Mass and Energy Balances Assignment
Q1. In a frozen food plant, atmospheric air is to go through a pre-cooler to be partially dehydrated so that during its passage through a large cold room used for food storage excess ice formation can be avoided on the chilling coils in the room.
We have an intake atmospheric air at 26.8oC and 102 kPa, with a relative humidity of 43.2%, and a flow rate of 2150 m3/h. It is firstly cooled in the pre-cooler to 4.5oC and 102 kPa to partially condense the water from the intake air prior to it entering the cold room. Answer the following and make sure you state clearly any assumptions you may have made.
(a) What is the molar flow rate of dry air and water vapour in the feed air?
(b) What is the molar humidity and absolute humidity of the feed air?
(c) What is the mole fraction of water in the air stream out of the pre-cooler?
(d) What is the rate of water removal in the pre-cooler?
(e) After 30 days of operation the cold room is defrosted. Given that the vapour pressure of ice (i.e. the sublimation pressure) at -18.0oC is 125 Pa, calculate the mass of liquid water that will defrost.
Q2. The normal boiling point of propane is - 42.1? and the normal boiling point of n-butane is - 0.5oC.
(a) Calculate the mole fraction of the propane in a liquid mixture that boils at -31.2oC and 1 atm.
(b) Calculate the corresponding mole fraction of the propane in the vapour phase at - 31.2oC and 1 atm.
(c) Plot the temperature vs. propane mole fraction phase diagram for this binary system as accurately as you can. Label the diagram properly and clearly including the T - x curve, T - y curve and all phase domains. Mark in the diagram the normal boiling points for both pure species, and the calculated molar fractions in parts (a) and (b). Provide the spreadsheet you used to generate the phase diagram.