Ferro-hydrodynamic induced convection flow and heat transfer of nanofluids in a corrugated wall enclosure

This study aims to improve heat transfer by utilizing Kelvin forces and inducing magnetic-induced convection in ferro-hydrodynamic convection, in conjunction with nanoparticle migrations. The fundamental equations governing the conservation of mass, momentum, energy, and nanoparticle mass were formulated as partial differential equations. As primary terms, the model incorporated the buoyancy, Lorenz, and Kelvin forces. In this context, temperature variations in the presence of a variable magnetic field generate a temperature-dependent body force. This can induce fluid circulation. Thus, even without gravitational force, magnetic force can stimulate convection heat transfer flows. The study thoroughly examined the impact of magnetic source placement on heat transfer. An increase in Ha from 0 to 100 reduced the average Nusselt number (NuAvg) by approximately 60% in all cases, regardless of the magnetic source position. However, the magnetic field number (Mnf) and its effect on NuAvg are dependent on the magnetic source's position

The thermal charging performance of finned conical thermal storage system filled with nano-enhanced phase change material

Data Availability Statement: Data is contained within the articleCopyright: © 2021 by the authors. A latent heat thermal energy storage (LHTES) unit can store a notable amount of heat in a compact volume. However, the charging time could be tediously long due to weak heat transfer. Thus, an improvement of heat transfer and a reduction in charging time is an essential task. The present research aims to improve the thermal charging of a conical shell-tube LHTES unit by optimizing the shell-shape and fin-inclination angle in the presence of nanoadditives. The governing equations for the natural convection heat transfer and phase change heat transfer are written as partial differential equations. The finite element method is applied to solve the equations numerically. The Taguchi optimization approach is then invoked to optimize the fin-inclination angle, shell aspect ratio, and the type and volume fraction of nanoparticles. The results showed that the shell-aspect ratio and fin inclination angle are the most important design parameters influencing the charging time. The charging time could be changed by 40% by variation of design parameters. Interestingly a conical shell with a small radius at the bottom and a large radius at the top (small aspect ratio) is the best shell design. However, a too-small aspect ratio could entrap the liquid-PCM between fins and increase the charging time. An optimum volume fraction of 4% is found for nanoparticle concentration.Funding: This research received no external funding

Thermal behavior and energy storage of a suspension of nano-encapsulated phase change materials in an enclosure

The energy storage capability of a suspension of Nano-Encapsulated Phase Change Material (NEPCM) nanoparticles was addressed in an enclosure during the charging and discharging process. The nanoparticles contain a Phase Change Material (PCM) core, which are capable to absorb a notable quantity of thermal energy on melting. There is a heat pipe in the cavity at the bottom corner, which is enhanced by a layer of metallic matrix. The natural convection flow occurs due to a temperature gradient during the charging or discharging process. The particles of NEPCM move with the natural convection flow and contribute to heat transfer & storage of thermal energy. The regulating equations for the heat transfer & flow of the NEPCM suspension were established & converted in the non-dimensional type. The finite element method (FEM) was utilized in resolving the equations. The results show that there was a rise in the rate of heat transfer & storage of total energy with a rise in nanoparticles volume fraction. The decrease of the Stefan number from 0.2 to 0.6 increases the total stored energy by 25%. The fusion temperature is another important parameter in which its behavior depends on the charging or discharging process

The Thermal Charging Performance of Finned Conical Thermal Storage System Filled with Nano-Enhanced Phase Change Material

A latent heat thermal energy storage (LHTES) unit can store a notable amount of heat in a compact volume. However, the charging time could be tediously long due to weak heat transfer. Thus, an improvement of heat transfer and a reduction in charging time is an essential task. The present research aims to improve the thermal charging of a conical shell-tube LHTES unit by optimizing the shell-shape and fin-inclination angle in the presence of nanoadditives. The governing equations for the natural convection heat transfer and phase change heat transfer are written as partial differential equations. The finite element method is applied to solve the equations numerically. The Taguchi optimization approach is then invoked to optimize the fin-inclination angle, shell aspect ratio, and the type and volume fraction of nanoparticles. The results showed that the shell-aspect ratio and fin inclination angle are the most important design parameters influencing the charging time. The charging time could be changed by 40% by variation of design parameters. Interestingly a conical shell with a small radius at the bottom and a large radius at the top (small aspect ratio) is the best shell design. However, a too-small aspect ratio could entrap the liquid-PCM between fins and increase the charging time. An optimum volume fraction of 4% is found for nanoparticle concentration

Thermal Energy Storage and Heat Transfer of Nano-Enhanced Phase Change Material (NePCM) in a Shell and Tube Thermal Energy Storage (TES) Unit with a Partial Layer of Eccentric Copper Foam

Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size.QC 20210907</p

Mixed convection of nano-encapsulated phase change suspensions in a wavy wall lid-driven trapezoid cavity

The improvement of heat transfer and energy storage are crucial tasks in many renewable energy applications. The thermal and hydrodynamic performances of a nano-encapsulated phase change material (NEPCM) suspension are investigated under a mixed convective heat transfer regime inside a trapezoidal enclosure. As the host fluid and dispersed NEPCM particles circulate in the enclosure, the nanoparticle cores absorb/release heat and undergo a phase transition process, enhancing heat transfer. The governing equations were scaled into a general non-dimensional format and then solved by the finite element method. The influence of nanoparticles fusion temperature and concentration, as well as the wavy wall characteristics and Richardson number, was addressed on heat transfer. A suitable fusion temperature of the nanoparticles can boost the heat transfer rate by 8%. Furthermore, by employing 5% NEPCM particles at a dimensionless fusion temperature of 0.1, the Nusselt number achieved was 9.05. This marks a significant 37% rise when contrasted with a base fluid, which only had a Nusselt number of 5.7