Chapter 6, Problem 6.84P

An experiment is conducted to determine the average mass transfer convection coefficient of a small droplet using a heater controlled to operate at a constant temperature. The power history required to completely evaporate the droplet at a temperature of $37°\text{C}$ is shown in the sketch. It was observed that, as the droplet dried, its wetted diameter on the heater surface remained nearly constant at a value of 4 mm.

1. Calculate the average mass transfer convection coefficient based on the wetted area during the evaporation process when the droplet, heater, and the dry ambient air are at $37°\text{C}\text{.}$
2. How much energy will be required to evaporate the droplet if the dry ambient air temperature is $27°\text{C,}$ while the droplet-heater temperature remains at $37°\text{C?}$