共查询到20条相似文献，搜索用时 640 毫秒
1.
Ruan Denfang 《保鲜与加工》1999,(1):66-71
Combined image method with heat source function method,heat conduction due to moving heat sources is analysed in semi infinite body and cylinder with heat exchanging on its surface.The distribution of temperature is obtained when the wall temperature is constant and the wall heat flux is zero.The result is useful for engineering calculation. 相似文献
2.
The heat transfer process in the louvered fin heat exchanger is analyzed,and the corresponding physical and mathematical models on the coupled conduction-convective heat transfer for the louver fin geometry are proposed.The control volume-based finite element method(CVFEM) is employed to solve numerically the problem.The computed(results) reveal the flow structure and heat transfer in the geometry in detail.Compared with the empirical correlation of heat transfer and friction coefficients previously proposed,the computed results show better consistency with the experimental results. 相似文献
3.
Due to their enhanced cost-effectiveness and efficiency over traditional borehole exchangers, energy piles are increasingly used in Ground Sourced Heat Pump (GSHP) projects. In this paper, the structural characteristics of these two types of heat exchangers and their heat transfer mechanism were discussed firstly. The thermal response tests (TRT) were performed on two testing energy piles in one GSHP project in Nanjing, China. The TRT results were then used to verify the numerical simulations, which suggests that the heat exchange performance of energy piles is superior to that of the traditional borehole exchangers. Meanwhile, the numerical simulation method used in this paper was considered applicable to the optimization design of ground heat exchangers in GSHP system. 相似文献
4.
The river water source heat pump system is an important technique to utilize renewable energy in Chongqing and heat exchanger can influence overall energy efficiency of system obviously. A test was carried out to study the heat transfer efficiency of double pipe heat exchanger with semicircular reentrant tube. It was found that the heat transfer efficiency would increase while curvature of semicircular reentrant tube rose. And when the ratio of R to r was five, heat transfer efficiency for semicircular reentrant tube would be increased 2.5% than that of straight double pipe heat exchanger. Flow, temperature field and heat transfer process of semicircular reentrant tube were simulated with computational fluid dynamics(CFD) tool to study the heat transfer mechanism. The modified RNG κ ε Turbulence Model was adopted to ensure the accuracy of simulation analysis under the situation of rotary flow and great curvature. Thus, it was indicated that there was obvious secondary flow vertex in reentrant tube. And disturbance of vertex on boundary layer was the main reason for which heat transfer efficiency of double pipe heat exchanger would increase as curvature of semi toroidal reentrant tube rose. Based on the experiment and simulation, the recommended curvature for reentrant tube was proposed with the consideration of sediment in river water and heat transfer efficiency of heat exchanger. 相似文献
5.
The experimental study of the flow resistance and heat transfer characteristics are conducted for water and ethylene glycol solution (66% Wt) flowing in the heat exchanger with small rectangular microchannels . The heat exchanger having the channels of 0.4 mm in width, 2.0 mm in height, and 20 mm in length is heated by a hearing rod at the bottom surface, the upper and two side surfaces are adiabatic. During experiments, the Reynolds number are ranged from 2 to 2 500. The experimental results show that the flow friction factor decreases and Nusselt number increases with increasing Reynolds number for water and ethylene glycol solution. At a fixed Reynolds number, the Nusselt number for ethylene glycol solution with larger Prandtl number is greater than that for water. Meanwhile, the correlations of flow resistance and heat transfer in the heat exchanger with small channels are obtained for engineering application. 相似文献
6.
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. 相似文献
7.
High thermal resistance resulted by fouling in heat exchanger restricts the application of sewage source heat pump (SSHP) system. The fouling forming mechanism was applied with solid-liquid fluidized bed technique for fouling prevention and removing of SSHP system. Shearing stress model of solid-liquid fluidized bed heat-exchanger is analyzed, and collision stress model is modified. Preventing and removing fouling mechanisms of solid-liquid fluidized bed technique by shearing stress and collision stress was explained. An experimental study on how to solve the fouling problem (such as fouling prevention and removing, heat transfer enhancement, etc) is discussed. The results of theory and experiment show that solid-liquid fluidized bed technique can be used not only to increase convection coefficient, but also to restrict fouling growing, it can effectively solve the fouling problem in SSHP system. 相似文献
8.
Kang Gewen Liu Fei Xu Zongjun Tong Qinmin 《保鲜与加工》1997,(1):43-49
The models for dynamic heat transfer of chips and tools are developed based on analysing heat source distributions in orthogonal dry cutting process,and a procedure is proposed to compute the temperature distributions of chips and tools,and the heat partition coefficients between the tools and the chips. 相似文献
9.
This paper describes the double layer horizontal ground source heat pump systems constructed in 1998 with the buried depth of 0.9 m and 1.8 m. The program of study includes experimental equipments, heat exchanger size, testing meter and methods for data analysis. In addition, the heating and cooling performance at typical days are also illustrated. Among the influencing factors on the performance of the ground source heat pump systems, the parameter of heat exchanger and operation patterns of heat pump systems are analyzed.A heat transfer model has been set up for horizontal heat exchanger. 相似文献
10.
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. 相似文献
11.
With the acceleration of urbanization,our cities become hotter and hotter.A good control on the heat environment of buildings is useful to improve people's living standard.Considering the phenomenon of "urban heat island",this paper analyzed the influence of a building on other buildings and its surrounding environment due to its form,allocation and thermal character of building materials from the angle of heat reflection,and brought up a proposal to resolve this problem.It opens a new way to improve the thermal environment of a city. 相似文献
12.
The heat release rate is the key factor that determines fire hazards. In order to find out the characters of heat release rate and their relation with other parameters. The authors introduce the oxygen consumption principle which cone calorimeter applies, and then expound the calculation of heat release rate in detail. The heat release rate of several kinds of representative materials has been studied by means of cone calorimeter in the different irradiances. Test results shows that HRR and TFI^-1/2 vary linearly with the irradiances. 相似文献
13.
Wu Chengbo 《保鲜与加工》1998,(1):88-94
By the calculation and experiment,analysed the heat transfer characteristies in waste gas of the high temperature exchanger.The results which the reasonable vertical and horizontal distances were obtained,these turned out that the metallic rediation net was the effectve method intensified heat transfer in hot waste gas.The infulence of the velcity and temperature of waste gas on the multiple heat transfer caefficrent of the exchanger was studied by the experiment data. 相似文献
14.
A sewage-water shell-tube heat exchanger with the function of de-fouling was proposed and designed for sewage-source heat pump. Its new simulation program which relies on a distribution parameter computational method was set up. Then the model was solved with the method of Matrix Control. Based on the model, the distribution of bilateral fluid temperature were studied, under the conditions of different flow rates and heat exchange area before and after the de-fouling. Results showed that there will be heat anti-transfer phenomenon if the heat exchanger area is bigger than need and the region of this phenomenon was point out. Setting the function of auto-de-fouling in shell-tube heat exchanger and reducing the equipment's volume accordingly can make the sewage-water heat exchanger run in the best conditions. 相似文献
15.
Based on the first and the second laws of thermodynamic, the entropy generation of heat transfer process from the inside to the outside through a duct is analyzed. A dimensionless entropy generation number based on the fluid of inside duct is introduced and an analytical expression for the dimensionless entropy generation number is obtained. The effect of some dimensionless parameters on the irreversibility performance of heat transfer process through a duct is discussed. The results show that an optimal Reynolds number of fluid inside duct is found to make dimensionless entropy generation number minimum , the dimensionless entropy generation number increases with the increment of the ratio of the Reynolds number of inside and outside duct fluids, dimensionless inlet temperature difference and dimensionless characteristic geometric dimension. The results from this paper provide a reference for the thermodynamic performance evaluation on the basic heat transfer process through a duct and enhancement in double sides of duct. 相似文献
16.
This paper introduces the current status and development of modeling of the underground heat exchanger for a GSHP and several typical models used abroad are provided in details. 相似文献
17.
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. 相似文献
18.
19.
Heat tolerance in spring wheat. I. Estimating cellular thermotolerance and its heritability 总被引：1，自引：0，他引：1
High temperature is a major environmental stress factor limiting wheat (Triticum aestivum L.) productivity. Improvement of
heat tolerance in wheat is an important breeding objective. Genetic variation in cellular thermotolerance among 56 spring
wheat cultivars was evaluated at the seedling stage of growth by cell membrane thermostability (CMS) and triphenyl tetrazolium
chloride (TTC) assays. A subset of eight lines was also evaluated at the flowering stage using the same assays. With both
assays Average thermotolerance tended to decrease from the seedling to the flowering stages. However, thermotolerance was
well correlated between growth stages among the eight cultivars for both CMS (r = 0.92; p = 0.004) and TTC (r = 0.84; p =
0.050). The correlation between TTC and CMS among the eight cultivars tested at the seedling and the flowering growth stages
was significant (r = 0.74; p = 0.031 and r = 0.75; p = 0.029, respectively). The same correlation was less strong, though
still significant (r = 0.32; p = 0.014) across 56 cultivars at the seedling stage. In a study of the cross V747 (tolerant)/Barkaee
(susceptible), broad sense heritability was estimated at 89% for TTC. Most of the genetic variance was additive. CMS in seedlings
of 16 cultivars was positively and significantly (p ≤ 0.05) correlated with yields of these cultivars in each of four hot
environments in Mexico, Sudan, India, and Brazil. The same correlations for TTC were positive but nonsignificant.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
为了研究长沙市城区的热岛特征及变化规律,利用长沙市城区和郊区气象观测站的观测数据,通过统计分析,对长沙市城区热岛强度时间分布特征进行了研究。结果表明：（1）21年间（1988—2008年）长沙市平均热岛强度为0.92℃,年均变化在0.76~1.46℃之间。（2）热岛强度的季节变化规律是秋、冬季强,春、夏季弱。（3）热岛强度日变化表现为夜间比白天强;夏季整天存在热岛现象,其他季节表现为快速形成和快速消失的现象。结论表明：长沙市热岛强度的年变化与城市建设的进程相一致;近20年来,长沙市城区和郊区的气温同步增高,同时热岛强度越来越大,说明全球气候变暖加剧了城市热岛效应,同时也是人类活动结果的影响。 相似文献