| The flexible thin-film heater with ohmic heating has many advantages such as high heat generation efficiency, easy heat-removing, high surface power density and less corrosion, etc. By adhering on insulating substrates, the flexible thin-film heater can be applied to various heating devices. In recent years, the flexible thin-film heater has been widely used for architecture, industry, agriculture, military, household articles and so on, mainly for heating and deicing. In this paper, the flexible thin-film heater has been designed and studied, including its simulation of temperature field distribution, preparation of insulating thermal conductive films and thermal insulative films, along with the design and testing of its control system.The temperature field distribution simulation of the heater is made by means of software ANSYS. According to aerodynamics principles, as well as the simulation result made under special environment and speed, the layout of electro-heat alloys was designed. Besides, dry lamination and gravure printing technology were adopted to fabricate the metal film heater.The paper also discussed preparation of PVDF/AlN compound films which were treated by means of blended solution method, using a thermometer to test their thermal conductivity. The results indicate that, the thinner the thickness of PVDF/AlN compound films, and the higher the AlN content, the better the electronic conduction of compound films. The minimum thickness of compound films is 0.10mm and the highest AlN content is 60%. After this, preparation of PI films and SiO2/PI compound films were fabricated by tape casting method, and a pulling machine was used to test extensibility of the films, a thermometer to test thermal conductivity. The results show that the extensibility and thermal conductivity of PI films dopped SiO2 are better than those undoped. The extensibility of compound films has been optimized by increasing SiO2 content. When the mass ratio of SiO2 arrives at 15%, the tensile length of compound film achieves 0.95 and the tolerance to tension reaches 82 N. As soon as SiO2 content exceeds 15%,the extensibility of films becomes worse. The test of thermal conductivity makes it clear that heat transfer efficiency is up to the highest when SiO2 content is 15% and film thickness is 0.05mm. Further more, porous PI films were also made by corrosion using 30% hydrofluoric acid, PI films plating aluminum by vacuum vapor plating technology. Thermal conduction analysis was also done, applying the method mentioned above. It shows that the thermal insulation effect of porous PI films is not satisfying, however, the PI films plating aluminum with thickness 10um under could reduce the heater's surface temperature from 210℃to 170℃. In short, PI films and SiO2/PI compound films can be used as thermal conductive ones, but PVDF/AlN compound films are not suitable, for they can only withstand 140℃. Besides, the thermal insulation effect of porous PI films for micron thickness is moderate. Compared with it, PI films plating aluminum achieve better thermal insulation effect.Besides, generation of pulses controlling heating rate was programmed by C language in SCM 89s52. To change electrify time, we could only adjust the width of LOW/HIGH level through programming on-line. The testing result shows that the voltage across the thin film heater is 205.2 V and the width of LOW/HIGH level of pulses is 3:200.When the heater is placed in the air at 25℃or so, its power density reaches 7.02 W/cm2 with surface temperature of 54.0℃~68.2℃, which can meet the requirements of the theme.
|
PDF Full Text Request