Subcooled Nucleate Boiling Research Articles

Research of Thermal Hydraulic Conditions Effect on PWR CIPS Risk

In order to reveal the effect of thermal hydraulic conditions on the PWR CIPS risk, the evaluation of a PWR CIPS risk in the first cycle under different core flow rates, average primary temperatures, power levels, and primary pressures was conducted by combining thermal hydraulic codes LINDEN and CRUD (Chalk River unidentified deposit) analysis software CAMPSIS. The research result illustrating the essential effect of thermal hydraulic conditions on CIPS is changing the SNB (subcooled nucleate boiling) level of the fuel assembly’s surface; thus, boron precipitation and local power distribution will be affected. Theoretical evidence and statistical support of the effect of thermal hydraulic conditions on the PWR CIPS risk could be obtained via this research.

Effects of heat flux on fuel crud deposition and sub-cooled nucleate boiling in simulated PWR primary water at 13 MPa

This work aimed to evaluate the effects of two different heat fluxes (20 W/cm2 and 80 W/cm2) on fuel crud deposition behavior and sub-cooled nucleate boiling (SNB) behavior in simulated primary water of a pressurized water reactor at 13 MPa. The SNB behavior on the fuel cladding tubes was periodically monitored using an acoustic emission (AE) technique during the deposition tests. The number of boiling AE signals emitted on the fuel cladding tubes at 80 W/cm2 was greater than that at 20 W/cm2 throughout the deposition test. After the crud deposition tests, the amount of crud formed on the cladding tubes at 80 W/cm2 increased by about 3.6-times compared with that at 20 W/cm2. In this paper, the effect of heat flux on fuel crud deposition is discussed from the viewpoint of the degree of SNB.

Effects of dissolved hydrogen on fuel crud deposition and subcooled nucleate boiling in PWR primary water at 328 °C

This work aimed to evaluate the effects of dissolved hydrogen (DH) on the crud deposition and subcooled nucleate boiling (SNB) behavior of fuel cladding tubes in a simulated primary coolant of a pressurized water reactor at 328 °C and 13 MPa. The SNB characteristic occurring on the fuel cladding tubes was periodically observed using an acoustic emission method during the deposition tests. There was little difference in the energy distribution and hit number of the boiling acoustic signals at three difference DH concentrations ranging from 0 to 70 cm3/kg H2O. The difference in the amount of crud particles on the cladding tube at each DH condition was also minor. The effect of DH on crud deposition is discussed from the viewpoint of the SNB behavior, the solubility of Ni and Fe, and the change in the crud morphology.

Experimental Investigation of the Onset of Subcooled Nucleate Boiling in an Open-Pool Nuclear Research Reactor

Abstract The IPR-R1 TRIGA nuclear research reactor at the Nuclear Technology Development Center (CDTN), in Belo Horizonte (Brazil), is a pool type reactor. The maximum core power is 250 kW cooled by natural circulation of light water and an open surface. Fuel to coolant heat transfer patterns must be evaluated as function of the reactor power in order to assess the thermal hydraulic performance of the core. The heat generated by nuclear fission in the reactor core is transferred from fuel elements to the cooling system through the fuel/cladding (gap) and the cladding to coolant interfaces. The objective of the thermal and hydrodynamic projects of the reactors is to remove the heat safely, without producing excessive temperature in the fuel elements. The regions of the reactor core where boiling occurs at many different power levels can be determined from the heat transfer coefficient data. As the reactor core power increases the heat transfer regime from the fuel cladding to the coolant changes from single-phase natural convection to subcooled nucleate boiling. Experimental results indicated that subcooled pool boiling occurs at the cladding surface in the reactor core central channels at power levels in excess of 60 kW. However, due to the high heat transfer coefficient in subcooled boiling the cladding temperature is quite uniform along most of the active fuel rod region and do not increase very much with the reactor power. An operational computer program and a data acquisition and signal processing system were developed as part of this research project to allow on line monitoring of the operational parameters.

Numerical Simulation of Subcooled Nucleate Boiling by Coupling Level-Set Method with Moving-Mesh Method

A new numerical procedure coupling the level-set method with the moving-mesh method to simulate subcooled nucleate pool boiling is proposed. Numerical test problems have validated this new method. The simulation of bubble dynamics during nucleate boiling under liquid subcooling shows that this novel adaptive method is more accurate in determining interfacial heat transfer than a computational method based on uniform grids with the same number of mesh points.

A Thermocapillary Mechanism for Lateral Motion of Bubbles on a Heated Surface During Subcooled Nucleate Boiling

Both thermocapillary flow and the concerted motion of bubbles toward each other in subcooled nucleate boiling have been mentioned in the literature on boiling phenomena, but never associated with each other. Also, it has been shown in previously unrelated contributions that thermocapillary flow around bubbles of sparingly soluble gas can cause those bubbles to aggregate on a warm surface. The conjunction of these observations leads to the hypothesis that mutual entrainment in thermocapillary flow might drive bubbles toward each other during nucleate boiling of a subcooled liquid. An approximate equation for estimating the observability of such motion is presented. The effect would be especially important in cases where the bubble release rate is low such as boiling on horizontal down-facing surfaces and boiling in microgravity.

Experimental Examination of Forced-Convection Subcooled Nucleate Boiling and Its Application in Microgravity

Experimental Examination of Forced-Convection Subcooled Nucleate Boiling and Its Application in Microgravity

On the Mechanism of Forced-Convection Subcooled Nucleate Boiling

In highly subcooled nucleate boiling the bubbles grow and collapse while sliding along the heated surface, so that there is no net vapor transport away from the surface. A long-standing question exists as to whether conduction and convection between the bubbles, or latent heat transport through the bubbles, is the dominant heat transfer mechanism. It is shown here by simple calculations that the sliding of the bubble results in augmentation of microlayer evaporation under the bubble by a factor of two or more over a stationary bubble with a continuous microlayer. It appears therefore that the latent heat transport mechanism may be dominant at large bulk subcoolings.

Superheat Layer Thickness Measurements in Saturated and Subcooled Nucleate Boiling

An experimental study of temperature profiles in water boiling on a horizontal copper surface is reported for incipient boiling conditions and for 20,000, 50,000, and 100,000 Btu/hr-ft2 heat flux at various levels of subcooling ranging from 0 to 105 deg F. The extrapolated superheat layer thickness results for the incipient boiling conditions lend support to Hsu’s mathematical model for bubble nucleation. Increasing heat flux and decreasing subcooling were observed to result in a decreasing extrapolated superheat layer thickness. Analysis of some additional results for Freon-113 boiling on a glass surface indicated that the thickness of the extrapolated superheat layer was governed by the bubble flux density which was influenced by both heat flux and subcooling.

Mass-Transfer Model in Subcooled Nucleate Boiling

The mass-transfer model of subcooled boiling, conceived in 1952 by N. W. Snyder, is reviewed. Described is an experiment in which a water-vapor bubble was studied from its growth on a heated surface, through a thermal layer, and into a turbulent stream of subcooled water flowing parallel to the heated surface. The effectiveness of the turbulent subcooled stream in removing heat deposited by condensation on the surface of the bubble was determined. The results show that the thermal-energy transport associated with the mass-transfer mechanism in boiling heat transfer can be absorbed effectively at the top of the bubble. Also given are the results of a theoretical investigation in which two models of bubble dynamics were derived. The first model describes the artificial bubble produced in the experiment just noted. The second model describes the dynamics of a bubble growing on a heated surface, into a subcooled liquid, and with an evaporating thin liquid film below the bubble on the heated surface. The results show that the importance of the mass-transfer mechanism has been underestimated in the past and that this mechanism is responsible for a substantial portion, or almost all, of the heat transfer in subcooled nucleate boiling in forced convection.

Closure to “Discussions of ‘Mass-Transfer Model in Subcooled Nucleate Boiling’” (1969, ASME J. Heat Transfer, 91, pp. 411–412)

Closure to “Discussions of ‘Mass-Transfer Model in Subcooled Nucleate Boiling’” (1969, ASME J. Heat Transfer, 91, pp. 411–412)