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    Effect of louvered curved-baffles on thermohydraulic performance in heat exchanger tube
    (2023-02-01)
    Jayranaiwachira, Nuthvipa
    ;
    Promvonge, Pongjet
    ;
    Thianpong, Chinaruk
    ;
    Promthaisong, Pitak
    ;
    Skullong, Sompol
    The paper presents an experimental study of convection enhancement in a tube heat exchanger using louvered curved-baffle (LCB) vortex generator (VG). The heat transfer and pressure loss of air as a working fluid, flowing in an isothermal-fluxed tube were measured having Reynolds numbers (Re) between 4760 and 29,300. The LCB elements were arrayed on two tape sides in a V-shape with a 30° attack angle. At a fixed baffle height, the LCB had three axial pitch ratios (PR) from 0.5 to 1.5 and six louver angles (θ) from 0° to 90°. Thermal enhancement factor (TEF), Nusselt number (Nu), and friction factor (f) are often utilized to analyze the effect of VG geometrical variables on thermohydraulic performance. The measured results demonstrated that the LCB-inserted tube has a significantly larger Nu and f than a plain tube functioning alone, and that the Nu and f tend to rise when PR and θ decline. Using the LCB increases Nu and f by approximately 2.59-4.66 and 3.8-39.37 times, respectively. The maximal TEF is achieved for the LCB at PR = 1, θ = 45° and lower Re. Empirical correlations for Nu and f were evaluated and found to fit measured data well, with discrepancies by ± 9% and ±10%, respectively.
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    Heat transfer rate of swirling impinging jets issuing from a twisted tetra-lobed nozzle
    (2020-12-01)
    Wongcharee, Khwanchit
    ;
    Kunnarak, Kengkla
    ;
    Chuwattanakul, Varesa
    ;
    Eiamsa-Ard, Smith
    Heat transfer augmentation by swirling impinging jets delivered through twisted tetra-lobed nozzles (T-LT) is reported. Impinging jets delivered through a circular nozzle (CT: non-swirling jet) and a tetra-lobed nozzle (LT: non-swirling jet) were also tested for comparison. Experimental results showed that Nusselt numbers of impinging jets delivered through all nozzles were increased with Re and decreasing L/Dh. At a given jet Reynolds number (Re) and a jet-to-plate spacing (L/Dh), the impinging jets delivered through the twisted tetra-lobed nozzles and tetra-lobed nozzle yielded superior heat transfer to that delivered by a circular nozzle. For the jets delivered through the twisted tetra-lobed nozzles, the stagnation Nusselt number (Nu) was decreased while the radial heat transfer distribution was improved with decreasing twist ratios of the nozzle. For the investigated range, the jet delivered through the twisted tetra-lobed nozzle with twist ratio of 4.0 yielded a maximal average Nusselt number. Furthermore, the twisted tetra-lobed nozzles (T-LT) with twist ratios of y/Dh = 2.0, 3.0, 4.0 and 5.0 generate higher heat transfer rates than those of the circular nozzle (CT: non-swirling jet) by around 27.7%, 25.0%, 21.6% and 19.3%, respectively.