Dissertation Defense – Chaolun Zheng


Date/Time: January 12, 2021 2:00PM – 4:00PM

Prof. Bao Yang (Chair)
Prof. Amir Riaz
Prof. Peter B. Sunderland
Prof. Teng Li
Prof. Chunsheng Wang (Dean Representative).

Zoom Link: https://umd.zoom.us/j/94210112455?pwd=MjVWRS9TVXR4cENFb2t3aTlTR0ljUT09

Abstract: Absorption chillers, which utilize heat as the primary energy input, have been considered a more environment-friendly alternative to vapor-compression cooling systems. The thermodynamic properties of absorbent generally limit the performances of absorption chillers. In the first part of the dissertation, a new method to determine the molecular interaction energies is developed. The molecular interaction energies can be related to many macroscopic thermodynamic properties, such as desorption heat and hygroscopicity. From the studies on ionic liquid absorbents, it is found that a shorter alkyl group in anion would produce higher interaction energy with water, thus increasing the hygroscopicity. In contrast, the fluorination of anion would reduce its interaction energy with water, thus reducing the hygroscopicity. A new formula is also developed using interaction energies to predict the desorption heat of absorbents, which is an essential parameter for evaluating absorbent performances. The second part of the dissertation focuses on the development of a microemulsion-based absorption chiller consisting of an electrostatic desorber, a nozzle-based absorber and an evaporator. Due to the tiny droplet size, it is thermodynamically challenging to regenerate the absorbed water in a liquid form from a microemulsion state. The electrostatic desorber would first utilize heat to transform the microemulsion absorbent into a macroemulsion state. The voltage is then applied to the absorbent to expedite the regeneration. Therefore, the electrostatic desorber can regenerate the absorbed water in a liquid form, which eliminates the latent heat requirement, offering the potential to improve energy efficiency. Inspired by the honeycomb shape, electrodes in the desorber are arranged in a multi-hexagon pattern, enabling a large desorber volume without increasing the voltage amplitude. The potential cooling power is improved by over 50 times compared to the original single-electrode desorber. The nozzle-based absorber&evaporator system utilizes nozzles to generate microemulsion absorbent and water in small droplet size to enhance the absorption and evaporating process.  Combining the electrostatic desorber and the absorber&evaporator system, the complete absorption chiller could run continuously and achieve a cooling power of about 100 W.