EXPERIMENTAL INVESTIGATION ON BOILING HEAT TRANSFER OUTSIDE THE LOW FINNED TUBE WITH SHROUD

Based on analysis of pool boiling characteristics outside low finned tube, this paper describes a simple method, using enhancing shroud to improve the performance of boiling heat transfer outside the low finned tube. The experiment results show that the boiling heat transfer coefficient can be 7-up to 10-fold enhanced by using shroud. The efficiency of a shroud is related to the size of two windows, heat flux and physical characteristics of test fluids.     

AN EXPERIMENTAL RESEARCH ON ENHANCEMENT OF HEAT TRANSFER OF FINNED TUBES IN REFRIGERANT HEAT EXCHANGER

In this paper,the comparative experimental research that air flows through theout-surface of a single row finned tubes is done in a drawing wind tunnel and the three differnetshapes of rectangluar finned tubes are compared with a plain finned tube that is usually used in therefrigerant heat exchanger, the useful results are obtained. The results show that,in the range ofwind velocity flowing through the marrowest area, W_(max)=2.5m/s to 8.5m/s,the average convec-tion heat transfer coefficient of the two-side V-groove finned tube is higher than that of rectangluarplain finned tube,It is a new type finned tube that has good heat transfer performance and it isworth poplarlzing.     

INFLUENCE OF THE GEOMTRIC PARAMETERS OF LOW FINNED TUBE ON BOLHING HEAT TRANSFER AND OPTIMIZATION OF THE PARAMETERS

On the basis of the mechanism of the boiling heat transfer on low finned tube, the influence of the geometric parameters of low finned tube on boiling heat transfer is synthetically analyzed and relevant criteria which affect the optimal structure of low finned tube is deduced in this paper. The boiling heat transfer experiment on low finned tube is conducted. Distilled water and R-113 are used as test fluids The experiment is performed at local atmospheric pressure. Synthesizing a large amount of experimental data, the semiempirical equations for the optimal geometric parameters of lowfinned tube are established     

Experiment for Condensing Heat Transfer Performance in a New Type of Horizontal Three Dimensional Inner Microfin Tubes

A new type of three dimenstional inner microfin tube is devoloped. Under four different pressures and in the range of condensing mass velocities from 33 to 153 kg/m2 . s,and by the experimental study of the three kinds of tubes with different microfin parameters, the performances of the condensation heat transfer for R11 in the horizontal microfin tubes and obtained. The experiments show that the inner microfin tube is a hopeful and nighty effective condensing heat transfer enhancement tube.     

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.     

EXPERIMENTED INVESTIGATION OF EFFECT OF THE INCLINATION ON HEAT TRANSFER ON TUBE

The present paper discribes experiment research of effect of the inclination on heat transfer on 9 kinds of plain tubes in atomosphere, working fluids are distill water and ethanel. Experinent result show very obvious effect of inclination of pool boiling heat transfer. The larger heat transfer increases, the larger the inclination does. The correlation obtained on 524 experiment data can be used for reference to engineering design in prospect of heat transger coefficient.     

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.     

THE EFFECT OF THE CONVECT1VE HEAT TRANSFER IN THE ENTRANCE REGION OF THE TUBE ON THE HEAT TRANSFER IN THE TRBE -MOUTH REGION OF THE HIGH TEMPERATURE HEAT EXCHANGE EQUIPMENT

The effect of the convective heat transfer in the entrance region of the tube on the temperature field and the maximum temperature of the tube material in the tube -mouth region of the high temperature heat exchange equipment is examined by numerical analysis. The computations on the basis of four different formulas for convection heat transfer coefficient are performed. The computed results indicate that the efect can not be ignored as for heat protection of the tube -mouth region and it is resapnable and secure that the mean convective heat transfer coefficient with taking account of the effect of the entrance region is used in the thermal design of the tube -mouth region.     

Heat Transfer and Friction Characteristics for Cross-flow over Staggered External Three-dimensional Finned Tube Banks

In this paper, the heat transfer and friction characteristics for cross-flow over staggered new external three-dimensional finned tube banks developed by the Chongqing University of China are investigated by means of cross optimization experiment. The results of experiment show that the rate of heat transfer is enhanced from 1.5 to 2.5 and the ratio of pressure drop is increased from 1 to 3.5 compared to the bare tubes in the range of Reynolds numbers Re=2 900-14 000. The heat transfer and friction factor correlations are obtained through step by step regression and then, the influence of geometric parameters of fins on the characteristics of heat transfer and friction is analyzed.     

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.     

Degital Simulation for the Direct Torque Control of Induction Motors Using the Circle Flux Path

This paper introduces the importance of developing the Ground-Source Heat pump and describes the prospects of it.with the method used abroad to acquire the temperature profiles within surrounding soil of the underground heat exchanger with buried tubes, in this paper the line heat source theory and thermal resistance network analysis method were used to set up the heat transfer model.The original temperature of the ground is determined by calculation and is compared with test results. Experiments of running single tube and running three series connection tubes are carried out on the built underground exchangers of vertical buried tube type.And the data which can provide reference for the Ground-Soure Heat pump technique are acquired.     

Convection Heat Transfer Coefficient Distribution Over the Single Rectangle Fin Surface

Rectangle fin is widely used in different kinds of heat exchangrs. Convection heat transfercoefficient distribution over the fin surface is one of the theorehcal problems in research on enhancement of heat transfer. In this paper, a tube with an attached rectangular fin is used for a model and thefin surface is divided into a network of nodes by the finite difference techinque. When the wind velocityis u= 4. 5 m/s. the temperature distribution of discretization is obtained by experimental measurement,then the convection heat transfer coefficient of all nodes are soved by using the methed of inverse heatconduction problem. Through checking with heat balance methed, the results show that the solution cancorrectly express the actual heat transfer situation.This result is useful to experimental research onenhancement of heat transfer for finned for heat exchangers.     

美国梾木(Cornus spp.)花粉活力及萌发特性

为了了解美国梾木花粉活力及萌发特性,采用扫描电镜技术对13个美国梾木无性系花粉形态进行观测与方差分析,并采用荧光显微技术和TTC染色法对无性系2号花粉萌发特性及花粉活力进行观察。结果显示:(1)不同无性系间花粉大小差异不显著,但外壁纹饰差异较大,极面沟距的变异系数最高且遗传最为稳定。(2)花序开花率为75%时花粉活力最高,整花4℃条件下短期保存花粉活力较高。(3)授粉后,多数花粉可在柱头上正常萌发,72 h后花粉管即可进入子房。研究认为,花粉外壁及极面沟距可作为鉴定美国梾木无性系的形态指标,美国梾木花粉活力及萌发特性是抗逆及丰产杂交组合的重要保证。     

Heat transfer performance analysis of lithium bromide solution falling film evaporation in vertical tube

For making the refrigeration system directly driven by low temperature waste flue gas heat more efficiently,an experimental research on the heat transfer of vertical in tube laminar falling film with different heat fluxes and different concentrations of lithium bromide solution is conducted.The outcome of falling film evaporation experiments show that the heat transfer coefficient increases with the decrease of inlet concentration of lithium bromide solution and significantly increases with the increase of heat flux.Based on multiple linear regression calculation of experimental data,an experimental correlation of falling film heat transfer coefficient is obtained.A falling film generator of lithium bromide absorption chiller is designed from the correlation,and the immersed generator whose heat load is equal to the falling film generator is designed.The comparison of the two generators on heat transfer coefficient,weight and volume of heat transfer components shows that the falling film generator has great advantages.     

Analysis of coupled heat transfer between freezing soil,water and horizontal heat exchange tube

The research object is the coupled heat transfer effect between freezing soil,water and horizontal heat exchange tube,use finite volume numerical method to dispersed solving for continuity equation and heat transfer equation of unsaturated freezing soil,gives part of the temperature fields and freezing percentage distribution graphs,and analyzes the reason of the coupled heat transfer.The analysis result shows that:the temperature field of freezing soil are some horizontal lines parallelling to the ground surface.The peak value of solid-liquid phase change region appears in the upper part where there is backwater pipe,the low value appears in the place where there isn't horizontal heat exchange tube.The horizontal heat exchange tube makes the freezing front deviate towards the ground surface.The arrangement difference of inlet and outlet position of horizontal heat exchange tube will effect the size and position of the phase change region of freezing soil.Arranging the backwater pipe at one side or middle position is the optimized mode.     

Experiments on Convective Heat Transfer for Various Media Flowing Turbulently in Tubes with Three Dimensional Internally Extended Surface

This paper presents the experimental results of convective heat transfer performance in 5 copper tubes with three dimensional internally extended surface, with flow of various test fluid in the Reynolds number range of 8,000 to 80,000. Water and mixture of ethylene glycol with water (the ethylene glycol weight content equals 55%) are chosen as test fluid. The effect of the physical properties for test fluid on heat transfer performance in the tubes with three dimensional internally extended surface is discussed. The heat transfer correlation is obtained by the experimental data.     

THE EFFECTS OF HEAT CONDUCTING CROSS-SECTION AREA AND AXIAL HEAT CONDUCTION ON THE HEAT TRANSFER IN THE TUBE-MOUTH REGION OF THE HIGH TEMPERATURE HEAT EXCHANGE EQUIPMENT

In this paper the heat transfer in the tube-mouth region of the high temperatur heat exchange equipment is deeply analysed. The effect; of the heat conducting cross-section area of the tube-mouth region and axial heat conduction along the tube on the temperature field is emphatically examined by numerical computation, and then the relation of the highest temperature in the tube with the elongated tube length is established. The computed results in this paper are compared with those without taking account of these two factors. It is shown that the effect can not be ignored for the corrosion-protection by controlling temperature.     

The Influence of Width of Flag-type Inserts on the Forced Convection of Oil in a Tube

Experimental study of forced convection heat transfer in a horizontal circulartube with ladder-shaped flag-type insert is performed to investigate the characteristics of fluid flow ,heat transfer and the influence of width of flag insert.The working fluid is 30# turbine oil.Theresult shows that the increase of W/D causes the increase of heat transfer coefficient and resistanceforce of fluid flow. The heat transfer coefficient can be enhanced mainly within the length of ninetimes of inner diameter of tube for oil.In the range of experiment, the value of creteria to evaluatethe combined effect is between 1.13 and 1.59.     

Thermodynamic Analysis of River Water Fouling on Constant Wall Temperature Tube of Small Diameter

In order to improve utilization of cold and heat source from river, turbulence theory and entropy generation theory were adopted to analyze the effect of fouling on convective heat transfer performance in small diameter tube of constant wall temperature.It is found that the entropy generation caused by conduction of fouling plays a more important role in total entropy generation of heat transfer process through a duct than that in cveast rate of caused by temperature difference.The entropy generation caused by viscous flow is more than the entropy generation caused by temperature difference in flow with bigger Reynolds and small radius.The increase rate of entropy generation monotonically increase with Reynolds and the generation process of fouling resistance.Thereafter, the effect of fouling resistance on the heat transfer performance of water source heat pump heat exchanger should be paid more attention, when river water are used as the cold and heat source of heat pump.     

ANALYSIS AND CALCULATION OF CONDENSATION HEAT TRANSFER ON HORIZONTAL LOW-FINNED TUBE ATTACHED BY A POROUS DRAINAGE STRIP

An analytical model was proposed for the condensation heat transfer on the horizontal low-finned tube attached by a porous drainage strip, and compared with the experimental data with a good agreement. The permeability of the porous drainage strip was also experimentally determined.