可抑制表面自然對流之奈米碳管叢表面隔熱元件

Abstract

自奈米碳管問世以來，一直是備受矚目的研究對象，其優秀的性質更使奈米碳管在許多領域中被認為具有廣泛應用的潛力，奈米碳管因為有著高熱導率的特性，使得許多研究嘗試將奈米碳管作為散熱或熱交換的媒介，而這些研究也獲得了極大的成功，但同時奈米碳管也因為有著相當特殊的幾何特性，讓它在儲能、隔熱上也有發展的潛力。 本研究以實驗法探討奈米碳管叢在材料表面上的隔熱效果，藉由量測奈米碳管叢表面散熱情形，量化奈米碳管叢對自然對流氣流的影響，探討奈米碳管的隔熱能力與特性，並研究其特殊性質之成因，同時也藉由改變碳管的種類與幾何性質，實驗找出具有最佳隔熱效果的奈米碳管叢參數。 本研究發現奈米碳管叢在材料表面時，可以減少將近60%之自然對流，使對流熱交換率減低到只有原先的43%，研究也發現奈米碳管叢之隔熱能力會隨其高度上升而增加，高度高於12μm的單層奈米碳管叢具有最佳的隔熱效果，其中無填鐵奈米碳管叢的隔熱能力大於填鐵奈米碳管叢，而多層奈米碳管叢則因為其特性而不具有隔熱效果，奈米碳管叢的隔熱能力會隨著物體與環境溫度差增加而上升，當溫差大於70°C時，奈米碳管叢具有最佳隔熱效果。

Carbon nanotube is a remarkable research topic since it has been discovered. It is believed that carbon nanotube has the potential to be applied in many different fields due to its great property. Carbon nanotube has high thermal conductivity, making it an ideal heat transfer medium for various applications. Furthermore, the special geometry of carbon nanotube also makes it has the potential to become a heat insulation device. In this study, the capability of heat insulation of carbon nanotube is discovered by experimental method. By studying the heat transfer coefficient above the surface of carbon nanotube, the affect between carbon nanotube and natural convection will be exposed. The capability of heat insulation of different kinds of carbon nanotube is compared in the study. Carbon nanotube can suppress 60% of natural convection of the surface. The heat transfer coefficient is reduced to 43% of the original value. The capability of heat insulation will increase with the height of carbon nanotube. The single layer carbon nanotube with the height which is more than 12μm has the best capability of heat insulation. The capability of heat insulation of non iron-filled carbon nanotube is better than iron-filled carbon nanotube. Multiple layers carbon nanotube do not have the capability of heat insulation. This study also shows that the capability of heat insulation of carbon nanotube will also increase with the temperature difference between the surface and the environment. When the temperature difference between the surface and the environment is more than 70°C, carbon nanotube will have the best capability of heat insulation.