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An air heater for an industrial application consists of an
insulated, concentric tube annulus, for which air flows through a
thin-walled inner tube. Saturated steam flows through the outer
annulus, and condensation of the steam maintains a uniform
temperature TsTs on the tube surface.
Consider conditions for which air enters a 50-mm diameter tube
at a pressure of 5 atm, a temperature of Tm,i=Tm,i= 17°C,
and a flow rate of m˙=m˙= 0.03 kg/s , while
saturated steam at 2.455 bars condenses on the outer surface of the
tube. If the length of the annulus is L=L= 5 m, what
are the air mean outlet temperature Tm,oTm,o and air
pressure drop ΔpΔp from inlet to outlet? What is the mass
rate at which condensate leaves the annulus? Evaluate the
properties of air at 325 K.
Step 1
What is the mean air velocity at the inlet, in m/s?
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Step 2
What is the value of the Nusselt number?
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Step 3
What is the air mean outlet temperature, in °C?
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Step 4
What is the air pressure drop from inlet to outlet, in
atm?
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Step 5
What is the rate of heat transfer to the air, in W?
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Step 6
What is the rate that steam condenses in the annulus, in
kg/s?