical tube, the average heat transfer augmentation ratio for the two finned tubes is 71% and 103%, but associated with a flow resistance increase of 90% and 140%, respectively. A higher fin height gives a higher heat transfer rate and a larger friction flow resistance. The tests for flow-boiling heat transfer are carried out in 3D internally micro-finned helical tube with a curvature of 0.0605 and a length of 0.668 m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D internally micro-finned helical tube is increased by 40–120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance is increased by 18–119%, respectively.
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Numerical investigations on cold gas dynamic spray process with nano- and microsize particles
- Authors: Jen, Tien-Chien , Li, Longjian , Cui, Wenzhi , Chen, Qinghua , Zhang, Xinming
- Date: 2005
- Subjects: Numerical simulation , Cold gas dynamic spraying , Microparticles , Copper particles , Platinum particles
- Type: Article
- Identifier: uj:5265 , http://hdl.handle.net/10210/14934
- Description: The particle velocity in cold gas dynamic spraying (CGDS) is one of the most important factors that can determine the properties of the bonding to the substrate. In this paper, the acceleration process of microscale and sub-microscale copper (Cu) and platinum (Pt) particles inside and outside De-Laval-Type nozzle is investigated. A numerical simulation is performed for the gas-particle two phase flow with particle diameter ranging from 100 nm to 50 lm, which are accelerated by carrier gas nitrogen and helium in a supersonic De-Laval-type nozzle. The carrier gas velocity and pressure distributions in the nozzle and outside the nozzle are illustrated. The centerline velocity for two types of particles, Pt and Cu, are demonstrated. It is observed that the existence of the bow shocks near the substrate prevents the smaller size particles (less than 0.5 lm) from penetrating, thus leads to poor coating in the actual practices. Furthermore, the extended straight section may have different optimal length for different size particles, and even may be unnecessary for sub-microsize particles.
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Heat transfer augmentation in 3D inner finned helical pipe
- Authors: Li, Longjian , Cui, Wenzhi , Liao, Quan , Mingdao, Xin , Jen, Tien-Chien , Chen, Qinghua
- Date: 2004
- Subjects: Heat transfer , Helical tubes
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16052 , uj:15733 , Citation: • Li, L. et al. 2004, “Heat transfer augmentation in 3D inner finned helical pipe,” ASME Heat Transfer/Fluids Engineering Conference, July 11-15, 2004, Charlotte, North Carolina, Vol. 3, pp. 139-143. HT-FED2004-56430. ISSN: 0-7918-4692-X.
- Description: Abstract: Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m.Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%~120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%~119%.
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