Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
An experimental study of frost growth under the influence of streamwise vortices in a laminar
channel flow is presented. A new model of frost growth is developed to normalize the growth
rate of frost with respect to the effects of environmental parameters and time. This
normalization and a scale analysis show that the dimensionless frost thickness grows with the
square root of environmental time, a single parameter capturing environmental and temporal
effects. Experimental plain-channel data obey this relationship to within the uncertainty of the
measurements. Also in agreement with the model, the data show no significant dependence on
channel location or on Reynolds number (for 5OO<Re<2500 based on hydraulic diameter).
Comparisons of model predictions to data from previous studies demonstrate good agreement
with these independent data obtained under other conditions. The growth patterns of frost
behind a delta-wing fixed to the surface of the channel are explained using flow visualization
results. The appearance of frost on the surface occurs sooner, and the frost has an internal
structure in regions where the vortices impose a flow toward the surface different from regions
unaffected by vortices. Horseshoe vortices form at the junction of the channel and wing and
the interaction of tip vortex and horseshoe vortex were qualitatively observed. The maximum
frost height behind the delta wing in the spanwise direction is compared to the plain channel
results: frost growth rate under the influence of the streamwise vortex was approximately 13%
higher than for the plain-channel case.Air Conditioning and Refrigeration Project 5
