In the whole polytropic process, whenever V increases or decreases,system eitherpurely absorbs or purely releases heat, unless Q=0.

• 对多方过程，当V增大或减少时，要么全部Q＝0，要么全部过程吸热或放热．而对非多方过程，热容量是变量，其吸、放热比较复杂