Effect of modified expansion pipe nozzle on heat transfer enhancement  with impinging jet

Natthaporn Kaewchoothong; Makatar Wae-hayee; Passakorn Vessakosol; Chayut Nuntadusit

Authors

Natthaporn Kaewchoothong Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hatyai, Songkhla, 90112, Thailand
Makatar Wae-hayee Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hatyai, Songkhla, 90112, Thailand
Passakorn Vessakosol Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hatyai, Songkhla, 90112, Thailand
Chayut Nuntadusit Department of Mechanical Engineering, Faculty of Engineering, Prince of Songkla University, Hatyai, Songkhla, 90112, Thailand

Keywords:

impinging jet, expansion pipe nozzle, air entrainment, heat transfer enhancement

Abstract

The aim of this study is to experimentally and numerically investigate the flow and heat transfer characteristics of impinging jet from expansion pipe with some modifications. The expansion pipe without air entrainment hole, with 4 and 8 air entrainment holes and hollow expansion pipe were connected to pipe nozzle and assessed to obtain the condition of heat transfer augmentation. The results from cases with expansion pipe were compared with cases of conventional pipe (without expansion pipe). In this study, the inner diameters of main pipe and expansion pipe were d=17.2 mm and D=68.8 mm (i.e., D=4d), respectively. The jet-to-plate distance (the distance from main pipe outlet to impingement surface) was varied at H=4d, 6d and 8d. The length of expansion pipe was fixed at L=2d, 4d and 6d. The comparison of all results was based on constant jet mass flow rate with Reynolds number of jet from the main pipe nozzle at Re=20,000. An infrared camera was used to measure the temperature distribution on the impingement surface, and the measured data were subsequently evaluated to gain Nusselt number distributions on the surface. The 3-D numerical simulation with SST k-ω turbulence model was carried out to investigate the flow field. The results show that the amount of ambient air entrained to the hollow expansion pipe is larger than the case of expansion pipe with air entrainment holes. Consequently, the heat transfer on the impingement surface for the case of hollow expansion pipe can be enhanced massively, especially for case of L=2d at H=4d.

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