Critical Heat Flux Enhancement Research Articles

Critical heat flux enhancement using composite porous structure produced by selective laser melting

• Uniform porous structures (with single pore size) and Composite porous structures（with two different pore sizes) are fabricated by selective laser melting. • Composite porous structure has the best heat transfer performance. • Critical heat flux enhancement of up to 3.2 times is achieved. • Gas-liquid flow characteristics of the composite porous structure is analyzed. Cross scale composite porous structures have been proved to have a better effect on enhanced boiling heat transfer. Accurate control of composite pore size and porous structure thickness is important for the study of enhanced boiling heat transfer. In this study, composite porous structures were manufactured with selective laser melting (SLM) technique from aluminum alloy (AlSi10Mg) powder. The heat transfer characteristics of a composite porous structure with composite pores (0.6 mm small pores and 2 mm large pores) for pool boiling under atmospheric pressure were investigated. A comparative analysis was performed with the uniform porous structure (0.6 mm pores) and the composite porous structure. The results shown that the composite porous structure can significantly increase the critical heat flux (CHF) compared to the plain copper surface. The CHF of the composite porous structure was higher than that of the uniform porous structure with the same height. As the height increases, the nucleate boiling heat transfer performance with composite porous structures will decrease, due to the larger gas–liquid resistance as a result of the height increment. In the range of 1.5–4.5 mm studied in this research, the 1.5 mm high composite porous structure achieves the maximum increase in CHF. The maximum CHF was 346.6 W/cm 2 , which was 3.2 times that of the plain surface. The large pores in the composite porous structure can play a role of shunting to reduce the escape resistance of the bubbles, which can further enhance CHF.

Effect of Nanofluids on the Enhancement of Boiling Heat Transfer: A Review

Boiling heat transfer can play a vital role in the two-phase flow applications. The analysis of the boiling hat transfer enhancement is of importance in such applications and the enhancement can be mostly conducted by using various active and passive techniques. One type of passive techniques is the enhancement of heat transfer by nanofluids. This article presents an extensive review on the effect of different nanofluids on the enhancement of heat transfer coefficient (HTC) and critical heat flux (CHF) for both pool as well as flow boiling. Nanoparticles addition to a working fluid is done arbitrarily to improve the thermophysical properties which in turn improves heat transfer rate. Numerous works have been done in the studies on nanofluid boiling. Among various nanoparticles, the most frequently used nanoparticles are Al2O3 and TiO2. In the case of binary nanoparticles, the most commonly used combination is Al2O3 and TiO2. After reviewing the relevant literatures, it is found that for pool boiling, the maximum HTC is increased to 138% for TiO2 nanoparticles and the maximum CHF is increased to 274.2% for MWCNTs. Conversely, in flow boiling the maximum HTC is increased to 126% for ZnO nanoparticles and the maximum CHF increased to as 100% for GO nanoparticles. In addition, when two or more nanoparticles in succession or binary nanofluids are used the CHF in pool boiling increased up to 100% for Al2O3 and TiO2 as well as the CHF in flow boiling increased up to 100% for Al2O3, ZnO, and Diamond. Though the information of the coefficient of heat transfer and the critical heat flux varied for different nanofluids and vary from experiment to experiment for each of the nanofluids. This variation happens because the coefficient of heat transfer and the critical heat flux in boiling is dependent upon several factors.

Method for calculating the critical heat flux at pool boiling on structured surfaces

A method of the critical heat flux enhancements at pool boiling using rough structures of various regular and irregular geometries is investigated. The experimental data are compared, and the critical heat flux is calculated since the V. V. Yagov model, which considers the additional inflow of liquid into the evaporation zone due to the action of capillary forces in the porous space. Based on the comparison of experimental and calculated data, it is concluded that the model is not universal for all microstructured surfaces. Recommendations for the calculation are given.

Flow boiling critical heat flux enhancement via different-mode-interacting boiling in narrow gaps

Flow boiling heat transfer has the potential to achieve the required phase-change performance cooling in narrow gaps. To further improve the critical heat flux (CHF) and heat transfer coefficient (HTC) in flow boiling, a method of different-mode-interacting boiling (DMIB) involving the interaction between neighboring boiling of different heat flux areas or different modes of nucleate and film boiling was utilized. We employed a nonuniform heating plate, in which copper and Polytetrafluoroethylene (PTFE) with different thermal conductances were alternately arranged near the upper surface to achieve a spontaneous nonuniform temperature distribution. Experiments were performed using a square heating surface (10 mm × 10 mm) with two material widths (W) of different materials. The results were compared with a uniform plate using deionized water as working fluid under the conditions of inlet subcooling ΔTsub = 2.0, 10, 20, and 30 K, flow velocity v = 0,1, 0.2, and 0.4 m/s, and gap size h = 1.0, 2.0, and 5.0 mm. The nonuniform surfaces of W = 0.5 and 1.0 mm are found to significantly enhance the CHF at all values of v, ΔTsub, and h. The enhancement of CHF and HTC was owing to the high efficiency of the DMIB and reasonable liquid supply on the nonuniform surfaces. In addition, v and ΔTsub had a significant effect on the CHF and HTC, whereas the trends were identical. The reduction in v and ΔTsub could increase the ratios of CHF, where the highest enhancement ratio achieved was 89% at h = 1.0 mm, ΔTsub = 2.0 K, and v = 0.1 m/s. Moreover, increments in v and ΔTsub led to higher HTC enhancements, whereas the highest ratio increased by a factor of 12 at h = 5.0 mm, ΔTsub = 30 K, and v = 0.4 m/s.

CHF enhancement of downward-facing saturated pool boiling on the SCGS-modified surfaces with multi-scale conical pin fin structures

Enhancing the critical heat flux (CHF) of external reactor vessel cooling (ERVC) to achieve the strategy of in-vessel retention (IVR) has been deemed as an essential requirement for the security of modern commercial PWR nuclear power plants. A new type of multi-scale conical pin fin structures had been designed to meet this need. These conical structures of four different axial heights (1.0, 1.5, 2.0 & 2.5mm) and similar radial geometric parameters were fabricated on four heating surfaces of copper substrates by supersonic cold gas spray technique (SCGS), and the conical pin fin structures were combined with a thin layer of micro porous structures. Transient-state (quenching) and steady-state (heating) pool boiling experiments had been respectively conducted on 6 different downward-facing surfaces under different inclination angles including 5°, 30°, 45°, 60°, 75° & 90° (in vertical), which included above-mentioned four pin fin surfaces, a plain surface and a coated surface covered with a 1mm-thick layer of uniform porous coating fabricated by SCGS with copper particles. The experimental results showed that the CHF increased with the inclination angles. The CHF of all the SCGS-modified surfaces were significantly enhanced compared with those of the plain surface. The maximum CHF value and the maximum CHF enhancement belonged to the 2.0mm-height pin fin surface whose CHF values were more than 1.7 times of those of the plain surface, and up to 2.1 times in 90°. The 1.0mm pin fin surface had the greatest performance in boiling heat transfer coefficient (HTC) and its CHF-enhancing performance also greatly exceeded that of 1.0mm uniform porous coating surface. Remarkable performances of multi-scale conical pin fin structures had been experimentally confirmed, hence the safety margin of IVR-ERVC will be greatly enhanced after adopting them. In addition, the CHF enhancement mechanism of the multi-scale conical pin fin structures was analyzed.

Study on boiling heat transfer of surfactant solution on grooved surface

In the present study, the coupling effect of wire-cutting grooved surface and surfactant (Sodium dodecyl sulfate, SDS) in pool boiling heat transfer is studied experimentally. Based on visualization, the bubble growth at the onset of bubble formation is measured, and the results are found to yield the reported empiric laws in the functional form of heat diffusion growth. In addition, the surfactant is found to improve the bubble nucleation on the heated surface with a shorter growth time and smaller departure diameter. Moreover, the grooved surface is also easier to nucleate than the smooth one, that is, the onset of bubble formation on the grooved surface is advanced, and thus the coupling effect further enhances the bubble nucleation. For the heat transfer, the SDS solution presents good heat transfer performance at low and medium heat flux in comparison to the DI water, and the coupling effect with the grooved surface would lead to further enhancement, by which the heat transfer coefficient (HTC) is maximally increased by about 238%. In addition, there are three main forms of bubbles found during the boiling of SDS solution, including small bubbles, discrete bubbles and large bubbles. The discrete bubbles are found to be formed by the entrainment of the upper foam due to the liquid convection. At relatively high heat flux, there is bubble crowding in the boiling of surfactant solution, accompanied by the expansion and contraction of bubble clusters and significant fluctuation of near-wall temperature. Furthermore, the bubble crowding seems to cause the premature dryout and the low critical heat flux (CHF), and could be attributed to the good nucleation ability and the repulsion between bubbles, which also result in the heat transfer enhancement of SDS solution in low and medium heat flux. Therefore, the enhancement of HTC and CHF cannot be achieved simultaneously in the present method.

Spray Cooling on Enhanced Surfaces: A Review of the Progress and Mechanisms

Abstract The rapid development of high-power electronic, energy, and propulsion systems has led us to the point where the performances of these systems are limited by their cooling capacities. Current electronics can generate heat fluxes up to 10–100 W/cm2, and heat flux over 1000 W/cm2 needs to be dissipated with a minimum coolant flow rate in next-generation power electronics. The multiple efficient heat transfer mechanisms have made spray cooling a high heat flux, uniform and efficient cooling technique proven effective in various applications. However, the cooling capacity and efficiency of spray cooling need to be further improved to meet the demands of next-generation ultrahigh-power applications. Engineering of surface properties and structures, which is enabled by state-of-the-art manufacturing techniques, can fundamentally affect the liquid–wall interactions in spray cooling, thus becoming the most promising way to enhance spray cooling. However, the mechanisms of surface-enhanced spray cooling are diverse and ambiguous, causing a lack of clear guiding principles for engineered surface design. Here, the progress in surface engineering-enhanced spray cooling is reviewed for surface structures of millimeter, micrometer, and nanometer scales and hierarchical structured surfaces, and the performances from the reviewed literature are evaluated and compared. The reviewed data show that spray cooling can achieve a critical heat flux (CHF) above 945.7 W/cm2 and a heat transfer coefficient (HTC) up to 57 W/cm2K on structured surfaces without the assistance of secondary gas flow and a CHF and an HTC up to 1250.1 W/cm2 and 250 W/cm2K, respectively, on a smooth surface with the assistance of secondary gas flow. A CHF enhancement up to 110% was achieved on a hybrid micro- and nanostructured surface. A clear map of enhancement mechanisms related to the scales of surface structures is proposed, which can help the design of engineered surfaces in spray cooling. Some future concerns are proposed as well. This work helps the understanding and design of engineered surfaces in spray cooling and provides insights for interdisciplinary applications of heat transfer and advanced engineering materials.

Numerical investigation on the effects of non-gaussian random and regular textured rough surface on critical heat flux

Modified surfaces with rough structure have been widely employed to enhance the critical heat flux (CHF) in the heat transfer engineering. Since any structure diagram in its intersecting surface can be treated as spectrum/signal in 2D dimensions, and any spectrum in time domain and in frequency domain can be transformed into sine transforms by the Fourier. Thus, in this article, the effects of the non-gaussian random rough surface and the ordered sine function structured surface were investigated on the CHF enhancement using the fast Fourier transform (FFT) method and the hybrid thermal lattice Boltzmann method (LBM). It finds out that for the non-gaussian random rough surface, CHF is enhanced with decreasing the skewness of the surface. The enhancement seems limited with further reduced the skewness. Besides, the CHF enhancement will be improved by increasing surface wettability. For regular textured surfaces, increasing either the amplitude or the periodicity of the surface structures initially increases the CHF and then the enhancement is impeded with further increase. It concludes that there exists an optimal design of the surface morphology with either non-gaussian random structure or the ordered sine function structure for the CHF enhancement in pool boiling.

Burnout Investigation of Small Diameter Tubes Immersed in Nanofluids

This paper deals with research into pool boiling critical heat flux (CHF) of water–Al2O3, water–TiO2 and water–Cu nanofluids on horizontal stainless steel tubes. The experiments were conducted under atmospheric pressure. Nanoparticles were tested at concentrations of 0.001%, 0.01%, 0.1% and 1% by weight. Ultrasonic vibration was used in order to stabilize the dispersion of the nanoparticles. Although dispersants were not used to stabilize the suspension, the solutions tested showed satisfactory stability. Experimental measurements were performed with stainless steel tubes of three outside diameters: 1.6, 3 and 5 mm. Enhancement of CHF was observed to be independent of the concentration and material of the nanoparticles and tube diameter, with simultaneous heat transfer degradation. Built up during the boiling process, nanolayers improve substantially the heating surface wettability. A correlation is suggested for the CHF prediction during pool boiling of nanofluids.

Liquid film-induced critical heat flux enhancement on structured surfaces.

Enhancing critical heat flux (CHF) during boiling with structured surfaces has received much attention because of its important implications for two-phase flow. The role of surface structures on bubble evolution and CHF enhancement remains unclear because of the lack of direct visualization of the liquid- and solid-vapor interfaces. Here, we use high-magnification in-liquid endoscopy to directly probe bubble behavior during boiling. We report the previously unidentified coexistence of two distinct three-phase contact lines underneath growing bubbles on structured surfaces, resulting in retention of a thin liquid film within the structures between the two contact lines due to their disparate advancing velocities. This finding sheds light on a previously unidentified mechanism governing bubble evolution on structured surfaces, which has notable implications for a variety of real systems using bubble formation, such as thermal management, microfluidics, and electrochemical reactors.

Composite porous surfaces of microcavities for enhancing boiling heat transfer

Enhancing boiling heat transfer by surface modification has the potential to increase the efficiency of energy systems and to address thermal management bottlenecks in electronics. In order to realize simultaneous enhancement of critical heat flux (CHF) as well as heat transfer coefficient (HTC) for boiling heat transfer processes, we developed a porous surface covered by microcavities (MCPS), which was fabricated by the three-step method of a powder sintering technique followed by chemical modification methods. The pool boiling heat transfer properties of MCPSs were systematically investigated in atmospheric pressure conditions, together with the bubble dynamics characteristics. The results showed that compared to plain Cu surfaces (PCSs), a 2.2 times higher CHF, a 2.5 times higher HTC as well as 85% lower onset of nucleate boiling (ONB) were demonstrated on the MCPSs. Owe to the formation of numerous microcavities and capillary-induced liquid rewetting, compared with PCPSs, the MCPS could increase the nucleation density, reduce bubble departure diameter and increase departure frequency. Finally, the wicking velocity of different surfaces obtained from the capillary wickability tests showed that there was a good linear relationship between the wicking velocity and CHF. The results showed that the liquid supply with capillary wickability could prevent the expansion of dry spots and maintain a higher CHF. This study provides a high-performance surface modification, which leads to significant industrial application prospects for high-power microelectronics cooling.

Effects of confined space on the critical heat flux under the pool-boiling condition

The most popular mechanism of the critical heat flux (CHF) triggering is dry-out through bubble packing, which prevents the liquid inflow onto the heater. It is common knowledge that the generated upward bubble flow on the heater easily blocks a small flow path for the downward liquid inflow during pool boiling. This blocked hydrodynamic liquid flow path normally leads to dry-out and CHF on the heated surface. In the present study, we design a unique test section to assess the effect of a small flow path and the wall through the installation of a cylindrical wall close to the heater. We measure the CHF for various diameters and heights of the cylindrical wall and notice an interesting trend in the plots. Contrary to common knowledge, we find the CHF enhancement in a narrowed hydrodynamic flow path between the heater and cylindrical wall compared to the bare CHF performance. From this result, the enhancement mechanism is suggested based on the accelerated inflow bulk liquid and shortening period between growing and departing bubble by the confined wall effect. This is the first study to report on the relationship between the CHF and the diameter and height of the cylindrical wall.

The synergetic effects of the surface wettability and the patterned nanostructure on boiling heat transfer enhancement

Engineering nano-structured surfaces with mixed/thermo-responsive wettability offer a new approach to improve the boiling performances of advanced thermal systems, such as the solar system and the heat dissipation systems in nuclear power plants, where more efficient cooling and higher safety limits are extremely desirable. In this study, five groups of surfaces: a) plain surfaces, b) nanofilm coated surfaces, c) patterned surfaces with superhydrophilic nanograss, d) patterned surfaces with superhydrophobic nanograss, f) patterned surfaces with thermo-responsive wettable nanograss are investigated for their boiling performances. It is found that the nanofilm coated surfaces show improved maximum heat transfer coefficient (HTCmax) as well as critical heat flux (CHF) compared with the plain surface. The patterned surfaces shift the boiling curves to left, and the CHF increases with increasing nanograss cover density. The surfaces with thermo-responsive wettability, which responses to the external heating/cooling stimuli by gradually increasing or decreasing the wettability, show the most optimal CHF enhancement. This study serves as a proof-of-concept for efficient heat transfer through carefully fabricated nano-structured wettability-enhanced surfaces.

Effect of material arrangement pattern on different-mode-interacting boiling in narrow gaps with two liquid supply systems

• Effect of different-mode-interacting boiling in narrow gaps on CHF is investigated. • Different material patterns inside plate with material pitch and gap size are investigated. • Performances are compared for cross and parallel arrangements and conventional form. • Effect of open forms of narrow gaps of 4 sides and 2 sides is also investigated. • Cross arrangement pattern shows significant augmentation of CHF in 4-sides-open. Different-mode-interacting boiling has been proven to improve the critical heat flux (CHF) inside narrow gaps in a water pool in previous studies. This method expands the area of the wetted region and delays the occurrence of CHF with the irregular movement of the vapor and liquid near the boundary between two thermally different materials with interaction of different boiling modes on the non-uniform conductance plate. In the present study, while retaining the characteristics of this method, further improvement of heat transfer characteristics was investigated. To increase the density of different material boundaries, a new arrangement of low-conductance material with cross-type geometry was adopted. The performance on a horizontally arranged 20 mm square copper surface was compared with those of parallel arrangement and the conventional form. Furthermore, performance under the open forms of narrow gaps to surrounding liquid of 2 sides and 4 sides were examined with gap size and material pitch as parameters. Significant enhancements in CHF are achieved in cross-type arrangements. The maximum CHF of 1140 kW/m 2 and 946 kW/m 2 with large increases of 83% and 75% were achieved for 4-sides-open and 2-sides-open systems, respectively.

Experimental and numerical study of Pool boiling and critical heat flux enhancement using water based silica Nanofluids

Experimental and Numerical Studies on saturated pool boiling have been carried out over a nichrome wire submerged in both distilled water and silica–water based nanofluids. The concentrations of the silica nanoparticles are varied from 0.01 vol.% to 0.05 vol.% in step size of 0.01. Numerical simulation has been carried out by using Mixture Multiphase Approach. Moreover, heat flux values by applying traditional Rohsenow correlation and the surface-liquid constant (Csf) for wire and nanofluids is proposed that fits the experimental as well as numerical data. From the present work, it is inferred that the numerical solutions are in good agreement with the experimental data. Furthermore, thin nanoparticle coatings on heating surface were observed after each experiment. Critical Heat Flux enhancement in nanofluids may be due to the deposition of nanoparticles over the heater surface. Also, the Critical Heat Flux of nanofluids was found to be 38.5% higher (at 0.03 vol.% of silica nanoparticles concentration) as compared to distilled water.

Microtube Surfaces for the Simultaneous Enhancement of Efficiency and Critical Heat Flux during Pool Boiling.

Boiling is an essential process in numerous applications including power plants, thermal management, water purification, and steam generation. Previous studies have shown that surfaces with microcavities or biphilic wettability can enhance the efficiency of boiling heat transfer, that is, the heat transfer coefficient (HTC). Surfaces with permeable structures such as micropillar arrays, in contrast, have shown significant enhancement of the critical heat flux (CHF). In this work, we investigated microtube structures, where a cavity is defined at the center of a pillar, as structural building blocks to enhance HTC and CHF simultaneously in a controllable manner. We demonstrated simultaneous CHF and HTC enhancements of up to 62 and 244%, respectively, compared to those of a smooth surface. The experimental data along with high-speed images elucidate the mechanism for simultaneous enhancement where bubble nucleation occurs in the microtube cavities for increased HTC and microlayer evaporation occurs around microtube sidewalls for increased CHF. Furthermore, we combined micropillars and microtubes to create surfaces that further increased CHF by achieving a path to separate nucleating bubbles and rewetting liquids. This work provides guidelines for the systematic surface design for boiling heat transfer enhancement and has important implications for understanding boiling heat transfer mechanisms.

Enhancement of pool boiling performance using MWCNT based nanofluids: A sustainable method for the wastewater and incinerator heat recovery

Recovery of the wastewater heat and incinerator heat is an important stage of the design and optimization of the industrial thermal management system. Recovery and reuse of wastewater heat are also important for energy sustainability. Heat recovery boilers are mostly used in the industry for heat recovery. The performance of the heat recovery boilers is mainly depending on the Critical heat flux value of the cooling fluid. Various studies have suggested that the nanofluids are a better working fluid than conventional cooling fluids like water and ethylene glycol. Thus, in this study, we used MWCNT based nanofluids as a cooling fluid and compared its performance with the water. Because water is the conventional cooling fluid used in wastewater heat recovery. We have reported the bubble dynamics data, including the departure diameter, departure frequency, bubble growth time and bubble wait time. These results revealed that the incorporation of the MWCNT based nanofluids leads to the surface modification of the heater surface and the enhancement of critical heat flux.It was observed that by using a 0.005 vol% of MW-CNT in water, critical heat flux can be enhanced to 2.14 W/m2. This recorded critical heat flux enhancement is 62.12% more than the critical heat flux required for the water. At 0.005 vol% of MWCNT concentration, the heat-transfer coefficient is enhanced by 30%. The enhancement in the CHF is due to the enhanced surface wettability of the heating surface by a nanofluid. Furthermore, there is the deposition of the nanoparticles on the surface of the heater which causes CHF to enhance. This deposition also useful for critical heat flux enhancement.

Retraction: Process of liquid supply to heated surface by a honeycomb porous plate for critical heat flux enhancement

Various surface modifications controlling wettability and wickability have effectively enhanced the critical heat flux (CHF) in saturated pool boiling. Among them, this paper focuses on the CHF enhancement using a honeycomb porous plate (HPP). The HPP, which is commercially available, was generally used to filter exhaust gases from combustion engines, and has micron-order pores and millimeter-order holes which is called as a “cell”. Once an HPP was installed on the heated surface, the CHF in saturated pool boiling of water was improved more than approximately three times compared with a bare surface. The enhancement may be caused by: (1) the liquid supply due to capillarity, (2) liquid flowing down through the cells of an HPP due to gravity onto the heated surface, and (3) the release of vapor generated through the cells. However, the liquid supply process to heated surface due to (1) and (2) has not been clarified yet. Therefore, it is necessary to elucidate the detailed liquid supply mechanism for further CHF enhancement. In the present paper, two separate sets of experiments have been designed to investigate the liquid supply effect to the heated surface independently, namely, (1) automatic liquid supply due to capillary action by the porous part and (2) bulk liquid flowing down through the cells of an HPP. In summary, the measured values from the experiment extracting the liquid supply due to capillarity were in good agreement with the proposed capillary limit model. Moreover, for the high heat flux region (more than 3.5 MW/m2), the liquid supply due to the capillary force is dominant in enhancing the CHF. It was concluded that the keys to further CHF enhancement were the promotion of gas-liquid circulation based on the capillary limit model and improvement of wickability of the heated surface.

Investigations of near-wall bubble behavior in wire heaters pool boiling

Current work establishes a pool boiling critical heat flux prediction method based on percolation theory. For the first time, we observe the experimental bubble footprint?s power-law distributions with almost the same exponent in wire heaters? water pool boiling crisis, which is borne out strongly that boiling crisis is a typical continuum percolative scale-free behavior, and its characteristics seems not to be influenced by the critical heat flux value. The proposed 1-D Monte-Carlo method successfully simulates the phase transition of interactive near-wall bubbles. This research enriches and extends applications of continuum percolation theory in boiling phenomena, and could be an instruction for the followed critical heat flux enhancement studies.

Enhanced flow boiling in microchannels by incorporating multiple micro-nozzles and micro-pinfin fences

Phase-change heat transfer is a promising approach for high-power electronics cooling. However, the chaotic two-phase transport and dominant laminar flow in microchannels inhibits flow boiling performance. Thus, the ability to coordinate the two-phase transport in a highly favorable fashion would be highly desired. In this study, a new microchannel configuration by incorporating capillary micro-pinfin fences and multiple micro-nozzles has been proposed to sustain thin liquid film evaporation, promote mixing and global liquid supply simultaneously. A new boundary layer covered with thin liquid film is activated by the capillary micro-pinfin fences along the sidewalls of the channel. Additionally, the sustainable thin liquid film is maintained using capillary effect, which can promote the capillary-driven flow inside the gap between micro-pinfin fences and the sidewalls. As a result, significantly enhanced flow boiling has been achieved on both DI-water and HFE-7100. A critical heat flux (CHF) up to 944 W/cm2 has been demonstrated using DI-water at a mass velocity of 600 kg/m2 s, accounting for a 43% enhancement compared to the configuration of multiple micro-nozzles without capillary micro-pinfin fences. Compared to the base configuration of plain wall microchannels, the enhancement of CHF is over threefold at a mass velocity of 389 kg/m2s. Equally important, this new microchannel configuration works well on dielectric fluids, which is challenging to promote CHF due to their unfavorable thermophysical properties. A CHF of 287 W/cm2 with a noticeable enhancement of 56% has been achieved at a mass velocity of 2772 kg/m2 s on HFE-7100 at room temperature. Moreover, the enhancements of heat transfer coefficient (HTC) on HFE-7100 are more noticeable compared to that of DI-water. For example, 120% higher HTC at a moderate mass velocity of 693 kg/m2 s has been realized. All the enhancements are achieved without the escalating pressure drop.