Showing 8 results for Pool Boiling
Touraj Malekpour, Ali Keshavarz Valian, Masoud Zia Bashar Hagh, Bagher Soleimani,
Volume 15, Issue 10 (1-2016)
Abstract
In recent years, many researches have investigated nanofluids pool boiling and reported some contradictory results. In this study, the pool boiling heat transfer of water- alumina and TiO2-water nanofluids at saturated temperature was investigated experimentally. The experiments were conducted to investigate the impact of concentration and type of nanofluid on the pool boiling heat transfer of brass surface. Water- alumina and TiO2-water nanofluids with volumetric concentration of 0.0025-1% and 0.0025, 0.01, 0.25 % was used, respectively. An experimental setup with a cylindrical heated test section made of brass and surface roughness of 0.2µm was designed and fabricated. The experimental results showed that, the heat transfer decreases as the nanoparticles added into the pure water base fluid. At a constant heat flux, the heat transfer coefficient decreases as the alumina volumetric concentration increments from 0.0025 to 0.01% and then increases for further addition from 0.01 to 1%. The TiO2-water nanofluids performance with respect to the water-alumina nanofluids was not very promising. That means, the boiling heat transfer decreases while the boiling surface temperature increase at a constant heat flux.
Amir Mirza Gheitaghy, Hamid Saffari, Jafar Salehi,
Volume 15, Issue 12 (2-2016)
Abstract
Boiling is a remarkably efficient heat transfer method and is commonly used in daily life and industrial applications. Changing the physical and chemical structure of hot surface in some methods as making a porosity in a manner of enhancing boiling process is an interesting topic in recent decay. In this paper, porous metal micro/nano structural surfaces is produced in order to augmentation of boiling heat transfer on copper surface by the one- and two-stage electrodeposition method. The pictures in micro and nanoscale are captured to identification of structure and surface characteristics as porosity and capillarity are estimated. Next, the effects of structures in enhancing the pool boiling are measured experimentally. So then, boiling heat transfer profiles that demonstrate heat flux versus wall superheat, are derived for water fluid. Pool boiling curves of enhanced surfaces is compared with polished surface and results of other researchers to determine the efficiency improvement. Furthermore, comparison the effect of electrodeposition process time on obtained structures shows higher porosity, capillary and strength of structure with lower process time (30 sec) lead to further enhancement of pool boiling.
Ali Abdollahi, Mohammad Reza Salimpour, Nasrin Etesami,
Volume 16, Issue 2 (4-2016)
Abstract
Boiling heat transfer is one of the most applicable heat transfer processes within the industry. In this paper, the pool boiling heat transfer of Fe3O4 /water nanofluid (ferrofluid) in atmospheric pressure has been analyzed, experimentally. The nanofluid in this study, has been synthesized in a single step and retains high stability. The replication and accuracy of the testing machine has been studied for deionized water for three times, indicating an appropriate concordance with the literature. Considering different volume concentrations of the nanofluid has revealed that boiling heat transfer in high concentrations decreases with an increase of concentration, while it rises with the increase of concentration in low concentrations. Hence, boiling heat transfer coefficient in 0.1% volume concentration nanofluid has been measured to be the optimum value which increases up to 43%. The roughness of boiling surface was varied with the deposition of nanoparticles in various conditions of nanofluid concentration, and heat flux. It is noteworthy that in the present research, the effects of surface roughness changes due to nanoparticles deposition and the impact of passing time on boiling process have been investigated, for the first time. Therefore, several experiments have been designed in order to study the change of nanoparticles deposition due to the change of nanofluid concentration and boiling surface heat flux. The results indicate that boiling heat transfer of deposited surfaces at low heat fluxes decreases; while it rises at high heat fluxes.
Mehdi Mohammadi, Morteza Khayat,
Volume 17, Issue 12 (2-2018)
Abstract
Pool boiling has the ability to remove large heat flux at low difference temperature of wall and this can be further enhanced by using surface modification methods. This article investigates pool boiling heat transfer on 4 levels with different orientations. For this purpose, a laboratory device was designed and built. The main goal of providing a simple and cost-effective manner with high durability in industrial applications, to having the highest amount of critical heat flux at the lowest level of super-heated temperature difference. The results show that surface roughness factor causing a delay in connecting the bubbles and heat flux increased slightly. In addition to roughness factor, two factors separating bubbles from the fluid in the heat dissipation and more power nucleation sites and micro-bubble layer can be more important than the surface roughness. The surface polished in one direction with lower roughness has higher critical heat flux than circular rough surface. Ultimately to combine bubble separation and more feed the micro layer with made micro channel. With this method it could be increased 131% critical heat flux and 211% heat transfer coefficient.
S. Nasiri, Sh. Talebi, M.r. Salimpour,
Volume 18, Issue 9 (12-2018)
Abstract
Investigating of boiling process is one of the attractive fields for researchers, because of many applications in industry such as heat exchangers and air condition systems. One of the important and effective factors in pool boiling heat transfer is the heating surface geometry. In present article, pool boiling of dionized water and Fe3O4/water nanofluid at atmospheric pressure have been analyzed on smooth and grooved copper surfaces, experimentally. The effect of rectangular, circular and triangular grooves with the same pitch on boiling heat transfer is the main aim of present article. The results have showed that the boiling heat transfer coefficient of dionized water in circular and rectangular grooved surfaces has enhanced 92% and 48.9%, respectively, and has reduced 33.1% in triangular grooved surface toward the smooth surface. Also, the boiling heat transfer coefficient of Fe3O4/water nanofluid in circular grooved surfaces has increased 40.7% and has decreased 21.8% and 88.7% in rectangular and triangular grooved surfaces, respectively, toward the smooth surface. The corners existence in rectangular and triangular geometries causes thermal resistance increasing and heat transfer coefficient decreasing toward circular geometry. Also, the groove area, the mechanism of bubbles creation and nanoparticles deposition content on different surfaces are effective on the boiling heat transfer. For investigation of depth effect, the grooves depth was increased in different geometries. By adding depth, the boiling heat transfer coefficient of water and nanofluid has increased up to 43.5% and 40.6%, respectively, because of heat transfer surface and nucleation sites density augmentation.
M. Khayat, M. Mohebie,
Volume 19, Issue 11 (11-2019)
Abstract
This study aims to investigate the effect of nanoparticle deposition on the boiling surface in the presence of microchannel on the characteristics of boiling heat transfer. In this experimental study, the copper boiling surfaces including polished circular surface, rectangular and trapezoidal microchannels were used. The microchannels include feeding sub-channels perpendicular to the main channel, which increases the boiling surface and separates the downward cool fluid flow and upward hot bubbles. Nuclear boiling experiments on microchannel surfaces in the presence of a hybrid water-based nanofluid containing 70% titanium oxide and 30% OH-based multi-wall carbon nanotubes in volumetric concentrations of 0.1% and 0.5% have been conducted. The results of nanofluid boiling experiments on both microchannel surfaces show that with increasing concentrations, critical heat flux and heat transfer coefficient increases and the highest increase in critical heat flux and heat transfer coefficient is related to the hybrid nanofluid with 0.5 % volumetric concentration on the surface with trapezoidal microchannel and their values are 64.64% and 344.76%, respectively, compared to pure water boiling on the polished copper surface. Also, in boiling of pure water on the deposited surfaces with nanoparticles, the greatest increase in critical heat flux and heat transfer coefficient is related to the surface with trapezoidal microchannels with 0.1% volumetric concentration and 0.5% and volumetric concentration and their values are 120.16% and 149.4% respectively, compared to pure water boiling on the polished copper surface.
Mohsen Khooshehchin, Samira Ghotbinasab, Akbar Mohammadidoust,
Volume 21, Issue 5 (4-2021)
Abstract
Increasing heat transfer and preventing sedimentation in equipment have always attracted the attention of engineers. In this work, the variations of salt concentration were effective on bubble diameter, departure frequency and generation points and its sediments acted as a heat transfer resistance. Therefore, first, the effect of ultrasonic waves on salt sedimentations in pool boiling was investigated. The results revealed that the ultrasonic waves had positive effect by suspending the soluble particles in the fluid and preventing them from precipitating on the surface of heat transfer. Increasing turbulences and perturbations due to changes in bubble dynamic and cavitation phenomenium, led to improve the heat transfer coefficient, significantly. The role of roughness on the surface heat transfer in bubble production was other investigation of the work. Bubble production by increasing the roughness with ultrasonic wave’s irradiation had direct and important effects on enhancing the heat transfer. Finally, salt and nanofluid sediments were compared. The nanoparticles precipitate faster and more easily under the bubble layer, but less in the salt solution if its dissolution is maintained. The ultrasonic waves were employed at three powers of 30%, 60% and 90%. Finally, the heat transfer coefficient and bubble departure diameter increased as 8.43% and 7.54%, respectively. In addition, the sedimentation decreased by 37.19%. As a result, the waves reduced their deposition by preserving salt dissolution.
Mohammadali Mohammadi, Saeid Niazi, Younes Bakhshan, Jamshid Khorshidi,
Volume 23, Issue 2 (1-2023)
Abstract
The present study examined the pool boiling process in a specific geometry by designing and constructing a laboratory complex. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on a ring wire in deionized water at different temperatures. According to the results, increasing the number of rings and fluid temperature decreased the critical heat flux. In the case of a ring wire with a constant number of rings, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the number of rings, a fluid with a constant temperature and applying critical heat flux values. In a ring wire with a constant number of rings, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient decreased at critical heat flux values. The diameters of the produced bubbles were enhanced by increasing heat flux and they separated from the rings when combined. At the beginning of the reddening of the ring wire, a critical heat flux occurred, and considering 110% of the time required for the critical heat flux, the images of the state of the ring wire after the critical heat flux are presented.
