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.     

Experimental Study on Refrigeration Performance of Fin-tube With Circular Hole Under the Frost Condition

The performance of heat transfer of fin-tube with circular hole is better than fin-tube without hole if there is no frost,but what is the situation if under the frost condition.Tthe comparison study on performance of heat transfer and refrigeration is carriedout under the frost condition for the heat exchanger with three kinds of fins: circular and half circular hole,circular hole,plane form.The experiment process is finished through the refrigeration system of icebox.In the course of experiment,the influence of frost process to the diameter of circular hole;is analyzed The real refrigeration amount,heat transfer coefficient and real refrigeration coefficient of the three kinds of fins are compared;compare the effect of energy saving of enforced fins is given.The fin efficiency is calculated method and make out the real convection coefficient to disclose the situation of heat transfer of fins is lnade out.Results: compared with plane form fin,the following results are for fin-tube with circular hole: average heat transfer coefficient rise 11.53%,convection coefficient rises 18.84%,real refrigeration coefficient rises 6.83%,virtual refrigeration amount rises 6.02%,electricity saving is 6.39%.Fin-tube with circular hole is the best form for the three kinds of fins.     

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.     

Numerical simulation and on-site test of anincreasing pipe gas delivery capacity device

The theoretical analysis and experiment show that the wall oscillation can reduce the friction drag of the pipe. The operation mechanism, on-site test and numerical simulation of the Increasing Gas Delivery Capacity Device for the Pipe (IGDCDP) invented by the author are introduced in the paper. The on-site test shows that the IGDCDP can not only reduce the friction drag, but also enhance the gas delivery capacity obviously in the natural gas network. The numerical simulation results show that at the time of inducing some new vortex disturbance waves, the pressure pulse wave generated from the impinging edge has an effect on the oscillation cavity wall to cause oscillation with the large structured vortex rings, so the oscillation cavity is the main component that generating the pulsed jet.     

ALYSTS OF THREE-FLUID SEPARATE TYPE HEAT PIPE EXCHANGER

An analytical model for the separate type heat pipe exchanger with three different fluids is presented. A univeral basic temperature transfer matrix equation can be applied to predict the heat transfer performance of parallel-or counter-flow in which heat is transfered between one hot fluid and two cold fluids or between two hot fluids and one cold fluid. The calculation of a real engineering example proves the proposal model to be reliable.     

Dynamic Heat Transfer Analysis of a Water Storage Roof

On the basis of analyzing the complicate heat and humid exchange between the outdoor air and the water layer of the roof,the authors obtained a heat transfer model and it's transmit matrix. The temperature and heat flux responses of the internal roof surface is greatly lowered than that of non-water layer roof. It can be concluded that the maintenance of a water layer on the roof is a good way to resist the fluctuation of outdoor temperature and significantly reduce the cooling load of a building.     

Effects of Heat Transfer Coefficient of External Window on Residential Buildings in Subtropical Areas

Using Designer's Simulation Toolkit DeST h developed by Tsinghua University, research was carried out on the energy consumption of a typical residential building in Ningbo, P. R. China, with a focus on the heat transfer coefficient of external windows facing every direction. Results show that variation of the heat transfer coefficient of external windows in all directions has a substantial effect on energy consumption for heating but little effect on energy consumption for cooling. It is difficult to decrease cooling energy consumption by decreasing the heat transfer coefficient of external windows in summer. The heat transfer coefficient of external windows facing south has a significant effect on building energy consumption, but the windows facing north have less effect, and those facing east and west have the least impact. Decreasing the heat transfer coefficient of external windows facing north and south from 4.7 to 3.2 produces the most favorable performance cost ratio for energy saving investments. Reasons for the decrease in the heat transfer coefficient of external windows leading to increased air conditioning energy consumption were discussed. The conclusions are useful for guiding energy efficient building design in other subtropical cities.     

热管管外结冰过程研究

通过对热管制冰传热过程的理论分析,得出影响结冰速率的主要因素是热管的温度与半径.建立了管外结冰一维传热模型,分别以半径和时间为步长对结冰速率进行迭代求解,并利用半径微元法得出了不同温度以及不同圆管半径下的制冰速率曲线.与试验结果相比,所得理论模型能够较好地与其吻合.     

Heat Transfer Performance of Capillary Mats Using Wet Construction in Winter

For the capillary mats using wet construction, a winter experiment designed to investigate the heat transfer performance was described, and the heat transfer performance analysis which contains the comparisons between different pipe space and different thickness of cement mortar surface was carried out. As a result, compared with that of the traditional radiant heating pipes, the capillary mats of wet construction require supply water with lower temperature, and it shows good heat transfer performance and system energy efficiency as well. According to the demand of indoor heat dissipation and human comfort as well as the coupling relationship between the temperature of supply water and surface construction thickness, it is suggested that the proper construction method should be comprehensively considered in practical applications.     

Numerical Calculation of Fin Efficiencies and Performances of Rectangular Flat Fins with Modified Geometry

Numerical calculation with FEM was carried out for the fin efficiencies of common rectangular flat fin and three flat fins with modified geometry The result shows that the general heat tasfer performance of fin B2 is higher than that of common flat fin, but the fin efficiency is lower. Both the performances of heat transfer and fin efficiences of fin C and fin D are higher than those of common flat fin. The work of this paper is valuable for optimization design of high efficient fin.     

STUDY OF AIR LAYER FOR MOISTURE PREVENTION

This paper studies and proves the function of air layer for moisture prevention based on the fundamental theories of heat and mass transfer in porous medium and in air layer and through contrastive model experiment. The result shows that the air infiltration will largely reduce the heat resistance of heat insulant.     

Heat Transfer Model and Application of Buried Tube Heat Exchanger for Ground Source Heat Pump

This paper introduces the theoretical basis and application method for heat transfer model of buried tube (pipe in pipe and U- type) heat exchanger for ground source heat pump, and a practical example is calculated. Then, the calculation results are analyzed and discussed. In particular, the correlation coefficient and calculation method of tube group exchanger is discussed; the method for determining known parameter and some basic data for main procedure GSHP.HTM is analyzed. The calculation formula and data sampling for JSW.HTM subroutine is introduced. At last, the problems in application of calculation procedure, to which should pay attention, are discussed.     

Researches on Heat Flow Meter with Own Intellectual Property

In this paper ,the innovational research is based on widely absorbing patents and applied technique at home and abroad and pointing out the disadvantage and ameliorative method of heat/low meter. According to the principle of therrnopile, and the three - dimensional loop wire laying is substituted by new - style plane wire laying. The construction and manufacture of new - style heat flow meter is declared. The new method will facilitate the manufacture and reduce the cost and the high precision feeler is assured by consistent line length, capacitance, resistance and inductance and the cost of determination in present demarcation will be cheaper than traditional feeler of heat flow meter. The high precision energy saving detection instrument is provided for the field of heat energy.     

GGH heat transfer enhancement and a new type heat exchangerin the desulphurization system of wet flue gas

This paper conducts in-tube heat transfer experiments in a three dimensional fin tube with 102 mm outer diameter.Compared with the smooth tube,the heat transfer enhancement ratio is between 1.65 and 1.7,and the pressure drop ratio is between 1.65 and 1.7.Based on the analysis of the heat transfer and tube surface temperature,a new type heat exchanger is put forward.Moreover,the design and calculation method is explored.The engineering example indicate that not only the tube surface temperature is higher than the smooth tube,but also the quantity of heat is increased by about 20% than the smooth tube.Compared with other types,the new type heat exchanger has a overall better performance.     

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.     

Analysis of Heat Transfer during the Response Time of Temperature Sensor Fire Detector

This paper analyzes the heat transfer principle of temperature sensor fire detector, establishes mathematical model of heat transfer with considering the effect of radiation heat transfer and presents a new calculation method for the response time. The results of calculation show that when the environment temperature is rather low and the response temperature is set higher, the effect of radiation heat transfer on response time shouldn't be neglected. This paper may be helpful in appraising fire safety and designing alarm system.     

Numerical Simulation of Laminar Mixed Convection Heat Transfer in Vertical Narrow Rrectangular Channels

Using N-S function, and transforming the gravity item to temperature and differential pressure related items, the authors simulate the mixed convection heat transfer in vertical narrow rectangular channels. The results reveal that intense chimney effect exists in cross-section of the whole field and nearby the wall of the channel, When flow is laminar, the velocity of main flow will be decreased, disturbing nearby the heating wall is strengthened, and the convection heat transfer of vertical narrow rectangular channel is enhanced. It also can destroy the uniformity of the heat transfer coefficient distribution. Considering the reliability of equipment, this kind of convection pattern only can be used in low heat flux. The buoyancy-influencing model putted forward can predict mixed convection heat transfer, and also can be used to simulate the turbulent mixed-convection heat transfer problem.     

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。     

The Effect of Aspect Ratio on Natural Convection in a Cavity with Discrete Heaters and a Vertical Heat Sink

SIMPLE method is used to study the influence of aspect ratio on the natural convection in an enclosure with five discrete heat sources on a vertical wall and an isothermal heat sink on another vertical wall. The range of aspect ratio is from 3. 0 to 12. 22. At high aspect ratio, multiple secondary flow cells can be found,which enhance heat transfer strongly and cause the highest heat transfer coefficient based on cooling area Nuc. With the decrease of aspect ratio,secondary flow cells become weaker gradually and finally reach the lowest Nuc at H/W = 7. 35. If H/W continues to decrease,natural convection is gradually developed,and heat transfer is improved. At H/W = 3. 67,Nuc becomes stable. Then the decrease of aspect ratio will not affect heat transfer. Besides, A heat transfer correlation including the influence of aspect ratio is .also provided.     

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.