The shell and tube heat exchanger is a versatile and ubiquitous equipment for heat transfer. They are widely used as oil coolers, power condensers, preheaters in power plants, steam generators in nuclear power plants, in process applications, and in chemical industry. A large cylindrical shell houses a collection (bank) of tubes. Fluid motion occurs both on the shell (external flow) and the tube side (confined or internal flow). A common terminology in heat exchangers is “passes”, Eg. 1-shell pass, 2-tube passes. A pass is the number of times the fluid transverses from one end to another. This is achieved using a 180C bend in direction of flow.

Calculations: There are also two commonly used algorithms to solve heat transfer problems in a shell and tube heat exchanger:

1. LMTD method: This is used mainly for the design problem. For the performance problem this needs an iterative solution.
2. ε-NTU method: The effectiveness (ε) and number of transfer units (NTU) can also be used to solve both the problems. Though this method is not as simple as the LMTD method, it can be used to solve both the problems in a non-iterative sequence of steps.

Heat exchangers involve transport of heat through multiple resistances, and the local resistance depends on various factors such as the local boundary layer thickness, presence of fouling, and the thermal conductivity of the wall that separates the shell-side fluid from the tube-side fluid. A macroscopic heat balance across the heat exchanger leads to the definition of an overall heat transfer coefficient (which is inversely proportional to the overall resistance to heat transfer).

$$ \frac{1}{UA} = \frac{1}{h_iA_i} + \frac{R''{f,i}}{A_i} + \frac{\ln(D_o/D_i)}{2πkL} + \frac{R''{f,o}}{A_o} + \frac{1}{h_oA_o} $$

where,
 U is the overall heat transfer coefficient
 h_i is the inside heat transfer coefficient
 h_o is the outside heat transfer coefficient
 A_i is the inside heat transfer area
 A_o is the outside heat transfer area

A is the either of the two areas depending on whether U is inner/outer (or hot/cold) such that U_iA_i = U_oA_o, (R”_f,i, R”_f,o) are the area-based fouling resistances, (D_i, D_o) are the inner and outer diameter of the tube, respectively, k is the thermal conductivity of the tube wall, L is the thickness of the tube, (h_i, h_o) are the convective heat transfer coefficients.

Practical Considerations:

1. Allow the system to reach steady state.
2. Make sure that the valves are in proper position.
3. Provide small increments to the control valves or temperature set-points. Wait for the system to respond with a change before making further increments or decrements in the control variables.
4. Be aware of hot surfaces and liquids and avoid direct skin contact.
5. Note down zero error at the beginning of the experiment.

Conclusion: This manual provides insights into how flow rate and temperature affect the heat transfer coefficient in shell and tube heat exchangers. By understanding these effects, you can optimize heat exchanger performance, improve energy efficiency, and make informed design decisions.