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Research Papers: Forced Convection

Experimental Investigation of Convection Heat Transfer in High Pressure and High Temperature Gas Flows

[+] Author and Article Information
Francisco I. Valentín

Department of Mechanical Engineering,
City College of New York,
New York, NY 10031
e-mail: fiv@creare.com

Ryan Anderson

Department of Chemical and
Biological Engineering,
Montana State University,
Bozeman, MT 59717
e-mail: ryan.anderson@montana.edu

Masahiro Kawaji

Department of Mechanical Engineering,
City College of New York, Energy Institute,
New York, NY 10031
e-mail: kawaji@me.ccny.cuny.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 7, 2016; final manuscript received March 28, 2017; published online May 9, 2017. Assoc. Editor: Ali Khounsary.

J. Heat Transfer 139(9), 091704 (May 09, 2017) (12 pages) Paper No: HT-16-1561; doi: 10.1115/1.4036524 History: Received September 07, 2016; Revised March 28, 2017

This work focuses on an experimental investigation of convection heat transfer to a gas in a vertical tube under strongly heated conditions at high temperatures and pressures up to 943 K and 65 bar. A unique test facility for convection heat transfer experiments has been constructed, and used to obtain experimental data useful for better understanding and validation of numerical simulation models. This test facility consists of a single flow channel in a 2.7 m long, 0.11 m diameter graphite column with four 2.3 kW heaters placed symmetrically around the 16.8 mm diameter flow channel. Upward flow convection experiments with air and nitrogen were conducted for inlet Reynolds numbers from 1300 to 60,000, thus covering laminar, transition, and fully turbulent flow regimes. Experiments were performed at different flow rates (3.8 × 10−4 to 1.5 × 10−2 kg/s) and heater power up to 6 kW. Importantly, the data analysis considered the thermophysical properties of the gas and graphite changing with temperature and pressure. Nusselt number results are further compared to existing correlations. The effect of pressure and heater power on degraded heat transfer is examined. The analyses of the experimental data showed significant reductions in Reynolds number of up to 50% and Nusselt numbers of up to 90% between the gas inlet and outlet.

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Figures

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Fig. 1

(a) Schematic of the high pressure/high temperature gas flow loop, (b) detailed pressure vessel schematic, and (c) schematic of the thermocouple locations where 1–4 represent different axial heights

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Fig. 2

Modified high pressure/temperature gas flow loop

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Fig. 3

Nitrogen circulation system with a gas booster pump

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Fig. 4

Typical heat loss profile measured and fitted polynomial

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Fig. 5

Average graphite temperature profiles for ten equidistant planes: (a) data for air at 23.8 bar, 0.015 kg/s, and 473 K initial midplane graphite temperature and (b) data for nitrogen at 61 bar, 4.1 × 10−3 kg/s, and 843 K midplane graphite temperature

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Fig. 6

Wall and bulk temperature profiles and their differences for: (a) nitrogen at 47.6 bar, 1.4 × 10−3 kg/s (Rein ≈ 5000), 853 K midplane graphite temperature and (b) nitrogen at 51 bar, 4.3 × 10−3 kg/s (Rein ≈ 15,400), 823 K midplane graphite temperature

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Fig. 7

Comparison of average Nusselt number data for air with modified Dittus–Boelter correlation (Eq. (7)) covering transitional and turbulent flow regimes, obtained under different pressures, flow rates, and heater power. Fluid properties were evaluated at the average bulk temperature calculated from energy balances.

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Fig. 8

Variations of average Nusselt numbers with Re0.8Pr0.4 for nitrogen data with fluid properties evaluated (a) assuming a linear bulk temperature profile and (b) at the average of the 11 local bulk temperatures obtained from an energy balance

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Fig. 9

Comparison of local Nusselt number data for (a) air and (b) nitrogen with modified Dittus–Boelter and Gnielinski correlations

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Fig. 10

Reynolds number reductions due to heating for (a) air at 13.6 bar and a midplane temperature of 623 K and (b) nitrogen at pressures of 51 and 61.2 bar and a midplane temperature of 853 K

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Fig. 11

Axial variations of local Nusselt numbers in the flow channel for (a) air and (b) nitrogen; legend corresponds to inlet and outlet Reynolds numbers (×10−3)

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Fig. 12

Axial variations of parameters leading to reductions in the local Nusselt and Reynolds numbers: (a) air at 13.6 bar, 0.015 kg/s, 473 K midplane graphite temperature, Rein = 49,200, Reout = 34,500 and (b) N2 at 61 bar, 3.9 × 10−3 kg/s and 853 K midplane graphite temperature, Rein = 13,900, Reout = 7700

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Fig. 13

Local Nusselt number versus local Reynolds number at the ninth axial plane near the test section outlet for 16 nitrogen tests

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Fig. 14

(a) Axial reductions in local Reynolds number for nitrogen under different heater power: 48 bar, 1.4 × 10−3 kg/s, (b) percent reduction in local Reynolds number as a function of the outlet gas temperature (from 18 nitrogen experiments at two pressures: 52 bar and 62 bar and average gas velocities: 0.1–0.6 m/s), (c) variation of the mean heat transfer coefficient (HTC) with the mean Reynolds number, and (d) mean heat transfer coefficient as a function of the mean bulk temperature for the same data shown in (c)

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Fig. 15

(a) Variation of mean heat transfer coefficient with pressure for nitrogen under fixed conditions (1.9 × 10−3 kg/s and 1.5 × 10−3 kg/s, 863 K midplane graphite temperature) and (b) Eq. (12) divided by Tout plotted for 18 nitrogen runs

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