Thermal switch is very important in today’s world and it has varies of applications including heat dissipation and engine efficiency improving. The commercial thermal switch based on mechanical design is very slow and the structure is too complicated to make them smaller. To enable fast thermal switch as well as to make thermal switch more compact, I try to use second-order phase transition material to enable our thermal switch. Noticing the transition properties of thermoresponsive polymer for drug delivery, its potential in thermal switch can be expected. I used Poly(N-isopropylacrylamide) (PNIPAM) as an example to show the abrupt thermal conductivity change of thermoresponsive polymer solutions below and above their phase transition temperature. A novel technique, transition grating method, is used to measure the thermal conductivity. The ratio of thermal switch up to 1.15 in transparent PNIPAM solutions after the transition is observed. This work will demonstrate the new design of using second-order phase transition material to enable fast and efficient thermal switch. / Master of Science / Controllable thermal conductivity (thermal switching) is very important to thermal management area and useful in a wide area of applications. Nowadays, mechanical thermal conductivity controller device suffers from large scale and slow transition speeds. To solve these problems, I tired the phase transition thermoresponsive polymers to create quick thermal switching because the thermal conductivity will change with the phase. Thermoresponsive polymers show sharp phase changes upon small changes in temperature. Such polymers are already widely used in biomedical-like applications, the thermal switch applications are not well-studied. In this work, I tested Poly(N-isopropylacrylamide) (the abbreviation is PNIPAM) as an example to show the quick thermal conductivity changing ability of thermoresponsive polymer when the transition was happened .I used a novel approach, called the TTG, transient thermal grating. It has easy setup and high sensitivity. The thermal conductivity switching ratio as high as 1.15 in transparent PNIPAM solutions after transition is observed. This work will give new opportunities to control thermal switches using the phase change of thermoresponsive material or abrupt other phase change material in general.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/86837 |
| Date | 29 November 2018 |
| Creators | Ma, Yunwei |
| Contributors | Mechanical Engineering, Tian, Zhiting, Diller, Thomas E., Huxtable, Scott |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial 4.0 International, http://creativecommons.org/licenses/by-nc/4.0/ |
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