•Pool boiling HTC of R-1233zd(E) alternative to R-123 and R-245fa is investigated.•Tests are conducted on the smooth tube with the effect of POE lubricant oil.•Heat transfer coefficients of ...R-1233zd(E) are lower than that of R-123 and R-245fa.•With the effect of POE-oil (ω: 0–10%) HTCs degraded by up to 43%.•The nucleation sites are significantly affected by the oil addition.
Pool boiling heat transfer characteristics of low pressure and low GWP refrigerant R-1233zd(E) alternative to R-123 and R-245fa on a smooth copper tube are investigated with the influence of POE (polyolester)-lubricant oil POEC-220 (220 cSt). The experiments were conducted at a saturation temperature of 10°C, and 26.7°C in 10−90 kWm−2 heat flux range. The mass concentration of POEC-220 oil varied from 1−10%. The obtained results exhibit that the addition of POE lubricant to the pure low-pressure refrigerant R-1233zd(E) degraded the heat transfer performance. The average degradation of heat transfer coefficients (HTCs) for mass concentration of oil 1%, 3%, 5%, and 10% are 9.40%, 7.16%, 15.31%, and 42.87% respectively when compared to that of pure refrigerant. It is found that the nucleation sites are especially reduced at the bottom part of the test tube. Yet, either Augmentation or reduction of HTC with the presence of lubricant oil is mainly attributed to the absolute pressure (low/medium/high) of the working refrigerant/fluid/system/evaporator, the mass concentration of oil, boiling surface, and applied heat flux. However, augmentation in the HTC with less oil addition (e.g., less than 5%) can be seen for absolute pressures between 150 and 700 kPa.
In-Vessel Retention (IVR) is a key technology to retain the molten core in the reactor vessel during severe accidents of Pressurized-water reactors (PWRs). In order to gain the safety margin of IVR, ...it is crucial to enhance the critical heat flux (CHF) of the reactor vessel, which is submerged in a water pool. To enhance the CHF, we have designed and additive-manufactured porous grid plates with a 3-D printer for design flexibility. We measured the CHF for the porous grid plate on the boiling heat transfer surface and found that the CHF was enhanced by 50 % more than that of the bare surface. The CHF enhanced more with a narrower grid pitch and a lower grid height. The visual observation study revealed that the vapor film was formed at the bottom of the grid plate.
Recently, increasing the heat transfer rate in boiling systems using nanofluids has attracted great attention. Researchers use nanofluids to escalate the heat transfer in boiling. Nanofluids, due to ...their hydrophilicity and hydrophobicity, can affect heat transfer boiling positively or oppositely. In the present study, the application of various silica nanofluid concentrations on the pool boiling was investigated using the Eulerian–Eulerian approach. In this approach, liquid water was denoted as the continuous flow. Additionally, vapor was considered as the dispersed flow. To simulate such a multiphase flow phenomenon, a single-phase mixture model was utilized for silica nanoparticles and liquid water, and the simulation is done by considering the Eulerian–Eulerian approach for silica nanofluid. Furthermore, numerical correlations are proposed based on the results to calculate three different parameters, namely heat transfer coefficient (HTC), bubble departure diameter, and nucleation site density. The finite volume method (FVM) is applied to solve equations. Furthermore, the RPI model is developed to investigate heat transfer. Various nanofluid concentrations and heat fluxes are studied to understand how they affect heat transfer coefficient, nanofluid velocity, and vapor volume fraction. The results showed that the modifications caused by silica nanofluid on the surface could improve the numerical results. Besides, the heat transfer coefficient rose by 49.35% with a nanofluid volumetric concentration of 0.1%. The increasing effect of nanofluid concentration is so dominant at high heat fluxes.
•The innovative thin film boiling was comprehensively compared with pool boiling.•The boiling curve of thin film boiling was delicately divided into three segments.•A hybrid model was set up and the ...results agreed well with experimental tests.•Underlying mechanisms for the unique behavior and ultrahigh heat flux were revealed.
Ultrahigh heat flux of over 1 kW/cm2 can be achieved by a new thin film boiling regime, of which the variation of boiling curve is considerably different from that of pool boiling. However, there is a lack of quantitative analysis for the distinctive thin film boiling. In this work, comprehensive comparison was made between the well-studied pool boiling and the newly-achieved thin film boiling. The boiling curve of thin film boiling was divided into three segments and mathematical models were set up for each segment in a way that correlations for pool boiling were adopted and modified according to the similarity and difference between pool boiling and thin film boiling, respectively. It was found that the modeling results agreed very well with the experimental results, indicating that the hybrid model revealed the underlying mechanism for the unique behavior and ultrahigh heat flux of the thin film boiling. In brief, the higher heat transfer coefficient or larger slope of the boiling curve was related to the special water supply mode of thin film boiling, in which the water flowed vertically through the heat surface and consequently enhanced heat transfer by promoting the spread of superheated layer and the bubbles on the heating surface. As for the ultrahigh heat flux and the unique negative slope of the boiling curve, it was attributed to the very thin yet continuously decreased thickness of the liquid layer, which was another essential feature of the thin film boiling. The hybrid model in this work can provide both quantitative insight for fundamental understanding and future guidance for practical application of thin film boiling.
With the development of simulation technology and programs, it became necessary to study the models that control equations’ solutions and influence the results. The models having control over solving ...equations of multiple phases and materials are investigated. They include (Volume of Fluid (VOF), mixture, Eulerian) controlling the governing equations. The study was conducted depending on the boiling point of the water. The activation of these three models is carried out to find out which one is better for solving the issue of boiling compared to previous numerical and empirical research with the study of the surface tension coefficient that affects the behavior of phases in a contaminated manner. The best model explored in the case of boiling is VOF for the merging of steam bubbles, the velocity of flows 0.257 m/s for both water and steam, and the phase transition. The effectiveness of the VOF model is mirrored by higher efficiency and accuracy of the solution with velocity 0.257 m/s and volume fraction 0.9997. The activation of the surface tension factor 0.072 property simulates the real conditions surrounding the materials used in boiling, but it significantly increases the turbulence and distribution of gas bubbles.
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•Pool boiling of silica nanofluid over an inclined surface was investigated.•Heater orientation has a dramatic effect on pool boiling of nanofluid.•Effect of initial roughness of ...surface on characteristics of boiling was studied.•Boiling heat transfer was enhanced over a nanocoated surface.
Pool boiling of SiO2/water nanofluid over a copper flat plate heater at various inclinations of the heater surface was investigated experimentally. In this work, the effect of heater surface orientation on changes in surface roughness and on the characteristics of nanofluid boiling was studied. We examined pool boiling of silica nanofluid at various concentrations (<0.1vol.%) and various heater orientations from a horizontal state (0°) to a vertical state (90°). The results showed that in nanofluid boiling, increasing the inclination angle of the heater surface from 0° to 90° increases the critical heat flux (CHF) and decreases the boiling heat transfer coefficient (BHTC), while in boiling DI water, both for CHF and BHTC, decreases with the angle of the heater surface. Atomic force microscope images from the heater surface which has been boiled in nanofluids illustrated that surface roughness varies with the orientation of the surface. It was found that deposition of nanoparticles and bubble movements have important effects on nanofluid boiling over inclined surface. In addition, the performance of the boiling of DI water on a nanocoated surface was examined. The results showed that CHF and BHTC increase in comparison with the boiling of DI water on a bare heater.
We use the phase field method to track the gas–liquid interface based on the gas–liquid two-phase flow in the pool boiling process, and study the bubble nucleation, growth, deformation, departure and ...other dynamic behaviors on the heating surface under microgravity. By simulating the correlation between liquid undercooling and bubble dynamics, we find that the bubble growth time increases with the increase of liquid undercooling, but the effect of liquid undercooling on bubble height is not significant. Meanwhile, the gas–liquid–solid three-phase contact angle and the gravity level will also have an effect on the bubble growth time and bubble height. With the increase of the contact angle, the bubble growth time and bubble height when the bubble departs also increase. While the effect of gravity level is on the contrary, the smaller the gravity level is, the larger the bubble height and bubble growth time when the bubble separates.
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•Pool boiling experiment performed on mesochannel, microstructured porous.•The combination of two enhancement techniques was also included.•Mesochannel was cut with EDM method on ...copper surface.•Micro porous coating was fabricated with electrodeposition method.•Boiling curves for water at atmospheric pressure was obtained.•Enhancement mechanisms identified based on nucleation site density.•Bubble-induced liquid motion and increasing surface area were also identified.
Increasing the computational capability of microelectronics and growing miniaturization trend lead to high heat flux hot spots that require efficient thermal management. Pool boiling has the ability to remove large heat fluxes at low wall superheat and this can be further enhanced by using surface modification methods. In this paper, the experimental investigation of nucleate pool boiling heat transfer on copper mesochannel, microstructured porous coating and combination of them is performed. The mesochannel with a width of 400μm and a depth of 500μm is cut with Wire Electric Discharge Machine (WEDM) on copper surface. Microstructured porous coating is prepared by two-stage electrodeposition of copper on polished copper surface. Then by the combination of these methods, porous copper electrodeposited on mesochannel to achieve the high performance boiling surface. The morphology of three samples are examined with Scanning Electronic Microscopy (SEM). The nucleate pool boiling experiments were conducted under atmospheric pressure using a water under saturation conditions and their pool boiling heat transfer performances were compared. It was found that the integration of microporous copper on microchannel surface can effectively enhance the boiling performance. A critical heat flux (CHF) of 170W/cm2 (2.1-fold enhancement) and heat transfer coefficient (HTC) of 23.5W/cm2k (3.9-fold enhancement) was obtained in comparison to plain surface. A visualization study on bubble formation and release from individual plates was conducted to bolster the experimental results.
•Pool boiling heat transfer enhancement with biosurfactant particles deposited surfaces has been reported.•Surface morphology of the surfactant deposited surfaces has been modified.•Surfactant ...treated surfaces show higher roughness and better wettability.•The modified surfaces show 188% enhancement HTC and 152% enhancement in CHF.
The present work reports an experimental investigation of pool boiling of deionized water on a surfactant particle deposited heating surfaces. Heating surfaces made of copper are prepared by depositing surfactant particles through pool boiling of biosurfactant (Rhamnolipid) solutions at different concentrations (100–400 ppm of surfactant particles). Pool boiling experiments of deionized water have been performed with surfactant deposited heating surfaces, and results have been compared with the pool boiling of deionized water on a plain heating surface. Characterization of surfactant deposited heating surfaces indicates the presence of other elements like carbon, oxygen, silicon, chlorine, and potassium. The roughness of surfactant treated surfaces are 4–10 times more than the fresh heating surface, and their wettabilities are more than the fresh heating surface. Surfactant treated surfaces show a maximum 188% enhancement in heat transfer coefficient and 152% enhancement in critical heat flux as compared to the fresh heating surface. Porous structures are formed on the surfactant treated surfaces during boiling with the deionized water, which helps in heat transfer and critical heat flux enhancement through capillary wicking effects at high heat flux. However, no heat transfer enhancement has been observed when fresh pool boiling experiments of biosurfactant solutions have been performed with the surfactant deposited heating surfaces.
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•CHF is enhanced for HPP regardless of heater orientation.•CHF for combination of NDS+HPP showed the most enhanced CHF in literatures so far.•Combined effects of HPP and NDS are key to improving CHF ...performance.
One of the main concerns regarding in-vessel retention (IVR) during a severe accident is guaranteeing sufficient cooling performance to avoid the melt-through of the pressure vessel. In such an event, the vessel is submerged in water, and boiling is occurred to remove the heat. However, the main problem is that there is a limit to the pool boiling heat transfer at the outer surface of the reactor vessel due to occurrence of critical heat flux (CHF) conditions. Therefore, to enhance the capability of IVR in light-water reactors during states of emergency, methods of increasing the CHF should be considered. In our previous study, it was demonstrated that the pool boiling CHF can be increased approximately twofold by simply attaching a honeycomb porous plate to an upward-facing plain heated surface under saturated and atmospheric conditions. On the other hand, it is well known that the CHF for a heated surface is greatly enhanced by nanoparticle deposition because of the resulting improvement in surface wettability. In IVR, it is important to determine the CHF for downward-facing heated surfaces. Therefore, the objective of this paper is to examine the effect of the heater orientation on the CHF in combination with surface modification by honeycomb porous plate attachment and nanoparticle deposition. A pool boiling CHF experiment of water is performed under saturated temperature and atmospheric pressure conditions. Compared with a plain surface, the CHF is shown to be greatly increased by a combination of the honeycomb porous plate attachment and nanoparticle deposition, even under downward-facing heater conditions. Additionally, the CHF enhancement increases as the orientation of the heated surface approaches downward-facing.
