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 was investigated using both experimental methods and CFD simulations with ANSYS Fluent. Experiments were performed in a custom-designed test setup, where water flowed through a horizontal copper tube immersed in a pressurized tank. A constant surface temperature was maintained via saturated pool boiling of R134a. Tests were conducted across seven different Reynolds numbers ranging from 24,000 to 100,000. Convective heat transfer coefficients were evaluated using the Wilson plot method, based on measured temperature, pressure, and flow rate data. Numerical simulations were carried out for both plain and helical screw insert-equipped tubes under identical boundary conditions. The simulated Nusselt numbers showed good agreement with empirical correlations, while the friction factor values from simulations were consistently higher than those predicted by standard correlations. When compared to the plain tube, the helical screw insert significantly increased pressure loss, with the friction factor rising by approximately eight times. At the same time, heat transfer performance improved, with Nusselt numbers increasing by up to 29% in experiments and 19% in simulations at the highest Reynolds number tested (Re ≈ 100,000). These findings demonstrate that while the helical insert enhances thermal performance, it introduces a notable hydraulic penalty—an important trade-off for compact heat exchanger design.