The impact of hot air temperature on drying energy efficiency is significant and can be illustrated through specific examples.
Firstly, we know that during the drying process, the main function of hot air is to transfer heat to the material, causing the surface moisture of the material to evaporate. When the temperature of hot air increases, it carries more heat, thereby increasing the amount of heat transferred to the material per unit time and accelerating the evaporation rate of moisture. This means that more moisture can be removed within the same drying time, thereby improving drying efficiency.
However, excessively high hot air temperatures are not always beneficial for improving drying energy efficiency. Because when the temperature is too high, on the one hand, it may cause surface coking or discoloration of the material, affecting product quality; On the other hand, excessively high temperatures can also result in more energy being wasted on heating the air rather than effectively drying the material. In this case, energy consumption will increase while energy efficiency will decrease.
Taking the combined drying of cotton fabric and absorbent paper samples as an example, the energy consumption actually decreases with the increase of microwave power. But in this process, the energy consumption of the microwave system slightly increases with the increase of power. This is because the moisture migration rate is very high, and the dielectric properties of the sample sharply decrease with the decrease of moisture content, resulting in a sharp decrease in its utilization efficiency of microwave energy. In this case, if the temperature of the hot air is also too high, not only will it not improve the drying efficiency, but it will also increase unnecessary energy consumption and reduce energy efficiency.
Another example is a compressed air dryer. During the drying process of compressed air, if the inlet temperature is too high, the water removal effect of the freeze dryer will be reduced. Because the freeze dryer liquefies gaseous water into liquid water through the principle of refrigerant heat exchange, and achieves the effect of compressed air drying by discharging it through a drainage device. Excessive temperature can lead to an increase in saturated moisture content, thereby reducing the drying effect. Similarly, for adsorption dryers, an increase in temperature will also increase the pressure load on the adsorbent, reducing its adsorption capacity.
In summary, the impact of hot air temperature on drying energy efficiency is complex. In practical operation, it is necessary to set and adjust the hot air temperature reasonably based on the properties of the material, the requirements of the drying process, and considerations of energy consumption, in order to achieve the best drying effect and energy efficiency.
