熱交換器數值模擬分析

本研究主要探討鰭管式熱交換器與管束式熱交換器以及結合鰭管式與管束式的複合式熱交換器模型的廢熱回收率差異。研究使用Ansys/ Fluent對這三種不同形式的熱交換器進行熱流分析。首先我們針對三種不同形狀(平板型、尾翼型、眼型)鰭片的鰭管式熱交換器進行熱流分析。廢氣入口溫度設為823K時，三種不同鰭片型式鰭管式熱交換器的廢熱回收率均約26%，但是壓損分別為81.2022Pa(平板型)、67.6403Pa (尾翼型)、64.2693 Pa (眼型)，因此使用眼型鰭片較為適合。若於冷側裝設高度為8mm的眼型鰭片時，可將廢熱回收率由26%提升至29%%；裝設高度為8mm的長平板型鰭片時，可將廢熱回收率由26%提升至32%。針對鰭管式、管束式、複合式熱交換器在廢氣入口溫度為1223K時進行熱流分析，將複合式熱交換器的鰭管側與兩側裝設眼形鰭片的鰭管式熱交換器相比，兩者的廢熱回收率均約37%；將複合式熱交換器的管束側與管束式熱交換器相比，兩者的廢熱回收率均約42%。針對複合式熱交換器建立一燃燒室進行熱流分析，研究結果顯示在管束彎折角度的情況下，複合式的鰭管側、管束側空氣出口與排氣入口距離增加時，排氣入口處會由逆向流變化為交錯流，並改善空氣直接回流的問題，此外若於管束出口處附近裝設管束支撐板也能有相同改善效果。

關鍵字

計算流體力學；熱交換器；廢熱回收

並列摘要

This study focuses on the differences in recovery waste heat between finned tube heat exchangers, tube-bundle heat exchangers, and composite heat exchanger models that combine fin-tube and tube-bundle heat exchangers. Use Ansys/Fluent to perform heat flow analysis for these three different forms of heat exchangers. First, conduct heat flow analysis on fin-and-tube heat exchangers with fins of three different shapes (flat plate type, tail type, eye type). The exhaust gas inlet temperature is set to 823K, the waste heat recovery rate of the three different fin type fin-and-tube heat exchangers are approximately 26%, but the pressure loss is 81.2022Pa (flat type), 67.6403Pa (tail type), 64.2693Pa (eye type), therefore it is more suitable to use eye type fins. If eye-shaped fins with a height of 8mm are installed on the cold side, the waste heat recovery rate can be increased from 26% to 29%; when long flat fins with a height of 8mm are installed, the waste heat recovery rate can be increased from 26% % to 32%. A analysis of heat flow was performed for finned tube, tube-bundle, compound heat exchangers at an exhaust gas inlet temperature of 1223K. A fin tube with eye-shaped fins installed on the fin tube side and both sides of a compound heat exchanger. Compared with the type heat exchanger, the waste heat recovery rate of both are approximately 37%; The waste heat recovery of both the bundle side and the tube bundle heat exchanger is approximately 42%. A combustion chamber was built for the composite heat exchanger to conduct heat flow analysis. The research results show that under the condition of the bending angle of the tube bundle, when the distance between the air outlet and the exhaust inlet on the fin tube side and the tube bundle side of the composite type increases . The reverse flow at the exhaust inlet will change from reverse flow to cross flow, and the problem of direct air return will be improved. In addition, if a tube bundle support plate is installed near the outlet of the tube bundle, the same improvement effect can also be achieved.