Heat and mass transfer to spheres in high‐temperature surroundings

An experimental investigation of the combined natural and forced convective effects was carried out which involved the measurement of the rate of evaporation of water from porous stationary spheres (1/4, 3/8 and 1/2‐in. in diameter) under steady conditions in an electrically‐heated stainless steel chamber. The spheres were suspended in a stream of super‐heated steam at atmospheres ranging from 50 to 1000°K. Both the opposing and aiding flow cases were investigated. The Reynolds number varied from 0 to 1489 and the turbulence intensity was less than 1%. The parameter [( Gr )/( Re 2 )] was found to be of fundamental importance in correlating the results. The rates of heat transfer in the mixed flow region for the opposing flow case was higher than for aiding flow. The transition between the two mechanisms was found to be gradual but very complex in the case of opposing flow.