Heat Transfer in Tubes in the Transitional Flow Regime

Meyer, Josua P.

doi:10.1615/ihtc15.kn.000003

Cited by 23 publications

(18 citation statements)

References 41 publications

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“…It was charged with nitrogen to an operating pressure of 3.3 MPa and the maximum operating mass flow rate was 10 kg/s. A bypass valve (5) was installed between the accumulator (4) and the bank of two different sized Coriolis mass flow meters (6), each with its own range of accuracies. The valves were installed to make it possible to switch between the Coriolis mass flow meters, as well as to allow water to flow back into the cold water reservoir.…”

Section: Components Of Circulation Loopmentioning

confidence: 99%

“…In most of these cases, heat exchangers were designed to operate either in the laminar or the turbulent flow regime. Usually the transitional flow regime is avoided [5], as this flow regime is not yet well understood [6]. Predictions are unreliable [7], uncertain and unstable [8], the behaviour is complex [9] and the mechanism of transition is unclear [10].…”

Section: Introductionmentioning

confidence: 99%

“…There are specifically two groups that have dedicated attention to experimental investigations in the transitional flow regime. The first groundbreaking work was performed by Ghajar and his co-workers from Oklahoma State University [12][13][14][15][16], and the second by Meyer and his coworkers at the University of Pretoria [1,5,[17][18][19][20]. Ghajar and his co-workers investigated three different types of inlets at constant heat flux conditions in smooth tubes (macro and micro).…”

Section: Introductionmentioning

confidence: 99%

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Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Meyer

Abolarin

2018

International Journal of Heat and Mass Transfer

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HIGHLIGHTS• Experimental investigation of transitional flow regime in tubes with twisted tapes.• Results based on heat transfer coefficients and pressure drops.• Transitional flow regime was influenced by variation in twist ratios.• Variation in heat fluxes influenced the transitional flow regime.• Transition is earlier as the twist ratios and heat fluxes reduced. ABSTRACTThe purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in the transitional flow regime of twisted tape inserts in a circular tube.Experiments were conducted in a circular tube with an internal diameter of 19.0 mm and a length of 5.27 m, and twisted tape inserts with twist ratios of 3, 4 and 5. A square-edged geometry was used at the tube inlet and it was experimentally operated with water flowing through it while the tube was heated with a constant heat flux. The experiments were conducted at three different heat fluxes of 2, 3 and 4 kW/m 2 . The experimental set-up was operated between Reynolds numbers of 400 and 11 400, and the Prandtl numbers varied between 2.9 and 6.7. Two methods were used to identify the transition points of the different heat fluxes and twist ratios. The first method used the standard deviation of the temperature measurements, and the second method used three linear curve fits on a log-log scale. The curve fits made it possible for correlations to 1 be developed for the non-dimensionalised heat transfer coefficients and friction factors, which took twist ratio, heat flux and Reynolds number into consideration. For the same heat flux, it was found that the Colburn j-factors increased as the twist ratios decreased, and transition started earlier. When the twist ratio was kept constant and the heat flux was varied, higher heat fluxes delayed the transition from laminar to transitional flow. The friction factors were found to increase as the twist ratio decreased. When both the twist ratio and the Reynolds number were kept constant, an increase in heat flux was found to decrease the friction factor.

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Section: Components Of Circulation Loopmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Meyer

Abolarin

2018

International Journal of Heat and Mass Transfer

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“…Although most heat exchangers operate in the turbulent flow regime, the best compromise between high heat transfer coefficients and low pressure drops might be in the transitional flow regime, between laminar and turbulent flow [9]. However, designers are usually advised to avoid this flow regime [10], since the flow is believed to be unstable and chaotic, and little design information is available [9]. According to a recent review paper by Meyer [9], the transitional flow regime has been mainly investigated by Professor Ghajar from…”

Section: Introductionmentioning

confidence: 99%

“…However, designers are usually advised to avoid this flow regime [10], since the flow is believed to be unstable and chaotic, and little design information is available [9]. According to a recent review paper by Meyer [9], the transitional flow regime has been mainly investigated by Professor Ghajar from…”

Section: Introductionmentioning

confidence: 99%

Relationship between pressure drop and heat transfer of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes

Everts

Meyer

2018

International Journal of Heat and Mass Transfer

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Highlights• The flow regime boundaries were the same for heat transfer and pressure drop. • Friction factor correlations for developing and fully developed flow. • Average Nusselt number correlations for developing and fully developed flow. AbstractLimited work has been done specifically focussing on the relationship between pressure drop and heat transfer in the transitional flow regime. The purpose of this study was therefore to experimentally investigate and compare the pressure drop and heat transfer characteristics of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes. An experimental set-up was designed, built and validated against data from literature. A smooth circular test section with an inner diameter of 11.5 mm, and maximum length-to-diameter ratio of 872, was used.Pressure drop and heat transfer measurements were taken at Reynolds numbers between 500 and 10 000 at different heat fluxes. Water was used as the test fluid and the Prandtl number ranged between 3 and 7. A total of 364 mass flow rate measurements, 36 809 temperature measurements and 2 583 pressure drop measurements were taken. Pressure drop and heat transfer measurements were taken simultaneously and the relationship between pressure drop and heat transfer was determined. It was found that the Reynolds numbers at which transition started and ended was the same for the pressure drop and heat transfer results. Correlations were developed to determine the relationship between heat transfer and pressure drop, as well as the average Nusselt numbers, in the laminar, transitional, quasi-turbulent and turbulent flow regimes, for both developing and fully developed flow in mixed convection conditions. It was found that the relationship between heat transfer and pressure drop can be used as an additional criterion to distinguish the different flow regimes. Graphical abstract

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Effect of CuO‐, SiO₂‐, and Al₂O₃‐based nanofluids on automotive cooling systems from laminar to turbulent flow regime—A CFD study

et al. 2022

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In recent studies, much attention has been given to nanofluids suggesting that adding nanoparticles in base fluids offers a higher heat transfer rate compared with conventional fluids. This study is based on the numerical investigation of different types of nanofluids, consisting of CuO (50 nm), SiO2 (40 nm), and Al2O3 (15 nm) nanoparticles at different volume concentrations. Several simulations were performed from low to high Reynolds numbers, corresponding to laminar and turbulent flow regimes using ANSYS‐Fluent CFD solver. Results suggest that under a laminar flow regime with the same Reynolds number of 2000, CuO‐based nanofluids perform better as compared with SiO2 and Al2O3‐based nanofluids with Nusselt number (Nu) having percentage increase of 90% and 60% comparing with SiO2‐ and Al2O3‐based nanofluids, respectively. However, at higher Reynolds numbers when the flow is turbulent, Al2O3‐based nanofluids demonstrate better performance having a percentage increase in Nusselt numbers equal to 40% and 23% as compared with CuO and SiO2‐based nanofluids respectively under the same Reynolds number of 15,000. This implies that turbulence has a significant effect on heat transfer rate, and is not only related to thermal conductivity. This study will help in designing more compact cooling systems for engines and the internal environment of motor vehicles.

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Heat Transfer in Tubes in the Transitional Flow Regime

Cited by 23 publications

References 41 publications

Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Relationship between pressure drop and heat transfer of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes

Effect of CuO‐, SiO₂‐, and Al₂O₃‐based nanofluids on automotive cooling systems from laminar to turbulent flow regime—A CFD study

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Heat Transfer in Tubes in the Transitional Flow Regime

Cited by 23 publications

References 41 publications

Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Heat transfer and pressure drop in the transitional flow regime for a smooth circular tube with twisted tape inserts and a square-edged inlet

Relationship between pressure drop and heat transfer of developing and fully developed flow in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes

Effect of CuO‐, SiO2‐, and Al2O3‐based nanofluids on automotive cooling systems from laminar to turbulent flow regime—A CFD study

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Effect of CuO‐, SiO₂‐, and Al₂O₃‐based nanofluids on automotive cooling systems from laminar to turbulent flow regime—A CFD study