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In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range. [ABSTRACT FROM AUTHOR]

Gaseous helium is being considered as a cryogen for a variety of high-power density applications. It is capable of reaching operational temperature levels as low as 20 K. This paper presents a time efficient method of designing and modeling a high-temperature superconducting dc cable. The analysis is an extension of a previously presented mathematical model in which the volume element method was used to characterize the fluid flow and heat transfer by conduction, convection, and radiation through a flexible cable cryostat. A system of ordinary differential equations was formulated using the fundamental principles of thermodynamics. The computational domain consists of volume elements distributed in three dimensions to account for the spatial dependence of the model. The pressure drop of the gaseous helium was calculated based on the Darcy–Weisbach correlation. Additionally, the temperature distribution was solved numerically using adaptive time-stepping. The obtained solutions converge within a timescale on the order of seconds to minutes, and the steady state results along with a transient analysis is discussed. [ABSTRACT FROM PUBLISHER]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical simulation of the heat and mass transfer in the two different Maisotsenko Cycle (M-Cycle) heat and mass exchangers used for the indirect evaporative cooling in different air-conditioning systems. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process, thus quantifying the overall heat exchangers’ performance. The mathematical model was validated against the experimental data. Numerical simulations reveal many unique features of the considered units, enabling an accurate prediction of their performance. Results of the model allow for comparison of the two types of heat exchangers in different applications for air conditioning systems in order to obtain optimal efficiency. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical simulation and optimization of the heat and mass transfer processes in the indirect evaporative air cooler. The heat exchanger uses a novel combined parallel and regenerative counter-flow arrangement. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process. Mathematical model was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented unit. The exchanger was compared with the conventional regenerative unit. The results of comparison show, that the presented unit is characterized by higher effectiveness. The impact of the selected unitless operating factors on the performance of the investigated heat exchanger was established. The conducted multi-criteria optimization allowed to establish Pareto-optimal operating conditions and preferable climatic zones for the presented heat exchanger. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model based on a three-phase theory, which is used to describe the mass and heat transfer between the gas and solids phases in a batch fluidised bed dryer. In the model, it is assumed that the dilute phase (i.e., bubble) is plug flow while the interstitial gas and the solid particles are considered as being perfectly mixed. The thermal conductivity of wet particles is modelled using a serial and parallel circuit. The moisture diffusion in wet particles was simulated using a numerical finite volume method. Applying a simplified lumped model to a single solid particle, the heat and mass transfer between the interstitial gas and solid phase is taken into account during the whole drying process as three drying rate periods: warming-up, constant rate and falling-rate. The effects of the process parameters, such as particle size, gas velocity, inlet gas temperature and relative humidity, on the moisture content of solids in the bed have been studied by numerical computation using this model. The results are in good agreement with experimental data of heat and mass transfer in fluidised bed dryers. The model will be employed for online simulation of a fluidised bed dryer and for online control. [Copyright &y& Elsevier]