Matching Items (2)
Filtering by
- All Subjects: Mechanical Engineering
- Member of: Theses and Dissertations
Description
Air conditioning is a significant energy consumer in buildings, especially in humid regions where a substantial portion of energy is used to remove moisture rather than cool the air. Traditional dehumidification methods, which cool air to its dew point to condense water vapor, are energy intensive. This process unnecessarily overcools the air, only to reheat it to the desired temperature.This research introduces thermoresponsive materials as efficient desiccants to reduce energy demand for dehumidification. A system using lower critical solution temperature (LCST) type ionic liquids (ILs) as dehumidifiers is presented. Through the Flory-Huggins theory of mixtures, interactions between ionic liquids and water are analyzed. LCST ionic liquids demonstrate superior performance, with a coefficient of performance (COP) four times higher than non-thermoresponsive desiccants under similar conditions. The efficacy of ionic liquids as dehumidifiers is assessed based on properties like LCST temperature and enthalpic interaction parameter.
The research also delves into thermoresponsive solid desiccants, particularly polymers, using the Vrentas-Vrentas model. This model offers a more accurate depiction of their behaviors compared to the Flory-Huggins theory by considering elastic energy stored in the polymers. Moisture absorption in thin film polymers is studied under diverse conditions, producing absorption isotherms for various temperatures and humidities. Using temperature-dependent interaction parameters, the behavior of the widely-used thermoresponsive polymer (TRP) PNIPAAm and hypothetical TRPs is investigated. The parameters from the model are used as input to do a finite element analysis of a thermoresponsive dehumidifier. This model demonstrates the complete absorption-desorption cycle under varied conditions such as polymer absorption temperature, relative humidity, and air speed. Results indicate that a TRP with enhanced absorption capacity and an LCST of 50℃ achieves a peak moisture removal efficiency (MRE) of 0.9 at 75% relative humidity which is comparable to other existing thermoresponsive dehumidification systems. But other TRPs with even greater absorption capacity can produce MRE as high as 3.6. This system also uniquely recovers water in liquid form.
ContributorsRana, Ashish (Author) / Wang, Robert RW (Thesis advisor) / Green, Matthew MG (Committee member) / Milcarek, Ryan RM (Committee member) / Wang, Liping LW (Committee member) / Phelan, Patrick PP (Committee member) / Arizona State University (Publisher)
Created2023
Description
This thesis explores the possibility of fabricating superconducting tunnel junctions (STJ) using double angle evaporation using an E-beam system. The traditional method of making STJs use a shadow mask to deposit two films requires the breaking of the vacuum of the main chamber. This technique has given bad results and proven to be a tedious process. To improve on this technique, the E-beam system was modified by adding a load lock and transfer line to perform the multi-angle deposition and in situ oxidation in the load lock without breaking the vacuum of the main chamber. Bilayer photolithography process was used to prepare a pattern for double angle deposition for the STJ. The overlap length could be easily controlled by varying the deposition angles. The low-temperature resistivity measurement and scanning electron microscope (SEM) characterization showed that the deposited films were good. However, I-V measurement for tunnel junction did not give expected results for the quality of the fabricated STJs. The main objective of modifying the E-beam system for multiple angle deposition was achieved. It can be used for any application that requires angular deposition. The motivation for the project was to set up a system that can fabricate a device that can be used as a phonon spectrometer for phononic crystals. Future work will include improving the quality of the STJ and fabricating an STJs on both sides of a silicon substrate using a 4-angle deposition.
ContributorsRana, Ashish (Author) / Wang, Robert Y (Thesis advisor) / Newman, Nathan (Committee member) / Wang, Liping (Committee member) / Arizona State University (Publisher)
Created2019