噴霧型儲冰技術之液滴過冷結晶實驗研究與分析

An Experimental Study on the Crystallization of Supercooled Water Spray Droplets for Cold Storage Application

游凱欣(Kai-Hsin Yu)

指導教授 ： 蔡尤溪

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00291

摘要

台灣地區目前尚在運轉的儲冰系統，以全凍結式居多，顯然有其存在的原因，綜觀其主要的成功因素為穩定性高，系統足稱堪用，但不可諱言的，它存在著釋冰緩慢的缺點，容易造成不完全溶冰的問題，儲冰槽內若存有千年冰是一種浪費。
上述針對儲冰式空調的發展過程，以及現況的敘述做為本研究的背景說明，本研究將以創新的理念來發展一種新型儲冰空調技術，擬採空冷方式將液滴與空氣直接接觸做熱交換，使液滴於空氣中快速形成冰晶，並將冰晶做儲存，本技術開發的基本概念為善用液滴的微小粒徑(100μm~500μm)，在空中飄行期間，形成極大的液體表面積(As)，以及液滴飄行的速度(U)，有利於熱傳係數的提高，並且包含數值模型計算，於不同參數中之熱傳係數與質傳係數關係比較之。在這種環境下可使每粒液滴在瞬間(1.5sec~3sec)，即快速的凍結，它可以連續性的產出冰晶，並遠離結晶區，不會有靜態製冰因冰層加厚，致使熱傳效率遞減的問題。
根據實驗結果可得在3秒內獲得(100μm~500μm)結晶粒子，不同的參數變化，藉由實驗得知不同大小之粒徑利用理論模型驗證出其不同粒徑、不同熱傳面積導致不同之熱傳量，可得知粒徑越小熱傳係數較高，熱傳量亦較高，可利用此種實驗結果，運用於噴霧結晶上，選用較小粒徑之噴頭，可獲得最佳結晶效果。

關鍵字

儲冰 ； 液滴 ； 噴霧 ； 結晶

並列摘要

Presently most air-conditioning ice storage systems are of total freeze type due to its stable operation and simplicity. However there are problems in this system such that slow discharge and much un-melting ice in the storage tanks. Therefore a new concept of direct contact heat transfer of water droplets in cold air environment is studied experimentally. The objective is to achieve quick freezing and crystallization for ice storage. An experiment was setup for spraying water mist of diameters 100μm~500μm so that the large surface area of airborne droplets would allow rapid heat mass transfer.
In the research different models of heat mass transfer were applied for comparison of heat mass transfer coefficients. It was found in the experiments that the droplets freeze quickly (1.5 ~ 3 seconds) into crystals without the problems of thicker ice and reduction of heat mass transfer effects. Crystals in the range of 100μm~500μm was obtained in less than 3 seconds. Different parameters were used in the analysis for the size distribution of the water droplets. The results of higher heat transfer coefficients for smaller diameters agreed well with the theoretical models. The results of this research can be used in spray crystallization.

並列關鍵字

Ice Storage ； water droplets ； spray ； ice crystallization

參考文獻

北科技大學冷凍空調工程系碩士班，台北，2002。

科技大學冷凍空調工程系碩士班，台北，2001。

[1] Y. Teraoka, A. Satio and S. Okawa, “Study on anisotropy of growth rate of ice crystal in supercooled water”, International Journal of Refrigeration, vol. 27, 2004, 242-247.

predict dry snow metamorphism in generalized thermal conditions”, Cold Regions Science and Technology, vol. 37, 2003, pp. 213-226.

[4] C. H. Cheng and C.C. Shiu, “Frost formation and frost crystal growth on a cold plate in atmospheric air flow”, International Journal of Heat and Mass Transfer, vol. 45, 2002, pp. 4289-4303.