Experimental measurements of the effective thermal conductivity of a lithium titanate (Li 2TiO 3) pebbles-packed bed (original) (raw)
Related papers
Effective Thermal Conductivity of Lithium Ceramic Pebble Beds for Fusion Blankets: A Review
Fusion Science and Technology, 2005
The use of lithium ceramic pebble beds has been considered in many blanket designs for the fusion reactors. Lithium ceramics have received a significant interest as tritium breeders for the fusion blankets during the last three decades. The thermal performance of the lithium ceramic pebble beds plays a key role for the fusion blankets. In order to study the heat transfer in the blanket, the effective thermal conductivity of the lithium ceramics pebble beds has to be well measured and characterized. The data of effective thermal conductivity of lithium ceramic pebble beds is important for the blanket design. Several studies have been dedicated to investigate the effective conductivity of the lithium ceramics pebble beds. The objective of this work is to review and compare the available data, presented by various studies, of effective conductivity of lithium ceramic pebble beds in order to address the current status of these data.
Packed pebble bed of ceramic solid breeder materials viz. lithium titanate or meta-titanate (Li2TiO3),lithium orthosilicate (Li4SiO4) etc. is being considered for fusion blankets. During the breeding of tritium,helium will be produced and also it is proposed to flow helium from outside through the bed to extracttritium, as well as to remove thermal energy from the bed. Experimental determination of thermal prop-erty data of the pebble bed under helium gas flow is important for the blanket design. Such study ofdetermination of effective thermal conductivity with flowing helium condition was not performed pre-viously. Though, it is known that with an increase in gas flow rate, the effective thermal conductivity ofpebble bed increases, it is necessary to conduct experiments to know the exact values and the degree ofvariation. Model and experimental setup used in our previous study was used to for this present work.Effects of process parameters viz., helium gas flow rate, bed temperature, pebble size etc. on the effective∗
Experimental measurement of effective thermal conductivity of packed lithium-titanate pebble bed
Fusion Engineering and Design, 2012
Lithium titanate is a promising solid breeder material for the fusion reactor blanket. Packed lithium titanate pebble bed is considered for the blanket. The thermal energy; that will be produced in the bed during breeding and the radiated heat from the reactor core absorbed must be removed. So, the experimental thermal property data are important for the blanket design. In past, a significant amount of works were conducted to determine the effective thermal conductivity of packed solid breeder pebble bed, in helium atmosphere, but no flow of gas was considered. With increase in gas flow rate, effective thermal conductivity of pebble bed increases. Particle size and void fraction also affect the thermal properties of the bed significantly. An experimental facility with external heat source was designed and installed. Experiments were carried out with lithium-titanate pebbles of different sizes at variable gas flow rates and at different bed wall temperature. It was observed that effective thermal conductivity of pebble bed is a function of particle Reynolds number and temperature. From the experimental data two correlations have been developed to estimate the effective thermal conductivity of packed lithium-titanate pebble bed for different particle Reynolds number and at different temperatures. The experimental details and results are discussed in this paper.
2017
Lithium based ceramics such as Lithium Titanate (Li2TiO3), Lithium Orthosilicate (Li4SiO4) and Lithium Zirconate (Li2ZrO3) are promising solid breeder materials used in the Test Blanket Module (TBM) for the extraction of tritium. These breeders should have good thermal properties especially thermal conductivity as well as good tritium breeding characteristics. The thermal properties of tritium breeders are important for the blanket design. The tritium breeding reaction occurring in the pebble bed is an exothermic reaction liberating a large amount of heat. Thus generated heat is transmitted through the packed pebble bed. With the increase in temperature of the pebble bed the tritium breeding ratio decreases. As a result heat produced must be effectively removed from the pebble bed in order to maintain the required tritium breeding ratio. This can be achieved if the thermal conductivity and heat transfer of the packed bed is high. In this study the pebbles of Li2TiO3, Li4SiO4, LiO2 a...
EXPERIMENTAL MEASUREMENTS OF THE INTERFACE THERMAL CONDUCTANCE OF A LITHIUM METATITANATE PEBBLE BED
The thermal properties of the lithium ceramics pebble beds have a significant impact on the temperature profile of the Helium Cooled Pebble Bed blanket and the extraction of heat from the pebble beds to the coolant. The literature review showed a lack of experimental data on the interface thermal conductance (h) of lithium metatitanate pebble beds, therefore the objective of this study is to present experimental values of h. The measuring technique is based on the principles of steady state and axial heat flow methods. The lithium metatitanate pebble bed is single size (Ø1.7-2.0mm pebbles) with a packing fraction of 61%. The values of h were measured at the interface of the pebbles with their container's wall (made of stainless steel 316). The results showed that h increased from 1800 to 5300W/m 2 .K with the increase of the wall temperature from 24 to 570 C. The theoretical values of h, calculated by three models, were compared with the experimental values. The theoretical and experimental values of h showed similar behavior with the increase of temperature. The present values of h will help to create a reliable database of the thermal properties of the lithium ceramics pebble beds.
Influence of gas pressure on the effective thermal conductivity of ceramic breeder pebble beds
Fusion Engineering and Design, 2017
Lithium ceramics have been considered as tritium breeder materials in many proposed designs of fusion breeding blankets. Heat generated in breeder pebble beds due to nuclear breeding reaction must be removed by means of actively cooled plates while generated tritiums is recovered by purge gas slowly flowing through beds. Therefore, the effective thermal conductivity of pebble beds that is one of the governing parameters determining heat transport phenomenon needs to be addressed with respect to mechanical status of beds and purge gas pressure. In this study, a numerical framework combining finite element simulation and a semi-empirical correlation of gas gap conduction is proposed to predict the effective thermal conductivity. The purge gas pressure is found to vary the effective thermal conductivity, in particular with the presence of various sized gaps in pebble beds. Random packing of pebble beds is taken into account by an approximated correlation considering the packing factor and coordination number of pebble beds. The model prediction is compared with experimental observation from different sources showing a quantitative agreement with the measurement.
A Comparative Study on the Effective Thermal Conductivity of a Single Size Beryllium Pebble Bed
Solid breeder blankets generally use beryllium-helium pebble beds to ensure sufficient tritium breeding. The data of the effective thermal conductivity, kff of beryllium pebble beds is important to the design of fusion blankets. It serves as a database for benchniarking the models of pebble beds. The objective of this paper is to review and compare the available data (obtained by several studies) of the effective thermal conductivity of beryllium pebble beds in order to address the current status of these data. Two comparisons are presented: one for the data of kff versus bed mean temperature and the second one for the data of kff versus external applied pressures. The data (kff versus bed temperature) reported by Enoeda et al. [1], Dalle Donne et al. 7, and UCLA, have a similar particle size and packing fraction. Despite their similarity, the standard deviation values of their data are around 32%. Also, the data of the effective thermal conductivity as a function of mechanical pres...
Fusion Science and Technology, 2017
Characterizing the thermo-physical properties of the ceramic breeder pebble bed is an integral step of developing breeder blankets for fusion energy applications. To that end, thermal conductivity is an important parameter to identify. In granular pebble bed materials, the thermal conductivity depends on the solid pebble material as well as any gas filling the interstitial void spaces, thus an effective thermal conductivity (k eff) of the bulk is used. A transient hot-wire apparatus is developed through a collaborative study between the Fusion Science and Technology Center at UCLA and the National Fusion Research Institute (NFRI) to measure the effective thermal conductivity of Korean-made Li 2 TiO 3 pebble beds. In this study, current is pushed through a single strand of high purity platinum wire. The heat generated is conducted away by the surrounding pebble bed; the logarithmic change in temperature being used to calculate the rate of heat conductance. The apparatus is filled with roughly an atmosphere of helium and placed in a furnace to test the pebble bed under reactor relevant temperatures. Results and future improvements are presented.
Development of Lithium Titanate Ceramic for the Test Blanket Module (TBM) in Fusion Reactor
2010
This is to certify that the thesis entitled "DEVELOPMENT OF LITHIUM TITANATE CERAMIC FOR THE TEST BLANKET MODULE (TBM) IN FUSION REACTOR" being submitted by Mr. Bhabani Sankar Sahu, for the degree of Master of Technology (Research) in Ceramic Engineering to the National Institute of Technology, Rourkela, is a record of bonafide research work carried out by him under my supervision and guidance. His thesis, in my opinion, is worthy of consideration for the award of degree of Master of Technology (Research) in accordance with the regulations of the institute. The results embodied in this thesis have not been submitted to any other university or institute for the award of a Degree.
Journal of Nuclear Materials, 2007
One of the possible configurations of test blanket module (TBM) which will be tested during the ITER operation phase is made up of neutron multiplier and breeder as pebble beds. This paper describes an experimental device for the determination of the pebble bed conductivity in presence of interstitial air. The tests were performed with a simultaneous compression of the bed in order to obtain the effective bed conductivity versus the axial deformation for several values of the temperature. The effective conductivities of LiSiO 4 and Li 2 TiO 3 pebble beds, both in air and in vacuum, were determined. The packing factors of the beds were measured by means an ad hoc built instrumentation, based on the gamma ray backscattering. The experimental results have been compared with those of a theoretical model developed by the authors, obtaining a good agreement in terms of bed conductivity and stiffness.