Solar thermoelectric system modeling

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 152-155).Recent years have witnessed a trend of rising electricity costs and an emphasis on energy efficiency. Thermoelectric (TE) devices can be used either as heat pumps for localized environmental control or heat engines to convert heat into electricity. Thermoelectrics are appealing because they have no moving parts, are highly reliable, have high power densities, and are scalable in size. They can be used to improve the overall efficiency of many systems including vehicle waste heat, solar thermal, HVAC, industrial waste heat, and remote power for sensor applications. For thermoelectric generators to be successful, research progress at the device level must be made to validate materials and to guide system design. The focus of this thesis is thermoelectric device testing and system modeling. A novel device testing method is developed between room temperature range and 230°C. The experimental technique is capable of directly measuring an energy balance over a single leg, with a large temperature of 2-160°C. The technique measures all three TE properties of a single leg, in the same direction, with significantly less uncertainty than other methods. The measurements include the effects of temperature dependent properties, side wall radiation loss, and contact resistance. The power and efficiency were directly measured and are within 0.4 % and 2 % of the values calculated from the property measurements. The device property measurement was extended to higher temperatures up to 600°C. The experimental system uses an inline unicouple orientation to minimize radiation losses and thermal stress. Two major experimental challenges were the construction of a high temperature calibrated heater and a thermocouple attachment technique. We investigated skutterudite materials which are of interest to many research groups due to their high thermoelectric figure-of-merit (ZT), and good thermomechanical properties. Unlike room temperature Bi2Te 3 devices, skutterudite module construction techniques are not well established and were a major challenge in this work. Skutterudite device samples were fabricated by a direct bonding method in which a rigid electrode is sintered directly to the TE powder during press. Compatible electrode materials were identified and evaluated based on thermal stress, parasitic electrical/thermal resistance, chemical stability and ease of prototype fabrication. The final electrodes solutions were Co2 Si with the P-type and CoSi2 with the N-type. The direct hot press process was modified into what we call a hybrid hot press to produce device samples with strong bonds and no cracks. Preliminary accelerated aging tests were conducted to evaluate the long term chemical stability of the TE-electrode contacts. We demonstrated ZTff = 0.74 for the N-type between 52°C and 595°C corresponding to 11.7% conversion efficiency and Zlff = 0.51 for the P-type between 77°C and 600°C corresponding to 8.5% efficiency. The maximum efficiency of the NP unicouple was measured to be 9.1% at ~550°C. The effective ZT and efficiency measurement includes electrical contact resistance, and parasitic thermal/electrical resistance in the electrodes, and heat losses at the sides of the legs. Thus we have included all the parasitic loss effects that are present in a real unicouple. The efficiency values measured in this work are among the highest recorded for a skutterudite unicouple. The TE-electrode combinations meet all the criteria for device testing and offer a practical, manufacturable solution for module construction. Solar thermal power generation is fast becoming cost competitive for utility scale electricity with 380 MW electric currently installed. Parabolic trough concentrators have proven economical and reliable but their efficiency is limited by the maximum temperature of the heated fluid. We explored the idea of a solar thermoelectric topping cycle (STET) in which a thermoelectric generator (TEG) is added at high temperature to increase the overall efficiency of the solar Rankine cycle. In this design the perimeter of the receiver tube is covered with thermoelectrics so that the absorber temperature is raised and the energy rejected from the TEG is used to heat the fluid at its originally specified temperature. A heat transfer analysis was carried out to determine the overall system efficiency. A parametric study was performed to identity design constraints and put bounds on the total system efficiency. The system performance was simulated for all conceivable concentrations and fluid temperatures of a solar thermal trough. As the absorber temperature increases more power is generated by the TEG but is offset by a rapidly decreasing absorber efficiency which results in only a marginal increase in net power. It was concluded that for the proposed STET to increase the system efficiency of a state of the art trough system by 10% requires a ZI =3 TEG, which is well beyond the state-of-the-art thermoelectric materials.by Andrew Muto.Ph.D

Device testing and characterization of thermoelectric nanocomposites

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 67-68).It has become evident in recent years that developing clean, sustainable energy technologies will be one of the world's greatest challenges in the 21st century. Thermoelectric materials can potentially make a contribution by increasing energy efficiency of some systems. Thermoelectric materials may play a role in the large scale energy industry, specifically in the applications of refrigeration and waste heat recovery. In this work a novel thermoelectric material will be tested for conversion efficiency. A Bi₂Te₃ nanocomposite has been developed by the joint effort of Prof. Gang Chen's group at MIT and Prof. Zhifeng Ren's group at Boston College. The material exhibits enhanced thermoelectric properties from optimized nanoscale structures and can be easily manufactured in large quantities. In order to better characterize its performance a novel power conversion measurement system has been developed that can measure the conversion efficiency directly. The measurement system design will be described in detail; important design considerations will be addressed such as measuring heat flux, optimizing the load matching condition and reducing electrical contact resistance. Finally the measured efficiency will be compared to the calculated efficiency from a temperature-dependent properties model. It will be shown that a Ni layer must be attached to the nanocomposite to allow soldering and power conversion testing. Results of this work will show that the nanocomposite efficiency is higher than the commercial standard. Electrical contact remains a challenge in realizing the potential efficiency.by Andrew Muto.S.M

Global Calculations of Density Waves and Gap Formation in Protoplanetary Disks using a Moving Mesh

We calculate the global quasi-steady state of a thin disk perturbed by a low-mass protoplanet orbiting at a fixed radius using extremely high-resolution numerical integrations of Euler's equations in two dimensions. The calculations are carried out using a moving computational domain, which greatly reduces advection errors and allows for much longer time-steps than a fixed grid. We calculate the angular momentum flux and the torque density as a function of radius and compare them with analytical predictions. We discuss the quasi-steady state after 100 orbits and the prospects for gap formation by low mass planets.Comment: Accepted to Ap

fMRI-compatible rehabilitation hand device

BACKGROUND: Functional magnetic resonance imaging (fMRI) has been widely used in studying human brain functions and neurorehabilitation. In order to develop complex and well-controlled fMRI paradigms, interfaces that can precisely control and measure output force and kinematics of the movements in human subjects are needed. Optimized state-of-the-art fMRI methods, combined with magnetic resonance (MR) compatible robotic devices for rehabilitation, can assist therapists to quantify, monitor, and improve physical rehabilitation. To achieve this goal, robotic or mechatronic devices with actuators and sensors need to be introduced into an MR environment. The common standard mechanical parts can not be used in MR environment and MR compatibility has been a tough hurdle for device developers. METHODS: This paper presents the design, fabrication and preliminary testing of a novel, one degree of freedom, MR compatible, computer controlled, variable resistance hand device that may be used in brain MR imaging during hand grip rehabilitation. We named the device MR_CHIROD (Magnetic Resonance Compatible Smart Hand Interfaced Rehabilitation Device). A novel feature of the device is the use of Electro-Rheological Fluids (ERFs) to achieve tunable and controllable resistive force generation. ERFs are fluids that experience dramatic changes in rheological properties, such as viscosity or yield stress, in the presence of an electric field. The device consists of four major subsystems: a) an ERF based resistive element; b) a gearbox; c) two handles and d) two sensors, one optical encoder and one force sensor, to measure the patient induced motion and force. The smart hand device is designed to resist up to 50% of the maximum level of gripping force of a human hand and be controlled in real time. RESULTS: Laboratory tests of the device indicate that it was able to meet its design objective to resist up to approximately 50% of the maximum handgrip force. The detailed compatibility tests demonstrated that there is neither an effect from the MR environment on the ERF properties and performance of the sensors, nor significant degradation on MR images by the introduction of the MR_CHIROD in the MR scanner. CONCLUSION: The MR compatible hand device was built to aid in the study of brain function during generation of controllable and tunable force during handgrip exercising. The device was shown to be MR compatible. To the best of our knowledge, this is the first system that utilizes ERF in MR environment

Virtual-crystal approximation that works: Locating a composition phase boundary in Pb(Zr_{1-x}Ti_3)O_3

We present a new method for modeling disordered solid solutions, based on the virtual crystal approximation (VCA). The VCA is a tractable way of studying configurationally disordered systems; traditionally, the potentials which represent atoms of two or more elements are averaged into a composite atomic potential. We have overcome significant shortcomings of the standard VCA by developing a potential which yields averaged atomic properties. We perform the VCA on a ferroelectric oxide, determining the energy differences between the high-temperature rhombohedral, low-temperature rhombohedral and tetragonal phases of Pb(Zr_{1-x}Ti_x)O_3 at x=0.5 and comparing these results to superlattice calculations and experiment. We then use our new method to determine the preferred structural phase at x=0.4. We find that the low-temperature rhombohedral phase becomes the ground state at x=0.4, in agreement with experimental findings.Comment: 5 pages, no figure

Kaon differential flow in relativistic heavy-ion collisions

Using a relativistic transport model, we study the azimuthal momentum asymmetry of kaons with fixed transverse momentum, i.e., the differential flow, in heavy-ion collisions at beam momentum of 6 GeV/c per nucleon, available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory (BNL). We find that in the absence of kaon potential the kaon differential flow is positive and increases with transverse momentum as that of nucleons. The repulsive kaon potential as predicted by theoretical models, however, reduces the kaon differetnial flow, changing it to negative for kaons with low momenta. Cancellation between the negative differential flow at low mementa and the positive one at high momenta is then responsible for the experimentally observed nearly vanishing in-plane transverse flow of kaons in heavy ion experiments.Comment: Phys. Rev. C in pres

Activation-Induced Cytidine Deaminase (AID) Deficiency Causes the Autosomal Recessive Form of the Hyper-IgM Syndrome (HIGM2)

AbstractThe activation-induced cytidine deaminase (AID) gene, specifically expressed in germinal center B cells in mice, is a member of the cytidine deaminase family. We herein report mutations in the human counterpart of AID in patients with the autosomal recessive form of hyper-IgM syndrome (HIGM2). Three major abnormalities characterize AID deficiency: (1) the absence of immunoglobulin class switch recombination, (2) the lack of immunoglobulin somatic hypermutations, and (3) lymph node hyperplasia caused by the presence of giant germinal centers. The phenotype observed in HIGM2 patients (and in AID−/− mice) demonstrates the absolute requirement for AID in several crucial steps of B cell terminal differentiation necessary for efficient antibody responses

Pan-cancer Alterations of the MYC Oncogene and Its Proximal Network across the Cancer Genome Atlas

Although theMYConcogene has been implicated incancer, a systematic assessment of alterations ofMYC, related transcription factors, and co-regulatoryproteins, forming the proximal MYC network (PMN),across human cancers is lacking. Using computa-tional approaches, we define genomic and proteo-mic features associated with MYC and the PMNacross the 33 cancers of The Cancer Genome Atlas.Pan-cancer, 28% of all samples had at least one ofthe MYC paralogs amplified. In contrast, the MYCantagonists MGA and MNT were the most frequentlymutated or deleted members, proposing a roleas tumor suppressors.MYCalterations were mutu-ally exclusive withPIK3CA,PTEN,APC,orBRAFalterations, suggesting that MYC is a distinct onco-genic driver. Expression analysis revealed MYC-associated pathways in tumor subtypes, such asimmune response and growth factor signaling; chro-matin, translation, and DNA replication/repair wereconserved pan-cancer. This analysis reveals insightsinto MYC biology and is a reference for biomarkersand therapeutics for cancers with alterations ofMYC or the PMN

Genomic, Pathway Network, and Immunologic Features Distinguishing Squamous Carcinomas

This integrated, multiplatform PanCancer Atlas study co-mapped and identified distinguishing molecular features of squamous cell carcinomas (SCCs) from five sites associated with smokin

Pan-Cancer Analysis of lncRNA Regulation Supports Their Targeting of Cancer Genes in Each Tumor Context

Long noncoding RNAs (lncRNAs) are commonly dys-regulated in tumors, but only a handful are known toplay pathophysiological roles in cancer. We inferredlncRNAs that dysregulate cancer pathways, onco-genes, and tumor suppressors (cancer genes) bymodeling their effects on the activity of transcriptionfactors, RNA-binding proteins, and microRNAs in5,185 TCGA tumors and 1,019 ENCODE assays.Our predictions included hundreds of candidateonco- and tumor-suppressor lncRNAs (cancerlncRNAs) whose somatic alterations account for thedysregulation of dozens of cancer genes and path-ways in each of 14 tumor contexts. To demonstrateproof of concept, we showed that perturbations tar-geting OIP5-AS1 (an inferred tumor suppressor) andTUG1 and WT1-AS (inferred onco-lncRNAs) dysre-gulated cancer genes and altered proliferation ofbreast and gynecologic cancer cells. Our analysis in-dicates that, although most lncRNAs are dysregu-lated in a tumor-specific manner, some, includingOIP5-AS1, TUG1, NEAT1, MEG3, and TSIX, synergis-tically dysregulate cancer pathways in multiple tumorcontexts