Dtermination of The Suppression Faction of Chen''s Model in Flow Boiling

In present paper, the suppression factor of Chen's model is determined, based on the force and heat balance on a vapour bubble and Clausius-Clapeyron equation, the active nucleate cavity size of flow boiling surface and its disperse characteristic. Furthermore, the correlation is attained using Chen' model and the present suppression factor from the experimental data of R134a and R22 for a smooth tube. The correlation agrees well with the experimental data. It demonstrates the present suppression factor is able to promote the accurate which predicts the heat transfer coefficient of flow boiling in Chen's model.     

Heat Transfer Performance of Horizontal Enhanced Condenser Tubes

In this paper, experimental results on heat transfer performance of a low integral-fin tube, thermoexcel-C tube (C tube) and a new horizontal double-side enhanced condenser tube (GC tube) have been reported for condensation of R-11. Within our experimental scope,the overall heat transfer coefficient of the GC tube can increase more than 5 times that of the smooth tube . And the relevant friction factor inside the GC tube can be 7 times that of the smooth tube. The Second law of thermodynamics was applied to develop a new criterion to assess the heat transfer performance of the GC tube,the C tube,the low integral-fin tube,and the DAC tube[1] (another doubleside enhanced condenser tube). The result shows the heat transfer performance of the GC tube is superior to the other tubes from a thermodynamical viewpoint.     

Experimental Study of Flow and Heat Transfer in Heat Exchanger with Small Channels

The experimental study of the flow resistance and heat transfer characteristics are conducted for water and ethylene glycol solution (66% Wt) flowing in the heat exchanger with small rectangular microchannels . The heat exchanger having the channels of 0.4 mm in width, 2.0 mm in height, and 20 mm in length is heated by a hearing rod at the bottom surface, the upper and two side surfaces are adiabatic. During experiments, the Reynolds number are ranged from 2 to 2 500. The experimental results show that the flow friction factor decreases and Nusselt number increases with increasing Reynolds number for water and ethylene glycol solution. At a fixed Reynolds number, the Nusselt number for ethylene glycol solution with larger Prandtl number is greater than that for water. Meanwhile, the correlations of flow resistance and heat transfer in the heat exchanger with small channels are obtained for engineering application.     

Analysis for Heat Transfer in Micro-annular Channel with Unsymmetrically Heated Walls in Slip Flow Regime

A theoretical analysis is presented for heat transfer in micro-annular channel with an adiabatic wall and a heated wall with uniform wall temperature in slip flow regime. The energy equations with the boundary conditions of temperature jump are solved for the hydrodynamical and thermal fully developed laminar flow of the incompressible fluid in this microchannel. The influences of the Kn number, the ratio of inner diameter to outer diameter on the heat transfer characteristics are discussed respectively. The results show that the Nusselt number in microchannel decreases with the increasing of Kn number comparing with that in macrochannel.     

Experimental Studies of Forced Convective Heat Transfer and Pressure Drop of Ethylene Glycol in Tubes with Three Dimensional Internally Extended Surface

In this paper,the reSults are presented from experimental investigation on heattransfer performance in seven copper tu bes with three dimensional internally extended surface(3-DIEST)varying in axial pitch,circumferential pitch,height, width and arrangement form of fins. The forced con vective heat transfer and pressure drop of ethylene glycol flowing in the 3-DLESTShave been tested in the Revnolds number range from 250 to 6,000 and the Prandtl number rangefrom 60 to 90.The average stanton number in the most superior 3-DIEST can be increased about2.4times in the laminar flow.and4.5 times in the transitional flow and turbulent flow as com-pared with that in the smooth tube. And the friction factor between fluid and tube wall can be 1.7times in laminar flow. and 4 times in transitional flow andturbulent flow inside the 3-DIEST as much as those inside the smcoth tube.     

Effect of High-frequency Thermal Disturbance on Soil Temperature around the Metro Tunnels

Soil temperature prediction model around the subway metro tunnels is constructed with the consideration of coupled heat transfer between range temperature and surrounding soil. Finite difference method is adopted for numerical solution of the model, and the solving results in certain conditions are compared to validate the analytical solution. The high-frequency thermal disturbance brought by train operation is simplified into three different forms, and the predictive model of soil temperature is used to calculate the corresponding soil temperature response. It is indicated that temperature fluctuations of range air and the wall are accompanied with high-frequency thermal disturbance, but the impact on soil temperature distribution inside is limited.     

Pressure Drop and Evaporative Heat Transfer Characteristics of Air-water Bubbling Flow

A new kind of evaporative heat transfer experiment for the cooling process of condensers is conducted. The test coil is immersed in an air-water bubbling layer. The air-water two-phase flow passes through the heating tubes of the coil. Due to the motion of the air bubbles in the water, a thin water film forms on the surface of the heating tubes. As the air bubbles passing by the tubes the water is evaporated into the air. The tubes of coil reject heat to the water film, and the evaporation of the water film then rejects heat to the air bubble stream. This heat transfer mode significantly increases the heat transfer coefficient between tubes and air. The consumption of the power of a water pump can be decreased. Moreover, the airflow rate required is less than that of an air-cooled condenser.The pressure drop of air through air-water bubbling layer and the heat transfer between the tubes and water are experimentally investigated in the paper. The results show that the factors affecting the pressure drop and the heat transfer coefficient involve the pore geometry of sieve plate, the height of the air-water bubbling layer, the air flow rate through the sieve plate and the heat flux of tubes. The heat transfer coefficient between tube and water is two times larger than that of falling film of water on the outer surface of tube.     

武汉与重庆典型地质结构下的地埋管换热性能

地埋管地源热泵换热器的换热性能受到不同地质结构的影响。以武汉和重庆地区的典型地质构成为边界条件,建立了三维地埋管的单孔双U管换热模型,通过模型计算,获得了两种地质条件下的地埋管换热性能,以重庆地区的地源热泵热响应测试结果以及工程运行数据出发,对模型的计算结果进行了验证,结果表明,模型吻合度较好,可以应用于工程分析。以模型为条件,进行地质结构对换热性能的影响度分析,预测了两地地埋管地源热泵的换热性能并计算得到换热器的平均换热系数分别为武汉地区K₁=1.65（W/m·K）,重庆地区K₂=1.51（W/m·K）。     

Selection of Direction Types of Tubes in Spray Type Sewage Heat Exchanger

In recent years, sewage source spray heat exchanger was widely used in sewage source heat pump systems with its higher heat transfer coefficient, easier operation and maintenance and less energy, etc. In this paper, we studied the direction arrangement of heat exchange tubes of spray heat exchanger. And the heat transfer coefficient, film coverage, effective area ratio has been studied through mathematical tools and CFD simulations and other means. The results showed that in the sewage-source heat pump project, when the engine room area is relatively small but highly space is sufficient, the vertical arrangement of spray heat exchanger tubes can obtain a good effect.     

Experimental Study of Ground-source Heat Pump Systems with Horizontal Heat Exchanger

This paper describes the double layer horizontal ground source heat pump systems constructed in 1998 with the buried depth of 0.9 m and 1.8 m. The program of study includes experimental equipments, heat exchanger size, testing meter and methods for data analysis. In addition, the heating and cooling performance at typical days are also illustrated. Among the influencing factors on the performance of the ground source heat pump systems, the parameter of heat exchanger and operation patterns of heat pump systems are analyzed.A heat transfer model has been set up for horizontal heat exchanger.     

Design and experimental analysis of the heat transfer panel with capillary imbibition core

Serpentine radiant heat transfer pipes(SRHTP)are expensive and with low heat exchanged, so the heat transfer panel with capillary imbibition core (HTPCIC) is put forward. HTPCIC is composed by potassium citrate-plaster (PCP), and PCP board becomes a uniform channel of which the flow rate is 55.3% when water is cooling medium. By changing the emissivity of HTPCIC' surface(low emissivity 0.23,high emissivity 0.95)and the temperature of cold-water(7~18 ℃), at 26 ℃ (±1 ℃), heat transfer characteristics of HTPCIC are analyzed whose average pore radius is 0.015 mm and porosity is 55.3%. The experimental results show that the cooling capacity of HTPCIC meets the requirements of conventional radiation air-conditioning, and compared with SRHTP, the initial cost reduces by 80%. Moreover, regression equation of the HTPCIC heat transfer guideline is proposed: Nu=0.029Re0.21Pr2.6θ0, which provides basis for establishing a complete design theory.     

Influence of x gear on the Flow Characteristic of the Second Kind of Compound Gear Pump

The paper analysed the influence of x gear on the movement law of each engaging point and the flow characteristic of the second kind of compound gear pump with x gear.The formula of flowrate and flow pulse are given with the best type of instruction.