Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item ADVANCED ABSORPTION MATERIALS AND THEIR APPLICATION IN REFRIGERATION(2021) Zheng, Chaolun; Yang, Bao BY; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)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 evaporation 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.Item Performance Investigation of CHP Equipment(2005-11-03) Bian, Ji; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Cooling Heating & Power systems for Buildings (BCHP) are attracting more attention due to their advantages as compared to conventional energy systems. As a developing technology, there are still problems to be solved. Fuel flexibility and dynamic response between different machines in the system are two of the main issues to be investigated. This study presents research conducted on a BCHP system that is composed of a microturbine, an absorption chiller and a solid desiccant unit that are driven by the microturbine's exhaust gas to provide cooling and dehumidification. It demonstrates the feasibility of operating the microturbine that is originally designed for natural gas on propane and analyzes the reasons for the efficiency reduction when operating on propane. It further presents a model that describes the transient behavior of the absorption chiller, which requires a much longer period to reach its steady state compared with the microturbine.Item THE DEVELOPMENT OF AN AIR-COOLED ABSORPTION CHILLER CONCEPT AND ITS INTEGRATION IN CHP SYSTEMS(2004) Liao, Xiaohong; Radermacher, Reinhard K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on the feasibility, crystallization issues, and the integration of LiBr-H2O air-cooled absorption chillers into Cooling, Heating and Power (CHP) systems. The concept of an air-cooled system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr-H2O solution then becomes the main issue in the operation of the unit, since the air-cooled absorber tends to operate hotter than the water-cooled absorber due to the relative heat transfer characteristics of the coolant leading to crystallization of the working fluid. Differently from the conventional approaches to air-cooled absorption chillers, novel temperature control strategies in conjunction with a specialized application is proposed. This prevents crystallization but presents unique system integration challenges and opportunities. A model to accurately reflect the thermodynamic characteristics of air-cooled absorption chillers and to facilitate control is developed as part of this research, and field experiments that simulate air-cooled conditions with a water-cooled absorption chiller, which was driven by the waste heat of a microturbine, were conducted to validate the feasibility of the air-cooled concept and the accuracy of computer model. While CHP provides a good opportunity for the application of air-cooled absorption chillers, system integration issues need to be investigated. The capital cost of CHP equipment and the load fluctuation of a commercial building restrict the advantage of designing a unit sized for peak load. Therefore, the conventional Heating Ventilation and Air Conditioning (HVAC) system is needed to pick up the residual loads. Thus, the result of an extensive system integration analysis is that CHP should be arranged in series with the HVAC system to ensure obtaining more operating hours at its full capacity, so that the cost savings achieved through the recovery of waste heat are fully realized to repay its higher initial capital cost. The primary energy savings are presented for all potential configurations. As a part of this research a fully integrated CHP system has been installed and instrumented at the Chesapeake Building. It is a commercial office building on the University of Maryland campus. The experimental setup, data processing, and experience gained are detailed here. Based on the computer simulation, extensive experiments, first hand installation, operation and maintenance experience, valuable guidelines on the integration of an air-cooled absorption chiller in CHP are developed. All the guidelines are also applicable to water-cooled absorption chillers.