Wang Zhenying, Orejon Daniel, Sefiane Khellil, Takata Yasuyuki
International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Micromachines (Basel). 2020 Feb 13;11(2):193. doi: 10.3390/mi11020193.
In all kinds of liquid desiccant dehumidification systems, the temperature increase of the desiccant solution due to the effect of absorptive heating is one of the main reasons of performance deterioration. In this study, we look into the thermal effects during vapor absorption into single hygroscopic liquid desiccant droplets. Specifically, the effect of substrate conductivity on the transient heat and mass transfer process is analyzed in detail. The relative strength of the thermal effect and the solutal effect on the rate of vapor absorption is investigated and compared to the thermal effect by evaporative cooling taking place in pure water droplets. In the case of liquid desiccants, results indicate that the high thermal conductivity of copper substrates ensures more efficient heat removal, and the temperature at the droplet surface decreases more rapidly than that on Polytetrafluoroethylene (PTFE) substrates. As a result, the initial rate of vapor absorption on copper substrates slightly outweighs that on PTFE substrates. Further analysis by decomposing the vapor pressure difference indicates that the variation of vapor pressure caused by the temperature change during vapor absorption is much weaker than that induced by the concentration change. The conclusions demonstrate that a simplified isothermal model can be applied to capture the main mechanisms during vapor absorption into hygroscopic droplets even though it is evidenced to be unreliable for droplet evaporation.
在各类液体除湿系统中，由于吸收热效应导致除湿溶液温度升高是性能恶化的主要原因之一。在本研究中，我们研究了水蒸气吸收到单个吸湿液体除湿剂液滴过程中的热效应。具体而言，详细分析了基底电导率对瞬态传热传质过程的影响。研究了热效应和溶质效应在水蒸气吸收速率上的相对强度，并与纯水滴中发生的蒸发冷却热效应进行了比较。对于液体除湿剂，结果表明铜基底的高导热性确保了更有效的散热，液滴表面温度比聚四氟乙烯（PTFE）基底上的温度下降得更快。因此，铜基底上水蒸气的初始吸收速率略高于PTFE基底上的吸收速率。通过分解蒸气压差的进一步分析表明，水蒸气吸收过程中温度变化引起的蒸气压变化远小于浓度变化引起的蒸气压变化。结论表明，一个简化的等温模型可用于捕捉水蒸气吸收到吸湿液滴过程中的主要机制，尽管已证明该模型对液滴蒸发不可靠。
