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Technical Briefs

Thermally Developing Single-Phase Flows in Microtubes

[+] Author and Article Information
Mehmed Rafet Özdemir

School of Engineering and Design,
Brunel University,
Uxbridge, Middlesex UB8 3PH, London, UK

Ali Koşar

Faculty Member
Mechatronics Engineering Program,
Sabanci University,
Orhanli, Tuzla, Istanbul, 34956, Turkey
e-mail: kosara@sabanciuniv.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 21, 2012; final manuscript received February 23, 2013; published online June 6, 2013. Assoc. Editor: Alfonso Ortega.

J. Heat Transfer 135(7), 074502 (Jun 06, 2013) (7 pages) Paper No: HT-12-1065; doi: 10.1115/1.4023881 History: Received February 21, 2012; Revised February 23, 2013

The pressure drop and heat transfer due to the flow of de-ionized water at high mass fluxes in microtubes of ∼ 254 μm and ∼ 685 μm inner diameters is investigated in the laminar, transition and the turbulent flow regimes. The flow is hydrodynamically fully developed and thermally developing. The experimental friction factors and heat transfer coefficients are respectively predicted to within ±20% and ±30% by existing open literature correlations. Higher single phase heat transfer coefficients were obtained with increasing mass fluxes, which is motivating to operate at high mass fluxes and under thermally developing flow conditions. The transition to turbulent flow and friction factors for both laminar and turbulent conditions were found to be in agreement with existing theory. A reasonable agreement was present between experimental results and theoretical predictions recommended for convective heat transfer in thermally developing flows.

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Figures

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Fig. 1

Experimental Test Setup

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Fig. 2

Schematic of the test section

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Fig. 3

Friction micro-scale – Reynolds number profile (254 μm tube)

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Fig. 4

Friction factor – Reynolds number profile (254 μm tube)

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Fig. 5

Friction factor – Reynolds number profile (685 μm tube)

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Fig. 6

Single-phase heat transfer coefficient – heat flux profile for thermocouple 1 (254 μm tube)

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Fig. 7

Single-phase heat transfer coefficient – heat flux profile for thermocouple 1 (685 μm tube)

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Fig. 8

(a) Ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 1 (254 μm tube); (b) ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 2 (254 μm tube); (c) ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 3 (254 μm tube)

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Fig. 9

(a) Ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 1 (685 μm tube); (b) ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 2 (685 μm tube); (c) ratio of theoretical Nusselt number to experimental Nusselt number for thermocouple 3 (685 μm tube).

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