- 學位論文
雙壓並聯蒸發冷凝式冰水主機之性能測試及模擬
Performance Test and Simulation of Evaporative Cooling Chiller with Parallel Compressors
摘要
本研究以濕盤管的熱質傳模式為基礎，建立蒸發式冷凝器的分析方法，並與壓縮機及蒸發器性能關係式結合建立整體冰水機能力數值輔助計算程式，輔以測試數據比對驗證，以探討各項設計參數對冰水主機性能之影響。性能實測以一10冷凍噸之雙壓縮機並聯蒸發式冷凝式冰水機原型機進行，其主要構件由雙台渦卷式壓縮機組、硬焊板式蒸發器、及蒸發式冷凝器所組成，工作流體為冷媒R22，其中冷凝器採用外徑為9.52mm的內螺紋銅管所組成。模擬分析中分別針對熱、質傳係數進行比較計算，選出適合之經驗公式；本研究測試數據及模擬結果比對誤差約在± 8%以內。各項參數模擬結果顯示：使用冷凝內螺紋管可提升整體系統COP約6.7%。增減風量對於系統效能之影響程度隨環境與負載變化而改變，而在固定送風機與冷凝器橫截面積條件下，增加管排會使系統風阻增加造成風量下降，並且降低冷媒流速，影響增加熱傳面積對整體COP的改善效益，在外氣濕球溫度24℃時熱傳面積由8.9增加至14.8m2使COP由4.7增加至4.87。適當減少管數的配置可使COP落差不超過1%而達到減少管排成本之效果。性能測試結果顯示本雙渦卷並聯壓縮之冰水機於外氣濕球溫度24℃時，全載系統SCOP(製冷能力/總耗電)可達4.12，半載系統SCOP為4.27；冷卻動力佔半載總系統耗電約27.4%，其中循環水幫浦即佔17.8%，根據蒸發冷卻式系統的需求特性選配較適當之幫浦與風機來改善冷卻動力，是提高半載時的SCOP是一大關鍵。
並列摘要
In this study, a numerical calculation program of chiller performance has been established. It includes an analytical heat and mass transfer model of the evaporative condenser, correlations of evaporator performance and compressor performance. The program was verified by test data, and used to study the effects of various design parameters on chiller performance. The prototype of the performance test is a 10RT dual parallel compressor evaporative condenser chiller. The main components of the prototype are: two scroll type compressors, a brazed plate evaporator, and an evaporative condenser. The working fluid is refrigerant R-22, and micro-fin tubes with outside diameter of 9.52mm are used in the condenser. Empirical correlations of heat and mass transfer coefficient are determined by comparing the tests results with the calculation of several correlations. In this study, the discrepancy between the test data and simulation results are less than ± 8%. The predictions of the present model show that the use of internal micro-fins improves the overall system COP by about 6.7%. The system performance is affected by the air flow rate, and the ambient temperature conditions. For a fixed cross-sectional area of condenser using the same type of blower, the air flow rate decreases with the increase of the number of tube rows because the system impedance increases. The refrigerant flow rate also decreases as the total cross-sectional area increases with increasing number of tubes per pass. Therefore, the improvement of overall COP due to the increment of heat transfer area is not as significant as expected. When the outside air wet bulb temperature is 24 ℃ and the heat transfer area increases from 8.9 to 14.8m2, the COP will increase from 4.7 to 4.87. By reducing the number of tubes, a cost reduced design results in a reduction of COP by less than 1%. Performance test results of the chiller having parallel dual-compressors at the outside air wet bulb of 24 ℃ show that the full-load SCOP (cooling capacity / total power) is 4.12, and the half-load SCOP is about 4.27. At half-load, the cooling power takes approximately 27.4% of the total system power consumption, in which 17.8% comes from the circulating water pump. For improving the half-load SCOP of the chiller, it is important to choose a proper circulating water pump and a blower which matches the characteristic impedance of the condenser.