Experimental investigation of heat transfer in transient boiling

Turbulent flow and heat transfer in an annular geometry have been previously studied experimentally or numerically. Velocity and temperature profiles have been measured and correlations for the wall shear stress and heat transfer have been derived. However there exists no study in turbulent flow for a semi annular geometry. This work aims to study steady and transient convection in a semi annular test section for a wide range of Reynolds numbers from 10,000 to 60,000, the inner cylinder being heated by Joule effect. The velocity profile in the symmetry plane is measured by Particle Image Velocimetry and the temperature of the inner heated cylinder is measured by infrared thermography. The experimental re sults are complemented by numerical simulations which give also access to the velocity and temperature profiles in the whole test section.These results are compared to those obtained in an annular geometry for the same inner and outer cylinders radii and an equivalent flow rate. The velocity and temperature profiles and the wall shear stress are the same as in an annular section in an angular sector of p/2 around the symmetry plane. Both velocity and temperature profiles follow a logarithmic law. In steady convection, the local heat transfer has been characterized in several azimuthal positions. The local Nusselt number can be expressed versus a Reynolds number based on the local friction velocity. Characteristic thermal boundary layer thicknesses are also defined. Finally, transient convection tests are performed with a square power generation. The wall heat transfer and the evolution of the liquid temperature near the wall have the same self similar evolution, with a characteristic time scale, which only depends on the flow Reynolds number.

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“…In this section, we introduce the main features of the facility. More details can be found in [1]. The test section has a semi annular section.…”

Section: Experimental Set-up and Measurements Techniquesmentioning

confidence: 99%

“…1). To conduct experiments in a simple geometry but similar to this sub channel, an experimental set up was designed by Visentini et al [1]. To measure the wall temperature with a high temporal and spatial precision, the infrared thermography is used and so an optical access to the wall is needed.…”

Section: Introductionmentioning

confidence: 99%

Turbulent flow and transient convection in a semi-annular duct

Baudin

Colin

Ruyer

et al. 2016

International Journal of Thermal Sciences

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“…Although there were several studies about the transient boiling, especially in pool boiling, not all the physical mechanisms are understood. Moreover, except for Visentini et al [12] study in pool boiling, none of the previous studies were made in a geometry similar to the one found in a nuclear core. The latter is idealized as a flow in an annular cross section with equivalent hydraulic diameter of the typical sub-channel defined between neighboring rods (in yellow 1 in Fig.…”

Section: Introductionmentioning

confidence: 99%

“…1). To conduct experiments in a simple geometry but similar to this sub-channel, an experimental set-up was designed by Visentini et al [12]. To measure the wall temperature with a high temporal and spatial resolution, the infra-red thermography was used and so an optical access to the wall was needed.…”

Section: Introductionmentioning

confidence: 99%

“…In order to study the ONB in our experiment, the wall is heated by Joule effect with different power steps for short times to simulate transients, unlike the previously mentioned studies where the walls are usually heated with exponential powers. This was done for different Reynolds numbers and sub-cooling in the continuity of the studies initiated by Visentini et al [12].…”

Section: Introductionmentioning

confidence: 99%

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Transient flow boiling in a semi-annular duct: From the Onset of Nucleate Boiling to the Fully Developed Nucleate Boiling

Scheiff

Baudin

Ruyer

et al. 2019

International Journal of Heat and Mass Transfer

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This paper presents an investigation of the transient Onset of Nucleate Boiling (ONB) on a vertical heated surface cooled by an upward flow. The duct geometry used (semi-annulus with a heated inner wall) make this study very similar to a fuel rod in a Pressurised Water Reactor (PWR). This test section is then heated with different power steps to show the ONB and observe its propagation along the wall. The fluid used is the refrigerant HFE7000 flowing with flow rates corresponding to Reynolds numbers from 0 to 60,000 and subcoolings Jakob numbers from 8 to 33. Synchronised infra-red (IR) thermal measurements and high-speed camera visualizations provided new data which helped to develop models to characterise the Onset of Nucleate Boiling and the transition to the Fully Developed Nucleate Boiling regime (FDNB). This very finely characterized local behaviour provides an original insight for the onset of nucleate boiling in such sub-cooled convective configuration. It is shown that boiling is initiated by nucleation at a few specific sites and then propagates in the wake of a large vapor pocket flowing along the wall. Analysis of wall to fluid heat transfer evidences a short heat transfer degradation phase below the first vapor pocket, followed by a very effective cooling in its wake. The wall to fluid heat transfer during this transition toward fully developed nucleate boiling appears uncorrelated to the power dissipated within the heating element or to flow conditions.

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Review of Pool Boiling Heat Transfer During Power Transients

Pinto

Murallidharan

2021

Lecture Notes in Mechanical Engineering

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Experimental investigation of heat transfer in transient boiling

Cited by 29 publications

References 20 publications

Turbulent flow and transient convection in a semi-annular duct

Turbulent flow and transient convection in a semi-annular duct

Transient flow boiling in a semi-annular duct: From the Onset of Nucleate Boiling to the Fully Developed Nucleate Boiling

Review of Pool Boiling Heat Transfer During Power Transients

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