A pressure cooker maintains a constant pressure while food cooks in a water-steam mixture. If the pressure is higher than atmospheric, the water in the cooker boils at a higher temperature and makes cooking faster. Constant pressure is maintained at a small opening in the lid of the cooker with a “petcock.” As heat is added to the cooker and the pressure rises, the weight of the petcock allows just enough steam to escape to maintain constant pressure.
a.) What mass of petcock should be used to maintain a pressure of 100 kPa gage for a cross-sectional area of 4 mm2 at the opening? Atmospheric pressure is 100 kPa.
b.) Under these conditions what is the temperature of the water-steam mixture?