A miniature reciprocating expander is being developed as part of a larger program to develop a heat actuated heat pump for portable applications. By utilizing the higher energy density of liquid hydrocarbon fuels relative to batteries, a heat actuated heat pump would be able to provide cooling for much longer than motor driven units of equal weight. A prototype expander has been constructed and demonstrated to produce up to 22 W of shaft power at 2500 rpm using 60 psig, room temperature nitrogen as the input. Assuming adiabatic conditions, the expander appears to operate at up to 80% isentropic efficiency. However, when heat inflow to the expander is accounted for, the resulting polytropic efficiency is about 10% lower. In addition to experimental results, models of expander performance with different loss mechanisms are presented. These mechanisms include over- and under-expansion, in-cylinder heat transfer, clearance volume, friction, and valve pressure drop. / Graduation date: 2005

Miniature energy and chemical systems (MECS) are miniature thermal, fluid, and chemical devices in the mesoscale size range between a sugar cube and a human fist. MECS take advantage of improved rates of mass and heat transfer that have been observed at the microscale. There are many potential applications for MECS, including manportable cooling and decentralized chemical processing. However, this potential has not been realized due to limitations in microfabrication. MECS devices require: 1) the fabrication of complex geometries incorporating microscale features; and 2) the thermal, mechanical and chemical properties of engineering metals. This thesis centers on developing a process for producing high-aspect-ratio, MECS devices in stainless steel. In order to achieve this goal, laser ablation and diffusion bonding were employed in a metal microlamination (MML) process. The process involves stacking and bonding a series of laminates with low-aspect-ratio features to produce a composite device with high-aspect-ratio features (20:1). Laser ablation was used to form many laminates of 0.003" 302 stainless steel. These laminates were then joined via diffusion bonding. The process developed in this thesis is unique in that it: 1) permits the MECS designer greater freedom in specifying microchannel widths; and 2) has produced microscale features in excess of 20:1 aspect ratio. Microchannels and microfins in excess of 20:1 aspect ratio were fabricated in stainless steel using this method. Resultant microchannels were tested by flowing air through them at various flow rates and measuring the resulting pressure drop. Experimental results were compared with theoretical calculations and other technical literature. Findings suggest that the preliminary efforts to build a MECS device resulted in significant air blockage in the microchannel passageways. Sources of this blockage include bent fins, warpage and misalignment among others. Further process refinements are needed to prove the economic viability of this process. / Graduation date: 1998

An experimental and analytical study of a microchannel ammonia-water desorber was conducted in this study. The desorber consists of 5 passes of 16 tube rows each with 27, 1.575 mm outside diameter x 140 mm long tubes per row for a total of 2160 tubes. The desorber is an extremely compact 178 mm x 178 mm x 0.508 m tall component, and is capable of transferring the required heat load (~17.5 kW) for a representative residential heat pump system. Experimental results indicate that the heat duty ranged from 5.37 kW to 17.46 kW and the overall heat transfer coefficient ranges from 388 to 617 W/m2-K. The analytical model predicts temperature, concentration and mass flow rate profiles through the desorber, as well as the effective wetted area of the heat transfer surface. Heat and mass transfer correlations as well as locally measured variations in the heating fluid temperature are used to predict the effective wetted area. The average wetted area of the heat and mass exchanger ranged from 0.25 to 0.69 over the range of conditions tested in this study. Local mass transfer results indicate that water vapor is absorbed into the solution in the upper stages of the desorber leading to higher concentration ammonia vapor and therefore reducing the rectifier cooling capacity required. These experimentally validated results indicate that the microchannel geometry is well suited for use as a desorber. Previous experimental and analytical research has demonstrated the performance of this microchannel geometry as an absorber. Together, these studies show that this compact geometry is suitable for all components in an absorption heat pump, which would enable the increased use of absorption technology in the small capacity heat pump market.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Garimella, Srinivas; Committee Member: Allen, Mark; Committee Member: Fuller, Tom; Committee Member: Jeter, Sheldon; Committee Member: Wepfer, William. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains ix, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-75).

D. Tech. Mechanical Engineering, Mechatronics and Industrial Design / Heat pump drying (HPD) is a proven efficient method in food drying industries and more efficacious than traditional South African industrial and agricultural drying methods, providing high energy efficiency with controllable temperature, air flow, air humidity and large energy saving potentials. In the last decade the market of heat pump (HP) systems for water heating and space cooling/heating has been well developed in South Africa, but the development of heat pumps (HPs) for industrial and agricultural drying has been very slow. In the case of optimization of HPD systems, most literature studies concentrate on optimization of the drying parameters; however it is important to note that the overall performance of the HPD system, which consists of two subsystems, the HP and drying system, depends on working conditions and the two subsystems interact with each other. It is therefore important that the HP and the dryer should not be examined or optimized separately. Therefore, in this study, an air source heat pump system was designed, constructed, installed and analysed as a single integrated unit for drying fruits. The main objective of the study was to carry out experimental investigations on optimization of an air source heat pump for drying South African fruits.

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Drying is a common process in a number of industries. Products such as furs, wools, textiles, clay, timber, grains, fruits, and vegetables, at some stage, require drying. Review of the literature reveals that commercial dryers are highly inefficient due to various factors. One such factor is that commercial dryers are generally not equipped with heat recovery facilities. Heat pumps can provide a very efficient means of recovering both sensible and latent heat, hence energy loss can be substantially reduced. Furthermore, a heat pump always delivers more heat than the work input to the compressor. These two salient features render heat pump drying a premium alternative for efficient use and conservation of energy in drying industries.