Microwave heating of a coating on a temperature-sensitive substrate

Abstract

Microwave heating has been considered for the heating of a coating in contact with a temperature-sensitive substrate. A methodology was developed to conduct a microwave heating feasibility study for a candidate system. The study consisted of dielectric property determination, development of heat transfer models to determine the heat generation rates necessary to achieve a desired temperature distribution, calculation of the required electric field strength given the dielectric properties and heat generation rates, and examination of whether the microwave heating could be performed with available equipment. Sol-gel processing of a 1Microwave heating has been considered for the heating of a coating in contact with a temperature-sensitive substrate. A methodology was developed to conduct a microwave heating feasibility study for a candidate system. The study consisted of dielectric property determination, development of heat transfer models to determine the heat generation rates necessary to achieve a desired temperature distribution, calculation of the required electric field strength given the dielectric properties and heat generation rates, and examination of whether the microwave heating could be performed with available equipment. Sol-gel processing of a 1µm-thick boehmite coating on a non-woven polypropylene substrate was chosen as the candidate system. It was desired to selectively heat the boehmite to 2500 C without damaging the polypropylene, which degrades at 1500 C. Dielectric measurements indicated that the boehmite could be heated to 2500 C using microwave energy. Microwave heating of the system was then modeled using three techniques: an approximate analytical solution based on Composite Green's Functions, a finite difference solution, and an approximate lumped capacitance solution. It was determined that the heat generation rates necessary to produce the desired temperature distribution would require field strengths beyond practical limitations for the specific boehmite-polypropylene system considered. -thick boehmite coating on a non-woven polypropylene substrate was chosen as the candidate system. It was desired to selectively heat the boehmite to 2500 C without damaging the polypropylene, which degrades at 1500 C. Dielectric measurements indicated that the boehmite could be heated to 2500 C using microwave energy. Microwave heating of the system was then modeled using three techniques: an approximate analytical solution based on Composite Green's Functions, a finite difference solution, and an approximate lumped capacitance solution. It was determined that the heat generation rates necessary to produce the desired temperature distribution would require field strengths beyond practical limitations for the specific boehmite-polypropylene system considered.