Nucleate Boiling Heat Transfer Research Articles

Experimental study of nucleate boiling heat transfer of refrigerant-oil mixture on various modified surfaces

As a crucial component of refrigeration and heat pump system, the evaporator performance directly affects system efficiency. Due to the lubricating oil in the compressor circulating into the evaporator, studying the nucleate boiling heat transfer (NBHT) of refrigerant-oil mixture is of greater practical and guiding significance. Surface modification technology has opened up a new avenue for enhancing NBHT of refrigerant-oil mixture. Therefore, experimental study was conducted on NBHT characteristics of R134a-POE mixture and R1234ze(E)-POE mixture on smooth surface, initial laser-ablated surface, stabilized laser-ablated surface, machined surface, and composite processed surface. The effects of oil concentration (ω), surface microstructure and surface wettability on NBHT of refrigerant were discussed and analyzed, and the underlying heat transfer mechanisms were elucidated. The research indicates that for NBHT of refrigerant-oil mixture, surface microstructure has a greater impact than surface wettability. To enhance heat transfer coefficient (HTC), it is crucial to establish a surface pattern comprising alternating regions of high and low nucleation sites to mitigate bubble interaction and coalescence. Once this objective is attained, enhancing surface wettability can be contemplated. The addition of oil promotes foaming and induces tornado-shaped bubble group, which facilitate heat transfer. However, the rise in mixture viscosity and surface tension exerts a more pronounced adverse effect on heat transfer, outweighing the positive impacts of foaming and tornado-shaped bubble group. Consequently, the presence of oil diminishes HTC. And as ω and heat flux increase, HTC further decreases. Additionally, the increase in vaporization nuclei on modified surface leads to a higher local ω, the increase in ω further weakens the enhanced heat transfer effect of modified surface, and thus narrows the difference in HTC among various modified surfaces. The research results aim to uncover the mechanisms by which surface wettability, surface microstructure, and lubricating oil affect NBHT of refrigerant.

Experimental and parametric study in pool boiling enhancement with self-induced jet impingement on the microporous copper surface using R1336mzz(Z)

Enhancing pool boiling performance is of significant interest for cooling high-power electronics. This paper introduces a self-induced jet impingement device designed for practical boiling enhancement. Using R1336mzz(Z) as the working fluid, we performed an experimental and parametric study on a microporous copper surface, considering the distinct characteristics of this device. Our results demonstrate that, due to the promotion of bubble detachment and the ensuring of sustained liquid absorption, the self-induced jet impingement device augments the Critical Heat Flux (CHF) on the microporous copper surface effectively. Nonetheless, the large predominant size of nucleation sites on this surface highlights the boiling suppression effect from jet impingement, resulting in a minor decrease in the Nucleate Boiling Heat transfer coefficient (hNB). Parametric evaluations reveal that strategies promoting the circulation flow of working fluid have a positive impact on CHF enhancement. Conversely, this device might negatively influence boiling heat transfer on microporous copper surface under conditions of liquid scarcity due to the restricted total flow area of jet holes. Our study indicates CHF and hNB@CHF enhancements of up to 196.0% and 291.0%, culminating in 73.7 W/cm2 and 78.2 kW/(m2∙K), respectively, compared to the boiling performances of standard pool boiling on the non-microporous copper surface.

Experimental investigation on self-induced jet impingement boiling using R1336mzz(Z)

Pool boiling performance enhancement has attracted considerable interest on high power electronic cooling. In this paper, we introduce a self-induced jet impingement device for practical boiling enhancement, achieved by integrating the guidance tube with an orifice plate. With R1336mzz(Z) as the working fluid, we conduct visualization and parametric investigations on the pool boiling performance, considering the varying characteristics of this device. Visualization snapshots confirm the liquid-vapor separation and indicate that the two-phase flow pattern in the guidance tube eventually stabilizes as a churn-annular flow. Our findings suggest that self-induced liquid jet impingement has a minimal effect on the nucleate boiling heat transfer coefficient (hNB) under a certain heat flux, around 75 % CHF of the standard pool boiling, as the single-phase heat transfer is weakened due to the low thermal conductivity of R1336mzz(Z). As the heat flux intensifies, we observe substantial enhancements in both the Critical Heat Flux (CHF) and the Maximum Nucleate Boiling Heat transfer coefficient (hMNB) resulted from the delayed onset of boiling crisis, owing to the additional liquid supply and the promotion on vapor exhausting. The parametric studies reveal that the flow rate of the liquid jet, amplified by either extending the length or the inner diameter of the guidance tube, or by increasing the number of jet holes, positively impacts the boiling performance. However, these improvements show diminishing returns. Our study shows enhancements in CHF and hMNB of up to 69.5 % and 36.7 %, respectively, compared to the standard pool boiling.

A lattice Boltzmann investigation of the saturated pool boiling heat transfer on micro-cavity/fin surfaces

Saturated pool boiling heat transfer on micro-cavity and micro-fin surfaces is examined by a mesoscopic phase change lattice Boltzmann method. The important interfacial processes and boiling heat transfer performance are explored concerning the effects of micro-structure configurations, specifically fin and cavity, and micro-structure parameters, including fin/cavity shape, height, length, and spacing between fins/cavities. It is discovered that both the micro-cavity and micro-fin surfaces are conducive to bubble nucleation and can enhance nucleate boiling heat transfer (NBHT) when compared with the smooth surface. By comparing fin and cavity surfaces, it is found that micro-cavity is more conducive to bubble nucleation, whereas micro-fin is more conducive to bubble departure. As a result, micro-cavity surface has a higher NBHT while a micro-fin surface has a higher critical heat flux (CHF). The saturated pool boiling heat transmission is significantly influenced by the micro-structure parameters as well, i.e., the boiling on the rectangular cavity/fin surfaces has an earlier nucleation time while that on the conical surfaces has a faster bubble escape speed. The mass of residual bubble left over after the bubble department increases with cavity/fin height, which leads to the advance of CHF. On the other hand, the CHF increases as the distance between micro-structures. Additionally, with the increase in micro-structure length, the CHF increases for the micro-cavity surface whereas decreases for the micro-fin surface. Finally, a series of fitting equations between CHF and the micro-structure parameters are presented and an improved hybrid surface is developed based on the theoretical predictions.

Nucleate boiling heat transfer during water–IN–oil emulsion drop impact onto a heated solid surface

The phenomenon of collision of fuel droplets with the walls of the combustion chamber largely determines the formation of the air-fuel mixture. The main attention in the study is paid to establishing the influence of the hydrodynamic parameters of the drop-wall interaction on the heat transfer during nucleate boiling of a drop of an n-decane-based water-in-oil emulsion. A drop of emulsion impacts onto a quartz glass surface heated to a temperature from 140 °C to 260 °C at Weber numbers (We) from 20 to 1000 and Reynolds numbers (Re) from 250 to 8000. The contact (evaporation) time of liquid droplets is measured experimentally. As a result, it becomes possible to derive an empirical model of the contact time τc, taking into account the dimensionless temperature of the heat exchange surface θ, as well as the main driving forces of the drop-wall interaction (inertia, viscosity and surface tension) at Re from 40 to 3000 and We from 1 to 1085. A complex mechanism of nucleate boiling in an emulsion drop is proposed. It involves injecting an intense vapor flow into a growing bubble from a near-wall microlayer and from the entire surface of the bubble, which is in contact with the n-decane and microdrops of water. An empirical model is introduced to predict the heat flux density at the solid-liquid interface during the contact of emulsion drops with a heated surface at nucleate boiling, q″, and tested at Re from 50 to 8000 and We from 20 to 1000. The empirical models allow evaluating the considered characteristics of heat transfer during the formation of an air-fuel mixture in the combustion chamber of the engine, taking into account the effects of the nucleate boiling nonlinearity and the collision of drops with the wall.

Experimental analysis of pool boiling heat transfer on surfaces fabricated by electric discharge coating

The recent advances in the growth of miniature high power devices have led to the increased need for dissipation of large amount of heat generated in those devices. Compared to single phase cooling techniques, boiling provides a more effective two-phase heat dissipation method. Micro-structures in the boiling surface help to enable higher rate of heat transfer by providing air pockets for bubble generation. The present experimental study involves fabrication of micro-structured surfaces by employing Electric Discharge Coating (EDC) process. The surfaces were prepared by depositing a composite coating of titanium and copper microparticles on a copper surface at different current settings. The surfaces obtained were hydrophobic in nature which resulted in a decrease in the surface superheat at boiling incipient. Pool boiling experiments and analysis were performing on it by using deionized water as the boiling fluid. The Critical Heat Flux (CHF) also improved in the modified surfaces due to the globular structures formed with increased cavity sizes and porosity. The average Nucleate Boiling Heat Transfer Coefficient (NBHTC) increased to 206% and the surface superheat decreased by 42% for the best performing surface.

Thermal management of power electronics using nanofluids and nucleate boiling heat transfer technique

Nucleate boiling is an efficient solution for thermal management of power electronics where high-intensity heat flux needs to be transferred in a compact space. Both micro surfaces and nanofluids are used in literature to enhance the performance of nucleate pool boiling heat transfer systems; however, the effect of nanofluids over the microporous surface still needs to explore in several phase change heat transfer applications. The study’s objective is to examine the performance of nanofluid over microporous surfaces in Nucleate Boiling Heat transfer (NBHT) and performs a comparative analysis with plain and micro-porous surfaces. The study analyzed three ceramic (Alumina) nanofluids for nucleate pool boiling heat transfer (NBHT) over plain and microporous surfaces. The literature reported enhanced performance of nanofluids over the plane surface is verified in the study before proceeding to the detailed analysis over the microporous surface. Three different concentrations of 0.005%, 0.0005%, and 0.00005% were tested for the nanofluid. For plane surface, the critical heat flux (CHF) has been increased to 1035 [kW/m2] for Alumina from 783 [kW/m2] for deionized water, with the average increase in heat transfer coefficient (HTC) being 46.5%. The maximum CHF has been reported for micro-porous surfaces with a value of 1110 kW/m2. Out of the tested surfaces and fluids combination, the micro-porous surfaces with deionized water have been concluded as the most efficient surface with the highest heat transfer capacity for thermal management of high-power electronics and other high heat flux applications.

Molecular Dynamics Study on Enhanced Nucleate Boiling Heat Transfer on Nanostructured Surfaces with Rectangular Cavities

Molecular Dynamics Study on Enhanced Nucleate Boiling Heat Transfer on Nanostructured Surfaces with Rectangular Cavities

Parametric Effects of Heater Size, Contact Angle, and Surrounding Vessel Size on Pool Boiling Critical Heat Flux From Horizontal Surfaces

Abstract Saturated water at one-atmosphere pressure was boiled on horizontal flat copper disks of diameters 1.0, 1.5, and 2.0 cm, respectively. The contact angle was varied from about 10 to 80 deg by controlling thermal oxidation of the disks, while the surrounding vessel size was changed by placing glass tubes of different inner diameters around the disks. Nucleate boiling heat transfer data were obtained up to critical heat flux (CHF), where vapor removal pattern was photographed. Vapor jet diameter and the dominant wavelength at water–steam interface were measured from the photographs for the well wetted disks. For well wetted surfaces, the magnitude of CHF increased when the heater size was reduced from 2.0 to 1.0 cm. Improving the wettability enhanced the CHF substantially, whereas the increased size of the liquid-holding vessel had a smaller effect. The highest measured CHF is 233 W/cm2 or 2.11 times Zuber's CHF prediction for infinite horizontal flat plates. It was obtained on a 1.0-cm-diameter disk of contact angle about 10 deg surrounded by a large vessel. The CHF for this surface was increased from 203 to 233 W/cm2 when the ratio of heater size to surrounding vessel size was decreased from 1 to about 0.

On the wetting behavior of surfaces in boiling

Nucleate boiling heat transfer is strongly influenced by surface wettability as characterized by the Young's contact angle, θY. The contact angle is usually obtained from measurements on sessile droplets on horizontal test surfaces, but in the case of water at high temperatures and pressures, θY values from droplet experiments appear to be typically 30°–50° higher than values needed to explain bubble departure sizes for similar surfaces and temperatures. We explain the differences between θY values for droplets and vapor bubbles by using the surface adsorption theory of Adamson. This theory suggests that in the case of bubble formation in high pressure boiling, as the non-wetted surface inside the bubble is in contact with a saturated vapor, it will be covered by an adsorbed liquid layer of nanoscale thickness. Droplet experiments, on the other hand, generally use autoclaves pressurized by permanent gases in which the vapor pressure is far below saturation: in these relatively dry gases, the adsorbed liquid nanolayer is expected to be absent. We suggest that the presence of the adsorbed layer in the case of vapor bubbles will increase the work of formation of a new wetted surface by an amount comparable to the liquid surface tension, resulting in a significant reduction in θY. We show that by applying Adamson's model with plausible choices for unknown parameters, it is possible to explain the magnitude of the differences in θY in bubble and droplet experiments and to explain why θY appears much less sensitive to surface material conditions in the case of departing vapor bubbles than in the case of sessile droplets. We conclude that θY measurements for sessile droplets on heated surfaces in pressurized gas rather than saturated vapor environments may not be relevant to vapor bubbles and values should not be used directly in models of nucleate boiling.

Heat-transfer characteristics of CO[formula omitted] boiling flow in the regenerative cooling channel of an Mg/CO[formula omitted] powder rocket engine for Mars missions

To solve the problem of thermal protection posed by the long working time of Mg/CO2 powder rocket engines, an experimental system is designed to study the heat-transfer characteristics of liquid CO2 in the regenerative cooling channel. How the heat flux, coolant temperature, mass flux, and back pressure influence the heat-transfer coefficient, the thermodynamic quality, and the gas-phase formation point of nearly saturated CO2 is studied. The heat-transfer coefficient is found to increase with increasing mass flux or decreasing inlet temperature. Higher heat flux increases the rate of bubble formation and promotes nucleate-boiling heat transfer, but it also intensifies the film boiling, thereby degrading the heat-transfer performance. Lower back pressure does not affect the heat-transfer performance in the nucleate-boiling region, but it worsens it in the film-boiling region. It is also found that the classical boiling-heat-transfer models do not predict the experimental heat-transfer coefficient well. Combined with experimental data, how reduced pressure affects heat transfer is considered, and a new empirical correlation formula is proposed for the heat-transfer coefficient of CO2 near saturation. The optimized model can successfully predict 90.23% of the experimental data, and the prediction accuracy is improved greatly. The present research provides a theoretical basis for designing a regenerative cooling scheme for an Mg/CO2 powder rocket engine.

Effects of Water and 50% Ethylene-Glycol Coolant Characteristics on Nucleate Boiling Heat Transfer in IC Engine Cooling System

Effects of Water and 50% Ethylene-Glycol Coolant Characteristics on Nucleate Boiling Heat Transfer in IC Engine Cooling System

Effects of LLC Flow Characteristics and Surface Roughnesses on Nucleate Boiling Heat Transfer Mechanisms in IC Engine Cooling System

Effects of LLC Flow Characteristics and Surface Roughnesses on Nucleate Boiling Heat Transfer Mechanisms in IC Engine Cooling System

Nucleate boiling heat transfer of R-134a and R-134a/POE lubricant mixtures on smooth tube

The present study examines the influence of polyolester lubricant oil (POEA-68 and POEA-170) with R-134a on the nucleate pool boiling performance for a horizontal smooth tube. The heat flux ranges from 10 kW/m2 to 90 kW/m2 and the lubricant mass fraction varied from 1% to 10% at a saturation temperature of 10 °C, 0 °C and, −6 °C, respectively. The experimental results show that the heat transfer coefficient (HTC) of the pure refrigerant is increased with an increase in saturation temperature. But the presence of lubricant oil alters the HTC considerably. The addition of 3% POEA-68 lubricant shows the highest 29.3% HTC enhancement relative to pure refrigerant at a supplied heat flux of 70 kW/m2 and at a saturation temperature of 0 °C. Whereas for R-134a/POEA-170 lubricant mixture at 3% of mass fraction, the highest enhancement in HTC was around 26% at a supplied heat flux of 70 kW/m2 and −6 °C saturation temperature. The bubble size is reduced and the bubble density is increased appreciably with the addition of POE oil. It was observed that the HTC of lubricant-refrigerant mixtures differs appreciably with the variation of lubricant oi mass fraction (ω). The HTC first decreases at a very low mass fraction (ω≤1%), followed by an appreciable increase in the range of 1% ≤ ω ≤ 3%, and finally reveals a continuous decline for the higher mass fraction. The dramatic decrease in HTC for lubricant-refrigerant mixture is associated with mass transfer resistance and a significant increase in surface tension.

Urban concentrated photovoltaics: Advanced thermal management system using nanofluid and microporous surface

Distributed clean energy generation through solar radiation has always been considered as the best available potential, however its successful and effective implementation in within the built urban environment is restricted with technological limitations in materials, heat transfer, high cost and limited installation space. Among various solar energy options, Concentrated Photovoltaic (CPV) technology required low installation area due to its high efficiency. Efficient thermal management for CPV system could furthur enhance its cell efficiency and maximum concentration ratio, which results in lowering its cost and installation area. A unique combination of nanofluid over microporous surface has been tested in Nucleate Boiling Heat Transfer (NBHT) system, as a thermal management technique for CPV. The performances of the NBHT system is tested and comparatively analyzed for microporous surfaces, nanofluid, and hybrid-micro nano surfaces. During testing of nanofluid over a microporous surface, the deposition of nanoparticles resulted in blocking of micropores and disturbed the original enhancing phenomena. The decrease in performance is observed with an increase in the concentration of nanofluid: 0.0001%, 0.001%, and 0.01%. Microporous surfaces with deionized water as working fluid resulted in maximum performance enhancement, in critical heat flux (CHF) and heat transfer coefficient (HTC). Compared to the standard plain surface (P), the CHF of the microporous surface increased by 62%, from 690 kW/m2 to 1120 kW/m2, while the average increase in HTC is 101%. The experimental results from NBHT experiments are then coupled with an analytical model for the corresponding CPV performance of electrical efficiency, maximum concentration ratio, and required installation area.

Performance evaluation of self-cooling concentrating photovoltaics systems using nucleate boiling heat transfer

Abstract In this study, nucleate boiling heat transfer (NBHT) based self-cooling thermal management system is designed and thermodynamically analyzed for high concentrating photovoltaics (CPV). The overall self-cooling system, consisting of two rows of CPV i.e. CPV 1 and CPV 2, iscoupled with the absorption cooling (AbC) system. Thermal energy from CPV 1 is supplied to AbC system to produce cooling, which is then used to reduce the temperature of CPV 2. Both CPV systems work simultaneously under the same solar energy conditions, hence, the demand and supply of energy are continuously in phase. Under the designed conditions, CPV 1, with an installed capacity of 66.4 kW, an operating temperature of 375.3 K and electrical efficiency of 35.5%, has the ability to cool down about 50.6 kW of CPV 2 system with an operating temperature of 335.8 K and 37.5% of electrical efficiency. A parametric study is performed to analyze the performance of the overall system at various working conditions and installed capacities. Furthermore, the designed system is analyzed for two different types of multi-junction solar cells and three different types of coolants: water, ethanol, and n-pentane. Due to higher latent heat, water has been proven to perform better working fluid with higher ability of concentration ratio. The optimum NBHT operating temperatures for CPV1 and CPV2 were found to be about 353 K and 349 K with maximum overall system efficiency of 36.64%.

Nucleate boiling heat transfer and critical heat flux (CHF) from micro-pit surfaces

This paper studies pool boiling enhancement on the micro-pit surfaces. Microscale pits fabricated on plain surface are able to reduce boiling incipience superheat, and improve both nucleate boiling heat transfer coefficient and critical heat flux (CHF). Boiling enhancement magnitudes have a weak dependence on the micro-pit diameter, but increase monotonously with decreasing the pit depth. There exists an optimum pit-to-pit spacing for the maximum boiling enhancements, which is virtually identical to bubble departure diameter, and estimated using the capillary length. The major mechanism behind is that this spacing is favorable for alleviating hydrodynamic instabilities induced by the counterflow between liquid inflow and vapor outflow. The highest heat transfer coefficient and CHF using water as fluid under the present conditions are 70.0 kW/m2K and 165.7 W/cm2, improved by 58.8% and 33.7% compared to the plain surface, respectively, at micro-pit diameter of 100 μm, depth of 100 μm and spacing of 2.5 mm. Finally, a correlation devised for predicting the nucleate boiling heat transfer coefficient on the micro-pit surfaces by incorporating dimensionless pit depth is proposed, with MAE of 8.3%.

Effects of Coolant Flow Characteristics and Channel Surface Temperature on Nucleate Boiling Heat Transfer in IC Engine Cooling System

Effects of Coolant Flow Characteristics and Channel Surface Temperature on Nucleate Boiling Heat Transfer in IC Engine Cooling System

A Review of Modern Methods for Enhancing Nucleate Boiling Heat Transfer

The main results obtained for the last decade in studying the possibilities of enhancing boiling heat transfer and increasing critical heat fluxes are reviewed. Heat transfer enhancement methods involving the use of a modified/structured boiling surface obtained by means of mechanized processing, electrochemical technologies, plasma and ion deposition, laser emission, and subcooled liquid boiling are considered.

Nucleate boiling heat transfer performance of different laser processed copper surfaces

ABSTRACTPresent study reports the nucleate pool boiling characteristics of micro structured copper surface developed by utilizing two different laser systems, namely, pulsed Nd:YAG laser and continuous wave laser. Tests are conducted at atmospheric pressure and saturation temperature by using water as pool liquid. Enhancement in heat transfer coefficients was observed over all laser processed surfaces. The maximum enhancement in heat transfer coefficient was found to be 136% and 93% for the micro structured surfaces developed by using continuous wave and pulsed laser, respectively, compared to the reference smooth surface. The enhancement in heat transfer performance of micro structured surfaces are due to the presence of surface pores, grooves and micro cavities generated due to laser melting process.