Entropy production analysis and cooling time calculation for an open hemispherical cavity in natural convection

Abstract

A numerical investigation of natural convection from an open hemispherical cavity is conducted in this study. The entropy production analysis and estimation of cooling time is the prime objective here. The study is conducted for different Rayleigh numbers [Formula: see text], the surface temperatures (350–550 K) and radius of curvature ratios of the hemisphere vary from 1 to 5. The problem is simulated in ANSYS Fluent 19. The perspective of both the first and second thermodynamic law is included in the modified function ( I/Q) to make the analysis. Entropy production because of fluid friction and heat transfer and corresponding irreversibilities are calculated, and obtained results are compared with the thermo-fluid behavior of the problem. The heat transfer enhances with an increment in the curvature radius and Rayleigh number for the given temperature. Also, entropy production, mainly contributed by heat transfer and fluid friction, has a lesser contribution. When the non-dimensional radius rises from 1 to 5, the dimensionless heat transfer increases from 5 to 24.05, almost five times for Ra = 103 and T*  = 1.67. The entropy generation grows from 0.0011 to 0.0147 W/K when the non-dimensional temperature rises from 1.17 to 1.67 for R* = 5 and Ra = 103. A similar observation for Ra = 107 is noticed. With an increase in non-dimensional radius, the entropy generation rate increases up to five times. Moreover, the induced heat transfer irreversibility rises with the curvature radius, whereas fluid friction irreversibility reduces. The cooling time of the body is computed using lumped capacitance method.