Transcript Slide 1
THERMODYNAMICS Properties of Pure Substance Properties of Pure Substance Pure Substance A substance that has a fixed chemical composition throughout oil air water Properties of Pure Substance Properties of Pure Substance In this picture of a geyser in Yellowstone National Park, water is present as steam from the geyser, as liquid water in the pools, as snow on the ground, and as ice. Since water is a pure substance, a mixture of steam, liquid water, snow, and ice is still a pure substance. Properties of Pure Substance Phase Change Processes Properties of Pure Substance T-υ Diagram T, °C υ, m3/kg Properties of Pure Substance Consider: Piston-cylinder device containing liquid water at 20°C, 1 atm State : Properties of Pure Substance Heat is added until about 40°C T , liquid expands slightly, υ Piston moves up * State : Properties of Pure Substance Add more heat T= 100°C Phase: liquid - any addition of heat will vaporize State: Properties of Pure Substance More heat added-boils ~T constant until completely vaporized ~increase in volume, decrease liquid level, increase vapor Midway- equal L&V State: Properties of Pure Substance More heat until last liquid vaporizes Lost of heat vapor will condense (become liquid) State: Properties of Pure Substance More heat T ,υ Lost of heat, T , condensation will not occur until it reaches 100°C State: Properties of Pure Substance Properties of Pure Substance Properties of Pure Substance X Water boils at 100°C Properties of Pure Substance Psat & Tsat “The temperature at which water starts boiling depends on the pressure.” Tsat – Saturation T ~ T at which pure substance changes phase Psat – Saturation P ~ P at which pure substance changes phase Properties of Pure Substance Properties of Pure Substance Properties of Pure Substance Properties of Pure Substance Properties of Pure Substance Properties of Pure Substance Property Table Temperature Corresponding saturation P Properties of Pure Substance Enthalpy Outlet (P,υ, u) Inlet (P,υ, u) H = U+PV (kJ) h = u+Pυ (kJ/kg) Properties of Pure Substance Problem A rigid tank contains 50 kg of saturated liquid water at 90°C. Find the pressure in the tank and the volume of the tank. Properties of Pure Substance Saturated Liquid Vapor Mixture Proportions (L&V) Vapor Liquid Properties? Properties of Pure Substance Saturated Liquid Vapor Mixture Proportions of Liquid & Vapor x mvapor mtotal x = quality / dryness fraction mtotal = mg + mf Properties of Pure Substance Saturated Liquid Vapor Mixture Total V of the wet vapour = (V vapour) + (V liquid) V = mv = xmvg + (1-x)mvf Specific volume v of the wet vapour v = xvg + (1-x)vf v = vf + x vfg where vfg = vg - vf Properties of Pure Substance Saturated Liquid Vapor Mixture In general, for any intensive property r (v,h,u,s) of a wet vapour, Properties of Pure Substance Saturated Liquid Vapor Mixture x=1, no liquid,dry saturated vapor x=0, no vapor, saturated liquid 0<x<1, saturated liquid vapor mix x<0, x>1, impossible Properties of Pure Substance Saturated Liquid Vapor Mixture A rigid tank contains 10 kg of water at 90°C. If 8 kg of water is in the liquid form and the rest is vapor, determine the pressure and the volume of the tank. Properties of Pure Substance Superheated Vapor Determine the temperature of water at P=0.5MPa and h=2890 kJ/kg. Linear Interpolation x x1 y2 y1 y y1 x2 x1 T h y1 200 y y2 250 2855.4 x1 2890 x 2960.7 x2 Properties of Pure Substance Compressed Liquid Determine the internal energy of compressed liquid water at 80°C and 5MPa. Ideal Gas Equation of State PV=nRT PV=mRT Ru R MW or Pυ=RT R = gas constant Ru=universal gas constant, Ru=8.314 kJ/kmolK MW=molecular weight of the gas Ideal Gas Determine the mass of air in a room whose dimensions are 4m x 5m x 6m. (MWair= 29 kg/kmol)