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Research Papers: Micro/Nanoscale Heat Transfer

Quenching of a Heated Rod: Physical Phenomena, Heat Transfer, and Effect of Nanofluids

[+] Author and Article Information
Arnab Dasgupta

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India
e-mail: arnie@barc.gov.in

A. S. Chinchole

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India
e-mail: chinchole@barc.gov.in

P. P. Kulkarni

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India
e-mail: parimalk@barc.gov.in

D. K. Chandraker

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India
e-mail: dineshkc@barc.gov.in

A. K. Nayak

Reactor Engineering Division,
Bhabha Atomic Research Centre,
Trombay,
Mumbai 400085, India
e-mail: arunths@barc.gov.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received December 15, 2015; final manuscript received June 29, 2016; published online August 16, 2016. Assoc. Editor: P. K. Das.

J. Heat Transfer 138(12), 122401 (Aug 16, 2016) (7 pages) Paper No: HT-15-1790; doi: 10.1115/1.4034179 History: Received December 15, 2015; Revised June 29, 2016

The physical phenomena of rewetting and quenching are of prime importance in nuclear reactor safety in the event of a loss of coolant accident (LOCA). Generally, top spray or bottom flooding concepts are used in reactors. Numerical simulation of these processes entails the use of the concept of a rewetting velocity. However, heat transfer just before and after the rewetting front is often assumed in an ad hoc fashion. The present work aims to evaluate the surface heat flux during quenching as a function of surface temperature. The experiments presented herein are primarily applicable to the bottom flooding scenario with high flooding rate. In the experiments, a rod heated above Leidenfrost point is immersed in a pool of water. The surface temperature was recorded using a surface-mounted thermocouple. The surface heat flux was then determined numerically and hence can be related to a particular value of surface temperature. This type of data is useful for numerical simulations of quenching phenomena. In addition to this, high-speed photography was undertaken to visualize the phenomena taking place during the rewetting and quenching. Both subcooled and saturated water pools have been used and compared in the experiments. Surface finish was seen to influence rewetting process by a mechanism which here is termed as “transition boiling enhanced film boiling.” The effect of using nanofluids was also studied. No marked change is observed in the overall quenching time with nanofluids, however, the initial cooling is apparently faster.

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References

Figures

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Fig. 1

Heat transfer mechanisms during reflooding, adapted from [1]

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Fig. 2

Schematic of the experimental setup

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Fig. 3

(a) Radiograph of the heater and (b) assumed schematic for modeling

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Fig. 4

Temperature versus time data during quenching in a saturated pool. Thermocouple location on the rod is shown as a dot.

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Fig. 5

Intermittent patches of wetting and reforming of film. Film boiling existing at (a) gives way to a patch of contact (b) which grows (c). (d) Contact ceases and film boiling is reinstated.

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Fig. 6

Transition boiling (a) near thermocouple location and (b) near bottom of the rod

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Fig. 7

Temperature versus time data during quenching in a subcooled pool. Thermocouple location on the rod is shown as a dot.

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Fig. 8

Effect of nanofluid concentration on quenching: (a) quenching curve and (b) rate of cooling

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Fig. 9

Surface heat flux in saturated pool

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Fig. 10

Surface heat flux in subcooled pool

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Fig. 11

Surface heat flux for (a) 0.01% Al2O3 and (b) 0.05% Al2O3

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Fig. 12

Water versus nanofluids on the surface heat flux versus surface temperature plot

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