Heat Exchanger

  • #1

Homework Statement



Steam is passing a pipe that has cold water flowing through. I need to find the change in temperature from when the water enters the pipe to when it leaves the pipe.


Homework Equations



First i found the total thermal resistance using:
R_total=R_in+R_(f,in)+R_conduction+R_out

Where R_in and h_in is:
R_in=1/(h_in pi D_in L_pipe )
h_in=k_w/D_H Nu

R_(f,in) = 0 due to negligble build up on the pipe

R_conduction is:
R_cond=ln⁡(D_out/D_in )/(2k_m πL_pipe )

R_out is:
R_out=1/(h_out A_(total,out) )

I then put R_total into this formula:
Q=UA= 1/R_total =m ̇Cp(T_out- T_in )_cold

and rearranged for:

(T_out- T_in )_cold=Q/(m ̇C_p )=1/(R_total m ̇Cp)

The Attempt at a Solution



These are the values that I have either been given or calculated from the above equations. I'm more worried about my method as opposed to the correct value.

Constant / Variable Value Units
D_in 0.032 m
L_pipe 3.68 m
k_w 0.58 -
D_H 0.032 m
μ 855e-06 Ns/m^2
ρ 1000 Kg/m^3
V 20 m/s
Re 60000 -
c_p 4.1818 J/(kgK)
Pr 7.21 -
Nu 8.91 -
n 0.4 -
h_in 161.5 W/(m^2K)
R_in 0.0167 °C/W
D_out 0.035 m
k_m 16 -
R_cond 2.42e-04 °C/W
A_(total,out) 0.002959 m^2
h_out 4455 W/(m^2K)
R_out 0.07586 °C/W
R_total 0.0928 °C/W
Q 10.77 W
m ̇ 0.2 kg/s


THIS GAVE ME A TEMPERATURE DIFFERENCE OF ABOUT 12 DEGREES CELCIUS WHICH SEEMS WAY TOO BIG.

Any help at all would be good, and I'm wide open to criticism:approve:. I would really appreciate your help with this as it is going in my undergrad thesis.

Thank you very much,

Brandon
 

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