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Visual-Basic Program on Double-Pipe Heat Exchangers Performance Powered by Supercritical H2O
|Contributors: ||NTOU:Department of Mechanical and Mechatronic Engineering|
Supercritical water;Double-pipe heat exchanger;Heat transfer coefficients;Visual-Basic
|Issue Date: ||2013-10-07T03:03:18Z
|Abstract: ||中文摘要 本研究旨在探討超臨界水套管式熱交換器熱傳性能，實驗上建置一套量測系統，由已知的套管式熱交換器尺寸與實驗量測進出口溫度數據，建立一套計算程式，計算在穩態或暫態時的熱傳性能，結果並加以比較。 本研究將由3組實驗數據，分別為Case1：180kg/hr、20MPa、Case2：180kg/hr、30MPa及Case3：300kg/hr、30MPa。運轉初期，靠近電阻加熱器的後端熱交換器HE3其升溫較快，反之，前端的熱交換器HE1其升溫較緩，經一段時間後各點溫度漸趨穩定。電阻加熱器為本設備中溫度最高的區域，程式中也針對不同條件下，進行管壁外表最高溫度及熱傳量之計算，以供安全考量。 熱傳分析首先進行能量平衡由於HE1與HE2之結構管徑相同，故可將HE1與HE2串聯為一組大型的熱交換器進行能量平衡，其三組數據之誤差分別為Case1：38%、Case2：2.3%、Case3：6%。熱傳計算過程理論上採用5種熱傳模式，計算總括熱傳係數與實驗值做比較，其平均誤差分別為80%、56% 與35%，在低壓低流量下，量測誤差較大，而且熱傳效果較差。另與中國學者楊冬等人之同樣高壓臨界水研究進行比較，實驗口徑約為本設備的3倍，其熱傳係數實驗值約高過本研究12% 與32%，因為其管型為內螺紋管，若扣除熱傳性能較本研究光裸管為佳之效應，其結果應該相當接近。 本程式使用Visual-Basic結合Microsoft Excel撰寫，程式具有查詢熱物理性質之功能。使用者輸入量測溫度、壓力、流量及溫度變化率後，首先進行能量平衡驗證。熱傳分析採用對數平均溫差法（LMTD），求得實驗值的總括熱傳係數，其次計算出理論管側及殼側熱傳係數與總括熱傳係數進行比較。藉由電腦程式的計算，可提升計算效率，減少錯誤，節約運算時間，達到最佳的效果。|
Abstract The objective of this study is to investigate the thermal performance of double-pipe heat exchangers powered by supercritical water. An experimental facility built by TPRI was used to conduct the tests. To analyze the data, a computer program has been developed to calculate the heat transfer coefficients in both steady and transient states. Three groups of experimental data were taken under the conditions of Case1: 180kg/hr, 20MPa; Case2: 180kg/hr, 30MPa and Case3: 300kg/hr, 30MPa. During the heating process, the heat exchanger HE3 closest to the resistance heater was firstly heated, and then extended to HE2 and HE1. Eventually, the whole system reached a steady state and the history of temperatures at the inlet and exit at each heat exchanger were recorded. The maximum temperature in the resistance heater is also noted, which provides the safety consideration in a practical running. The energy balance in each heat exchanger is made to assure the consistence with the first law in thermodynamics. Due to the same structure in HE1 and HE2, they can be taken as a combined exchanger during the analysis. Five kinds of heat transfer correlations based on the experimental observations at ordinary pressures were used to predict the overall heat transfer coefficient and with which compared with the experimental data. The error was found to be around 80, 56 and 35% in each case. This deviation is suspected to the low values of pressure and flow rate. At the same pressure and working fluid as the present study, the Chinese scholars Yang whose results in heat transfer coefficient are higher than the present data by 12% and 32%. However the tube used in that paper is a inner threaded pipe and three times larger in diameter, comparing with the present study with bare tube, the results are comparable. The program was coded in Visual-Basic combined with Microsoft Excel, program owns query hot physical properties of features. Once the measured temperatures, pressure, flowrate and temperature change rate have been determined, the energy balance is validate first. Then the overall heat transfer coefficient can be found by LMTD method. Finally, the results are made to compared with those theoretically calculated values in both of tube side and shell-side heat transfer coefficient and the overall heat transfer coefficients. Through the computer program work, one can improve the computational efficiency , reduce errors, and save computing time to achieve the best results.
|Appears in Collections:||[機械與機電工程學系] 博碩士論文|
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