Measurement of convective heat transfer coefficients in a randomly packed bed of silica gel particles using IHTP analysis

The purpose of this research is to determine the convective heat transfer coefficient (h(t)) for airflow through two randomly packed beds of microporous silica gel particles of nearly uniform diameter (i.e., for the average diameter of 1.60 and 2.58 mm). The experimental test facility was developed to induce a transient step change in the inlet uniform airflow while the temperature was measured at several locations within the silica gel beds (x/L = 0.29, 0.48, 0.69). The transient test data were simulated numerically using the volume averaging method for air flow through a homogeneous packed bed of particles for a range of Reynolds numbers (40 < Re-dh < 100). The convective heat transfer coefficient was determined by using the numerical inverse method to minimize the difference between the simulated and experimental temperature profiles. The sensitivity analysis stated that the thermocouple placed at the middle of the test section (x/L = 0.48) had the highest sensitivity during the first 400 s of transient testing. Using the ht values obtained by the inverse calculations, a good agreement is obtained within the experimental uncertainty limits for the experimental and numerical temperature temporal profiles at different locations within the beds; but the agreement is best using the transient temperature data at x/L = 0.48. Based on the ht values, a new correlation between Nusselt number and Reynolds number is presented with lower uncertainty (the maximum uncertainty of +/- 30%) compared to the correlations in the literatures. It was found that the proposed correlation is in agreement with the data in literature within their uncertainty bounds. (C) 2016 Elsevier Ltd. All rights reserved.