Phase Change Heat Transfer Process Research Articles

Effect of the self-rewetting fluids on heat transfer performance of gravity heat pipes with sintered porous wick

The distribution of the working fluid in a heat pipe directly affects the phase change heat transfer process. This paper explores how self-rewetting fluids (SRWF) and porous wicks affect the distribution of working fluids and heat transfer efficiency in gravity heat pipe (GHP). We sintered a porous wick onto the evaporator section and tested two working fluids: water and SRWF (3 % butanol aqueous solution). The filling ratio of the working fluid φ was varied from 11.5 % to 46 %. We found that at large filling ratios, porous wick surface will immerse in liquid, and at small filling ratios the heating surface will lack of liquid. Consequently, the GHP operates at a lower temperature at a filling ratio of 23 % compared to 11.5 % and 46 %. The type of working fluid significantly impacts the operating temperature and temperature uniformity. The Marangoni effect of the SRWF enhances the rewetting of the fluid in the porous wick, but this effect is only observed after the temperature reaches the inflection point (where the SRWF exhibits minimum surface tension). Before this point, the GHP operating temperature with SRWF is relatively higher than with water. Correspondingly, the temperature uniformity on the evaporator section is better when using SRWF. At φ = 23 %, Q = 500 W the temperature uniformity improved by 66 %. At Q = 660 W the evaporator heat transfer coefficient increased from 3991.6 W/m2K to 6130.5 W/m2K which is a 53.6 % improvement over water. We used an infrared camera to visualize the rewetting phenomenon of SRWF in the heated porous wick, confirming that SRWF can rewet the dry-out area, thus validating our hypothesis.

Analytical modeling of desublimation of a phase change material (PCM) in a porous medium with temperature-dependent volumetric heat sink and convection due to air-mixed vapor

The desublimation phase change heat and mass transfer process in a porous medium occurs during the conversion of vapor into solid form, which has several applications in chemical deposition and industrial coating. For economic feasibility, reducing the operating time of the conventional desublimation technique is of much interest. Toward this goal, current work presents a mathematical model for desublimation that accounts for a volumetric heat sink connected with temperature. A linear profile of the volumetric heat sink varying with temperature is modeled within the frozen region. Further, the rate of water vaporization (with mixed air) produces a convective term, which is also accounted for in the frozen region. Despite previous studies on desublimation phase change process, there is still insufficient mathematical modeling of this particular phenomena. The solution to the governing set of dimensionless partial differential equations is obtained analytically by employing the space-time transformation. Results indicate that the rate of desublimation process becomes faster with increasing the strength of the volumetric heat sink, which results in the reduction of the total operating time to desublimate of a phase change material. Higher values of the dimensionless temperature parameters also accelerate the desublimation process. On the other hand, a larger value of the convective term is found to slow down the desublimation process. The dimensionless moisture concentration profile in the vapor region increases with increasing the value of the Luikov number. Observations from this study are expected to aid in the fundamental design of processes including industrial coating, preservation of biological products, and evaporative deposition where desublimation plays a key role.

The mechanism by which thermal coupling leads to an asymptotic maldistribution stability boundary for flow boiling in parallel channels

Phase change heat transfer processes are attractive for the efficient thermal management of advanced semiconductor devices, with flow boiling in parallel microchannel heat sinks being one promising solution. However, there are several implementation challenges associated with two-phase flow in parallel microchannels, particularly flow maldistribution, which can adversely affect performance and reliability. Two-phase flow models can be useful in predicting and understanding the instability mechanisms that leads to maldistribution, such that parametric performance trends and safe regions of operation can be identified. Channel-to-channel thermal coupling has been shown to alleviate maldistribution, but it is not yet understood why this effect is limited to some critical lateral thermal conductance above which there is no further benefit. In the current work, a two-phase flow model with a lumped thermal capacitance representation of the heat sink wall is developed to identify the mechanism for this asymptotic maldistribution stability boundary for thermally coupled microchannels. The lumped model allows the nature of stability boundary to be explained via a scaling analysis of the eigenvalues. In such systems, it is identified that a single eigenvalue determines the occurrence of flow maldistribution. Scaling analysis shows that, for small values of thermal conductance, this eigenvalue becomes a quadratic function of thermal coupling, which enhances the stability of microchannels and moves the stability boundary. However, for large values of thermal conductance, the eigenvalue is dependent only on the fluid properties, leading to a limit at which thermal coupling can no further improve stability or affect the stability boundary. The lumped model developed in this work enables mechanistic understanding of the role of channel-to-channel thermal coupling on mitigating flow maldistribution and therefore may offer important guidance on the design of flow boiling systems and heat sinks.

Identifying steady and pulsatile two-phase flow regimes with pressure drop signals and acoustic emissions

Identifying two-phase flow regimes is vital for understanding phase-change heat and mass transfer processes. Traditionally, flow regime identification has relied on subjective flow visualization studies, which are then converted to flow regime maps applicable to specific operating conditions. However, these conventional, largely subjective, maps fall short in predicting abrupt changes in flow patterns that often occur during regular operation of vapor compression and absorption heat pumps and other thermal systems. Conventional flow regime maps are also inadequate for addressing the transient, intermittent, or periodic flow regimes that occur in boiling and condensation enhanced using acoustic and other emerging techniques. Therefore, there is a pressing need for alternative flow regime identification techniques that can adapt and reliably track rapid and local changes in two-phase hydrodynamics. Promising candidates for dynamic flow pattern classification include high-resolution pressure drop signals and acoustic emission spectra, which can provide insights into the local hydrodynamics within a flow channel. To assess the feasibility of these measurement techniques, differential pressure and condenser microphone measurements are recorded alongside high-speed videos of a two-phase flow of saturated R134a. The total mass flux and vapor quality are varied to understand the effects of phase velocity and liquid inventory on wave propagation in the channel. Additionally, forced oscillations are introduced to a steady two-phase flow to analyze their impact on flow patterns and their corresponding pressure drop and acoustic signals. Statistical analyses, including Gaussian mixture modeling, are employed to reveal characteristic pressure drop probability associated with each flow pattern, which form the basis for developing a model capable of predicting flow regimes in both steady and oscillating flows. The resulting framework introduces a new flow regime identification technique that can adapt to dynamic operating conditions, benefiting a wide range of thermal systems and phase-change processes.

Phase change in a one-dimensional functionally graded material

Functionally graded materials (FGMs) are a class of materials with engineered microstructure to achieve spatial variation in properties so as to serve a desired function. While FGMs have been well-researched for their structural properties, there is a lack of investigation of FGMs in solid-liquid phase change heat transfer processes. A well-designed functionally graded phase change material (FG-PCM) may overcome some of the well-known limitations of the phase change process. In order to investigate this possibility, this work presents a theoretical model to predict phase change propagation in a one-dimensional FG-PCM containing an arbitrary spatial variation in thermal conductivity, thermal diffusivity and latent heat. The problem is solved using the method of eigenfunction expansion to determine the temperature distribution, wherein, spatial variation in thermophysical properties listed above is accounted for by deriving a first-order matrix ordinary differential equation in the coefficients of the series solution. Results are found to correctly reduce to the well-known Stefan solution under special conditions. The impact of variation in thermophysical properties is investigated in detail. It is found that while spatial variation in thermal conductivity and latent heat has a significant effect on the rate of phase change, the impact of the thermal diffusivity function is negligible for realistic values of the Stefan number. The effect of the Stefan number governing this problem on the rate of melting is investigated. The nature of phase change under linear (1+aξ), polynomial (1+aξn) and exponential (eaξ) functional forms of thermophysical properties is investigated. It is shown that an appropriate choice of these spatial functions may help overcome the well-known self-limiting nature of phase change and produce a nearly-linear phase change propagation curve. For example, results show 33% increase in phase change propagation for a linear (1+5ξ) variation in thermal conductivity compared to baseline. The theoretical tools developed here may help design and optimize functionally graded PCMs towards improved phase change heat transfer in applications of practical interest.

Analysis of the performance of mixed refrigerant chillers based on the impact of exergy glide temperature matching coefficient

A glide temperature matching model based on the exergy matching coefficient was established for the phase change heat transfer process of non-azeotropic mixed refrigerants. The exergy loss rate of the temperature difference and the exergy loss rate of the glide temperature in the condenser and evaporator were analyzed, and the temperature matching coefficient of mixed refrigerants parameter πglide was derived to indicate mixed refrigerants with large refrigeration capacity. The model was experimentally verified by the performance of three types of mixed refrigerants in chillers. The results show that the higher the glide temperature, the bigger the condenser πglide of the mixed refrigerants and the worse the temperature-matching effect. The smaller the πglide of the evaporator, the better the temperature-matching effect, and at the same time, the greater the cooling capacity. This model can be used for predicting the different component mixtures of working fluids.

Heat transfer simulation and performance optimization of plate-type phase change energy storage unit

As the core of the phase change energy storage technology, the heat transfer performance of the phase change energy storage unit has an important impact on the operating efficiency of the energy storage system. In this study, a three-dimensional CFD model of the plate-type phase change energy storage unit is established to simulate the melting process of paraffin wax. Three types of plate-type phase change energy storage unit models are established, without fins, single fin, and double fins. The influence of cylindrical fin on natural convection melting process of paraffin is studied, which provides the basis for the design and performance optimization of plate-type phase change energy storage unit, and improve its application value. The results show that the melting time of paraffin in the energy storage unit without fins is 858 s, and the melting time is shortened to 827 ~ 842 s after adding single fin. The melting time of paraffin wax with single fin is lower than that with double fins. For the plate-type phase change energy storage unit, adding fins at the central section can effectively improve the melting rate of phase change material. The single fin A located at the lower part of the central section has the greatest promotion effect on paraffin melting. The key to enhance the phase change heat transfer process in plate-type phase change energy storage unit is the paraffin in the lower half of the symmetry plane.

Molecular dynamics calculations of the enthalpy of vaporization for different water models

Phase-change heat transfer processes involving water play a key role in numerous societal applications, such as electrical power generation, microelectronics cooling, or water desalination. Advanced computational tools, such as molecular dynamics (MD), are increasingly being used to simulate these processes, especially on nanostructured surfaces and in nanoparticle suspensions, to gain insight into the unique nanoscale physics at play. In these studies, it is critical to use models of the water molecule that yield accurate predictions of water’s thermophysical properties, particularly its enthalpy of vaporization. Here, we use MD to determine the enthalpy of vaporization (hfg) for six common water models and four different values of the cutoff radius (i.e., the intermolecular distance beyond which interactions are simplified or ignored). The most accurate prediction of hfg (within 2 % of the value tabulated by ASHRAE) comes from the TIP3P water model with a cutoff radius of 14 Å. We also conducted a preliminary study of the variation of hfg with pressure and found reasonable agreement between simulations and tabulated ASHRAE data (<7% error). This work provides physical insights into the sensitivity of the predicted macroscopic thermophysical properties of water to minute changes in the atomic-level properties and is expected to inform future MD-based studies of phase change processes of water, especially as they occur at elevated pressures and on nanostructured surfaces and in nanoconfined geometries.

Application of graded phase change materials for solar energy inter-seasonal storage heating and thermal storage characteristics

Abstract In this paper, firstly, the heat transfer characteristics of the stepped phase change accumulator are studied, and the location of the solid-liquid phase interface is determined by the phase fraction in a fixed grid scheme, while the phase change heat transfer process is simulated using Fluent. Secondly, for the phase change heat transfer problem, the enthalpy-porosity method in the Solidification/Melting model is used to treat the solid-liquid mixed paste region of the phase interface as a porous media region, and the evaluation system is constructed in terms of heat storage and discharge efficiency, heat storage, and heat recovery efficiency. Then the mathematical model, boundary conditions and solution parameters of the stepped phase change heat accumulator are set, and the data analysis of the effect of the pool height-to-diameter ratio on the heat storage in the solar inter-seasonal storage heating system is carried out by using ANSYSCFD software. The results show that the heat storage of the system also shows an overall increasing trend with the increase of the pool height-to-diameter ratio, and the heat storage of the system increases faster when the height-to-diameter ratio increases from 0.2 to 1.0 in sequence, and the heat storage of the system increases less when the height-to-diameter ratio changes between 0.9 and 1.8, and basically tends to be stable. This study realizes the graded heat storage and graded heat use of solar energy, which is useful for the research of solar heat supply and heat storage.

Experimental and numerical investigation on thermal characteristics of the heat sink integrating 3D vapor chamber heat spreader and liquid cooling fins

The traditional vapor chamber/ heat pipe heat sink in high-power chip heat dissipation structures consists of two separate parts. The contact thermal resistance between these parts leads to an increase in thermal resistance during the heat transfer process. To mitigate the contact thermal resistance and improve the heat dissipation performance of vapor chamber heat sinks, this paper proposes a heat sink integrating a 3D vapor chamber heat spreader and liquid cooling fins. Experiments and simulations were carried out to analyze the heat transfer characteristics under different heating powers. The pressure drop and thermal resistance were calculated to analyze the internal phase-change heat transfer process and capillary heat transfer limit. The simulation results were in close agreement with the experimental data for heating powers ranging from 397 to 795 W, with the thermal resistance of the proposed heat sink of about 0.04℃/W. Compared to three traditional vapor chamber heat sinks operating under the same heat flux, the proposed type exhibited a noteworthy enhancement in the heat transfer performance, leading to a reduction in thermal resistance by approximately 44% to 67%.

Numerical method for gas-liquid two-phase flow with phase change heat transfer considering compressibility using OpenFOAM

The numerical simulation of phase change heat transfer is important for predicting the gas-liquid two-phase flow and heat transfer characteristics and optimizing the phase change heat dissipation system. For the isovolumetric phase change heat transfer process, the compressibility of the gas phase has a significant impact on the simulation accuracy. A numerical simulation method of flow and phase change heat transfer considering gas-liquid two-phase compressibility is established based on VOF method using OpenFOAM in this paper. This method introduces a generalized phase change source term and a compressible source term to improve the isoAdvector geometric reconstruction algorithm and establishes a method for capturing the phase interface of a compressible two-phase flow. The phase change flux based on the phase interface is converted into a phase change source term based on the unit volume by calculating the phase interface density. The compressible term of the governing equation is constructed and its implicit discrete method is proposed. The coupling between velocity and pressure is realized based on the PISO algorithm. A numerical calculation method for phase change heat transfer of compressible two-phase flow is established. The effectiveness and accuracy of the proposed numerical method for predicting the heat transfer characteristics of phase change flows are verified by the simulation of vertical flat film condensation and film boiling. The numerical simulation results are in good agreement with the experiment. Compared with the other numerical simulation methods, the proposed method considering the influence of the compressibility of the gas phase on the flow and heat transfer characteristics in the heat pipe has high accuracy in predicting the gas-liquid two-phase flow, capturing the evolution characteristics of the phase interface and predicting the phase change heat transfer. The numerical simulation method can provide algorithm support for the numerical simulation of compressible two-phase flow phase change heat transfer and the design of a phase change heat dissipation system.

Numerical study on the effect of thermal diffusivity ratio in phase change heat transfer of crude-oil using lattice Boltzmann method

When the long distance crude-oil pipe-line is stopped, the crude-oil will solidify gradually with the decrease of the temperature in the pipe-line. The solid-liquid thermal diffusivity can reflect the ability of heat diffusion in the phase change heat transfer process of crude-oil stop-transport. Based on the mathematical model of oil phase transition heat transfer established by enthalpy method, the lattice Boltzmann method is used to solve the governing equations of oil phase transition heat transfer. According to the simulation results, the phase change heat transfer process of crude-oil is divided into three-stages, and the mechanism of the phase change heat transfer process of crude-oil is studied. The results show that the influence of solid-liquid thermal diffusion ratio increase gradually with time. When Fourier number ?0.043, Nusselt number and convective heat transfer intensity of mobile phase interface slightly decrease with the increase of solid-liquid thermal diffusivity ratio. The research results of this paper can provide a reference for controlling the stoppage time of pipe-line.

Review of phase change heat transfer enhancement by metal foam

• Enhancement characteristics of metal foam on solid-liquid phase change heat transfer and liquid-gas phase change heat transfer are reviewed. • The mechanism of metal foam enhancing phase change heat transfer and the factors affecting the phase change heat transfer process are comprehensively discussed. • Existing methods for optimizing phase change heat transfer performance within metal foam are classified and evaluated. • The practical applications of metal foam enhanced phase change heat transfer in recent years are summarized and compared. • This review will lead to a better understanding on the designing and applying of efficient metal foam-phase change heat transfer systems. Metal foam is a novel multifunctional material with high porosity, high surface density, and excellent heat transfer performance. Embedding metal foams into phase change heat transfer systems can be used to improve the comprehensive heat transfer performance, which is receiving increasing attention in the field of thermal management. This paper focuses on the lasted advances in solid-liquid phase change heat transfer and liquid-gas phase change heat transfer within metal foams, and specifically analyzes the influencing factors on phase change heat transfer performance as well as the mechanism of metal foam effects on phase change heat transfer. Different optimized techniques for improving phase change heat transfer within metal foams and the current state of metal foam engineering applications for improving phase change heat transfer are reviewed and discussed. It is concluded that the addition of metal foam can significantly enhance the heat transfer performance of solid-liquid phase change systems and liquid-gas phase change systems, but it is accompanied by an inhibitory effect on natural convection, an obstructive effect on bubble overflow and an elevated effect on pressure drop. The application of gradient porous structure, metal foam fins, V-groove structure or changing the surface wettability of metal foam is a feasible way to alleviate the above problems. Meanwhile, it is pointed out that the heat transfer performance of phase change within metal foam is influenced by the interaction of various factors, and some key issues regarding the influence mechanism of PCM-device orientation, pore distribution, surface wettability, and structural properties on heat transfer performance still need to be studied to develop more efficient and compact heat sinks.

Constructing a ghost fluid layer for implementation of contact angle schemes in multiphase pseudopotential lattice Boltzmann simulations for non-isothermal phase-change heat transfer

The PP scheme (primitive pseudopotential-based scheme), the MP scheme (modified pseudopotential-based scheme) and the IVD scheme (improved virtual-density scheme) are the three most widely used contact angle schemes in pseudopotential lattice Boltzmann (LB) models to simulate wetting characteristics of multiphase flow over solid surfaces under isothermal conditions. In this paper, we apply these schemes to simulate the problem of sessile droplet evaporation on a heated substrate, which is an example of non-isothermal phase-change heat transfer process. It is found that the substrate heating effect destabilizes algorithms of these schemes in certain ranges of contact angles of a heated substrate. The droplet interface shapes simulated by the PP scheme and the MP scheme are inaccurate at obtuse contact angles due to large fluid density variations near the wall. The spurious currents near the droplet triple-phase contact line are very large in the MP scheme, causing the deformation of the Marangoni vortex shape inside the droplet and the erroneous droplet interface temperature distribution near the triple-phase contact line. The addition of a special ghost fluid layer on the wall proposed in this study can improve numerical stability of the PP and the MP schemes for application under non-isothermal conditions as well as under high saturated liquid/vapor density ratios. Although the IVD Scheme (with the nearest fluid layer temperatures above the heated wall chosen for calculating the effective mass of wall nodes) is also stable at low liquid/vapor density ratios, its numerical stability at high density ratios is not as robust as those of the PP and the MP schemes if a special ghost fluid layer is added in these schemes. It is shown that by adding such a special ghost fluid layer on the wall, large near-wall fluid density variations diminish in the PP and MP schemes and accurate droplet interface shapes can be recovered at obtuse contact angles. The spurious current in the MP schemes can be also reduced and accurate Marangoni vortex shapes in the droplet and droplet interface temperature distribution near the triple-phase contact line can be predicted.

Optimization on a novel irregular snowflake fin for thermal energy storage using response surface method

In this study, the horizontal sleeve phase change heat storage unit filled with RT55 is taken as the research object. Providing at the low thermal conductivity of phase change materials (PCM), this work proposes using an irregular snowflake-shaped longitudinal fin structure to improve the melting performance of horizontal latent heat storage sleeves (LHTES) under natural convection and to numerically simulate the phase change heat transfer process. Here, Thermal assessments on the melting fraction, temperature field, velocity distribution, and heat storage for melting are made. Results demonstrate that the snowflake fin structure significantly shortens the full melting time of LHTES, saving 45.92% time compared to the traditional fin structure. This study reveals that moderate changes of fin length, width, shape, and distribution angle could shorten the heat filling time. As a result of aggregated evaluation of the heating time, heat storage capacity, and heat storage temperature, the study determined the optimal fin distribution angle α to be 40°. This work further optimized the geometric parameters using the response surface method (RSM) and proved that the optimal solution to be the fin end length at 13mm, the width at 0.58mm, and the bifurcation angle at 40°.

Solidification performance analysis of bionic spider web vertical latent heat system based on response surface method optimization

The vertical sleeve phase change heat storage unit filled with RT55 is taken as the research object. Aiming at the low thermal conductivity of phase change materials, a vertical latent heat storage sleeve (LHTES) with spider web structure optimized by response surface method is proposed to improve the solidification performance of latent heat storage system, and the phase change heat transfer process is simulated by numerical simulation method. The enhanced heat transfer characteristics of phase change material (PCM) unit in casing with different spider web fin sizes are studied. The results show that reasonably changing the fin spacing, main fin thickness and branch fin thickness of spider web shape fins can reduce PCM solidification time and evaluation temperature correspondingly, and increase the heat dissipation of LHTES. Combining PCM solidification time, heat release of LHTES and PCM average temperature as evaluation indexes, the solidification heat performance of LHTES is comprehensively analyzed, and the geometric parameters of fins are optimized by response surface method (RSM), and the optimal solution is obtained as follows: the spider web fin spacing (H) is 30.00 mm, the spider web main fin thickness (m) is 3.91 mm, and the spider web branch fin thickness (L) is 2.64 mm. Finally, the economic analysis finds that the spider web structure LHTES has high economic efficiency.

Theoretical modeling of solid-liquid phase change in a phase change material protected by a multilayer Cartesian wall

Theoretical modeling of solid-liquid phase change processes is of much interest in energy storage and thermal management. While most theoretical phase change models assume that the phase change material (PCM) is in direct contact with the thermal source/sink, in most practical scenarios, the two are separated by a thick wall, which, in some cases, may comprise multiple heterogeneous layers. Accounting for thermal conduction through the multi-layer wall is important to ensure accuracy of the predicted phase change characteristics. This paper presents theoretical analysis of phase change in a system comprising a PCM and a multi-layer Cartesian wall using the eigenfunction expansion method and analysis of multi-layer thermal conduction. Thermal contact resistance between wall layers, and between the wall and PCM are accounted for. The predicted phase change front propagation is shown to agree well with past work for special case of a homogeneous wall, as well as with numerical simulations. Two distinct timescales in the solution, related to diffusion through the wall and phase change propagation in the PCM are identified. The impact of the imposed temperature, wall thermal diffusivity and thickness are presented in non-dimensional forms. Practical problems related to design of a PCM wall for energy storage are solved, showing two very different characteristics of stainless steel and polypropylene walls, as well as the impact of wall thickness on phase change propagation. The results presented here improve the fundamental understanding of phase change heat transfer processes, and are particularly relevant for relatively thick, thermally insulating walls over relatively short time periods, for which a resistance approximation for the wall is not accurate.

Thermal performance analysis of triple casing latent heat system based on sinusoidal function type corrugation

The natural convection disappears and the melting rate of phase change material (PCM) decreases in the microgravity environment of spacecraft operation. For the characteristics of low thermal conductivity of phase change materials, a triple casing based on sinusoidal function type corrugated structure as latent heat storage system (TTES) is proposed to improve the melting performance of the latent heat storage system. In this paper, the study model is simplified to a 2D model using commercial CFD software to numerically simulate the phase change heat transfer process, and the heat transfer characteristics of the sinusoidal function type corrugated triple casing and the effect of Reynolds number on the melting process are investigated. The results show that: the joint action mechanism of sinusoidal corrugation structure and phase change material local heat transfer can significantly shorten the heat charging time; reasonable change of corrugation period and crest height can shorten the heat charging time and increase the heat storage; comprehensive analysis of heat charging time, heat storage and average heat flux, through single-factor optimization to obtain a sinusoidal pipe with corrugation period between 100 mm and 150mm and crest height around 15 mm on The comprehensive performance of flow heat exchange has the best effect.

Numerical simulation and conceptual design of an MW-grade space heat pipe radiator

In recent years, nuclear reactor systems have been widely used in the space. The design of a radiator is of great importance as its heat dissipation performance directly determines the upper limit of the overall output power of the space nuclear propulsion system. In the present paper, a space radiator is divided into heat dissipation units, among which the heat pipes and fins are numerically modeled and analyzed. Kalium was selected as the working medium in the heat pipe, and the size of the heat pipe was designed based on the limitations, with the length of the evaporation section and the condensation section as 150 mm and 250 mm, respectively. VOF- Lee model was applied to simulate the phase-change heat transfer process inside the heat pipe, by setting the parameters of the hot-end temperature, the cold-end heat flux, etc. In addition, S2S model was used to examine the influences of thickness and width of the fin on the heat dissipation performance, so as to determine the optimal fin size. Finally, the heat pipes and fins were assembled into a whole radiative cooling system, with a mass-area ratio below 7 kg/m2 and a total heat dissipation power at 3.58 MW.

Liquid-to-vapor phase change heat transfer evaluation and parameter sensitivity analysis of nanoporous surface coatings

The goal of this research is to create a deep learning approach coupled with explainable artificial intelligence (DL-XAI) to evaluate the liquid-to-vapor phase change heat transfer in nanoporous surface coatings. Over the years, nanoporous coated surfaces have been employed to increase the efficacy of the liquid-to-vapor phase change heat transfer process. Despite a considerable body of experimental data on the pool boiling of coated nanoporous surfaces, the pool boiling phenomenon of these surfaces with various working fluids is poorly understood. In this study, random forest-based optimization (RF) has been used to tune the hyper-parameters for the DL model. The optimized model can predict the desired parameter with an R2 = 0.99. Besides, the parametric analysis has been performed to highlight the impact of each parameter on the output parameter. Through XAI, heat flux, conductivity of the substrate material and the pore diameter are unveiled to be the most influencing surface features for the nanoporous coatings. The proposed method can be used to optimize nanoporous coated surfaces for various working fluids.