Shell and Tube Exchanger Design Problem

[AAMAIK]

Homework Statement

51300 kg/hr caustic soda (= 1.115, = 0.349 Btu/lb ∙ ℉ ∙ ft) leaves a dissolver at 190℉ is to be cooled to 120℉ using water at 80℉ which will be heated to 120℉. Knowing that the specific heat and the viscosity at the mean of 0.88 Btu/lb ∙ ℉ and 0.76 cp respectively. Plant practice permits the use of 1.25 in triangular pitch with 1 in OD, 16 ft tube length, 14 BWG. Use a combined dirt factor of 0.002 and pressure drops of 10 psi. Design a suitable heat exchanger.

Homework Equations

I used the basic design procedure in Lecture 7 B as a guide to design the HE.

The Attempt at a Solution

Which fluid is the tube side fluid and which is the shell side fluid, if caustic soda is more corrosive than water and it has a smaller flow rate than water?
To estimate the value of the overall heat transfer coefficients for preliminary analysis, what values for the film heat transfer coefficients should I take for the caustic soda if it contains 11 % NaOH and water?
What changes in the design parameters should I consider when redesigning the Shell and tube HE if the calculated length of the tube is larger than the given tube length (6.81 m > 4.87 m)?

New Doc 2018-11-24 04.24.39.pdf Contains images of my attempt at solving the problem

 

[LightHero]

.For the first question, the caustic soda should be the tube side fluid and the water should be the shell side fluid. This is because the caustic soda is more corrosive than water and has a smaller flow rate. For the second question, the overall heat transfer coefficient can be estimated by using the following formula: U=1/((1/hc)+(R/k)+ (1/ho)). Where hc is the convection heat transfer coefficient of the tube side, R is the thermal resistance of the tube wall, and ho is the convection heat transfer coefficient of the shell side. For the caustic soda, the film heat transfer coefficient should be taken to be 0.5 Btu/hr-ft2-°F and for the water it should be taken to be 0.25 Btu/hr-ft2-°F.For the third question, if the calculated length of the tube is larger than the given tube length, then the design parameters should be changed to reduce the tube length. This can be done by increasing the number of tubes, reducing the tube diameter, or increasing the pitch to tube diameter ratio.