An AISI 316 stainless steel spherical container is used for storing chemicals undergoing exothermic reaction that provides a uniform heat flux of 60?kW/m2 to the container’s inner surface. The container has an inner diameter of 1 m and a wall thickness of 5 cm. To prevent thermal burns on individuals working around the container, it is necessary to keep the container’s outer surface temperature below 50°C. If the ambient temperature is 23°C, determine the necessary convection heat transfer coefficient to keep the container’s outer surface temperature below 50°C. Is the necessary convection heat transfer coefficient feasible with free convection of air? If not, discuss other options to prevent the container’s outer surface temperature from causing thermal burns.

Question

Answer 1

An AISI 316 spherical container is used for storing chemical undergoing exothermic reaction that provide a uniform heat flux to its inner surface. The necessary convection heat transfer coefficient to keep the container’s outer surface below 50°C is to be determined.

Assumptions 1 Steady operating conditions exist. 2 Negligible thermal storage for the container. 3 Temperature at the surface remained uniform.

Analysis The heat rate from the chemical reaction provided to the inner surface equal to heat rate removed from the outer surface by convection



The convection heat transfer coefficient can be determined as



To keep the container’s outer surface temperature below 50°C, the convection heat transfer coefficient should be



Discussion From Table 1-5, the typical values for free convection heat transfer coefficient of gases are between 2–25 W/m2?K. Thus, the required h > 1840 W/m2?K is not feasible with free convection of air. To prevent thermal burn, the container’s outer surface temperature should be covered with insulation.