Fluids

Research

13 pages, 6172 KiB

Open AccessArticle

Numerical Investigation of Conjugate Natural Convection in a Cavity with a Local Heater by the Lattice Boltzmann Method

by Nikita S. Gibanov and Mikhail A. Sheremet

Fluids 2021, 6(9), 316; https://doi.org/10.3390/fluids6090316 - 3 Sep 2021

Cited by 10 | Viewed by 2367

A numerical study of conjugate thermogravitational convection in a closed cavity with a local heater of square or triangular shape placed on a heat-conducting substrate using the double distribution function of the lattice Boltzmann method has been carried out. The side walls of [...] Read more.

A numerical study of conjugate thermogravitational convection in a closed cavity with a local heater of square or triangular shape placed on a heat-conducting substrate using the double distribution function of the lattice Boltzmann method has been carried out. The side walls of the research area are maintained at a constant minimum temperature. The influence of the geometric shape of the heating element, the Rayleigh number, and the material of the heat-removing substrate on the thermohydrodynamic parameters has been studied. As a result of the research, the joint effect of these mentioned parameters on the efficiency of heat removal from the heater surface has been established. It has been found that a rise of the bottom wall thermal conductivity causes an increase in the average Nusselt number at the heater surface. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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15 pages, 5197 KiB

Open AccessArticle

Energy Saving and Charging Discharging Characteristics of Multiple PCMs Subjected to Internal Air Flow

by Ahmed J. Hamad

Fluids 2021, 6(8), 275; https://doi.org/10.3390/fluids6080275 - 6 Aug 2021

Cited by 5 | Viewed by 2444

Abstract

One essential utilization of phase change materials as energy storage materials is energy saving and temperature control in air conditioning and indirect solar air drying systems. This study presents an experimental investigation evaluating the characteristics and energy savings of multiple phase change materials [...] Read more.

One essential utilization of phase change materials as energy storage materials is energy saving and temperature control in air conditioning and indirect solar air drying systems. This study presents an experimental investigation evaluating the characteristics and energy savings of multiple phase change materials subjected to internal flow in an air heating system during charging and discharging cycles. The experimental tests were conducted using a test rig consisting of two main parts, an air supply duct and a room model equipped with phase change materials (PCMs) placed in rectangular aluminum panels. Analysis of the results was based on three test cases: PCM1 (Paraffin wax) placed in the air duct was used alone in the first case; PCM2 (RT–42) placed in the room model was used alone in the second case; and in the third case, the two PCMs (PCM1 and PCM2) were used at the same time. The results revealed a significant improvement in the energy savings and room model temperature control for the air heating system incorporated with multiple PCMs compared with that of a single PCM. Complete melting during the charging cycle occurred at temperatures in the range of 57–60 °C for PCM1 and 38–43 °C for PCM2, respectively, thereby validating the reported PCMs’ melting–solidification results. Multiple PCMs maintained the room air temperature at the desired range of 35–45.2 °C in the air heating applications by minimizing the air temperature fluctuations. The augmentation in discharging time and improvement in the room model temperature using multiple PCMs were about 28.4% higher than those without the use of PCMs. The total energy saving using two PCMs was higher by about 29.5% and 46.7% compared with the use of PCM1 and PCM2, respectively. It can be concluded that multiple PCMs have revealed higher energy savings and thermal stability for the air heating system considered in the current study. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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12 pages, 4831 KiB

Open AccessArticle

Natural Convection Melting Influence on the Thermal Resistance of a Brick Partially Filled with Phase Change Material

by Nadezhda S. Bondareva and Mikhail A. Sheremet

Fluids 2021, 6(7), 258; https://doi.org/10.3390/fluids6070258 - 14 Jul 2021

Cited by 9 | Viewed by 2581

Abstract

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 [...] Read more.

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%. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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Graphical abstract

16 pages, 3108 KiB

Open AccessArticle

The Magneto-Natural Convection Flow of a Micropolar Hybrid Nanofluid over a Vertical Plate Saturated in a Porous Medium

by A. Mahdy, E. R. El-Zahar, A. M. Rashad, W. Saad and H. S. Al-Juaydi

Fluids 2021, 6(6), 202; https://doi.org/10.3390/fluids6060202 - 27 May 2021

Cited by 42 | Viewed by 3058

Abstract

In this study, we investigate the convective flow of a micropolar hybrid nanofluid through a vertical radiating permeable plate in a saturated porous medium. The impact of the presence or absence of the internal heat generation (IHG) in the medium is examined as [...] Read more.

In this study, we investigate the convective flow of a micropolar hybrid nanofluid through a vertical radiating permeable plate in a saturated porous medium. The impact of the presence or absence of the internal heat generation (IHG) in the medium is examined as well as the impacts of the magnetic field and thermal radiation. We apply similarity transformations to the non-dimensionalized equations and render them as a system of non-linear ODEs (Ordinary Differential Equations) subject to appropriate boundary conditions. This system of non-linear ODEs is solved by an adaptive mesh transformation Chebyshev differential quadrature method. The influence of the governing parameters on the temperature, microrotation and velocity is examined. The skin friction coefficient and the Nusselt number are tabulated. We determine that the skin friction coefficient and heat transport rate increase with the increment in the magnetic field. Moreover, the increment in the micropolarity and nanoparticle volume fraction enhances the skin friction coefficient and the Nusselt number. We also conclude that the IHG term improved the flow of the hybrid nanofluid. Finally, our results indicate that employing a hybrid nanofluid increases the heat transfer compared with that in pure water and a nanofluid. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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15 pages, 3919 KiB

Open AccessArticle

Unsteady MHD Mixed Convection Flow of Non-Newtonian Casson Hybrid Nanofluid in the Stagnation Zone of Sphere Spinning Impulsively

by Essam R. El-Zahar, Abd El Nasser Mahdy, Ahmed M. Rashad, Wafaa Saad and Laila F. Seddek

Fluids 2021, 6(6), 197; https://doi.org/10.3390/fluids6060197 - 26 May 2021

Cited by 52 | Viewed by 2826

Abstract

In the present analysis, an unsteady MHD mixed convection flow is scrutinized for a non-Newtonian Casson hybrid nanofluid in the stagnation zone of a rotating sphere, resulting from the impulsive motion of the angular velocity of the sphere and the velocity of the [...] Read more.

In the present analysis, an unsteady MHD mixed convection flow is scrutinized for a non-Newtonian Casson hybrid nanofluid in the stagnation zone of a rotating sphere, resulting from the impulsive motion of the angular velocity of the sphere and the velocity of the free stream. A set of linearized equations is derived from the governing ones, and these differential equations are solved numerically using the hybrid linearization–differential quadrature method. The surface shear stresses in the

x

- and

y

-directions and the surface heat transfer rate are improved due to the Casson

β_{o}

, mixed convection

α

, rotation

γ

and magnetic field

M

parameters. In addition, as nanoparticles, the solid volume fraction (parameter

ϕ

) increases, and the surface shear stresses and the rate of heat transfer are raised. A comparison between earlier published data and the present numerical computations is presented for the limiting cases, which are noted to be in very good agreement. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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19 pages, 7454 KiB

Open AccessArticle

Numerical Computation of Dufour and Soret Effects on Radiated Material on a Porous Stretching Surface with Temperature-Dependent Thermal Conductivity

by Tahir Naseem, Umar Nazir, Essam R. El-Zahar, Ahmed M. Algelany and Muhammad Sohail

Fluids 2021, 6(6), 196; https://doi.org/10.3390/fluids6060196 - 24 May 2021

Cited by 12 | Viewed by 2132

Abstract

The current research is prepared to address the transport phenomenon in a hydro-magnetized flow model on a porous stretching sheet. Mass and heat transport are modeled via temperature dependent models of thermal conductivity and diffusion coefficients. Accordingly, the involvement of radiation, chemical reaction, [...] Read more.

The current research is prepared to address the transport phenomenon in a hydro-magnetized flow model on a porous stretching sheet. Mass and heat transport are modeled via temperature dependent models of thermal conductivity and diffusion coefficients. Accordingly, the involvement of radiation, chemical reaction, the Dufour effect, and the Soret effect are involved. The flow presenting expression has been modeled via boundary layer approximation and the flow is produced due to the experimental stretching sheet. The governing equations have been approximated numerically via shooting method. The efficiency of the scheme is established by including the comparative study. Moreover, a decline in the velocity field is recorded against the escalating values of the porosity parameter and the magnetic parameter. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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14 pages, 1223 KiB

Open AccessArticle

HVDC Converter Cooling System with a Phase Change Dispersion

by Ludger Fischer, Ernesto Mura, Geng Qiao, Poppy O’Neill, Silvan von Arx, Qi Li and Yulong Ding

Fluids 2021, 6(3), 117; https://doi.org/10.3390/fluids6030117 - 12 Mar 2021

Cited by 6 | Viewed by 7292

Abstract

High voltage direct current converters require efficient cooling of thyristors via heat sinks. Currently, infrastructures use deionised water as a means of cooling the high voltage direct current converters; however, recent research has shown that other fluids have potential to offer more efficient [...] Read more.

High voltage direct current converters require efficient cooling of thyristors via heat sinks. Currently, infrastructures use deionised water as a means of cooling the high voltage direct current converters; however, recent research has shown that other fluids have potential to offer more efficient cooling. Phase change dispersions are a new class of heat transfer fluids that employ the latent heat of phase change, thus offering isothermal cooling during melting. For cooling applications, the temperature increase during operation is thus lowered when using phase change dispersions (compared to water) and consequently, the heat sink and thyristors surface temperatures are reduced. In this investigation, a phase change dispersion with non-conductive components, high stability, high capacity and low viscosity has been developed and tested. An experimental setup of a real size heat sink has been installed and the heat transfer behaviour of both the formulated phase change dispersion and water have been investigated and a comparison has been presented. Using water as the heat transfer fluid, the temperature increase from inlet to outlet of the heat sink was 4 K and with the formulated phase change dispersion (at the same mass flow rate and heat input) the temperature increase was 2 K. The phase change dispersion caused a 50% reduction in the heat sink surface temperature. Furthermore, the global heat transfer coefficients obtained for the phase change dispersion were found to be independent of the heating input applied, unlike the trend found for water, additionally, the global heat transfer coefficients were found to be similar to those obtained for water at the same mass flow rates and reached a maximum value of 6100 W m

^{2}

K

^{- 1}

. Despite this, the pressure drops and viscosities obtained for the phase change dispersion were higher than for water. Overall, the current investigation demonstrates the ability of using a phase change dispersion as a cooling fluid for the cooling of electronic components, which thus far is limited to using air and water cooling and cannot reach the cooling capacity achieved by phase change dispersions. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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15 pages, 3146 KiB

Open AccessArticle

Simulation of Thermal Radiation and Turbulent Free Convection in an Enclosure with a Glass Wall and a Local Heater

by Igor V. Miroshnichenko, Aidar A. Toilibayev and Mikhail A. Sheremet

Fluids 2021, 6(2), 91; https://doi.org/10.3390/fluids6020091 - 23 Feb 2021

Cited by 7 | Viewed by 2647

Abstract

In this study, a numerical modelling of thermal radiation and turbulent thermogravitational convection in a large-scale chamber containing a thermally-generating element is conducted. The lower border of the cabinet is maintained under adiabatic conditions, while on the other walls the convective boundary conditions [...] Read more.

In this study, a numerical modelling of thermal radiation and turbulent thermogravitational convection in a large-scale chamber containing a thermally-generating element is conducted. The lower border of the cabinet is maintained under adiabatic conditions, while on the other walls the convective boundary conditions (Robin boundary condition) are used. The managing equations with corresponding restrictions are transformed using the stream function–vorticity formulation and then solved by employing a finite difference method. The influence of both the height and wall emissivity of the heated source on fluid motion and the heat transmission in a large-scale chamber is investigated. Our results of the calculations on non-uniform grids with algebraic transformation are in excellent agreement with other available experimental and numerical outcomes for turbulent thermal convection in enclosures. The computations indicate that the average total Nusselt number is enhanced up to 2 times with an increase in the heater height. The results show that the surface emissivity of the heat source has a great influence on the total thermal transference coefficient. Furthermore, a growth of the heater surface emissivity has no significant effect on the flow structure. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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15 pages, 10221 KiB

Open AccessArticle

Numerical Analysis of Tube Heat Exchanger with Perforated Star-Shaped Fins

by Mladen Bošnjaković and Simon Muhič

Fluids 2020, 5(4), 242; https://doi.org/10.3390/fluids5040242 - 13 Dec 2020

Cited by 11 | Viewed by 3238

Abstract

This article discusses the possibility of further reducing the mass of the heat exchanger with stainless steel star-shaped fins while achieving good heat transfer performance. For this purpose, we perforated the fins with holes Ø2, Ø3, and Ø4 mm. Applying computational fluid dynamics [...] Read more.

This article discusses the possibility of further reducing the mass of the heat exchanger with stainless steel star-shaped fins while achieving good heat transfer performance. For this purpose, we perforated the fins with holes Ø2, Ø3, and Ø4 mm. Applying computational fluid dynamics (CFD) numerical analysis, we determined the influence of each perforation on the characteristics of the flow field in the liquid–gas type of heat exchanger and the heat transfer for the range of Re numbers from 2300 to 16,000. With a reduction in the mass of the fins to 17.65% (by Ø4 mm), perforated fins had greater heat transfer from 5.5% to 11.3% than fins without perforation. A comparison of perforated star-shaped fins with annular fins was also performed. Perforated fins had 51.8% less mass than annular fins, with an increase in heat transfer up to 26.5% in terms of Nusselt number. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Dynamics in Energy Systems)

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