A capacitor is made by taking two sheets of aluminum foil, each 0.022 mm thick and placing between them a sheet of paper which comes from a ream of 500 sheets, the ream being 5.5 cm thick with sheets measuring 216 mm by 279 mm. What is the capacitance of the capacitor made this way if the dielectric constant of the paper is 3.7? THE ANSWER SHOULD BE (18nF)

As part of an industrial process, air as an ideal gas at 10 bar, 400k expands at steady state through a valve to a pressure of 4 bar. the mass flow rate of air is 0.5 kg/s. the air then passes through a heat exchanger where it is cooled to a temperature of 295k with negligible change in pressure. the valve can be modeled as a throttling process, and kinetic and potential energy effects can be neglected. (a) for a control volume enclosing the valve and heat exchanger and enough of the local surroundings that the heat transfer occurs at the ambient temperature of 295 k, determine the rate of entropy production, in kw/k. (b) if the expansion valve were replaced by an adiabatic turbine operating isentropically, what would be the entropy production? compare the results of parts (a) and (b) and discuss.