Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G19: Invited Session: Caloric Materials and Advances in Solid State Cooling Technologies |
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Sponsoring Units: FIAP DMP Chair: Jun Cui, Pacific Northwest National Laboratory Room: Mission Room 103B |
Tuesday, March 3, 2015 11:15AM - 11:51AM |
G19.00001: Magnetocaloric cooling: the phenomenon and materials Invited Speaker: Vitalij Pecharsky The discovery of the giant magnetocaloric effect in Gd$_{\mathrm{5}}$Si$_{\mathrm{2}}$Ge$_{\mathrm{2}}$ and other R$_{\mathrm{5}}$T$_{\mathrm{4}}$ compounds (R $=$ rare earth metal and T is a Group 14 element) generated a broad interest in the magnetocaloric effect and magnetic refrigeration near room temperature in particular, and in magnetostructural transitions in general. Reports on the giant magnetocaloric effect in other systems soon followed. These include MnFeP$_{\mathrm{x}}$As$_{\mathrm{1-x}}$ and related compounds, La(Fe$_{\mathrm{1-x}}$Si$_{\mathrm{x}})_{\mathrm{13}}$ and their hydrides, Mn(As$_{\mathrm{x}}$Sb$_{\mathrm{1-x}})$, CoMnSi$_{\mathrm{x}}$Ge$_{\mathrm{1-x}}$ and related compounds, Ni$_{\mathrm{2}}$MnGa and some closely related Heusler phases, and a few non-metallic systems. A common feature observed in all giant magnetocaloric effect materials is the enhancement of the magnetic entropy change by the overlapping contribution from the lattice. In addition to the interplay between magnetic and lattice entropies, both of which are intrinsic materials' parameters that in principle can be modeled theoretically from first principles, extrinsic parameters such as microstructure and nanostructure, have been found to play a role in controlling both the magnetostructural transition(s) and magnetocaloric effect. Both the intrinsic and extrinsic parameters are, therefore, important in order to maximize magnetocaloric effect. The role of different control parameters and the potential pathways towards materials exhibiting advanced magnetocaloric effect will be discussed. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:27PM |
G19.00002: Elastocaloric cooling materials and systems Invited Speaker: Ichiro Takeuchi We are actively pursuing applications of thermoelastic (elastocaloric) cooling using shape memory alloys. Latent heat associated with martensitic transformation of shape memory alloys can be used to run cooling cycles with stress-inducing mechanical drives [1]. The coefficient of performance of thermoelastic cooling materials can be as high as 11 with the directly measured DT of around 17 $^{\circ}$C. Depending on the stress application mode, the number of cycles to fatigue can be as large as of the order of 10$^{5}$. Efforts to design and develop thermoelastic alloys with long fatigue life will be discussed. The current project at the University of Maryland is focused on development of building air-conditioners, and at Maryland Energy and Sensor Technologies, smaller scale commercial applications are being pursued. This work is carried out in collaboration with Jun Cui, Yiming Wu, Suxin Qian, Yunho Hwang, Jan Muehlbauer, and Reinhard Radermacher, and it is funded by the ARPA-E BEETIT program and the State of Maryland.\\[4pt] [1] Jun Cui, et al. ``Demonstration of high efficiency elastocaloric cooling with large DT using NiTi wires,'' Applied Physics Letters 101, 073904 (2012). [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 1:03PM |
G19.00003: Modeling and design aspects of active caloric regenerators Invited Speaker: Kurt Engelbrecht A cooling device based on a solid caloric material using, for example, the elastocaloric, magnetocaloric, barocaloric or electrocaloric effect has the potential to replace vapor-compression based systems for a variety of applications. Any caloric device using a solid refrigerant may benefit from using a regenerative cycle to increase the operating temperature span. This presentation shows how all active caloric regenerators can be modeled using similar techniques and how they are related to passive regenerator performance. The advantages and disadvantages of using a regenerative cycle are also discussed. The issue of hysteresis in caloric materials is investigated from a system/thermodynamic standpoint and the effects on cooling power and efficiency are quantified using a numerical model of an active regenerator using model caloric materials with assumed properties. The implementation in a working device will be discussed for elastocaloric and magnetocaloric cooling devices. It is shown that demagnetization effects for magnetocaloric systems and stress concentration effects in elastocaloric system reduce the overall effect in the regenerator and care must be taken in regenerator design for both technologies. Other loss mechanisms outside the regenerator such as heat leaks are also discussed. Finally, experimental results for active magnetic regenerative cooler are given for a range of operating conditions. The most recently published device uses a regenerator consisting of Gd and three alloys of GdY and has demonstrated a \textit{COP} over 3. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:39PM |
G19.00004: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 1:39PM - 2:15PM |
G19.00005: Effective Mass of Thermoelectric Materials with Non-Parabolic Kane Bands Invited Speaker: G. Jeffrey Snyder Effective mass is a concept commonly used to describe electronic transport in semiconductors using a classical analogy to the kinetic theory of gasses. We describe many important electronic transport parameters explicitly with an electronic band mass including: Density of states, charge carrier concentration, mobility, and in particular for thermoelectrics, the Seebeck coefficient. For systems with known electronic band structures these properties can be calculated leading to subtly different definitions of effective mass. In the free electron or parabolic band model the effective masses are the same and we use the term effective mass interchangably. However the differences between these defintions or uses of effective mass become apparent in non-parabolic band structures where it is desirable to describe the transport in terms of a effective mass that changes with energy (or Fermi Level). For example Kane bands, which become more linear and less parabolic at higher energy, have an increased density of states and therefore higher DOS effective mass than a parabolic band. While it is often assumed that also results in a higher thermopower (Seebeck coefficient), calculations of thermopower and Hall carrier concentration from the Kane model show the thermpower is actually reduced. Examples in thermoelectric materials will be discussed. [Preview Abstract] |
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