Heat water in a sealed container (the water does not fill it completely) to a certain pressure; determine the amount of steam generated
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Let’s take a practical example: a closed tank with a diameter of 3.5 meters and a height of 10 meters, in which the water level is at 6 meters. The initial water temperature is 20°C, and the pressure inside the tank is at atmospheric level. Heating heats the water in the tank to 120°C. May I ask how much water vapor is generated inside the tank at 120°C? (This is a pressure-variation heating process)
Is this a math test? At 120°C, the pressure is 0.2 MPa; the density of saturated steam is 1.122, π*3.5/2 squared x 4
Using the method below, I wonder if it will work? P*V1=n*R*T ; ρ120*(V0-V1)+18*n=ρ20*V20 P——the saturated vapor pressure of water at 120°C ； V1 —— Volume of water vapor at 120°C (unknown) ； n — the amount of water vapor at 120°C (unknown). ρ120 —— Density of water at 120°C ； V0 —— Volume of the tank ； ρ20 —— density of water at 20°C ； V20 — the volume of water at 20°C.
This post was last edited by bfdlwolf on 2019-6-2 at 16:53. The total volume V is equal to π*r2*h; where r = 3.5/2 and h = 10, so V = 96.16 m3. The total mass m is equal to the density of water multiplied by its volume – the density of water at 20°C under standard pressure is 998 Kg/m3. Thus, V_water = 57.70 m3, and m_total = 57582.1 Kg. When water in a closed tank is heated to 120°C, gas-liquid equilibrium is reached. At this point, V_total = V_vapor + V_liquid, and m_total = m_vapor + m_liquid = ρ_vapor*V_vapor + ρ_liquid*V_liquid. The density of saturated water vapor at 120°C is 1.122 Kg/m3, while the density of saturated water at the same temperature is 945 Kg/m3. Using these values, it is possible to calculate the amount of water vapor present
Thank you! I think it should be calculated in this way. I have one more question: at an initial temperature of 20°C, the upper space is filled with air at normal pressure. I wonder if this affects the calculation?
Thank you, sir. May I ask where the second formula comes from?
Second formula: At 120°C, the mass of water in the liquid phase plus the mass of water in the gas phase is equal to the mass of water in the liquid phase at 20°C. The water in the gas phase at 20°C is ignored here.
First, calculate the pressure inside the tank at 120 degrees using PV/T. Consult the property sheet to find the saturated vapor pressure of water vapor at 120 degrees; this will allow the calculation of the amount of water vapor present in the tank. Then, use the vapor density at 120 degrees to determine further values