Question

Calculate the entropy production for the piston-cylinder power producing cycle you analyzed in Problem 1. Consider that all heat flows into the system come from a constant temperature source of 1800K and that all heat flows out of the system are to a constant temperature of 250 K. Will this cycle operate? Which process should be altered in order to improve the efficiency of the system or to make it work?

Problem 1:

. A simple, effective electric load leveling technique is to use excess produced electricity to pump water into a hill top reservoirs during off peak hours and then discharging it during peak electrical demand periods. This simple, old style energy storage concept is increasingly being used to have a more effective power generation system. The drawback to this technique is that one has to operate in a hilly or mountainous region. Someone has suggested an alternative that can be applied at any location. In this alternative, a reclaimed concrete mass is to be raised using excess generated electrical power. The density of the reclaimed concrete is the same as concrete. During excess electrical power production periods, this mass will be raised using a pulley-motor combination. During the peak power demands the mass will be lowered using a pulley-electric generator to produce power. The effect of the friction in the pulley is a tangential force that operates at the outer pulley circumference that interfaces with the cable. This force, Ffric, is proportional to the mass being lifted by the following relationship: Ffric = 0.008(lifted weight) [note: the force is proportional to the weight, a force, not the mass]. There is a similar loss in the cable-winding pulley, but the relationship is Fpulley = 0.003(lifted weight). Frictional losses ultimately are converted to heat losses to the environment. The lifting tower containing this mass has an above ground height limit of 30 m and a below ground depth limit of 30 m. The device can be considered to be isothermal during these processes.

Answer 1