第8章热力学第一定律祥解.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * DESCRIPTION: Carbon dioxide, leaked slowly out of the fire extinguisher onto a black felt cloth, produces dry ice, which can be easily seen. Adiabatic expansion and cooling occur when the CO2 gas comes out of the nozzle under high pressure and expands in the atmosphere. Enough is produced to pass the cloth around the class so that students can feel that it is actually cold. This experiment is a bit more complicated than simple adiabatic expansion. The carbon dioxide actually exists in the fire extinguisher as a liquid, so that much of the cooling is due to the evaporation of the liquid CO2 before it is ejected from the nozzle. * DESCRIPTION: Carbon dioxide, leaked slowly out of the fire extinguisher onto a black felt cloth, produces dry ice, which can be easily seen. Adiabatic expansion and cooling occur when the CO2 gas comes out of the nozzle under high pressure and expands in the atmosphere. Enough is produced to pass the cloth around the class so that students can feel that it is actually cold. This experiment is a bit more complicated than simple adiabatic expansion. The carbon dioxide actually exists in the fire extinguisher as a liquid, so that much of the cooling is due to the evaporation of the liquid CO2 before it is ejected from the nozzle. * * * * * * V3 V4 V p(atm) 1 3 2 V1 等压过程： * 解: [例9-1]在一大玻璃瓶内装着干燥空气，初时气体温度与室温T0相同，气压p1比大气压p0稍高，若打开瓶上阀门让气体与大气相通发生膨胀，当其压强降到p0时即关闭阀门，这时气体温度稍有下降，待气体温度重新回升到室温时测得气体压强为p2。求气体的热容比。 以瓶内剩余气体为系统,先后经历以下两准静态过程（绝热膨胀，等体升温） 绝热 等体 * 例题、有8×10-3kg氧气，体积为0.41×10-3m3 ，温度为27℃。如氧气作绝热膨胀，膨胀后的体积为4.1×10-3m3 ，问气体作多少功？如作等温膨胀，膨胀后的体积也为4.1×10-3m3 ，问气体作多少功？ 解： 绝热方程： * [例] 一定量的理想气体，经一准静态过程由 A 到 B , 如图，试用图形面积表示该过程的 解： o V P A B D C TA SB E F 过 A 作等温线 TA 过B 作绝热线 SB * Engine 8.5 Cycles and The Carnot Cycle Beyond Energy Conservation To turn all the thermal energy into work Not all the thermal energy in a thermal system is available to do work. * High temperature reser