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Research Papers: Evaporation, Boiling, and Condensation

On Development of a Semimechanistic Wall Boiling Model

[+] Author and Article Information
Saurish Das

ANSYS Fluent India Pvt Ltd.,
Plot No. 34/1,
Pune Infotech Park,
MIDC, Hinjewadi,
Pune 411057, India
e-mail: Saurish.das2013@gmail.com

Hemant Punekar

ANSYS Fluent India Pvt Ltd.,
Plot No. 34/1,
Pune Infotech Park,
MIDC, Hinjewadi,
Pune 411057, India
e-mail: Hemant.Punekar@ansys.com

1Present address: Department of Chemical Engineering and Chemistry, Technical University of Eindhoven, STW 0.27, Helix, Het Kranenveld, Eindhoven 5612 AZ, The Netherlands.

2Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 22, 2014; final manuscript received February 18, 2016; published online March 22, 2016. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 138(6), 061501 (Mar 22, 2016) (10 pages) Paper No: HT-14-1032; doi: 10.1115/1.4032833 History: Received January 22, 2014; Revised February 18, 2016

To predict nucleate boiling, a novel semimechanistic wall boiling model is developed within a mixture multiphase flow framework available in ansys fluent. The mass transfer phenomenon is modeled using an evaporation–condensation model, and enhancement of wall-to-fluid heat transfer due to nucleate boiling is captured using a 1D empirical correlation, modified for 3D computational fluid dynamics (CFD) environment; hence this model can be used for a complex-shaped coolant passage. For a series of operating conditions, the present model is rigorously validated against available experimental data in which a 50% volume mixture of aqueous ethylene glycol was used as coolant. Subsequently, this model is applied to study boiling heat transfer for a typical automobile exhaust gas recirculation (EGR) cooler under a typical condition.

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Figures

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Fig. 1

The computational domain used to validate the present model. To mimic the experiments [14], a similar domain size is used. Simulations are performed at three different channel cross sections to check the effects of channel height on boiling heat transfer.

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Fig. 2

Comparison between the experimental data [14] and the present numerical results at 90 °C coolant inlet temperature; 1, 2, and 3 bar (absolute) operating pressures, inlet plug flow velocities of (a) 0.25 m/s, (b) 0.5 m/s, and (c) 1 m/s. Channel height = 10 mm.

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Fig. 3

Comparison between the experimental data [14] and the numerical results at 3 bar (absolute) operating pressure; coolant inlet temperatures of 90 °C and 120 °C with inlet plug velocities of (a) 0.5 m/s and (b) 1 m/s. Channel height = 10 mm.

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Fig. 4

The effect of the channel height. Inlet plug velocity = 0.25 m/s, operating pressure = 2 bar (absolute), coolant inlet temperature = 90 °C, and channel height = 10 mm, 25 mm, and 58 mm.

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Fig. 5

The effect of channel shape. Comparison between the experimental [14] and the numerical results at 1 bar absolute pressure, coolant temperature of 90 °C, and inlet plug velocity of 0.25 m/s for different channel shapes: convex and concave. Channel height = 10 mm.

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Fig. 6

Contour plots of the vapor volume fraction for inlet velocity = 0.5 m/s, inlet temperature = 90 °C, and operating pressure = 1 bar (Tsat = 108 °C), with varying wall temperatures: (a) 100 °C, (b) 120 °C, (c) 130 °C, and (d) 137 °C. Channel height = 10 mm. As expected with increasing the wall temperature, the vapor formation also increased.

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Fig. 7

Contour plots of the vapor volume fraction for inlet temperature = 90 °C, operating pressure = 1 bar, and wall temperature = 130 °C with different inlet velocities of (a) 0.25 m/s, (b) 0.5 m/s, and (c) 1 m/s. Channel height = 10 mm. With increasing the bulk velocity, the vapor formation decreases, i.e., suppression of the nucleate boiling.

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Fig. 8

The geometry of a typical EGR cooler used in the numerical simulation. EGR cooler is a one kind of shell and tube heat exchanger used to decrease the temperature of the exhaust gas. To perform the conjugate heat transfer analysis, both the shell (casing) and the tubes are meshed (i.e., numerically resolved) along with two separate fluid zones: coolant and exhaust gas.

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Fig. 9

(a) Contour plots of the coolant velocity at the cut-plane. (b) and (c) Contour plots of the vapor volume fraction at the cut-plane and the coolant side surface of the tubes, respectively. In the stagnation zone (zone B in the figure), the high tube wall temperature causes the high vapor formation that is prone to an uncontrolled boiling situation.

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Fig. 10

(a) Coolant side wall temperature distribution. A high-temperature hot spots are found in the stagnation zone. (b) and (c) The temperature distribution at the cut-plane and the outer casing of the EGR cooler. The wall temperature distribution at the solid wall can be used as an input for an accurate solid thermal stress and/or fatigue analysis.

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