碳氫冷媒冰箱除霜性能和點燃風險研究

Study on Performance and the Risk of hydro-carbon Refrigerant Combustion Inside Refrigerator during Defrosting

楊進丁(Chin-Ting Yang) ； 游家政(Cha-Chian Yu)

《燃燒季刊》 72期 (2011/02) Pp. 12-21

https://doi.org/10.30041/CQ.201102.0002

摘要

冰箱是現代家庭保存食物的重要設備，目前一般冰箱大部份使用的冷媒為HFC-134a，但是HFC-134a會造成溫室效應，如能使用自然冷媒HC-600a代替，不但性能、系統均不需大幅度修訂，且能達到環保減少溫室氣體排放。但冰箱蒸發器有結霜影響熱傳的問題必須除霜，可是電熱除霜時電熱器表面溫度有可能超過HC-600a燃點，導致意外發生，因此本研究將家用冰箱改成HC-600a冷媒。並且利用PLC（可程式控制器）執行duty-cycle加熱模式來限制電熱器(Heater)的溫度，使不會達到冷媒的燃點而燃燒。實驗結果發現，使用電熱器連續除霜時電熱器溫度仍會低於燃點460℃，但是當有外物掉落電熱器表面導致散熱不良時，實驗曾量測到570℃，也就是說如果自然冷媒外洩時在除霜過程仍有被點燃的危險。透過使用PLC控制電熱線1分鐘On/30秒off時，電熱器表面最高溫度會大幅降至122℃，且比連續除霜節能22%。當加熱模式改為1分鐘On/60秒off時，電熱器表面最高溫降至75℃，且比連續除霜節能28%。雖然加入duty cycle控制加熱模式除霜時間較長，但加熱器表面溫度遠低冷媒燃點，且皆有20%以上的節能，非常適合碳氫冷媒HC-600a系統採用。

關鍵字

碳氫冷媒 ； 除霜 ； 加熱模式

並列摘要

Refrigerators are the most important equipment to keep food for families. The refrigerants used in most of refrigerator are still HFC-134a. But the global warming effect of HFC-134a is much larger than carbon dioxide. By replacing of natural refrigerant HC-600a can reduce the green house gas emission. But for this kind of refrigerator, the defrosting process will be a serious problem. Because that the temperature of heater surface could excess the ignition temperature of refrigerant. In this study, a refrigerator with HC-600a refrigerant is used to test the defrosting effects with PLC controller. The PLC will control the heater to release heat in duty cycles. This control will limit the temperature of heater surface to prevent igniting of refrigerant when the leakage happened.
Experimental results show that , in normal process, the temperature for continuous heater defrosting still below ignition temperature 460℃.But if something covered on the surface of heater during defrosting process, the temperature could as high as 570℃. When the heater controlled by duty cycle 1 minute on/ 30 seconds off, the maximum heater temperature is 122℃, and the energy saving during defrosting process is 22%. If the duty cycle is changed to 1minute on/ 1 minute off, the temperature reduced to 75℃, and the energy saving is 28%. For the safety and environmental issues, we recommend the heater with duty cycle control is suitable for refrigerator with natural refrigerant HC-600a.

並列關鍵字

HC Refrigerant ； Defrosting ； Duty Cycle