Author: Segen Sara A. Habte

Author: Jian Zhou

Title: VOLUMETRIC SOLAR ABSORBING FLUIDS AND THEIR APPLICATIONS IN TWO-PHASE THERMOSYPHON

Date/time: May 22nd at 1:00pm EST

Location: 2164 DeWALT Seminar Room, Glenn L. Martin Hall.

Zoom: https://umd.zoom.us/j/3656005874?omn=94830805862)

Committee members:

Dr. Bao Yang, Advisor and Chair
Dr. Peter B. Sunderland
Dr. Amir Riaz
Dr. Yunho Hwang
Dr. Chunsheng Wang, Dean’s Representative

Abstract:

A two-phase thermosyphon is a passive system utilizing gravity to transfer working fluids. The working fluids of a two-phase thermosyphon must undergo vaporization and condensation in the same system. Two-phase thermosyphons can also be used as solar collectors. Traditional solar collectors utilize surface absorbers to convert incident solar radiation into thermal energy, but those systems feature a large temperature difference between the surface absorbers and heat transfer fluids, resulting in a reduction in the overall thermal efficiency. Volumetric solar absorbing fluids serve both as solar absorbers and heat transfer fluids, therefore significantly improving the overall efficiency of solar collectors. Comparing to pure fluids, nanofluids possess both enhanced thermal conductivity and solar absorption capacity as volumetric absorbing fluids. Nanofluids, when serving as volumetric solar absorbing fluids, are so far reported to work only at relatively low temperatures and in a single-phase heat transfer regime due to stability issue. This research investigates the possibility of using nanofluids, especially graphene oxide (GO) nanofluids, as volumetric solar absorbing fluids in two-phase thermosyphons. Despite their reputation as both stable and solar absorptive among nanofluids, graphene oxide nanofluids still deteriorate quickly under boiling-condensation processes (~100 °C). The solar transmittance of the GO nanofluids declines from 38 to 4%, during the first 24 h of testing. Further investigation shows that the stability deterioration is caused by the thermal reduction of GO nanoparticles, which mainly featured with de-carboxylation and de-hydroxylation. A commercial dye named acid black 52, when dissolved in water, exhibits great broadband solar absorption properties and excellent stability. It remains stable for over 199 days in two-phase thermosyphon, and their transmittance in solar spectral region varies less than 9%. The stability of acid black 52 aqueous solution is further confirmed with the 191-day enhanced radiation test, as it shows less than 5% transmittance change in solar spectral region.

Author: Edwin Fishman

Title: The Natural Response of Uniform in Air and Partially Submerged in a Quiescent Water Body

Date/time: April 24th at 10:00am

Location: 3179K Aerospace Engineering Conference Room, Glenn L. Martin Hall.

Committee members:
Professor James Duncan, Advisor & Chair
Professor Miao Yu
Professor Kenneth Kiger

Abstract:

The free vibration of three aluminum plates (.4 m wide, 1.08 m long) oriented horizontally is studied experimentally under two fluid conditions, one with the plate surround by air and the other with the bottom plate surface in contact with a large undisturbed pool of water.  Measurements of the out of plane deflection of the upper surfaces of the plates are made using cinematic Digital Image Correlation (DIC) over the center portion of the surface  and optical tracking of the center point. Three plate geometries and boundary conditions are studied: A uniform plate with 6.35 mm thickness pinned at the two opposite narrrow ends (UP), a uniform plate with 4.83 mm thickness simply supported at one narrow end and clamped at the opposite end (UC), and a stepped plate with thickness varying from 12.7 mm to 6.35 mm pinned at two opposite narrow ends (SP). The plate’s free response is induced using an impact hammer at three locations along the center-line of the plate. Video frames of the plate’s motion are collected from stereoscopic cameras and processed using DaVis-Strainmaster and MATLAB to extract full-field displacements as a function of time. 2-degree-of-freedom displacements of the plate center are collected from tracking the center target’s motion. Time and frequency response plots are presented for comparison between the half-wet and air cases and analysis of their dynamics. It is found that the added mass of the water results in lower measured natural frequencies and modified mode shapes. These results are compared to mode shapes/frequencies produced in Creo Simulate and found to agree. Further experiments are discussed.

Author: Zahra Nozarijouybari

Title: Optimal Probing of Battery Cycles for Machine Learning-Based Model Development 

Date/time: April 29th at 2:00pm

Location: 2162 DeWALT Conference Room, Glenn L. Martin Hall.

Committee members:
Professor Hosam Fathy, Advisor & Chair
Professor Mark Fuge
Professor Steven A. Gabriel
Professor Teng Li
Professor Chunsheng Wang, Dean’s Representative

Abstract: