dc51bf9c-5d91-4483-895d-2b2e06c4b607 66 4 5 decimal

&[DATE] &[TIME] - &[FILENAME]

Steam to air heat exchanger

In a steam heating system, air is heated by being passed over some tubes through which steam flows steadily. Steam enters the heat exchanger at 30 psia and 400 F at a rate of 15 lbm/min and leaves at 25 psia, 212 F. Air enters at 14.7 psia and 80 F and leaves at 130 F. Determine the volume flow rate of air at the inlet.

]]>

When a liquid or gas flows rhrough a pipe, it always do that because there is a pressure gradient at the edges of the pipe: P1 > P2. In this heating process, parameters will change along the air pipe: temperature will grow, enthalpy will grow, pressure will drop, volume will grow, speed will grow. Pressure loss will only be caused by hydraulic friction in pipe and local resistances. Air energy depends very slightly on pressure; so for the calculations, we may assume isobaric process.

Check for the above statement: with final air temp, when pressure drops from initial pressure to 1 psi,
energy only changes by 0.39% H T 130 °F * P 1 psi * 14.7 psi * 21 mat Air CoolProp_Props vectorize kJ kg / 454.2618 454.0847 21 mat

Data

P.air 14.7 14.7 21 mat psi * :

T.air 8013021 mat °F * :

P.steam 302521 mat psi * :

T.steam 40021221 mat °F * :

Solver

h.steam H T T.steam P P.steam Water CoolProp_Props vectorize : kJ kg / 2879.3592 419.2195 21 mat

Δh.steam h.steam 1 el h.steam 2 el - : kJ kg / 2460.1398

G.steam 15 lb min / * :

ΔQ Δh.steam G.steam * : kW 278.9752

T T.steam 1 el P P.steam 1 el Water CoolProp_Phase gas

T T.steam 2 el P P.steam 2 el Water CoolProp_Phase liquid

h.air H T T.air P P.air Air CoolProp_Props vectorize : kJ kg / 426.1132 454.0847 21 mat

Δh.air h.air 2 el h.air 1 el - : kJ kg / 27.9715

G.air ΔQ Δh.air / : lb min / 1319.2756

V.air_inlet G.air D T T.air 1 el P P.air 1 el Air CoolProp_Props / : 8.4662 m 3^s / *