The followings are the equations that I used to simulate the variation of the wafer temperature with respect to the temperature of the plate, spin speed, and air-gap thickness

Temperature of the baking plate used in the simulation = 150 C
Temperature of the chill plate = 25 C
Ambient temperature = 25 c

Spinning speed ranges from 150 rpm to 1000 rpm
Air-Gap thickness ranges from 0.5 mm to 3.5 mm

The graph below shows how variation in both air-gap thickness and spin speed 
affects the temperature of the wafer during heating and chilling. 

The graph below shows how variation in both air-gap thickness and spin speed 
affects the temperature variation during steady state.