Session: 16-01: Poster Presentations

Paper Number: 140785

140785 - Improving Heat Spreading in Adsorbent Beds in Adsorption-Based Air Conditioning Systems 

Abstract: 

Adsorption-based air conditioning systems provide an attractive alternative to traditional vapor compression-based air conditioning systems in residential applications since adsorption-based systems (1) use water instead of a high-GWP fluid as the refrigerant, and (2) do not run on electric power, instead relying on an external heat source to desorb water molecules from at least one adsorbent bed in the system. These desorbed molecules then draw heat from an inside airspace via a downstream cooling unit as they are re-adsorbed into the adsorbent bed. At issue is that the adsorbent bed contains a low thermal diffusivity, thereby requiring a large generation temperature from the external heat source to effectively desorb water molecules throughout the adsorbent bed. This study therefore explores the improvement of the effective thermal diffusivity of the adsorbent bed through the addition of highly conducting additives. This project first explores the available common effective thermal conductivity models for adsorbent beds and the ability to reproduce results from these models to match existing experimental data. Next, extensions of the bed model are developed to integrate the effect of highly conducting additives, effectively creating a composite model with an enhanced thermal conductivity but a reduced area for molecular adsorption. A tradeoff therefore exists between the increased heat spreading ability and the increased size requirement of the overall adsorbent bed to compensate for the loss of adsorbent area. This tradeoff is explored in detail, demonstrating an optimal level of highly conducting additives to achieve the goal of minimizing the generation temperature. The method to explore this tradeoff is to develop a theoretical relation relating the adsorbent bed properties (geometry, thermal conductivity, bead diameter, and adsorbent area), and the thermal conductivity, aspect ratio, and volume fraction of additives. The amount of heat released from a point source is found as that which achieves the required desorption temperature throughout the entire bed, and the generation temperature is the temperature of the bed adjacent to the point source. Finite element modeling is used to replicate the theoretical temperature distribution to verify the implementation of both approaches. Then, the finite element models are adapted to indicate the potential for nonuniform additive distributions to further reduce the generation temperature in the adsorbent bed, including the use of optimization on the models to determine the proper distribution of additives to minimize generation temperature. The physical limits of these approaches to reduce generation temperature are concluded based on these analyses.

Presenting Author: Emily Sommers Villanova University

Presenting Author Biography: I am a graduate student in the Villanova University Masters program for Mechanical Engineering. I graduated Cum Laude with an undergraduate Bachelor of Science in Mechanical Engineering with a minor in Biomedical Engineering and a concentration in Solid Mechanics. I am passionate about making a difference in the world and firmly believe this project will do so.

Authors:

Emily Sommers Villanova University
Aaron Wemhoff Villanova University