Determination of Boiling Film Coefficient for a Heated Horizontal Tube in Water-Saturated Wick Material

Abstract

Using an absorbent wick material saturated with a coolant has become attractive from a design standpoint for some missile-cooling applications. However, published data for predicting film coefficients are very limited. In this study, boiling film coefficients for a 1.0-in. OD horizontal copper tube embedded in water-saturated ceramic fiber-wick material were correlated over a heat-flux range from 1000 to 10,000 Btu per hr sq ft by the dimensionless equation hCG′CμK0.6ρLσP20.21=0.072DeG′μ−0.77 where G′=QAελ The presence of wick material next to a heat-transfer surface decreases turbulence in the region near the surface, increases the effective surface area, and provides active sites for bubble formation. This produces a higher film coefficient at low heat flux than occurs with pool boiling. At higher heat flux, the wick-boiling film coefficient was lower than for pool boiling.