熱差式氣體流量計之感測模式及氣流道效應分析

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/1937

Title:	熱差式氣體流量計之感測模式及氣流道效應分析
Authors:	呂學明;Xiung-Ming Lu
Contributors:	機械工程研究所
Keywords:	熱質流量計;TMFM;FLUENT
Date:	2000-07-04
Issue Date:	2009-09-21 11:34:46 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	此研究探討熱質流量計中的感應管在不同感測電路（定溫度、定電流）下的熱流特性及不同氣流道幾何外型（一字型、ㄇ字型與倒U型管）對兩加熱段的影響，並以套裝軟體FLUENT根據實驗狀況對感應管熱流場進行數值模擬。數值模擬的重點是在感應管加熱段維持定溫下，分析感應管管壁的熱散失現象及管內流場溫度變化，探討三種幾何外型的氣流道對加熱段的熱通量的影響，從數值模擬中發現不同速度剖面影響加熱段熱通量。本文分別利用定溫、定電流感測電路作熱差實驗量測實驗，探討加熱線圈的熱通量差、溫度差與流量的關係，由實驗中我們發現定溫感測電路易受環境溫度影響，反應時間較快，輸出電壓和流量呈一非線性關係，定電流感測電路工作溫度範圍較廣，反應時間較慢，輸出電壓和流量大致呈線性關係。我們利用定溫感測模式之實驗數據和數值模擬結果作比較，數值模擬和定溫感測的實驗數據比較仍有差距存在，差距是由於自製感應管無法使兩加熱線圈長度相同所造成的。但改以兩加熱段的熱通量差做比較，可去除實驗和數值解二者差距，二者的吻合度佳。 This study analyze the thermal and flow characteristics of the sensor tube in a thermal mass flow meter (TMFM) via the thermal-difference experiment and numerical simulations. Experiments were performed to study the thermal responses of two types of sensing circuit (constant-temperature and constant-current modes), and effects on the heating section with three different flow passages of sensor tube. Numerical simulations obtained from software packages (FLUENT) were also performed to validate experimental results. Simulations emphasized on the following issues: 1) analysis of the heat loss phenomena from the sensor tube wall, 2) predictions of temperature variation inside the tube, 3) effects of flow passages on the thermal flux of the heating section of the tube. Measurements from the thermal-difference experiments were made via the constant- temperature and constant-current sensing circuits; which were used to analyze the relations among the thermal-difference (temperature and thermal flux) from the two heating sections and the flowrate passing through the sensor tube. Experimental results show that sensor tube with the constant-temperature mode has faster response time, its output voltage and flowrate relation is nonlinear, and it was prone to influence of environmental temperature. The characteristics of sensor tube with the constant-current sensing circuit was: wider range of working temperature, slower response time, and roughly a linear relation between output voltage and flowrate. Disagreement of the thermal flux of the two heating sections among the measurement data with the constant-temperature mode and the numerical simulations do exist. Such discrepancy should caused by the unequal length of two handmade heating coils wrapped around the sensor tube. The discrepancy was eliminated by comparison in terms of the thermal flux difference from two heating sections, and good agreement were obtained between numerical and experimental approaches.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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