Question

QUESTION ONE gw constitrat a) State Dalton's law of partial pressures be taken to occupy the entre vchure. (2 marks) b) When are the dry-bulb and dew temperatures identical? (2 marks) c) Define the dew point temperature. (2 marks) The reaperture d) Moist air at 20°C, 1 bar, 43% relative humidity and a volumetric flow rate of 900 m/h enters a control volume at steady state and flows along a surface maintained at 65 °C, through which heat transfer occurs. Liquid water at 20 °C is injected at a rate of 5kg/h and evaporates into the flowing stream. For the control volume, Wcv=0, and kinetic and potential energy effects are negligible. Moist air exits at 32 °C, 1 bar. With the help of the psychrometric chart provided, determine the rate of heat transfer, in kW. (14 marks) [20 marks)

Answer 1

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Dalton's law of partial pressures 1) It states that total pressure of a mixture of gases is equal to sum of the partial pressures of component gases: P total = Pgas1+Pgas2+Pgas3+...... It can also be expressed using the mole fraction of a gas 2) When the dry-bulb, wet-bulb and the dew point temperatures intersect, that is by definition at the saturation Curve, 100% RH. Shortly when there is 100% Humidity

3) The dewpoint temperature is what the air can no longer hold all of the water vapor which is mixed with it, and some of the water vapor must condense into liquid water. The dew point is always lower than or equal to air temperature. 4) Formula to calculate : max1/max2 = h2-h3/h3-h1 Rate of Heat Transfer = Q/t = KA(T2-T1)/ Find the enthalpy values according the temperature given at the psychrometric chart. This will result in giving the h1, h2, h3 values for different temperature. Once we substitute the values we can find the heat transfer