Frost Growth on Cold Flat Plate: a Correlation for the Diffusion Resistance Factors

Abstract

The condensation of the vapor of water contained in the humid air on low temperature surfaces is a very frequent phenomenon. When the surface is below zero degrees, an ablimation of the vapor of water phenomenon happens, depositing as frost on the cold surface.

In this work a numeric computational model is developed for to simulate the frost formation and his growth process on low temperature plates. The frost formation is a common operational problem in fins of evaporators used in low temperature warehouses. This deposit affects the heat transfer reducing the refrigeration capacity; therefore, one better understanding of this phenomenon is of great interest.

During this work several analytic-experimental investigations were revised. Of particular interest they were the proposals [1], [2] relative to the effective diffusion coefficient.

Based on a control volumes analysis a non-linear system of differential partial equations is obtained: a mass diffusion equation and energy equation besides a group of auxiliary relationships that allow to close the system and defining interface and contour conditions. The finite differences method is used to solve the system. The equations are transformed to linear equations and resolved iteratively using the Thomas’ algorithm for tridiagonal systems.

The program allows obtaining in transient form the distribution of temperatures in the frost layer, its variation of thickness and growth, also the influence on the same process of the Reynolds’ number, the humid air temperatures, etc.

A strong influence of the diffusion resistance factors used in the reproduction of experimental data was observed. Then, is generated a correlation to determine these factors that it turns out to be function of the humid air and the cold flat plate temperatures.