A novel repair method for the lifespan and performance improvement of a shell-and-tube heat exchanger: A thermo-mechanical approach

Heat exchangers play a critical role in the functioning of many engineering systems. Shell-and-tube heat exchangers (STHEs) are more traditional and widely used devices due to their efficiency, versatility, and ability to handle a range of flow conditions and fluid types. STHEs experience a number of problems over time, including corrosion, mechanical wear, or leaking, and thus need repairs to keep operating. This study has introduced a novel repair approach for extending the lifespan of damaged STHE tubes by fitting new tubes. An original thermo-mechanical model, including the analyses of the STHE, thermal contact resistance between the fitted tubes, and mechanical design of the built structures, is proposed for the problem solution, and all governing equations are simultaneously solved in Engineering Equation Solver (EES). All submodels are validated with analytical or experimental data, and good agreements are obtained. The most significant design parameters and their effects on the thermal and mechanical performances of an STHE are parametrically investigated. Results reveal that increasing the contact surface slope over 10 degrees but lowering the effective surface roughness below 3 mu m provides an advantage for keeping the heat load of the STHE high. Among the interference fits, the locational interference fit is the most advantageous in terms of thermal and mechanical performances relative to other fit conditions. Both increasing operating pressure and tube diameter are two key pillars that can allow for a safety factor > 1.5. Fitting tube materials are parametrically independent and applicable to any STHE tube diameter as the yield strength > 300 MPa. Even if all tubes are press-fitted, the maximum heat load drop in the current repair method corresponds to 4.23 % which is lower than the tolerable value i.e., <10 % of the initially planned heat load.