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.     

AN EXPERIMENTAL STUDY OF BOILING HEAT TRANSFER ON SMOOTH TUBE BUNDLES

This paper introduces the clarifying influence of the intertube spacing, the tube arrangement,the heat flux and the working fluid on boiling heat tra(?)sfer of smooth tube bundles. The tube bundles include the arrangements of twin tubes, triple tubes, seven tubes and thirteen tubes. The relative intertube spacing of the tube bundles is from 0. 9 to 3. 3. Experimental results show that the tube position and intertube spacting have no effect on boiling curves for the region of fully-devoloped boiling. And they considerably affect the heat transfer coefficient for the transition region between natural convection and nucleate boiling. In general,the heat transfer coefficient in the transition region for the upper tubes can be enhanced by 0. 5 to 1. 5 times.     

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.     

THERMODYNAMIC ANALYSIS AND PERFORMANCE EVALUATION OF CONVECTIVE HEAT TRANSFER THROUGH DUCTS

A second law analysis is carried out on convective heat transfer in fully developed region with constant wall temperature through circular, trianglar and rectangular ducts. Besides, the entropy generation rate expression is obtained and the loss rate of available energy in convective heat transfer processes is defined as well. At the same time, the influence of initial temperature difference between fluid and wall as well as the influence of fluid friction on the loss rate of available energy is discussed. Then, the thermodynamic performances of several typical ducts are compared. Finally , the optimum initial temperature difference with the minimum loss rate of available energy is also obtained.     

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.     

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     

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.     

THERMODYNAMIC ANALYSIS AND OPTIMIZATION OF CONVECTIVE HEAT TRANSFER THROUGH A HORIZONTAL ANNULUS

A second law analysis is carried out on convective heat transfer through a horizontal annulus with constant heat flux. The entropy generation rate expression is obtained,and the influence of heat transfer across a finite temperature difference and fluid friction on the entropy generation rate is discussed. The optimum geometric parameters of a horfzontal annulus is found for which the entropy generated is minimum. The optimum fluid velocity which corresponds to the optimum geometric parameters is recommended.     

AN EXPERIMENT ON HEAT TRANSFER BY MICROWAVE THAWING IN A FOOD ANALOGUE MATERIAL

The one-dimensional heat transfer of microwave thawing in a food analogue material is experimentally studied. The results show that the phase change region is narrow and the latent heat is quickly released due to the effect of the microwave energy. Besides, in the rising section of the temperature after thawing. the internal heat source makes the temperature at the central point rise more quickly than that at other parts of the tested element.     

NUMERICAL STUDY OF NATURAL CONVECTION HEAT TRANSFER IN A PARTIAL CAVITY

A numerical analysis is carried out for the unsteady and steady, two-dimensional, laminar natural convection heat transfer in a square partial cavity. The partial cavity consists of two horizontal adiabatic surfaces, a vertical hot surface and a cold surface with varied opening. The results are obtained for Ra = 10~3-10~6 and Y0 = 0.0-1.0. This study shows that the opening size has significant effect on the flow and heat transfer in partial cavity, and the. extent of its effect changes with different Rayleigh numbers.     

CONDENSATION HEAT TRANSFER ON THE THREE-DIMENSIONAL EXTENDED SURFACE TUBE ATTACHED BY A POROUS DRAINAGE STRIP

An experimental study was carried out for the condensation heat transfer on the three dimensional extended surface tube attached by a porous drainage strip. The results show that the combination of the three dimensional extended surface and the porous drainage strip is the effective method enhancing condensation heat tiansfer on the horizontal tube. The change of the shape arid depth of the axial grooves results in a 10% vaitation of condensation heal transfer coei ficienls. In the range of the experiments, for aocohol as the working fluid, the enhancement is up to 152%, and for water, 185% as compared with the horizontal low-finned tube.     

NUMERICAL STUDY OF FLOW AND HEAT TRANSFER IN AN INCLINED RECTANGULAR FIN GROOVE

Flow and heat transfer are numerically studied in a rectangular fin groove when the fin base is heated with contsant temperature. Rayleigh number, inclination , aspect ratio, thick ness and conductivity of the fin are systematically changed to examine their effects. Five flow patterns are found, local and average characteristics are given, and the mechanism of heat transfer is discussed. The results can be used as a reference for fin designs.     

STUDY ON HEAT TRANSFER MATHEMATICAL MODEL BETWEEN BILLETS AND ROLLERS FOR THE SECONDARY COOLING ZONE IN BILLET CONTINUOUS CASTING

A mathematcal model of heat transfer between the billet and the roller for the seeondary cooling zone in billet continuous casting is established. By means of the simulated test,a regres sion relation between the heat flow from the billet into the roller and the surface temperature and cast ing speed and spray water density obtained. The calculated theoretical values for change of surface temperature are in agreement with the measured data, these studies may contribut to the quantitative analysis and the calculation of the heat transfer of the secondary cooling zone.     

A STUDY OF THE MECHANISM OF HEAT-TRANSFER DURING METAL HEATING WITH IMPINGING JET

The mechanism of heat transfer during sheet metals heating with impinging jet in a rapid heating furnace is studied with experiments and mathematical simulating methods. It is shown that the heat exchange between metals and impinging jet occurs mainly in the lower region of the hearth,most of which is carried out in the manner of convective heat transfer,and the convective portion of the total heat fluxing to metal is up to 80%. Furthermore,it is also found that the reverse heat flux from metals to the wall, which is a new heat transfer phenomenon, takes place in the late heating period, and the intenser the convective heat transfer in the furnace is, the earlier the reverse radiation occurs.     

HATURAL CONVECTION HEAT TRANSFER JN AN ENCLOSURE WITH A LOCAL INTERNAL HEAT SOURCE

Numerical analysis is made for the unsteady and steady, two-dimensional laminar natural convection in an enclosure caused simultaneously by the external heating and a local internal heat source. The velocities and temperature profiles are given, the average and local Nusselt numbers for the hot and cold surfaces obtained, and the equivalent relative intensity of the internal heat source, the critical equivalent relative intensity of the internal heat source and the transient control regime defined. The results show that there exist five flow patterns with changing the external or internal Rayleigh number, and the heat transfer performance for each flow pattern region is different.     

冷却干燥通风过程中粮仓内热湿耦合传递的数值模拟

基于多孔介质传热传质的理论,建立了一种冷却干燥通风过程中粮仓内热湿耦合传递的数学模型。借助数值模拟的方法,对冷却干燥通风过程中粮仓内温度和水分的变化进行了模拟研究,得到了冷却干燥通风过程中粮堆内部热量传递和水分迁移的基本规律。     

外温作用下储粮建筑围护结构的传热研究

通过介绍西安的地理位置和气候条件,对位于西安的储粮建筑进行了外温作用下粮仓围护结构的传热研究,给出了最适合粮仓夜间机械通风的时间,为降低低温储粮的能耗提供了有力保障.     

粮食仓房隔热性能对低温储粮效果的影响

研究分析了不同粮食仓房围护结构、隔热保冷性能对粮温变化的影响。提出了对于不同的地区、不同类型的粮仓、不同围护结构的要求；并提供了一般建筑结构的粮食仓房隔热性能及改造的常用技术。     

COMBINED HEAT TRANSFER OF TURBULENT NATURAL CONVECTION AND SURFACE RADIATION IN AN OPEN CAVITY

A numerical study is carried out for the combined heat transfer of turbulent natural convection and surface radiation in an two-dimensional open square cavity with only one heated wall. The results show that the radiation significantly affects the velocity and temperature fields,and it can reduce the turbulent natural convection heat transfer as well as enhance it. For different Rayleigh number and temperature difference ratio,the overall heat transfer rates and the portion of radiation present different variation patterns.     

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.