my_papers.bib

@InProceedings{karaki:1389,
	author 		= {Karaki, Wafaa and Li, Peiwen and {Van Lew}, {Jon Thomas} and Valmiki, M.M. and Chan, Cholik and Stephens, Jake},
	booktitle 	= {ASME 2011 5th International Conference on Energy Sustainability},
	doi 		= {10.1115/ES2011-54134},
	title 		= {{Experimental Investigation of Thermal Storage Processes in a Thermocline Storage Tank}},
	year 		= {2011},
	type 		= {Conference},
	abstract	= {This paper presents an experimental study and analysis of the heat transfer of energy charge and discharge in a packed-bed thermocline thermal storage tank for application in concentrated solar thermal power plants. Because the energy storage efficiency is a function of many parameters including fluid and solid properties, tank dimensions, packing dimensions, and time lengths of charge and discharge, this paper aims to provide experimental data and a proper approach of data reduction and presentation. To accomplish this goal, dimensionless governing equations of energy conservation in the heat transfer fluid and solid packed-bed material are derived. The obtained experimental data will provide a basis for validation of mathematical models in the future.}
}
@InProceedings{karaki:725,
	author 		= {Karaki, Wafaa and {Van Lew}, {Jon Thomas} and Li, Peiwen and Chan, Cholik and Stephens, Jake},
	booktitle 	= {ASME 2010 4th International Conference on Energy Sustainability},
	doi 		= {10.1115/ES2010-90209},
	title 		= {{Heat Transfer in Thermocline Storage System With Filler Materials: Analytical Model}},
	year 		= {2010},
	type 		= {Conference},
	abstract	= {Parabolic trough power systems utilizing concentrated solar energy have proven their worth as a means for generating electricity. However, one major aspect preventing the technologies widespread acceptance is the deliverability of energy beyond a narrow window during peak hours of the sun. Thermal storage is a viable option to enhance the dispatchability of the solar energy and an economically feasible option is a thermocline storage system with a low-cost filler material. Utilization of thermocline storage facilities have been studied in the past and this paper hopes to expand upon that knowledge. The heat transfer between the heat transfer fluid and filler materials are governed by two conservation of energy equations, often referred as Schumann [1] equations. We solve these two coupled partial differential equations using Laplace transformation. The initial temperature distribution can be constant, linear or exponential. This flexibility allows us to apply the model to simulate unlimited charging and discharging cycles, similar to a day-to-day operation. The analytical model is used to investigate charging and discharging processes, and energy storage capacity. In an earlier paper [2], the authors presented numerical solution of the Schumann equations using method of characteristics. Comparison between analytical and numerical results shows that they are in very good agreement.}
}
@Article{Li2011,
	abstract 	= {This paper examined the features of three typical thermal storage systems including: 1) direct storage of heat transfer fluid in containers, 2) storage of thermal energy in a packed bed of solid filler material, with energy being carried in/out by a flowing heat transfer fluid which directly contacts the packed bed, and 3) a system in which heat transfer fluid flows through tubes that are imbedded into a thermal storage material which may be solid, liquid, or a mixture of the two. The similarity of the three types of thermal storage systems was discussed, and generalized energy storage governing equations were introduced in both dimensional and dimensionless forms. The temperatures of the heat transfer fluid during energy charge and discharge processes and the overall energy storage efficiencies were studied through solution of the energy storage governing equations. Finally, provided in the paper are a series of generalized charts bearing curves for energy storage effectiveness against four dimensionless parameters grouped up from many of the thermal storage system properties including dimensions, fluid and thermal storage material properties, as well as the operational conditions including mass flow rate of the fluid, and the ratio of energy charge and discharge time periods. Engineers can conveniently look up the charts to design and calibrate the size of thermal storage tanks and operational conditions without doing complicated individual modeling and computations. It is expected that the charts will serve as standard tools for thermal storage system design and calibration.},
	author 		= {Li, Peiwen and {Van Lew}, {Jon Thomas} and Chan, Cholik and Karaki, Wafaa and Stephens, Jake and O’Brien, James E},
	doi 		= {10.1016/j.renene.2011.08.032},
	journal 	= {Renewable Energy},
	volume 		= {39},
	title 		= {{Similarity and generalized analysis of efficiencies of thermal energy storage systems}},
	year 		= {2012},
	type 		= {Article}
}
@Article{Li20112130,
	author 		= {Li, Peiwen and {Van Lew}, {Jon Thomas} and Karaki, Wafaa and Chan, Cholik and Stephens, Jake and Wang, Qiuwang},
	doi 		= {10.1016/j.solener.2011.05.022},
	journal 	= {Solar Energy},
	volume 		= {85},
	title 		= {{Generalized charts of energy storage effectiveness for thermocline heat storage tank design and calibration}},
	year 		= {2011},
	type 		= {Article},
	abstract	= {Solar thermal energy storage is important to the daily extended operation and cost reduction of a concentrated solar thermal power plant. To provide industrial engineers with an effective tool for sizing a thermocline heat storage tank, this paper used dimensionless heat transfer governing equations for fluid and solid filler material and studied all scenarios of energy charge and discharge processes. It has been found that what can be provided through the analysis is a series of well-configured general charts bearing curves of energy storage effectiveness against four dimensionless parameters grouped up from the storage tank dimensions, properties of the fluid and filler material, and operational conditions (such as mass flow rate of fluid and energy charge and discharge periods). As the curves in the charts are generalized, they are applicable to general thermocline heat storage systems. Engineers can conveniently look up the charts to design and calibrate the dimensions of thermocline solar thermal storage tanks and operational conditions, without doing complicated modeling and computations. It is of great significance that the generalized charts will serve as tools for thermal energy storage system design and calibration in energy industry.}
}
@Article{Liu20109186,
	author 		= {Liu, Hong and Li, Peiwen and {Van Lew}, {Jon Thomas}},
	doi 		= {10.1016/j.ijhydene.2010.06.043},
	journal 	= {International Journal of Hydrogen Energy},
	volume 		= {35},
	title 		= {{CFD study on flow distribution uniformity in fuel distributors having multiple structural bifurcations of flow channels}},
	year 		= {2010},
	type 		= {Article},
	abstract	= {This work studied the issues of uniform flow distribution for general application in fuel cells, fuel processing chemical reactors, and other industrial devices. A novel method for uniform flow distribution was proposed, in which multiple levels of flow channel bifurcations were considered to uniformly distribute a flow into 2n flow channels at the final stage, after n levels of bifurcation. To study the effect of the flow channel bifurcation structure and dimensions on the flow distribution uniformity, numerical analysis was conducted. Parameters such as the flow channel length and width at each level of bifurcation as well as the curvature of the turning area of flow channels were particularly investigated. Important results concerning the geometrical design of flow distributors for better flow distribution and uniformity are presented. The best structure of a flow distributor was selected based on the criterion of flow distribution uniformity and low pressure loss. Since the studied novel flow distributor distributes a flow into a number of parallel channels in a remarkable uniformity, the flow distribution structure is expected to be widely used in fuel cells, fuel cell systems, and variety of industrial reactors and heat exchangers to significantly improve the performance of these devices. The studied flow regime is limited to laminar flow. A CFD tool FLUENT was used for the simulation. The numerical treatment of convection terms in governing equations was based on the QUICK scheme, and the coupled computation solving for pressure and velocity fields was based on the SIMPLE algorithm.}
}
@Article{Liu2011a,
	author 		= {Liu, Hong and Li, Peiwen and {Van Lew}, {Jon Thomas} and Juarez-Robles, Daniel},
	doi 		= {10.1016/j.expthermflusci.2011.10.015},
	journal 	= {Experimental Thermal and Fluid Science},
	volume 		= {37},
	title 		= {{Experimental study of the flow distribution uniformity in flow distributors having novel flow channel bifurcation structures}},
	year 		= {2012},
	type 		= {Article},
	abstract	= {Symmetric flow channel bifurcations were proposed in this article for the purpose of creating better flow uniformity in flow distribution. Two categories of flow channel bifurcation structures were considered. Characteristic parameters that can identify and standardize the structural design of the flow channel bifurcations were designated. Six flow distributors, divided into two groups, were fabricated for experimental testing. Each group of distributors is distinguished by one basic channel bifurcation structure category, but distributors within a group differ in the characteristic parameters exhibited in their designs. The axial velocities of the airflow at the exit of the distributor flow channels were measured experimentally, and the uniformity of the flow distribution was investigated for each distributor. Comparison and evaluation of the figure-of-merit of flow distribution uniformity is made for the six studied flow distributors. The novel concept of symmetrically bifurcated flow distributor designs and the experimental results and conclusions obtained in this study are of great significance to the development of high performance industrial devices, such as heat exchangers, reactors, fuel cells, heat sinks, and fluid product packaging machines.}
}
@Article{Valmiki2012a,
	author 		= {Valmiki, M.M. and Karaki, Wafaa and Li, Peiwen and {Van Lew}, {Jon Thomas} and Chan, Cholik and Stephens, Jake},
	doi 		= {10.1115/1.4006962},
	journal 	= {Journal of Solar Energy Engineering},
	volume 		= {134},
	title		= {{Experimental Investigation of Thermal Storage Processes in a Thermocline Tank}},
	year 		= {2012},
	type 		= {Article},
	abstract	= {This paper presents an experimental study of the energy charge and discharge processes in a packed bed thermocline thermal storage tank for application in concentrated solar power plants. A mathematical analysis was provided for better understanding and planning of the experimental tests. The mathematical analysis indicated that the energy storage effectiveness is related to fluid and solid material properties, tank dimensions, packing schemes of the solid filler material, and the durations of the charge and discharge times. Dimensional analysis of the governing equations was applied to consolidate many parameters into a few dimensionless parameters, allowing scaling from a laboratory system to an actual industrial application. Experiences on the system design, packing of solid filler material, system operation, and data analysis in a laboratory-scale system have been obtained in this work. These data are used to validate a recently published numerical solution method. The study will benefit the application of thermocline thermal storage systems in the large scale concentrated solar thermal power plants in industry.}
}
@InProceedings{vanlew2009,
	author 		= {{Van Lew}, {Jon Thomas} and Li, Peiwen and Chan, Cho Lik and Karaki, Wafaa and Stephens, Jake},
	booktitle 	= {ASME 2009 International Mechanical Engineering Congress and Exposition},
	doi 		= {10.1115/IMECE2009-11701},
	title 		= {{Transient Heat Delivery and Storage Process in a Thermocline Heat Storage System}},
	type 		= {Conference},
	year 		= {2009},
	abstract	= {Parabolic trough power systems utilizing concentrated solar energy have proven their worth as a means for generating electricity. However, one major aspect preventing the technologies widespread acceptance is the deliverability of energy beyond a narrow window during peak hours of the sun. Thermal storage is a viable option to enhance the dispatchability of the solar energy and an economically feasible option is a thermocline storage system with a low-cost filler material. Utilization of thermocline storage facilities have been studied in the past and this paper hopes to expand upon that knowledge. The current study aimed to effectively model the heat transfer of a working fluid interacting with filler material. An effective numerical method and efficient computation schemes were developed and verified. A thermocline storage system was modeled under specific conditions and results of great significance to heat storage design and operation were obtained.}
}
@Article{vanlew133,
	author 		= {{Van Lew}, {Jon Thomas} and Li, Peiwen and Chan, Cholik and Karaki, Wafaa and Stephens, Jake},
	doi 		= {10.1115/1.4003685},
	journal 	= {Journal of Solar Energy Engineering},
	volume 		= {133},
	title 		= {{Analysis of Heat Storage and Delivery of a Thermocline Tank Having Solid Filler Material}},
	type 		= {Article},
	year 		= {2011},
	abstract	= {Thermal storage has been considered as an important measure to extend the operation of a concentrated solar power plant by providing more electricity and meeting the peak demand of power in the time period from dusk to late night everyday, or even providing power on cloudy days. Discussed in this paper is thermal energy storage in a thermocline tank having a solid filler material. To provide more knowledge for designing and operating of such a thermocline storage system, this paper firstly presents the application of method of characteristics for numerically predicting the heat charging and discharging process in a packed bed thermocline storage tank. Nondimensional analysis of governing equations and numerical solution schemes using the method of characteristics were presented. The numerical method proved to be very efficient, accurate; required minimal computations; and proved versatile in simulating various operational conditions for which analytical methods cannot always provide solutions. Available analytical solutions under simple boundary and initial conditions were used to validate the numerical modeling and computation. A validation of the modeling by comparing the simulation results to experimental test data from literature also confirmed the effectiveness of the model and the related numerical solution method. Finally, design procedures using the numerical modeling tool were discussed and other issues related to operation of a thermocline storage system were also studied.}
}
@Article{VanLew2015a,
	author 		= {{Van Lew}, {Jon Thomas} and Park, Yi-Hyun and Ying, Alice and Abdou, Mohamed},
	doi 		= {10.1016/j.fusengdes.2015.06.012},
	journal 	= {Fusion Engineering and Design},
	volume 		= {In press},
	title 		= {{Modifying Young's modulus in DEM simulations based on distributions of experimental measurements}},
	year 		= {2015},
	type 		= {Article},
	abstract	= {The discrete element method, as currently employed by members of the fusion community, is rooted on the assumption that each pebble is a perfectly elastic material that obeys Hertz's theory for normal interaction. This assumption impacts the magnitude of inter-particle forces predicted by the models. We scrutinize the Hertzian assumption with single-pebble crush experiments with carefully recorded force-displacement responses and compare them to the non-linear forces predicted by a Hertzian pebble with bulk properties reported in literature. We found each pebble generally has a non-linear force response but with varying levels of stiffness that qualitatively matched the curves from Hertz theory. Assuming Hertzian interaction, we backed-out an elastic modulus for each pebble. We define a softening coefficient, κ, as the ratio of the pebble's elastic modulus to the sintered bulk value from literature. After determining the κ value for every pebble in our batch, we discovered a probability distribution for different batches. The distribution is attributed to the varying micro-structure of each pebble. We incorporate the results into our DEM algorithms, distributing κ values at random to pebbles satisfying the probability curves of experiments. DEM simulations of pebble beds in oedometric compression are carried out to determine macroscopic responses of stress–strain, contact force distributions at maximum stress, and a prediction of pebbles crushing at that point. In all cases studied here, the pebble beds with modified Young's modulus had smaller overall contact forces and fewer predicted crushed pebbles.}
}
@Article{VanLew2015,
	author 		= {{Van Lew}, {Jon Thomas} and Ying, Alice and Abdou, Mohamed},
	doi 		= {10.13182/FST14-937},
	journal 	= {Fusion Science and Technology},
	volume 		= {68},
	title 		= {{Coupling Discrete Element Models of Ceramic Breeder Pebble Beds to Thermofluid Models of Helium Purge Gas Using Volume-Averaged Navier-Stokes and the Lattice-Boltzmann Method}},
	year 		= {2015},
	type 		= {Article},
	abstract	= {Pebble-scale models of the interactions inside packed beds are critical for determining alterations to thermophysical properties in the wake of changes to the packed bed due to cracking, sintering, or creep-deformation of the ceramic pebbles. Simultaneously, the helium purge gas flow through the pebble bed can change; while not specifically playing a role as coolant, it does have an impact on the thermal transport in the volumetrically heated bed. We present numerical tools that are capable of resolving pebble-scale interactions coupled to bed-scale thermofluid flow. The new computational techniques are used to show that maximum temperatures in pebble beds do not increase drastically in spite of the significant amount of cracking induced in our numerical model. Furthermore a complete flow field of helium moving through densely packed spheres is modeled with the lattice-Boltzmann method to reveal the strong effect of slow-moving helium gas on flattening temperature profiles in pebble beds with nuclear heating.}
}
@Article{VanLew2014,
	author 		= {{Van Lew}, {Jon Thomas} and Ying, Alice and Abdou, Mohamed A},
	doi 		= {10.1016/j.fusengdes.2014.04.066},
	journal 	= {Fusion Engineering and Design},
	volume 		= {89},
	title 		= {{A discrete element method study on the evolution of thermomechanics of a pebble bed experiencing pebble failure}},
	year 		= {2014},
	type 		= {Article},
	abstract	= {The discrete element method (DEM) is used to study the thermal effects of pebble failure in an ensemble of lithium ceramic spheres. Some pebbles crushing in a large system is unavoidable and this study provides correlations between the extent of pebble failure and the reduction in effective thermal conductivity of the bed. In the model, we homogeneously induced failure and applied nuclear heating until dynamic and thermal steady-state. Conduction between pebbles and from pebbles to the boundary is the only mode of heat transfer presently modeled. The effective thermal conductivity was found to decrease rapidly as a function of the percent of failed pebbles in the bed. It was found that the dominant contributor to the reduction was the drop in inter-particle forces as pebbles fail; implying the extent of failure induced may not occur in real pebble beds. The results are meant to assist designers in the fusion energy community who are planning to use packed beds of ceramic pebbles. The evolution away from experimentally measured thermomechanical properties as pebbles fail is necessary for proper operation of fusion reactors.}

}
@Article{ying2011isfnt,
	author 		= {Ying, Alice and Reimann, Jorg and Boccaccini, Lorenzo and Enoeda, Mikio and Kamlah, Marc and Knitter, Regina and Gan, Yixiang and van der Laan, Jaap G and Magielsen, Lida and {Di Maio}, Francesco Paolo and Dell'Orco, G. and Annabattula, Ratna Kumar and {Van Lew}, {Jon Thomas} and Tanigawa, Hisashi and van Til, Sander},
	doi 		= {10.1016/j.fusengdes.2012.02.090},
	journal 	= {Fusion Engineering and Design},
	volume 		= {87},
	title 		= {{Status of ceramic breeder pebble bed thermo-mechanics R\&D and impact on breeder material mechanical strength}},
	year 		= {2012},
	type 		= {Article},
	abstract	= {Among the international fusion solid breeder blanket community, there exists steady progress on the experimental, phenomenological, and numerical characterizations of the pebble bed effective thermo physical and mechanical properties, and of thermomechanic state of the bed under prototypical operating conditions. This paper summarizes recent achievements in pebble bed thermomechanics that were carried out by members of the IEA Fusion Nuclear Technology Subtask I Solid Breeding Blanket. A major goal is on developing predictive capability while identifying a pre-conditioned equilibrium stress state that would warrant pebble bed integrity during operations. The paper reviews and synthesizes existing computational modeling approaches for pebble bed thermomechanics prediction, and differentiating points of convergence/divergence among existing approaches. The progress toward modeling benchmark is also discussed. These advancements have led to a framework to help navigate future research.}
}
@Article{VanLew2016,
	author 		= {{Van Lew}, {Jon Thomas} and Ying, Alice and Abdou, Mohamed},
	abstract = {We apply coupled computational fluid dynamics and discrete element method (CFD-DEM) modeling tools with new numerical implementations of pebble fragmentation to study the combined effects of granular crushing and ensemble restructuring, granular fragment size, and initial packing for different breeder volume configurations. In typical solid breeder modules, heat removal from beds relies on maintaining pebble–pebble and pebble–wall contact integrity. However, contact is disrupted when an ensemble responds to individually crushed pebbles. Furthermore, restructuring of metastable packings after crushing events are, in part, dependent on gravity forces acting upon the pebbles. We investigate two representative pebble bed configurations under constant volumetric heat sources; modeling heat removed from beds via inter-particle conduction, purge gas convection, and contact between pebble beds and containers. In one configuration, heat is removed from at walls oriented parallel to the gravity vector (no gap formation possible); in the second, heat is removed at walls perpendicular to gravity, allowing for the possibility of gap formation between bed and wall. Judging beds on increase in maximum temperatures as a function of crushed pebble amount, we find that both pebble bed configurations to have advantageous features that manifest at different stages of pebble crushing. However, all configurations benefit from achieving high initial packing fractions.},
	doi 		= {10.1016/j.fusengdes.2016.02.059},
	journal 	= {Fusion Engineering and Design},
	type 		= {Article},
	title 		= {{Numerical study on influences of bed resettling, breeding zone orientation, and purge gas on temperatures in solid breeders}},
	volume 		= {109-111},
	year 		= {2016}
}
@Article{Panchal2016,
	abstract 	= {The effective thermal conductivity (keff) of lithium meta-titanate (Li2TiO3) pebble beds is an important parameter for the design and analysis of IN LLCB TBM (Indian Lead Lithium Ceramic Breeder Test Blanket Module). The keff of Li2TiO3 pebble beds under stagnant helium gas have been determined numerically using different uniform packing structures and random close packing (RCP) structures. The uniform packing structures of Li2TiO3 pebble bed are modelled by using the simple cubic, body centered cubic and face centered cubic arrangement. The packing structure of the RCP bed of Li2TiO3 pebbles is generated with the discrete element method (DEM) code. keff of Li2TiO3 pebble beds with different packing fractions have been reported as function of temperature; keff of the RCP Li2TiO3 pebble bed is compared with reported experimental results from literature. The numerically determined keff of the Li2TiO3 pebble bed agrees reasonably well with the experimental data.},
	author 		= {Panchal, Maulik and Chaudhuri, Paritosh and {Van Lew}, {Jon Thomas} and Ying, Alice},
	doi 		= {10.1016/j.fusengdes.2016.08.027},
	type 		= {Article},
	journal 	= {Fusion Engineering and Design},
	title	 	= {{Numerical modelling for the effective thermal conductivity of lithium meta titanate pebble bed with different packing structures}},
	volume 		= {112},
	year	 	= {2016}
}

@Article{Panchal2016,
	abstract 	= {The effective thermal conductivity (keff) of lithium meta-titanate (Li2TiO3) pebble beds is an important parameter for the design and analysis of IN LLCB TBM (Indian Lead Lithium Ceramic Breeder Test Blanket Module). The keff of Li2TiO3 pebble beds under stagnant helium gas have been determined numerically using different uniform packing structures and random close packing (RCP) structures. The uniform packing structures of Li2TiO3 pebble bed are modelled by using the simple cubic, body centered cubic and face centered cubic arrangement. The packing structure of the RCP bed of Li2TiO3 pebbles is generated with the discrete element method (DEM) code. keff of Li2TiO3 pebble beds with different packing fractions have been reported as function of temperature; keff of the RCP Li2TiO3 pebble bed is compared with reported experimental results from literature. The numerically determined keff of the Li2TiO3 pebble bed agrees reasonably well with the experimental data.},
	author 		= {Panchal, Maulik and Chaudhuri, Paritosh and {Van Lew}, {Jon Thomas} and Ying, Alice},
	doi 		= {10.1016/j.fusengdes.2016.08.027},
	type 		= {Article},
	journal 	= {Fusion Engineering and Design},
	title	 	= {{Numerical modelling for the effective thermal conductivity of lithium meta titanate pebble bed with different packing structures}},
	volume 		= {112},
	year	 	= {2016}
}

@inproceedings{turney2016explicit,
  title={Explicit Two-Phase Modeling of the Initiation of Saltation over Heterogeneous Sand Beds},
  author={Turney, FA and Kok, JF and Martin, RL and Burr, DM and Bridges, N and Ortiz, CP and Smith, JK and Emery, JP and {Van Lew}, {Jon Thomas}},
  booktitle={AGU Fall Meeting Abstracts},
  year={2016},
  type={Conference}
}

@article{doi:10.1080/15361055.2017.1333830,
author = {Christopher Kang and Yi-Hyun Park and {Jon Thomas} {Van Lew} and Alice Ying and Mohamed Abdou and Seungyon Cho},
title = {Transient Hot-Wire Experimental System for Measuring the Effective Thermal Conductivity of a Ceramic Breeder Pebble Bed},
journal = {Fusion Science and Technology},
volume = {72},
type={Article},
number = {3},
pages = {263-270},
year  = {2017},
doi = {10.1080/15361055.2017.1333830},
abstract = { 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 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 Li2TiO3 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. }
}