噴淋式蒸發器熱傳效率之模擬

The Simulation of Spray Type Evaporator Performance

鄭全宏(Chuan-Hung Cheng)

指導教授 ： 馬小康

國立臺灣大學/工學院/機械工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00398

摘要

本文彙整文獻中有關噴淋式蒸發器之熱傳理論及兩相流疊加式模型，並與使用冷媒為工作液體之噴淋式蒸發實驗數據做比較，發現文獻中之噴淋式蒸發模型忽略熱通量或核沸騰之影響，因此無法有效預測高熱通量之實驗數據；而兩相流之疊加式模型直接套用於噴淋式蒸發將高估其核沸騰項。因此提出以疊加式模型為基礎之改良模型，以噴淋實驗結果所修正之沸騰抑制係數，代入疊加式模型中，可有效預測光滑管噴淋式蒸發之熱傳係數，其誤差約在 ±25﹪以內。接著，依照同樣的步驟，計算出在增強管(Tu-B)時以噴淋實驗結果所修正之沸騰抑制係數，將噴淋式蒸發器在預測增強表面(Tu-B)之管外熱傳性能時，誤差不超過 ±30% 。此外，本文並提出計算潤滑油影響因素之經驗公式，計算結果與實驗值誤差為 ±30% 以內。
本文並開發出能準確預測出噴淋式蒸發器與滿溢式蒸發器的電腦輔助設計軟體，在演算上藉由單元式e-NTU method將蒸發器內分為多區塊分別計算其熱傳性能，其優點為可分段算出每區塊為飽和或過熱不同情況時之熱傳性能，較以往使用管集平均法計算熱傳性能更加準確。此外，由程式模擬結果可得不論為熱傳性能或水側壓力降，噴淋式蒸發器皆比滿溢式蒸發器佳，其與實驗結果吻合。

關鍵字

熱傳 ； 模型 ； 蒸發 ； 噴淋 ； 滴淋

並列摘要

The effect of nucleate boiling has been ignored in the predictive models and correlations for falling film evaporation in the previous studies. A new predictive model based on the superposition model in two-phase convection was developed to account for the nucleate boiling effect in falling film evaporation. The nucleate boiling suppression factor in the superposition model was found to different from that in the flooded evaporator or flow in pipes. A new suppression factor correlation with the plain tube is proposed and curve fitted from the experimental data of falling film evaporation using R-11, R-123, R-22, R-141b and R-134a from three different sources. The new model predicts the experimental data with the plain tube within ±25 %. Similarly, another suppression factor correlation was obtained from the experimental data of the Tu-B surfaces. This new model predicts the experimental data with the Tu-B surfaces within ±30 %. Besides, the present study developed a correlation to account for the lubricant effects on falling film evaporation. The lubricant effect correlation predicts the experimental data within ±30 %.
This study also developed a computer code, which used the elemental NTU-ε model to predict the heat transfer and pressure drop of flooded type and spray type evaporators.The results of prediction are in good agreement with the available experimental data. Parametric studies performed by the computer code reveals that the spray type evaporator has better heat transfer performance and smaller pressure drop than the flooded type.

並列關鍵字

Evaporation ； Falling film ； Spray ； Model

參考文獻

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