OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 5 Effect of location of pulsation This section reports the effects of pulsation location. Two cases were considered: – pulsation located downstream of the flow. – pulsation located upstream of the flow. Pulsation located at the downstream of the flow Fig. 7 illustrates the increase in the mean heat transfer (HT) coefficient with increasing Re and heat input (Q). The enhancement ranges from 20% to 27% at f = 3.33 Hz and Q = 100 W, and from 30% to 36% at f = 1 Hz. Tables 2 and 3 present values of h and Nu for various Re and Q without pulsation. As Re and Q increase, Nu increases steadily, indicating improved HT performance. Fig. 7. Heat transfer as a function of Re at varying heat input, with pulsation frequencies of f = 1 Hz and f = 3.33 Hz at downstream pulsation Ta b l e 2 Surface HT coefficient (h) at different Re and heat input without pulsation Experimental heat transfer coefficient, h Re Q = 25 W Q = 50 W Q = 75 W Q = 100 W 6,753 22.1 33.04 40.25 47.13 9,504 27.92 34.48 42.77 48.74 11,618 32.11 36.88 45.4 51.26 13,414 35.53 41.19 49.89 54.29 Ta b l e 3 Variations in Nu with Re at different heat input without any pulsation Nusselt number, Nu Re Q = 25 W Q = 50 W Q = 75 W Q = 100 W 6,753 23.43 31 37 44 9,504 29.59 32 40 45 11,618 34.04 34 42 48 13,414 37.66 38 46 50
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