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Marc T. Dunham

Bio: Marc T. Dunham is an academic researcher from Stanford University. The author has contributed to research in topics: Thermoelectric effect & Combined cycle. The author has an hindex of 8, co-authored 20 publications receiving 335 citations. Previous affiliations of Marc T. Dunham include Sandia National Laboratories & University of Minnesota.

Papers
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Journal ArticleDOI
TL;DR: In this article, a review of high efficiency thermodynamic cycles and their applicability to concentrating solar power systems, primarily focusing on high-efficiency single and combined cycles, is provided, and an estimate of a combined receiver and power cycle operating temperature is provided for the cycles considered and compared to the traditional approach of optimization based on the Carnot efficiency.
Abstract: This paper provides a review of high-efficiency thermodynamic cycles and their applicability to concentrating solar power systems, primarily focusing on high-efficiency single and combined cycles. Novel approaches to power generation proposed in the literature are also highlighted. The review is followed by analyses of promising candidates, including regenerated He-Brayton, regenerated CO2-Brayton, CO2 recompression Brayton, steam Rankine, and CO2–ORC combined cycle. Steam Rankine is shown to offer higher thermal efficiencies at temperatures up to about 600 °C but requires a change in materials for components above this temperature. Above this temperature, CO2 recompression Brayton cycles are shown to have very high thermal efficiency, potentially even exceeding 60% at 30 MPa maximum pressure and above 1000 °C maximum temperature with wet cooling. An estimate of a combined receiver and power cycle operating temperature is provided for the cycles considered and compared to the traditional approach of optimization based on the Carnot efficiency. It is shown that the traditional approach to optimizing the receiver and turbine inlet temperatures based on Carnot is generally not sufficient, leading to an optimum temperature shift of more than 100 °C from the Carnot case under various conditions.

214 citations

Journal ArticleDOI
15 Dec 2015-Energy
TL;DR: In this article, the authors derive and explore comprehensive design guidelines for optimizing power output of microfabricated thermoelectric generators (mTEGs) and discuss the incompleteness of ZT for different combinations of thermal conductivity, electrical conductivity and Seebeck coefficient.

78 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of nanovoids on the thermal conductivity of highly doped, high-power factor polysilicon thin films using time-domain thermoreflectance was examined.
Abstract: The ability to tune the thermal conductivity of semiconductor materials is of interest for thermoelectric applications, in particular, for doped silicon, which can be readily integrated in electronic microstructures and have a high thermoelectric power factor. Here, we examine the impact of nanovoids on the thermal conductivity of highly doped, high-power factor polysilicon thin films using time-domain thermoreflectance. Voids are formed through ion implantation and annealing, evolving from many small (∼4 nm mean diameter) voids after 500 °C anneal to fewer, larger (∼29 nm mean diameter) voids with a constant total volume fraction after staged thermal annealing to 1000 °C. The thermal conductivity is reduced to 65% of the non-implanted reference film conductivity after implantation and 500 °C anneal, increasing with anneal temperature until fully restored after 800 °C anneal. The void size distributions are determined experimentally using small-angle and wide-angle X-ray scattering. While we believe multi...

26 citations

Journal ArticleDOI
TL;DR: In this article, the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films with metallic-like conductivities can be obtained with high power factors in excess of 800 μW m−1 K−2.
Abstract: DOI: 10.1002/aelm.202001190 materials with high zT values are available, solid-state waste heat recovery schemes become practically attractive for increasing system energy efficiencies.[1] Organic conductors and semiconductors are compelling systems for near-ambient thermoelectric applications because of their intrinsically low thermal conductivity, elemental ubiquity, and scalable, low-temperature processing, rendering organic electronics commercially viable despite reduced efficiencies relative to their inorganic counterparts.[2] The physical robustness of polymer materials expands their markets to flexible applications and curved surfaces for which the cost of custom design of rigid thermoelectric devices would exceed their value. Additionally, conductive polymer-based materials exhibit weaker coupling between S, κ, and σ than inorganic materials, mainly due to two factors: 1) the relatively low carrier concentrations and mobilities result in a weak correlation between the thermal and electrical conductivities; and 2) the non-band-like nature of the density of states leads to nontraditional relationships between the Seebeck coefficient and electrical conductivity.[2,3] These relaxed interdependencies bound a vast design space for synthesis, processing, and doping of organic materials to increase their overall figure of merit. This optimization process is focused on improving the electrical transport properties of organic materials, which have historically limited their performance in thermoelectric energy conversion. To increase the thermoelectric viability of conductive polymers, research efforts have focused on increasing the electrical conductivity and Seebeck coefficient of polymer material systems, such as poly(3,4-ethylenedioxythiophene):poly(styrenes ulfonate) (PEDOT:PSS). PEDOT:PSS consists of a conjugated hydrophobic polymer (PEDOT) within an insulating hydrophilic matrix (PSS), which dopes PEDOT to increase the conductivity and helps to disperse any excess PEDOT in water. However, the insulating PSS that remains in deposited films does not contribute to electrical conduction and prevents the PEDOT phase from ordering with a consequently higher conductivity. The electrical conductivity of this formulation can be improved through preand postdeposition treatments, involving various acids (camphorsulfonic acid,[4] dichloroacetic acid,[5] H2SO4, and p-toluenesulfonic acid[8]), solvents (dimethyl sulfoxide,[9] ethylene glycol (EG), diethylene glycol, methanol (MeOH),[10] and formamide[11]), and surfactants.[12,13] These methods have produced electrical conductivities of nearly 5000 S cm−1 and simultaneous enhancements of the Seebeck coefficient through Polymer-based materials hold great potential for use in thermoelectric applications but are limited by their poor electrical properties. Through a combination of solution-shearing deposition and directionally applied solvent treatments, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films with metallic-like conductivities can be obtained with high power factors in excess of 800 μW m−1 K−2. X-ray scattering and absorption data indicate that structural alignment of PEDOT chains and larger-sized domains are responsible for the enhanced electrical conductivity. It is expected that further enhancements to the power factor can be obtained through device geometry and postdeposition solvent shearing optimization.

25 citations

Journal ArticleDOI
TL;DR: In this paper, a reduced order thermo-fluidic model is developed to predict the effect of both heat flux and liquid charge on the overall device thermal performance, which is validated against experimental results from a prototype device to agree within ±25%.

25 citations


Cited by
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

29,323 citations

01 Jan 2007

1,932 citations

Journal ArticleDOI
TL;DR: This review aims to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics.
Abstract: The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

951 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a methodology to predict hourly beam (direct) irradiation from available monthly averages, based upon combined previous literature findings and available meteorological data, and illustrate predictions for different selected STC locations.
Abstract: Concentrated solar power plants (CSPs) are gaining increasing interest, mostly as parabolic trough collectors (PTC) or solar tower collectors (STC). Notwithstanding CSP benefits, the daily and monthly variation of the solar irradiation flux is a main drawback. Despite the approximate match between hours of the day where solar radiation and energy demand peak, CSPs experience short term variations on cloudy days and cannot provide energy during night hours unless incorporating thermal energy storage (TES) and/or backup systems (BS) to operate continuously. To determine the optimum design and operation of the CSP throughout the year, whilst defining the required TES and/or BS, an accurate estimation of the daily solar irradiation is needed. Local solar irradiation data are mostly only available as monthly averages, and a predictive conversion into hourly data and direct irradiation is needed to provide a more accurate input into the CSP design. The paper (i) briefly reviews CSP technologies and STC advantages; (ii) presents a methodology to predict hourly beam (direct) irradiation from available monthly averages, based upon combined previous literature findings and available meteorological data; (iii) illustrates predictions for different selected STC locations; and finally (iv) describes the use of the predictions in simulating the required plant configuration of an optimum STC. The methodology and results demonstrate the potential of CSPs in general, whilst also defining the design background of STC plants.

834 citations

Proceedings Article
01 Jan 2009
TL;DR: This paper summarizes recent energy harvesting results and their power management circuits.
Abstract: More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC-DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

711 citations