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The cooling of electronic elements is one of the most important problems in the development of architecture in electronic technology. One promising developing cooling method is heat sinks based on the phase change materials (PCMs) enhanced by nano-sized solid particles. In this paper, the influence of the PCM’s physical properties and the concentration of nanoparticles on heat and mass transfer inside a closed radiator with fins, in the presence of a source of constant volumetric heat generation, is analyzed. The conjugate problem of nano-enhanced phase change materials (NePCMs) melting is considered, taking into account natural convection in the melt under the impact of the external convective cooling. A two-dimensional problem is formulated in the non-primitive variables, such as stream function and vorticity. A single-phase nano-liquid model is employed to describe the transport within NePCMs.

A two-dimensional numerical investigation of turbulent convective heat transfer due to a confined slot jet impinging on an isothermal moving surface is accomplished. The confined geometry has an upper adiabatic surface parallel to the heated moving plate and the slot jet is in the middle of the confining adiabatic wall. The working fluids are pure water or a nanofluid, which in this case was a mixture of water and Al2O3 nanoparticles. The governing equations are written adopting the k-ε turbulence model with enhanced wall treatment and the single-phase model approach for the nanofluids. The numerical model is solved using the finite volume method with the Ansys Fluent code. Two geometric configurations regarding two values of the jet distance from the target surface are considered in the simulations. The concentration of nanoparticles ranges from 0% to 6%, with a single diameter equal to 30 nm, Reynolds numbers ranging from 5000 to 20000, and a moving surface-jet velocity ratio between 0 and 2 are examined in the investigation. The aim is to study the system behaviors by means of local and average Nusselt numbers, local and average friction factor/skin friction factor, stream function, and temperature fields. Results show that the presence of nanoparticles determines an increase in the dimensionless heat transfer but, as expected, does not affect the friction factor. The local and average increase in Nusselt numbers is also due to a combined effect of the moving plate and nanofluids.

The constant growth of urban agglomerations with the development of transport networks requires the optimal use of energy and new ways of storing it. Energy efficiency is becoming one of the main challenges of modern engineering. The use of phase change materials in construction expands the possibilities of accumulating and storing solar energy, as well as reducing energy consumption. In this study, we consider the problem of the effect of natural convection on heat transfer in a building block containing a phase change material. Heat transfer, taking into account melting in brick, was analyzed at various temperature differences. The mathematical model was formulated in the form of time-dependent equations of conjugate natural convection using non-dimensional stream function, vorticity, and temperature. The equations describing melting, taking into account natural convection, were solved using the finite difference method. Smoothing parameters were used to describe phase transitions in the material. As a result of calculations, local characteristics of heat and mass transfer at various points in time were obtained, as well as changes in temperature profiles on the side surfaces. It is shown that with a large volume of melt, natural convection increases heat loss by more than 10%.

Modern technologies of thermal power engineering make it possible to design and build systems using renewable energy sources. Often, energy accumulation and storage require the development and adaptation of appropriate systems, the simplest of which are passive systems based on phase-change materials. In this study, a numerical analysis of heat transfer in a brick wall containing several materials with different melting temperatures is carried out. The unsteady two-dimensional conjugate problem of phase transitions is considered, taking into account natural convection in the melt, which has been solved using the developed in-house finite difference technique. A numerical experiment has been carried out for a brick block with several rectangular inserts filled with PCMs under various external thermal conditions. As a result of the numerical analysis, it has been shown that the relative arrangement of materials with different melting points has a significant impact on the heat transfer and heat exchange between the environment and the room.

Many passive heat controlling technologies are based on the use of phase change materials. As a rule, at low operation temperatures, close to environmental conditions, paraffins or fatty acids with melting points of 20–90 °C are used. However, the low thermal conductivity of these materials requires the development of various heat transfer enhancers satisfying technical requirements. In this work, the possibility of nanoparticle application to the heat transfer augmentation inside a closed copper radiator filled with pure n-octadecane, depending on the thermal conditions of the local heater and other system parameters, are numerically investigated.

Nowadays, the heat transfer enhancement in electronic cabinets with heat-generating elements can be achieved using the phase change materials and finned heat sink. The latter allows to improve the energy transference surface and to augment the cooling effects for the heat sources. The present research deals with numerical analysis of phase change material behavior in an electronic cabinet with an energy-generating element. For an intensification of heat removal, the complex finned heat sink with overall width of 10 cm was introduced, having the complicated shape of the fins with width of 0.33 cm and height H = 5 cm. The fatty acid with melting temperature of 46 °C was considered as a phase change material. The considered two-dimensional challenge was formulated employing the non-primitive variables and solved using the finite difference method. Impacts of the volumetric heat flux of heat-generating element and sizes of the fins on phase change material circulation and energy transference within the chamber were studied. It was shown that the presence of transverse ribs makes it possible to accelerate the melting process and reduce the source temperature by more than 12 °C at a heat load of 1600 W/m. It should also be noted that the nature of melting depends on the hydrodynamics of the melt, so the horizontal partitions reduce the intensity of convective heat transfer between the upper part of the region and the lower part.

The issue of thermal control plays an important role in the development of technical systems of computing and radio equipment. Temperature conditions are an important factor in the performance and durability of devices. New models of heat sink containing materials with phase transitions “solid body–liquid” are appeared. In the present paper, the numerical study of natural convection melting/solidification of phase change material inside a finned heat sink with a local heater having time-dependent volumetric heat flux has been carried out. An unsteady conjugate phase change problem has been solved taking into account natural convection in the melt, in the presence of a heat-dissipating copper profile. The energy equation has been formulated using a special smoothing function of temperature. The equations of hydrodynamics have been formulated using non-primitive variables, namely the stream function and vorticity. The system of transient differential equations of natural convection, taking into account the melting process and the heat-generating and heat-conducting element, has been solved using the finite-difference method. Analysis has been performed for different values of the volumetric heat generation within the heater and the periodic volumetric heat generation frequency. Obtained results have shown that a rise of the volumetric heat generation frequency leads to an increase in the amplitude of the average temperature within the heater that can have a negative effect on the system operation.Graphic abstract

Purpose The main aim of this work is to perform a numerical analysis on natural convection with entropy generation in a partially open triangular cavity with a local heat source. Design/methodology/approach The unsteady governing dimensionless partial differential equations with corresponding initially and boundary conditions were numerically solved by the finite difference method of the second-order accuracy. The effects of dimensionless time is studied, and other governing parameters are Rayleigh number (Ra = 103 − 105), Prandtl number (Pr = 6.82), heater length (w/L = 0.2, 0.4 and 0.6) and distance of heater ratio (δ/L = 0.3). Findings An increase in the Rayleigh number leads to an increment of the fluid flow and heat transfer rates. Average Bejan number decreases with Ra as opposed to the average Nusselt number and average entropy generation. High values of Ra characterize a formation of long-duration oscillating behavior for the average Nusselt number and entropy generation. Originality/value The originality of this work is to analyze the entropy generation in natural convection in a one side open and partial heater-located cavity. This is a good application for electronical systems or building design.

Melting and solidification problems are important in applications of many industries. In the present work mathematical simulation of natural convection with phase transition inside an enclosure with a local heat source has been carried out. Partial differential equations with corresponding initial and boundary conditions have been solved using the finite difference method. The effect of temperature differences on fluid flow and heat transfer has been discussed.

Phase change problems with natural convection in the liquid phase are of prime importance in accurate technological applications. In this work a melting of pure gallium in a rectangular cavity heated from the left wall is simulated using the finite difference method. Numerical algorithm based on dimensionless variables stream function and vorticity has been checked by experimental data of previously published papers. The effect of the grid size on results of calculations was identified. Motion of phase front and changing parameters of heat and mass-transfer were studied