Improve the utilization rate of thermal energy for heating element on design of the whole appliance

- Apr 30, 2020-

After the electric heating tube converts electrical energy into heat energy, heat energy will be lost in the propagation path. The loss in the process of heat propagation becomes the main factor affecting the heat energy utilization rate of the electric heating tube. For different heating media, the proportions of heat transfer methods are different, and the loss factors are also different. According to the nature of the heating medium, electric heating tubes can be divided into three categories:
(I) For heating liquids (water, edible or non-edible oils, etc.);
(2) Use heated gas (still or flowing air, etc.);
f3) For heating other substances (inlaid in aluminum, alloys, etc.).
The main modes of heat propagation are radiation, convection and conduction. For example, an electric heating tube that uses water as a heating medium mainly depends on heat conduction during work (natural convection occurs in the liquid due to the density difference caused by the temperature gradient, and convection in the fluid will occur simultaneously with heat conduction) and electromagnetic radiation. It has good thermal conductivity with solids and good contact. The electric heating tube used to heat liquid can obtain higher energy utilization through heat conduction. The thermal conductivity of most liquids decreases with increasing temperature, but the thermal conductivity of water increases with increasing temperature, its value is O. From 17W / (m · K) to 0.7w, (m · K), it is a good heat conduction medium, so the electric heating tube using water as the heating medium has a very high heat utilization rate, and the surface load can be designed to be more heating Metals and gases are larger. The utilization rate of electromagnetic radiation heat conduction is far less than heat conduction. Different objects have different capabilities for absorbing infrared rays of heat rays, even if the same object has different capabilities for absorbing infrared rays of different wavelengths. The absorption efficiency of infrared rays depends on the matching of the wavelength and the absorption spectrum of the heated substance. When the radiation spectrum of the heating element (component) matches the absorption spectrum of the heated body (workpiece), the thermal efficiency is the highest, and the ray that cannot be absorbed will penetrate the material or be reflected back. Therefore, to apply infrared heating, it is necessary to select an appropriate infrared radiation source according to the type of heated object, so that its maximum radiation power is concentrated in the absorption wavelength range of the heated object to obtain
Heating effect. The absorption spectrum of water has a high peak for mid-infrared around 3000 nm. According to Wien's displacement law, the high temperature required to match such an absorption spectrum metal shell cannot be achieved in normal use, and the metal shell of the electric heating tube has strong reflection or absorption of infrared rays, so the radiation emitted by the heating wire is affected by its The barrier cannot be transferred into the medium water. At present, the space for energy efficiency improvement at the level of electric heating tube components is very limited. The energy efficiency of electric heating products mainly depends on the end product design of the whole machine. More factors than electric heating tube components are involved here, but based on the analysis of the structure and material of electric heating tubes , Is the basis of design that cannot be ignored for improvement.