文档介绍：International Journal of Heat and Mass Transfer 45 (2002) 4289–4303
ate/ijhmt
Frost formation and frost crystal growth on a cold plate
in atmospheric air flow
Chin-Hsiang Cheng *, Chiuan-Che Shiu
Department of Mechanical Engineering, Tatung University, 40 Chungshan N. Road, Sec. 3 Taipei, 10451 Taiwan, ROC
Received 12 September 2001; received in revised form 26 March 2002
Abstract
The present study is concerned with the spatial variation of the frost thickness as well as the pattern of the frost
crystals formed on a cold plate in atmospheric air. Experimental results regarding the two-dimensional variation of the
frost thickness at the leading edge and observation on the growth of the frost crystals on the frost formation are
provided. A microscopic image system is used to observe the structure of the frost layer. The environmental variables
considered in this study include the velocity, temperature, and relative humidity of the air (V, Ta, and /), as well as the
surface temperature of the cold plate (Tw), which is varied by adjusting the cooling refrigerant temperature (Tref ). The
ranges of the physical variables considered in this study are 2 6 V 6 8 m/s, 18 6 Ta 6 30 °C, 40% 6 / 6 70%,
À18 6 Tref ðand TwÞ 6 0 °C. Ó 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Frost thickness; Frost crystal; Cold plate; Image system
1. Introduction tion in recent years. As reported by Emery and Siegel [1],
a 50–75% decrease in heat transfer and a substantial
When atmospheric air flows over a surface of which increase in pressure drop are caused by frost formation
the temperature is below the dew point temperature of on pact heat exchanger. Therefore, owing to the
the air, the water vapor in the air will condense on the subtle influence of frost formation on thermal and flow
surface. Furthermore, when the surface temperature is characteristics of the heat exchangers, the frost forma-
lower than the freezing point of the liquid condensate, t