細微粒在微管束熱交換器中的熱泳沈降

Abstract

本研究利用熱泳效應的原理，設計出可用以去除細微粒，且流量及效率皆能兼顧的熱泳沈降器。此熱泳沈降器的結構近似一熱交換器，但不同的是由兩組溫度不同之方管管排交錯組成。加熱管排令氣體增溫，冷卻管排令氣體降溫，並使微粒在降溫的過程中因熱泳效應而沉降於冷卻管排表面上。微管束熱泳沈降器不斷地提供均勻的高溫度梯度，來提高對微粒的收集效率。 本研究以常溫實驗氣體攜氯化鈉微粒進行收集效率實驗。當冷熱管排表面溫度差為45.5∼88.9℃時，微管束熱泳沈降器對細微粒的收集效率達50∼92％，相較於Messerer et al.（2004）所設計的沉降器有更好的收集效率。另外，以數值模擬計算出沈降器內部溫度分佈及微粒沈降效率，再與實驗值進行比較。冷熱管壁表面溫度差為88.9℃時，收集效率的模擬值與實驗值相當地接近，所以模擬的結果對沉降器的設計改進有很大的幫助。

The deposition of fine particles in a miniature pipe bundle heat exchanger system has been investigated. In order to increase the collection efficiency of the traditional thermophoretic precipitator, a miniature pipe bundle precipitator was designed to operate at high inlet temperature, high flow rate and high collection efficiency. The new precipitator consists of alternate tubes in two different temperature. The gas temperature is increased by the heated tubes and decreased by the cooled tubes, and the particles can deposit on the cooled tubes by thermophoresis in the process of gas temperature decreased. The miniature pipe bundle thermophoretic precipitator can maintain a high temperature gradient to improve the collection efficiency. The system has been tested for the collection efficiency with sodium chloride particles and experimental gas of normal atmospheric temperature at different heat exchanger temperatures and flow velocities. When the temperature difference between the heated tubes and cooled tubes is in the range of 45.5℃ to 88.9℃, the miniature pipe bundle thermophoretic precipitator can collect particles in 50~92％. Test results show the current miniature tube bundle heat exchanger is promising to remove fine particles more efficiently than Messerer et al.(2004) designed. In addition, we calculated out temperature profile and particle deposition efficiency of this precipitator with numerical simulation, then compared with experimental value. When the surface temperature difference is 88.9℃, the simulation value of collecting efficiency is close to experiment value, and the helpful result of simulation can improve the design of the precipitator.