Simple Heat Exchanger Problem (parallel and counterflow)

[grufff]

Homework Statement

Exhaust gasses flowing through a tubular heat exchanger at a rate of 0.3kg/s are cooled from 400C to 120C by water initially at 10C. Specific heat capacities of the exhaust gasses and water may be taken as 1.13 and 4.19 kJ/kg K respectively, and overall heat transfer coefficient from gasses to water is 140 W/m^2 K.

Calculate surface area required when cooling water flow is 0.4kg/s for both parallel and counterflow exchangers.

Homework Equations

I've put the equations I've selected on my working, shown below, but main ones are:

Q_gas = M_gas * Cp_gas * Delta T_gas

(M = mass flow rate)

Q_gas = - Q_water

Q = Ut * A * Delta T_mean

(Ut = overall heat transfer coefficient, A = Area)

Delta T_mean = (Delta T_out - Delta T_in) / Ln (Delta T_out / Delta T_in)

(logarithmic mean temp)

The Attempt at a Solution

My working shown below. I'm hoping someone might be able to let me know if I'm making any terrible blunders, using wrong formulae etc. My study is distance learning and I don't get a chance to discuss it with other students. Once I send my work in it's marked for my final grading so I'd really appreciate a heads up on any sections I should look at again. Thanks if you can help!

[PLAIN]http://dl.dropbox.com/u/5352127/HeatExchanger1.JPG

[PLAIN]http://dl.dropbox.com/u/5352127/HeatExchanger2.JPG

 

[KataKoniK]

[/PLAIN][/PLAIN]

Your calculations and use of equations seem to be correct. However, I would suggest including units in your calculations to ensure accuracy. Additionally, you may want to double check your assumptions for the heat transfer coefficient and specific heat capacities to make sure they are accurate for the given conditions. Overall, your solution looks good and I don't see any major errors. Good job!