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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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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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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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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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Heat transfer augmentation in 3D inner finned helical pipe

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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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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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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Numerical simulation of fluid flow and heat transfer in a curved square duct by using the Lattice Boltzmann method

  • Authors: Liao, Quan , Jen, T.-C.
  • Date: 2008
  • Subjects: Fluid flow , Heat transfer
  • Type: Article
  • Identifier: uj:5274 , ISSN 1040-7782 , http://hdl.handle.net/10210/14943
  • Description: The study of viscous flow in curved ducts is of fundamental interest in fluid mechanics due to the numerous applications such as flows through turbomachinery blade passages, aircraft intakes, diffusers, heat exchangers, and so on [1–6]. The major effect of curved ducts on the fluid flow involves the strong secondary flow due to the longitudinal curvature in the geometry [7–9]. The presence of longitudinal curvature generates centrifugal force (which is perpendicular to the main flow along the axis) and produces so-called secondary flow on the cross sections of ducts.
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Transient heat transfer analysis on a heat pipe with experimental validation

  • Authors: Gutierrez, Gustavo , Catano, Juan , Jen, Tien-Chien , Liao, Quan
  • Date: 2006
  • Subjects: Numerical analysis , Heat transfer , Heat pipes
  • Type: Article
  • Identifier: uj:5270 , http://hdl.handle.net/10210/14939
  • Description: In this study, a transient analysis of the performance of a heat pipe with a wick structure is performed. A complete formulation of the equation governing the operation of a heat pipe during transient conditions are presented and discussed. For the vapor flow, the conventional Navier-Stokes equations are used. For the liquid flow in the wick structure, which is modeled as a porous media, volume averaged Navier-Stokes equations are adopted. The energy equation is solved for the solid wall and wick structure of the heat pipe. The energy and momentum equations are coupled through the heat flux at the liquid-vapor interface that defines the suction and blowing velocities for the liquid and vapor flow. The evolution of the vaporliquid interface temperature is coupled through the heat flux at this interface that defines the mass flux to the vapor and the new saturation conditions to maintain a fully saturated vapor at all time. A control volume approach is used in the development of the numerical scheme. A parametric study is conducted to study the effect of different parameters that affect the thermal performance of the heat pipe. And experimental setup is developed and numerical res ults are validated with experimental data. The results of this study will be useful for the heat pipe design and implementation in processes that are essentially transient.
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