Preheating period:

q_p = 23705 x 0.2871(180-176) + 1250 (180-176) = 3.2274 × 10⁴ Btu/hr

Change in air temp. is = [(3.2274 × 10⁴ )/(1.27 × 10⁶ )] × (313 - 176) = 2.67°F

Air temperature at the end of preheat = 209 + 2.64 = 212°F

 

Heating period:

q_s = 23705 × 0.2871 (261-180) + 24 (261-180) = 5.542 x 10⁵ Btu/hr

Air temperature at the start of heating = 313 – 45.38 = 267°F

Evaporating period:

q_p = 1.27 x 10⁶ – 5.542 x 10⁵ – 3.2274 x 10⁴ = 6.83 x 10⁵ Btu/hr

The mean temperature difference given as