OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 3 2025 Ta b l e 4 Nu at different heat inputs with pulsation frequency, f = 1Hz and 3.33Hz when pulsating mechanism is mounted downstream Reynolds number Nusselt number, Nu f = 1.0 Hz f = 3.33 Hz Re 25 W 50 W 75 W 100 W 25 W 50 W 75 W 100 W 6,753 31 34 40 46 44 47 55 58 9,504 33 35 43 49 48 52 62 67 11,618 36 38 47 51 54 54 62 67 13,414 42 45 51 55 56 60 67 71 Ta b l e 5 HT Coefficient vs. Reynolds Number at Various Heat Inputs for Pulsation Frequencies f=1Hz and 3.33 Hz when pulsating mechanism is mounted upstream Reynolds number Nusselt number, Nu f = 1.0 Hz f = 1.0 Hz Re 25 W 50 W 75 W 100 W 25 W 50 W 75 W 100 W 6,753 26 32 38 44 37 42 48 54 9,504 29 34 40 47 41 43 53 56 11,618 29 35 43 49 44 48 56 60 13,414 34 39 48 52 52 53 61 63 Nu demonstrably improves with increasing heat input. The findings indicate that as Re and heat input increase, the mean heat transfer coefficient (hmean) also increases. At f = 1 Hz, a 17–23% increase in the heat transfer (HT) coefficient is observed at Q = 100 W. Pulsation located at the upstream of the flow Similarly, upstream pulsation enhances heat transfer (HT) as Re and Q increase. At Q = 100 W and f = 1 Hz, the HT enhancement ranges from 22% to 26%, while at f = 3.33 Hz, it ranges from 29% to 33%. The generally higher Nu values observed under downstream pulsation, as shown in Tables 4 and 5, suggest its superior HT effect. Effects of pulsation frequency Table 6 shows that increasing the pulsation frequency (f) from 1 Hz to 3.33 Hz significantly increases the experimental heat transfer coefficient (hexpt.) and the experimental Nusselt number (Nuexpt.). For instance, at Re = 6753 during downstream pulsation, hexpt. rises from 32.91 to 47.15, and Nuexpt. rises from 30.96 to 44.36. Similarly, at Re = 13,414 and f = 3.33 Hz, hexpt. and Nuexpt. reach 60.75 and 57.15, respectively. Figs. 8, a–d illustrate the relationship between the Reynolds number (Re), heat input (Q = 25 W and 100 W), pulsation frequency (1 Hz, 3.33 Hz), pulsation location (upstream, downstream), the surface heat transfer coefficient (h), and the Nusselt number (Nu). Higher Re improves heat transfer at both heat inputs. In all cases, the 3.33 Hz pulsation produces the highest h and Nu values, particularly with downstream pulsation. Downstream pulsation consistently outperforms upstream pulsation. Both frequency and Re enhance thermal performance, with more pronounced effects at higher heat inputs (100 W). These trends indicate that pulsation settings are crucial for optimizing heat transfer.
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