Chemical Engineering Answers

Air with a humidity, YM, of 0.012 kg H2O / kg dry air enters a recirculating drier, where it removes some water from a solid material (S) and leaves with a humidity, YP, of 0.030 kg H2O/kg dry air. A fraction of the wet air leaving the drier is removed from the process and the rest is recycled. Fresh make-up air with a humidity, YF, of 0.004 kg H2O/kg dry air is mixed with the recycled air. The water (W) removed from the solid material S leaves in the system in stream P? Calculate (a) The mass of water removed per kg of feed air supplied (4 marks) (b) The percentage of wet air removed after the drier. (4 marks)

a)  Write down the equation for the relationship between the shear stress and the shear rate for Newtonian fluid defining the variables and parameters used.

b) Oil with a density of 770 kg m⁻³ flows through a pipe with a diameter of 30 cm at a rate of 20,000 tonnes per day. Calculate the velocity of the oil in the pipe.

c)  A liquid flows in a hosepipe of internal diameter 1.8 cm with a velocity of 150 cm s^-1. Calculate the velocity of the water in the nozzle at the end of the pipe which has a diameter of 0.75 cm.

d) Water  at 20°C and 1 atm has a density = 998.0 kg/m3. Calculate the density at 35°C to 3 significant figures if the coefficient of volume

∆𝜌𝜌⁄𝜌𝜌

expansion of the water is given by 𝛽𝛽 = − = 0.337x10^-3 K^-1.

∆𝑇𝑇

e) A brick wall with 0.1 m thickness (k = 0.7 W m⁻¹K⁻¹) is exposed to a cold wind at 270 K through a convection heat transfer coefficient of

                          40 W m⁻²K⁻¹. On the other side is calm air at 330K, with a convection

heat transfer coefficient of 10 W m⁻²K⁻¹. Calculate the rate of heat transfer per unit area (heat flux).

A distillation column is fed with a stream of ethanol, propanol and butanol

flowing at a total rate of 1350 kg h⁻¹ and containing 20 wt% ethanol. The top product consists of 80% of the ethanol and 50% of the propanol contained in the feed. All of the 500 kg h⁻¹ of butanol in the feed ends up in the bottom product. Calculate the bottom product component mass flow rates.

A stream of aqueous sulphuric acid of 62.4 wt% H₂SO₄ is mixed with pure water in a stirred vessel to produce a stream of 20.5 wt% acid. What ratio of water to concentrated acid should be used?

Write in words the Conservation Equation and State what is meant by an Open System and a Closed System

Air is compressed from 1 bar , 300 K to 5 bar in a steady flow compressor at the rate of 1200

kg/h. The inlet and outlet pipe diameters are 10 cm each. The rating of compressor is 100

hp. For air, Cp=3.5R, Cv = 2.5R. Assuming ideal gas, estimate the heat transfer rate.