SORPTION-BASED DEHYDRATION SYSTEMS: THEORY-TO-DEMONSTRATION

Author

Masoud Ahmadi, Michigan Technological UniversityFollow

Date of Award

2022

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Sajjad Bigham

Committee Member 1

Seong-Young Lee

Committee Member 2

Hassan Masoud

Committee Member 3

Kyle R. Gluesenkamp

Abstract

Dehydration or drying is one of the ubiquitous, often most energy-intensive, processes in various industrial, residential, and commercial applications, reflecting a large energy market size in the industrial and residential sectors. Conventional dryer systems utilizing either electric resistance elements or more commonly fossil fuels such as natural gas with a maximum COP (Coefficient of Performance) of 1 suffer from low energy efficiency. Existing condensing dehydration systems including heat pump dryers, however, need to significantly cool the air to achieve dehumidification. The added cooling and subsequent heating to return the air to the desired drying temperature consume substantial energy and thus reduce drying performance. As such, state-of-the-art fuel-driven clothes dryers suffer from sensible and latent (i.e., humidity) losses, mainly due to enthalpy losses associated with warm humid air leaving the dryer. The energy efficiency of a clothes dryer system can be potentially improved if part of the thermal energy, currently wasted, is captured. This dissertation introduces a novel sorption-based drying concept to overcome shortcomings that deteriorate energy efficiency in existing gas, electric, or heat pump dryer systems. The system employs a liquid-desiccant solution to directly capture air humidity, thereby allowing circulation of the air in a closed loop to achieve high drying energy efficiency. In other words, the system captures waste latent heat from the moisture produced during the dehydration process and reuses it to improve energy efficiency. First, a comprehensive quasi-steady-state thermodynamic modeling is developed to predict transient response and overall drying performance (i.e., time and energy metrics) of the proposed sorption-based dehydration concept employed for a clothes dryer application. The developed model considers the details of both the dryer unit and the sorption cycle. The analysis showed a drying time of 44 minutes and a specific moisture extraction rate (SMER) of 1.71 kgwater/kWh, reflecting a 112% energy improvement compared with stateof-the-art gas clothes dryers. The promising results showed the potential of the sorptionbased dehydration system to take advantage of the available waste thermal energy and improve energy efficiency.At the heart of the proposed sorption-based drying system, a liquid-desiccant-based dehumidifier module is responsible for the dehumidification process. Existing liquiddesiccant-based air dehumidification systems suffer from a poor liquid flow distribution which deteriorates their moisture removal rate. In the proposed dehumidifier, the capillary forces and wickability effect of textured surfaces are altered to minimize the liquiddesiccant flow rate of the fully wetted state, thereby transforming the physics of interfacial desiccant flow distribution. At a water vapor pressure potential of 3 kPa and a solution flow rate of 2.8 g/s, experimental results indicated a moisture removal rate of 0.16 g/m2-s for a textured surface concept with a capillary length scale of 3 mm, a 28% improvement compared with that of smooth-plate dehumidifier surfaces. A high moisture removal rate of the textured surface at a low desiccant flow rate led to a high thermal efficiency of 0.75 at a water vapor pressure potential of 5.6 kPa and a lithium bromide (LiBr) flow rate of 2.8 g/s. Next, a liquid-desiccant-based dehumidification cycle was developed and integrated into a commercially available residential clothes dryer drum. Then, the performance of the system was fully investigated using the standard fabrics based on the DOE standard clothes dryer test procedure. The effect of sorption cycle working conditions such as desorber solution flow rate and desorber temperature were examined. The experimentally measured drying performance of the system showed a maximum combined energy factor (CEF) of 8.2 lbmdry-bone /kWh at a drying time of 70 minutes. The energy efficiency offered is significantly higher than standard clothes dryers. Also, the primary energy efficiency of the proposed fuel-driven system is more than two times better than the most advanced vapor compression heat pump clothes dryers (VCHP-CDs). The results of this dissertation showed the great promise of the sorption-based dehydration technology. The sorption-based drying concept was comprehensively examined through detailed modeling and extensive experimentations. Further research is needed to improve the reliability of the concept, reduce the overall cost of the system, and realize the potential of the concept for other industrial drying applications.

Recommended Citation

Ahmadi, Masoud, "SORPTION-BASED DEHYDRATION SYSTEMS: THEORY-TO-DEMONSTRATION", Campus Access Dissertation, Michigan Technological University, 2022.

https://doi.org/10.37099/mtu.dc.etdr/1495