•This review explores passive enhancement of pool boiling using surface modification.•Examined are macrosacle, microscale, nanoscale and multiscale (hybrid-scale) techniques.•Addressed are ...performance goals of inhibiting incidence hysteresis and increasing both nucleate boiling heat transfer coefficient and CHF.•Shown is that micro and nano surface features are susceptible to blockage and changes in performance over time.
This paper provides a comprehensive review of published articles addressing passive enhancement of pool boiling using surface modification techniques. They include macroscale, microscale, and nanoscale surfaces, as well as multiscale (hybrid-scale), and hybrid-wettability techniques. Different enhancement methods are assessed in terms of underlying fluid routing mechanisms and ability to achieve three distinct heat transfer goals: eliminating incipient boiling hysteresis, increasing nucleate boiling heat transfer coefficient, and ameliorating critical heat flux (CHF), especially for inert dielectric coolants that are both highly wetting and possess relatively poor thermophysical properties. While different enhancement scales are shown to provide different degrees of success in achieving the three goals, it is shown that both microscale and nanoscale surface features are susceptible to blockage, resulting in deterioration of the enhancement over time. This review also points to scarcity of sufficiently sized databases for a given enhancement scheme in terms of fluid type, surface material, size, and orientation, enhancement shape, pattern, and scale, and operating pressure. This renders available findings less-than-adequate tools for design of practical cooling systems.
•Three-dimensional pseudo potential lattice Boltzmann model is built up to study boiling on two-tier hierarchical structured surface.•Mechanism of accelerated bubble departure on hierarchical ...surfaces with upward-orientation secondary pillar is revealed.•Lateral-orientation secondary structures can deteriorate heat transfer and bring larger flow resistance.•Hierarchical structured surface with upward-orientation secondary pillars achieves best boiling performance at high wall temperature.
In this paper, pool boiling on two-tier hierarchical structured surface is investigated with three-dimensional LB method. Two-tier pillar structures with different scales are designed, termed as primary and secondary pillar, respectively. On the hierarchical surface with upward-orientation secondary pillars, the bubble departure is promoted. And, the heat transfer can be improved by increasing the primary pillar spacing and enhancing surface wettability. Increasing the height of secondary pillar is favorable for enhancing capillary wicking, but can also bring greater flow resistance. On the hierarchical surface with lateral-orientation secondary pillars, the heat transfer is limited by the large flow resistance. With the enlargement of primary pillar spacing, the impact brought by flow resistance is moderated, and the heat flux can be enhanced. Finally, the boiling performance regarding the effect of wall temperature is concerned, where the structured surface with upward-orientation secondary pillars show the better boiling performance than other structured surfaces.
•An experimental study of nucleate pool boiling amelioration is investigated considering four-step electrodeposited micro/nanostructured porous surface.•Effects of etched surfaces, strip pattern, ...checkered pattern and effective surface area are studied.•Pool boiling augmentation mechanism based on visualization of bubble dynamics on surfaces is exhibited.•Heat transfer coefficient enhancement of up to 181% is achieved.
Boiling is regarded as the most efficient process for heat transfer, which received great attention for the usage in wide range of applications. Hence, many efforts have focused on improving the pool boiling process by varying the physical and chemical characteristics of the surfaces through different procedures such as generating porosity and enhancing wettability. This paper, presents an experimental investigation of improved pool boiling performance of distilled water in atmospheric pressure through four-step electrodeposition of micro/nano porous on patterned copper surfaces. Before the initiation of electrodeposition process, the samples are etched through photolithography procedure. The surfaces are analyzed by the images of scanning electronic microscopy (SEM), also open and interconnected porous surfaces, which are covered by micro grains of different sizes are observed. Moreover, the influence of different parameters including etched surfaces, strip pattern, checkered pattern as well as the effective area of the surface have been evaluated. The obtained experimental results revealed the enhanced heat flux as a result of capillarity performance of the surface, which was compatible with the increase in the heat flux. Furthermore, the increased bubbles departure frequency besides the amplified nucleation sites density (NSD) in accordance with the augmented effective surface and porosity were demonstrated. Additionally, it was found that the maximum heat flux and heat transfer coefficient (HTC) equal to the respective values of 112.4 W/cm2 and 16.1 W/K.cm2 were attributed to the four-step electro-deposited porous surfaces at room temperature. Hence, approximately 181% enhancement was achieved compared to the usage of plain surface.
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•Ultra-high pool boiling performance with selectively sintered open microchannels.•CHF of 420W/cm2 at wall superheat of 1.7°C with HTC of 2.9MW/m2°C was obtained.•Studied the effect of channel width ...on selectively sintered open microchannels.•Driving heat transfer mechanisms are identified for wide and narrow channels.
Recent developments in the microelectronics industry has placed increasing demand on developing high heat flux removal systems. Pool boiling offers a simple technique without introducing complicated header configurations and moving parts. Enhancement in pool boiling is achieved by delaying critical heat flux (CHF) and increasing heat transfer coefficient (HTC), which dictates the heat removal capability of a surface. This study focuses on the effect of channel width on the performance and heat transfer mechanisms on open microchannel surfaces with three coating configurations: (i) sintered-throughout, (ii) sintered-fin-tops, and (iii) sintered-channels. Pool boiling performance is obtained with water at atmospheric pressure for 300μm, 500μm and 762μm channel widths. The separate liquid–vapor pathways in narrow channels, with sintered coatings only inside the channel, yielded an unprecedented performance with a CHF of 420W/cm2 based on the 1cm2 projected area at a wall superheat of 1.7°C at the fin top surface, resulting in an HTC of 2.9MW/m2°C. High speed videos were taken to understand the underlying mechanism. Furthermore, liquid–vapor pathways were identified to explain the parametric trends observed for each selectively enhanced configuration set.
Direct cooling with inert and hazards free dielectric liquids may well become the method of choice for thermal management of future electronic systems. Owing to the efficiency of phase-change process ...and the ease of natural circulation, pool boiling is of great interest for this application. The present review consolidates a large number of pool boiling experimental data for dielectric and other highly wetting liquids subject to engineered surfaces with elaborating the related augmentation mechanisms. Potential micro/nano engineered surfaces are categorized into one-dimensional (either CHF or HTC enhancing) and two-dimensional (both CHF and HTC) enhancement surfaces. The enhancement mechanisms along with the bubble dynamics of these enhanced surfaces are discussed briefly. Furthermore, a general classification of electronics coolants (dielectric, non-dielectric, and nanofluids) along with their thermophysical properties is made; especially the problems associated with the dielectric liquids are discussed. Finally, the potential mechanisms for higher HTCs and CHFs are identified.
•Effect of ranged pressure 0.9 to 97 kPa on CHF of Novec7100 pool boiling is studied.•Although CHF decreases with decreasing pressure, trend differed in low pressure range.•New trend showing CHF ...minima at saturation temperatures around 0 °C, is shown.•Difference between experiment and zuber correlation increased with decreasing pressure.•Self-induced subcooled boiling caused by the static pressure of the liquid is discussed.
Highly efficient cooling is an urgent requirement with the development of miniaturization and high heat generation in electronic and electrical devices. Generally, a dielectric fluid is used as the working fluid for immersion cooling technology with boiling heat transfer, which has great potential to solve the requirement. However, basic knowledge of the boiling heat transfer under a wide range of thermal conditions is lacking, especially for low-pressure conditions, and this is important in low-temperature environments. In this study, a widely used dielectric fluid was adopted, and its boiling heat transfer characteristics under subatmospheric pressure were investigated experimentally. An airtight boiling vessel was designed to control the saturation temperature of the test fluid, and pool boiling experiments for the Novec 7100 were conducted for saturation temperatures from −40 °C to 60 °C. The Novec 7100 boiling heat transfer deteriorated with decreasing saturation temperature. With the decrease in saturation temperature, the critical heat flux (CHF) first decreased and then slightly increased under a saturation temperature lower than 20 °C, indicating the underestimation of conventional correlations. Visualization showed that “self-induced subcooled boiling,” with the static pressure of the liquid layer upon the boiling surface having a similar magnitude to the vapor saturation pressure, occurred. This is considered the major reason for the CHF enhancement under low pressure.
•Aluminum-based micro pin fins are proposed to enhance the pool boiling of the refrigerant R1233zd(E).•The effect of the scale of micro pin fins on the pool boiling of R1233zd(E) is experimentally ...studied in ther range of 100 μm-500 μm.•The maximum values of heat transfer coefficient (HTC) and critical heat flux (CHF) are respectively realized by 100 μm and 150–200 μm micro pin fins.•A prediction model for the CHF of R1233zd(E) boiling on micro pin finned surfaces is given.
With the continuous development of chip integration and information technology, the heat dissipation has become a major limitation on the performance of electronic devices such as 5 G base stations, data centers and so on, and meanwhile a challenge of conventional single-phase convection cooling methods. Boiling shows prospective in high heat flux cooling and energy saving due to the utilization of latent heat. R1233zd(E), an environmentally friendly refrigerant (GWP=1, ODP=0) with a freezing point of -107 °C, is a potential working fluid in phase-change heat sinks for geographical applications. Nevertheless, the poor boiling performance of R1233zd(E) on plain surface due to the limitations in thermophysical properties must be enhanced. Moreover, conventional heat sinks are mostly copper-based, which makes them inconvenient for transportation and installation, and costly for production as well. In this work, micro-pin fins in the range of 100–500 μm are fabricated on the aluminum surface to enhance the pool boiling of R1233zd(E). Moreover, the influence of their size and saturation pressure on the bubble behavior, critical heat flux (CHF) and heat transfer coefficient (HTC) is experimentally and theoretically investigated. The results show that the increase of pressure, as well as the ensuing various nucleation sites and capillary effect to rewet the evaporation region, can lead to an increase in the CHF and HTC. Notably, the 150–200 μm micro pin-finned surfaces reach the highest CHF and 100 μm one owns the highest HTC, which is 214 % and 383 % higher than that of plain surface, respectively. By considering the balance of capillary effect and bubble convolution effect, a model of CHF is proposed to reveal the mechanism of the optimum size of the micro pin fins. The predicted CHFs have an inaccuracy of less than ±20 % compared to experimental values. This paper makes up for the lack of basic experimental data on pool boiling of R1233zd(E) on aluminum surface, which thus provides guidance for the design of phase-change heat sinks such as thermosyphons, 3D vapor chamber (3D-VC) and microchannels.
•Ammonia/Fe3O4 nano-refrigerant is used to improve the pool boiling HT in a nanochannel.•The presence of an external magnetic field.•Using the molecular dynamics (MD) simulation.•Boiling behavior can ...be perceived in the nano-refrigerant by changing the external HF.•As the external HF increases, the maximum velocity increases.
Pool boiling is distinguished by its capacity to eliminate excessive heat fluxes (HFs) at low temperatures. In recent decades, the optimal design of flooded evaporators elevated the significance of pool boiling HT with refrigerant to conserve natural resources and energy. The industry highly regards this process on account of its superior heat transfer (HT) coefficient in comparison to other HT mechanisms. Among the types of boiling, pool boiling has a special place due to its ability to remove HFs at low temperatures. This study was the first to investigate the boiling characteristics of the ammonia/Fe3O4 nano-refrigerant in a copper (Cu) nanochannel (NC) through molecular dynamics (MD) simulations. The primary goal was to investigate the effect of external HF (EHF) and external magnetic field amplitude (EMFA) on nanostructures' atomic behavior (AB) and thermal behavior (TB). The research findings indicate that increasing the applied EHF led to increased particle movement and the HT rate. By changing the EHF, boiling behavior in the nano-refrigerant may also be seen. Maximum (Max) velocity (Vel.) increased to 8.970 Å/ps when the EHF increases to 0.5 W/m2. Atomic collisions and particle mobility both increase when the EHF increases. Therefore, the maximum temperature value increases to 359.46 K. When the EMFA applied to the nano-refrigerant reaches to 0.5 T, the maximum values of the parameters, such as the Temp. and the velocity, reach to 410.07 K, and 11.802 Å/ps, respectively.
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This paper presents a proposition of a dual grid (DG)-based coupled deep reinforcement learning (DRL) and computational fluid dynamics (CFD) method for active flow control. The DG-DRL-CFD method uses ...a dual-resolution grid, with a coarser grid for the training phase and a finer grid for the testing phase of the DRL-CFD method. Further, after a validation study for our DRL-CFD-based parallelized in-house solvers, this paper presents a performance study for a periodic suction/ejection-based drag reduction for a cylinder in a channel-confined flow. Using an immersed boundary method for CFD on a Cartesian grid, this novel DG-DRL-CFD method is shown to result in almost same accuracy (within 1%) in a substantially reduced computational time as compared to the traditional DRL-CFD method (on the finer uniform grid). Finally, using a sharp interface level set method for an axisymmetric two-phase flow, this paper presents an application of the DR-DRL-CFD method for an oscillating base plate-based enhancement of heat transfer during nucleate pool boiling. As compared to our recent CFD study-based parametric study for the nucleate pool boiling problem, the present DG-DRL-CFD method leads to a profile and frequency of plate-oscillation that results in a larger value of average Nusselt number Nuavg for the plate. The coupled DRL-CFD method leads to plate oscillation profile giving higher enhancement in Nuavg, compared to an open-loop control strategy that involves a parametric sweep involving multiple simulations.
•A dual grid (DG) based novel method is proposed which couples deep reinforcement learning and CFD for active flow control.•The method is validated on the problem of flow past cylinder with suction/ejection based drag reduction.•The method is applied to nucleate boiling with oscillating base plate where plate position is controlled using DRL.•The enhancement of Nusselt number is found to be higher than open-loop control strategy that involves a parametric sweep.
•A series of pool boiling tests was conducted on CuO/H2O nano-suspensions.•Surface was modified using CNC machine to produce uniform fins.•The HTC value was quantified and bubble formation was ...studied.•Fouling formation was evaluated over 1000 minutes of operation.•Behaviour of the system was also analysed over a steady state condition.
In the present research, the general aim is to understand further the potential effect of the surface shape and geometrical specification of rectangular parallel fins developed on the surface on the heat transfer coefficient, bubble formation, and fouling of the nanoparticles. To achieve this, the boiling thermal performance of the copper oxide nano-suspension (NS) was quantified on the modified surfaces with different geometrical specifications, including the width and height of the fins and space between fins. Results showed that the designed fins reduce the rate of the fouling of the nanoparticles on the boiling surface such that the best thermal performance was achieved for the surface modified with the fins with more towering height and smaller width. Also, the fouling thermal resistance was found to follow an asymptotic behaviour while developing three regions of inception, growth, and equilibrium. During the inception of fouling, negative values were measured for the fouling thermal resistance, which was attributed to the enhancement in the specific surface area and thermal performance of the system. Overall, the presence of the fins improved the thermal performance of the system in comparison with the plain surface.
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