A 2-m³ insulated tank contains saturated vapor steam at 4MPa.Avalve on top of the tank is opened, and saturated vapor escapes. During the process any liquid formed collects at the bottom of the tank, so only the saturated vapor exits. We want to find the mass that has escaped when the final pressure is 1 MPa. Taking an average exit enthalpy is not very accurate, so divide the process into two or three steps with piecewise average values of the exit enthalpy for a better estimate. Use, for example, (4-3), (3-2), and (2-1) MPa as the steps in which the problem is solved.