Joule heating-based measurement methodology for high-fidelity heat exchanger performance evaluation under non-uniform flow conditions

Non-uniform inlet flow is common in installed heat exchangers, but conventional two-fluid tests only measure the overall heat duty and cannot show where in the core performance is lost. The present method resolves heat transfer inside a tube bank by using a low-temperature-coefficient wire inside each tube to impose a known Joule heat flux, combined with four-wire resistance thermometry of the tube walls. The method was applied to a 159-tube, 15-row bank with the wall temperature measured row by row, giving inlet-referenced coefficients with an instrument uncertainty of 2.3%. The bank was evaluated under two inlet conditions: a uniform, well-conditioned inflow and flow downstream of a 90° turning baffle. Behind the baffle, the first-row coefficient was 30% lower than with the uniform inlet, whereas the effectiveness at equal mass flow changed by less than one percentage point, showing that bulk metrics can hide large local penalties. Steady RANS simulations matched the uniform-inlet data closely but under-predicted the coefficients behind the 90° turning baffle by 11%–23%. The method offers an accurate and inexpensive way to study installation effects in heat exchanger development and simulation.