Determine the necessary surface area if the overall heat transfer coefficient is 1.135 kW/m2 K.

 

A.    A tubular heater of the counterflow type is used to heat 1.26 kg/s of fuel oil (cp = 3.14 kJ/kg K) from 10∞C to 26.7∞C. Heat is supplied by means of 1.51 kg/s of water which enters the heater at 82∞C.

(a)   Derive an equation relating the temperatures of oil and water at any section of the heater.

(b)   Determine the necessary surface area if the overall heat transfer coefficient is 1.135 kW/m2 K.

 

B.    Water is evaporated continuously at 100°C in an evaporator by cooling 500 kg of air per hour from 260∞C to 150∞C. Calculate the heat transfer surface area required and the steam evaporation per hour, if the liquid enters at 100∞C. Take U0 = 46 W/m2 K and cp of air 1.005 kJ/kg K. At 100∞, hf g = 2257 kJ/kg.

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