相变材料（PCM）冷却背心已被证明可以降低人类在不同环境条件下进行多种活动的热应力。然而，随着环境变热和活动持续时间延长，冷却背心的性能会恶化。这就需要使用熔化温度（MT）相对较低的PCM包来产生显著的冷却效果。另一方面，会出现两个问题，第一个问题是增加PCM体重，增加人体新陈代谢。第二，在活动开始时穿上背心可能会感到太冷而不适，因为此时不需要明显降温。例如，建议将活动持续时间（50分钟）划分为两次时间相同的比赛。在第一回合中，使用一件特定PCM熔化温度为28°C的背心，在第二回合中，使用另一件较低熔化温度为21°C的背心。 因此，应用所提议的策略将在初始预热阶段和第二阶段提供所需的冷却效果，在第二阶段需要更强的冷却效果，同时在每回合中仅携带所需的数据包重量。为了检验所提出的策略，对六名男性参与者进行了实验，他们在高温条件下（40°C和40%相对湿度）进行了50分钟的中等强度活动。测试四个条件以评估拟定策略:1）不穿背心，2）在整个50分钟（MT-28）内穿一件装满28°C数据包的背心，3）在整个50分钟内（MT-21）穿一件装满21°C数据包的背心，4）在第一轮25分钟比赛中穿一件装满28°C数据包的背心，然后在第二轮25分钟比赛（MT-21）中穿一件装满21°C数据包的背心- 28-21). 研究结果显示，在MT-28-21中，无背心情况下，局部皮肤温度、热舒适性和躯干热感觉进一步显著改善约4.5°C，尤其是在第二回合中，参与者可能已经开始达到或已经达到MT-21和MT-28中的不适感和热感觉水平。研究结果还表明，仅在MT-21病例中，无背心病例的出汗率显著降低约18%。关键词:相变材料；热环境、人体热反应；热舒适和感觉。引用:2018年年度会议，德克萨斯州休斯顿，会议论文

Phase change material (PCM) cooling vests have been shown to reduce heat strain of humans performing many types of activities for a certain duration at different ambient conditions. However, as the environment gets hotter and for prolonged activity durations, the cooling vest performance deteriorates. This necessitates the use of PCM packets with a relatively low melting temperature (MT) to have a significant cooling effect. On the other hand, two issues will arise, which first entail additional PCM weight that increases the human metabolism. Second, discomfort due to a too cold sensation upon wearing the vest at the start of activity might be present, since significant cooling at that time is unnecessary. It is proposed to divide the activity duration, of 50 minutes, for example, into two equally-timed bouts. In the first bout, a vest with a certain PCM melting temperature of 28 °C, for example, is used and in the second bout, another vest with packets of a lower melting temperature of 21 °C, for example, is used. Thus, applying the proposed strategy would provide the needed cooling effect in the initial warming up stage and in the second stage where a stronger cooling effect is desired, while only carrying the necessary weight of the packets in each bout. In order to examine the proposed strategy, experiments on six male participants performing cycling for 50 minutes at moderate activity in hot conditions (40 °C and 40 % relative humidity) are performed. Four conditions are tested to assess the proposed strategy: 1) no vest is worn, 2) one vest filled with 28 °C packets is worn for the whole 50-min period (MT-28), 3) one vest filled with 21 °C packets is worn for the whole 50-min period (MT-21) and 4) a vest filled with 28 °C packets is worn for the first 25-min bout followed by wearing a second vest filled with 21 °C packets for the second 25-min bout (MT-28-21). The findings of the study showed further significant improvements in local skin temperatures by about 4.5 °C from no vest case, thermal comfort and torso thermal sensation in MT-28-21, especially in the second bout where the participants would have started to reach or have reached uncomfortable and hot sensation levels as in cases MT-21 and MT-28. The findings also showed significant reduction in sweat rate from no vest case in case MT-21 only, by about 18%.Keywords: Phase change material; hot environment, human thermal responses; thermal comfort and sensation.