The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low,due to the poor thermal conductivity of the materials.The recent phenomenal advancement in nano...The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low,due to the poor thermal conductivity of the materials.The recent phenomenal advancement in nano technology provides an opportunity for an appreciable enhancement in the thermal conductivity of the phase change materials.In order to explore the possibilities of using nano technology for various applications,a detailed parametric study is carried out,to analyse the heat transfer enhancement potential with the thermal conductivity of the conventional phase change materials and nano enhanced phase change materials under various flow conditions of the heat transfer fluid.Initially,the theoretical equation,used to determine the time for outward cylindrical solidification of the phase change material,is validated with the experimental results.It is inferred from the parametric studies,that for paraffinic phase change materials with air as the heat transfer fluid,the first step should be to increase the heat transfer coefficient to the maximum extent,before making any attempt to increase the thermal conductivity of the phase change materials,with the addition of nano particles.When water is used as the phase change material,the addition of nano particles is recommended to achieve better heat transfer,when a liquid is used as the heat transfer fluid.展开更多
Ce-incorporated apatite（Ce-HA） nano-scale particles with different Ce percentage contents（atomic ratio of Ce to Ce ＋ Ca is 5%,10%and 20%,respectively） were synthesized via a simple wet chemical method in this stu...Ce-incorporated apatite（Ce-HA） nano-scale particles with different Ce percentage contents（atomic ratio of Ce to Ce ＋ Ca is 5%,10%and 20%,respectively） were synthesized via a simple wet chemical method in this study.The crystal structure,chemical groups,thermal stability,crystal morphologies and crystal sizes of the Ce-HA nano-particles were characterized by X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,and transmission electron microscopy（TEM）.The influences of reaction temperature,reaction time,pH value,and the atomic ratio of Ce to Ce ＋ Ca on the structure and performance of Ce-HA particles were studied.The results show that the lattice constants,particle sizes,crystallinity and thermal stability of Ce-HA vary with the doped Ce contents.With the increase of Ce content,the lattice constants of the Ce-HA nano-particles remarkably increase but the particle size,crystallinity and thermal stability gradually decrease.The reaction temperature as well as the reaction time has no significant effect on the properties of the final products,while the pH value has a direct relationship with their final chemical composition.The obtained Ce-HA nanosize particles possess potential application in preparing artificial bone implants,bone tissue engineering scaffold and other bioactive coatings.展开更多
Nano-scale rutile phase was transformed from nano-scale anatase upon heating, which was prepared by a sol-gel technique. The XRD data corresponding to the anatase and rutile phases were analyzed and the grain sizes of...Nano-scale rutile phase was transformed from nano-scale anatase upon heating, which was prepared by a sol-gel technique. The XRD data corresponding to the anatase and rutile phases were analyzed and the grain sizes of as-derived phases were calculated by Sherrer equation. The lattice parameters of the as-derived anatase and rutile unit cells were calculated and compared with those of standard lattice parameters on PDF cards. It was shown that the smaller the grain sizes, the larger the lattice deformation. The lattice parameter a has the negative deviation from the standard and the lattice parameter c has the positive deviation for both phases. The particles sizes had preferential in-fluence on the longer parameter between the lattice parameters of a and c. With increasing temperatures, the lattice parameters of a and c in both phases approached to the equilibrium state. The larger lattice deformation facilitated the nucleation process, which lowered the transformation temperature. During the transformation from nano-scale anatase to rutile, besides the mechanism involving retention of the {112} pseudo-close-packed planes of oxygen in anatase as the {100} pseudo-close-packed planes in rutile, the new phase occurred by relaxation of lattice deformation and adjustment of the atomic sites in parent phase. The orientation relationships were suggested to be anatase {101}//rutile {101} and anatase <201>//rutile<111>, and the habit plane was anatase (101).展开更多
Nano-scale Tb-incorporated apatite （nano-Tb-AP） particles with different Tb contents （Tb/（Tb＋Ca）） of 0%, 5%, 10% and 20% were synthesized through a simple wet chemical method in this study. The crystal structur...Nano-scale Tb-incorporated apatite （nano-Tb-AP） particles with different Tb contents （Tb/（Tb＋Ca）） of 0%, 5%, 10% and 20% were synthesized through a simple wet chemical method in this study. The crystal structure, thermal stabilities, chemical groups, crystal morphologies and crystal sizes of the nano--Tb-AP particles were characterized by X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, and transmission electron microscopy （TEM）, respectively. It was found that lattice constants, particle sizes, crystalline and thermal stability varied with the doped Tb contents. With the increasing of Tb content, the lattice constants, particle size, length/diameter ratio, crystalline and thermal stability of nano-Tb-AP gradually decrease. Especially, almost all the 20%Tb-AP nano particles had been decomposed at 1200 ℃ while only a few of the decomposed products （β-TCP） were detected in the Tb-free nano apatite powders： This kind of nano-scale Tb-incorporated apatite exhibits an extremely potential clinic application because it integrates both the excellent biological functions of Tb element and apatite in human body.展开更多
文摘The heat transfer performance of the phase change materials used in free cooling and air conditioning applications is low,due to the poor thermal conductivity of the materials.The recent phenomenal advancement in nano technology provides an opportunity for an appreciable enhancement in the thermal conductivity of the phase change materials.In order to explore the possibilities of using nano technology for various applications,a detailed parametric study is carried out,to analyse the heat transfer enhancement potential with the thermal conductivity of the conventional phase change materials and nano enhanced phase change materials under various flow conditions of the heat transfer fluid.Initially,the theoretical equation,used to determine the time for outward cylindrical solidification of the phase change material,is validated with the experimental results.It is inferred from the parametric studies,that for paraffinic phase change materials with air as the heat transfer fluid,the first step should be to increase the heat transfer coefficient to the maximum extent,before making any attempt to increase the thermal conductivity of the phase change materials,with the addition of nano particles.When water is used as the phase change material,the addition of nano particles is recommended to achieve better heat transfer,when a liquid is used as the heat transfer fluid.
基金supported by the National Natural Science Foundation of China(Nos.51072159 and 51273159)the Fundamental Research Funds for the Central University and Program for New Century Excellent Talents in Universities(Chinese Ministry of Education,NCET-08-0444(2301G107aaa))
文摘Ce-incorporated apatite（Ce-HA） nano-scale particles with different Ce percentage contents（atomic ratio of Ce to Ce ＋ Ca is 5%,10%and 20%,respectively） were synthesized via a simple wet chemical method in this study.The crystal structure,chemical groups,thermal stability,crystal morphologies and crystal sizes of the Ce-HA nano-particles were characterized by X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,and transmission electron microscopy（TEM）.The influences of reaction temperature,reaction time,pH value,and the atomic ratio of Ce to Ce ＋ Ca on the structure and performance of Ce-HA particles were studied.The results show that the lattice constants,particle sizes,crystallinity and thermal stability of Ce-HA vary with the doped Ce contents.With the increase of Ce content,the lattice constants of the Ce-HA nano-particles remarkably increase but the particle size,crystallinity and thermal stability gradually decrease.The reaction temperature as well as the reaction time has no significant effect on the properties of the final products,while the pH value has a direct relationship with their final chemical composition.The obtained Ce-HA nanosize particles possess potential application in preparing artificial bone implants,bone tissue engineering scaffold and other bioactive coatings.
文摘Nano-scale rutile phase was transformed from nano-scale anatase upon heating, which was prepared by a sol-gel technique. The XRD data corresponding to the anatase and rutile phases were analyzed and the grain sizes of as-derived phases were calculated by Sherrer equation. The lattice parameters of the as-derived anatase and rutile unit cells were calculated and compared with those of standard lattice parameters on PDF cards. It was shown that the smaller the grain sizes, the larger the lattice deformation. The lattice parameter a has the negative deviation from the standard and the lattice parameter c has the positive deviation for both phases. The particles sizes had preferential in-fluence on the longer parameter between the lattice parameters of a and c. With increasing temperatures, the lattice parameters of a and c in both phases approached to the equilibrium state. The larger lattice deformation facilitated the nucleation process, which lowered the transformation temperature. During the transformation from nano-scale anatase to rutile, besides the mechanism involving retention of the {112} pseudo-close-packed planes of oxygen in anatase as the {100} pseudo-close-packed planes in rutile, the new phase occurred by relaxation of lattice deformation and adjustment of the atomic sites in parent phase. The orientation relationships were suggested to be anatase {101}//rutile {101} and anatase <201>//rutile<111>, and the habit plane was anatase (101).
基金supported by the Fundamental Research Funds for the Central Universitythe National Natural Science Foundation of China (No. 51072159+1 种基金51273159)Program for New Century Excellent Talents in Universities (Chinese Ministry of Education,NCET-08-0444)
文摘Nano-scale Tb-incorporated apatite （nano-Tb-AP） particles with different Tb contents （Tb/（Tb＋Ca）） of 0%, 5%, 10% and 20% were synthesized through a simple wet chemical method in this study. The crystal structure, thermal stabilities, chemical groups, crystal morphologies and crystal sizes of the nano--Tb-AP particles were characterized by X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, and transmission electron microscopy （TEM）, respectively. It was found that lattice constants, particle sizes, crystalline and thermal stability varied with the doped Tb contents. With the increasing of Tb content, the lattice constants, particle size, length/diameter ratio, crystalline and thermal stability of nano-Tb-AP gradually decrease. Especially, almost all the 20%Tb-AP nano particles had been decomposed at 1200 ℃ while only a few of the decomposed products （β-TCP） were detected in the Tb-free nano apatite powders： This kind of nano-scale Tb-incorporated apatite exhibits an extremely potential clinic application because it integrates both the excellent biological functions of Tb element and apatite in human body.
