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Solar Thermal Storage System
Phase Change Materials(PCMs)
|Issue Date: ||2009-08-11 01:19:16 (UTC+8)|
|Abstract: ||大自然藉由微生物的轉換及石化原料儲存了大量的太陽能，然而這些過程需要花很長的時間，而以目前使用石化原料的速率，將不到一個世紀，這些能源將使用殆盡。所以全世界的科學家正積極地尋求替代能源與再生能源，而他們另一重要課題便是與開發新能源同樣重要的開發儲存能源的裝置。也就是說將能源作有效而適當地的方式儲存起來，待需要時能夠快速安全而便利地供應出來。而儲存能源方式的研究，不但可以解決太陽能日夜供需不均的問題，更可改善能源使用效率與可靠度。因此，儲能的研究在現今能源短缺的時代，扮演著重要的角色。整合太陽能熱能之儲存系統，可將太陽能的利用將變得更具吸引力與可靠性。由於白天時太陽能之供給是充足的，但夜間時幾乎是零。因此，白天時太陽能必須被有效利用儲存以應付夜間時的需求。而相變化材料在溶解時所吸收之潛熱，由於具有高儲存密度及在儲存過程中能維持等溫的特性，可達成上述目的，因此引起普遍且廣泛的研究熱潮。藉由使用適當設計的太陽能收集器，太陽能可快速的轉換成熱能。上述這個技術最被廣泛使用的例子為家庭式太陽能熱水器，目前這個技術提供了全天均可隨時使用到熱水，而這是由於水本身可視為吸收太陽能的儲存材料。新式的能量儲存系統係使用相變化材料(PCM)來儲存太陽能。PCM 係以固、液相之間的轉換來儲存能源。並且，作為儲存太陽能之PCM 的熔點應在30-80℃之範圍才適用。目前在台灣現有的食品烘焙機，多使用天然氣及電器加熱，很少使用太陽能。本計畫將開發24 小時的烘焙機，以太陽能為主，電能為輔。使用相變化材料(PCM)在日照時除了提供固定溫度的熱空氣，更可將多餘的太陽能儲存於儲熱材料，當夜間沒有日照時也可持續提供熱空氣，如此有效節省能源及增加食品加工的品質。本計畫，將參考Pangavhane於2002所發表的以自然對流方式及集熱板與烘焙箱分開裝置為主，改良其集熱板為不同熔點溫度的石臘管，輔以電熱的設計，可達到24恆溫的空氣，同時可兼顧食品加工品質及節約能源；第一年與廠商共同開發食品烘焙機的機台設計與性能測試(含太陽能集熱板的性能測試)，PCM的熱傳特性測試，第二年將該機台商品化並新增系統分析的軟體程式，針對該烘焙機針對不同的需要可做模擬分析，包括熱交換器的熱傳係數計算，以及各項系統參數(諸如光照條件、儲能材料溫度、熱空氣的溫度及流量大小等)的動態分析。將系統設計模組化，輔助廠商舊產品的改良及新產品的開發。
Nature has been storing vast amounts of solar energy in the form of bio-mass and petroleum products. However, this process takes a very long time. If the present rate of exploitation of readily available store energy in fossil fuels continues, then the fossil fuels may be depleted completely in a century or so. The scientists all over the world are in search of new and renewable energy sources. One of the options is to develop energy storage devices, which are as important as developing new sources of energy. The storage of energy in suitable forms, which can conventionally be converted into the required form, is a present day challenge to the technologists. Energy storage not only reduces the mismatch between energy supply and demand but also improves the performance and reliability of energy systems and plays an important role in conserving the energy. The utilization of solar energy can be more attractive and reliable if associated with a heat storage system. Since the solar energy supply is variable in daytime and zero at night, considerable amount of solar energy should be stored during the daytime to meet the demands at night. For this purpose, latent heat of fusion of Phase Change Material (PCM) is of great interest on account of high storage density and its isothermal nature of the storage process. Solar energy can be readily converted to heat energy with the use of suitably designed solar collectors. The most widely used application of this technology is the domestic solar water heater. Essentially, this provides hot water that can be used at any time. This is because the water itself acts as its own thermal store for the absorbed solar energy. The new energy storage system uses phase change materials (PCMs) for the storage of heat derived from solar energy. PCMs work by storing energy in changing phase from solid to liquid i.e. melting. The temperature of PCMs should be in the range of 40-80 ℃ for the storage of solar energy. The minimum quantity for which domestic solar water heaters are available in the market is 100 liters and the cost of the system is about NTD. 35,000. But these solar water heaters can not maintain the temperature of the water at the desired temperature level when solar radiation not available. So by the use of the PCMs, solar energy can be store in the form of thermal energy, which can be utilize during off peak hours. In the present time, most of the dryer devices use the nature gas or electric power as the energy sources. The solar energy is rarely developed for this kind of usage. In this project, we will develop a 24-hours dryer device which energy comes from solar energy, and partly from electric power.We use PCMs to store the energy and maintain the heated air temperature, day and night. It would not only saved the energy, but also increase the fruit heating quality. According the paper of Pangavhane published in Energy journal 2002, he used the natural convection and individual solar collector and heating box as a solar dryer device, we modify the collector by adding some paraffin wax with different melting temperatures in the tubes. We design the device with changeable temperatures by using electric heated. The dryer performances would include the heat transfers rate between the tubes and air, the relationship of the temperature difference and air flow rate. In the next year project, we plan to develop the software program to be a package to assist the manufacturer design the specifications for different kinds of dryer processes.
|Appears in Collections:||[機械工程系所] 研究計畫|
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