Consider a coupled shell-in-tube heat exchange device consisting of two identical heat exchangers A and B. 

Air flows on the shell side of heat exchanger A, entering at T_h,i,A = 520 K and m_h,A = 10kg/s. Ammonia flows in the shell of heat exchanger B, entering at T_c,i,B  = 280 K, m_c,B = 5kg/s. The tube-side flow is common to both heat exchangers and consists of water at a flow rate m_C,A = m_h,B with two tube passes. The UA product increases with water flow rate for heat exchanger A as expressed by the relation UA_A =  a + bm_c,A where a = 6000 W/K and b = 100 J/kg · K. For heat exchanger B, UA_B = 1.2UA_A.

(a) For m_c,A = m_h,B = 1kg/s, determine the outlet air and ammonia temperatures, as well as the heat transfer rate.
(b) The plant engineer wishes to fine-tune the heat exchanger performance by installing a variable speed pump to allow adjustment of the water flow rate. Plot the outlet air and outlet ammonia temperatures versus the water flow rate over the range 0kg/s ≤ m_c,A = m_h,B ≤ 2kg/s. 

Transcribed Image Text:

Air ThiA = 520 K mA = 10 kg/s A Water mA = MAB = 1 kg/s Pump Ammonia Tci,B= 280 K m. B = 5 kg/s B