تحليل حرارتي-ترموديناميكي و بهينه سازي مبدلهاي هواخنك تبخيري

چكيده انگليسي :

Thermal and Thermodynamic Analysis and Optimization of Deluged Air Cooled Heat Exchangers Zabihollah Bahrami Zabih722@gmail com Date of Submission 16 11 2009 Department of mechanical engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Mohammad Reza Salimpour Salimpour@cc iut ac ir Abstract In this project thermal analysis of both dry and evaporative air cooled heat exchangers was performed For this purpose the effect of different parameters like ambient temperature process fluid mass flow rate geometrical parameters of heat exchanger evaporation rate etc upon the performance of dry and evaporative heat exchangers was investigated For dry air cooled heat exchangers it was observed when the ambient temperature was increased the outlet temperatures of both air and process flow was increased too Also it was seen that the increment of inlet air reduced the mass flow rate of required air as a result of lowered air density Furthermore heat transfer was reduced due to lower mass flow rate and higher inlet temperature of air It was also observed that increasing the process flow rate caused an increase in the outlet temperatures of both air and process fluids Investigating the results of heat exchanger geometry showed that the reduction in the fin to fin root diameters ratio led to decrease in air mass flow rate and heat transfer rate of the heat exchanger In the evaporative air cooled heat exchangers it was observed despite of vast variations in inlet air temperature outlet temperatures of air and process fluids experienced negligible changes which were due to more evaporation rate at higher inlet temperatures In addition when the ambient temperature increased air mass flow rate and heat transfer rate decreased but the reduction rate was less than that of dry air cooled heat exchangers Although the variation of air flow rate with process fluid flow rate was very slight but heat transfer rate increased with the process flow rate rise which was due to increased heat load It was observed that for a given heat transfer rate fan rotation rate was higher in lower evaporation rates but with the increase in the deluged water over the heat transfer surfaces and consequently higher evaporation rates the fan rotation speed approached to a rather constant value Also the increase in the ambient temperature caused more fan rotation rate which was due to lower density of air in higher temperatures Furthermore air mass flow rate decreased with the increase of the deluged water whilst it was not sensible to the ambient temperature Also a thermodynamic second law analysis was performed to investigate the effects of different geometry and flow parameters on the air cooled heat exchanger performance For this purpose the entropy generation due to heat transfer and pressure loss of internal and external flows of the air cooled heat exchanger was calculated and it was observed that the total entropy generation has a minimum at special tube side Reynolds number Also it was seen that the increasing of the tube side Reynolds number resulted in the rise of the irreversibility of the air cooled heat exchanger The results also showed when air side Reynolds number decreased the entropy generation rate of the external flow reduced Finally based on the computed results a new correlation was developed to predict the optimum Reynolds number of the tube side fluid flow Keywords air cooled heat exchanger thermodynamic analysis thermal analysis entropy generation remanent irreversibility

بهرامي، ذبيح الله

تحليل حرارتي-ترموديناميكي و بهينه سازي مبدلهاي هواخنك تبخيري

بازگشت ناپذيري باقيمانده , بهينه سازي ترموديناميكي , توليد آنتروپي