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Ahmet Sari - One of the best experts on this subject based on the ideXlab platform.

  • thermal energy storage properties of mannitol fatty acid esters as novel organic solid Liquid Phase Change materials
    Energy Conversion and Management, 2012
    Co-Authors: Ahmet Sari
    Abstract:

    Abstract In this study, four kinds of mannitol–fatty acid esters were synthesized as novel organic Phase Change materials (PCMs) for thermal energy storage applications. The structural characterization of synthesized mannitol hexastearate (MHS), mannitol hexapalmitate (MHP), mannitol hexamyristate (MHM) and mannitol hexalaurate (MHL) were carried out using Fourier Transform Infrared (FT-IR), Proton Nuclear Magnetic Resonance ( 1 H NMR), and 13 C NMR spectroscopy methods. Thermal energy storage properties and thermal reliability of the synthesized PCMs were determined using differential scanning calorimetry (DSC) method at a heating rate of 1 °C/min. DSC results showed that the melting temperatures of the PCMs were in the temperature range of 42–65 °C and their latent heat values spanned between 145 and 202 J/g. The latent heats of these PCMs are low compared to mannitol but they fall into the same range as fatty acids. The synthesized PCMs have much lower Phase Change temperatures and supercooling degree (about 1–8 °C) and compared to the mannitol. They have also better odor, noncorrosivity and thermal durability properties as compared to the fatty acids. Thermal cycling test consisted of repeated 1000 melting/solidification cycles also revealed that the synthesized PCMs have good thermal reliability. In addition, thermal conductivity of the PCMs was increased significantly by addition of expanded graphite (EG) at 10 wt%. Based on all results it can be concluded that the synthesized PCMs, MHS, MHP, MHM and MHL esters can be considered as promising solid–Liquid PCMs for solar heating applications.

  • galactitol hexa stearate and galactitol hexa palmitate as novel solid Liquid Phase Change materials for thermal energy storage
    Solar Energy, 2011
    Co-Authors: Ahmet Sari, Özgür Lafçi, Alper Bicer, Mustafa Ceylan
    Abstract:

    Abstract Galactitol has a melting point of 187.41 °C and a fusion enthalpy of 401.76 J g −1 . Its melting temperature is not suitable for many thermal energy storage applications although it has good latent heat storage capacity compared to the several traditional Phase Change materials (PCMs). The galactitol also has high supercooling degree as about 72 °C. These unfavorable properties limit the usage potential of galactitol in thermal energy storage applications. However, the Phase Change temperature and supercooling degree of galactitol can be reduced to a reasonable value and therefore its feasibility for energy storage systems can be increased. For this aim, in this study, galactitol hexa stearate (GHS) and galactitol hexa palmitate (GHP) were prepared as novel solid–Liquid PCM by means of esterification reaction of the galactitol with palmitic acid and stearic acid. The GHP and GHS esters were characterized chemically using FT-IR and 1 H NMR techniques. By using DSC analysis method, the melting temperature and latent heat value of the PCMs were determined as 31.78 °C and 201.66 J g −1 for GHP ester and 47.79 °C and 251.05 J g −1 for GHS ester. Thermal cycling test showed that the prepared PCMs had good thermal reliability after thermal 1000 melting–freezing cycles. Thermogravimetric analysis (TGA) results revealed that the PCMs have good thermal stability over their working temperatures. In addition, thermal conductivity of the prepared PCMs was increased as about 26.3% for GHP and 53.3% for GHS by addition of 5 wt.% expanded graphite. Based on all results it can be concluded that the prepared GHP and GHS esters can be considered as promising solid–Liquid PCMs for many energy storage applications such as solar energy storage, indoor temperature controlling in buildings, production of smart textile and insulation clothing due to their good energy storage properties.

  • synthesis thermal energy storage properties and thermal reliability of some fatty acid esters with glycerol as novel solid Liquid Phase Change materials
    Solar Energy Materials and Solar Cells, 2010
    Co-Authors: Ahmet Sari, Alper Bicer, Ali Karaipekli, Cemil Alkan, Ahmet Karadag
    Abstract:

    Abstract The synthesis, thermal energy storage properties and thermal reliability of some fatty acid esters with glycerol as novel solid–Liquid Phase Change energy storage materials were investigated. The esters were synthesized by means of the Fischer esterification reaction of the glycerol with myristic, palmitic and stearic acids. The chemical structures of esters were proven by FT-IR and 1H NMR techniques. The melting temperatures and latent heats of the synthesized esters were found in the range of 31–63 °C and 149–185 J/g, by DSC method. The results showed that the esters as Phase Change materials (PCMs) had good thermal reliability with respect to the 1000 thermal cycles. TGA analysis was performed to determine thermal stability of the esters. The thermal conductivity of the PCMs was also improved significantly by adding 5 wt% expanded graphite. Based on all results it can also be concluded that the synthesized esters can be considered as potential PCMs for thermal energy storage.

  • synthesis characterization thermal properties of a series of stearic acid esters as novel solid Liquid Phase Change materials
    Materials Letters, 2009
    Co-Authors: Ahmet Sari, Alper Bicer, Ali Karaipekli
    Abstract:

    Abstract This paper deals with the synthesis, characterization, thermal properties and thermal reliability of a series of stearic acid esters as a novel solid–Liquid Phase Change material (PCM) for thermal energy storage. The ester compounds were synthesized via the reaction of stearic acid with n-butyl alcohol, isopropyl alcohol and glycerol and characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H Nuclear Magnetic Resonance (1H NMR) techniques. Thermal properties of the esters were measured by differential scanning calorimeter (DSC) method. DSC results indicated that the melting temperatures and latent heats of the synthesized PCMs are in the range of 23–63 °C and 121–149 J/g, respectively. The thermal cycling test including 1000 cycling was conducted to determine the thermal reliability of the synthesized PCMs. The thermal conductivities of the PCMs were also increased by adding 5 wt.% EG into the esters. Based on the results, it is concluded that the synthesized esters as novel PCM have significant energy storage potential due to their satisfactory thermal properties, good thermal reliability and thermal conductivities.

  • form stable paraffin high density polyethylene composites as solid Liquid Phase Change material for thermal energy storage preparation and thermal properties
    Energy Conversion and Management, 2004
    Co-Authors: Ahmet Sari
    Abstract:

    Abstract This paper deals with the preparation of paraffin/high density polyethylene (HDPE) composites as form-stable, solid–Liquid Phase Change material (PCM) for thermal energy storage and with determination of their thermal properties. In such a composite, the paraffin (P) serves as a latent heat storage material and the HDPE acts as a supporting material, which prevents leakage of the melted paraffin because of providing structural strength. Therefore, it is named form-stable composite PCM. In this study, two kinds of paraffins with melting temperatures of 42–44 °C (type P1) and 56–58 °C (type P2) and latent heats of 192.8 and 212.4 J g −1 were used. The maximum weight percentage for both paraffin types in the PCM composites without any seepage of the paraffin in the melted state were found as high as 77%. It is observed that the paraffin is dispersed into the network of the solid HDPE by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The melting temperatures and latent heats of the form-stable P1/HDPE and P2/HDPE composite PCMs were determined as 37.8 and 55.7 °C, and 147.6 and 162.2 J g −1 , respectively, by the technique of differential scanning calorimetry (DSC). Furthermore, to improve the thermal conductivity of the form-stable P/HDPE composite PCMs, expanded and exfoliated graphite (EG) by heat treatment was added to the samples in the ratio of 3 wt.%. Thereby, the thermal conductivity was increased about 14% for the form-stable P1/HDPE and about 24% for the P2/HDPE composite PCMs. Based on the results, it is concluded that the prepared form-stable P/HDPE blends as composite type PCM have great potential for thermal energy storage applications in terms of their satisfactory thermal properties and improved thermal conductivity. Furthermore, these composite PCMs added with EG can be considered cost effective latent heat storage materials since they do not require encapsulation and extra cost to enhance heat transfer in the paraffin.

Jing Ding - One of the best experts on this subject based on the ideXlab platform.

Xiaoxi Yang - One of the best experts on this subject based on the ideXlab platform.

Qing Liu - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional multiple relaxation time lattice boltzmann models for single Phase and solid Liquid Phase Change heat transfer in porous media at the rev scale
    Applied Thermal Engineering, 2019
    Co-Authors: Qing Liu, Xiangbo Feng
    Abstract:

    Abstract In this paper, three-dimensional (3D) multiple-relaxation-time (MRT) lattice Boltzmann (LB) models are developed for single-Phase and solid-Liquid Phase-Change heat transfer in porous media at the representative elementary volume (REV) scale. These models are developed in the framework of the double-distribution-function (DDF) approach: the flow field is solved by an isothermal MRT-LB model with the D3Q15 or D3Q19 lattice based on the generalized non-Darcy model, while the temperature field is solved by a thermal MRT-LB model with the D3Q7 lattice. In the 3D DDF-MRT model for solid-Liquid Phase-Change heat transfer in porous media, the enthalpy method is employed to capture the solid-Liquid Phase interface in an implicit manner. Mesoscopically, the effective enthalpy is defined as the basic evolution variable of the enthalpy-based MRT-LB model, and as a result, the temperature and Liquid-fraction fields can be solved without iteration procedure. The practicability and accuracy of the proposed models are demonstrated by numerical simulations of several 3D single-Phase and solid-Liquid Phase-Change heat transfer problems in porous media at the REV scale. It is shown that the 3D DDF-MRT models for convection heat transfer in porous media are second-order accurate in space. In addition, the influences of Darcy number and porosity on the melting (solidification) processes of 3D melting (solidification) with convection in a cubical porous cavity are investigated by the enthalpy-based DDF-MRT model.

  • lattice boltzmann methods for single Phase and solid Liquid Phase Change heat transfer in porous media a review
    International Journal of Heat and Mass Transfer, 2019
    Co-Authors: Qing Liu, Wenquan Tao
    Abstract:

    Abstract Over the past 30 years, the lattice Boltzmann (LB) method has been developed into a versatile and powerful numerical methodology for computational fluid dynamics and heat transfer. Owing to its kinetic nature, the LB method has the capability to incorporate the essential mesoscopic physics, and it is particularly successful in modeling transport phenomena involving complex boundaries and interfacial dynamics. Up to now, the LB method has achieved great success in modeling fluid flow and heat transfer in porous media. Since the LB method is inherently transient, it is especially useful for investigating transient solid-Liquid Phase-Change processes wherein the interfacial behaviors are very important. In this article, a comprehensive review of the LB methods for single-Phase and solid-Liquid Phase-Change heat transfer in porous media at both the pore scale and representative elementary volume (REV) scale. The review first introduces the fundamental theory of the LB method for fluid flow and heat transfer. Subsequently, the REV-scale LB method for fluid flow and single-Phase heat transfer in porous media and the LB method for solid-Liquid Phase-Change heat transfer are discussed in detail. Moreover, the applications of the LB methods in single-Phase and solid-Liquid Phase-Change heat transfer in porous media are reviewed. The LB modeling and predictions of the effective thermal conductivity of porous materials are also reviewed. Finally, further developments of the LB method in the related areas are briefly discussed.

  • enthalpy based multiple relaxation time lattice boltzmann method for solid Liquid Phase Change heat transfer in metal foams
    Physical Review E, 2017
    Co-Authors: Qing Liu
    Abstract:

    In this paper, an enthalpy-based multiple-relaxation-time (MRT) lattice Boltzmann (LB) method is developed for solid-Liquid Phase-Change heat transfer in metal foams under the local thermal nonequilibrium (LTNE) condition. The enthalpy-based MRT-LB method consists of three different MRT-LB models: one for flow field based on the generalized non-Darcy model, and the other two for Phase-Change material (PCM) and metal-foam temperature fields described by the LTNE model. The moving solid-Liquid Phase interface is implicitly tracked through the Liquid fraction, which is simultaneously obtained when the energy equations of PCM and metal foam are solved. The present method has several distinctive features. First, as compared with previous studies, the present method avoids the iteration procedure; thus it retains the inherent merits of the standard LB method and is superior to the iteration method in terms of accuracy and computational efficiency. Second, a volumetric LB scheme instead of the bounce-back scheme is employed to realize the no-slip velocity condition in the interface and solid Phase regions, which is consistent with the actual situation. Last but not least, the MRT collision model is employed, and with additional degrees of freedom, it has the ability to reduce the numerical diffusion across the Phase interface induced by solid-Liquid Phase Change. Numerical tests demonstrate that the present method can serve as an accurate and efficient numerical tool for studying metal-foam enhanced solid-Liquid Phase-Change heat transfer in latent heat storage. Finally, comparisons and discussions are made to offer useful information for practical applications of the present method.

  • double multiple relaxation time lattice boltzmann model for solid Liquid Phase Change with natural convection in porous media
    Physica A-statistical Mechanics and Its Applications, 2015
    Co-Authors: Qing Liu
    Abstract:

    Abstract In this paper, a double multiple-relaxation-time lattice Boltzmann model is developed for simulating transient solid–Liquid Phase Change problems in porous media at the representative elementary volume scale. The model uses two different multiple-relaxation-time lattice Boltzmann equations, one for the flow field and the other for the temperature field with nonlinear latent heat source term. The model is based on the generalized non-Darcy formulation, and the solid–Liquid interface is traced through the Liquid fraction which is determined by the enthalpy-based method. The present model is validated by numerical simulations of conduction melting in a semi-infinite space, solidification in a semi-infinite corner, and convection melting in a square cavity filled with porous media. The numerical results demonstrate the efficiency and accuracy of the present model for simulating transient solid–Liquid Phase Change problems in porous media.

  • Double multiple-relaxation-time lattice Boltzmann model for solid-Liquid Phase Change with natural convection in porous media
    arXiv: Fluid Dynamics, 2015
    Co-Authors: Qing Liu
    Abstract:

    In this paper, a double multiple-relaxation-time lattice Boltzmann model is developed for simulating transient solid-Liquid Phase Change problems in porous media at the representative elementary volume scale. The model uses two different multiple-relaxation-time lattice Boltzmann equations, one for the flow field and the other for the temperature field with nonlinear latent heat source term. The model is based on the generalized non-Darcy formulation, and the solid-Liquid Phase Change interface is traced through the Liquid fraction which is determined by the enthalpy method. The model is validated by numerical simulations of conduction melting in a semi-infinite space, solidification in a semi-infinite corner, and convection melting in a square cavity filled with porous media. The numerical results demonstrate the efficiency and accuracy of the present model for simulating transient solid-Liquid Phase Change problems in porous media.

Weilong Wang - One of the best experts on this subject based on the ideXlab platform.