太阳能干燥相变储热水箱的放热性能

Heat release performance of heat storage water tank with phase-change material in solar drying system

为降低传统干燥能耗,强化太阳能干燥用储热水箱的储放热能力,在普通储热水箱中添加了硬脂酸/膨胀石墨相变储热材料,研究了放热温差、储热单元体积对装置放热性能的影响。研究结果表明:相变储热水箱放热时间、放热量随着放热温差和储热水箱中储热单元体积的增加均有所提升,储热单元的添加对储热水箱的放热效果影响更为显著。放热效率则随着放热温差的增大而降低,随着储热水箱中储热单元体积的增加而显著提升;储热水箱中储热单元体积为35%时,相变储热水箱的放热时间比普通储热水箱最多提升了1.26倍,放热温度最大可提高8.7℃,热效率最多可提高22.56%。

Drying is an essential process for a large number of industrial and agricultural products. In order to reduce energy consumption of traditional drying, improve its utilization efficiency and strengthen the capacity of heat storage water tank for solar drying, the stearic acid/expanded graphite composite phase-change material(PCM) with melting point of 52.74 ℃ and latent heat of 169.90 J/g was added into the conventional heat storage water tank in this paper. The schematic structure of the solar drying system mainly consisted of solar collector, drying oven, heat storage water tank and phase-change thermal energy storage units. The effect of heat release temperature difference and heat storage unit volume on the heat release performance of the device was studied under the same heat release conditions. The total volume of the PCM containers in the heat storage water tank was 15%, 25% and 35%, respectively. The heat storage water tank was heated to 60, 65 and 75 by using solar ℃collector in heat storage process. Then the heat storage water tank was used to provide heat for the drying oven, and the heat release process was finished when the temperature of drying oven was 40 ℃. The results showed that the addition of heat storage unit had a remarkable effect on the water temperature of the storage tank, provided a lot of heat in the latent heat release stage, and slowed down the rate of the decreasing in water temperature. In addition, the heat discharge time increased with the increase of temperature difference and heat storage unit volume, and heat storage unit volume affected more. When the heat storage unit volume in the heat storage water tank was 35%, the heat discharge time of latent heat was 1.26 times more than that of conventional heat storage water tank, and within the same heat discharge time, the heating temperature of the PCM heat storage water tank could be increased by 7.7, 8.2 and 8.7 ℃, respectively in the initial exothermic temperature of 60, 65 and 70 ℃ compared to that of conventional water tank. The actual heat output of the conventional heat storage water tank increased with the increase of temperature difference, which was more significant than that of PCM heat storage water tank. Moreover, the heat efficiency of PCM heat storage water tank was reduced with the rise of temperature difference while that of conventional heat storage water tank was increased in the solar drying system. The heat efficiency of PCM heat storage water tank was increased with the increase of heat storage unit volume, and it could be increased by 22.56% at most when the heat storage unit volume in the heat storage water tank was 35%. The thermal performance of the PCM incorporation into heat storage tank is significantly enhanced in relation to energy capacity, operation time under a temperature range, which is acceptable for low-temperature solar thermal application.