Biphilic Surfaces Research Articles

The temperature dependent dynamics and periodicity of dropwise condensation on surfaces with wetting heterogeneities

HypothesisBiphilic surfaces, namely surfaces comprising hydrophilic areas with a (super)hydrophobic background, are used in nature and engineering for controlled dropwise condensation and liquid transport. These, however, are highly dependent on the surface temperature and subcooling. ExperimentsHere, biphilic surfaces were cooled inside a rotatable environmental chamber under controlled humidity. The condensation dynamics on the surface was quantified, depending on the subcooling, and compared to uniform superhydrophobic (USH) surfaces. Rates of condensation and transport were analyzed in terms of droplet number and size, covered area and fluid volume over several length scales. Specifically, from microscale condensation to macroscale droplet roll-off. FindingsFour phases of condensation were identified: a) initial nucleation, b) droplets on single patches, c) droplets covering adjacent patches and d) multi-patch droplets. Only the latter become mobile and roll off the surface. Cooling the surface to temperatures between T = 2–16 °C shows that lowering the temperature shortens some of the condensation parameters linearly, while others follow a power law, as expected from the theory of condensation. The temperature dependent condensation dynamics on (super)biphilic surfaces is faster in comparison to uniform superhydrophobic surfaces. Nevertheless, within time intervals of a few hours, droplets are mostly immobile. This sets guiding lines for using biphilic surfaces in applications such as water collection, heat transfer and separation processes. Generally, biphilic surfaces are suitable for applications in which fluids should be collected, concentrated and immobilized in specific areas.

Out-of-Plane Biphilic Surface Structuring for Enhanced Capillary-Driven Dropwise Condensation.

Rapid and sustained condensate droplet departure from a surface is key toward achieving high heat-transfer rates in condensation, a physical process critical to a broad range of industrial and societal applications. Despite the progress in enhancing condensation heat transfer through inducing its dropwise mode with hydrophobic materials, sophisticated surface engineering methods that can lead to further enhancement of heat transfer are still highly desirable. Here, by employing a three-dimensional, multiphase computational approach, we present an effective out-of-plane biphilic surface topography, which reveals an unexplored capillarity-driven departure mechanism of condensate droplets. This texture consists of biphilic diverging microcavities wherein a matrix of small hydrophilic spots is placed at their bottom, that is, among the pyramid-shaped, superhydrophobic microtextures forming the cavities. We show that an optimal combination of the hydrophilic spots and the angles of the pyramidal structures can achieve high deformational stretching of the droplets, eventually realizing an impressive "slingshot-like" droplet ejection process from the texture. Such a droplet departure mechanism has the potential to reduce the droplet ejection volume and thus enhance the overall condensation efficiency, compared to coalescence-initiated droplet jumping from other state-of-the-art surfaces. Simulations have shown that optimal pyramid-shaped biphilic microstructures can provoke droplet self-ejection at low volumes, up to 56% lower than superhydrophobic straight pillars, revealing a promising new surface microtexture design strategy toward enhancing the condensation heat-transfer efficiency and water harvesting capabilities.

Evaporation Dynamics of Sessile and Suspended Almost-Spherical Droplets from a Biphilic Surface

Research in the field of the evaporation of liquid droplets placed on surfaces with special wetting properties such as biphilic surfaces is of great importance. This paper presents the results of an experimental study of the heat and mass transfer of a water droplet during its evaporation depending on the direction of the gravitational force. A special technique was developed to create unique substrates, which were used to physically simulate the interaction of liquid droplets with the surface at any angle of inclination to the horizontal. It was found that the suspended and sessile droplets exhibited fundamentally different evaporation dynamics. It was shown that the suspended droplets had a higher temperature and, at the same time, evaporated almost 30% faster.

Investigation of biphilic microgroove surface on condensation Enhancement: A 3D Lattice Boltzmann method study

• A 3D LBM model with novel boundary scheme is developed. • Droplet critical sliding radius is adopted for optimum microgroove design. • Suction and bridging mode are analyzed to unravel the enhancement mechanisms. • Biphilic microgroove surfaces enhance suction mode and inhibit bridging mode. Condensation heat transfer enhancement is valued in numerous engineering fields for the goal of carbon neutrality. Surface modification provides a passive approach for sustainable dropwise condensation, which is crucial for the enhancement. Microgroove surfaces have received much attention among various modified surfaces due to their excellent droplet nucleation and removal ability. Therefore, to elucidate the enhancement mechanisms and determine the optimum microgroove geometry design, a 3D Lattice Boltzmann Method model is developed in this study. A three-layered hybrid boundary scheme is proposed with better numerical stability. The effect of wettability, groove geometry, and orientation are studied for mechanism analysis. Results show that suction and bridging modes are two major droplet behaviors on microgroove surfaces. The suction mode can accelerate the droplets’ sliding-off process and lead to a smaller departure radius, while the bridging mode could deteriorate the enhancement performance by causing strip-like liquid films. Based on theoretical and simulation results, optimum geometry is proposed under the range of 1 ≤ W G ∗ ≤ 2 , 0 ≤ S G ∗ ≤ 2 , sin ( π - θ ) W G ∗ + S G ∗ > 2 sin ( π - θ ) , and D G ∗ ≅ 1 + sin ( θ - π / 2 ) . The heat flux of the best case is enhanced by 126.9% compared with the result of a plain hydrophobic surface. Furthermore, the enhancement performance of biphilic microgroove surfaces with hydrophilic grooves is discussed. It is found that the suction mode is enhanced while the bridging mode is inhibited, which leads to superior enhancement performance of 140.4% even compared with pure hydrophobic microgroove surface. Finally, surface orientation is studied to analyze the biphilic microgrooves’ condensation enhancement. The downward-facing surface can suppress the suction mode inside the hydrophilic regions and enhance direct departure behaviors on the hydrophobic ridge regions. These conclusions provide a valuable guide for surface modification design and unraveling the enhancement mechanisms.

Extraordinary enhancement of nucleate pool boiling on intrinsically biphilic graphene nanostructured surfaces

• We use graphene nanoplatelets (GNPs) of varied wettability to enhance nucleate boiling. • Hydrophobic GNPs enhances boiling heat flux up to 219% as compared to uncoated case. • A profound heat transfer coefficient enhancement of 230% is obtained. • A drastic temperature drop of 36.1°C on the heated surface is achieved by using GNPs. • Hydrophobic GNPs manifests as a natural biphilic coating favorable to nucleate boiling. Miniaturized electronics components require effective heat removal to ensure their reliability and long-lifespan. Here, the importance of surface wettability of graphene nanoplatelets (GNPs) coatings in the thermal performance enhancement of subcooled pool boiling is elucidated. The boiling enhancement of superhydrophilic, hydrophobic and superhydrophobic GNPs coatings, is compared and benchmarked with that of the uncoated copper surface. The hydrophobic GNPs case manifests extraordinarily enhanced boiling performance. When compared with the uncoated copper surface, the boiling heat flux and the heat transfer coefficient are enhanced up to 219%, and 230%, respectively. A significant temperature decrease up to 36.1°C and an effectiveness of 3.19 as compared to the uncoated case are obtained. Besides the nanoporosity of GNPs coatings which is favourable to bubble nucleation, the unique nanostructure of the hydrophobic GNPs, which possesses a combination of hydrophilic and hydrophobic characteristics provide synergetic effect on the vapor bubble growth and departure rates. The hydrophobic GNPs is a single coating endowed with biphilicity naturally. This study incorporates facilely fabricated GNPs coatings while showcasing the importance of the wettability of GNPs in nucleate pool boiling. We envisage that the intrinsically biphilic GNPs coating has an immense potential in the highly demanding thermal management of electronics devices.

Pool boiling enhancement via biphilic surface comprising superhydrophilic TiO2 and superhydrophobic Teflon arrays

The ever-increasing power density overloads the heat removal capability of miniaturized power electronic devices and thus an efficient liquid cooling method needs to be strategized. Herein, we introduce a biphilic surface consisting of both superhydrophilic TiO2 and superhydrophobic Teflon. The purpose of this unique combination is to decrease the superheat (Tsat) by efficiently releasing vapor bubbles via the superhydrophobic surface and to increase the critical heat flux (CHF) using efficient wetting supplied by the superhydrophilic surface. The superhydrophilic TiO2 layer was deposited by the room temperature aerosol deposition method, whereas the superhydrophobic Teflon dots were deposited by the atmospheric supersonic cold spraying method. Each Teflon dot was 1 mm in diameter and the dots were patterned in the form of n×n arrays, where n varied from 1 to 5. The optimal CHF (187 kW·m−2), superheat, and effective heat transfer coefficient (4.6 kW·m−2·k−1) were observed for the 4 × 4 sample, beyond which the cooling effect deteriorated because of the excessive area covered by the Teflon dots. While the Teflon dots facilitated efficient bubble release, securing sufficient flow passage with the aid of a hydrophilic wetting area was also critical; thus the combination of the superhydrophobic and superhydrophilic surfaces was optimally balanced.

Lattice Boltzmann Simulation of Optimal Biphilic Surface Configuration to Enhance Boiling Heat Transfer

To study the processes of boiling on a smooth surface with contrast wettability, a hybrid model was developed based on Lattice Boltzmann method and heat transfer equation. The model makes it possible to describe the phenomena of natural convection, nucleate boiling, and transition to film boiling, and, thus, to study heat transfer and the development of crisis phenomena in a wide range of surface superheats and surface wetting characteristics. To find the optimal configuration of the biphilic surface, at the first stage a numerical simulation was carried out for a single lyophobic zone on a lyophilic surface. The dependences of the bubble departure frequency and the departure diameter of the bubble on the width of the lyophobic zone were obtained, and its optimal size was determined. At the next stage, the boiling process on an extended surface was studied in the presence of several lyophobic zones of a given size with different distances between them. It is shown that in the region of moderate surface superheat, the intensity of heat transfer on biphilic surfaces can be several times (more than 4) higher compared to surfaces with homogeneous wettability. Based on numerical calculations, an optimal configuration of the biphilic surface with the ratios of the lyophobic zones’ width of the order of 0.16 and the distance between the lyophobic zones in the range of 0.9–1.3 to the bubble departure diameter was found.

Atmospheric Water Harvesting on Micro-nanotextured Biphilic Surfaces

Atmospheric Water Harvesting on Micro-nanotextured Biphilic Surfaces

Surface effects on Sub-cooled pool boiling for smooth and laser-ablated silicon surfaces

Smooth and laser-ablated silicon surfaces with wettability ranging from SHI (super-hydrophilic) to SHO (super-hydrophobic) are tested in subcooled pool boiling of water. The experiment focuses on the observation of bubble phenomena using a high-speed camera and the measurement of surface temperature using an infrared camera. The formation and departure of vapor bubbles from the surfaces are found to vary significantly with the surface wettability. Nucleate boiling curves show that both the heat transfer coefficient and the critical heat flux increase with the surface wettability changing from SHO to SHI. For the hydrophilic surfaces (smooth and textured), the heat transfer coefficient increases with the heat flux. For the hydrophobic surfaces (smooth and textured), the heat transfer coefficient decreases with the increasing heat flux. The effect of the surface wettability is quantitatively assessed using the surface-fluid factor. It is found that the factor's value increases with the surface wettability changing from SHI to SHO. The surface effect for the hydrophilic surfaces remains relatively constant over the nucleate boiling range, whereas for the hydrophobic surfaces the effect shows significant dependency on the heat flux. These findings are also revealed from the boiling tests on a biphilic surface consisting of a SHO region and a SHI region.

Biphilic surface to improve and stabilize pool boiling in vacuum

• Water pool boiling performance on a biphilic surface at 10–103 kPa was studied. • The change in bubbles dynamics compared to bare surface was observed. • The heat transfer enhancement up to 3.7 times was obtained. • Biphilic surface led to boiling stabilization at pressures down to 10 kPa. To date the usage of biphilic surfaces is one of the most promising ways to simultaneously enhance heat transfer and increase critical heat fluxes during boiling. However, the vast majority of studies devoted today to the influence of surfaces with mixed wettability on boiling performance refer to atmospheric pressure conditions. At the same time, the problems of heat transfer rate increasing and stabilizing the boiling process at subatmospheric pressures are particularly acute, which is associated with some features of boiling in a vacuum and its high practical relevance. The paper presents the results of experimental study on the local boiling characteristics, including the bubble departure diameters and emission frequencies, and the heat transfer rate during water boiling on a biphilic surface in the pressure range of 10–102 kPa. As a result of experiments, it was shown that the hydrophobic areas of the fabricated biphilic surface are the sites of continuous vapor bubbles generation in the entire range of the studied pressures. At the same time, the slight increase in the size of detached bubbles and their emission frequency from the hydrophobic spots was observed with pressure reduction. It was also demonstrated that in the range of low pressures (less than 40 kPa), the biphilic surface is characterized by noticeably smaller bubble departure diameters and much higher emission frequencies compared to bare surface. The analysis of boiling curves obtained using IR thermography revealed that the developed biphilic surface provides a significant heat transfer enhancement - up to 3.7 times during boiling at subatmospheric pressures compared to bare surface. Moreover, a significant decrease in the surface superheating and in the amplitude of integral temperature oscillations is observed, which represents the boiling stabilization at low subatmospheric pressures (less than 20 kPa) for the fabricated surface.

Droplet jumping physics on biphilic surfaces with different nanostructures and surface orientations under various air pressure conditions

Suffering from the adhesion of condensing water droplets, surface condensation performance is severely degraded. On a biphilic surface, condensing droplets efficiently nucleate while spontaneously being effectively removed from the surface due to the coalescence-induced droplet jumping phenomenon, significantly improving the surface condensation performance. However, it remains a challenge to appropriately tune the biphilic surface structure to maximize the droplet jumping performance and improve the condensation. Here, we report an experimentally verified droplet jumping theory that can optimize the biphilic surface structure, maximizing the droplet jumping height on the biphilic surface. Effects of surface orientation and air pressure are also investigated. The heat flux on the optimized biphilic surface can be enhanced by ∼43% and ∼139% compared with that on the superhydrophobic surface and a normal copper plate under atmospheric conditions, respectively, while that of the water collection flux can be improved by ∼61% and ∼273%, respectively. • A droplet jumping theory on biphilic surfaces is developed and verified • Surface structure, orientation, and air pressure are studied theoretically • The biphilic surface is optimized to maximize the droplet jumping height • Condensation heat transfer of the optimized biphilic surface is enhanced notably To maximize the droplet jumping height on a biphilic surface, Zhu et al. develop a droplet jumping theory, considering the surface structure, orientation, and air pressure. The optimized biphilic surface significantly enhances the condensation heat transfer, which benefits various thermal applications.

Biphilic jumping-droplet condensation

Jumping-droplet condensation on rough superhydrophobic surfaces exhibits increased heat-transfer rates when compared with dropwise condensation on smooth hydrophobic surfaces. However, the performance of superhydrophobic surfaces is limited by the low individual droplet growth rates associated with their extreme apparent advancing contact angles. Here, we report that biphilic surfaces having smooth, low-surface-energy spots on a superhydrophobic background exhibit a 10× higher jumping-droplet condensation heat-transfer coefficient when compared with homogeneous superhydrophobic surfaces. Our detailed condensation heat-transfer modeling coupled with numerical simulations of binary and coordinated droplet coalescence show that spot wettability should not be optimized toward minimizing droplet nucleation energy barriers. Rather, spot wettability should be optimized to minimize droplet adhesion while maximizing individual droplet growth rates. Model-predicted design optimization of a variety of biphilic surfaces is validated against experiments. Our findings provide design guidelines for biphilic surface development to maximize condensation heat transfer.

Micro/nanoscale surface on enhancing the microchannel flow boiling performance: A Lattice Boltzmann simulation

Microchannel Heat Sink (MCHS) has been widely adopted in thermal engineering fields, such as refrigerators, chip cooling, battery packs, etc. To meet the ever-increasing demand for heat dissipation, surface modification methods adopting micro/nanoscale-modified surfaces have received considerable attention. In this paper, an advanced micro/nanoscale surface modification design is proposed based on a Lattice Boltzmann method (LBM) simulation study. Coupled boundary treatments at the inlet/outlet are developed with better numerical stability. The effects of surface wettability and micropillar on MCHS heat transfer performance are analyzed through bubbles' dynamic behaviors, Nusselt number, heat flux, and pressure drop. Design-based suggestions are proposed, and the enhancement mechanisms are explained. Results show that hydrophobic surface is more preferred for temperature-sensitive devices with low superheat requirement (Ja<0.1115), while the hydrophilic surface is more preferred for devices with a large heat dissipation requirement (Ja≥0.1286). Furthermore, the micropillar surfaces with pillar geometric factor Sp of 7 can yield the optimum heat transfer performance under a wide range of superheat conditions. Finally, an advanced design of a biphilic micropillar surface is proposed with superhydrophobic regions located at the top of the pillars, and other regions remain hydrophilic surfaces. An excellent heat transfer enhancement of 105.8% is achieved even compared with a pure hydrophilic micropillar surface. The enhancement is attributed to the superhydrophobic top regions efficiently blocking the bubbles merging process, which leads to more intense bubbles departure. These results provide a valuable guide for MCHS design and unravel the enhancement mechanism of the flow boiling process.

The Impact of Alumina Nanofluids on Pool Boiling Performance on Biphilic Surfaces for Cooling Applications

This work aims to study the impact of nanofluids with alumina particles on pool boiling performance. Unlike most studies, which use a trial-and-error approach to improve boiling performance parameters, this study details the possible effects of nanoparticles on the effective mechanisms of boiling and heat transfer. For this purpose, biphilic surfaces (hydrophilic surfaces with superhydrophobic spots) were used, which allow the individual analysis of bubbles. Surfaces with different configurations of superhydrophobic regions were used. The thermophysical properties of fluids only vary slightly with increasing nanoparticle concentration. The evolution of the dissipated heat flux and temperature profiles for a nucleation time frame is independent of the fluid and imposed heat flux. It can be concluded that the optimal concentration of nanoparticles is 3 wt%. Using this nanoparticle concentration leads to lower surface temperature values than those obtained with water, the reference fluid. This is due to the changes in the balance of forces in the triple line, induced by increased wettability as a consequence of the deposited particles. Wherefore, smaller and more frequent bubbles are formed, resulting in higher heat transfer coefficients. This effect, although relevant, is still of minor importance when compared to that of the use of biphilic surfaces.

Influence of Surface Wettability on Bubble Formation and Motion

Bubble dynamics plays an important role in boiling heat transfer, and surface wettability affects bubble behaviors. In the present work, the effects of surface superhydrophilicity (SHI) and superhydrophobicity (SHO) on bubble dynamics are experimentally studied by observing the formation and motion behaviors of air bubbles and vapor bubbles on varied surfaces. For air bubbles to better mimic vapor bubbles, the air bubbles are introduced in a water pool by injecting airflow from a through hole of the surface. Air bubble tests are first conducted on homogeneous SHO and SHI surfaces, respectively. It is observed that surface wettability significantly affects the bubble size and departure frequency. To discover the dynamic behaviors of a bubble under both SHI and SHO, a biphilic surface with SHI and SHO areas is fabricated, and air bubbles are injected right on the biphilic border between the two areas. It is observed the wettability contrast significantly displaces the air bubbles, which spread only onto the SHO area. The biphilic surface is fabricated for the pool boiling test. Vapor bubbles are observed at different stages of the nucleate boiling, showing surface effects similar to the observations of air bubbles. Not only does this study present the influence of surface wettability on air and vapor bubble behaviors but also it provides useful implications for understanding and optimizing the biphilic surface design for enhancing boiling heat transfer.

Effect of fluoropolymer spots on pool boiling heat transfer

In this paper, the investigation of pool boiling heat transfer on biphilic micro/nanostructured surfaces is presented. An array of micrococoons from silicon oxide nanowires was synthesized on the surface of a copper heater using the gas-jet electron beam plasma chemical vapor deposition method. The biphilic properties of the surface were achieved by applying fluoropolymer spots by hot wire chemical vapor deposition. Technology of creating biphilic surfaces was developed and boiling curves were obtained for used samples. The advantages of using a biphilic surface to enhance heat transfer were demonstrated in comparison with a smooth surface and a micro-nanostructured surface without local hydrophobic fluoropolymer regions. This technology can be applied to enhance boiling heat transfer.

Investigation of heat transfer during evaporation of droplets of Fe3O4 nanofluids from biphilic surfaces

In this work, unique biphilic substrates were prepared with a sharp spatial gradient of the contact angle of wetting. Experimental studies of the process of evaporation of liquid droplets lying on the structured surfaces have been carried out. In the experiment, the dynamics of the temperature of an evaporating droplet was compared depending on its orientation in space. It was found that suspended droplets of 0.1 wt % Fe3O4 nanofluid have a higher evaporation temperature and a higher evaporation rate as compared to sessile droplets.

Biphilic Surfaces with Optimum Hydrophobic Islands on a Superhydrophobic Background for Dropwise Flow Condensation.

Sustaining dropwise condensation is of great importance in many applications, especially in confined spaces. In this regard, superhydrophobic surfaces enhance condensation heat transfer performance due to the discrete droplet formation and rapid removal. On the other hand, droplets tend to nucleate easier and faster on hydrophobic surfaces compared to superhydrophobic ones. To take advantage of the mixed wettability, we fabricated biphilic surfaces and integrated them to small channels to assess their effect on thermal performance in flow condensation in small channels. Hydrophobic islands in the range of 100-900 μm diameter were fabricated using a combination of wet etching, surface functionalization, and physical vapor deposition (PVD) techniques. Condensation experiments were performed in a minichannel with a length, width, and height of 37, 10, and 1 mm, respectively. Here, we report optimum island diameters for the hydrophobic islands in terms of the maximum thermal performance. We show that considering the optimum point for each steam mass flux corresponding to the best heat transfer performance, the condensation heat transfer coefficient is increased by 51, 48, 42, 40, and 36% compared to the plain reference hydrophobic surface for steam mass fluxes of 10, 20, 30, 40, and 50 kg/m2 s, respectively. The optimum island diameters are obtained as 200, 300, 400, 400, and 500 μm, with the ratios of hydrophobic to superhydrophobic surface areas (A* = Ahydrophobic/Asuperhydrophobic) of 3.2, 7.6, 14.4, 14.4, and 24.4%, for steam mass fluxes of 10, 20, 30, 40, and 50 kg/m2 s, respectively. The liquid film forming on the liquid-vapor interface acts as an insulation layer and generates thermal resistance, and bridges appear on the patterned areas and deteriorate the thermal performance. Therefore, it is crucial to characterize the role of droplet mobility on biphilic surfaces to avoid the occurrence of bridging. Through visualization, we demonstrate that the optimum conditions correspond to enhanced droplet nucleation and rapid sweeping regions, where droplet pinning and bridging do not occur. The trends in condensation heat transfer with surface mixed wettability can be divided into three regions: enhanced droplet nucleation and rapid sweeping, highly pinned droplet, and bridging droplet segments. We reveal that the interfacial heat transfer augmentation in the enhanced droplet nucleation and rapid sweeping region is due to both spatial control of droplet nucleation and an increase in the sweeping period. Furthermore, by fitting the experimental data, a correlation for predicting the optimum island diameter for biphilic surfaces is proposed for condensation heat transfer in confined channels, which will be a valuable guideline for engineers and researchers working on the design and development of thermal systems.

Pool boiling of nanofluids on biphilic surfaces

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions are prepared and used to act as surface interfaces with nanofluids (water with gold, silver and alumina nanoparticles) and infer on the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. The results show an evident benefice of using biphilic patterns, but with well-stablished distances between the superhydrophobic regions. Such patterns allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic surface between the superhydrophobic regions, which clearly contributes to cool down the surface. The effect of the nanofluids, for the low concentrations used here, was observed to play a minor role.

Effect of Surface Biphilicity on FC-72 Flow Boiling in a Rectangular Minichannel

Flow boiling is one of the most effective mechanisms in heat transfer thanks to the latent heat of vaporization. Surface modifications such as mixed-wettability have a considerable effect on the boiling heat transfer performance in terms of enhancement in boiling heat transfer as well as critical heat flux. This study introduces a new method of fabrication of biphilic surfaces, where C4F8 (Octafluorocyclobutane) islands are surrounded by silicon. Two different biphilic surfaces were fabricated and compared with the entirely uniform hydrophobic surface taken as a reference,. Each of the biphilic surfaces has three different sections, namely inlet, middle and outlet regions. The first region is mainly hydrophobic (inlet), while the third region is mainly hydrophilic (outlet). The heat transfer coefficients were obtained at different heat fluxes. Compared to the entirely uniform hydrophobic surface, the results show that biphilic surfaces enhance the boiling heat transfer performance by up to 50%. The visualization results revealed that the biphilic surfaces lead to more nucleation sites in the bubbly flow regime and break up the elongated bubbles in the slug flow regime.