内燃机、汽轮机等热机具有两个共同的特点:一,它们均利用气体作为工质膨胀作功;二,这些工质只能在高温下膨胀作功。若要使用低温热源,特别是温度在100℃以下的热源来直接作功,这个问题,目前尚处在研究阶段。但自然界中存在着大量的低温热源,例如温泉水、太阳热以及工厂中的低温热水,如何开发利用,是很重要的节能课题。有人设想利用低沸点、易气化的物质,例如乙醚、氟利昂等,在低温时蒸发气化,像蒸气那样推动活塞作功,但这些方案均在实践中失败了。近年来,由于发现了一种新型材料-记忆 Internal combustion engines, steam turbines and other heat engines have two common characteristics: First, they both use gas as working fluid to expand work; Second, these working fluids can only work at high temperatures. The problem of using low-temperature heat sources, especially those with temperatures below 100 ° C, is still at the research stage. However, there are a lot of low-temperature heat sources in nature, such as hot spring water, solar heat and low-temperature hot water in factories. How to develop and utilize them is a very important energy saving issue. Some people assume that the use of low boiling point, easy to vaporize substances, such as ether, freon, etc., vaporized at low temperatures vapor, like steam to promote the work of the piston, but these programs have failed in practice. In recent years, due to the discovery of a new type of material - memory