Heat transfer to Boiling Liquids

For the determination of the boiling film coefficients a knowledge of the temperature drop across the film under investigation is necessary. The bulk temperature of the liquid inside the evaporator is measured by a travelling thermocouple and the temperature of the tube wall, very near the film, at various levels are measured by fixed thermocouples. The installation of these thermocouples in the tube wall is a skilful and at the same time troublesome job. This laborious method has been avoided by finding out the combined annular film and wall coefficients, the value of which has been used in finding out the individual film coefficient from the general equation of the interrelationship between the overall heat transfer coefficient and the individual coefficients. An almost constant high value of the annular film coefficient has b6en assured by passing hot water through the outer annulus at a constant temperature and a constant high velocity. Boiling film coefficients of water in natural circulation vertical evaporator, with stainless steel tube and copper tube under low pressure and in Kestner evaporator at atmospheric pressure have been determined. Boiling film coefficients of organic liquids, ethyl alcohol and toluene, have been determined at low pressure in copper tube natural circulation vertical evaporator. In a forced circulation copper tube vertical evaporator the film coefficients of water, alcohol and toluene have been determined at boiling points below the atmospheric. All the observed film coefficients in different evaporators have been correlated with dimensional equations. In a pyrex glass tube natural circulation vertical evaporator the nature and the mechanism of boiling have been studied with water, alcohol, toluene and a solution of a frothing agent in water when the feed liquids are both saturated with and free from dissolved air. Attempts have been made to determine the latent heat of vapourisation of toluene at different temperatures