交錯層狀磁致冷再生器之數值分析

Numerical Analysis of Active Magnetic Regenerators with Staggered Laminated Plates

張哲維(Che-Wei Chang)

指導教授 ： 許文震

國立清華大學/工學院/動力機械工程學系/碩士(2020年)

摘要

磁致冷卻利用磁熱材料的磁熱效應，取代傳統冷媒壓縮與膨脹過程，降低冷卻系統的成本，且無冷媒使用。以熱流觀點而言，磁致冷再生器存在兩個技術關鍵：(1)固態磁熱材料與流體間熱傳過程中的熱傳效率不佳，操作頻率無法增大；(2)冷熱端軸向之熱傳損失，熱量會經由熱傳導方式由熱端傳向冷端，降低磁致冷再生器的性能。
不同於以往之平板設計，本研究將磁熱材料平板交錯置於冷卻系統中，奇數與偶數層斷點位置交錯。對相近的磁熱材料段而言，水平間中斷，相鄰兩層間差排。如此能增加熱端與冷端間磁熱材料熱傳導之熱阻，並增加徑向流，打破工作流體之邊界層，加強熱傳，以提升其操作頻率，進而增加磁致冷系統效能。
本研究藉由商業軟體數值模擬，建立8種長為80 mm 之二維模型，分析新結構之磁致冷系統在不同操作狀態的表現。於磁場變化0-1特斯拉、冷熱端溫度283 - 303 K、循環週期0.6秒、利用因數0.4時， “4 right holes, 0.5 mm”較原模型減少磁熱材料使用2.5%與壓降減少4%，且製冷功率由62.48升至69.10瓦，散熱需求功率由129.13降至113.42瓦。本研究證實，透過交錯層狀磁致冷再生器之設計，能增加磁致冷裝置之效能。並透過溫度場分析，推論近熱端處仍可局部減少磁熱材料的使用。

關鍵字

磁致冷卻 ； 磁熱材料 ； 磁致冷再生器

並列摘要

Magnetic refrigeration system, which functions without refrigerant consumption and compressor employment, is an ecofriendly novel refrigeration technology.
However, two heat transfer problems restrict the efficiency of active magnetic regenerator (AMR). (a) Operation frequency could not be enhanced due to deficient heat flux between magnetocaloric material (MCM) and working fluid. (b) The heat conduction from hot side to cold one hinders the refrigeration capacity.
The novel design which could increase the thermal resistance between the room temperature side and chilling temperature one and enhance the heat flux between two phases, was made. For a rectangular AMR plate, several rectangular staggered breaking points were employed instead of complete laminated plates. Breaking points of layers restricted the heat conduction effect from hot side to cold one. Furthermore, they brought secondary flow which broke boundary layers, and enhanced the heat convection effect.
The commercial software was employed and 8 two-dimensional models with a length of 80 mm were created to analyze the performance of new AMRs at different operating parameters.
Compared to the original model, "4 right holes, 0.5 mm" model reduces the usage of MCM by 2.5%, decreases the pressure drop of 4%, increases the cooling power from 62.48 to 69.10 watts, and reduces the heating power from 129.13 to 113.42 watts at the magnetic field changes of 0-1 Tesla, the temperature of the hot to cold ends of 283 - 303 K, the operation period of 0.6 seconds, and the utilization factor of about 0.4.
This study shows that the performance of magnetic refrigeration devices can be intensified by active magnetic regenerators (AMRs) with staggered laminated plates, and it is inferred by temperature distribution that the MCM usage could be decreased locally.

並列關鍵字

Magnetic refrigeration ； Magnetocaloric material (MCM) ； Active magnetic regenerator (AMR)

參考文獻

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