Evaporative Heat Transfer Coefficients During Sensible Heating of Milk

In this article, the evaporative heat transfer coefficients for sensible heating phase of milk in a stainless steel pot during khoa making by conventional heating method have been reported. Various indoor experiments were performed for sensible heating of milk in a stainless steel pot under open condition by varying heat inputs from 240 watts to 420 watts. The experimental data were used to determine the values of evaporative heat transfer coefficients which were observed to decrease with an increase in rate of heating. It is also observed that the evaporative heat transfer coefficient increases significantly with the increase in operating temperature for each rate of heat inputs. The experimental error in terms of percent uncertainty was also evaluated.

Evaporative Heat Transfer Analysis of a Heat Pipe With Hybrid Axial Groove

Through the application of thin film evaporation theory and the fundamental operating principles of heat pipes, a hybrid axial groove has been developed that can greatly enhance the performance characteristics of conventional heat pipes. This hybrid axial groove is composed of a V-shaped channel connected with a circular channel through a very narrow longitudinal slot. During the operation, the V-shaped channel can provide high capillary pressure to drive the fluid flow and still maintain a large evaporative heat transfer coefficient. The large circular channel serves as the main path for the condensate return from the condenser to the evaporator and results in a very low flow resistance. The combination of a high evaporative heat transfer coefficient and a low flow resistance results in considerable enhancement in the heat transport capability of conventional heat pipes. In the present work, a detailed mathematical model for the evaporative heat transfer of a single groove has been established based on the conservation principles for mass, momentum and energy, and the modeling results quantitatively verify that this particular configuration has an enhanced evaporative heat transfer performance compared with that of conventional rectangular groove, due to the considerable reduction in the liquid film thickness and a corresponding increase in the evaporative heat transfer area in both the evaporating liquid film region and the meniscus region.

Human skin wettedness and evaporative efficiency of sweating

Rates of evaporation and sweating were recorded for three acclimatized male subjects in hot humid conditions, the ambient parameters of which were set so that the various imposed evaporative rates required the same skin wettedness at different levels of sweating. Rectal and skin temperatures were measured. Results showed that during steady state occurring during the 2nd h of exposure each subject reached the required evaporative rate by means of increases in skin wettedness regardless of the level of sweating; the sweat evaporative efficiency, defined as the ratio between evaporative rate and sweat rate, decreased as skin wettedness increased, in a range between 0.74 and 1.0 Sweat efficiency fell to 0.67 for fully wet skin. The body temperatures did not increase with time if skin wettedness was less than unity. Evaporative heat transfer coefficient (he), maximum evaporative capacity, and wettedness were estimated on the basis of the observed decrease of sweat efficiency. The relationship between skin wettedness and sweat efficiency was interpreted as a combined effect of differences in local he as well as in local sweat rates.