Improving the Thermal Efficiency and Performance of Refrigeration Systems: Numerical-Experimental Analysis of Minimization of Frost Formation

Abstract

The frost growth on cold surfaces in evaporators is an undesirable phenomenon which becomes a problem for the thermal efficiency of the refrigeration systems because the ice layer acts as a thermal insulation, drastically reducing the rate of heat transfer in the system. Its accumulation implies an increase in energy demand and a decrease in the performance of various components involved in the refrigeration process, reducing its efficiency and making it necessary to periodically remove the frost, resulting in expenses for the defrost process. In the present work, a numerical-experimental analysis was performed in order to understand the formation process of porous ice in flat plates with different surface treatments and parameters. This understanding is of utmost importance to minimize the formation of porous ice on cold surfaces and improve equipment efficiency and performance. In this context, a low-cost experimental apparatus was developed, enabling an experimental analysis of the phenomenon under study. The environmental conditions evaluated are the temperature of the cold surface, room temperature, humidity, and air velocity. The material of the surfaces under study are aluminum, copper, and brass with different surface finishes, designated as smooth, grooved (hydrophilic), and varnished (hydrophobic). The numerical-experimental analysis demonstrates measurements and simulations of the thickness, surface temperature, and growth rate of the porous ice layer as a function of the elapsed time. The numerical results were in good agreement with the experimental results, indicating that the varnished surface, with hydrophobic characteristics, presents greater difficulty in providing the phenomenon. Therefore, the results showed that application of a coating allowed a significant reduction on the frost formation process contributing to the improvement of thermal efficiency and performance of refrigeration systems. KEYWORDSFrost layer growth; frost thickness; minimization of frost; hydrophobic surface; refrigeration systems Nomenclature Bi Biot number Bi mBiot number to mass transfer

Estudo numérico-experimental da formação de gelo poroso em placas planas de aço inoxidável

“…Seu depósito em superfícies frias altera o desempenho dos equipamentos de refrigeração, reduzindo a eficiência e exigindo um maior gasto energético para seu correto funcionamento (BIGLIA et al, 2022).…”