| Author: | Tsang, Hin Fai Andrew |
| Title: | Development of an adaptive food preservation system (AFPS) for management of total energy expenditure |
| Advisors: | Yung, Winco (ISE) |
| Degree: | Eng.D. |
| Year: | 2018 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Food -- Preservation Food -- Packaging |
| Department: | Faculty of Engineering |
| Pages: | xxi, 219 pages : color illustrations |
| Language: | English |
| Abstract: | This research project proposes the system and conceptual design of an Adaptive Food Preservation System (AFPS) and demonstrates how it manages the total energy expenditure in household food preservation. AFPS is motivated by the fact that efforts towards current energy efficiency in household food preservation predominantly focuses, directly or indirectly, on compressor efficiency of refrigerators while overlooking other opportunities. The total energy expenditure in food preservation can be broken down into the energy used in food manufacturing and logistics along a Cold Chain and those used in household refrigeration. If food is wasted during their shelf life in a refrigerator before being consumed, both of these types of energy will be lost. In addition, ensuring that foods are consumed before expiry is an effective way to manage total energy expenditure. Double thermal insulation is made up of primary insulation (AFPS packages) and secondary insulation (compartment wall and space). These are both active in that they can respond dynamically to different food characteristics, user requirements, and varying ambient conditions. The unique characteristic of the AFPS package is that customized temperature operations (fast freezing, long term low temperature maintenance, defrosting, and thawing) is provided to individual food items. As secondary insulation, the compartment wall and space together with recycled cold air from AFPS packages serve as a buffer between the ambient and the AFPS packages. This buffer reduces the thermal gradient between the food inside the packages and their immediate environment (compartment space), hence helping to minimize food storage temperature and its fluctuation. An Intelligent Control System is proposed to coordinate with all sub-systems in managing the total energy expenditure. Despite the significant effort of refrigeration industries and researchers, technologies of legacy refrigerators still cannot close all the gaps which cause losses of refrigeration energy and a number of other issues. The limitations and issues relate to thermal insulation, temperature operation, and user behaviour are the gaps that cause penalties to the total energy expenditure. These gaps can be categorized into the unproductive consumption of energy and energy wastage. Unproductive consumption of energy occurs when refrigeration is greater than what is absolutely necessary to pull down food temperature to a desirable level. One example is that not only foods but also the food container and the compartment wall are also refrigerated. Energy wastage occurs when energy is used while it is not necessary at all. One example is that compressor has to operate while it is not necessary. To address the above gaps, a system and conceptual design of AFPS is first proposed. Theoretical model analysis and experimentations are then executed to validate the effectiveness of key sub-systems. The primary insulation (AFPS packages), secondary insulation (compartment wall and space), and double thermal insulation as a whole, work together to reduce the unproductive consumptions and wastage. To validate the effectiveness of the primary insulation (AFPS package), theoretical and analytical models are proposed to predict package inlet and exit temperatures, freezing capacities, and freezing efficiencies. At 7 bar inlet pressure, the maximum available freezing efficiency, mean efficiencies with vacuum insulation and with ABS insulation of the AFPS Package and Vortex Tube Assembly are 6%, 4.66%, and 2.80%, respectively. AFPS technology consumes 0.18% in terms of time and 45% in terms of energy during fast freezing compared with what a typical household freezer consumes. To validate the secondary insulation (compartment wall and space), an optimal compartment temperature range was first calculated to reduce the thermal gradient (between foods and their immediate environment). This range was determined both theoretically and experimentally as between 10°C to 15°C. Theoretical model analysis has resulted in a reduction of thermal gradient between the chiller and compartment by 69.6% (compared with refrigerators) while experimentation has demonstrated a 50.2% reduction. Sources of deviation and the corresponding rectification are proposed to raise the reduction percentage. Experimentation has also demonstrated that recycled cold air exiting the simulated compartment box can reach as low as 13°C and at 3.4 m/s to improve condenser cooling. When the primary and secondary insulation work together as double insulation, it provides opportunities in food quality improvement when compared with today's refrigerators in which food items stack up on each other. Theoretical analysis results show that for a three/four-star rating, during one compressor on/off cycle, cooling time is reduced by 75% while warming time is increased by 1.81 times which translates into reduction of energy wastage and other benefits. Experimentation has resulted in 31% reduction and 2.91 times increase. For two-star rating, analytical results in cooling time reduction are 39% and 0.78 times, respectively, while the experimental results are 5% and 10.56, respectively. It can be concluded that the proposed system and conceptual design AFPS can effectively manage the total energy expenditure of food preservation by minimizing unproductive consumptions of energy and energy wastages. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 991022148525203411.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 4.55 MB | Adobe PDF | View/Open |
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