COMPARISON OF 2 METHODS FOR EVALUATING FLUID-TO-SURFACE HEAT-TRANSFER COEFFICIENTS

Fluid to surface heat transfer coefficients (h(fs)) were evaluated based on two analytical methods using transient time-temperature data obtained from regular objects. The first (rate method) was based on heating rate at any given location while the second (ratio method) was based on the ratio of temperature gradients at two locations. Regular shaped objects made from four test materials (Teflon, Lucite, polypropylene and Nylon) were used in the study under different experimental conditions. Depending on the ambient condition, test particle type, size and shape, h(fs) values ranged between 15 and 420 W/m(2) degrees C. The two methods generally compared well (p > 0.05), especially in situations where the associated Blot numbers were low (<10). However, larger variations were associated with the ratio method which in most cases also predicted higher hf, than the rate method. An error analysis indicated that both methods were sensitive to variations in parametric values when the associated h(fs) values were high (Bi > 20). Overall, the rate method gave more consistent and conservative h(fs) values.