热力学基础(2)2—5功与 P—V图如图—5所示,有一个无任何摩擦的密闭的活塞和气缸,气缸内的气体膨胀,虽然与外力大致保持平衡,活塞却缓慢移动。现在研究一下,由于外力向相反方向压缩,使活塞返回的情况。假定条件是:与外界没有热交换的绝热膨胀和绝热压缩过程。在过程1—2之间,气体对外界所作的功 I_(12)可表示如下: Thermodynamic Basis (2) 2-5 Power and P-V Diagram As shown in Figure -5, there is a closed piston and cylinder without any friction. The gas inside the cylinder is expanded. Although it is roughly balanced with the external force, the piston moves slowly . Now look at the case where the piston returns due to the compression of the external force in the opposite direction. Assumptions are: there is no heat exchange with the outside adiabatic expansion and adiabatic compression process. Between processes 1-2, the work done by the gas on the outside I_ (12) can be expressed as follows: