The project investigates a heat exchanger design concept for a furnace offgas pipe from an industrial furnace at Elkem. The goal is to develop a heat exchanging concept for harvesting exhaust heat using a numerical model. The proposed heat exchanger duct goes around a 3,2 m diameter pipe, and its initial size is taken as 70 mm high and 200 mm wide. The flow and temperature profiles in the heat exchange duct are solved using CFD simulation to determine the heat transfer and the temperature increase of the flow at the outlet of the duct. A parameter analysis was done on this model by varying the height and the width of the heat exchanger to determine the effect of those dimensions on the outlet temperature and heat transfer. The radiation heat transfer was also investigated. An alternative design was also tested where the heat exchanger duct goes twice around the furnace offgas pipe in a spiral-like shape. Finally, the effect on the silica layer inside the furnace offgas pipe was studied. By changing the height, there are few benefits other than increasing the mass flow. On the other hand, increasing the width results in a higher outlet temperature but less overall heat transfer. The results give a qualitative indication regarding how to design the heat exchanger depending on whether the requirements need higher outlet temperature or increased heat transfer. The thermal radiation analysis showed that neglecting radiation effects in the parameter studies was acceptable since their impact is insignificant. For the spiral configuration, the results were similar to a 400 mm wide heat exchanger duct. However, a 400 mm wide single-round heat exchanger is a simpler design. For the silica layer model, the results showed that the layer significantly affects heat transfer and is an essential factor to consider in the design.
Vélaverkfræði, Meistaraprófsritgerðir, Ofnar, Iðnaður, Varmaskiptar, Varmaflutningur, Varmi, Endurvinnsla, Mechanical engineering, Furnaces--Industrial applications, Heat exchangers, Heat transfer, Waste heat
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