Phase Heat Transfer Research Articles

Quantifying the controlling mechanisms of opposed flow flame spread: Influence of orientation, material, and external heating

The contribution of gas-phase and solid-phase heat transfer on opposed flow flame spread was quantified under a range of experimental conditions. The thermal gradient ahead of the flame front was determined using a temperature reconstruction method from time resolved temperature data. In all conditions tested, both gas phase and solid phase heat transfer displayed significant contributions to heating ahead of the flame front. PMMA samples were tested in three orientations - downward, horizontal, and lateral. It was found that the lateral configuration displayed the highest rate of flame spread (3.54 mm/min) compared to downward (2.67 mm/min) and horizontal (2.54 mm/min). Lateral spread also exhibited a lower magnitude of solid phase heat transfer compared to the other orientations. Trials that were externally heated showed lower contributions of solid phase heat transfer as the applied surface heat flux was increased. Both PMMA and POM samples were used to compare the effects of the presence of a sooting or non-sooting flame. The methodology provided in this work quantifies the relative contributions of gas-phase and solid-phase heat transfer in opposed flame spread scenarios.

Thermal and phase change process in a branching T-channel under active magnetic field and two rotating inner cylinders: Analysis and predictions by radial basis neural networks

Effects of combining the use of a magnetic field with rotating cylinders on the thermal processes and phase transitions in a T-shaped branching channel are examined. In the vertical channel, a PCM-packed bed zone is used, and rotating cylinders are used in both the vertical and horizontal channels. For a range of rotational Reynolds numbers (Rew between −300 and 300), Hartmann numbers (Ha between 0 and 80), and cylinder sizes (Rc1 and Rc2 between 0.01H and 0.2H), investigations are conducted for the effects of coupled forced flow, magnetic field, and rotating cylinder interactions on the efficiency of the thermal and phase change processes. When there is no magnetic field, the entire transition time (TF) may be lowered and at Rew=2000, the TF is reduced by about 42.5% in comparison to a stationary cylinder case (Rew=0). Employing rotations at the fastest speed results in a 26% boost in heat transfer. Thermal performance increases become 181% and 205% at Rew=0 and Rew=−2000, respectively, but the TF value drops by around 31.5% and 17.5% when highest magnetic field strength is considered. When magnetic field and a horizontal channel cylinder are employed, the T-channel system operates most well in terms of phase change and heat transfer process. Fast and accurate predictions of the dynamic aspects of the phase change process are obtained and the full phase transition time is correctly calculated by using the radial basis neural network technique.

3D numerical investigation on flow boiling characteristics in large length-to-diameter ratio microchannel

To meet the demand of thermal management with large power and high heat flux in the future engineering applications, more and more attentions have been draw to develop the two-phase microchannel cooling technology. In this work, a three dimensional numerical investigation is performed to study the influence of mass flux and heat flux on the two phase flow boiling characteristics in a single microchannel with large length-to-diameter ratio. The related calculation results show that the Volume of Fluid (VOF) model coupled with Lee model can predict the two phase pressure drop and heat transfer coefficient of the microchannel well. And the flow patterns in the microchannel are classified as bubbly flow, slug flow and annular flow, which can be captured by this numerical model precisely. Besides, the transient pressure drop augments with the increase of mass flux. But the effect of mass flux on the amplitude of quasi-steady pressure drop and the peak value of time-averaged heat transfer coefficient along the microchannel is small. At last, the amplitude of quasi-steady pressure drop increases with the augmentation of heat flux. The maximum and fully developed time-averaged heat transfer coefficients along the microchannel increase with the heat flux.

Environment-adaptable PAM/CMC semi-IPN hydrogels microspheres with high latent heat achieved through dual locking water strategy

Polyacrylamide (PAM) hydrogel is easy to prepare and has been widely used in industrial and biomedical fields. But its mechanical properties and environmental adaptability are very poor. In this work, by introducing carboxymethyl cellulose (CMC) into the PAM crosslink network, a semi-interpenetrating (semi-IPN) network structure was constructed to improve the mechanical properties of PAM hydrogels. PAM/CMC hydrogel microspheres (HMPs) with semi-IPN structure were successfully prepared by in-situ precipitation droplet crosslinking polymerization (PDIC). On this basis, a double locking water strategy was proposed and achieved: firstly, lithium chloride (LiCl) was introduced into PAM/CMC hydrogel to retain the internal water; secondly, the PAM/CMC HMPs were coated with single layer graphene oxide (GO) to restrain the loss of free water on the HMPs surfaces. The morphology, the state of water in HMPs, the compression performance, phase transition behavior and heat transfer performance of the GO coated PAM/CMC/LiCl HMPs (GO@HMPs) were further studied. The experimental results showed that the CMC could effectively improve the compression performance of PAM HMPs, and the PAM/CMC HMPs had also good compression recovery performance. The anti-dehydration performance of PAM/CMC HMPs was effectively improved by the double locking water strategy. The latent heat of GO@HMPs was higher than that of the current commercial phase change microsphere materials. The GO@HMPs had excellent heat absorption ability and were expected to be used in infrared stealth and thermal camouflage fields.

Heat Transfer and Friction Correlations for R134a With Offset Strip Fin Surface

Single phase heat transfer analysis of R134a refrigerant (liquid phase) has been carried out using Computational Fluid Dynamics (CFD) approach for offset strip fin. Colburn j factor and Fanning friction factor are predicted for offset strip fin. The correlations are developed at Reynolds number range of 100-15000. The effect of fin geometry (fin spacing, fin height, fin thickness and lance length) on the enhanced heat transfer and pressure drops were investigated. Colburn j factor and fanning friction factor f, correlations have proposed in terms Re and geometry parameters (h/s, t/s, t/l) for liquid refrigerant R134a in the present study. Two separate correlations have proposed for the low and high Re regions i.e. Between Re of 100-1000 and Re of 1000-15000. The numerical results are validated with experimental results, results are found in good agreement with experimental results. Variation is found less than 5%.

Dynamics of a Laser-Induced Cavitation Bubble near a Cone: An Experimental and Numerical Study

A bubble’s motion is strongly influenced by the boundaries of tip structures, which correspond to the bubble’s size. In the present study, the dynamic behaviors of a cavitation bubble near a conical tip structure are investigated experimentally and numerically. A series of experiments were carried out to analyze the bubble’s shape at different relative cone distances quantitatively. Due to the crucial influence of the phase change on the cavitation bubble’s dynamics over multiple cycles, a compressible two-phase model taking into account the phase change and heat transfer implemented in OpenFOAM was employed in this study. The simulation results regarding the bubble’s radius and shape were validated with corresponding experimental photos, and a good agreement was achieved. The bubble’s primary physical features (e.g., shock waves, liquid jets, high-pressure zones) were well reproduced, which helps us understand the underlying mechanisms. Meanwhile, the latent damage was quantified by the pressure load at the cone apex. The effects of the relative distance γ and cone angle θ on the maximum temperature, pressure peaks, and bubble position are discussed and summarized. The results show that the pressure peaks during the bubble’s collapse increase with the decrease in γ. For a larger γ, the first minimum bubble radius increases while the maximum temperature decreases as θ increases; the pressure peak at the second final collapse is first less than that at the first final collapse and then much greater than that one. For a smaller γ, the pressure peaks at different θ values do not vary very much.

A nonlocal theory of heat transfer and micro-phase separation of nanostructured copolymers

Directed self-assembly of block copolymer (BCP) has shown promise as a nano-patterning technology for various applications such as microelectronics, semiconductor manufacturing and biotechnology. In this paper, we present a thermodynamically consistent nonlocal model of phase transformation and heat transfer for BCP via the continuum theory of mixtures. Our model is developed based on the mass and energy balances of each phase and a set of microforce balances to describe the dynamics of microphase separation during self-assembly and the size and memory effects of heat conduction in BCP thin films. We derive constitutive relations for coupling the phase field and temperature through upscaling the self-consistent field theory of polymers, and present the connections between the derived nonlocal heat conduction model and the phonon Boltzmann transport equation. We provide a finite element solution of the proposed model that includes unconditionally stable time-stepping schemes, and we perform various numerical experiments that showcase different features of the model. Furthermore, we conduct three-dimensional numerical experiments of laser zone annealing process to qualitatively investigate the effect of laser velocity on the self-assembly behavior of BCP thin films. Our results show that the proposed model can simulate essential features of thermally induced phase responses of BCPs, consistent with experimental observations and high-fidelity simulations.

Digital assessment of phase changes and heat transfer for hydrates in microstructures using X-ray CT imaging

Natural gas-hydrates are plural clean energy resource with rich deposits, and hydrate behavior significantly affects the exploration, production and utilization of these energy resources. However, technical difficulties for effective production and utilization of these energy sources still exist. Hydrate formation using xenon and NaBr brine and X-ray computed tomography (CT) imaging experiments are conducted to investigate microstructural morphology phase behaviors of hydrates, and a novel multi-phase color difference separation method to segment the pore, hydrate, water and grain phases is proposed. Effects of underground temperature gradient on thermal properties during the phase changes of hydrates are analyzed, and their effects on flow properties are studied. Results indicate that the temperature fraction, hydrate phase fraction, latent-heat thermal energy (LTE) and total enthalpy decrease with increasing temperature gradient. Hydrates rapidly form approximately at time = 250s for temperature gradient of 50 K and time = 500s for temperature gradients of 100 K, 150 K, 200 K and 300 K, and the hydrate phase equals to each other approximately at time = 95s. The stable LTE and total enthalpy approaches to a maximum when the temperature gradient is 150 K. Moreover, the temperature fraction and total enthalpy decrease on average by 4.73%, 4.69% and 76.13%, 75.87%, and the hydrate phase fraction increases by 7.89% and 7.88% with increasing microporosity and micropore size from 34.66% to 41.93% and from 37.53 μm to 43.22 μm, respectively. The temperature fraction and total enthalpy increase on average by 5.29% and 76.67% with increasing pore-scale hydrate saturation from 0.73 to 1.00. The LTE remains constant with an increase in hydrate pore-scale variables of microporosity, micropore size and hydrate saturation from 34.66% to 41.93%, from 37.53 μm to 43.22 μm and from 0.73 to 1.00, respectively. In addition, numerical permeability computed by the proposed relation of microporosity and pore-scale hydrate saturation agrees well with experimental results, with the average errors all less than 5%. The temperature and total enthalpy in phase change heat transfer of hydrates improve the permeability. The LTE in phase change heat transfer of hydrates hardly changes the permeability, and hydrate phase decreases the permeability. This work provides the quantitative and qualitative evaluations of phase change and heat transfer behaviors of gas-hydrates, which are helpful and provide excellent tools to develop the techniques for the exploration, production and utilization of these energy resources to decrease the energy crisis.

CFD Modeling of Phase Change during the Flashing-Induced Instability in a Natural Circulation Circuit

Flashing-induced instability (FII) has a significant impact on the safe operation of a natural circulation circuit, a phenomenon frequently encountered in the cooling systems of advanced light water reactors. While one-dimensional system codes are commonly used for the engineering design and safety analysis of FII, there is a strong academic interest in understanding the underlying physical mechanisms. To address this, high-resolution computational fluid dynamics (CFD) simulations serve as a valuable tool. However, the current state of CFD modeling for two-phase flows with phase change, which are particularly highly transient fluctuating flashing flows, is still in its early stages of development. In this study, we establish a CFD model that focuses on interphase heat transfer to analyze the phase change during FII. By incorporating experimental data from the literature, we investigate the transient flow field and thermodynamic behavior in the riser of the GENEVA test facility. The study provides valuable insights into the non-equilibrium and interfacial transfer phenomena during the phase change as well as the effect of high-frequency fluctuation. Additionally, we discuss in detail the challenges associated with FII modeling and the limitations of the current model. We also provide suggestions for potential improvements in future numerical studies. The results show that the thermal phase change and heat transfer coefficient model adopted for the simulation reasonably captures the evaporation and condensation process. However, it tends to under-predict the evaporation rate, which results in a larger pressure drop through the riser. The observation that the void fraction close to the wall is higher than that in the riser center evidences that the reliable modeling of bubble size distribution as well as the inclusion of non-drag forces are important for predicting the transverse void distribution. Furthermore, it reveals that both the temperature and pressure change in an FII, and their effects on phase change should be taken into account simultaneously.

MATHEMATICAL MODELING AND NUMERICAL STUDY OF BIOMASS FIXED CARBON GASIFICATION IN A DENSE BED AT ATMOSPHERIC PRESSURE. PART 2. ANALYSIS OF NUMERICAL RESULTS

Using the constructed two-dimensional model of aerodynamics, heat-mass transfer and chemical reaction of coke-ash residue in a steam-air mixture at a pressure of 1 atm, taking into account interphase convective heat transfer, radiative-conductive heat transfer of the solid phase, radiative and conductive heat transfer of the bed with the reactor wall, gravitational forces and aerodynamic resistance, the unsteady process of lignin gasification in a fixed bed was theoretically investigated. It is shown that: 1) the maximum value of biomass temperature of 887 °С is reached in the oxidation zone, where exothermic reactions prevail over endothermic reactions; 2) the specified temperature turns out to be lower than the temperature of the beginning of ash deformation of 1050 °С, which indicates the slag-free operation of the gas generator; 3) the largest yield of gasification products occurs in the redox reaction zone, where heat absorption dominates over heat release; 4) a slag pad is formed near the grate, protecting the grate from overheating; 5) the largest changes in discrete phase movement speeds are observed in the oxidizing and reducing zones of the gas generator from –5.791.10−5 m/s до –1.86.10−5 m/s due to the change in particle diameter from 10 mm to 6.83 mm (ash). Bibl. 12, Fig. 6.

Reactive Transport Processes in Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells are devices that directly convert chemical energy to electricity. A hydrogen oxidation reaction takes place on the anode side, generating protons and electrons. In the cathode, oxygen reduction reaction involving oxygen, proton and electron occurs, producing water and heat. The water content in PEMFCs should be maintained at a reasonable amount to avoid water flooding or membrane dehydration. The thermal management and water management of PEMFCs are important for an efficient and stable operation of PEMFCs. Inside the multiscale spaces of PEMFCs, multiphase flow with a phase change, heat and mass transfer, proton and electron conduction, and electrochemical reaction simultaneously take place, which play important roles in the performance, lifetime and cost of PEMFCs. These processes should be well understood for better designing PEMFCs and improving the thermal management and water management.

Experimental investigation and modelling of the hydrate formation kinetics based on hydrate pore-scale distribution in porous media

Hydrate technology has a bright future for innovations in water, energy, and environmental applications. A reliable and applicable kinetic model of gas hydrate formation is essential for developing hydrate technology. In this work, the experiments of methane hydrate formation with different water saturation SA are conducted in the Cubic Hydrate Simulator (CHS), where the pressure profile and temperature distribution are measured. A new kinetic model integrating hydrate pore-scale distribution is established, assuming that the reaction area AS is controlled by the aqueous phase surface area along the gas-soluble direction. This new model is employed to replicate the experimental process numerically by the history-matching method, and the intrinsic reaction rate constant K0 is determined to be 850.0 mol/m2/Pa/s. In addition, we quantitatively distinguish the characteristics of the water pore-scale distribution in the excess-water, cementing-water, and excess-gas environments. The new model has been validated to be more excellent than those with four currently available models for the hydrate formation, and the sensitivities of the kinetic parameters are discussed in detail. The results show that the spatial distributions of the temperature T and hydrate saturation SH spatial distribution are heterogeneous in CHS due to the phase change and heat transfer effect. The excellent performance of the hydrate formation kinetics gives us strong confidence in the reliability and accuracy of the new model. This provides reliable predictions and mechanistic understandings of hydrate formation kinetics in the porous media.

Numerical analysis of conjugate convection heat transfer in an open cavity with different phase change materials surrounded by plexiglass

Phase change (PC) process and convection inside an open cavity equipped with two different PCMs are analyzed with the finite volume method with ANSYS Fluent. The analysis is conducted for three different Grashof number (Gr) values for fully and partly open configurations. It is observed that the PC becomes fast when the object is closer to the exit for the fully open case. The partly open case results in higher thermal performance improvements while the average Nusselt number (Nu) increment is 94.5% for PCM-18. PC and heat transfer characteristics are influenced by both material and location of the PCM. At Gr = 3.79 × 108, the average Nu rises by about 50% when PCM-22 is used instead of PCM-18. Location and type of PCM provide excellent tool for controlling the phase transition and heat transfer dynamics with a fully and or partly open cavity.

An impact of radiation on laminar flow of dusty ternary nanofluid over porous stretching/shrinking sheet with mass transpiration

The goal of current research is to determine the laminar boundary layer problem for the two-dimensional flow of ternary dusty nanoparticles through a porous stretching/shrinking sheet in the presence of radiation and mass transpiration. Generalized partial differential equations are converted to nonlinear ordinary differential equations after demonstrating an appropriate similarity transformation. Exact solutions are subsequently provided for the resulting system of equations. The development of ternary dusty nanofluids has significantly improved the heat transmission process for manufacturing and industrial applications, as well as in nanotechnology research. The influence of the various interesting parameters on the flow and heat transfer is analyzed and discussed in detail through plotted graphs. It was found that the basic similarity equations admit two phases for both stretching/shrinking surfaces. Graphs are used to illustrate the findings of this work. We found that the velocity fields increase with an increase in the inverse Darcy number value for the case stretching sheet while opposite effects can be observed in the shrinking case. Moreover, the magnitude of particle interaction parameter enhances as the solution domain raises. The findings disclose that the performance of ternary nanofluid phase heat transfer is improved compared to dusty phase performance.

Numerical investigation on effects of fuel rod with different shapes of bow deformation on the subcooled boiling of coolant in a fuel assembly

AbstractThe Eulerian two‐phase boiling model of the subcooled boiling of coolant in a 3 × 3 fuel assembly is established and compared with the experimental data to verify its accuracy. The effects of four shapes of bow deformation on subcooled boiling flow and heat transfer characteristics are obtained by comparing and analyzing the distributions of thermal–hydraulic parameters, including the axial wall superheat, liquid phase temperature, axial void fraction, various heat fluxes, heat transfer coefficient, and turbulent kinetic energy. All shapes of bow deformation will lead to the redistribution of coolant among different subchannels, and the distributions of thermal–hydraulic parameters would be greatly affected. The bow deformation of fuel rod easily causes local boiling, which results in local high temperature of liquid phase and bubble accumulation, and a decrease in the area of high liquid phase heat transfer coefficient on the surface of bowing fuel rod. Additionally, the non‐uniform distribution of turbulent kinetic energy caused by bow deformation in different axial sections not only affects the heat transfer performance of coolant, but also causes the increment in pressure drop, which has negative effects on the safe operation of the nuclear reactor. This paper can provide data and theoretical support for engineering design.

Lattice Boltzmann simulation of coupled depressurization and thermal decomposition of carbon dioxide hydrate for cold thermal energy storage

CO2 hydrate is a potential cold thermal energy storage material with latent heat of 500 kJ/kg, however, the dissociation principle of CO2 hydrate is different from that of solid-liquid phase change materials and therefore, exploring the dissociation mechanism of CO2 hydrate is of great significance for efficient cold storage. In this paper, a new lattice Boltzmann model is proposed, considering dissociation kinetics, two phase flow, heat transfer, latent heat, surface reaction, thermal buoyancy and variable parameter depended with temperature. The necessity of the temperature consideration related with latent heat and buoyancy is clarified. For the combined effect of depressurization decomposition and thermal decomposition of CO2 hydrate dissociation, depressurization decomposition diminishes as time increases and initial pressure increases and thermal decomposition enhances as hot wall temperature increases. The fully dissociated Fo is 0.544, 0.514, 0.604, 0.628, showing a first decreasing and then increasing trend while initial pressure increases from 0 to 0.002, 0.004, 0.006 lu. As hot wall temperature increases from 8, 10, 12–14 °C, the fully dissociated Fo is 0.566, 0.544, 0.473 and 0.419 respectively. This new lattice Boltzmann model is of significance in providing guidance for the future cold thermal energy storage system application by using CO2 hydrate.

Numerical investigation on effects of fuel rod with different bow deformation ratio X on two-phase boiling and flow performances of coolant in fuel assembly

The bow deformation of fuel rod usually occurs in Pressurized Water Reactor (PWR). As the flow channel in fuel assembly changes due to the bowing, coolant in subchannels is redistributed, which influences flow and heat transfer performances of coolant. In this article, based on Eulerian two-phase model and RPI boiling model, a 3 × 3 fuel assembly with bow deformation is studied in the STAR-CCM+, and typical C-shape bow deformation happens to the center fuel rod. The effects of fuel rod with different bowing degrees on coolant two-phase boiling and flow performances are compared. Numerical model is verified by comparing with the experimental data. The results show that significant local boiling occurs in the bowing region and liquid phase temperature increases dramatically in subchannels where cross-sectional area decreases if bow deformation ratio X less than 0.5. The averaged void fraction in bowing region gradually increases with the bowing degree, and it increases dramatically if X less than 0.2. Besides, the axial position of the initial boiling is gradually advanced, and the area of high liquid phase heat transfer coefficient on the wall of bowing rod decreases sharply when X less than 0.4. Meanwhile, the cross flow reduces gradually with the increase of bowing degree, indicating that bow deformation will inhibit the generation of cross flow. The turbulent kinetic energy of coolant in the region with reduced cross-sectional area greatly decreases when X less than 0.2, and the inhomogeneity of distribution brings great challenge to the safe operation of nuclear reactor core. Besides, excessive bow deformation will cause a great pressure drop.

Experimental study of direct contact condensation of spent vapor in a cocurrent flow packed tower under negative pressure

AbstractCondensers are often required in power generation systems to condense the exhaust steam generated at the end of the turbine. This paper will investigate the enhanced condensation process of spent steam in a parallel flow type. The operating parameters of steam temperature (Tcond), steam flow rate (Gin), cooling water temperature (Tin), and cooling water flow rate (Lw) will affect the condensation effect by changing the gas–liquid arrangement in the tower. In this experiment, an orthogonal test was designed in the Raschig ring to investigate the significance of these four operating parameters on the experimental results. Different types of packings have different condensation effects due to different accumulation methods. The same type of packing has a different surface area, resulting in different contact areas between the gas and liquid phases during condensation. In this experiment, four different packings will be investigated to find their condensation performance. This paper uses the size of subcooling (ΔT) as an indicator to evaluate the effectiveness of condensation, and the values of condensation rate (R), number of liquid phase heat transfer units (NTUL), and total volume heat transfer coefficient (Kv) are used as a reference for the effectiveness of condensation. The results show that the overall condensation effect of regular packing is better than that of random packing, The average condensation rate of regular packing is 95%, the average condensation rate of random packing is 90%, the subcooling of regular packing is about three to five smaller than that of random packing, the heat transfer coefficient of regular packing is about 1.5 times of that of random packing. And by fitting the Kv data for different packings, an empirical formula was obtained that can be used to predict the Kv size of other packings.

Numerical study on particle distribution characteristics of slush hydrogen in a cryogenic tank

A numerical model considering phase change and heat transfer was established by the Euler-Euler two-fluid method to investigate the storage characteristics and two-phase flow field of slush hydrogen. Numerous numerical simulations were performed to discuss the effect of particle diameter (dp = 0.02–0.5 mm), content of solid hydrogen (αs = 10%–50%), and heat leakage (q = 50–200W·m−2) on the flow field. It was found that particle deposition could occur during the storage process, and there exist moving vortices with contrary directions under specific conditions. The sedimentation characteristics and vortex size are influenced by many factors including particle size, solid hydrogen content, and heat leakage. An increase in particle size could lead to the strengthening of precipitation and the expansion of the counterclockwise vortex region on the right side of the tank. And the increase in solid hydrogen content could result in more deposition and more collisions and friction between particles. Moreover, the increase in heat leakage could increase the area of the counterclockwise vortex. Numerical results of the deposition and flow field characteristics in the storage tank could clearly show the physical law of the slush hydrogen so that the uniform distribution of slush hydrogen could be promoted for efficient storage and application.

The simulation analysis on the influence of non-closed droplet structure on thermal/ flow performance of pin fin heat sinks

In order to improve the heat transfer performance of microchannels, considering from balance flow resistance and increasing heat transfer area, a non-closed droplet pin fin array microchannel has been designed. The purpose of this paper is to study the inner influence of non-closed droplet structure on convection heat transfer by means of simulation. Through the simulation tool ANSYS Fluent, the working conditions of heat flux density from 5 W/cm2 to 85 W/cm2 are simulated respectively, with the inlet flow as 1.5 kg/h and the inlet fluid temperature as 40 °C unchanged. Along with the increase of heat flux density (5 W/cm2 ⩽ q ⩽ 85 W/cm2), the pressure drop, the bottom temperature as well as the heat transfer coefficient continue to rise, but the rising rates are various. Such variation could be explained by the different heat exchange processes: single phase heat transfer, bubble nucleation, growth and migration and then dry phenomenon, which can be observed from the vapor phase distribution results. The distribution of vapor phase under multiple heat flux explains the variation of pressure and temperature in different stages. It could be concluded that the non-closed droplet pin fin has a strong fractal effect on the fluid. After multiple shunting and confluence, the flow velocity of the fluid on both sides is significantly greater than that between the fins, whose average velocity is 0.135 m/s faster than that between the pins. Besides, the heat transfer effect of the corresponding walls on both sides is also better than that between the pin fins. Because the pin fin has the characteristics of droplet structure, the boundary layer on both sides of the pin fin will be separated and the heat transfer performance will be enhanced. The temperature of the pin fin head is lower, and the temperature of the pin fin tail is higher, with an average difference as about 9.32 °C. The comparison research between non-closed droplet and traditional droplet pin fin has been conducted, as well. It could be concluded that when 5 W/cm2<q < 60 W/cm2, the heat transfer coefficient of the opening droplet microchannel is higher, with pressure drop lower. The main reason is that the improvement of the non-closed structure reduces the kinetic energy loss caused by the collision, and promotes the emergence and growth of the vaporization core.