Characteristics of Heat Transfer Coefficient Derived from Application of Heat-Mass Transfer Analogy on Sublimating Naphthalene Disk Data

摘要

The Chilton-Colburn heat and mass transfer analogy j-factor equations wereapplied to the weight loss data of sublimating naphthalene disks. Circular naphthalene disks were placed at five locations on a stationary copper manikin, under constant temperature and wind speed in an environmental chamber. The life-size manikin modelled the human body contour. Regional convective heat transfer coefficients (hc) were determined by applying strictly the analogy equations, without any extraneous body shape approximation or extrapolation. Theoretically, the analogy should yield hc, directly. However, we found that the heat transfer coefficients derived from naphthalene disk sublimation data (hn) were substantially larger than some reported hc, values. Under comparable environmental conditions, hn overestimated hc, by a factor of approximately three. As an average, hn = 3.35 hc. Similar degrees of overestimation also were evident when two other independently reported j factor formulations, both derived specifically from naphthalene sublimation data, were used. The resultant coefficient hn, resembled more closely, in its numerical magnitude, to the evaporative transfer coefficient, rather than hc. This raises a question about the exact nature of the coefficient hn. With sublimation weight loss data from naphthalene disks mounted on the human body, does the application of the heat-mass transfer analogy yield directly the convective heat transfer coefficient, or perhaps a quantity more closely resembles the evaporative heat transfer coefficient. A review of the literature finds evidences to support the latter assertion.