How to Approach the Heat Exchanger Design Project (Shell-and-Tube HE2, Light Oil Cooling)

The best way to approach a heat exchanger design project is to fix the duty from the oil side first, estimate an overall coefficient U, size the tubes and shell from it, then recalculate U from the film coefficients and repeat until the error sits between 0% and +20%. Every mark in the brief comes from showing that loop clearly, with the right fluid on the right side. This guide walks through it step by step.

If you would rather have a specialist look over your working, our engineering assignment help page explains how that works.

What the assessment is really asking

The HE2 shell-and-tube design project casts you as an engineer sizing an exchanger that cools a light oil stream with water. You choose between designing HE2 alone (Option 1) or pairing it with an existing exchanger, HE1 (Option 2), where you also solve for the split water flows and temperatures. The page notes that some flow values appear only in the brief’s figure, so take those from your own copy.

Underneath the story, the task is an iteration exercise. You are not asked to find the best possible exchanger. You are asked to show that a sensible design converges: the U you assumed and the U you calculated agree within the stated tolerance, the velocities are practical, and the size is believable.

Handwritten work is required, and printed solutions are not accepted, so the layout of your pages matters as much as the numbers.

Marks and word split

The brief does not publish a word count or a mark split on its question page, so check your own document. Until then, use this suggested split for effort rather than as a rule.

Step-by-step plan

1. Choose Option 1 or Option 2 and say why. If you pick Option 2, solve the HE1 balances before anything else.
2. Calculate the duty from the oil: mass flow times specific heat times temperature drop.
3. Find the water outlet temperature, then the log-mean temperature difference and the correction factor F.
4. Estimate U from the typical-values table in your brief and compute the area.
5. Pick a standard tube and one of the permitted lengths, then compute the tube count on a triangular pitch of 1.25 times the outside diameter.
6. Choose two or four tube passes and check the water velocity.
7. Find the bundle and shell diameters from the brief’s formulas and constants.
8. Calculate the tube-side coefficient, then the baffle spacing, shell-side area, velocity and coefficient.
9. Add the fouling factors and wall resistance, and calculate U.
10. Work out the error. If it is outside 0% to +20%, pick a new U and repeat.
11. Write the summary the brief asks for.

The reference sample for the shell-and-tube HE2 design, for study use only uses illustrative inputs to show all eleven steps with every number worked.

Section-by-section guidance

Energy balance and temperature profile

Fix the duty from the oil, because its inlet and outlet temperatures and properties are the ones you are given. Then work out the water outlet temperature from that duty. If the water outlet comes out hotter than the oil outlet in a counter-current layout, there is a temperature cross, and the design will not work. State the check in one line.

For the F-factor, calculate R and P and then use the standard expression or chart for one shell pass with an even number of tube passes. If F falls below about 0.8, change the temperature plan or the pass arrangement before going further.

Tubes, layout and passes

Pick a standard tube from the table and write down its outside diameter, inside diameter and wall. Choose a length from the list the brief allows. Divide the required area by the area of one tube to get the tube count, then round up to a number your pass arrangement can share equally.

Passes are the main tool for velocity. If water crawls along at 0.5 m/s in two passes, four passes will roughly double the speed for the same tube count. The guidance on the question page suggests 1 to 2.5 m/s, so quote the velocity you got and show it is inside that window.

Tube-side coefficient

Work out the Reynolds number with the inside diameter, the Prandtl number from the water properties, and apply Dittus–Boelter with the exponent 0.4 for a fluid being heated. Show that the flow is turbulent before using it. Convert Nusselt number to h_i using the inside diameter.

Shell-side coefficient

This is where most marks are lost. Use the equivalent diameter for a triangular pitch, not the tube diameter. Flow area depends on the shell diameter and baffle spacing, so keep a running note of the chosen baffle fraction (between 0.2 and 1 of the shell diameter, according to the brief). Then use the Kern-style correlation your course teaches and say which one.

If you are unsure how to present a long calculation like this in a clean coursework layout, our coursework writing help covers structure and formatting.

Overall U and the error check

Add the resistances in series: shell film, shell fouling, tube wall, tube fouling and tube film, remembering that inside terms must be scaled to the outside area. Invert to get U. Then calculate the error with the formula in your brief. A negative error means your design is undersized for the assumed U, so you must iterate even if the number looks close.

What a higher-scoring answer looks like

The strong versions all give a number, a reason and a link back to a criterion in the brief.

Mark-maximising checklist

• Every equation is written before values are substituted, and every value carries units.
• The duty is fixed from the oil side and the water outlet is checked for sense.
• F is calculated, not guessed, and its value is stated.
• Reynolds and Prandtl numbers are shown, with a flow-regime check.
• Water velocity sits in the 1 to 2.5 m/s range.
• Fouling factors use the highest value in each range, as the brief requires.
• The iteration is shown as a table with at least two trials, ending inside 0% to +20%.
• The summary lists every item the brief asks for, including the area on an outside-diameter basis.
• Option 2 answers state m₁, m₂, m₃, T₁, T₂ and T₃, and confirm the combined outlet temperature.

Before you hand in, a second reader can catch sign slips and unit errors. Our assignment review service is built for that kind of marker-style check.

Common mistakes

• Wrong stream placement. Putting the dirtier or higher-pressure fluid on the shell side is listed in the brief as a failure condition.
• Changing only the baffle spacing. When the error is out of range, the question page advises changing U, tube length or passes. Baffle spacing alone moves the answer too little.
• Mixing diameters. Using the outside diameter in the tube-side Reynolds number, or the inside diameter in the area, quietly throws off every later figure.
• Forgetting the F-factor. Using the plain log-mean difference oversizes or undersizes the area.
• Not rounding the tube count up. Round down and the area falls short of the requirement.
• Stopping at a negative error. An error below zero means the exchanger is too small for the assumed U.
• Printed pages. The brief asks for handwriting; check how your department wants any typed summary handled.

Student worries and pain points

The most common worry is the sheer number of steps. Break it into three blocks on separate pages: duty and temperature, geometry, then coefficients and error. Redoing a trial then means redoing only the third block with new tube numbers.

Another worry is not having the reference tables to hand. Your brief supplies typical U values, tube sizes, constants for the bundle formula and fouling factors, so copy the exact row you use onto your page. Markers want to see where each value came from.

Finally, many students are unsure how many iterations to show. Two or three well-explained trials beat six rushed ones. Show the first failed trial in full, then list later trials in a table.

If handwriting is the sticking point, consider drafting each calculation on rough paper first, checking it with a calculator, and only then copying it neatly.

FAQs

Which fluid goes on the tube side?

Water normally goes in the tubes, since it is easier to clean and its velocity is set by the pass count. The oil goes on the shell side. The brief lists incorrect stream placement as a failure, so state your reason.

How do I choose the first U?

Use the typical-values table in your brief for a light organic liquid cooled by water and pick a value from the middle of the range. The first guess is allowed to be wrong; the iteration exists to correct it.

Why do I need an F-factor?

A shell-and-tube exchanger with several tube passes is not purely counter-current, so the log-mean difference overstates the driving force. F corrects for that. Values well below 0.8 suggest a poor temperature plan.

What if my error is negative?

A negative error means the calculated U is lower than assumed, so the exchanger would be too small. Lower the assumed U, or change the length or passes, and repeat the calculation until the error lies within 0% and +20%.

Can I use any tube length?

The brief lists standard lengths between 1.83 m and 7.32 m. Pick one from that list and justify it against the shell diameter, since a very long, thin shell is awkward to build and service.

Do I need to do pressure drop?

The steps on the question page do not list pressure drop, so follow your brief. Where it does not ask, a short remark that velocities are practical is usually enough.

If you want help applying this plan to your own figures, you can send your brief through the assignment submission page to get a quote.