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.     

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.     

The Numerical Simulation of Casting Process for Making Metal Matrix Composites

In this paper,a numerical simulation of the casting process for making the MMC.using the PEM, is studied.The convection of liquid metal and the release of latent heat of solidification are taken into account.The algorithm and program for axisymmetric casting model are developed to the problem of coupling between flow and heat transfer,as well as phase change.The variational curves of temperature,the position of flow front and the distrsbutions of volume fraction of solid metal in matrix and their variation with time are obtained.The influences of technological paarmeters to casting are discussed.     

A STUDY OF THERMOTECHNICAL CHARACTERISTICS IN FORCED CONVECTION BATCH FURNACE

An experimental study of heat transfer mechanism and characteristics of high velocity circulation combustion gas in a batch heat treatment furnace with high velocity burner was presented. The regular patterns of variation of total heat flux, heat convection and radiation heat fluxes given heating materials with heating time were obtained. It was revealed from the results of experiment and calculation that inverse heat flux of metal radiation is an unavoidable heat transfer characteristic.     

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.     

Experiments on the eutectic salt used as low temperature cool storage material

Binary eutectic salt is fit for low temperature cool storage in industry based on the theory of thermodynamics. Two sorts of binary eutectic salt were found by the experiments of freezing and melting. The thermophysical properties including freezing point, melting point, super-cooling degree and thermal stability during phase change process were investigated. The results show that these two sorts of binary eutectic salt are hope to be suitable for low temperature cool storage.     

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.     

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.     

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.     

A NUMERICAL STUDY ON NATURAL CONVECTION IN A CLOSED CAVITY PARTIALLY FILLED WITH POROUS MEDIUM

The present paper decribes numerical analytical results of natural convection in a closed cavity partially filled with porous medium by means of Forchheimer-Brinkman model. The effects of heated rate,permeability,height of porous region,heat conduction coefficients and aspect ratio on flow and heat transfar in the cavity are systematically investigated. Velocity and temperature fields in the cavity are given and dependence of average Nu on time is obtained.     

Numerical Computation of 3-D Laminar Boundary Layer Equations of Natural Convection Heat Transfer

Coordinate transformation and Box method already succeed in solving boundary layer equations of compelling convection heat transfer,but the solution of natural convection heat transfer has not been informed.For examining the compute accuracy of solving natural convection heat transfer by using this method,this paper numerically computes 3 D laminar boundary layer equations of natural convection heat transfer of stand strip by using this method,the computational results agree with the experimental data from the published paper.The results shows that using this method to solve the equations is feasible.     

Adapted thermal imaging for the development of postharvest precision steam-disinfection technology for carrots

Postharvest carrots are brushed, hydro-cooled to 4–6 °C and treated with chemical fungicide before storage to prevent soft rot caused by Sclerotinia sclerotiorum (Lib.) de Bary during storage. Replacement of the fungicide with high-temperature surface heat treatment poses a dilemma: excessive heating will cause damage whereas insufficient heating will result in incomplete disinfection. This problem is further compounded by the difficulty in providing uniform surface heating. To alleviate this problem, a system for the uniform application of high-temperature short-duration steam disinfection was developed using accurate real-time temperature monitoring of individual produce segments by thermal imaging. Uniform short-duration high-temperature heat was delivered from above by steam jets combined with electric steam-drying elements and reflectors. Produce was subjected to rotational and linear motions to expose each surface segment to the same amount of heat. The novel use of thermal imaging to monitor surface temperature in steam systems was essential for determining transferred heat and heating uniformity in a treated object. The resultant, uniform application of short-duration high-temperature steam provided surface heat-disinfection with minimal internal heating and damage. Application of the steam treatment immediately after carrot hydro-cooling reduced post-storage phytotoxic color change by 60–80% and resulted in significantly reduced sensitivity to post-storage soft rots caused by S. sclerotiorum. Carrot sprouting was not increased by the steam treatment, suggesting retention of the hydro-cooling's physiological effect. These results suggest that precise heat treatment can be optimally applied after hydro-cooling to improve postharvest quality of carrots in a procedure that is harmless to man and the environment.     

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.     

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.     

Subway Station Plate Evaporative Cooler Heat and Mass Transfer of Falling Film under Gas liquid Cross flow Condition

With the influence of the different gas Reynolds number and liquid Reynolds number on falling film heat and mass transfer of subway station plate evaporative cooler, the experiment was carried out by non contact infrared thermal imaging technology under gas liquid cross flow condition. The results indicated that during the increasing of liquid Reynolds number the thickness of liquid film increased and the temperature difference between liquid film inlet and outlet decreased in determined heating water temperature which weakened the heat transfer of liquid film. However, the increase of liquid Reynolds number strengthened the liquid film turbulence that enhanced heat transfer. Under the synergistic effect of these two factors, there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat and mass transfer coefficient of liquid film.     

考虑谷物呼吸的仓储粮堆热湿耦合传递研究

粮食作为生物性多孔介质,具有呼吸特性。一般粮食收获后,大部分时间在密闭不通风状态下存储。以粮堆内局部热湿耦合传递过程作为研究对象,分析了不通风状态下的圆筒形粮仓在自然对流条件下由于温度梯度影响而产生近似冬夏季工况的温度分布和水分转移,借助多物理场数值模拟软件(COMSOL)进行数值模拟,将粮食呼吸作用产热、产湿量以热源、湿源项考虑在数学模型中,通过对温度场、水分场的描述指导工程实践。     

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.     

湘白蜡的光热模拟氧化及产物分析

研究旨在通过模拟湘白蜡在光、热等环境条件下的氧化过程,反映湘白蜡的环境稳定性和氧化特征,以期为湘白蜡的开发利用和科学贮藏提供参考依据。以300nm紫外光辐照和50℃、75℃、100℃热催化作为模拟氧化条件,通过对新鲜及氧化湘白蜡的理化指标、TG与IR分析,揭示氧化湘白蜡与新鲜湘白蜡的性质差异;采用GC-MS对新鲜及氧化湘白蜡的组成分析,明确新鲜湘白蜡及其氧化产物的种类与组成;在此基础上,结合氧化产物特征提出了光、热对湘白蜡氧化过程的催化加速的作用程度及方式。结果表明：光、热对湘白蜡的催化氧化均有一定活性,在45d氧化期内,300nm紫外辐照与50℃热催化对白蜡的氧化较弱,100℃条件下湘白蜡的氧化较为剧烈,酸值达到69.38 mgKOH/g,皂化值达到195.07 mg KOH/g。湘白蜡氧化过程中主要有降解和氧化两种反应。降解是湘白蜡分子中的长碳链裂解缩短的过程,表现为熔融峰值的降低、低熔点组分的增多及氧化产物中高级烷酸碳原子数量的高度连续性及相对含量分布的均衡性;氧化是虫白蜡分子中降解所得的游离烷烃、高级烷醇、高级烷酸继续氧化的过程,表现为酸值、皂化值的升高及羧基红外特征吸收峰的增强与分裂。     

呼和浩特地区不同类型日光温室光热性能研究

本研究主要对新引进的日光温室与当前厚墙体温室的光热性能进行对比研究,为呼和浩特地区日光温室的建设提供参考依据.根据4种类型日光温室小气候监测数据,分析温室内外日平均温度、温室内外日最低温度、温室内外日最高温度、温室内光照度等气象要素变化规律.双膜双被日光温室为室内温度水平最高的日光温室,越冬期间(1月12日-2月21日...     

Volatilization combustion mechanism analysis and experiment of coalfield fire

According to the volatile combustion, the mathematical and physical models on the volatilization combustion of coal field fire area are established. The governing equations are analyzed by analytic method. The parameters such as volatilization combustion speed, the content of volatile component and the flame temperature are obtained at relatively high temperature environment. According to the solutions, the flame temperature of the volatilization combustion is calculated by the heat insulation temperature in the light of the low-heat value of the volatile component. Due to the free or forced convection in the actual fire area, the true temperature would be lower than the calculation. Through experiment, heating process takes the greatest impact on the heating surface but least on inner parts. The temperature is increased and the heating surface temperature will exceed the temperature and continue increasing, which indicates that the coal begins oxidation. While the airflow is increased, the temperature will be slightly increased. The temperature is descent more slightly in the coal temperature because of thermal radiation.