Numerical and Experimental Performance Assessment of Helical Screw Inserts in a Horizontal Evaporator Tube

The influence of a helical screw insert on heat transfer and pressure drop in a circular tube under single-phase water flow conditions was investigated using both experimental techniques and CFD simulations with ANSYS Fluent. Experiments were conducted with water flowing through a horizontally oriented copper tube located in a pressurized tank, across seven different Reynolds numbers ranging from 24,000 to 100,000. A constant surface temperature was maintained via saturated pool boiling of R134a surrounding the tube. The internal flow characteristics were assessed based on measured pressure, temperature, and flow rate data, with convective heat transfer coefficients evaluated using the Wilson plot method. Simulations were conducted for both plain and insert-equipped tubes under identical conditions. The results for the helical insert case aligned well with experimental observations. Compared to literature correlations, heat transfer results were similar, though friction factor predictions were underestimated. A 19% improvement in heat transfer was observed with the insert, accompanied by a significant increase in pressure drop.