Incipient Boiling Wall Superheat Research Articles

Experimental research on the incipient boiling wall superheat of sodium

Incipient boiling wall superheat of sodium flowing in annulus was experimentally investigated. The annulus was 800 mm in length, 6 mm as inside diameter and 10 mm as outside diameter. The heat flux in the experiment was from 128 to 846 kW/m2, with inlet subcooling from 63.1 to 287.8 °C, mass flow rate from 7.2 to 122.0 kg/h and system pressure from 0.85 to 28.79 kPa. The experimental results indicated that the incipient boiling wall superheat increased with the increasing heat flux and inlet subcooling. And lower liquid velocity and system pressure could result in a higher incipient boiling wall superheat. Furthermore, a semi-empirical correlation was obtained from the experimental results. It was also found that the predicting results agreed well with the experimental data.

Vertically oriented TiO2 nanotube arrays with different anodization times for enhanced boiling heat transfer

Pool boiling of saturated water on a plain Ti surface and surfaces covered with vertically-oriented TiO2 nanotube arrays (NTAs) has been studied. The technique of potentiostatic anodization using non-aqueous electrolytes was adopted to fabricate three types of TiO2 NTAs distinguished by their anodization time. Compared to the bare Ti surface, the incipient boiling wall superheat on the TiO2 NTAs was decreased by 11 K. Both the critical heat flux and heat transfer coefficient of pool boiling on the TiO2 NTAs were higher than those from boiling on a bare Ti surface. The measured maximum critical heat flux and heat transfer coefficient values were 186.7 W/cm2 and 6.22 W/cm2K, respectively. Different performances for the enhancement of heat transfer by the three types of TiO2 NTAs were attributed to the different degrees of deformation in the nanostructure during boiling. Long-term performance of the nanomaterial-coated surfaces for enhanced pool boiling showed degradation of the TiO2 NTAs prepared with an anodization time of 3 hours.

Heat transfer characteristics of submerged jet impingement boiling of saturated FC-72

Global heat transfer characteristics of submerged jet impingement boiling of a highly wetting dielectric fluid (FC-72) on a heated copper surface are presented. The effect of variation of the jet exit Reynolds number (Re) on boiling incipience, fully developed nucleate boiling, and critical heat flux (CHF) are documented. The jet exit Re is varied by variations of the jet exit velocity and the jet nozzle diameter for a fixed surface diameter. High-speed visualization is used to supplement trends observed in the heat transfer data. Scenarios of low and high incipience wall superheat are identified, corresponding to partially or fully developed nucleate boiling condition upon initiation of boiling. For the high incipience wall superheat scenario, the time of spread of boiling activity over the heated surface during temperature overshoot is found to be inversely proportional to the wall superheat temperature at boiling incipience. The incipient boiling wall superheat temperature is found to be uncorrelated with jet Re and jet diameter. A cumulative probability distribution function is used to characterize the onset of boiling with wall superheat temperature. At a fixed Re, CHF increases with increasing jet velocity and with decreasing jet diameter, indicating that the jet kinetic energy is a key parameter in CHF enhancement. The CHF data are compared with available jet impingement CHF correlations from literature on free surface and confined jets. The free surface jet CHF correlation by Monde and Katto (1978) [1] is seen to best capture the experimental data trends for Re greater than 4000.

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor (LMFBR), whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature (300–700°C) and low Pe number (20∼70) and heat transfer with low temperature (250∼270°C) and high Pe number (125∼860), and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.

Nucleate Pool Boiling of a TURBO-B Bundle in R-113

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, copper TURBO-B tubes arranged in an equilateral triangular pitch, designed to simulate a portion of a flooded evaporator. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples. For increasing heat flux, the incipient boiling wall superheat of upper tubes decreased as lower tubes were activated. In the boiling region at low heat fluxes (≈ 1 kW/m2), the average bundle heat transfer coefficient was 4.6 times that obtained for a smooth tube bundle (under identical conditions) and 1.6 times greater than that obtained for a single TURBO-B tube; a similar bundle factor has been reported for a smooth tube bundle. At high heat fluxes (100 kW/m2), the average bundle heat transfer coefficient was 3.6 times that of a smooth tube bundle. Furthermore, there was still a significant bundle factor (1.22), contrary to a smooth tube bundle, where all effect of lower tubes was eliminated at high heat fluxes.

Heat transfer and boiling during forced convection of sodium in an induction-heated tube

On the sodium boiling loop (NSK) a series of forced convection boiling and heat transfer experiments has been performed. The test section was an HF-induction heated Ni-tube of 9 mm inner diameter and 168 mm heated length. The results of the preliminary liquid-phase heat transfer measurements at heat fluxes up to 720 W/cm 2 can be correlated by the equation Nu = 5.3 + 0.018 ⋅ P e 0.85 The boiling experiments have been performed under the following conditions: heat flux : 170 − 600 W / c m 2 pressure : 0.3 − 1 ata mass flow : 0.06 − 0.12 kg / sec ⁡ inlet subcooling : 85 − 170 ° C The incipient boiling wall superheat was between 40 and 125°C. It increased with increasing heat flux and decreased with increasing sodium velocity. In the whole range of parameters the phenomenon observed was violently pulsating boiling with partial discharge and subsequent refilling of the test section and strong oscillations of wall temperature. The course of the boiling process was mainly determined by the liquid phase pressure drop before the test section and the heat flux. At low pressure drops dryout of the test section occurred at heat fluxes of about 250 W/cm 2 . At high pressure drop generated by throttling no dryout could be observed at heat fluxes up to 400 W/cm 2 .