Calculation Of Temperature In Chemical Reaction Solution Radiated By Microwave Using FDTD And Leapfrog Technique

M.S. Candidate: Zhen Lin Advisor: Prof. Kama Huang In the research of microwave chemistry, the asymmetric distribution of electromagnetic fields in test tube makes it difficult to control the temperature inside the reacting solution, which will directly influence the process of the chemical reaction that heated by microwaves. So the simulation and control of the temperature in the chemical reacting solution becomes very important.The finite-difference time-domain (FDTD) method is wildly used in various areas of electromagnetic engineering. As the several minutes' reacting time is concerned, it's impossible to simulate the reaction process directly by FDTD. Because of the quite different velocity between microwave's vibration and chemical reaction, it would take a long time to calculate the problem in current personal computer. The traditional method to shorten the calculating time was to add a parameter in the thermal conduction function, however, which would reduce the calculation accuracy.In this paper, a new leapfrog technique based on the finite-difference time-domain (FDTD) method is used to simulate the interaction between microwaves and reacting solution in test tube placed in TEM cell. In this way, the long reacting time was divided into n equal parts. In each part, the parameters and the temperature of solution were set to constants. It's only necessary to calculate the electromagnetic fields in several periods by FDTD until the peak value of electric field not change. With the usage of the simplified calculating mode, the simulating time will reduce greatly while the calculating accuracy is guaranteed.The saponification reaction solution heated by microwaves in test tube placed in TEM cell was chosen as the experiment. The reaction-calculating mode was constructed. Maxwell's equations, thermal conduction equation and chemical reaction equation were solved together by FDTD and leapfrog technique. The temperature and its variety with reacting time in the test tube were calculated. Good agreement can be seen between the measured and calculated results.