Identification of heat transfer enhancement mechanism for multiple-jet impingement cooling with reversible reactive fluid

• Design of multi-jet impingement cooling with reversible reactive fluid is proposed. • Large eddy simulation is conducted to reveal thermo-chemical jet-to-jet interactions. • Nusselt number in reactive jets is enhanced by 300% compared to non-reactive jets. • The analogy between Nusselt and Sherwood numbers is captured in the reactive case. • Unsteady reactive heat transfer is governed by evolution and merging of vortex-rings. To achieve intensified and uniform heat transfer particularly in low-temperature environments, this work investigates using reversible reactive fluid N 2 O 4 /NO 2 in a multi-jet impingement cooling configuration for low-grade waste heat recovery. Five impinging jets arranged in an equilateral staggered pattern are analyzed by high-fidelity large eddy simulations to reveal flow dynamics, temperature distribution, species concentration, and chemical reactive behaviors. Time-mean results indicate that the combination of near-wall heat-absorbing and far-wall heat-releasing reactions significantly amplifies the wall-normal temperature gradient, resulting in up to 300% Nusselt number enhancements compared to the case without reaction. The reaction exhibits a limited impact on vortical structures from the opposing influences of viscosity increasing and molecular expansion. Instantaneous Nusselt number peaks migrate radially outward from the different jet centers and merge in the middle between adjacent jets, driven by the movement and break-up of unsteady vortex-rings. Proper Orthogonal Decomposition (POD) analysis further confirms that the vortex-ring structures are key contributors to the turbulent energy in the multi-jet impinging system. These small-scale eddies disrupt the local chemical equilibrium, triggering unsteady alternating shifts between endothermic and exothermic behaviors. Moreover, the instantaneous Nusselt number in the reactive case consistently remains 200% to 300% higher than that in the non-reactive cases.