湿帘体内强制换热机理分析

使用湿帘风机蒸发降温系统是保证温室、畜禽舍夏季正常生产的一项重要手段,而如何提高湿帘的降温效率是其核心问题。本文总结了近几十年来学者关于研究湿帘体内蒸发降温机理的分析方法,着重讨论各分析方法得出的结论,及其对提高湿帘的换热效率的指导意义,在此基础上提出更深入分析湿帘体内降温机理的分析方法,为进一步提高湿帘工作效率提出新的分析思路。

质子交换膜燃料电池及其发电系统模拟

本文通过质子交换膜燃料电池单电池子模型、布气管子模型、流场子模型相互耦合，对电池堆传热传质过程加以数值模拟，得到单电池及电池堆的流场、温场、当地电流密度分布、过电位分布；给定平均电流密度下单电池及电池堆输出电压等参数；并比较了平均电流密度、布气管尺寸对电池输出电压、堆内反应物分配的影响；在此基础上，对整个ＰＥＭＦＣ发电系统进行流程模拟和参数分析，得到平均电流密度、重整器Ｓ／Ｃ等主要参数对系统性能影响．

The mass and heat transfer process through the door seal of refrigeration

As one of the main reasons causing leakage heat load in a refrigerator,mass and heat transfer through refrigerator door seal is of great importance to be studied.In this paper,a model is presented for numerical simulation of mass and heat transfer process through refrigerator door seal,and an experiment apparatus is designed and set up as well for comparison.A two-dimensional model and tracer gas method are used in simulation and experiment,respectively.It can be found that the relative deviations of air infiltration rate between the simulated results and experimental results were less than 1%,and the temperature difference errors at two special points of the door seal were less than 2.03℃.In conclusion,the simulated results are in good agreement with the experimental results.This paper initially sets up a model that can accurately simulate the heat and mass transfer through the refrigerator door seal,and the model can be used in refrigerator door seal optimization research in the follow-up study.

A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system

The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis(CHFS)system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porous media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.

Simulation of alumina dissolution and temperature response under different feeding quantities in aluminum reduction cell

In the feeding process of aluminum electrolytic, feeding quantity of alumina affects eventually dissolved quantity at the end of a feeding cycle. Based on the OpenFOAM platform, dissolution model coupled with heat and mass transfer was established. Applying the Rosin-Rammler function, alumina particle size distribution under different feeding quantities was obtained. The temperature response of electrolyte after feeding was included and calculated, and the dissolution processes of alumina with different feeding quantities (0.6, 0.8, 1.0, 1.2, 1.4, 1.6 kg) after feeding were simulated in 300 kA aluminum reduction cell. The results show that with the increase of feeding quantity, accumulated mass fraction of dissolved alumina decreases, and the time required for the rapid dissolution stage extends. When the feeding quantity is 0.6 kg and 1.2 kg, it takes the shortest time for the electrolyte temperature dropping before rebounding back. With the increase of feeding quantity, the dissolution rate in the rapid dissolution stage increases at first and then decreases gradually. The most suitable feeding quantity is 1.2 kg. The fitting equation of alumina dissolution curve under different feeding quantities is obtained, which can be used to evaluate the alumina dissolution and guide the feeding quantity and feeding cycle.

A Simulation for the Piston Effect in Supercritical Carbon Dioxide with the Non-flow Model

A simulation for piston effect in supercritical carbon dioxide by employing a simple model is conducted. In the first place, the thermal properties of carbon dioxide near its liquid-vapor critical point are discussed. It is calcu- lated that the heat capacity ratio and isobaric expansion coefficient of supercritical fluids are extremely high. Furthermore, the simulation for piston effect in supereritical carbon dioxide between two infinite vertical walls is presented. The numerical results prove that piston effect has a much faster speed of heat transfer than thermal conduction under mierogravity conditions. Moreover, the piston effect turns out to be stronger when closer to the critical point.

Airside fin efficiencies for finned-tube heat exchangers with forced convection

The heat transfer and mass transfer fin efficiencies were analyzed numerically to show that popular models for heat transfer fm efficiency for circular fins are not always reasonable. The numerical results show that the effective heat transfer area of a circular fin increases several times faster than that of a straight fin for the same tube radius. Then, a simple but accurate heat transfer fin efficiency model was developed and verified by numerical results for a wide range of fin designs. This model predicts the heat transfer fin efficiency with absolute errors of less than 1%. The heat transfer and mass transfer fin efficiencies were found to be quite different for typical air flow with low relative humidity. Thus, these two fin efficiencies should not be assumed to be equal and a mass transfer fin efficiency model was developed, based on the heat transfer fin efficiency model. These heat transfer and mass transfer fin efficiencies are very useful for more accurate prediction for a wide range of practical applications.