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2. Thermal conductivity of silicon nanowire arrays with controlled roughness

Author

Massachusetts Institute of Technology. Department of Mechanical Engineering, Fang, Nicholas Xuanlai, Feser, Joseph P., Sadhu, Jyothi S., Azeredo, Bruno P., Hsu, Keng H., Ma, Jun, Kim, Junhwan, Seong, Myunghoon, Li, Xiuling, Ferreira, Placid M., Sinha, Sanjiv, Cahill, David G., Massachusetts Institute of Technology. Department of Mechanical Engineering, Fang, Nicholas Xuanlai, Feser, Joseph P., Sadhu, Jyothi S., Azeredo, Bruno P., Hsu, Keng H., Ma, Jun, Kim, Junhwan, Seong, Myunghoon, Li, Xiuling, Ferreira, Placid M., Sinha, Sanjiv, and Cahill, David G.

Abstract

A two-step metal assisted chemical etching technique is used to systematically vary the sidewall roughness of Si nanowires in vertically aligned arrays. The thermal conductivities of nanowire arrays are studied using time domain thermoreflectance and compared to their high-resolution transmission electron microscopy determined roughness. The thermal conductivity of nanowires with small roughness is close to a theoretical prediction based on an upper limit of the mean-free-paths of phonons given by the nanowire diameter. The thermal conductivity of nanowires with large roughness is found to be significantly below this prediction. Raman spectroscopy reveals that nanowires with large roughness also display significant broadening of the one-phonon peak; the broadening correlates well with the reduction in thermal conductivity. The origin of this broadening is not yet understood, as it is inconsistent with phonon confinement models, but could derive from microstructural changes that affect both the optical phonons observed in Raman scattering and the acoustic phonons that are important for heat conduction., United States. Defense Advanced Research Projects Agency (Contract DOE-DE-AR-0000041PF-ARRA)

Published
2013

4. Analysis and design of a multi-effect desalination system with thermal vapor compression and harvested heat addition.

Author

McKnight, Andrea Vozar, Georgiou, Marios, Seong, Myunghoon, and Georgiadis, John G.

Subjects
SALINE water conversion, SOLAR power plants, HEAT exchangers, WATER supply, SOLAR thermal energy
Abstract

The design and optimization of a concentrated solar power-desalination of seawater (CSP-DSW) plant is based on the accurate characterization and better integration of sub-components, such as the multiple effect distillation (MED). We set out to design and fabricate two pilot MED systems that consist of high performing components and involve a high degree of thermal integration with the rest of the system. An MED system with a series of thermal vapor compressors (TVCs) driven by heat harvested from the thermal storage subsystem of the CSP-DSW is proposed. An algorithm is presented which optimizes the gain output ratio (GOR) by varying of the number and entrainment ratio of TVCs. The use of modular parallel plate falling film heat exchangers and overall process thermal management increase the flexibility and overall efficiency of MED. Experience with the design and fabrication of a transparent single-effect experimental MED aimed to quantify the performance of the parallel plate falling film heat exchanger and to allow visualization of permeate vapor is discussed. A 10 kWt four-effect MED design is also described for use in a proof-of-principle CSP-DSW study to be performed at the Cyprus Institute. [ABSTRACT FROM AUTHOR]

Published
2011
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