Reliable one-dimensional approximate solutions for insulated oblate spheroid containers

Since there is no reliable surface-area formula available for the calculation of the heat-transfer characteristics of an insulated oblate spheroid, in this investigation, highly accurate oblate spheroid surface area is obtained by a simple numerical integration method. Based on the accurate oblate spheroid surface area, a reliable one-dimensional approximate solution of an insulated oblate spheroid container can be obtained with a one-dimensional RPSWT model. By comparing with accurate three-dimensional numerical results, it is found that in cases of low external convective coefficient (ho = 8.3 W m−2 K−1), long-short-axes ratio a/b≦3, and insulation thickness t/R2≦2, errors are within 3%. In rarer situations with a/b≦5 and t/R2≦2, the errors are within 5.5%. The above results are almost independent with the internal flow convective coefficient (hi from 30 to 105 W m−2 K−1) and dimensionless container size (0.5R2ho/Ks from 1.55 to 155).