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Atmospheric air at 100C WBT and 150 C DBT enters a heating coil whose temperature is 400C DBT

The bypass factor factor of heating coil is 0.4. Determine DBT, WBT and RH of the air leaving the coil and the amount of sensible heat added per kg of air

Subject:- Refrigeration and Air Conditioning

Topic:- Design of air conditioning systems

Difficulty:- Low

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Given $T_d1=15℃,T_w1=10℃,T_d3=40℃$,BPF=0.4

Dry bulb temperature of air leaving the coil:

$BPF=\frac{T_d3-T_d2}{T_d3-T_d1}$

$0.4=\frac{40-T_d2}{40-15}$

$T_d2=30℃$

Wet bulb temperature of the air leaving the coil:

From psychrometric chart we can find out the WBT i.e. the corresponding WBT for DBT at point 2:

$T_w2=16℃$

Relative humidity can also be find out from the psychrometric chart at point 2

$ϕ=20%$

The amount of sensible heat added:

From the psychrometric chart enthalpy at point 1 and 2 are

$h_1=30 kJ⁄kg,h_2=42kJ/kg$

Therefore sensible heat added to the air per kg of dry air:

$=h_2-h_1=42-30=12 kj/kg$