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汽车发动机的冷却系统,大部分仍采用水作为热交换介质。但水在4℃时比重最大,0℃时结冰,当结冰时,体积膨胀达9%左右(水的比重为0.917)。对冷却系统引起的应变,往往大于冷却系统材料的弹性变形范围。因而易使冷却系统装置造成严重的损坏甚至报废。另外由于水质的不同,对冷却系统的金属表面有腐蚀作用,还会引起冷却系统、热交换表面的水垢,从而大大降低冷却效果(水垢比黄铜导热系数低50倍)。
Most of the cooling systems of automobile engines still use water as the heat exchange medium. However, water has the largest specific gravity at 4 ° C and ice at 0 ° C. When it is frozen, the volume expands to about 9% (the specific gravity of water is 0.917). The strain on the cooling system is often greater than the range of elastic deformation of the cooling system material. As a result, the cooling system can easily cause serious damage or even scrapped. In addition, due to the different water quality, the metal surface of the cooling system has a corrosive effect, but also cause the cooling system, heat exchange surface scale, thereby greatly reducing the cooling effect (scale than the brass thermal conductivity 50 times lower).