Question 54 (Textile Technology & Fibre Science)
A counter-flow heat exchanger is attached to a stenter for waste heat recovery.
Consider the following data:
Ambient temperature : 30 oC
Temperature of exhaust from stenter : 150 oC
Temperature of exhaust at exit of heat exchanger : 100 oC
Specific heat of exhaust : 0.42 kcal·deg−1·kg−1
Specific heat of air : 0.24 kcal·deg−1·kg−1
At steady state, if the mass flow rates of the exhaust gas and the incoming air are the same, assuming heat loss as zero, the temperature (oC) of the air at the exit of the heat exchanger (towards the stenter), (rounded off to one decimal place), is __117.0 to 118.0__.
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Formula:
Heat(Q)=HcA(Thot-Tcold)
Where,
Hc=Specific heat
A=Mass flow rate
T=Temperature
As given in the question-
Exhaust in temperature=150o c
Exhaust out temperature=100o c
Ambient air in temperature=30o c
Hot air out temperature(t)=?
A1=A2 =A (Mass flow rate of the exhaust gas and the incoming air are same)
Hc1=0.42 kcal.deg-1.kg-1
Hc2=0.24 kcal.deg-1.kg-1
Heat in Exhaust(Q1)=Heat in air(Q2) (Heat loss is zero)
Hc1A1(Thot-Tcold)=Hc2A2(Thot-Tcold)
0.42 x A x (150-100) = 0.24 x A x (t-30)
87.5=t-30
t=117.5o c (Answer)