Liquid Phase Change Research Articles

Validation of a Simplified Numerical Model for Predicting Solid–Liquid Phase Change with Natural Convection in Ansys CFX

This paper presents a numerical model for simulating melting and solidification driven by natural convection, and validates it against a previous experiment. The experiment involved filling a rectangular aluminum enclosure with RT28HC Phase Change Material (PCM) to 95% of its capacity. To investigate the thermal behavior of the PCM during phase change, the enclosure underwent independent heating and cooling procedures. The simulation was conducted using ANSYS CFX®, and the additional heat source (AHS) method was implemented in conjunction with the Boussinesq approximation to account for the latent heat during melting and solidification driven by natural convection. This allowed the calculation of temperature fields, the melted fraction, and fluid dynamics during phase change. The momentum equations were modified to include a source term that accounted for a gradual decrease in fluid velocity as the PCM transitions from solid to liquid. To account for density variation, an artificial specific heat curve was implemented based on the assumption that the product of density and specific heat remains constant during phase change. The proposed numerical model achieved good agreement with the experimental data, with an average root mean square error of 2.6% and 3.7% for temperature profiles during charging and discharging simulations, respectively. This model can be easily implemented in ANSYS CFX® and accurately predicts charging and discharging kinetics, as well as stored/released energy, without any numerical convergence issues.

Effect of gas–liquid phase change of axial rotating heat pipe on fluid-thermal-solid behaviors of high-speed spindle

The thermal deformation control (TDC) of the high-speed spindle (HSS) is difficult to be realized because the nonlinear, non-steady, and varying influencing factors, and traditional cooling system cannot effectively dissipate the internal heat and realize TDC. It is expected to effectively export the internal heat of HSS with a reasonable design and manufacturing. To effectively realize HSS cooling and TDC, the effect of gas–liquid phase change of axially rotating heat pipe (ARHP) on fluid-thermal-solid behaviors of HSS is investigated. The ARHP, which is suitable for HSS cooling and TDC, is designed. Then an experimental platform is constructed to study the operation performance and heat dissipation performance (HDP) of the designed ARHP under different working conditions. The effects of the rotational speed, heat flux, and cooling air flow rate on HDP of ARHP are investigated. The designed ARHP is embedded into the original HSS (O-HSS) to dissipate the internal heat, and the silicone grease (SG) is used to fill the gap between the ARHP and shaft core of HSS, increasing the contact area and enhancing heat transfer. Then the fluid-thermal-solid coupling behavior of HSS is simulated and experimentally studied. To verify the effectiveness of the designed ARHP and the proposed heat dissipation scheme, the fluid-thermal-solid coupling behaviors of O-HSS, HSS with ARHP (ARHP-HSS), and HSS with ARHP and SG (ARHP-SG-HSS) are compared. The results show that the maximum temperatures of ARHP-SG-HSS and ARHP-HSS are reduced by 50% and 43.5% compared with that of O-HSS, respectively. Moreover, the maximum thermal balance time of O-HSS, ARHP-HSS, and ARHP-SG-HSS is 1450 s, 800 s, 500 s, respectively. The maximum thermal deformation (TD) ranges of O-HSS, ARHP-HSS, and ARHP-SG-HSS are [-35 μm, 25 μm], [-20 μm, 10 μm], and [-20 μm, 10 μm], respectively. The maximum TDs of ARHP-SG-HSS and ARHP-HSS are reduced by 76.5% and 58.8% compared with maximum TD of O-HSS, respectively.

Investigation on the temperature control performance and optimization strategy of a battery thermal management system combining phase change and liquid cooling

For ensuring the safety of lithium-ion batteries in application, keeping the temperature of the battery pack in the desired range is crucial under different operating condition. This paper incorporates experiments and the numerical model to design a novel thermal management system with the combination of the phase change material and liquid cooling for twelve cylindrical lithium-ion batteries. The experimental results reveal that at the ambient temperature of 35 °C, the maximum temperature and temperature difference of the blank control system during 1 C charge and 2 C discharge are 57.6 °C and 4.1 °C, while the maximum temperature difference is 3.6 °C with single liquid cooling. Compared with them, the maximum temperature of the coupled system is only 44.8 °C and the maximum temperature difference is less than 2 °C with superior cycling performance. Moreover, an electric-thermal model is proposed to study the cooling effect of coolant, from which controlling the coolant flow within 250 mL/min is the best choice. Based on these results, an optimization strategy of hierarchical management is proposed for the coolant flow and inlet temperature by monitoring the maximum temperature of the battery pack and ambient temperature. This strategy not only controls the temperature of the system in desired range under different ambient temperatures, but also reduces the unnecessary energy consumption of liquid cooling. The proposed system is scalable to be applied to the other types of batteries for thermal management.

Numerical investigation on electrohydrodynamic enhancement of solid–liquid phase change in three-dimensional cavities

As an active heat transfer enhancement technique, electrohydrodynamic has excellent potential to enhance the melting rate during solid–liquid phase change. In this work, the lattice Boltzmann method is adopted to investigate the electrohydrodynamic enhancement of solid–liquid phase change in three-dimensional cavities. The numerical method is firstly validated by several carefully chosen test cases, and then we conducted simulations under different governing parameters and aspect ratios. Results show that the interface morphologies obtained from pure electro-convection and pure thermo-convection are significantly different due to the different directions of the buoyancy and Coulomb forces. Besides, the augmentation of melting due to the electric effect becomes significant when the electric driving parameter T increases. For sufficiently high values of T, the melting performance is mainly dominated by the Coulomb force, and the influence of the thermal Rayleigh number in such a case is insignificant. Further, we note that the melting performance in the enclosure depends on the aspect ratio, and the lateral wall in a three-dimensional cavity with a relatively smaller aspect ratio usually inhibits the electro-convection. Finally, a comparison between the two-dimensional and three-dimensional simulations shows that the added dimension significantly affects the flow dynamics and the interface shape, which cannot be ignored for similar problems.

Experimental and numerical study of lithium-ion battery thermal management system using composite phase change material and liquid cooling

An efficient battery thermal management system can effectively control the temperature of the battery and prevent the occurrence of thermal runaway. In this work, the calibration calorimetry method is first used to determine the specific heat capacity and heat generation rate of a large-capacity battery considering the heat loss. Then three cases of large-capacities battery thermal management systems (BTMSs) are proposed, i.e., Case 1 with composite phase change material (CPCM) cooling only, Case 2 with liquid cooling only, and the hybrid Case 3 combined CPCM with liquid cooling. It is found that Case 3 owns the lowest maximum temperature of the battery module under the same condition. Moreover, the parameters affecting the thermal performance of Case 3 are studied, including the thickness of CPCM, inlet velocity of coolant, ambient temperature and discharge rate. A thickness of 4 mm for CPCM can effectively absorb the heat released by the batteries to achieve higher group efficiency of the battery module and lighter weight of the system. The lower velocity of 0.1 m/s is preferred in the simulation to balance the maximum temperature and pump power consumption. Moreover, Case 3 is well verified to control the maximum temperature and temperature difference of the battery module at 48.97 °C and 4.5 °C, respectively, even under the highest discharge rate of 2C and high ambient temperature of 37 °C, which shows effective improvement in the thermal safety of batteries.

A Review on Battery Thermal Management for New Energy Vehicles

Lithium-ion batteries (LIBs) with relatively high energy density and power density are considered an important energy source for new energy vehicles (NEVs). However, LIBs are highly sensitive to temperature, which makes their thermal management challenging. Developing a high-performance battery thermal management system (BTMS) is crucial for the battery to retain high efficiency and security. Generally, the BTMS is divided into three categories based on the physical properties of the cooling medium, including phase change materials (PCMs), liquid, and air. This paper discusses the effect of temperature on the performance of individual batteries and battery systems, at first. Then, a systematic survey of the state-of-the-art BTMS is presented in terms of liquid-based, PCM-based, and air-based BTMS. To further utilize the heat source of the vehicle, the BTMS integrated with the vehicle thermal management system (VTMS) is discussed. Finally, the challenges and future prospects for BTMS with the ability to cut off the thermal runaway are discussed. The primary aim of this review is to offer some guidelines for the design of safe and effective BTMS for the battery pack of NEVs.

Fabrication and performance evaluation of the flexible positive temperature coefficient material for self‐regulating thermal control

AbstractIn this study, three kinds of newly flexible positive temperature coefficient (PTC) materials are fabricated by a simple preparation method. Due to introducing the hybrid filler of carbon nanotube and carbon black, these materials exhibit remarkable PTC effect including the PTC intensity of more than four‐orders magnitude and the resistivity‐temperature coefficient of 154%/°C. The Curie points of PTC materials are regulated to room‐temperature range by the low melting phase and influenced by melting onset temperatures of their solid–liquid phase change. With the help of transmission electron microscope, the micro‐capsule structure of the phase change regions is observed, and the hybrid conductive fillers randomly distribute in the blend matrix to construct three‐dimensional conductive network. Using the PTC materials as a heating element, the equilibrium temperature of the controlled device can be maintained around their Curie point without any control method. Moreover, the adaptive thermal control effect becomes more obvious with the increase of ambient temperature and initial heating power. Furthermore, the thermal control accuracy fluctuates within 0.15°C without any external control method, and is improved to round 0.08°C in combination with the switch control method. This study provides a new method for the thermal control of electronic devices in the requirement of lightweight and miniaturization at low temperature environment.

Machine learning and multilayer perceptron enhanced CFD approach for improving design on latent heat storage tank

Solid-liquid phase change heat storage is an important method to solve the mismatch of the generation and usage of waste heat, which is conducive to decarbonization and energy conservation. However, there always exists inhomogeneity for the melting and temperature of the phase change material (PCM) in solid–liquid phase change heat storage. Changing the shape of the heat storage tank will change the distance of heat transfer to the phase change material, thus changing the heat storage performance. Therefore, this paper designed ten shapes of trapezoidal tank with different proportions of upper and lower radius. And the heat storage performance of ten cases were investigated through the designed numerical model, whose accuracy is convinced through comparison with experimental results. Many indexes are proposed to evaluate the properties of the latent heat thermal energy storage (LHTES) from the view of whole region, uniformity among subregions, and the storage heat performance of integrity. Except for drawing mass fraction, temperature, and streamline contours, the temperature proportion and the average velocity are proposed to quantitatively evaluate the temperature distribution and convection intensity. The results showed that the cases with larger upper radius are shorter than cases with larger lower radius. In addition, the shortest melting time is 17210 s, which is about 39.2% shorter by 11080 s than that of basic case. The evaluation from the view of uniformity also indicated that properly increasing the PCM amount is beneficial for improving the melting uniformity. The most uniform temperature and mass fraction are case 5 and case 4, respectively, with 12.92% and 38.28% improvement. Finally, one multilayer perceptron (MLP) network model is built to predict the melting fraction and total heat storage. After training, one model with a deviation lower than 10% between simulation and prediction is set up.

Liquid metal-filled phase change composites with tunable stiffness: Computational modeling and experiment

Liquid metal-filled phase change composites have promising applications as tunable stiffness components and reconfigurable structures in soft robotics, actuators, and metamaterials. At present, there is a lack of mechanistic understanding on the microscale-macroscale correlation of their mechanical behaviors. To fill this knowledge gap, we employ computational micromechanics modeling to simulate and reproduce the macroscopic mechanical behaviors of these liquid metal composites. Specifically, the liquid metal composites are simulated using representative volume elements and the particle-matrix interfaces are modeled as cohesive surfaces. The model is able to predict not only the stress-strain curves of the composites with temperature-induced phase transition but also progressive debonding between the particles and the polymer matrix. Moreover, the computational model also reproduces the debonding-induced Mullins effect of the liquid metal composites. The simulation results agree well with our experimental data by calibrating the modeling parameters carefully.

Thermal Management of Lithium-Ion Batteries Based on Honeycomb-Structured Liquid Cooling and Phase Change Materials

Batteries with high energy density are packed into compact groups to solve the range anxiety of new-energy vehicles, which brings greater workload and insecurity, risking thermal runaway in harsh conditions. To improve the battery thermal performance under high ambient temperature and discharge rate, a battery thermal management system (BTMS) based on honeycomb-structured liquid cooling and phase change materials (PCM) is innovatively proposed. In this paper, the thermal characteristics of INR18650/25P battery are studied theoretically and experimentally. Moreover, the influence of structure, material and operating parameters are studied based on verifying the simplified BTMS model. The results show that the counterflow, honeycomb structure of six cooling tubes and fins, 12% expanded graphite mass fraction and 25 mm battery spacing give a better battery thermal performance with high group efficiency. The maximum temperature and temperature difference in the battery in the optimal BTMS are 45.71 °C and 4.4 °C at the 40 °C environment/coolant, as against 30.4 °C and 4.97 °C at the 23.6 °C environment/coolant, respectively. Precooling the coolant can further reduce the maximum battery temperature in high temperature environments, and the precooling temperature difference within 5 °C could meet the uniformity requirements. Furthermore, this study can provide guidance for the design and optimization of BTMS under harsh conditions.

Solving heat conduction problems in the start-up stage of direct chill casting processes via a temperature-enthalpy mixed formulation based on the improved element-free Galerkin method

A novel approach to solve the transient heat conduction problem with moving boundary and solid↔liquid phase change involved in the start-up stage of direct chill casting (DCC) processes is introduced in this work, which is based on the improved element-free Galerkin (IEFG) method. The procedure is developed under a temperature-enthalpy mixed formulation of the internal energy balance, but the construction of improved moving least squares (IMLS) is required only to approximate temperature. The reliability and suitability of this approach have been first proven in a 1-D alloy solidification benchmark problem with exact solution, and subsequently used to solve a more complex three-dimensional applied thermal problem concerning the start-up stage of the DCC process of an aluminium alloy slab. The domain growth conditioned by the bottom block (moving boundary) is modelled moving down the nodes used to represent the problem domain at each time step, and adding a new nodes plane at the domain upper boundary. Outcomes have revealed the usefulness of this technique to overcome the difficulties concerning solid↔liquid phase change marked non-linearities and moving boundaries involved in the transient analysis of DCC heat transfer problems, allowing the achievement of accurate and stable results in a remarkably simple manner.

Numerical study of a new scheme of self-adaptive transpiration cooling

Phase change transpiration cooling based on the porous structure is one of the most potential thermal protection technologies. Compared with an active transpiration cooling system, a self-adaptive transpiration cooling system does not need additional pressure devices, which reduces the instability factors and the system's weight. Utilizing the properties of liquid phase change that generates high-pressure vapor, which expands spontaneously, this paper proposes a new self-adaptive transpiration cooling scheme with liquid phase change. To evaluate its feasibility, reliability, and cooling capability, a mathematical model and corresponding numerical strategy are firstly established and validated by theoretical analysis, then are used in simulations of transient characteristics of fluid flow and fluid–structure coupled heat transfer in the self-adaptive transpiration cooling process with various operating conditions. The analysis indicates that the self-adaptive transpiration cooling system can successfully realize the self-generation and self-pumping of vapor flow within the structure and keep vapor flow stable and timely response to time-varying heat flow. Moreover, with the shortening of structure length, self-generation of vapor flow and cooling performance are significantly strengthened and are gradually approaching their optimal states, which verifies this new cooling scheme's extremely high cooling potential.

High-enthalpy biphasic phase change organogels with shape memory function based on hydrophobic association and H-bonding interaction

Low-temperature solid–liquid organic phase change materials (OPCMs) offer tremendous opportunities in thermal management techniques but suffer from leakage problems above the melting temperature. Here, inspired with the universal hydro/organogels using three-dimensional polymer networks capable of holding large amounts of liquid solvents, a kind of form-stable high-enthalpy biphasic phase change organogels (BPCOGs) were developed by the integration of hydrophobic association for synthesizing intrinsic phase change matrices and H-bonding interaction for binding OPCM liquids. The porous phase separated poly(acrylamide-octadecyl acrylate) (P(AM-co-OA)) matrices with uniformly dispersed thermal conductive carbon nanotubes were fabricated from the hydrophobically associating hydrogels (HAHs), in which POA segments provide the phase change energy storage microdomains and the PAM network is capable of binding a series of melted OPCMs by hydrogen bond engineering. The fabricated BPCOGs possess form-stability, high phase change enthalpy (high up to 215.5 J g−1) and high energy storage efficiency (>90%), and show excellent electrical/optical-thermal energy conversion as well as shape memory performances. This study provides a universal strategy to prepare flexible biphasic OPCMs suitable for a variety of solid–liquid OPCMs including fatty alcohols, fatty acids and polyethylene glycol, and demonstrates the great potentials of these BPCOGs in solar energy utilization and functional flexible devices.

Synthesis and Properties of Dynamic Crosslinking Polyurethane/PEG Shape-Stable Phase Change Materials Based on the Diels–Alder Reaction

Phase change materials (PCMs) can absorb and release energy while keeping the temperature constant; hence, they play a crucial role in the thermal management field. Shape-stable phase change materials (SSPCMs) were synthesized by chemical crosslinking to address the liquid leakage problem of solid–liquid phase change materials (SLPCMs) during the phase change process. However, the abandoned SSPCMs cannot be reused and recycled, which seriously restricts their practical application. Herein, a polyurethane network containing Diels–Alder bonds was used as the enclosure compound to obtain the encapsulation of polyethylene glycol (PEG), and then, the chemical structure, crystallization behavior, and phase transition ability of SSPCMs were systematically investigated. The results showed that the SSPCMs-3 sample (300 wt % PEG) had the best comprehensive performance, an enthalpy value of 171.7 J/g, and no leakage at 80 °C for 1 h. Moreover, the structure, crystallization behavior, and phase transition ability of SSPCMs could also basically remain unchanged after multiple thermal cycling and reprocessing.

An energy-conservative DG-FEM approach for solid–liquid phase change

We present a discontinuous Galerkin method for melting/solidification problems based on the “linearized enthalpy approach,” which is derived from the conservative form of the energy transport equation and does not depend on the use of a so-called mushy zone. We use the symmetric interior penalty method and the Lax–Friedrichs flux to discretize diffusive and convective terms, respectively. Time is discretized with a second-order implicit backward differentiation formula, and two outer iterations with second-order extrapolation predictors are used for the coupling of the momentum and energy. The numerical method was validated with three different benchmark cases, i.e., the one-dimensional Stefan problem, octadecane melting in a square cavity and gallium melting in a rectangular cavity. The performance of the method was quantified based on the L 2 norm error and the number of iterations needed to convergence the energy equation at each time step. For all three validation cases, a mesh convergence rate of approximately O(h) was obtained, which is below the expected accuracy of the numerical method. Only for the gallium melting case, the use of a higher-order method proved to be beneficial. The results from the present numerical campaign demonstrate the promise of the discontinuous Galerkin finite element method for modeling certain solid–liquid phase change problems where large gradients in the flow field are present or the phase change is highly localized, however, further enhancement of the method is needed to fully benefit from the use of a higher-order numerical method when solving solid–liquid phase change problems.

Solid–Liquid Phase Change Composite Materials for Direct Solar–Thermal Energy Harvesting and Storage

Solid–Liquid Phase Change Composite Materials for Direct Solar–Thermal Energy Harvesting and Storage

Halloysite-based aerogels for efficient encapsulation of phase change materials with excellent solar energy storage and retrieval performance

Developing low-cost composite phase change materials with good shape stability, excellent mechanical strength, high thermal conductivity, large encapsulation ratio, strong light absorption and eminent solar-to-thermal conversion capacity is of great challenge to solve the scaling-up related issues of organic solid–liquid phase change materials during the utilization of solar energy. In this work, halloysite/poly(vinyl alcohol) and halloysite/poly(vinyl alcohol)/reduced graphene oxide aerogels with rich three-dimensional honeycomb structure were prepared by a freezing and freeze-drying method, which can significantly promote the encapsulation ratio of lauric acid in the pores of both aerogels and halloysite nanotube. Halloysite nanotube with high aspect ratio can improve the compressive strength of the aerogels and shape stability of the composite phase change materials, while reduced graphene oxide can reinforce the thermal conductivity and light absorption ability. After encapsulation of lauric acid, the halloysite/poly(vinyl alcohol) 9:1 and halloysite/poly(vinyl alcohol)/reduced graphene oxide 9:1 phase change composites demonstrate extraordinarily high latent heat of 195.4 J/g and 197.0 J/g, respectively, leading to high encapsulation ratios of 97.2 % and 98.1 % respectively, accompanied by good chemical and thermal stability over 300 thermal cycles. The thermal conductivity of lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide is remarkably elevated to 0.343 W/m∙K, exceeding 39.4 % that of pure lauric acid (0.246 W/m∙K). Besides, the lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide realizes a conspicuous solar-to-thermal conversion with solar absorption capacity of 95 % throughout the full spectrum of solar light. The marvelous improvement in the solar-to-thermal conversion efficiency can be attributed to thermally conductive interconnected network of halloysite nanotube and reduced graphene oxide. Thus, lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide and lauric acid@halloysite/poly(vinyl alcohol) are tentatively used in the catalytic hydrolysis of ammonia borane, and they can efficiently harvest, convert and store solar energy in the form of thermal energy and release it for the reaction, which obviously accelerates the extent of reaction with turnover frequency increasing from 29.50 (molH2/molcatalyst·min) at 25 °C to 59.18 and 41.74 (molH2/molcatalyst·min) under the heating of solar energy stored lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide and lauric acid@halloysite/poly(vinyl alcohol), respectively. This work paves a way for fabricating halloysite-based aerogel and composite phase change materials for thermal/solar energy saving application.

Investigation of high-enthalpy organic phase-change materials for heat storage and thermal management

The growing interest in phase-change materials (PCM) is related to their possible role in thermal energy storage and thermal management. The choice of materials depends strongly on the required temperature range, whereas the latent heat of solid–liquid phase transition has to be as high as possible. Among other organic PCM, sugar alcohols have gained some attention due to their availability and certain advantageous properties. However, the thermal processes in these materials still require investigation. In the present work, we focused on the materials with solid–liquid phase change within 80 °C–100 °C. A comprehensive literature survey was conducted to elucidate the available sugar alcohols relevant to this range. It was found that the use of pure materials of this type is not very practical, because of their scarcity in the required range and their specific features, like difficulties with crystallization and solidification. On the other hand, based on the literature, we have discerned three eutectic mixtures of erythritol with other organic materials, namely, erythritol–xylitol, erythritol–urea and erythritol– trimethylolethane (TME). In all those cases, it is remarkable that while the components commonly have rather high melting temperatures, the eutectic mixtures had the phase transitions in the required range. Still, each of these mixtures has its own peculiar features, especially at cooling and solidification. An extensive experimental study was performed to provide detailed visualization of these major processes. The results revealed the melting temperature and latent heat of the mixtures to be: 84 °C and 190 J g−1 for erythritol–xylitol, 82 °C and 227 J g−1 for erythritol–urea. Erythritol–TME has two phase transitions at 82 °C and 97 °C, with total latent heat of 198 J g−1. Based on the present findings, the erythritol–urea mixture is the best PCM candidate for the melting range within 80 °C–100 °C.

Thermophysical Characterization of Paraffins versus Temperature for Thermal Energy Storage

Latent heat storage systems (LHSS), using solid–liquid phase change materials (PCMs), are attracting growing interest in many applications. The determination of the thermophysical properties of PCMs is crucial for selecting the appropriate material for an LHSS and for predicting the thermal behavior of the PCM. In this context, the thermophysical characterization of four paraffins (RT21, RT27, RT35HC, RT50) at different temperatures, including the solid and liquid phases, is conducted in this investigation. This work is part of a strategic technological brick in the CERTES laboratory of the Paris Est University to build a database for phase change material properties. It contains the measurements of the thermophysical, optical and mechanical properties. It will serve as input for the numerical simulations to study the behavior of PCMs in LHSS. The temperatures and the latent heats of the phase transitions as well as the thermal dependence of the specific heat of the paraffins were evaluated by differential scanning calorimetry (DSC). In addition, the DSC measurements under successive thermal cycles revealed good reliability of the paraffins. Thermogravimetric analysis (TGA) was performed, and the results highlighted the thermal stability of the paraffins. Moreover, the evolutions of the thermal conductivities and diffusivities with temperature were measured simultaneously using the hot disk method. A discontinuity of the thermal conductivities was observed near the melting temperatures. Furthermore, the measurements of the densities of the paraffins at different temperatures were carried out. The volume changes and the coefficients of thermal expansion were assessed. The obtained outcomes of this study were compared with the available bibliographical data.

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF6]) system

AbstractThis article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF6], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time‐dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume‐of‐fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.