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Journal ArticleDOI

Convective Heat Transfer in a High Aspect Ratio Minichannel Heated on One Side

01 Feb 2016-Journal of Heat Transfer-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 138, Iss: 2, pp 021704
TL;DR: In this paper, the effect of asymmetric heating on the Nusselt number was analyzed using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl.
Abstract: Experimental results are presented for single-phase heat transfer in a narrow rectangular minichannel heated on one side. The aspect ratio and gap thickness of the test channel were 29:1 and 1.96 mm, respectively. Friction pressure drop and Nusselt numbers are reported for the transition and fully turbulent flow regimes, with Prandtl numbers ranging from 2.2 to 5.4. Turbulent friction pressure drop for the high aspect ratio channel is well-correlated by the Blasius solution when a modified Reynolds number, based upon a laminar equivalent diameter, is utilized. The critical Reynolds number for the channel falls between 3500 and 4000, with Nusselt numbers in the transition regime being reasonably predicted by Gnielinski's correlation. The dependence of the heat transfer coefficient on the Prandtl number is larger than that predicted by circular tube correlations, and is likely a result of the asymmetric heating. The problem of asymmetric heating condition is approached theoretically using a boundary layer analysis with a two-region wall layer model, similar to that originally proposed by Prandtl. The analysis clarifies the influence of asymmetric heating on the Nusselt number and correctly predicts the experimentally observed trend with Prandtl number. Furthermore, a semi-analytic correlation is derived from the analysis that accountsmore » for the effect of aspect ratio and asymmetric heating, and is shown to predict the experimental results of this study with a mean absolute error (MAE) of less than 5% for 4000 < Re < 70,000.« less

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Citations
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TL;DR: In this paper, the authors investigated the heat transfer characteristics of minichannel-based heat exchangers embedded with longitudinal vortex generators, both experimentally and numerically, and determined that the vortex generators can enhance the convective heat transfer up to three times with the designed parameter.

28 citations

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TL;DR: In this article , the performance of a direct contact membrane distillation (DCMD) has been investigated based on energy, exergy, economic and environmental analyses in the current study, and the results showed that the utilization of heat recovery heat exchangers significantly improves the system's operating conditions.

11 citations

Journal ArticleDOI
TL;DR: In this article, the effects of different parameters, such as the Reynolds number, mass fraction of n-Eicosane particles, and heating power, on the dimensionless wall temperature, local convective heat transfer effectiveness, temperature control effectiveness, figure of merit (FOM), and pressure drop are studied.

5 citations

Journal ArticleDOI
03 Jul 2021-Energies
TL;DR: In this article, the relationship between the flow pressure drop of the target mini-channel and the aspect ratio and Re is obtained by numerical simulation, and the maximum deviation between the correlation and the experimental value is 6%.
Abstract: In order to provide a theoretical basis for the thermal design of the neutron production target, flow and heat transfer characteristics are studied by using numerical simulations and experiments. A rectangular mini-channel experimental model consistent with the geometric shape of the heat dissipation structure of neutron production target was established, in which the aspect ratio and gap thickness of the test channel were 53.8:1 and 1.3 mm, respectively. The experimental results indicate that the critical Re of the mini-channel is between 3500 and 4000, and when Re reaches 21,000, Nu can reach 160. The simulation results are in good agreement with the experimental data, and the numerical simulation method can be used for the variable structure optimization design of the target in the later stage. The relationship between the flow pressure drop of the target mini-channel and the aspect ratio and Re is obtained by numerical simulation. The maximum deviation between the correlation and the experimental value is 6%.

5 citations

References
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Book
01 Jan 1955
TL;DR: The flow laws of the actual flows at high Reynolds numbers differ considerably from those of the laminar flows treated in the preceding part, denoted as turbulence as discussed by the authors, and the actual flow is very different from that of the Poiseuille flow.
Abstract: The flow laws of the actual flows at high Reynolds numbers differ considerably from those of the laminar flows treated in the preceding part. These actual flows show a special characteristic, denoted as turbulence. The character of a turbulent flow is most easily understood the case of the pipe flow. Consider the flow through a straight pipe of circular cross section and with a smooth wall. For laminar flow each fluid particle moves with uniform velocity along a rectilinear path. Because of viscosity, the velocity of the particles near the wall is smaller than that of the particles at the center. i% order to maintain the motion, a pressure decrease is required which, for laminar flow, is proportional to the first power of the mean flow velocity. Actually, however, one ob~erves that, for larger Reynolds numbers, the pressure drop increases almost with the square of the velocity and is very much larger then that given by the Hagen Poiseuille law. One may conclude that the actual flow is very different from that of the Poiseuille flow.

17,321 citations

01 Jan 1976

3,788 citations


"Convective Heat Transfer in a High ..." refers methods in this paper

  • ...The Gnielinski correlation [25], which is considered applicable as low as Re1⁄4 2100, is also plotted for comparison at the highest and lowest Prandtl number....

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  • ...In a similar manner to Gnielinski’s modification of the Petukhov correlation [25], the Reynolds number term can be modified slightly....

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01 Jan 1930

1,941 citations


"Convective Heat Transfer in a High ..." refers methods in this paper

  • ...A study by Sparrow and Cur [15] investigated mass transfer in a rectangular Table 1 Summary of studies investigating various heat transfer phenomena in narrow rectangular channels for MTR applications Institution/reactor Year Geometry Re P, T Parameter studied Result Reference GE and KAPL 1959 Rectangular channel; tgap¼ 0.1 in.; L w: 2.5 in. 18 in./36 in.; vertical flow 6000–200,000 4.5–13.8 bar; 20–134 C h1/, CHF h1/ 15–45% less than c.t. correlations; CHF values 1/3 of those predicted by c.t. correlations [9] ORNL/HFIR 1961 Rectangular channel; tgap¼ 0.043 in. 0.0057 in.; L w: 18 in. 1.06 in.; upflow 9000–270,000 1.0–39.5 bar f, h1/, CHF h1/ 10–20% greater than Sieder–Tate equation; CHF accurately predicted by Zenkevich–Subbotin correlation [10] MIT/MITR 1969 Rectangular channel; tgap¼ 0.090 in.; L w: 2.5 in. 24 in.; upflow 6500–20,000 1 bar,< 60 C h1/ h1/ 12% greater than modified Colburn correlation [11] MIT/MITR 1975 Rectangular channel; Dhyd¼ 2.16 mm; upflow 2200–14,000 1 bar, <60 C h1/ Results for finned channel only [12] JAERI/JRR-3 1984 Rectangular channel; tgap¼ 2.25 mm; L w: 50 mm 750 mm; upflow/downflow 100–50,000 <42 h1/ Turbulent flow: large spread in h1/ (6 20%), but recommends Dittus– Boelter; laminar flow: new correlation [14] 021704-2 / Vol. 138, FEBRUARY 2016 Transactions of the ASME Downloaded From: http://heattransfer.asmedigitalcollection.asme.org/ on 09/19/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use channel with a*¼ 0.0556 and 10,000<Re< 45,000....

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  • ...Sudo simply recommends use of the Dittus–Boelter equation (the McAdams correlation) for predicting turbulent single-phase heat transfer in such channels....

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  • ...4, is plotted along with the Dittus–Boelter equation (McAdams correlation) in Fig....

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  • ...The McAdams correlation [5], commonly referred to as the Dittus–Boelter equation (though it differs from the correlation developed by Dittus and Boelter [6]), has been used in prior safety analyses for the MIT Research Reactor (MITR)....

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