Match Properties of Heat and Mass Transfer Processes in the Internally-Cooled Liquid Desiccant System

Currently, there is a problem of developing effective methods to calculate heat and mass transfer processes during steam condensation from a vapor-gas mixture in industrial devices. This is due to the need to create new reliable and highly efficient designs of heat exchangers for various purposes. The finite element method has been used in the ANSYS Fluent software package during the numerical simulation. An experimental plant is tested in the pipeline of an industrial enterprise at the production site of the Technopolis KHIMGRAD industrial park (Kazan-city). The applicability of the Lee model to solve problems of water flow in a pipeline with partial evaporation is proved. This model allows you to accurately account for the processes of evaporation and condensation, which is important for the design of cooling and air conditioning systems. The authors have designed a three-dimensional model of the flow area of the experimental module and a CFD model to calculate temperatures, phase velocities and their concentrations, considering the peculiarities of the ongoing processes of heat and mass transfer. A slight effect on the heat flow of a 180° rotation during the flow of a liquid medium in the range of the Reynolds numbers 1800–2600 is shown. The developed model is verified with the results obtained at the experimental plant. It is established that the model reproduces experimental data well. An analysis of studies of heat and mass transfer processes during the fluid flow in channels in the presence of phase transitions is carried out. The problems of calculating the parameters of heat transfer during the movement of a fluid in a transient mode are revealed, especially at values of the Reynolds number close to 2000. The experimental plant diagram is presented. It is found that in the range of Reynolds numbers of 2600–3600, the calculated temperature values differ from the temperature values obtained experimentally by less than 0,42 %. During the partial transition of water into steam in the range of Reynolds numbers of 1800–2600, the deviations were less than 6 %, which confirms the adequacy of numerical modeling of calculating the heat transfer process in a pipe. It is shown that considering the influence of temperature on surface tension, the coefficient of thermal conductivity of water and the coefficient of dynamic viscosity of water is important to obtain accurate results. The proposed approach can be used to optimize the operating parameters of condensers and evaporators, as well as to accurately calculate the heat transfer coefficient and determine the areas of vapor formation. It will improve the energy efficiency of industrial installations and reduce the cost of equipment operation.

Nonequilibrium heat and mass transfer processes through liquid-vapor interfaces are studied through solutions of the Enskog-Vlasov (EV) equation and the corresponding system of EV26 moment equations. These models fully resolve liquid and vapor bulk regions and the diffuse interface connecting both. With that, evaporation and heat transfer processes can be studied without the need of modeled interface relations. Comparison of numerical results shows qualitative agreement of moment simulations with DSMC solutions of the EV equation, but quantitative differences. Interface resistivities for jump interface conditions are determined from the simulations, which show marked differences to those found from classical kinetic theory, where dimensionless resistivities are constants. In contrast, the EV models give temperature dependent resistivities, some negative off-diagonal resistivities, and indicate non-linear behavior where resistivities depend on mass and heat fluxes through the interface. In summary, the results point to the urgent need for systematic evaluation of resistivities over a wide range of conditions between weak and strong nonequilibrium, close to and far from the critical point.

A molecular dynamics study on the supercritical evaporation of liquid ammonia under forced convection conditions

In recent years, liquid desiccant air-conditioning systems have attracted much attention for its prominent potential of energy saving. In such systems, dehumidifiers/regenerators are the core components where heat and mass transfer occurs. The heat and mass transfer coefficients determine the accuracy of mathematical model which were used to design the dehumidifiers/regenerators. So, in this paper, the methods to obtain heat and mass transfer coefficients are evaluated theoretically. In order to enhance the mass transfer process, the internally cooled/heated dehumidifier/regenerator is designed and investigated experimentally and theoretically. Further, several advanced liquid desiccant air-conditioning systems are also introduced. Results show that the proposed equivalent integral mean method has high accuracy in calculating the coupled heat and mass transfer coefficients. Unlike Lewis number which was often assumed as one for describing heat and mass transfer between air and water, the defined Le factor may deviate appreciably from one in the heat and mass transfer process between air and liquid desiccant. The internally heated regenerators help to develop zero-carryover gas–liquid contactors because of much higher performance than adiabatic regenerators under low solution flow rate. It also helps to reduce energy consumption because of the high regeneration thermal efficiency, which indicates that the internally heated regenerators are promising and deserve much more renovation and application.

Studying the heat and mass transfer process of liquid desiccant for dehumidification and cooling

The object of this study was the processes of heat and mass transfer in a column heat exchanger with direct phases contact. The investigated problem is related to the need to determine the estimates of the kinetic characteristics of heat exchange during the concentration of solutions in a contact heat exchanger equipped with dual-flow trays. In particular, it was assumed that the determination of the influence of the gas velocity in the apparatus and the density of liquid irrigation of the plates, as well as the geometry of the plates, on the kinetic coefficients would make it possible to reveal the patterns of heat and mass exchange between the liquid and the air in contact with it in the column apparatus. It was determined that to increase the intensity of mass transfer in the gas and heat transfer in the liquid, it is necessary to increase the gas velocity and irrigation density. Then the gas velocity and irrigation density have approximately the same effect on the intensity of mass transfer in the gas and heat transfer in the liquid. When studying the effect of the geometry of the plate on the kinetic coefficients of heat transfer in the liquid and mass transfer in the gas, it was established that the value of the portion of the free cross section of the plate has a decisive influence on the value of the considered kinetic coefficients. A generalized equation was built, which makes it possible not only to calculate the enthalpy transfer coefficient during the interaction of sodium chloride solution with air but also to determine the limiting stage of this process. The results could be used to design a unit for concentrating a hot solution of sodium chloride by evaporating water during blowing with air in a contact heat exchanger. This would make it possible to obtain crystalline sodium chloride using secondary energy resources and other non-traditional sources of thermal energy

The process of heat and mass transfer between the air flow and the natural source of cold - ice is considered. It includes heat exchange by sensible heat and moisture exchange through latent heat transfer. This type of heat and mass transfer is observed in seasonal refrigeration storages for air conditioning systems. Snow or ice frozen during the cold season is used as a natural source of cold. The experimental setup created conditions for the contact of the flow of thermal air and natural sources of cold. The air flow is uniform. For this, the setup was carried out. Based on the analysis of experimental data, equations were obtained that determine the process of heat and moisture exchange. These are the dependences of the thermal Nusselt number on the Reynolds number and the diffusion Nusselt number on the Reynolds number. The heat transfer equations were compared with the previously obtained equations for non-uniform air flow in the experimental setup. Heat transfer with a uniform air flow is less intense at high Reynolds numbers from the considered interval. However, at lower air flow rates, the thermal Nusselt numbers become higher than at nonuniform air flow. These dependencies make it possible to calculate the dimensions of the required surface of contact of air with a natural source of cold for designing seasonal refrigeration storages.KeywordsCold accumulationHeat exchange (transfer)Moisture exchangeConditioningThermodynamic parameters

Acoustic streaming outside spherical particles and parameter analysis of heat transfer enhancement

Effectiveness–NTU relation for packed bed liquid desiccant–air contact systems with a double film model for heat and mass transfer

Use of single air extraction and injection to thermodynamically balance the combined heat and mass transfer process

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

Oil and gas companies and research organizations developed and implemented in industry for new ways and processes of extraction and refining of oil and gas. For example, in today's world there is an enormous amount of research in the theory of filtration with a sufficient set of various mathematical models and different approaches to solve them, but unfortunately the reality of developments in the oil and gas fields, more complex processes of filtration options, taking into account the kinetics heat and mass transfer, etc., which of course directly affects the process flow operation of the facility and information systems requires a "fast" response (calculation) and forecasting. The latter implies the formation of an adequate IT systems, computer simulation and its early settlement for the shortest time that can not be achieved without the use of modern programming packages. Similary problems in using of surfactants. Injection of heat-carriers include mass and heat transfers in two different areas, combined transition interfaces through the moving front and accompanied by phase changes. The last two characteristics describe a general class of problems known as the Stefan and Verigin types of problem. We developed and studied a variety of mathematical models of filtration in a porous media with kinetic relations of heat and mass transfer. Created a computational algorithm of the task. In studying the process of pumping Surfactants in a productive oil reservoir must consider thermal effects that are more convenient to define a kinetic equation of heat and mass transfer characteristics for two different areas, combined transition interfaces through the moving front and accompanied by phase changes, which defines a single constructive approach solving a general class of problems like Stefan and Verigin or Darcy-Stefan. We offered mathematical model describing the mass transfer processes for nonisothermal filtration with conditions of formation boundaries of "transition" zones and computational parallel algorithm for 3D case based on Web oriented applications.

Accurate numerical reconstruction of heat and mass transfer processes in particular applications, such a jet impingement, is difficult to obtain even with the use of modern computational methods. In the proposed paper, the flow and thermal phenomena occurring during single minijet impingement on the flat, concave and convex, heated surfaces were considered. Problem of impingement on non-flat surface, still not common and purely described in the literature, can be of big importance in engineering applications, such as the heat exchangers. Numerical analyses, based on the mass, momentum and energy conservation laws, were conducted with the OpenFOAM software. Focus was placed on the proper model construction, in which turbulence and boundary layer modelling was crucial, due to their significance in the heat transfer processes. Analysis of results obtained by RANS models focused mostly on the comparison of turbulent and hydrodynamics parameters.

The results of experimental studies of hydraulic resistance, heat and mass transfer characteristics of a prismatic lattice polymer regular packing for various options of its installation in space are presented. Based on the conducted experimental studies, the most rational design of packing installation was determined (taking into account the decrease in hydraulic resistance and the increase in the efficiency of heat and mass transfer processes), for which the geometric characteristics are given and empirical dependences are obtained, which make it possible to determine the value of the hydraulic resistance of the dry and irrigated packing, the values of the volumetric coefficients of mass transfer and heat transfer. The results of the study can be used in enterprises where different types of cooling towers or devices for conducting heat and (or) mass transfer processes, such as absorption, are used, as well as in the development of packed scrubbers.

Introduction. Radiative heat transfer in porous insulating materials at high temperatures was investigated in [1–3], and compound heat transfer under unsteady-state conditions in a material was investigated in [4]. Radiation transfer in the gray medium approximation substantially limits the adequacy of the model used in [5]. The present work, which is a continuation of [5], was performed by us with a view to account for the dependence of the optical properties of gas-permeable materials on radiation wavelength. The article describes a computational investigation of compound heat and mass transfer in a semitransparent gas-permeable material in the presence of phase transition and oxygen chemisorption in pores. An innovation in the formulation of the problem is accounting for the interaction of the radiation fi elds of optical inhomogeneities (pores and the particles intruded into a material) when calculating the material�c s optical properties. The optical properties of particles are usually calculated by the Mie theory [6], but at high concentrations the radiation fi elds of individual particles overlap, which is not taken into account in the Mie theory and leads to a large error in the calculated properties. To avoid the occurrence of such an error, in the present work the optical properties at a high particle concentration are calculated by means of the Maxwell–Garnett approximation [7] that accounts for the interaction of the radiation fi elds of the indicated inhomogeneities. Physical Model. We studied quartz that contained pores fi lled with air and vanadium dioxide particles in which 2 nd -order dielectric–metal phase transformations occur with heat liberation during cooling and heat absorption upon heating. Heat exchange with the surrounding medium proceeds by radiation and convection. We consider the processes of heat and mass transfer in a thin gas-permeable plane layer in one-dimensional approximation under conditions where radiative heat transfer is comparable with heat conduction in the solid skeleton and gas convection in the pores. Under conditions of heating or cooling, 2 nd -order dielectric–metal phase transition occurs in the vanadium dioxide particles, which is accompanied by oxygen chemisorptions and by a change in the crystalline structure of particles, with simultaneous liberation or absorption of heat in the material. These processes can be modeled by volumetric heat and mass sources that are introduced into the effective heat capacity of the material [5]. The absence of large pressure gradients in the gas leads to a relatively slow gas fi ltration, which allows us to assume that thermal equilibrium was achieved between the solid skeleton and the gas. The problem formulated is solved in the following approximation: the material under study is considered as a set of three continua inserted into one another. The components of this set are the continua of air in the pores, quartz (the material skeleton), and of the vanadium dioxide particles introduced into the skeleton. The thermophysical properties of continuous components are the effective properties in relation to the corresponding properties of a real material. Gas fi ltration in a material is modeled as the motion of a continuous air component characterized by a velocity fi eld and by the fi eld of specifi c air fl ow rates. Radiative transfer in the system considered occurs through the solid skeleton and gas in the pores. In modeling the radiative transfer, we took into account the processes of the radiation absorption, emission, and scattering. We assumed that the optical properties of a material were dependent on the wavelength. The effective heat capacity of the material depends on temperature and