scholarly journals Thermophysical Characterization and Numerical Investigation of Three Paraffin Waxes as Latent Heat Storage Materials

2019 ◽  
Author(s):  
Manel Kraiem ◽  
Mustapha Karkri ◽  
Sassi Ben Nasrallah ◽  
patrick sobolciak ◽  
Magali Fois ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Heat Storage ◽  
Numerical Study ◽  
Melting Process ◽  
Heat Transfer Mode ◽  
Transfer Mode ◽  
Paraffin Waxes ◽  
Thermophysical Characterization

Thermophysical characterization of three paraffin waxes (RT27, RT21 and RT35HC) is carried out in this study using DSC, TGA and transient plane source technics. Then, a numerical study of their melting in a rectangular enclosure is examined. The enthalpy-porosity approach is used to formulate this problem in order to understand the heat transfer mechanism during the melting process. The analysis of the solid-liquid interface shape, the temperature field shows that the conduction is the dominant heat transfer mode in the beginning of the melting process. It is followed by a transition regime and the natural convection becomes the dominant heat transfer mode. The effects of the Rayleigh number and the aspect ratio of the enclosure on the melting phenomenon are studied and it is found that the intensity of the natural convection increases as the Rayleigh number is higher and the aspect ratio is smaller. In the second part of the numerical study, a comparison of the performance of paraffins waxes during the melting process is conducted. Results reveals that from a kinetically RT21 is the most performant but in term of heat storage capacity, it was inferred that RT35HC is the most efficient PCM.

scholarly journals Numerical Study Using Microstructure Based Finite Element Modeling of the Onset of Convective Heat Transfer in Closed-Cell Polymeric Foam

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1769
Author(s):  
Jorge-Enrique Rivera-Salinas ◽  
Karla-Monzerratt Gregorio-Jáuregui ◽  
Heidi-Andrea Fonseca-Florido ◽  
Carlos-Alberto Ávila-Orta ◽  
Eduardo Ramírez-Vargas ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Finite Element ◽  
Natural Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Heat Transfer Mode ◽  
Transfer Mode ◽  
Closed Cell

The thermal performance of closed-cell foams as an insulation device depends on the thermal conductivity. In these systems, the heat transfer mode associated with the convective contribution is generally ignored, and studies are based on the thermo-physical properties that emerge from the conductive contribution, while others include a term for radiative transport. The criterion found in the literature for disregarding convective heat flux is the cell diameter; however, the cell size for which convection is effectively suppressed has not been clearly disclosed, and it is variously quoted in the range 3–10 mm. In practice, changes in thermal conductivity are also attributed to the convection heat transfer mode; hence, natural convection in porous materials is worthy of research. This work extends the field of study of conjugate heat transfer (convection and conduction) in cellular materials using microstructure-based finite element analysis. For air-based insulating materials, the criteria to consider natural convection (Ra=103) is met by cavities with sizes of 9.06 mm; however, convection is developed into several cavities despite their sizes being lower than 9.06 mm, hence, the average pore size that can effectively suppress the convective heat transfer is 6.0 mm. The amount of heat transported by convection is about 20% of the heat transported by conduction within the foam in a Ra=103, which, in turn, produces an increasing average of the conductivity of about 4.5%, with respect to a constant value.

scholarly journals Numerical Simulation of the Natural Convection with Presence of the Nanofluids in Cubical Cavity

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Mohamed Sannad ◽  
Abourida Btissam ◽  
Belarche Lahoucine
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Flow And Heat Transfer ◽  
Heating Section ◽  
The Right

This article consists of a numerical study of natural convection heat transfer in three-dimensional cavity filled with nanofluids. This configuration is heated by a partition maintained at a hot constant and uniform temperature TH. The right and left vertical walls are kept at a cold temperature TC while the rest is adiabatic. The fluid flow and heat transfer in the cavity are studied for different sets of the governing parameters, namely, the nanofluid type, the Rayleigh number Ra = 103, 104, 105, and 106, and the volume fraction Ф varying between Ф = 0 and 0.1. The obtained results show a positive effect of the volume fraction and the Rayleigh number on the heat transfer improvement. The analysis of the results related to the heat transfer shows that the copper-based nanofluid guarantees the best thermal transfer. In addition, the increase of the heating section size and Ra leads to an increased amount of heat. Similarly, increasing the volume fraction improves the intensification of the flow and increases the heat exchange.

Numerical Simulation of Paraffin Melting Process in an Inclined Channel

2021 ◽  
Vol 896 ◽  
pp. 111-116
Author(s):  
Yan Li ◽  
Guo You You ◽  
Zhu Qunzhi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Early Stage ◽  
Liquid Paraffin ◽  
Convection Heat Transfer ◽  
Melting Process ◽  
Heat Transfer Mode ◽  
Dominant Position ◽  
Transfer Mode ◽  
Higher Temperature

Numerical simulation of the melting of paraffin in the inclined straight channel shows that the melting speed of paraffin is faster in the early stage and gradually slows down in the later stage. It is found that heat conduction is the main heat transfer mode in the early stage of paraffin melting. With the increasing number of liquid paraffin, natural convection occurs in the liquid paraffin. The liquid paraffin with higher temperature flows upward due to the effect of buoyance and lift, and convection heat transfer gradually increases and takes the dominant position in the melting process.

Numerical Investigation of Coupled Surface Radiation and Natural Convection in a Triangular Shaped Roof (Gabel Roof) under Winter Conditions

2019 ◽  
Vol 392 ◽  
pp. 200-217
Author(s):  
Abdel Illah Amrani ◽  
Nadia Dihmani ◽  
Samir Amraqui ◽  
Ahmed Mezrhab
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Climatic Conditions ◽  
Surface Radiation ◽  
Working Fluid ◽  
Building Roof ◽  
Simpler Algorithm

In the building, roof is a major element contributing to the space thermal load. Due to its importance, this component has been widely studies in the literature and under various climatic conditions. In this paper, a numerical study was carried out for the coupling of natural convection and surface radiation heat transfer in a triangular shaped roof with eave (Gabel roof) for cold climates. The numerical solution is obtained using a finite volume method based on the SIMPLER algorithm for the treatment of velocity-pressure coupling. Concerning the radiation exchange, the working fluid (air) is assumed to be transparent, so only the solid surfaces (assumed diffuse-grey) give a contribute to such exchange. Governing parameters on heat transfer and flow fields are Rayleigh number (Ra), aspect ratio (A) and eave lengths (e*). Numerical results are obtained to display the isotherms, streamlines and the heat transfer rate in terms of local and average Nusselt numbers. We found that the production of several circular cells is proportional to the decrease of aspect ratio and the increase of Rayleigh number. In addition, the heat transfer is much more pronounced in the presence of thermal radiation.

Numerical Study of Natural Convection Heat Transfer Over a Cooling Stage

2017 ◽  
Author(s):  
Mohammad Rejaul Haque ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Ambient Air ◽  
Recirculation Region ◽  
Asymmetric Distribution ◽  
Computational Domain ◽  
Cooling Stage

Numerical study of natural convection phenomenon close to a cooling stage has been investigated in a two dimensionally controlled environment. The study was conducted for ambient air which was kept at constant temperature (22°C) and Prandtl number of this Newtonian fluid was taken as 0.71. The cooling stage was kept at 5°C and height of the stage was considered 0.02 m. The stage was located at the bottom on the computational domain. The center of cooling stage was placed at X = 0.35 m and X = 0.5 m respectively from the left boundary of the domain. Later, computational analysis was performed to solve coupled momentum and energy equations for appropriate boundary conditions. The study was performed for a range of Rayleigh number from 102 to 107. Thermal and hydrodynamic behavior was reported in terms of isotherms, streamlines and average Nusselt number calculation. The position of the stage significantly effects heat transfer and flow fields. Nusselt number was evaluated close to cooling stage. Streamlines resulted huge recirculation region which was symmetric about the vertical mid-centerline of the domain for cooling stage located at X = 0.5 m. The center of core vortices shifted near to the cooling stage as Rayleigh number increases ensuring enhancement of heat transfer. Additionally, increasing Rayleigh number induces significant buoyancy driven flow. The velocity of this driven flow increases towards left and right wall as Rayleigh number increases. Velocity profile was also evaluated due to flow inside the enclosure. A parabolic variation was observed for horizontal velocity component near the isothermal walls and it was found less significant compared to vertical component due to buoyancy driven flow. Moreover, the asymmetric distribution of isotherms created by eccentric position of the stage resulted better enhancement than centric position of the cooling stage. Finally, this results would help the researchers find the optimal position of any sample on a cooling stage subjected to convection phenomenon. This could be significant in the collection of experimental data for condensation and frost formation.

Natural Convection From Two Thermal Sources in a Vertical Porous Layer

2005 ◽  
Vol 128 (1) ◽  
pp. 104-109 ◽  
Author(s):  
Nawaf H. Saeid
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Separation Distance ◽  
Convection Flow ◽  
Thermal Sources ◽  
Heated Element

Numerical study of natural convection flow induced by two isothermally heated elements located on adiabatic vertical plate immersed in a Darcian porous medium is carried out in the present article. The natural convection is affected by the Rayleigh number, the separation distance between the elements, their temperature ratio, and the length of the upper element. The numerical results are presented as average Nusselt number versus Rayleigh number for wide ranges of the governing parameters. It is found that the heat transfer from the lower element is not affected by the presence of the upper element for equal temperatures of the elements. The heat transfer from the lower element can be enhanced by increasing the temperature of the upper element due to the suction effect. The average Nusselt number along the upper heated element is found to increase with the increase of any of the governing parameters.

scholarly journals Numerical Study on the Natural Convection of Air in a Cubic Cavity Subjected to a Yawing Motion

2019 ◽  
Vol 7 (7) ◽  
pp. 204 ◽  
Author(s):  
Yu ◽  
Zhang ◽  
Jia ◽  
Geng ◽  
Liu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Rotation Period ◽  
Rotation Frequency ◽  
Static Case ◽  
Governing Equations ◽  
Induced Velocity

Natural convections subjected to multi-Degree of Freedom (DoF) motion are much more complex than those in static case, and those subjected to yawing motion are the simplest and ideal case for investigating their characteristics due to less interactive parameters. In this paper, the characteristic of natural convection under yawing motion was studied systematically to clarify the interaction between yawing motion and thermal-dynamic behavior. First of all, the mathematical model was established in a non-inertial coordinate system, and the dimensionless governing equations were derived. Subsequently, the governing equations were discretized in the framework of the finite volume method, and a computer code was developed and validated. After that, the natural convection under yawing motion was calculated with different combinations of dimensionless parameters, and the influence of rotation frequency and amplitude on heat and mass transfer was investigated. It was found that the yawing motion plays a notable role in flow and heat transfer, depending on the relative magnitudes of rotation-induced velocity and buoyancy-induced velocity: At a lower Rayleigh number of 104, the Nusselt number on hot boundary is enhanced by approximately 25% when the rotation period is changed from 12 s to 2 s; while the changing in rotation period from 12 s to 2 s did not induce obvious difference in hot-boundary Nusselt number for a higher Rayleigh number of 105. It is concluded that the vertical-axis harmonic rotation enhances heat transfer if the rotation-induced velocity dominates the flow. The clarification of natural convection characteristic in yawing motion provides convenience for analyzing that in other multi-DoF systems.

scholarly journals Numerical analysis of PCM melting filling a rectangular cavity with horizontal partial fins

2020 ◽  
Vol 307 ◽  
pp. 01011
Author(s):  
Tarik Bouhal ◽  
Saïf ed-Dîn Fertahi ◽  
Oussama Limouri ◽  
Younes Agrouaz ◽  
Tarik Kousksou ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Melting Process ◽  
Heat Transfer Characteristics ◽  
Triangular Shape ◽  
Temperature Distributions ◽  
Exchange Area ◽  
The Right ◽  
Change Material

The present numerical study is conducted to analyze melting process within a rectangular enclosure filled by phase change material (PCM) vertically heated from one side. The right hot wall and the left cold wall are maintained at temperatures, Th=38.3 °C and Tc =28.3 °C, respectively, and it was filled by solid PCM Gallium initially at temperature Tc. The horizontal walls are insulated. A transient numerical model is developed to study the heat transfer and melting behaviours, and the natural convection is accounted. To enhance the heat transfer and the melting process of the PCM, fins with a rectangular and triangular shape are proposed. Moreover, the effects of both thermophysical properties and fins integration on the flow structure and heat transfer characteristics are investigated in detail. The melt fraction contours with the natural convection driven flow are performed and compared, as well as the temperature distributions for a Rayleigh number of around Ra= 106. It is found that the rate of the melting increases with the elevation in the values of specific heat capacity Cp as well as the thermal conductivity λ of the PCM Gallium. The results show also that the rectangular fin accelerates the PCM melting faster than the triangular fin’s shape thanks to the increased exchange area.

scholarly journals Effect of Al2O3 Nanoparticles and Cylindrical Pins on Natural Convection Heat Transfer in a C-Shaped Enclosure

2020 ◽  
Vol 12 (4) ◽  
pp. 499-515
Author(s):  
M. Y. Arafat ◽  
F. Faisal
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Al2o3 Nanoparticles ◽  
Simpler Algorithm

A numerical study has been conducted to investigate the transport mechanism of natural convection in a C-shaped enclosure filled with water-Al2O3 nanofluid for various pertinent parameters. The effects of the volume fraction of the Al2O3 nanoparticles, Rayleigh number, and radius of inserted cylindrical pins on the temperature, velocity, heat flux profiles and average Nusselt number have been investigated. General correlations for the effective thermal conductivity and viscosity of nanofluids are used for this analysis. The governing mass, momentum and energy equations are solved numerically with the finite volume method using the SIMPLER algorithm. The results show that addition of nanoparticle improves the heat transfer performance. Insertion of cylindrical pins of lower radius increases the average Nusselt number irrespective of Rayleigh number. But anomaly has been observed while pins of higher radius are inserted due to enormous disturbance in the fluid.

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