11-72 A single-pass cross-flow heat exchanger is used to cool jacket water (cp=4.18kJ/kgC) of a diesel engine from 90C to 60C, using air (cp=1.02kJ/kgC) with inlet temperature of 30C. Both air flow and water flow are unmixed. If the water and air mass flow rates are 42,000kg/h and 180,000 kg/h, respectively, determine the log mean temperature difference for this heat exchanger