The growing demand for energy efficiency and system durability has highlighted the need for multifunctional heat transfer components capable of operating in corrosive, humid, and freezing environments. With additive manufacturing (AM) technique offering geometric flexibility, AM stainless steel 316L (AM-SS) stands out for its mechanical robustness and temperature resilience. However, the lack of effective surface engineering strategies limits its utility in applications requiring controlled liquid-solid interactions. Here, we develop a scalable micro/ nanoengineering approach that exploits intrinsic two-dimension sub-grain features of AM-SS to construct threedimensional hierarchical micro/nanoarchitecture. By leveraging insights into the surface chemistry and material composition of pristine AM-SS, we developed a new electrochemical technique to selectively remove chromium-enriched nanoscale sub-grain boundaries. This process leads to the formation of previously unexplored micro-needle arrays, which are further functionalized with FeO(OH) nanosheets through a facile one-step oxidation treatment. The resulting surfaces exhibit ultra-low water adhesion, enhanced durability, and a 98 % reduction in corrosion rate. They also support jumping-droplet condensation with 23 % frost-free area at-15 degrees C. When infused with a low-surface-energy lubricant, the surfaces enable stable dropwise condensation of low-surface-tension fluids, such as ethanol, a surface behavior unachievable by microstructures formed on conventional stainless steel. Using copper foam cathodes, we scale the process to application-scale AM-SS tubes and demonstrate efficient ethanol condensation. This work not only overcomes critical challenges in surface functionalization of AM-SS but also provides a framework for developing multifunctional, high-performance surfaces across a broad spectrum of AM metals.

Facile surface micro/nanostructuring techniques for additively-manufactured (AM) aluminum alloy (AlSi10Mg) have recently been developed. The structuring techniques are not only highly scalable, but they also enable the tailoring of structure length scale and morphology to enhance pool boiling heat transfer coefficient. Our past study revealed that the structure cavity size of 5 mu m is favorable for bubble nucleation during pool boiling of dielectric fluid, HFE-7100, resulting in significant enhancements in the heat transfer coefficients (h). However, owing to the differences in thermophysical properties between different coolant fluids, including saturation temperature, latent heat of vaporization and surface tension, the required structure size range for bubble nucleation and capillary wicking force for liquid re-supply are expected to differ significantly. To explore the effect of structure length scale on the pool boiling performance of coolants with different thermophysical properties, this work develops a new surface structuring technique consisting of a dual-stage metallurgic heat treatment process and single-stage crystallographic etching process to tune the structure length scale across nearly two orders of magnitude, viz., from 0.3 to 15 mu m. Using coolant media of vastly different thermophysical properties, i.e., dielectric fluid HFE-7100 and deionized water, we show that while microcavities with sizes ranging from 3 to 8 mu m are favorable bubble nucleation sites for boiling of HFE-7100, which result in the enhancement of the maximum heat transfer coefficient ( h max ) by 83.4 to 103.8 % as compared to a conventional plain Al6061 surface, larger microcavity sizes of 10 to 15 mu m are required to effectively promote bubble nucleation of water. This large microcavity size range of 10 to 15 mu m, produced through rational nanoparticle agglomeration of the rich Si-phase in AM AlSi10Mg in elevated temperature, followed by an indirect removal process using a chemical process, is found to significantly increase h max of water by up to 259.9% as compared to conventional nanostructures formed on Al6061. In addition, the new AM structured surfaces also exhibit up to 26.6 % enhancement in critical heat flux (CHF) as compared to highly-wicking conventional nanostructured Al6061. In summary, by utilizing scalable fabrication techniques to tailor the structure length scale on AM AlSi10Mg, this work not only reveals the favorable microcavity sizes for bubble nucleation of different coolant fluids to enhance boiling, but it also provides useful micro/nanostructure design guidelines that can be adopted to enhance boiling of other coolants and phase change applications.

In this study, a three-dimensional topologically -optimized structure was developed to enhance the thermal energy storage performance of low -temperature phase change materials. The topology of the structure employed in the thermal energy storage device was developed using COMSOL Multiphysics by maximizing heat diffusion in a design domain with a constant temperature plate and adiabatic boundary conditions. The optimized thermal energy storage device was additively manufactured, and its thermal performance was experimentally characterized and compared against two conventional structures as baselines, viz., a plate fin and a pin fin structure. For the first time, this study seeks to determine the sole influence of fin topology on thermal energy storage performance by designing the fins with the same physical parameters, viz., surface area, volume, base plate size, and material. The fin structure volumes were set at approximately 5% of the simulated domain volume and were fabricated by Selective Laser Melting, a metal additive manufacturing technique. The fin structures were experimentally tested under three different constant plate temperatures (65 degrees C, 70 degrees C, and 75 degrees C) using two different phase change materials (RT35 and PEG1000). Their performances were evaluated by comparing the total charging time, melt fraction, and base plate temperature. Our results show that the topology of the optimized fin structure can reduce charging times by up to 9.1% when a constant plate temperature of 65 degrees C is applied. The topology of the optimized fins also achieved base plate temperatures that were up to 4 degrees C lower than conventional fins while having a more uniform distribution of heat to the phase change material within the housing. Additionally, by fixing the critical physical parameters of the fin structures, this work also shows that the fin topology plays a significant role in enhancing the melting performance of thermal storage devices.

This study involves the development of an air-cooled condenser with porous lattice P-cell structures of 7 mm unit cell size on the air-side from an aluminium alloy (AlSi10Mg) powder by selective laser melting (SLM). The internal flow channels for enhanced condensation of R134a were designed with triangular cross-sections and a hydraulic diameter of 5 mm. Experiments were conducted to evaluate the condenser's thermohydraulic performance. The results demonstrate that the P-cell design increased the heat transfer rate per unit volume and per air mass flow rate of the air-cooled condenser by a factor of 2.81 as compared to a conventional plate fin-and-tube heat exchanger. The fan power efficiency is comparable to a conventional plate-fin-and-tube heat exchanger. The feasibility of using SLM to fabricate a robust air-cooled condenser for high pressure operation is demonstrated.

This paper presents the results of the saturated pool boiling heat transfer performances of macrostructured fins fabricated by Selective Laser Melting, a metal additive manufacturing technique. A plain surface, two-dimensional triangular and rectangular fins, and three-dimensional pin and segregated fin array designs inves-tigated in this study were fabricated using AlSi10Mg. A dielectric fluid, HFE-7100, was used as the cooling medium in a water-cooled thermosyphon to test the structures under atmospheric conditions. A macro-fin design optimization approach was developed by experimentally characterizing the boiling performances and bubble dynamics in fin arrays with different fin parameters such as fin topology, angle, and height. From the results obtained, this study optimized and tuned the macrostructure design to eliminate the detrimental bubble dy-namics that were identified through high-speed visualization. Following a systematic study of the boiling characteristics of two-dimensional triangular and rectangular fins, and three-dimensional pin fins, the segregated fin array was developed to tackle the unfavorable bubble dynamics in these conventional fin geometries to enhance both critical heat flux and heat transfer coefficient. Various performance metrics were used to compare and evaluate the boiling performances of different fin topologies. From our studies, the segregated fin specimen (Seg-3) was determined to achieve the best balance between critical heat flux and heat transfer coefficient en-hancements, attaining a critical heat flux of 64.19 W/cm2 and a maximum heat transfer coefficient of 2.22 W/ cm2 & sdot;K, enhancing critical heat flux and heat transfer coefficient by up to 97.2 % and 43.1 % as compared to the plain surface, respectively. Furthermore, Seg-3 has achieved boiling enhancements with only 334 mm2 and 50.6 mm3 of surface area and fin volume, respectively, a substantial surface area and fin volume reduction as compared to conventional macro-fin geometries with the same fin height. In all, this work not only provides fundamental insights into the bubble dynamics in various macro-fin structures and their influence on the boiling performance, but it also presents a macro-fin design optimization strategy that can be adopted for other im-mersion cooling applications.

This study delves into the analysis of boiling-induced vibrations observed during a flow boiling experiment and explores their potential in predicting heat load through machine learning models. The frequency spectral analysis revealed that the dominant frequency ranges between 6.5 - 12.5 kHz, delineated into three distinct bands. Principal Component Analysis (PCA) underscored the significance of the 8 - 9 kHz peak, encapsulating around 65% of dataset variance. Diverse machine learning algorithms including decision tree regression, random forest regression, support vector regression, and multi-layer perceptron were rigorously evaluated. The Multi-Layer Perceptron (MLP) architecture with specific neuron configurations and a learning rate of 0.2 emerged as the superior model based on its minimal Mean Squared Error (MSE) and high R 2 score. Notably, all models exhibited inference times within the microsecond range. This amalgamation of vibration spectral analysis, machine learning model assessments, and inference time evaluations underlines the promising prospect of utilizing boiling-induced vibrations for real-time heat load prediction, showcasing superior performance compared to conventional methods.

In this paper, experiments have been conducted to study the heat transfer of a porous channel heat sink subjected to oscillating flow. The surface temperature distributions for both steady and oscillating flows were measured. The local and length-averaged Nusselt numbers were measured and analyzed. The experimental results revealed that the surface temperature distribution for oscillating flow is more uniform than that for steady flow. Due to the reversing flow direction, there are two thermal entrance regions for oscillating flow. The length-averaged Nusselt number for oscillating flow is much higher than that for steady flow. The porous channel heat sink subjected to oscillating flow can be considered as an effective method for cooling high-speed electronic devices.

A water flat plate heat pipe was designed, fabricated and tested. The axial heat conductance was obtained. This value was used together with the circuit software "SPICE" to calculate the temperature distribution along the surface of the heat pipe. Good agreement was obtained. A software was also developed to facilitate the design of a flat plate heat pipe. Comparison was made between the experimental and calculated results. Reasonable agreement was also achieved.

Abstract Appropriate arrangement of the fin structures in the evaporator and condenser not only enhances the heat transfer coefficient but also suppresses the increase of pressure drop. Due to this reason, a new method of using large-scale pin fins is explored to increase the heat transfer area and to modify the liquid film flow characteristics in the enhanced tubes. In the present study, four enhanced tubes and one plain tube were manufactured by selective laser melting. The working fluid is R407C and the enhanced tubes are eight short pin fins tube, five long pin fins tube, twisted pin fins tube and a tube filled with metallic foam. The results show that the shorter fin tube has the largest heat transfer coefficient for condensation at 3967 W/m2⋅K and the metallic foam tube demonstrates the largest heat transfer coefficient for boiling at 10606 W/m2⋅K. However, the shorter fins have the highest efficiency indices based on the heat transfer coefficient-pressure drop evaluation criterion and the heat transfer coefficient-area evaluation criterion. For condensation, the indices are 1.28 and 1.35, respectively. For boiling, the indices are 2.55 and 1.62, respectively.

This paper presents a numerical study of stratified flow condensation heat transfer in tubes with novel cross-section designs. A design framework of the novel cross-section geometry was developed by first studying and analyzing the condensate film distribution in a circular tube. It was found that the circular arc diameter and orientation have effects on the condensate film thickness. Based on this understanding, four different cross-section designs (models N1, N2, N3 and N4) formed by connecting circular arcs of different curvatures at various orientations were proposed. The heat transfer performances of these models were compared to a circular tube of the same perimeter. Our simulations show that all models possess higher average heat transfer coefficients than a circular tube when no accumulated condensate layer is present. Among all the models proposed, model N4 exhibits the largest heat transfer enhancement ratio of 1.42 at epsilon = 0.96. The design of model N4 utilizes small circular arcs which are arranged in an orientation that increases the effect of the gravitational force, providing significant condensate film thickness reduction over a large area. This study not only demonstrates the possibility of enhancing condensation heat transfer by simply varying the tube curvature but also provided a design guideline which can be employed for the development of novel cross-section tubes that can be fabricated by advanced manufacturing techniques such as selective laser melting.

Abstract Metal additive manufacturing (AM) enables unparalleled design freedom for the development of optimized devices in a plethora of applications. The requirement for the use of nonconventional aluminum alloys such as AlSi10Mg has made the rational micro/nanostructuring of metal AM challenging. Here, the techniques are developed and the fundamental mechanisms governing the micro/nanostructuring of AlSi10Mg, the most common metal AM material, are investigated. A surface structuring technique is rationally devised to form previously unexplored two‐tier nanoscale architectures that enable remarkably low adhesion, excellent resilience to condensation flooding, and enhanced liquid–vapor phase transition. Using condensation as a demonstration framework, it is shown that the two‐tier nanostructures achieve 6× higher heat transfer coefficient when compared to the best filmwise condensation. The study demonstrates that AM‐enabled nanostructuring is optimal for confining droplets while reducing adhesion to facilitate droplet detachment. Extensive benchmarking with past reported data shows that the demonstrated heat transfer enhancement has not been achieved previously under high supersaturation conditions using conventional aluminum, further motivating the need for AM nanostructures. Finally, it has been demonstrated that the synergistic combination of wide AM design freedom and optimal AM nanostructuring method can provide an ultracompact condenser having excellent thermal performance and power density.

Novel processing phenomena coupled with various alloying materials used in metal additive manufacturing (AM) have opened opportunities for the development of previously unexplored micro-/nanostructures. A rationally devised structure nanofabrication strategy of AM surfaces that can tailor the interface morphology and chemistry has the potential for many applications. Here, through an understanding of grain formation mechanisms during AM, we develop a facile method for tuning micro-/nanostructures of one of the most used AM alloys and rationally optimize the morphology for applications requiring low surface adhesion. We demonstrate that optimized AM structures reduce the adhesion of impaling water droplets and significantly delay icing time. The structure can also be altered and optimized for antiflooding jumping-droplet condensation that exhibits significant enhancement in heat transfer performance in comparison to nanostructures formed on conventional Al alloys. In addition to demonstrating the potential of functionalized AM surfaces, this work also provides guidelines for surface-structuring optimization applicable to other AM metals.

In this study, a topology-optimized heat sink is developed and applied to electronics cooling by utilizing a phase change material interspersed through a finned structure. The topology optimization is performed by the minimization of the global thermal compliance in the solution of the modified momentum equation with the Boussinesq approximation to account for natural convection. The optimized heat sink, namely the natural convection topology-optimized heat sink, was fabricated by Selective Laser Melting, a metal additive manufacturing technique. The natural convection topology-optimized heat sink was experimentally characterized based on its base temporal temperature and its operation time. The performance of our newly developed heat sink was then evaluated by comparing against a conventional heat sink design, a baseline design with no surface enhancements, and a second topology-optimized heat sink based on heat conduction. The results show that the natural convection topology-optimized heat sink has a lower base temperature compared to the conventional heat sink, but higher base temperature than the second topology-optimized heat sink during the PCM melting phase. However, the natural convection topology-optimized heat sink has an operation time which is 31.0% longer than all the other heat sinks with enhanced structures. Through visualization of the melting process, we can deduce that the longer operation time of the natural convection topology-optimized heat sink is primarily due to the movement of the melt front which results in a slower melting, while optimizing natural convection of the melted material. These mechanisms maintain a reasonably low heat sink base temperature.

The use of enhanced surfaces is an efficient method to improve filmwise condensation. Due to their immense potential, many enhanced structures were developed and investigated with the aim of improving natural and forced convection condensation heat transfer coefficients. This has resulted in large collections of predictive models and experimental data being reported. In this review, the developments in this field of research in the past few decades and the recent advances are collated and examined. This paper focuses on the review of natural convection condensation on the external surfaces of enhanced flat plates and tubes and forced convection condensation in enhanced tubes. The various models predicting the heat transfer coefficients on plain and enhanced surfaces are evaluated. For natural convection condensation, the liquid film-based models, semi-empirical models and numerical modes are reviewed whereas, for forced convection condensation, the gravity-dominated and vapor shear-dominated models are discussed. The effects of these enhanced structures on the liquid film and two-phase flow characteristics are analyzed and the various types of enhanced tubes and flat plates investigated are categorized. The manufacturing techniques employed to fabricate these surfaces are identified. A detailed evaluation of the heat transfer and pressure drop performances of the various enhanced surfaces is performed. In addition, their thermal performances are summarized and compared, and their associated heat transfer mechanisms are elucidated. For external condensation on a single tube row, three-dimensional fin structures were found to provide better thermal performance than two-dimensional structures, with some three-dimensional fin structures exhibiting more than 6 times the heat transfer coefficients of a plain surface. However, in a tube bundle, the heat transfer coefficient of three-dimensional fin tubes decreases more significantly with increasing tube row as compared to two-dimensional fin tubes. For convective condensation in circular tubes, the herringbone and pin fin tubes demonstrated better thermal and pressure drop performances than other internally enhanced tubes. Their efficiency indices were between 1.25 and 1.28. Based on the literature surveyed, the various experimental results are compared, existing research gaps are identified and frameworks for future research work are provided.

Abstract A topology-optimized structure for thermal management is developed. The topology optimization is performed based on the minimization of objective functions under natural convection in two-dimensional space. The Boussinesq approximation is included in the momentum equation to simulate natural convection. A RAMP-style function is applied to the thermal conductivity in the design domain so as to clearly define the solid and liquid regions. The solid region represents AlSi10Mg, a high thermal conductivity aluminum alloy that is used for additive manufacturing, while the liquid region represents the phase change material (PCM). The optimization was computed with COMSOL Multiphysics. The structure is successfully fabricated by Selective Laser Melting (SLM) using AlSi10Mg powder. Experimental investigations of this structure were performed together with two conventional designs fabricated with Al-6061; one with five longitudinal fins positioned radially from the heat source and the other with no surface enhancements. The PCM used in the experiments is RT44HC. The experiments involved allowing the PCM to completely melt at two heat rates of 27 and 48 W. All structures were placed in the horizontal orientation. Our preliminary experimental studies suggest that the topology-optimized structure has a lower rate of increase in base temperature during post-melting compared to the two conventional designs, primarily due to the efficient transfer of heat by natural convection.

The use of enhanced surfaces is an efficient method to improve filmwise condensation. Due to their immense potential, many enhanced structures were developed and investigated with the aim of improving natural and forced convection condensation heat transfer coefficients. This has resulted in large collections of predictive models and experimental data being reported. In this review, the developments in this field of research in the past few decades and the recent advances are collated and examined. This paper focuses on the review of natural convection condensation on the external surfaces of enhanced flat plates and tubes and forced convection condensation in enhanced tubes. The various models predicting the heat transfer coefficients on plain and enhanced surfaces are evaluated. For natural convection condensation, the liquid film-based models, semiempirical models and numerical modes are reviewed whereas, for forced convection condensation, the gravity-dominated and vapor shear-dominated models are discussed. The effects of these enhanced structures on the liquid film and two-phase flow characteristics are analyzed and the various types of enhanced tubes and flat plates investigated are categorized. The manufacturing techniques employed to fabricate these surfaces are identified. A detailed evaluation of the heat transfer and pressure drop performances of the various enhanced surfaces is performed. In addition, their thermal performances are summarized and compared, and their associated heat transfer mechanisms are elucidated. For external condensation on a single tube row, three-dimensional fin structures were found to provide better thermal performance than two-dimensional structures, with some three-dimensional fin structures exhibiting more than 6 times the heat transfer coefficients of a plain surface. However, in a tube bundle, the heat transfer coefficient of three-dimensional fin tubes decreases more significantly with increasing tube row as compared to two-dimensional fin tubes. For convective condensation in circular tubes, the herringbone and pin fin tubes demonstrated better thermal and pressure drop performances than other internally enhanced tubes. Their efficiency indices were between 1.25 and 1.28. Based on the literature surveyed, the various experimental results are compared, existing research gaps are identified and frameworks for future research work are provided.

A heat sink filled with phase change material (PCM) is an efficient thermal management device which utilizes the high latent heat of fusion of PCM in the cooling process. To improve the thermal performance of the PCM-based heat sink, a topology optimization (TO) strategy is devised to develop a new class of enhanced structures. This is achieved by carrying out a comprehensive numerical study to identify the effects of various thermal transport mechanisms on the TO design by considering two different heat transfer problems, i.e., steady-state heat conduction and transient heat conduction with phase change. To enable easy fabrication and performance evaluation of the new heat sink design predicted by the TO process, the resulting heat sink with tree-like structure was fabricated by selective laser melting (SLM), a metal additive manufacturing (AM) technique. Experimental characterization of the TO heat sink was carried out using three different types of PCMs, i.e., RT35, RT35HC and RT44HC and heat fluxes ranging from 4.00 kW/m2 to 7.24 kW/m2. Our experimental results show that the TO tree-like structure heat sink has better performance, exhibiting up to 4 degrees C lower wall temperatures, than the conventional fin-structure heat sink. At low heat fluxes, the best thermal performance can be obtained with RT35HC whereas at high heat fluxes, lower wall temperatures were achieved with RT44HC. In addition, the treelike structure increases operational time by up to 13% as compared to the fin-structure heat sink. The better thermal performance of the tree-like structure heat sink is due to its optimized heat conduction paths that allow heat from the concentrated heat source to be efficiently dissipated to the PCM. This work not only demonstrates the potential of enhancing electronics cooling with TO PCM-based heat sinks, but it also outlines key guidelines for the design and implementation of TO structures for other cooling applications.

In this paper, a theoretical model of filmwise condensation of steam on three-dimensional pin fins fabricated by selective laser melting (SLM), an additive manufacturing (AM) technique, is developed. The model considers the effects of surface tension and gravity on the liquid film flow over the pin fin surface. The three-dimensional nature of the liquid film flow over the fin flank and the unique features of the fin structures as a result of the laser melting process are modeled. Visualization studies are performed to verify the assumptions made in the model. From the modeling results, the local heat transfer coefficient and length-averaged heat transfer coefficient are obtained. The liquid film thickness at various locations of the pin fin is analyzed. The effects of fin tip dimensions, fin stem radius and fin pitch on the liquid film characteristics and heat transfer coefficient are systematically investigated. Our results showed that a thin film region exists in the flat and circular segments of the fin tip which cover approximately 25 – 30% of the fin surface. For a fixed fin diameter, it is found that the length-averaged heat transfer coefficient can be optimized by varying the dimensions of the flat and circular segments. A locally thin film region resulting from the suction effect is observed near the fin base for small fin spacings. However, the suction effect reduces with increasing fin spacing. Due to the three-dimensional nature of the pin fins which induces surface tension in the circumferential direction, the liquid film distribution is uniform. The differences in the length-averaged heat transfer coefficient at different circumferential locations are smaller than 5%. Finally, a comparison with existing experimental results demonstrates that a relatively accurate prediction of the average heat transfer coefficient can be achieved by our model with a maximum deviation of 8.3%.

Vapor condensation on metallic surfaces is a phase-change phenomenon that has widespread applications in many processes. Jumping-droplet-enhanced condensation is an effective mode of dropwise condensation due to its higher droplet removal rate, enabling more efficient heat transfer. However, maintaining stable jumping-droplet condensation, requires surface structures to be suitably designed to prevent droplet pinning and surface flooding. In recent years, using metal additive manufacturing (AM) processes to create heat exchanger surfaces has received significant attention due to its design freedom and versatility in fabricating highly complex functional parts. Here, we present a highly scalable method of fabricating superhydrophobic (SHP) AM surfaces from aluminum alloy, AlSi10Mg, and an experimental investigation of their thermal performance during steam condensation. The test samples were fabricated by Selective Laser Melting (SLM), an AM technique for producing metallic parts. Through detailed material characterizations, we found that it is possible to achieve superior superhydrophobicity on AM surfaces, with unique cellular-like nanoscale surface features, by simple chemical etching and functionalization processes. To understand the droplet dynamics and obtain insights on the effects of AM nanostructures on the condensate droplet morphology and jumping, we carried out condensation experiments with an environmental scanning electron microscope (ESEM) at low supersaturation of ∼1.06. The important relations between the fabricated AM nanostructure morphology and droplet dynamics are established by characterizing the droplet departure diameter and droplet jumping frequency. To determine the anti-flooding and condensation heat transfer performances of the AM SHP surfaces, pure vapor condensation experiments under higher supersaturation conditions were carried out in a well-controlled environmental chamber. Together with the aid of high-resolution imaging and heat transfer measurements, we demonstrate significant reduction in droplet pinning sites due to the implementation of the AM cellular-like structure. This reduces the thermal barrier between the condensing surface and surrounding vapor, and hence, increases the condensation heat transfer. Our results show that excellent droplet jumping performance and better droplet mobility can be achieved by using AM SHP surfaces as compared to conventional SHP aluminum extruded tubing. These results underscore the potential of advancing AM structured surfaces for jumping-droplet-enhanced condensation under high heat flux conditions.

As elaborated by Mudawar (Mudawar in IEEE Transactions on Component and Packaging Technologies 24:122–141, 2001 [1]), cooling technologies for electronic devices have shifted from natural convection to single-phase forced convection and then to phase-change cooling systems. The heat transfer performance limitations of natural and single-phase forced convection have driven the development of two-phase cooling or boiling heat transfer. Hence, two-phase cooling is generally considered to be one of the promising techniques for high heat flux electronic devices in the future. The bubble departure diameter (Db) and frequency (fd) are important parameters in bubble dynamics that directly affect boiling heat transfer performance. Surface heating, liquid heating, nucleation, bubble growth and departure occur continuously and repeatedly during the boiling process such that the cycle is normally known as an ebullition cycle. During the boiling process, a bubble is generated from an activated cavity on the boiling surface. The generated bubble grows during the bubble growth time and then departs from the nucleation cavity. The bubble diameter at the time of departure from the nucleation site is called the bubble departure diameter. The bubble departure frequency indicates how fast the bubble grows and departs from the cavity. It is affected directly by the bubble departure diameter. At the same heat flux, a smaller bubble departure diameter will result in a higher bubble departure frequency.