Heat Of Phase Transition Research Articles

Study on phase transition heat transfer of nanofluids in porous media based on LBM

In this paper, a lattice Boltzmann method is used to simulate the phase transition heat transfer of nanofluid in a miniature heat tube in a porous medium. Based on this, the existing research basis is summarized, the influence of nanoparticles on the thermal properties of the base solution is analyzed, the relevant thermal property prediction model is constructed, and the thermal property parameters of nanofluid are fitted. We generated porous media with different porosity with particle size of 100 micron to 150 microns. Combining the force form proposed by Gong with the exact difference method, the interparticle force is introduced. Based on the improved LBM model and the coupled energy equation, so as to analyze the phase transition heat transfer situation of nanofluids with different thermal properties in porous media.The study shows that nanofluidics can effectively enhance the heat transfer performance of heat pipe equipment.In a certain concentration limit, with the increase of volume concentration, the heat transfer performance of heat pipe is enhanced. The greater the temperature difference between the cold and heat source, that is, the higher the temperature of the heat source, the lower the cold source temperature, the better the heat transfer performance of the heat pipe. For the fluid flow in the porous media region, that is, the turbulent phenomenon that may occur in the porous media, and more vortices occur in the porous media with 40% and 50% porosity. Higher porosity has better heat pipe temperature uniformity.

Rational Mode Parameters of Power Units Operating in Modern Energy Market Conditions

The paper analyzes the operation of condensing and heating turbines in modern energy market conditions with an assessment of the impact of operating parameters of live and secondary steam on economic indicators. It has been shown that when operating at variable loads, the most effective in terms of high-pressure turbines is a rational reduction in the initial pressure ps (sliding pressure), which leads to an increase in thermal efficiency by 1-1.5%. The experimental results of a study of the vacuum effect in the condenser on fuel consumption are presented in the paper as well. Using a specific example of the K-320-26.5 turbine unit, the need for a rational choice of cooling water flow in winter season to ensure optimal vacuum is shown. The issue of choosing a rational steam reheat temperature tr is examined in more detail. It has been established that one of the main reasons for the decrease in the efficiency of turbine units when operating in variable modes is the irrational use of the reheat temperature and the heat of phase transition in the flow part of the low pressure cylinder. The physical explanation of these processes in the turbine as tr decreases is given in detail. It has been shown that, as a result of analyzing the operation of turbine units of various capacities, a rational choice of reheat temperature (reducing tr by 10-20 °C) increases thermal efficiency by 1-2 %, and turbine efficiency - by 0.4-1.0 %. It is recommended to consider the pressure of the hot steam of the high pressure cylinder (рs), the pressure in the condenser (рc=f(tcirc.water)), as well as the reheating temperature tr, which altogether leads to a reduction in heat consumption by 2.5-3.5 % as rational parameters of steam when operating in variable modes. In order to increase the economic efficiency of the operation of turbine units of TPPs and CPPs at reduced loads, it is recommended to revise the regulatory documentation on the current amendments for changes in the reheat temperature. It is stated that with strict adherence to the recommendations discussed above, fuel savings at TTPs and CHPs in Ukraine can amount to 250–300 thousand tons of coal per year.

Constraining the Onset Density for the QCD Phase Transition with the Neutrino Signal from Core-collapse Supernovae

The occurrence of a first-order hadron–quark matter phase transition at high baryon densities is investigated in astrophysical simulations of core-collapse supernovae, to decipher yet incompletely understood properties of the dense matter equation of state (EOS) using neutrinos from such cosmic events. It is found that the emission of a nonstandard second neutrino burst, dominated by electron antineutrinos, is not only a measurable signal for the appearance of deconfined quark matter but also reveals information about the state of matter at extreme conditions encountered at the supernova (SN) interior. To this end, a large set of spherically symmetric SN models is investigated, studying the dependence on the EOS and the stellar progenitor. General relativistic neutrino-radiation hydrodynamics is employed featuring three-flavor Boltzmann neutrino transport and a microscopic hadron-quark hybrid matter EOS class. Therefore, the DD2 relativistic mean-field hadronic model is employed, and several variations of it, and the string-flip model for the description of deconfined quark matter. The resulting hybrid model covers a representative range of onset densities for the phase transition and latent heats. This facilitates the direct connection between intrinsic signatures of the neutrino signal and properties of the EOS. In particular, a set of linear relations has been found empirically. These potentially provide a constraint for the onset density of a possible QCD phase transition from the future neutrino observation of the next galactic core-collapse SN, if a millisecond electron anti-neutrino burst is present around or less than 1 s.

Numerical study of thermodynamic and hydrodynamics in a type B LNG cargo tank during sloshing excitation

The hydrodynamics and thermodynamics properties in a type B liquefied natural gas (LNG) cargo tank during sloshing excitation are investigated in this research using the numerical model that takes phase transition and exterior heat leaking into account. In order to forecast the movement of the vapor–liquid interface, the mesh motion treatment in conjunction with the volume of fluid (VOF) approach is used. The user-defined function (UDF) realizes the sloshing excitation. Its viability is confirmed by comparing the numerical model with related fluid sloshing experiments. The impacts of various sloshing periods, amplitudes, and filling rates on the hydrodynamics and thermodynamic properties were examined using numerical analysis of heat flux, the mass of boil off gas (BOG), internal energy, and pressure in the LNG cargo tank. Even with varying filling rates, the numerical findings demonstrate that resonance happens if the sloshing period corresponds to the natural period. As a result, this research serves as essential for gaining a thorough comprehension of thermodynamic, hydrodynamics and BOG mass properties during sloshing excitations in marine LNG transport.

Artificial neural network-based optimization of heat absorption process of phase change materials in a novel-designed finned-plate latent heat storage system

As the world transitions to more renewable and clean energy sources, energy storage systems become crucial. They assist in storing surplus energy produced during peak production times and release it when there is a high energy demand. Phase change material (PCM) based latent heat storage systems are appropriate candidates for efficient thermal energy storage. Their ability to harness the latent heat of phase transitions provides energy density, temperature control, and reduced heat loss advantages, making them well-suited for various applications. In the current research, a novel plate latent heat storage system (P-LHS) inspired by plate heat exchangers was introduced to enhance heat absorption. Besides, to facilitate the limited thermal conductivity of the PCM and increase natural convection phenomena, several fins were applied within the P-LHS system. Artificial neural network (ANN) models were exerted to anticipate the duration needed for melting of 70 % (φ = 0.7) and 100 % (φ = 1) of the PCM. The input variables of the ANN models were the fin angle (β), the distance between two fins (D), and the fin's trail angle (α). This research examined different configurations of the fins within the P-LHS system to find the optimal one. In all the designed Tests, the heat absorption and temperature distribution within the PCM were accelerated; thereby, the melting time up to φ = 0.7 and φ = 1 was reduced remarkably compared to those in the fin-less P-LHS system. Besides, for the fastest full melting of the material in the P-LHS system, the optimal design 2 (OD2) was proposed, in which the fins should have the dimensions of α = 171.450°, β = 97.540°, and D = 27.545 mm. In OD2, the time needed until the melting of 70 % of the PCM was decreased by approximately 65.68 %. While, the necessary duration for the PCM to melt entirely was 1574 s, approximately 66.80 % less than the time needed for melting the substance in the system without fins (4741 s). This reduction in melting time was about 53 min, which is a significant amount of time in energy storage systems.

Thermal Stability and Flame Retardancy of Rigid Polyurethane Foam Composites Filled with Phase-Change Microcapsule.

The flammability of rigid polyurethane foam (RPUF) limits its application. A new type of chitosan phase-change microcapsule (CS/PCM) was successfully prepared by the condensation method with chitosan and gum acacia as the wall material and paraffin as the core material. CS/PCM was introduced into RPUF composite material as filler to improve the thermal and flame-retardant properties of polyurethane. The morphology, structure, thermal properties and flame retardancy of the materials were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and cone calorimetry. It is found that when the CS/PCM content is 30 wt%, the latent heat of phase transition of RPUF-30 is 12.308 J/g, the limiting oxygen index (LOI) is 26.1% and the fire risk is reduced. The flame-retardant mechanism shows that the barrier effect provided by chitosan plays an important role in effectively blocking the transfer of heat and combustible gas, and improving the flame-retardant property of the composite. This paper provides a new idea for the application of CS/PCM in RPUF.

Charge Assessment for Nitrate-Based Salt as a Phase Change Material for a Medium-Temperature Latent Storage Tank

Abstract The present study assesses the heat characteristic of the nitrate-salt mixture as a phase change material (PCM) for a medium-temperature latent storage system (LSS). Two binary and ternary mixtures are evaluated, which demonstrate different thermal behaviour. The highest melting and latent heat capacity is obtained by KNO3(0.4)/NaNO3(0.6) at 223.8 °C and 161.5 J/g. However, it has a higher supercooling degree with a partial phase transition between 217.6 °C and 251.5 °C, making it unfeasible for a medium-temperature LSS tank. The ternary mixture (TM) with NaNO2(0.4)/KNO2(0.53)/NaNO3(0.7) demonstrates a stable phase transition with minimum partial phase transition (22.1 °C) and suitable heat of fusion (98.1 J/g). Further evaluation through static thermal profiling demonstrates that the TM has a notable performance during solid-sensible charge with a charge level indicator (CLI) around 45.3 %–49.1 %. The TM can be charged up to 85.7 % until the end stage of the phase transition. It promotes a better storage capacity with suitable performance since the system can be charged effectively at a suitable temperature range (< 160 °C) for various applications. The micrograph observation indicates some dispersed particles and local agglomeration, which makes phase stabilization as an advantageous method to promote a stable phase change process. The TM can be considered a suitable PCM for a medium-temperature LSS tank that allows for a better solar thermal renewable system operation.

An Experimental Study on the Influence Solution Concentration and Nano-Additives on Cold Storage Performance of Tetrabutylammonium Bromide

Tetrabutylammonium bromide (TBAB) is considered a promising alternative cold energy storage material. Due to the high dissociation heat of phase transition at an atmospheric pressure of 278–293 K, which reaches 200–500 kJ/kg, this substance is considered an effective cold energy storage medium for air conditioning systems. In this paper, the cold storage crystallization process of TBAB solution with different concentrations was tested by conducting experiments and the phase transition’s temperature and latent heat were measured. Finally, the growth characteristics of TBAB hydrate crystals with different concentrations (10%, 20%, 30% and 40%) were analyzed. Considering the cold storage temperature, phase transformation temperature and latent heat, the cold storage effect is the best when 40% TBAB solution is used. Although single substance phase change materials have a long service life, they have problems with low thermal conductivity and high undercooling. Therefore, researchers usually improve the performance of phase change materials by adding other auxiliary materials, thereby enhancing their application prospects. Among these auxiliary materials, adding nano additives to phase change materials can significantly improve latent heat, thermal conductivity and nucleation ability, while also reducing undercooling. Therefore, we studied the influence of different nano-additives (Al2O3, SiC, TiO2 and ZnO) on phase change materials. The composites with excellent properties were screened by cooling step cooling curve and differential scanning calorimeter (DSC). Compared with pure TBAB solution, the phase transition latent heat of the composite phase change materials (PCMs) prepared by adding nanoparticles were significantly increased. The results show that adding nano-SiC into 40% TBAB solution can obtain better performance. This work not only provides reference for the further research, but also a sight to design the phase change materials for the application of new phase change cold storage materials.

Reversible thermochromic and heat storage coating for adaptive de/anti-icing and thermal regulation

In recent years, photothermal coatings have attracted researchers much attentions for anti-icing applications. However, the overheating due photothermal effect at midday or in non-icing period is inevitably encountered and results in the speed-up aging of the coatings. Herein, a reversible thermochromic phase-transition heat storage coating (TCHSC) containing thermochromic microcapsules is designed to adjust photothermal efficiency by discoloration during non-icing period. In cold surroundings, the coating surface shows black color and presents a high photothermal efficiency, which can transform solar energy into heat for anti-icing and de-icing effectively. Yet, the color of coating turns to white spontaneously in hot surroundings with a low photothermal generation efficiency, which avoids the overheating of coating. Besides, discoloration is caused by forming unconjuncted structure in thermochromic dye, and meanwhile the heat is stored during phase transition process of dye, which helps to adjust the temperature rising and cooling rate of coating and contributes to de/anti-icing. What’s more, discoloration temperature of thermochromic capsules can be tuned by adjusting the melting point of dye in thermochromic capsules. The TCHSC with heat regulation provides a new strategy to tackle the conventional overheating issue of photothermal anti-icing coating in summer or at midday, paving a key step towards its real applications.

Molecular dynamics study on the anomalous behavior of phase transition heats of alcohols at vapor–liquid interface

The surface adsorptions of methanol, ethanol and 1-propanol liquids at vapor–liquid interface are investigated with the surface adsorption theory and molecular dynamics simulations (MD). The surface layer thicknesses of these three liquids calculated with MD increase with temperature. It is found that the thickness of the surface layer becomes smaller as the intermolecular interaction becomes stronger. The heat of phase transition from the bulk to surface determined with the experimental surface tension data decreases from methanol to ethanol and increases from ethanol to propanol. This anomalous behavior is different from the usual one of the phase transition heats which changes monotonously with the alkyl chain length in literature. Since the reversible phase transition heat is equal to T(Ss-Sα), the entropy changes of these three liquids are calculated with MD simulations and are in agreement with the variation trend of phase transition heats determined from the experimental data. This is a qualitative confirmation of our surface adsorption theory from the viewpoint of the molecular dynamic simulations.

Preparation and thermal property enhancement of sodium acetate trihydrate-lithium chloride-potassium chloride expanded graphite composite phase change materials

Phase change materials (PCMs) present promising solutions for enhancing energy efficiency in solar heat pump systems. In our study, we have innovatively developed a composite PCMs (CPCMs) by combining sodium acetate trihydrate (CH3COONa·3H2O, SAT), lithium chloride (LiCl), potassium chloride (KCl), and incorporating expanded graphite (EG). This addition of high thermal conductivity EG was aimed at bolstering the CPCM's thermal stability. Our findings reveal that SAT-LiCl-KCl/EG CPCMs, with 14 wt% EG, significantly enhances thermal energy storage performance while preserving the fundamental phase change characteristics. The resulting CPCMs demonstrates a phase transition temperature of 49.3 °C and a latent heat of 196.4 J/g, ideally suited to meet the demands of hot water heat pump systems operating in the 45–50 °C range. Notably, the thermal conductivity of this CPCMs, following the incorporation of 14 wt% EG, registers at 4.54 W/(m K), representing a remarkable 10.6-fold increase compared to the SAT-LiCl-KCl ternary eutectic salt. To ensure long-term stability, secondary encapsulation with a thermally conductive sealant was applied. Subsequent tests involved subjecting the CPCM to 3000 heating/cooling cycles, resulting in minimal deviations, with the phase transition temperature shifting by approximately 1 °C and a modest 6 % reduction in latent heat of phase transition. These outcomes underscore the robustness and reliability of our developed composite phase change materials.

Supercooling degree decrease of barium hydroxide octahydrate employing 3D porous silver foam as supporting material

Inorganic hydrated salts possess high latent heat of phase transition and are promising phase change materials (PCMs). However, the issues of supercooling, low thermal conductivity, susceptibility to leakage, and phase separation significantly impediment the practical applications of inorganic hydrated salts. In this study, it is proposed to decrease the inorganic hydrated salt supercooling degree by increasing the surface roughness of the porous material and to load the nucleating agent silver (Ag) onto polydopamine (PDA) modified melamine foam (MF) by electroless plating to obtain 3D porous Ag foams, which are then utilized as support materials. The results demonstrated that the 3D porous Ag foam compounded with barium hydroxide octahydrate (BHO) can ameliorate the shortcomings of leakage and reduce the supercooling degree in the cooling process. The composite not only exhibits high enthalpy of over 248.5 J/g and high thermal conductivity of 1.82 W·m−1·K−1 but also has a low supercooling degree of 0.21 ℃. Furthermore, the composites exhibited superior shape stability and thermal cycling stability. This study provides an effective method for reducing the supercooling degree of inorganic hydration salts.

Условия закипания капель на поверхности тонкой плёнки оксида цинка при импульсном лазерном осаждении

The pulsed laser deposition (PLD) method is widely used in the production of different thin films. PLD has several advantages: flexible adjustment of parameters and controllability of processes and ease of synthesis of materials. The deposition of zinc oxide droplets during the synthesis of zinc oxide thin films by PLD is considered and the temperature and initial speed of droplets, which can boil on the thin film surface, are determined. The study of the process of the deposition of droplets from a ZnO target was carried out during the growth of thin films according to the traditional scheme for the PLD method. The process of the deposition of ZnO droplets during the PLD of ZnO films under vacuum conditions is considered. For the first time, it has been revealed that ZnO drops are boiling on the thin ZnO film surface. For the first time, the temperature and speed of solid and liquid drops of ZnO, at which they can boil when they hit the substrate, have been calculated taking into account the processes of heat loss through radiation and the heat of phase transition. Thus, for the first time, it has been established experimentally and confirmed in calculations that at the moment of collision some drops of ZnO are boiling. The role of the heat of phase transition and heat loss due to radiation during the flight of droplets during the PLD of ZnO thin films in a vacuum has been clarified. The temperature of a ZnO drop after a collision with a substrate was calculated in a wide range of initial speed and temperature taking into account heat losses due to radiation and heating from impact.

Intensification of heat exchange with a modified coolant in phase transition heat accumulators

The article presents the results of experiments on intensifying heat transfer of a paraffin heat accumulator using nanomaterials. The purpose of the work is to create a laboratory stand to test the effectiveness of a heat accumulator using a nanomodified coolant. The paper presents information about phase transition heat accumulators, a description of the laboratory bench, and the results of experiments. During the study, results were obtained that allowed us to evaluate the positive effect of the introduction of nanomodifiers on the operating cycle of a heat accumulator.

Studies on the Surface Adsorption of Binary Molten Salts.

The surface adsorption of eight binary molten salts, AgNO3-M1NO3(M1 = Li, Na, K, Rb), NaNO3-M2NO3 (M2 = K, Rb), Ca(NO3)2-CsNO3, and Cd(NO3)2-NaNO3, has been investigated. It is found that the surface tension and temperature of molten salts at constant pressure and mole fraction satisfy the same equation as that for pure liquid compounds reported in our previous works. The heats of phase transition from the bulk to the surface phase for eight molten salts are determined. The heats per unit area are all at the order of -10-2 J/m2. The phase transition is exothermic because the entropy in the surface phase is smaller than the entropy in the bulk phase. The ratio of the solute surface concentration to the solute bulk concentration is approximated as the first-order polynomials of the solute bulk concentration. Then, curves of the surface tension vs the solute bulk concentration are well fitted. The ratio (ΔcBs/ΔcBα) is used to interpret the changing trend of the surface tension with bulk concentrations of solute. It is also found that the surface tension of molten salts decreases linearly with the solute surface concentration.

НАПРЯМКИ ПОКРАЩЕННЯ ОСНОВНИХ ХАРАКТЕРИСТИК ТЕПЛОВИХ АКУМУЛЯТОРІВ ТА ТЕПЛОАКУМУЛЯЦІЙНИХ МАТЕРІАЛІВ

The article is devoted to the study of heat storage technologies as the main energy saving measure. The paper conducts a patent search and analyzes scientific papers that cover the issue and present the main material of existing technologies for thermal energy storage. The classification of the main types of heat accumulators (HA) and heat storage materials (HSM) is presented. Heat accumulators are classified: by the nature of accumulation; by the level of operating temperatures; by the duration of the charge-discharge period. The differences and design features of TAMs, advantages and disadvantages are analyzed. The main heat storage materials that are actually used or can be used in the future are identified. The thermophysical properties of heat storage materials, such as specific heat capacity, melting point, density, and density, are described.
 The methodology for calculating the volume of capacitive and phase-transition heat accumulators is determined based on the following initial data: the type of heat storage material, the type and thermal characteristics of the heat carrier, and the temperature drop of the heat storage material. Examples of the practical use of capacitive batteries are given, in particular, a tank battery in a solar heating system, as well as a gravel battery in a solar vegetable garden. The use of crystalline hydrates and organic low-melting compounds (fatty acids and paraffins) as phase-transition heat storage materials is described. The characteristics of thermochemical thermal accumulators, their principle of operation, and their advantages over capacitive and phase-transition accumulation units are presented. The reactions of enrichment of traditional carbon fuels are described, and examples of reactions that can be used as heat storage processes are given. Prospects for further research are identified.

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

Performance analysis of V-corrugated flat plate collector containing binary crystal thermal storage materials

Flat plate solar air collectors can further increase their overall thermal conductivity and heat storage capacity by using phase change materials (PCM) and refining their structural design, which will increase their stability and effectiveness of heat collection. Based on sodium sulfate decahydrate (SSD, Na2SO4·10H2O) and sodium acetate trihydrate (SAT, CH3COONa·3H2O), this research proposes a novel manufacturing procedure to manufacture a new binary mixed hydrated salt (SSD/SAT), which addresses phase separation and undercooling difficulties.The latent heat of phase transition hits 229 J/g−1 when the material's phase transition temperature is 61.71 °C. Furthermore, the numerical modeling of the SSD/SAT material's heat collection performance was conducted when it was integrated into a V-corrugated flat plate solar collector (VC-FPSC). The collector has been found to be able to extend the heat and boost the efficiency.

Two-phase flow and heat transfer on a cylinder via low-velocity jet impact

Combining the benefits of jet impact and phase-transition heat transfer, jet impact boiling has been widely adopted in industrial scenarios. Notably, owing to limitations of high-velocity jets, such as high impact stress and pumping pressure in liquid circuits, low-velocity jet impacting deserves more attention and explorations. In this paper, under an atmospheric environment with wall heating temperatures ranging from 36 °C to 128 °C, the two-phase flow and heat transfer characteristics (local surface temperature, boiling curves and liquid loss rate) of low-velocity jet impacting on a cylindrical surface are investigated by experiment, followed by the analysis on the effects of jet outlet velocity and impact height. The findings reveal that, with the increase of heat transfer rate, the heat transfer regimes in sequence are non-phase transition (single-phase convection and air-liquid two-phase convection) and nucleate boiling. The influences of jet impact height and outlet velocity on local surface temperatures are pronounced at non-phase transition stage. In impact region, along with average superheat, the growth rates of heat transfer rate and liquid loss rate increase significantly from non-phase transition to nucleate boiling stage, and slow down at anaphase of nucleate boiling stage. Interestingly, the increase in outlet velocity delays the onset of slowdown in growth of liquid loss rate to some extent. Overall, the heat transfer rate and liquid loss rate are significantly enhanced at higher jet outlet velocity of 0.60 m/s, but not affected significantly by impact height.

Two methods for thermal conduction analysis of bi-porous sintered structures

Loop heat pipes (LHPs) have consistently garnered attention for effectively managing thermal conditions in critical electronic components of spacecraft and satellites. Particularly intriguing are LHPs equipped with bi-porous capillary wicks, demonstrating commendable flow and thermal dissipation capabilities. Despite its significance for evaluating the phase-transition heat transfer in porous structures, the effective thermal conductivity (ETC) has not been understood mechanistically. This study aims to establish an efficient procedure for predicting ETC in bi-porous wicks through a comparative analysis of analytical and numerical methods. The analytical ETC expression was formulated using thermal resistance network and neck formation theory. Meanwhile, the numerical model utilized the Finite volume method (FVM) combined with a 3D porous structure created by Diffusion-Limited Aggregation (DLA) algorithm. The investigation revealed a congruence between two methods and the measured ETCs of interstitial-pore samples containing fine nickel powders. However, undesirable results were shown for coarse samples due to the irregular particle shapes. In samples with formation pores, the numerical model excels in characterizing the spatial distribution and scale of pores, albeit at the expense of time consumption and model complexity compared to the analytical one. Both methods prove valuable for ETC modeling of sintered bi-porous structures according to desired applications.