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daz18983
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Homework Statement
Nitrogen beginning at 50oC is pumped along a 30m length of Stainless Steel pipe at a flow rate of 1.5 litres per minute. The Pipeline is at ambient temperature 20oC. Find the temperature of the Nitrogen upon it leaving the end of the pipeline.
Pipe OD - 0.00635m
Pipe ID - 0.00457m
Pressure - 1bar
The following data is taken from a copy of 'An Engineering Data Book' -
Cp - Nitrogen at 20oC and 1 bar is 1.04 kJ/(kgK)
Homework Equations
From 'An Engineering Data Book' and 'Thermodynamics an Engineering Approach 4th Edition' i believed that i could work at the figures from the following equations -
Qdot /l = 2Pi.k.(T2-T1)/In(r2/r1)
Qdot = Heat Loss l = Length k = Thermal Conductivity T = Temperatures r = Radius
Wdot - Qdot = mdot.Cp.(T2-T1)
Wdot = Work Energy In Qdot = Heat Loss mdot = mass flow rate Cp = Specific Heat T = Temperatures
The Attempt at a Solution
using k = 15 (Which is the k of Stainless Steel)
I used Qdot /l = 2Pi.k.(T2-T1)/In(r2/r1)
which gave me a figure of 8.653 x 103 for Qdot
Then to calculate mdot i used the following -
mdot = Vdot / v
where Vdot = Volume flow rate and v = specific volume
Vdot = V / delta t
where V = Volume which is 1.5 litres and delta t = 60 seconds (take from flow rate)
therefore Vdot = 0.025 l/s = 25 x 10-5 m3/s
v = R.T1 / P
where R = Gas Constant which is 0.294 kJ/(kg.K) T1 is temperate 1 which is 323K and P is pressure which is 1 bar (1 x 105Pa)
this gives v to be 9.4962 x 10-4 m3/kg
using these mdot becomes 26.32632 x 10-3 kg/s
Now using Wdot - Qdot = mdot.Cp.(T2-T1)
I rearrage to get T2 on its own
therefore T2 = (-Qdot / mdot.Cp) + T1
note that Wdot = 0 and so has been removed
Therefore i get an answer of 50.3oC which is obviously WAY wrong? Can someone please help me with this. Even just a point in the right direction of the correct equations. This is not a homework or coursework question this an engineering question at work and I'm not too sure where to go with it.