Energy, Momentum, and Mass Transfer

Abstract

Abstract Conduction, convection, and radiation are not completely independent energy transfer modes. Energy transfer within a stationary medium is the product of its thermal conductivity and a temperature gradient. Except in thin stagnant films near solid boundaries, energy is transferred in fluids by buoyancy-driven convection at all scales. Film thickness depends on convection in a complicated way. All thermal insulation—cork, wool, foams—exploits the low thermal conductivity of air immobilized in pores. The thermal conductivity of moist air is somewhat less than that of dry air. Cooling of humans in water and air at the same temperature is not 24 times faster because the thermal conductivity of liquid water is 24 times greater than that of still air, even absent metabolism. Core temperatures of humans decrease only 2–4 times faster in water than in air. Odorants travel in perceptibly still indoor air much faster than by molecular diffusion.