A mist cooler is used to provide relief for a fatigued athlete. Water at T_i = 10°C is injected as a mist into a fan airstream with ambient temperature of T_∞ = 32°C. The droplet diameters are 100 μm. For small droplets the average Nusselt number is correlated by an expression of the form

(a) At the initial time, calculate the rate of convection heat transfer to the droplet, the rate of evaporative heat loss, and the rate of change of temperature of the droplet for two values of the relative humidity of the fan airstream,ϕ_∞ = 0.20 and 0.95. Explain what is happening to the droplet in each case.

(b) Calculate the steady-state droplet temperature for each of the two relative humidity values in part (a).

Transcribed Image Text:

Nup = TD/k = 2 D