聚苯乙烯真空保溫片熱傳機制之影響研究

Abstract

本研究係針對PE添加物在PS發泡過程，對真空保溫片芯材之結構與熱傳機制的效應進行探討。總計製作42組樣品，用來測試分析多孔發泡材結構與PE添加物對真空保溫片性能的影響。這些樣品係使用自行研發的批次式設備來製作，並可藉製程溫度與壓力來調整真空保溫片之芯材的發泡結構。本研究提出數個參數與定義芯材之發泡結構，如破孔率、平均胞體直徑、與固體容積率。本研究結果發現，在特定的固體容積率條件下，平均胞體直徑與破孔率有一線性相依的關係，同時存在著一最佳的平均胞體直徑可使總熱傳降低至最低。此外，輻射熱傳係數及其它熱傳係數的特徵，也可使用這些參數來描述與推測。增加2%的PE添加物是可有效地來改變胞體結構與降低熱傳，而增加PE添加物至5%時，對進一步改善性能效果的助益不大。在本研究中，獲得之最佳的熱傳導係數是4.4( )，是已發表真空保溫材性能之文獻中最好的。本研究中固體熱傳占真空保溫材之總熱傳的80%以上，主要是受固體容積率的影響。故高性能真空保溫材的改善原則，是儘可能的降低固體容積率以降低固體熱傳效應，然後維持平均胞體直徑在一最佳值。但應注意固體熱傳與輻射熱傳之消長，若固體容積率的降低方式是降低固體材料的質量時，因材料支撐大氣壓力的結構應力限制，胞體直徑會變小、或支架變細、或微胞壁膜變薄，這些變化也有可能增加輻射熱傳。

The effects of adding Polythene (PE) in (polystyrene) PS foaming material on the cell structure and the heat transfer of vacuum insulation panels (VIPs) are examined in this study. Totally 42 samples were fabricated and analyzed to examine the influence of porous foam structure and PE additive on VIP performance. The samples were produced by in-house equipment that was able to vary the foam structure by modulating the process temperature and pressure. Several parameters were proposed to describe the foam structure, namely, the broken cell ratio, the average cell size and the solid volume fraction. Under a specific solid volume fraction, the average cell size and the broken cell ratio are linearly correlated, and it was found that an optimum cell size exists such that the total heat transport is minimal. Furthermore, these parameters are also suitable for characterizing heat transfer coefficients of thermal radiation and other heat transports. Adding 2% PE was effective in altering the cell structure and reducing the heat transfer, while adding 5% PE did not improve the performance further. The lowest thermal conductivity found in this study is 4.4 , which is among the best published performances of VIP. The magnitude of solid conduction is mainly decided by the solid volume fraction and accounts for more than 80% of the total heat transport in VIPs. The rule of thumb of reducing VIPs’ heat transport is to decrease the solid volume fraction as much as possible, while maintaining an optimal average cell size. Nevertheless, attention should be paid to balancing solid conduction and thermal radiation. The reduction of solid volume fraction is normally accompanied by the decrease of solid mass, leading to weaker structural support such that smaller cell size is required to maintain structure integrity. The decrease of solid mass is therefore accompanied by slimmer struts and thinner membrane, which may largely enhance thermal radiation.