LIQUID-FILM COOLING, ITS PHYSICAL NATURE AND THEORETICAL ANALYSIS

Abstract : A discussion of the physical nature of liquid-film cooling gives special emphasis to those phenomena occurring at the gas-liquid interface. The interfacial mass and heat balances are discussed in detail, together with the phenomena of film instability and the entrainment of liquid by the gas stream. A review is presented of the pertinent heat-mass transfer analyses for the wall region wetted by the liquid film. The limitations of those analyses are noted, and an alternate correlation procedure is suggested that is applicable to the case where the gas flow is compressible and subject to the influence of a streamwise pressure gradient. In order to implement that correlation procedure, a method is developed whereby the temperature at the gas-liquid interface can be approximated analytically. A heat transfer analysis is presented for the wall region downstream of the liquid film. That analysis is based on a relatively simple flow model, and is applicable to the case where the gas flow is compressible and subject to the influence of a streamwise pressure gradient. Two wall conditions are considered: (a) the case where the wall is adiabatic; and (b) the case where the wall is cooled externally.