本文利用熱阻觀念，做簡單的物理分析，推導出ㄧ維球形相變化儲熱 材料熱傳方程式，並配合實驗驗證方程式的可靠度。在熱阻分析時， 假令固態相變化材料利用潛熱所吸收之熱量，等於外界工作流體所帶 進來的熱，並考慮「工作流體─球囊外壁」、「球囊外壁─球囊內壁」 以及「球囊內壁─液態相變化材料」三種熱阻，並以串聯方式進行系 統分析。其中忽略球囊殼的熱容效應，且液態相變化材料傳熱方式分 成純熱傳導與考慮熱對流兩種。 由結果發現影響儲熱時間之參數有球囊設計、相變化材料性質參 數以及工作流體性質參數。經由參數分析發現，工作流體性質中，隨 著工作流體的Nu 增加，總儲熱時間就會下降。球囊設計參數中，藉 由增大球殼熱傳導係數來縮小球殼與液態相變材料熱傳導係數之比值，能夠縮短系統儲熱時間。 並且要預估總融化時間，可以藉由液態相變化材料熱阻考慮熱對 流方程式來估算。若要知道確切融化位置，當融化位置係數>0.37 時， 使用液態相變化材料熱阻只考慮熱傳導方程式；當融化位置係數 <0.37 時，使用液態相變化材料熱阻考慮熱對流方程式。 This study analyzes one-dimensional spherical phase change material (PCM) heat transfer formula which derives from the concept of thermal resistance. The viability of this formula is validated by experimental data. In the analysis of thermal resistance, the heat which absorb by PCM is assumed equal to the heat which transfer from the heat transfer fluid (HTF). In the system, there are three types of thermal resistance in series connection, including HTF to capsule outside surface, capsule outside surface to inside surface, and capsule inside surface to PCM. Due to the specific heat of capsule is very small, the sensible heat of capsule is neglected. The heat transfer within liquid PCM is considered as two different types – only conduction and only convection. As the results, the parameters which affect the melting time include size and thickness of capsule, and thermal physical properties of capsule, PCM, and HTF. By the parameter analysis, the melting time is reduced as the Nusselt number of HTF is increasing, and the thermal conductivity of capsule is enhanced. To predict the melting time, it has good agreement by using the heat transfer formula with considering convection. To predict the melting surface location, when the melting location coefficient is larger than 0.37, using the heat transfer formula without considering convection has good agreement. But when the melting location coefficient is smaller than 0.37, using the heat transfer formula with considering convection has good agreement.
