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1.
One-dimensional models were usually utilized to describe the coupled heat and mass transfer processes in packed bed liquid desiccant–air contact systems. In this paper, a double film model was utilized for both parallel and countercurrent flow configurations. The model considered the effects of non-unity values of Lewis factor, unequal effective heat and mass transfer areas, liquid phase heat and mass transfer resistances, changes in solution mass flow rate and concentration. Within the relatively narrow range of operating conditions usually encountered in a specified application, a linear approximation was made to find out the dependence of equilibrium humidity ratio on solution temperature and concentration. Constant approximations of some properties and coefficients were further made to render the coupled equations linear. The original differential equations were rearranged and an analytical solution was developed for a set of newly defined parameters. Analytical expressions for the tower efficiency and other effectiveness values were further developed based on the analytical solution. Comparisons were made between analytical results and numerical integration of the original differential equations and the agreement was found to be quite satisfactory.  相似文献   

2.
Internally cooled or heated liquid desiccant–air contact units can be used for effective air dehumidification or desiccant regeneration, respectively. One-dimensional differential equations were utilized in the present study to describe the heat and mass transfer processes with parallel/counterflow configurations. The effects of solution film heat and mass transfer resistances, the variations of solution mass flow rate, non-unity values of Lewis factor and incomplete surface wetting conditions were all considered in the differential model. On considering the relatively narrow ranges of operating conditions in a specified application, the equilibrium humidity ratio of desiccant solution was assumed to be a linear function of its temperature and concentration. Constant approximations of some properties and coefficients were further made to render the coupled equations linear. The differential equations were rearranged and an analytical solution was developed for newly defined parameters. For four possible flow arrangements and three types of commonly used liquid desiccant solutions, results of analytical solutions were compared with those of numerical integrations over a wide range of operating conditions, and the agreement was found to be quite satisfactory. Further, the heat and mass transfer performances were analyzed and some guidance to improve the unit design was provided.  相似文献   

3.
This paper aims at developing an analytical model for the coupled heat and mass transfer processes in indirect evaporative cooling under real operating conditions with parallel/counterflow configurations. Conventionally, one-dimensional differential equations were used to describe the heat and mass transfer processes. In modeling, values of Lewis factor and surface wettability were not necessarily specified as unity. Effects of spray water evaporation, spray water temperature variation and spray water enthalpy change along the heat exchanger surface were also considered in model equations. Within relatively narrow range of operating conditions, humidity ratio of air in equilibrium with water surface was assumed to be a linear function of the surface temperature. The differential equations were rearranged and an analytical solution was developed for newly defined parameters. Also, performances with four different flow configurations were briefly discussed using the analytical model. Through comparison, results of analytical solutions were found to be in good agreement with those of numerical integrations.  相似文献   

4.
逆流填料式液体除湿系统传热传质过程的分析解法及应用   总被引:9,自引:1,他引:8  
通过对逆流填料式液体除湿系统传热传质过程数学模型的合理简化,推导出描述这一热质传递过程的常微分方程组的分析解,并与未简化数学模型的数值解作对比,二者具有良好的吻合性。所得分析解可用于分析填料高度上各参数的分布情况及各参量的变化对除湿性能的影响,并可用于除湿系统的设计校核计算等,具有较高的理论及应用价值。  相似文献   

5.
Abstract

The finite element method was used to solve Luikov's system of partial differential equations for neat, mass, and pressure transfer in capillary porous bodies. The finite element predictions were validated by comparing with exact solutions and the analytical results given by Mikhailov and Shishedjiev [1]. An application of the finite element method to the drying of wood (spruce) and a comparison based on an eigenvalue solution for simultaneous heat and mass transfer [2] are also provided. This technique was applied to study the coupled transport process in a silicon gel. The simulation indicated that the results obtained from the heat, mass, and pressure transfer model showed a marked difference from the results obtained by the heat and mass transfer model.  相似文献   

6.
The issues connected with the determination of thermal and moisture fields in early-age massive concrete are discussed here. The coupled equations, which govern the heat and mass transfer in early-age mass concrete as well as the initial and boundary conditions are presented. Next, the discretization in the space was made using the finite element method; the finite difference method was introduced for the discretization in time. As a result, the matrix form of the heat and moisture transfer equations was obtained. The proposed model was implemented in the original computer program TEMWIL, which can be applied to spatial massive structures in order to forecast the temperature and moisture distribution. Essential thermodiffusion coefficients for early-age concrete were also discussed. Finally, some computations concerning different curing conditions for the massive foundation slab were presented.  相似文献   

7.
New finite integral transform and the corresponding inversion formula are introduced for the solution of the diffusion equations in a finite region of arbitrary geometry and initial conditions with general coupling boundary conditions. The resulting eigenvalue problem does not fall within the range of the conventional Sturm-Liouville system and therefore a new integral condition was devised which serves as an orthogonality relation. The solutions obtained permit the studying of many new problems, such as heat transfer coefficients in concurrent flow double pipe heat exchangers, simultaneous heat and mass transfer in internal gas flows in a duct whose walls are coated with a sublimable material and elsewhere. In addition the Luikov system of equations of a simultaneous mass and heat transfer in a finite capillary porous body of arbitrary geometry are rearranged to the pure diffusion equations coupled only at boundary conditions and consequently to a special case of the problem studied here.  相似文献   

8.
Considerable work has been published on mathematically coupled nonlinear differential equations by neglecting thermodynamic coupling between heat and mass flows in reaction-transport systems. The thermodynamic coupling refers that a flow occurs without or against its primary thermodynamic driving force, which may be a gradient of temperature, or chemical potential, or reaction affinity. This study presents the modeling of thermodynamically coupled heat and mass flows of two components in a reaction-transport system with external heat and mass transfer resistances. The modeling equations are based on the linear nonequilibrium thermodynamics approach by assuming that the system is in the vicinity of global equilibrium. The modeling equations lead to unique definitions of thermodynamic coupling (cross) coefficients between heat and mass flows in terms of kinetic parameters and transport coefficients. These newly defined parameters need to be determined to describe coupled reaction-transport systems. Some representative numerical solutions obtained by MATLAB illustrate the effect of thermodynamic coupling coefficients on the change of temperature and mass concentrations in time and space.  相似文献   

9.
A linearized coupled model is developed for the heat and mass transfer in falling-film absorbers. Its accuracy is established by comparing the predictions with those of a non-linear model and a numerical simulation. Under certain conditions, the linearized model reduces to the log-mean-difference formulation. The linearized model yields analytical expressions that are used to determine heat and mass transfer coefficients from the experimental data for a horizontal tubular absorber and a vertical tube absorber. The overall Nusselt number and Sherwood number for the tubular absorber increase with increasing film Reynolds number and inlet cooling water temperature. The cooling water temperature distribution predicted by the linearized model agrees well with measurements.  相似文献   

10.
The coupled problem of heat and mass transfer during the solidification of high-water content materials like soils, foods, tissues and phase-change materials is developed. Assuming quasi-steady heat conduction in the frozen region, the system leads to a set of coupled ordinary differential equations. The model takes into account the influence of material characteristics and process variables on the advance of the freezing and sublimation fronts, temperature and water vapour profiles and weight loss. It was validated against the analytical solution of the freezing (without surface ice sublimation) of a semi-infinite medium and was extensively used to perform a parametric study.  相似文献   

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