Enhancement Of Effective Thermal Conductivity Research Articles

Enhancing the performance of composite phase change materials using novel triply periodic minimal surface structures

Organic phase change materials (PCMs) are widely used in thermal management applications owing to their high latent heats of fusion and low cost. Unfortunately, their poor thermal conductivities severely hamper the thermal transport process. Hence, PCMs are often hybridized with high thermal conductivity materials that promote phase change for time-sensitive applications and potentially increase the power density of thermal energy storage (TES) devices. Optimized thermally conductive networks with high-latent-heat PCM matrices are critical in the thermal management of high heat flux applications. With advancements in additive manufacturing, it has become easier to create complex topologies, such as triply periodic minimal surfaces (TPMS), that can further augment the performance of composite PCMs. TPMS surfaces have shown great promise in improving thermal transport performance but investigations into their thermal properties remain limited. In this study, the thermal performances of PCM infused TPMS structures of wall thicknesses varying from 0.4 mm to 0.8 mm were systematically investigated. The TPMS structures were designed using level-set equations, and each system of structures was fabricated by selective laser melting, a metal additive manufacturing technique. Numerical investigations were performed to understand the phase change dynamics of PCM in TPMS cells and experiments were performed to determine their thermal properties and phase change performance for thermal energy storage applications. Our simulations revealed that for structures with uniform wall thickness of 0.4 mm, the novel Neovius structure resulted in the highest effective thermal conductivity enhancement. For a given thickness, it is thus hypothesized that more complex TPMS topologies have higher surface areas and volumes which enhance their thermal conductivities. However, the complex shape of the Neovius structure could not be further uniformly thickened without self-intersecting geometries. Ultimately, a balance of both the surface area and thickness of the TPMS cell determines the thermal conductivity enhancement. Overall, the 0.6 mm thick IWP cells had the highest thermal conductivity of 13.84 W/m K, which was consistently verified in experiments. This is likely due to the fact that it has a larger surface area than the P structure but is also thicker than the 0.4 mm Neovius structure. To further demonstrate the potential application of our PCM-based TPMS design, low temperature thermal cycling tests were performed. Our results showed the IWP cell structure promoted a more uniform temperature distribution as compared to the P cell. Phase change in the 0.6 mm thick IWP cell structure was completed 1.4 times faster than the 0.8 mm thick P cell and 1.8 times faster than the 0.6 mm thick P cell. The purpose of this study is to provide useful guidelines for the selection of TPMS structures for various applications such as battery packs and spacecraft and to open doors for the co-optimization of materials and device geometry for enhanced energy and power density.

Vertically aligned carbon fibers-penetrated phase change thermal interface materials with high thermal conductivity for chip heat dissipation

Phase change thermal interface materials (PCTIMs) are receiving increasing attention but suffer from low thermal conductivity and are challenging to improve significantly. Here, vertically aligned short-cut carbon fibers (VASCFs) were employed for the first time to develop PCTIMs with high thermal conductivity. The most effective thermal conductivity enhancement was achieved by VASCFs, which were attributed to providing complete heat transfer paths, further verified by the finite element simulation. VASCFs were thus incorporated into an optimized mixture of silicon rubber (SR) and paraffin (PA) to fabricate form-stable phase change thermal pads. The VASCFs/PA/SR thermal pads achieved a thermal conductivity of as high as 7.00 W/(m·K), much higher than that of the previously reported PCTIMs. More significantly, it is revealed that the reduction in thermal impedance induced by the phase change of PA, led to the better heat dissipation performance of VASCFs/PA/SR, thus making the VASCFs/PA/SR phase change thermal pads show potential in practical applications.

Exploration of 3D stagnation-point flow induced by nanofluid through a horizontal plane surface saturated in a porous medium with generalized slip effects

Heat transfer enhancement is a contemporary challenge in a variety of fields such as electronics, heat exchangers, bio and chemical reactors, etc. Nanofluids, as innovative heat transfer fluids, have the potential to be an efficient tool for increasing energy transport. This benefit is obtained as a result of an enhancement in effective thermal conductivity and an alteration in the dynamics of fluid flow. Thus, this paper is concerned with heat transfer enhancement via nanofluids. The intention is to find numerical double solutions to the 3D stagnation-point flow (SPF) and heat transfer incorporated nanoparticles in a porous medium with generalized slip impacts. Appropriate similarity variables are used to non-dimensionalize the leading equations, which are then numerically solved using the three-stage Lobatto IIIa integration formula. The impacts of different parameters on the dynamics of flow and characteristics of heat transfer induced by nanofluids in the presence of an unsteady parameter, nanoparticle volume fraction, velocity slip parameter, and porosity parameter are investigated. Based on the latest findings, it is closed that the velocity slip improves the heat transfer as well as shear stress in the axial direction in both solutions, while the shear stress behaves oppositely in the respective lateral direction. In addition, the velocity profile remarkably enriches for both branch solutions, while the temperature distribution elevates for the upper branch and declines for the lower branch owing to the larger porosity parameter.

Utilization of carbonized water hyacinth for effective encapsulation and thermal conductivity enhancement of phase change energy storage materials

In this work, a biochar carrier was developed to adsorb phase change materials and enhance thermal conductivity. Six kinds of modified carbonized water hyacinth were prepared by freeze drying (or vacuum drying) combined with high-temperature carbonization. The pore volume and specific surface area (SSA) of FC900 are the highest, reaching 0.3153 cm3/g and 479.966 m2/g, which are 32% higher than those of VC900. The load rates of FC900 and VC900 on lauric acid-myristic acid-paraffin section (LMPS) are 75% and 65% respectively. Meanwhile, the phase transition enthalpy of LMPS/FC900 is 104.36 J/g, which is 20.75% higher than that of LMPS/VC900, and the phase transition temperatures are 25.93 and 26.77 °C respectively. After 500 times of heat storage and release experiments, LMPS/FC900 maintains a stable phase change peak, which has good thermal performance stability. Notably, the thermal conductivity of LMPS/FC900 is 0.4168 W/(m·K), which is 56.93% higher than that of LMPS. Otherwise, under the constant temperature environment of 50 °C, the heating time of LMPS/FC900 is 11.89% longer than that of LMPS/VC900, which has more excellent temperature control performance. This study concludes that the carbonization temperature of 900 °C and freeze-drying measures are the best preparation process for carbonized water hyacinth, and LMPS/FC900 has good thermal conductivity and phase change energy storage performance.

Effects of interfacial layer on thermal conductivity enhancement of solar salt-based nanofluids: Insights from molecular dynamics simulations

The interfacial nano-layers around the nanoparticles (NPs) affect the effective thermal conductivity (ETC) of molten salt-based nanofluids (MSBNFs), which brings challenge in fabricating MSBNFs with enhanced ETC. This paper presents insights into the interfacial layer and its effects on ETC of solar salt-based nanofluids through molecular dynamics simulation. The SiO 2 and Al 2 O 3 NPs with diameters of 1–2 nm and mass fractions of 0.5–2.0 wt% are considered. The results show that both the size and specie of NPs affect the thickness of the outer interfacial layer. The mass fraction has less significant effect on the thickness of interfacial layer, but is closely related to the degree of order in the interfacial layer. The ETC of MSBNFs varies with mass fraction and reaches the peak at a certain mass fraction. For MSBNFs with SiO 2 NPs and Al 2 O 3 NPs, the peak ETC occurs at mass fraction of 0.5 wt%, which increase by 3.5% and 7.0% at NP diameter of 1 nm respectively, and by 8.1% and 14.8% at NP diameter of 2 nm respectively. Detailed explanations to the physics of ETC enhancement of MSBNFs are presented in the view of interfacial layer from molecular level.

A theoretical model for effective thermal conductivity of open‐cell‐coated metal foams saturated with fluid/phase change material

The current research presents geometrical effective thermal conductivity (ETC) models for externally coated open-cell metal foams (MFs) saturated with fluid/phase change material (PCM) by considering three-dimensional configuration adopted from the tetrakaidecahedron structure. The three-dimension (3D) models consider different geometries, such as hexagonal and square, involving different shapes of ligaments (cylindrical, concave triprism) and nodes (cubic, pyramidal) for the analysis. The ETC of MF-composite increases with the coating thickness, the thermal conductivity of coating material, and infiltrating medium. The percentage enhancement in ETC is found to be significant with the increase in coating thickness compared with the increase in thermal conductivity of coating material and infiltrating medium. In addition, the ETC value increases with the increase in the porosity value, which can be explored at the manufacturing process during the design of thermal management systems (TMS). The present model involving hexagonal geometry with concave triprism ligaments and pyramidal nodes is found to be in excellent agreement with test data for all the infiltration cases with an average deviation of less than 3%. The present study reports the mathematical expressions for ETC as a function of various modeling parameters, which can be useful during the design of the TMS.

Enhancement of effective thermal conductivity of rGO/Mg nanocomposite packed beds

Engineering thermophysical properties of metal hydrides nanocomposites is crucial for effective thermal management during hydrogen storage reactions; however, the effect of microstructure on thermal transport mechanisms is still unclear. Here, we employed an integrated experiment-modeling approach to investigate microstructural factors that determine the effective thermal conductivity of individual reduced graphene oxide-magnesium (rGO/Mg) nanocomposites and their packed bed. The effective thermal conductivity of the rGO/Mg nanocomposite packed bed was measured by using guarded hot-plate method under various atmospheric conditions (i.e., vacuum, Ar and He). A microstructure-aware mesoscopic modeling revealed that anisotropy of the effective thermal conductivity of individual rGO/Mg nanocomposites plays an important role in determining the effective thermal conductivity of their packed bed. The validated mesoscopic model also disclosed a nontrivial interplay between the intrinsic rGO properties and the extrinsic composite structural features. Finally, quantitative sensitivity analysis based on the modeling framework is used to provide practical engineering guidance for controlling the thermal transport within nanocomposite packed beds.

Utilization of waste apricot kernel shell derived-activated carbon as carrier framework for effective shape-stabilization and thermal conductivity enhancement of organic phase change materials used for thermal energy storage

In this study, low-cost and eco-friendly AC obtained from waste apricot kernel shells (ACAS) was utilized to simultaneously solve the inherited drawbacks and enhance thermal conductivity of (Capric-Myristic acid (CA-MA), Lauryl alcohol (LAOH), n-Octadecane (OD) and Polyethylene glycol (PEG)) as different type organic PCMs. The ACAS/PCM composites had high PCM loading rates of up to 75 wt%, hence a high latent heat capacity of up to 193.7 J/g. Their melting and freezing temperatures varied in the range of 20.21–26.61 °C and 18.37–28.78 °C, respectively. All the prepared composites exhibited high thermal degradation resistance as well as high cycling stability even after 1200 melting-freezing cycles. The thermal conductivity of ACAS/CA-MA, ACAS/LAOH, ACAS/OD and ACAS/PEG was measured approximately 2.61, 2.40, 2.27 and 1.75 times higher than that of pure CA-MA, LAOH, OD and PEG, respectively. The advantageous TES characteristics of leak-proof composites make them favourable PCMs for low-temperature thermal management of buildings.

Enhancement of Effective Thermal Conductivity of Rgo/Mg Nanocomposite Packed Beds

Enhancement of Effective Thermal Conductivity of Rgo/Mg Nanocomposite Packed Beds

A study of metallic coatings on ceramic particles for thermal emissivity control and effective thermal conductivity enhancement in packed bed thermal energy storage

Ceramic particles based packed bed systems are attracting the interesting from various high-temperature applications such as thermal energy storage, nuclear cooling reactors, and catalytic support structures. Considering that these systems work above 600 °C, thermal radiation becomes significant or even the major heat transfer mechanism. The use of coatings with different thermal and optical properties could represent a way to tune and enhance the thermodynamic performances of the packed bed systems. In this study, the thermal stability of several metallic (Inconel, Nitinol, and Stainless Steel) based coatings is investigated at both high temperature and cyclic thermal conditions. Consequently, the optical properties and their temperature dependence are measured. The results show that both Nitinol and Stainless Steel coatings have excellent thermal stability at temperature as high as 1000 °C and after multiple thermal cycles. Contrarily, Inconel (particularly 625) based coatings shows abundant coating degradation. The investigated coatings also offer a wide range of thermal emissivity (between 0.6 and 0.9 in the temperature range of 400–1000 °C), and variable trends against increasing temperature. This work is a stepping-stone towards further detailed experimental and modelling studies on the heat transfer enhancement in different ceramic-based packed bed applications through using metallic coatings. • Thermal stability of nine metallic coatings on ceramics is tested up to 1000 °C. • Inconel 738 shows excellent thermal stability after long residency at 1000 °C. • Nitinol and Stainless Steel 304 present oxidation but not coating loss under cycles. • Thermal emissivity are between 0.6 and 0.9 in the temperature range of 400–1000 °C. • Effective thermal conductivity increases of 17% at 1000 °C can be attained.

Heat transfer growth of sonochemically synthesized novel mixed metal oxide ZnO+Al2O3+TiO2/DW based ternary hybrid nanofluids in a square flow conduit

In the current investigation, the heat transfer development with the turbulent flow of novel metal oxide-based ternary composite nanofluids of ZnO + Al2O3+TiO2/DW at varying wt.% concentrations (0.025, 0.05, 0.075, and 0.1) in a square heat exchanger below constant heat flux conditions was discussed. The new ternary composite nanofluids were synthesized by using the sonochemical technique. The ZnO + Al2O3+TiO2/DW based ternary composite nanofluids with their respective wt. % reveals an enhancement in effective thermal conductivity and heat transfer coefficient local and average with Reynolds numbers varying from 4550 to 20,367. The extreme growth in overall effective thermal conductivity was noticed up to 1.149 W/m-K at 0.1 wt% for ternary hybrid composite nanofluids at a maximum temperature 45 °C. Similarly, at 0.075 wt%, 0.05 wt%, and 0.025 wt% the overall effective thermal conductivity was recorded 1.118 W/m-K, 1.091 W/m-K, and 1.079 W/m-K correspondingly, which is greater than that of base fluid (DW), with improved thermo-physical characteristics for novel ZnO + Al2O3+TiO2/DW ternary hybrid composite nanofluids. Also, it shows an improvement in local and average heat transfer with a maximum growth of 0.1 wt %. The maximum heat transfer was observed for ZnO + Al2O3+TiO2/DW based Ternary hybrid composite nanofluids at 0.1 wt % concentrations, up to 900–5700 W/m2K, which is 89% higher than distilled water. While, an enhancement of 900–3870 W/m2K, 900–3350 W/m2K, 900–2750 W/m2K were observed for the other three wt. % 0.075, 0.05 and 0.025, respectively. The study revealed that the metal oxide based ternary hybrid composites nanofluids are suitable for nano coolant applications due to improved thermophysical characteristics and also it is applicable for energy management in industrial applications.

Effects of interface layer on the thermophysical properties of solar salt‐SiO 2 nanofluids: A molecular dynamics simulation

The microstructure and behaviors of the interface layer around the nanoparticle are strongly related to the overall thermophysical properties of molten salt-based nanofluids (MSBNFs). Understanding this link may enable the advanced heat transfer fluid (HTF) for concentrated solar power and other applications. In this study, a molecular dynamics (MD) model for solar salt (60 wt% NaNO3/40 wt% KNO3)-SiO2 nanofluid system is developed to estimate the characteristics of the interface layer and their effects on the overall specific heat capacity (SHC) and effective thermal conductivity (ETC) of MSBNFs. The results show that the SHC and thermal conductivity (TC) of the interface layer in MSBNFs are, respectively, 1.44-1.85 and 1.05-1.97 times higher than those of pure solar salt. The SHC of the interface layer has a significant effect on the overall SHC of the MSBNFs, but the interface layer is not the dominant influencing factor for the ETC enhancement of MSBNFs and thus has less effect on the overall ETC.

Microencapsulation of Molten Salt in Titanium Shell for High‐Temperature Latent Functional Thermal Fluid

Herein, a water‐limited sol–gel method is applied to fabricate microencapsulated phase change materials (MEPCMs) which have a sodium nitrate (NaNO3) core and a titanium dioxide (TiO2) shell. The MEPCM has a high melting temperature of 306.5 °C and a solidification temperature of 296.7 °C, which shows a potential usage as a high‐temperature compatible thermal storage medium for industrial waste heat recovery and concentrated solar power (CSP). The MEPCM is demonstrated to be thermally stable for 200 thermal cycles with a high latent heat of 135.3 J g−1. The high‐temperature latent functional thermal fluid (HT‐LFTF) is prepared by dispersing the NaNO3@TiO2 MEPCMs into thermal oil. The test results show that MEPCMs provide an 18.4% effective thermal conductivity enhancement and 131.7% effective specific heat enhancement compared with base thermal oil. The rheological test indicates that the MEPCMs added in the thermal oil enhance the viscosity of the suspension and it increases with the MEPCM concentration. This work provides a new type of thermal oil–based functional thermal fluid containing high‐temperature MEPCM and paves the way for the application of LFTF in high‐temperature heat storage and transfer.

Influence of metal foam morphology on phase change process under temporal thermal load

Variable morphology metal foams, embedded in phase change materials (PCMs), enhance heat transfer performance without sacrificing the volume available for the PCM. The present study is a numerical investigation of the effect of aluminum metal foam, having varying morphology, on the unidirectional melting process of n-octadecane under pulsating heat flux boundary condition. The interdependencies of metal foam morphology, mean porosity, pulse duration, average heat flux, and system size on the progress of melt fraction and isoflux surface temperature are studied. The effect of two graded and one uniform metal foam morphologies, three pulses, two average wall heat fluxes, two system sizes, and five different mean porosities are analyzed. The positive gradient of metal foam porosity (i.e., the increase in the porosity with distance from the isoflux surface) limits the increase in the surface temperature by more than 15 °C when compared with the uniform metal foam. As well as, graded metal foam reduces temperature fluctuation under pulse heating load by more than 20%. However, the positive gradient of metal foam has adverse effects on the overall melting time. The effect of metal foam morphology on heat transfer is observed to increase with the average heat flux, system size, and mean porosity of metal foams. In the presence of heating from the top, as discussed in the present study, melting processes are driven by heat conduction due to the limited presence of advection. Therefore, the significance of enhancement in effective thermal conductivity is higher in the presence of isoflux boundary on the top surface.

Thermal Conductivity of Nanofluids-A Comprehensive Review

The present study deals with a comprehensive review on the enhancement of effective thermal conductivity of nanofluids. The present article summarizes the recent research developments regarding the theoretical and experimental investigations about thermal conductivity of different nanofluids. The current study analyzes several factors those strongly affecting thermal conductivity of nanofluids include solid volume fraction, temperature, particle size, particle type, particle shape, different base fluids, magnetic field, pH, surfactant and ultrasonic time. In addition, different reasonably attractive models contributing augmentation of thermal conductivity of nanofluids are invoked. Finally, important heat transfer mechanisms namely Brownian motion, nanoclustering, thermophoresis, osmophoresis and interfacial nano-layer responsible for significant role in ameliorating the thermal conductivity and therefore the heat transfer characteristics of nanofluids are discussed.

Influence of effective thermal conductivity on hydrogen sorption in Mg-LaNi4.6Al0.4 composite hydride beds for thermal energy storage

Thermochemical energy storage using metal hydrides is well known. Appreciable quantities of heat energy interactions involved in the hydrogenation and dehydrogenation processes of metal hydride make the metal hydrides suitable for the storage of thermal energy. This paper discusses the synthesis, Pressure Concentration Isotherm (PCI) characterization and estimation of thermal properties of Mg + 50 wt% LaNi4.6Al0.4 composite hydride suitable for thermal energy storage. Maximum theoretical energy density of 918 kJ/kg can be achieved in the temperature range of 150–200 °C. Low values (0.1–1 W/mK) of effective thermal conductivity (ETC) of metal hydride beds is responsible for poor heat and mass transfer characteristics of metal hydride beds. The ETC of Mg + 50 wt% LaNi4.6Al0.4 composite hydride bed was augmented by fabricating two types of pellets. The sorption kinetic measurements were performed for three different configurations of metal hydride beds, one with powder composite hydride and remaining with two different types of pellets. Enhancement in ETC improved the heat and mass transfer characteristics of the composite metal hydride bed.

Cross-Plane and In-Plane Heat Conductions in Layer-by-Layer Membrane: Molecular Dynamics Study.

A material with anisotropic heat conduction characteristics, which is determined by molecular scale structure, provides a way of controlling heat flow in nanoscale spaces. As such, here, we consider layer-by-layer (LbL) membranes, which are an electrostatic assembly of polyelectrolyte multilayers and are expected to have different heat conduction characteristics between cross-plane and in-plane directions. We constructed models of a poly(acrylic acid)/polyethylenimine (PAA/PEI) LbL membrane sandwiched by charged solid walls and investigated their anisotropic heat conduction using molecular dynamics simulations. In the cross-plane direction, the thermal boundary resistance between the solid wall and the LbL membrane and that between the constituent PAA and PEI layers decrease with increasing degree of ionization (solid surface charge density and the number of electric charges per PAA/PEI molecule). When the degree of ionization is low, the cross-plane thermal conductivity of a constituent layer is higher than that of the bulk state. As the degree of ionization increases, however, the cross-plane thermal conductivity of PAA, a linear polymer, decreases because of the increase in the number of in-plane oriented polymer chains. In the in-plane direction, we investigated the heat conduction of each layer and found the enhancement of effective in-plane thermal conductivity again due to the in-plane oriented chain alignment. The heat conduction in the LbL membrane is three-dimensionally enhanced compared to those in the bulk states of the constituent polymers because of the electrostatic interactions in the cross-plane direction and the molecular alignment in the in-plane direction.

Performance optimization for shell-and-tube PCM thermal energy storage

Abstract Phase change material (PCM) based latent heat thermal energy storage (LHTES) systems have been a technology of increasing interests. Extensive experimental and numerical studies on the heat transfer enhancement of PCM have been reported. However, a thorough analysis of the effects of PCM heat transfer enhancement in combination with geometric optimization on the overall storage performance of an LHTES system is still lacking. In this work, a performance index, the effective energy storage ratio Est, based on the effectiveness-NTU theory, which set up a standard to compare TES systems, was adopted to evaluate the effective energy storage density of an LHTES system. Using the conjugate heat transfer analysis, we investigated the impact of the key parameters and flow conditions, including the geometric parameters (tube length-diameter ratio L/di, PCM volume ratio λ), turbulent versus laminar flow conditions of HTF, and the effective PCM thermal conductivity keff, on the performance indicator Est. It was found that the effective energy storage ratio increases with tube length-diameter ratio, and an optimal PCM volume ratio exists. Increasing the effective PCM thermal conductivity is only effective in enhancing the effective energy storage ratio when PCM volume ratio is above certain value. Over 500 sets of parametric studies were performed to optimize the PCM volume by maximizing the effective energy storage ratio. The results show that for both laminar and turbulent flow, optimal PCM volume ratio and maximal effective energy storage ratio increases with tube length-diameter ratio and effective PCM thermal conductivity. The enhancement of effective PCM thermal conductivity only noticeably increases maximal effective energy storage ratio when tube length-diameter ratio is above a certain threshold, i.e., around 800 for laminar flow and around 600 for fully turbulent flow. The fully turbulent flow greatly enhances the charging rate by 50 times and increases the capacity effectiveness at optimal PCM volume ratio to 0.6-0.9 from 0.2-0.8 at laminar flow conditions, but the maximal effective energy storage ratio of fully turbulent flows are generally lower than those of laminar flows. This work is the first systematic numerical analysis of the complete ensemble design factors of a shell-and-tube LHTES system, and it is recommended that the method could be a standard one for the engineering design of an LHTES system.

Understanding the thermal conductivity of Diamond/Copper composites by first-principles calculations

SThe present paper investigates the nanoscale thermal transport at diamond/copper (dCu) interfaces using the density functional theory (DFT) and the atomistic Green's function method. The DFT calculations show the boundary scattering become negligible for diamond particles larger than 10 μm. The temperature-dependent thermal conductivity of the dCu composite is predicted according to the thermal boundary conductance and thermal conductivity from DFT calculations. The results show a low thermal boundary conductance (18.5–26.9 MW/m2K at 300 K) at dCu interfaces causes the reduction in the thermal conductivity of dCu composites with small diamond particles or at low temperatures. Due to the dominant effects of interfacial resistance, adding small diamond particles (<16 μm) in a Cu matrix can only cause a reduction in the effective thermal conductivity of composites regardless of temperature. For diamond particles larger than 16 μm, the enhancement of effective thermal conductivity is most noticeable at relatively low temperatures (120 K ∼ 170 K), and thereafter the enhancement becomes smaller due to the decrease of the diamond thermal conductivity. The results provide insights to understand the mechanism of thermal transport at dCu interfaces and guidelines to engineer the thermal properties of dCu composites.

Non-Fourier heat conduction in oil-in-water emulsions

Emulsions have widely been used in various application, e.g. in energy system as a potential second refrigerant. However, there is a lack of comprehensive study on extraordinary effective thermal conductivity enhancement in the oil-in-water (O/W) emulsions, and effects of temperature and droplet size were not considered in the widely used models of effective thermal conductivity for the O/W emulsions. In this study, non-Fourier heat conduction characteristics in the O/W emulsions were investigated experimentally. The O/W emulsions were prepared with different droplet sizes by controlling the ultrasonic processing time. The O/W emulsions containing small droplets are stable. Effective thermal conductivity of O/W emulsions nonlinearly varies with droplet size, concentration, fluid properties and temperature. Small droplet size is beneficial for effective thermal conductivity enhancement of O/W emulsions. Thermal conductivity of fluids can be enhanced significantly especially at low concentration although thermal conductivity of oil is much lower than water conductivity, which could be due to non-Fourier heat conductions in O/W emulsions. Time lag ratio less than 1 indicates that no thermal waves exist in O/W emulsions, and diffusion-dominant non-Fourier heat conduction could exist in the O/W emulsions. A new model of effective thermal conductivity, which considers effects of fluid thermosphysical properties, oil concentration, droplet size and temperature, was developed for the O/W emulsions based on the measured data. This study could be helpful for exploring the mechanisms behind extraordinary heat conductivity enhancement phenomena of oil-in-water emulsions.