شبيه‌سازي عددي اثر ضريب‌ لوييس بر مشخصه هاي عملكردي برج خنك‌كن مرطوب با جريان مخالف

Numerical Simulation of Lewis factor effect on characteristic performance of a counter-flow wet cooling tower

در اين نوشتار براي هر سه ناحيه از برج خنك‌كن مرطوب با جريان مخالف، مدل هاي رياضي معتبري به‌منظور شبيه‌سازي عددي دقيق تر ــ نسبت به مطالعات پيشين ــ و بررسي عملكرد حرارتي آن ارايه شده است. اثر ضريب‌ لوييس بر مشخصه-هاي عملكردي برج خنك‌كن مرطوب همچون تلفات آب، دماي خشك هواي خروجي، دماي آب خروجي و نرخ دفع گرما در محدوده‌ي وسيعي از شرايط آب و هوايي، از حالت خشك تا اشباع و براي دو دماي خشك ?C10 و ?C‌40، براي هواي ورودي بررسي شده است. هوا در ضرايب كوچك‌تر لوييس بسيار سريع تر اشباع مي شود و به اين دليل نرخ تلفات آب براي ضرايب كوچك‌تر لوييس، مقدار بيشتري است. افزايش ضرايب لوييس به‌دليل بزرگ تر شدن نرخ انتقال حرارت جابه‌جايي باعث افزايش نرخ دفع گرما، كاهش دماي آب خروجي و افزايش دماي هواي خروجي مي‌شود. اگر هواي ورودي نسبتاً گرم و مرطوب باشد، اثر ضريب‌ لوييس بر مشخصه هاي عملكردي برج نامحسوس خواهد بود.

The most efficient equipment through which heat rejection processes may be realized is the cooling tower. Cooling towers are used to cool a warm water stream through evaporation of part of the water into an air stream. These zones are modeled and solved numerically using a computer code, and the developed models of these zones are validated against experimental data. The mathematical models of these cooling towers are developed and validated against the experimental data available in the literature. These devices basically consist of three zones, namely; spray zone, fill packing and rain zone. The spray and rain zones are often neglected, even though, in large cooling towers, a significant portion of the total heat that is rejected may occur in these zones. Therefore, the heat and mass transfer contribution of the spray and rain zones in cooling towers is discussed as well. Numerical results fall within the range of experimental measurements, and show a higher accuracy, compared with the results of previous researchers. The effect of Lewis factor on the characteristic performance of a wet cooling tower, such as water loss rates, outlet dry-bulb temperature of air, outlet water temperature and heat rejected rate, under a wide range of weather conditions, for two different dry bulb temperatures of air, 10°c and 40°c, is investigated using the Bosnjakovic equation. Air is saturated at a rapid rate for a lower Lewis factor, so, water loss rates get a higher value. The growth of the Lewis factor increases the heat rejected rate and the outlet air dry bulb temperature. Reduction of Lewis factor increases outlet water temperature, because of higher convection heat transfer. The Lewis factor has no effect on characteristic performance for warm and humid inlet air.