The factors that affect the drying rate of ceramic water cups are: heat transfer rate, external diffusion rate, internal diffusion rate, etc.
1. Heat transfer rate
Speeding up the heat transfer rate increases the drying rate:
① Increase the temperature of the drying medium, such as increasing the temperature of the hot gas in the drying kiln, increasing the hot blast furnace, etc., but the surface temperature of the green body cannot be increased too fast to avoid cracking;
②Increase the heat transfer area: if changing from single-sided drying to double-sided drying, layer the blanks or reduce the number of layers of the blanks and increase the contact surface with the hot gas;
③ Improve the convective heat transfer coefficient.
2. External diffusion rate
When drying is in the constant velocity drying stage, the external diffusion resistance becomes the main contradiction affecting the entire drying rate. Therefore, reducing the external diffusion resistance and increasing the external diffusion rate has the greatest impact on shortening the entire drying cycle. The external diffusion resistance mainly occurs in the boundary layer, so it should be done:
①Increase the flow velocity of the medium, reduce the thickness of the boundary layer, etc., and improve the convective heat transfer coefficient. It can also improve the convective mass transfer coefficient, which is beneficial to improve the drying speed;
② Reduce the water vapor concentration of the medium, increase the mass transfer area, and also improve the drying speed.
3. Internal diffusion rate
The internal diffusion rate of water is a combination of wet and thermal diffusion. Wet diffusion is the movement of water in materials due to humidity gradients, and thermal diffusion is the movement of water caused by temperature gradients in physics. To increase the rate of internal diffusion:
①Make the direction of thermal diffusion and wet diffusion consistent, that is, try to make the center temperature of the material higher than the surface temperature, such as far-infrared heating, microwave heating;
②When the direction of thermal diffusion and wet diffusion are consistent, heat transfer is strengthened and the temperature gradient in the material is increased. When the two are opposite, the enhanced temperature gradient can increase the resistance of heat diffusion, but it can enhance heat transfer, increase the temperature of the material, and increase the temperature of the material. Diffusion is increased, so drying can be accelerated;
③Reduce the thickness of the green body, and change from single-sided drying to double-sided drying;
④Reduce the total pressure of the medium, and benefit the son to increase the wet diffusion coefficient, thereby increasing the wet diffusion rate;
⑤ Other factors such as the properties and shape of the green body.