Modification of plumes and heat transfer in a thermal convection environment due to intermittent cold fluid injection

Experimental and numerical investigations of plume reorganization and heat-transfer enhancement in a buoyancy-driven laminar natural convection system subjected to intermittent cold-fluid injection are presented. Experiments are conducted in a thin rectangular enclosure filled with silicone oil and heated from bottom, with localized cold-fluid injection through orifices positioned along the heated surface. Shadowgraph visualization is used to characterize the transient evolution of convection structures over a Rayleigh-number range of 4.35 × 10 7 to 2.61 × 10 8 , with injection Reynolds numbers of 0.5, 1.5, and 2.5. Finite-volume simulations are performed using the SIMPLE algorithm and are validated against experimental thermal responses and Nusselt-number characteristics. A systematic comparison of single and paired orifice configurations is further conducted under equal injected-mass conditions to isolate the effect of injected mass. Intermittent injection disrupts the established plume and circulation structures, promoting plume fragmentation, fluid redistribution, and enhanced thermal transport along the heated surface. Among the investigated configurations, paired sidewall injection at X* = 0.083 and 0.92 provides the highest heat-transfer enhancement, up to 17.82% relative to the base case at the highest investigated Rayleigh number. Under identical injected-mass conditions, distributing the fluid through paired sidewall orifices is more effective than injecting the same amount of fluid through a single orifice. The present study demonstrates the thermal effectiveness of paired sidewall injection as a promising active technique for enhancing heat transfer in laminar natural convection within confined thermal systems.