The degradation of system perfonnance due to frost has prompted considerable investigation into the nature of heat and mass transfer processes occurring during the formation of frost as well as investigation into the properties of frost. The results of these investigations have generally indicated that the process of frost formation is complicated because of three factors:
1) The boundary layer solution is a transient one. As the frost layer grows in thickness, the thermal resistance of the frost layer changes both with respect to time and position. As the thermal resistance changes, the surface temperature of the frost layer changes with time and position and consequently the partial pressure of water vapor at the surface also changes. This changes the structure of the thermal and diffusion boundary layers, resulting in changes in the heat and mass transfer rates with time.
2) The frost properties are not constant but vary continuously during the development of the frost layer, although a quasi steady-state condition is eventually achieved. The variation in frost properties is generally quite significant.
3) The process of frost formation involves simultaneous heat and mass transfer. For the most part such problems dealing with forced convection have been analyzed using empirical heat and mass transfer data for flow past a circular cylinder.
Both experimental and analytical studies have been reported to date on the subject of frost formation. However, the analytical studies have primarily been based on steady state, empirical correlations for heat and mass transfer and have not taken into account variations in frost properties.
Citation: ASHRAE Transactions, Volume 78, Part 1, New Orleans, LA
Product Details
- Published:
- 1972
- Number of Pages:
- 16
- File Size:
- 1 file , 1 MB
- Product Code(s):
- D-NO-2231
