Influence of frost formation in tube-fin evaporators using a distributed model

Resumo

Evaporators are heat exchangers of the refrigeration systems used to transfer heat from the
refrigerated environment. Their low operating temperatures favor the frost formation on their surfaces that,
depending on its thickness, can reduce the evaporator cooling capacity. This work presents a distributed model
for analyzing the influence of formation and frost densification on the performance of tube-fin evaporators. The
fundamental equations of mass conservation, momentum, and energy conservation are used to model the
refrigerant flow. The energy conservation equation of the evaporator tube wall is also solved. On the airside, the
equations of mass conservation, momentum, and conservation of energy are employed to simulate the formation
and frost growth on the evaporator surface. The system of equations is integrated numerically and solved
iteratively by successive substitutions. The numerical results obtained in this work are compared with
experimental data available in the open literature. Considering the range of inlet refrigerant temperature, -25.9 to
-20.2 °C, the means absolutes deviations, regarding the cooling capacity and the frost mass are 8,1% e 6,0%,
respectively. Among all tests carried out, during the four-hour interval there was an average reduction of 8% in
the cooling capacity due to the concentration of frost on the surface of the tubes and fins.