Describe a suitable method for estimating the performance of a heat exchanger in the 2 shell, 4 tube pass configuration, and explain why this is required. A counter- current heat exchanger of this type, which can be assumed to have area 20m, is operated with an inlet temperature of the air of 150 C (shell side) and with a cold water stream inlet temperature of 20C. The cold side tube diameter is 8mm, and the water flow velocity through the tube is 4.5m.s. The air side flow rate is 1kg.s and the heat transfer coefficient can be assumed to be 55W.m2.K-. Apply the method that you have identified to estimate the heat transfer in this configuration, and the cold and hot stream outlet temperatures for this duty.