Pool boiling heat transfer to hydrocarbons and ammonia: A state-of-the-art review

Interest has grown in recent years to extend the use of hydrocarbons and ammonia as working fluids in refrigeration to new domains of application, despite their flammability. In the context of pool boiling heat transfer, this has created increasing research activities, particularly with regard to hydrocarbons. In contrast with this, only a few new experimental results have been added to the data set existing for ammonia in the literature. So this review will concentrate on hydrocarbons, while ammonia will be treated in a comparatively brief part.The review starts with the state-of-the-art that had been reached at about 1990. It continues with the data set for propane being taken as an example to highlight various reasons for the experimental data scatter that is found when different sources are compared for the same substance. In the main part, new results of 12 (aliphatic) hydrocarbons are discussed regarding the influence of heat flux q and reduced saturation pressure p∗ = ps/pc on the heat transfer coefficient α, and also the variation in α0 caused by the differences in the thermophysical properties of the 12 hydrocarbons at constant q0 and p0∗. It is shown that the dependencies of the heat transfer coefficient α on heat flux q and reduced pressure p∗, and on the thermophysical properties of the various fluids at constant values q0 and p0∗ can be correlated by general semi-empirical functions with comparatively narrow limits of error that do not reach far beyond the experimental scatter occurring when different sources are compared for the same substance. Before treating ammonia in a final section, the review on hydrocarbons closes with short discussions for mixtures of hydrocarbons, for the bundle effect, and for the behaviour of enhanced tubes.