DEN6208/7208/DENM028 - Assignment 2 Heat Exchanger Design Marking Guidelines The Problem The Figure below shows part of an air conditioning plant. In order to replace stale air in an office block,

90 m³/min of air is discharged to the outside and replaced by an equal amount drawn into the building. To save on the cost of heating this cold air a "run-around system is installed to use heat from the discharged air to pre-heat the fresh air. The system works on water flowing through the pipes which form two finned tube heat exchangers, one to extract heat from the outgoing air and the other to preheat the incoming air. The total heat transfer from one air stream to the other is 10 kW and it can be assumed that the pipes connecting the two heat exchangers are perfectly insulated. Determine a suitable geometry and size for the heat exchanger on the discharge side using a) a counter flow, tube in tube heat exchanger b) a "shell and tube style heat exchanger with fins on the air side of the tubes.