Numerical analysis of indoor natural convection heat transfer under different heat source location

The research object is indoor natural convection heat transfer under different heat source location,using FVM numerical method to dispersed solving for mass conservation equation and energy conservation equation.Researched distribution of streamline and isotherm and variation of Nu in powerhouse with Ra among 10 3~10 6 when different heat source location.The results of analysis indicate that when Ra=10 3, the isotherms expand outward centring on the heat source and present shapely arcuation.When increasing Ra,isotherm shape changes gradually,thin boundary layers appear on cold wall and hot wall.The streamlines are two symmetrically reverse vortexs.As increasing Ra, the vortexs change in size and move. As Ra=10 3,Nu reaches maximum in the case of D=0. the effect of heat source location on heat transfer quantity is obvious.The curve of Nu is steepest when D=0.5 and smoothest.There is a power relationship between Nu and Ra, the linear correlation fitting 90%.The conclusion provides a theory basis for the research of complex indoor heat transfer mechanism.     

Heat Transfer Characteristics of the Melting Process of the Metal Foam/Paraffin Compound Material

In order to enhance the heat transfer in the phase change heat storage device, a rectangular cavity filled with metal foam / paraffin wax is made. The melting heat storage experiment of foam metal / wax composite phase change material was carried out in the transverse wall temperature conditions. The temperature change curve is drawn according to different heating temperatures. Both the effects of natural convection in rectangular cavity on temperature distribution and the impact of heat transfer temperature difference on the thermal storage time are analyzed. The results show that the melting process of the paraffin in the body cavity is reinforced by the high thermal conductivity of copper foam. The remaining solid paraffin is accelerated to melt by the natural convection of the liquid paraffin formed near the heating surface; and the greater the heat transfer temperature difference is, the greater the natural convection is and the shorter the time for heat storage is.     

Conjugate Natural Convective Heat Transfer in an Enclosure with Discrete Protruded Heat Sources

The mathematic model on natural convection is proposed in a two-dimensional enclosure cavity with an isothermal heat sink at one vertical wall and five discrete protruded sources. Numerical study is performed to analyze the natural convection in the enclosure with a variety of aspect ratio, the range of which is from 3.0 to 12.22, Ra H is 10 7 and Pr is 30.The computed results show that the total heat transfer effect under the situation with discrete protruded heat sources is prior to that with flat wall heated. Moreover, when the aspect ratio is comparatively large, there is several secondary flow in the enclosure, which enhance the convective heat transfer. On the contrary, when the aspect ratio is small, the secondary flow weakened or disappeared, and the total convective heat transfer drop. Finally, the convective heat transfer criteria in the enclosure is obtained.     

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.     

Dropwise Condensation Heat Transfer Coefficient on the Horizontal Circular Surface with Radial Gradient Surface Energy

A theoretical model is developed for the dropwise condensation heat transfer on the horizontal circular surface with radial gradient surface energy based on the heat transfer model of individual condensate drop and the size distribution model of condensate drop on homogeneous condensation surface.The effect of variation of contact angle on the gradient surface on condensation heat transfer and condensate drop size distribution is taken account of in this model.The theoretical calculation method was obtained to predict the dropwise condensation heat transfer coefficient on the horizontal circular surface with radial gradient surface energy under various wall subcooled temperature,contact angle profile on wall surface,and working fluid.The effects of surface energy gradient,wall subcooled temperature,and thermophysical properties of condensate on the condensation heat transfer are discussed respectively.The calculation results show that the condensation heat transfer coefficient increases slightly with the increase of wall subcooled temperature.As latent heat and surface tension increasing,the condensation heat transfer coefficient increases.A larger surface energy gradient induces a larger condensation heat transfer coefficient.     

影响鹤望兰切花产量与质量的因素探讨

探讨夏季遮荫、冬季保温、喷雾、修剪等因素对鹤望兰切花产量与质量的影响,结果表明：夏季遮荫对切花产量与一级花率影响不显著,但比对照二、三级花率提高28.6%;冬季保温栽培能显著提高12月—翌年3月切花产量,比露地栽培提高182.4%,二、三级花率也提高19.1%;对大于25株/丛、10a龄的植株采用留10~19株的修剪方式全年产量比对照降低了15.1%,但能显著提高切花质量,一级花率比对照提高105.2%;采用修剪结合夏季遮荫、冬季保温、喷雾等处理措施既能提高鹤望兰切花年产花量,比修剪后露地栽培提高30.0%,也能提高切花质量,其中一级花率提高37.3%。     

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.     

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.     

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.     

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.     

柚苷酶生产菌TC-01发酵培养条件的优化及其酶学性质的初步研究

以黑曲霉TC-01菌株作为试验材料对其液态发酵条件及初步纯化后的柚苷酶的酶学性质进行研究。采用单因素试验优化碳、氮源对产酶的影响,利用Plackett-Burman设计筛选影响产酶的主要因素,最后通过响应面分析法对液体发酵培养条件进行优化,优化后柚苷酶酶活与初始相比提高了2.4倍,达到1 216.7 U/mL。对TC-01产柚苷酶中α-鼠李糖苷酶和β-D葡萄糖苷酶的酶学性质分别进行了研究,2个酶反应的最适反应温度均为60℃,在50℃以下保温1 h,2个酶的活力基本不受损失;2个酶最适pH值为4.0,α-鼠李糖苷酶在pH值4.0~8.0范围内稳定性较好,β-D葡萄糖苷酶在pH值5.0~7.0范围内稳定性较好;α-鼠李糖苷酶米氏方程Y=0.001 3X-4.0×10-6,Km=5.60 mmol/L,β-D葡萄糖苷酶米氏方程Y=0.001 8X-3.0×10-6,Km=1.03 mmol/L。     

Measurement method for spray cooling characteristics of industrial nozzle

In order to study the cooling characteristics of the nozzle, a test platform is designed and developed for spray cooling feature measurement based on unsteady state heat conduction. By heating and keeping Q215 metal samples up to some surface temperature, a series of temperature data are collected by S7-200 modules during spray force cooling. Through Visual C++6.0 and Matlab interface programming, a series of regression equation with thermodynamic property versus temperature, such as density, specific heat capacity, and thermal conductivity etc., and with temperature versus sample time are obtained. The surface heat transfer coefficient and spray cooling feature of nozzle can be indirectly measured by the regression equations. The relation between surface heat transfer coefficient versus temperature, spray pressure and water intensity are investigated by means of the testing equipment. The experiment result shows the method is feasible and can be used in spray cooling feature measurement for all kinds of nozzle.     

覆盖生态木屑对城市公园土壤温湿度的影响

为实现绿化垃圾的循环利用,量化评估覆盖生态木屑对土壤表层温湿度的影响。利用土壤温湿度计定期测定土壤表层温湿度持续1年。结果表明,冬季铺设生态木屑具有良好的保温保湿效果,不铺设木屑土壤含水率迅速下降到10%以下,铺设生态木屑15~20 cm后整个冬季土壤含水率都保持在16%以上,后者土壤温度比前者土壤温度高2℃以上。夏季铺设生态木屑5~10 cm的样树,含水率低于不铺生态木屑的对照组和其他试验组,但对温度的影响并不明显。冬季覆盖生态木屑对土壤表层具有明显的保温保湿效果,且覆盖生态木屑越厚保温保湿效果越显著;而夏季覆盖生态木屑的最佳厚度为5~10 cm,覆盖此厚度的生态木屑既可以起到海绵体吸收多余水分的作用,又不会因为覆盖生态木屑后树冠与根系间的温差增大导致的植物生理性缺水。因此,建议城市公园铺设生态木屑的厚度为5~10 cm。     

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.     

Mathematical model and its validation of coupled heat and moisture transfer for multilayer wall

Its rationality of temperature and water vapor partial pressure as driving potential for coupled heat and moisture transfer was demonstrated based on non-equilibrium thermodynamics. As water vapor partial pressure is a function of moisture content and temperature, mathematical model of coupled heat and moisture transfer for multilayer wall were established according to the theory of total differential. The approximate expressions between humidity content and relative humidity of air used in Budaiwi method could be avoided. The coefficients of mathematical model were simplified and could improve efficiency of solution. Its validation was illustrated by contrasting and analyzing the simulation results of a multilayer wall.     

秸秆带状覆盖对西北雨养区马铃薯农田土壤温度及产量的影响

为探明秸秆带状覆盖和地膜覆盖对马铃薯农田土壤热量传递和产量的影响,试验于2018-2019年进行,设置不同覆盖材料（地膜、秸秆）、覆盖时期（秋、春）、露地（CK）5个处理,研究不同覆盖对马铃薯农田土壤热量传递特性及产量的影响。结果表明,各处理在不同生育期和不同土层温度存在显著差异。与CK相比,2个生长季秸秆带状覆盖显著降低0~25cm土层土壤温度0.6℃~0.9℃,降温幅度为秋覆盖大于春覆盖,地膜覆盖提高土壤温度0.3℃~0.7℃。不同时期相比,地表覆盖存在增温和降温的双重效应,降温效应秸秆带状覆盖大于地膜覆盖,而增温效应地膜覆盖大于秸秆带状覆盖。地温日变化随气温的变化存在明显的滞后效应,覆盖显著抑制地温波动。覆盖具有“双抑制效应”,在低温时段抑制了土壤热量向大气的散失,高温时段抑制了地表对太阳辐射热量的吸收,且秸秆覆盖优于地膜覆盖,秋覆盖优于春覆盖,与CK相比,2个生长季秸秆覆盖温度梯度降低7.3~7.8℃/m,地膜覆盖降低3.4~6.3℃/m。秸秆带状覆盖增产14.7%,地膜覆盖增产25.3%,处理间单薯重的差异是引起产量差异的主要因素。因此,秸秆带状覆盖在西北雨养区马铃薯生产中具有应用推广价值。     

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.     

Numerical Study of FLow and Heat Transfer in Rectangular CHannel with Dimpled SUrface

This authors uses a physical model of the rectangular channel with dimpled surface to simulate the flow and heat transfer situation. On the basis of actual flow and heat transfer in the channel, it made the interrelated hypothesizes and built up the math model. They adopted the turbulent model, appliy the algorithm to resolve the pressure-velocity coupling and use the experimental data model to check up the feasibility of the model. By the study, the thesis shows the principle of the flow and heat transfer in narrow channel with a dimple surface and gets the factors and the conditions that affect the flow and heat transfer. The results show that the geometry structure and rank distributing of dimple affect the capability of heat transfer evidently. When Reynolds number is low, the capability of heat transfer becomes better as the number increases, and when Reynolds number is bigger than a critical point, there is a little influence.     

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.     

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.