Effect of aspect ratio on convection in a porous enclosure with partially active thermal walls

The aim of the present numerical investigation is to understand the effect of aspect ratio and partially thermally active zones on convective flow and heat transfer in a rectangular porous enclosure. Five different heating and cooling zones are considered along the vertical walls while the remaining portions of the sidewalls and top and bottom of the enclosure are adiabatic. The Brinkman-Forchheimer extended Darcy model is used in the study. The governing equations are solved by the finite volume method with the SIMPLE algorithm. The computations are carried out for a wide range of parameters and the results are presented graphically. The results reveal that the location of heating and cooling zones has a significant influence on the flow pattern and the corresponding heat transfer in the enclosure. The rate of heat transfer approaches to a constant value for very low values of the Darcy number. The heat transfer rate is decreased on increasing the aspect ratio.     

Understanding dengue fever dynamics: a study of seasonality in vector-borne disease models

Dengue fever dynamics show seasonality, with the disease transmission being higher during the warmer seasons. In this paper, we analyse seasonally forced epidemic models with and without vector dynamics. We assume small seasonal effects and obtain approximations for the real response of each state variable and also for the corresponding amplitude and phase via decomposition of the sinusoidal forcing into imaginary exponential functions. The analysis begins with the simplest susceptible-infected-susceptible (SIS) model, followed by the simplest model with vector dynamics, susceptible-infected-susceptible for hosts and uninfected-vector (SISUV). Finally, we compare the more complex susceptible-infected-recovered (SIR) and susceptible-infected-recovered for hosts and uninfected-vector (SIRUV) models and conclude that the models give basically the same information when we replace, in the SIR model, the human infectivity by a function of both human and mosquito infectivities.     

求解二维对流扩散方程的投影迭代法

鉴于目前流行的求解大型稀疏代数方程组的投影迭代法中,为提高迭代效率,在迭代前通常需要对稀疏矩阵进行预处理,改善迭代矩阵的条件数,从而减少迭代次数,这使得发展稀疏矩阵的存储技术变得尤为关键。基于二维对流扩散方程的四阶紧致差分格式,将其转化为代数方程组,得到其三对角块形式的系数矩阵,利用稀疏矩阵存储技术和预条件迭代法进行求解,并与传统的中心差分格式所得数值解进行比较,充分说明了方法的高效性和可靠性。     

Free and forced convection boundary layer flow through a porous medium with large suction

An analytical study is made of the free and forced convection boundary layer flow past a porous medium bounded by a semi-infinite vertical porous plate. Locally similar solutions are then obtained by a perturbation method for large suction. Solutions for the velocity and temperature distributions are shown graphically for various suction velocities and values of the driving parameter G_r/R, where G_r is the Grashof number and R_e is the Reynolds number. The corresponding values of the skin friction coefficient and the Nusselt number are finally shown in tabular form.     

对流换热理论在玻璃窑炉换热器设计中的应用

本文主要分析了管内层流对流换热时两种不同情况下努谢尔特准数的数值及在换热器设计中的指导意义。     

对流方程差分格式稳定性判定

用傅里叶稳定性分析法判断一维对流方程不同差分格式的稳定性．傅里叶稳定性分析法的基本思想是：对于线性微分方程,将解的误差做周期延拓并用傅里叶级数表示出来,然后考察每一个傅里叶级数分量的增大和衰减情况;根据傅里叶级数每一个分量随时间的变化情况,由放大因子判断差分格式的稳定性．用该方法对给定方程不同差分格式的稳定性进行了判断．     

工业厂房不同高宽比对室内温度分布的影响研究

以工业厂房的高宽比对室内温度分布的影响作为研究对象,采用质量守恒方程、能量守恒方程进行数值计算,研究了Ra数在103～106之间时,不同高宽比的工业厂房内的等温线、流线的分布特征和Nu数的变化。分析结果表明:随着Ra的增大,房屋内的热传输形式由热传导逐渐向对流传热转换,等温线由竖直逐渐变得水平;室内的流线为环绕于模型边界的两个涡,并随Ra的增大逐渐被分裂,在B=0.5,B=1时,分裂为2个涡流,在B=3,B=2时,分裂为3个涡流,并伴有低湍动状态;Nu数随Ra数的增大而增大,二者的曲线呈幂指数关系,B=3时Nu数最大,表明此时由高温壁面向低温壁面传递的总热量最多。     

空冷型光伏光热一体化系统的实验研究

对空冷型单晶硅光伏光热一体化系统进行了实验研究,充分肯定了光伏光热一体化系统对于提高电效率和利用热能的作用.通过对带有风机的空冷型强制对流单晶硅电池板与空冷型自然对流单晶硅电池板两者的电效率、净电效率和热效率的比较,探讨风机对于电池板散热的效果以及对其各项效率的影响.     

THE NATURAL CONVECTION OF AQUIFERS WITH CONSTANT HEAT SOURCES AND ITS INFLUENCE ON TEMPERATURE FIELDS

By combining sand tank tests with numerical simulations, this paper studies the temperature fields around constant heat sources to reveal the mechanism of the natural convection and its influence on the temperature fields in the process of energy storage. Using the "24-channel temperature auto acquisition system" developed by our research group in the tests, the temperatures are recorded at measuring points within the research area in the tests, the revised Brinkman equation and a transfer-convection balance model are used for solving the aquifer water-thermal coupling problems, and through comparison of the test results with the calcula- tion results, it is discovered that the influence ranges and the variations of the two temperature fields are consistent, which validates the mathematical model. On the basis of this, we also study the influences of the heat source positions and the boundary conditions on the temperature fields, and the results show that, under the natural convection, the heat source positions may influence the distri- bution of the temperature fields, thus affect the energy storage. For the same energy storage layer, the temperature field for the top energy storage is characterized by a smaller heat influence range and a relatively concentrated temperature distribution. However, when the heat source is at the bottom, the range of a temperature field, and the temperature is relatively dispersed, which is not favorable to heat recycle, with the same heat source position, the boundary conditions determine the size of the critical Rayleigh number, and thus have an influence on the occurrence and the strength of the natural convection, and accordingly, on the temperature fields.     

Thermal-environment characteristics and comfort of combined radiant-floor （Korean heating system ondol） and convective cooling system

The thermal-environment characteristics of the existing forced-convection cooling system were compared with those of the convective cooling system, which combined the radiant-floor cooling system using floor-heating panel typically applied to apartments in South Korea with the forced-convection cooling system using improved fan coil unit. The subjective warm/cool-feeling responses to the combined radiant-floor and convective cooling system in the questionnaire survey conducted among the test subjects were analyzed to establish the basic data for the combined cooling system. The results show that in the thermal-equilibrium condition, the vertical air temperature difference in the model living room is larger in the forced-convection-cooling condition. Most of the subjects feel a proper warm/cool feeling on their entire body, but they feel colder on the foot and lower body in the combined-cooling condition.