Experimental Study of Subcooled Pool Boiling around a Circular Rough Cylinder (original) (raw)
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Effect of surface characterization on the application of pool boiling heat transfer augmentation
Materials Today: Proceedings, 2021
This research article gives an idea about how the pool boiling heat transfer is affected due to the different surface characterization. In the present, study the pool boiling heat transfer coefficient was measured of different working fluid like Isopropyl Alcohol, Acetone and Ethyl Alcohol with three different surface roughness of the copper surface. Three Copper surfaces were taken and these were polished in different emery paper like 800, 1200 and 2000 grade and surface roughness was tested on the surface tester machine and these were kept on the pool-boiling chamber and worked as the boiling surfaces. By changing different working fluid the heat transfer coefficient (HTC) was measured. It is shown that heat transfer is affected due to the change in surface roughness. Surface roughness plays an important role to produce the nucleation cavity on the heating surface as a result of which heat transfer increases in case of the treated surfaces. Heat transfer coefficient is found to be highest on 800 surface roughness and lowest on 2000 surface roughness for all the working fluid. As the density of nucleation site is more on the 800 surface roughness so HTC is more for this surface as compared to other two surfaces.
Enhancement of Pool Boiling Heat Transfer over Plain and Rough Cylindrical Tubes
International Journal of Heat and Technology, 2021
Received: 21 May 2020 Accepted: 15 March 2021 This study investigates the pool boiling heat transfer of water over cylindrical heating tubes for different orientations and surface roughness of the tubes. First, two orientations of a smooth heating tube, horizontal and vertical, were used in the boiling chamber. For a given heat flux, the heat transfer coefficient achieved with the horizontal tube was always higher than that for the vertical tube. To investigate the influence of surface roughness, a rough heating tube with a fully rough outer surface was developed through a metal etching process. Under the same range of wall superheat, the rough tube enhanced the heat transfer rate significantly compared to the smooth tube. Finally, a modified heating tube (MHT) was developed by axially roughening half of the surface of an originally smooth tube. The orientation angle of the rough surface of this MHT was varied from 0° (horizontal-upward) to 180° (horizontal-downward) in the chamber....
Effect of surface roughness on pool boiling heat transfer
International Journal of Heat and Mass Transfer, 2000
The effect of surface roughness on pool boiling heat transfer coefficient and critical heat flux (CHF) at a copper surface having moderate wettability was studied in saturated water. Copper surfaces were polished with sandpapers of different average surface roughness (R a), ranging from 0.041 lm to 2.36 lm. Test measurements included static and dynamic contact angles for each of the nine surfaces tested. Although the surface roughness, R a , moderately influenced the contact angles, pool boiling test results successfully correlated with the coefficient, C sf , in the well-known Rohsenow correlation. The CHF showed noticeably strong dependence and an enhanced performance on the surface roughness as well. The CHF at the roughest surface (R a = 2.36 lm) was 1625 kW/m 2 , which is approximately twice as much of that at the smoothest surface (R a = 0.041 lm). The large increase in CHF with increasing surface roughness is considered to be a consequence of the capillary wicking from the surrounding liquid to the dry spot. A model for the CHF is obtained by modifying an existing correlation for pool boiling with the inclusion of the capillary wicking effect, and a comparison of the results with the experimental data shows good agreement when the wicking effect is included in the correlation.
Parametric Effects on Pool Boiling Heat Transfer and Critical Heat Flux: A Critical Review
Journal of Electronic Packaging
Pool boiling heat transfer offers high-performance cooling opportunities for thermal problems of electronics limited with high heat fluxes. Therefore, many researchers have been extensively studying over the last six decades. This paper presents a critical literature review of various parametric effects on pool boiling heat transfer and critical heat flux (CHF) such as pressure, subcooling, surface topography, surface orientation, working fluid, and combined effects. To achieve an optimal heat removal solution for a particular problem, each of these parameters must be understood. The governing mechanisms are discussed separately, and various options related to the selection of appropriate working fluids are highlighted. A broad summary of correlations developed until now for predicting CHF is presented with their ranges of validity. While proposed correlations for predicting CHF have been quite promising, they still have a considerable uncertainty (±25%). Finally, a correlation prop...
Subcooled pool film boiling heat transfer from small horizontal cylinders at near-critical pressures
International Journal of Heat and Mass Transfer, 2014
Experimental results for subcooled pool film boiling on small horizontal cylinders at near-critical pressures are presented. Experiments were performed with CO 2 was the test liquid and platinum wires (25.4, 76.2 and 100 lm diameter, D) as the test heaters. The pressure (P), liquid subcooling (DT sub) and bulk liquid temperature (T b) were varied parametrically. For the range of parameters investigated, the heat transfer coefficient (h) was found to be proportional to D À0.5. Because the dependence of h on D varies, a criterion has been developed to predict a priori what this dependence would be any given situation. Subcooled pool film boiling heat transfer coefficient data have been correlated. The correlation developed predicts almost all the experimental data from the current study to within ±10%. The strength of the new correlation is that it is applicable to a much wider range of experimental conditions (including level of gravity) and fluids as demonstrated by the fact that it predicts all of the data reported in the literature to within ±20%. Visual observations during experiments showed that the transitions in film boiling patterns are a function of the dimensionless cylinder diameter.
Effect of Heating Boundary Conditions on Pool Boiling Experiments
HVAC&R Research, 1999
The two widely used experimental methods for pool boiling experiments are evaluated. Boiling heat transfer data employing either the water heating or the electric heating method obtained by various researchers are compared and discussed. The electric heating method is a constant heat flux process, while the water heating method represents a pseudo-exponential temperature profile for the heating water along the tube. It is concluded that the temperature profile along the tube is the major cause of the difference between results from the two methods. The parameters that shape the temperature profile and cause differences are discussed. REVIEW OF RELATED WORK Dhir (1991) reviewed recent advances made toward a mechanistic understanding of nucleate and transition boiling over smooth surfaces for pure liquids. The four mechanisms that contribute to the total boiling heat flux under pool boiling conditions are transient conduction at the area of influence of a bubble growing on a nucleation site, evaporation at the liquid-vapor interface, enhanced natural convection in the immediate vicinity of a growing bubble, and natural convection over the area that has no active nucleation site. The significance of these mechanisms depends on the magnitude of the wall superheat and other system variables like heater geometry, size, material, thickness, orientation with respect to gravity, surface contamination, and system pressure. It was suggested that the boiling process is an aggregate of many subprocesses that are affected by many system variables. The that the understanding of the interaction of subprocesses was very limited, and that to understand the differences between boiling data, detailed models of all the subprocesses and their interactions should be considered.
International Journal of Thermal Sciences, 2014
In this study, an exhaustive research of the correlations integrating the effect of the diameter have been made; the results obtained with these correlations are compared with data of the recent literature relating to pool boiling outside a horizontal tube. The same data are analyzed and it was noted that the heat transfer coefficient increases when the diameter varies from 4 to 6.5 mm, then decreases from 6.5 to 51 mm. In this second interval, we propose a new correlation for the calculation of the heat transfer coefficient depending in addition to the diameter, the pressure and the roughness; satisfactory results are predicted, applied in the case of water, hydrocarbon and refrigerant. Then, simplified forms of correlations have been deduced for water and the R134a.
International Journal of Heat and Mass Transfer, 2018
The present study investigated the physical processes responsible for the variation in the boiling curve and critical heat flux (CHF) caused by liquid subcooling under atmospheric pressure in a rectangular flow channel; the flow channel was oriented 10°upward from the horizon. Bubble dynamics were examined using a high-speed camera and optical fiber microprobes. A solid copper block was utilized as a test heater and mounted above the flow channel to simulate the passive cooling system of an ex-vessel core catcher designed for nuclear power plants. Low mass flux and subcooling conditions ranging from 40-300 kg/m 2 s and 5-25 K, respectively, were applied at the inlet of the test section. At the mass flux value of 40 kg/m 2 s, large sliding bubbles were attributed to a key criterion for enhanced boiling heat transfer when the liquid subcooling was varied up to 15 K. The results showed that the CHF was weakly dependent on the degree of liquid subcooling, which deviates from the general trend reported by many researchers. A repetitive flow reversal along with a pressure shock appeared, owing to the rapid condensation at the exit, which added complexity to the analysis of the CHF. This study provides physical insights for understanding the subcooled flow boiling heat transfer mechanism (including the CHF) based on sophisticated experimental measurements, such as the visual capture of boiling dynamics using highspeed video and local void fraction.