It is proposed to cool oil in a counter-current, concentric tube heat exchanger composed of a thin-walled inner tube of 0.02 m diameter carrying oil and thin-walled, perfectly insulated outer tube of 0.05 m diameter carrying water. The oil flow rate is 50.0 kg min-1 and it has to be cooled from 90°C to 40°C using 60 kg min-1 water at 20°C. Calculate the heat load and the outlet water temperature.

You are then asked by your supervisor to design a concentric tube heat exchanger to operate under the following conditions: Cold Fluid m = 0.125 kg/s Cp 4200 J/kgK T₁ = 40°C To = 95°C Hot Fluid: m = 0.125 kg/s Cp = 2100 J/kgK T₁ = 210°C If the heat exchanger is characterised by uniform overall heat transfer coefficient, using the LMTD method, determine: e) The maximum possible heat transfer rate. f) The heat exchanger effectiveness. g) The ratio of the heat transfer area under parallel flow to the heat transfer area under counter flow. Comment on the answer.

Design a hydrocooling unit that can cool fruits andvegetables from 30 to 5°C at a rate of 20,000 kg/h under thefollowing conditions:The unit will be of flood type, which will cool the productsas they are conveyed into the channel filled with water. Theproducts will be dropped into the channel filled with water atone end and be picked up at the other end. The channel canbe as wide as 3 m and as high as 90 cm. The water is to becirculated and cooled by the evaporator section of a refrigerationsystem. The refrigerant temperature inside the coils is tobe 22°C, and the water temperature is not to drop below 1°Cand not to exceed 6°C.Assuming reasonable values for the average product density,specific heat, and porosity (the fraction of air volume ina box), recommend reasonable values for (a) the water velocitythrough the channel and (b) the refrigeration capacity ofthe refrigeration system.

Hot gas enters a finned-tube, crossflow heat exchanger at 300 °C and exits at 100 °C. Assume that both fluids are unmixed. The gas is used to heat pressurized water flowing at 1 kg/s from 35 °C to 125 °C. Assume constant properties and use 1000 J/kg K and 4197 J/kg K as the specific heat of the gas and the water, respectively. The overall heat transfer coefficient, based on the gas-side surface area is U₁ = 100 W/m² K. Please determine the required gas side surface area (Aʼn), using the NTU method. Repeat the problem using the LMTD method. Compare your results by quantifying the difference between the two methods with a percent difference and write an observation/conclusion for this result.