Question

Hot oil at 150 deg c is used to preheat a cold fluid at 30 deg c in a 1:1 shell and tube heat exchanger. The exit temperature of the hot oil is 110 deg
c. Heat capacities (product of mass flow rate and specific heat capacity) of both the streams are equal. The heat duty is 2 kw. Find out the overall heat transfer resistance (1/ua):

Answer 1

Answer:

Hot oil at 150 deg c is used to preheat a cold fluid at 30 deg c in a 1:1 shell and tube heat exchanger

Explanation:

Hot oil at 150 deg c is used to preheat a cold fluid at 30 deg c in a 1:1 shell and tube heat exchanger. The exit temperature of the hot oil is 110 deg

c. Heat capacities (product of mass flow rate and specific heat capacity) of both the streams are equal. The heat duty is 2 kw. Find out the overall heat transfer resistance (1/ua):

Answer 2

The overall heat transfer resistance in the $0.04\frac{c}{w}$.

Explanation:

$m_{1}cp_{1}=m_{2}cp_{2}$

$m_{1}cp_{1}(T-30)=m_{2}cp_{2}(150-110)$

$T-30=150-110$

$T=70^{0}c$

∠$MTD=$Δ$T_{1}-$Δ$T_{2}$$=72.82^{0}c$

$Q=2000w$

$\frac{1}{Q}=\frac{72.82}{2000}$

$=0.036\frac{c}{w}$

∠$MTD=$$80^{0}c$

$\frac{1}{Q}=\frac{80}{2000}$

$=0.04\frac{c}{w}$