Research

Focus Area 1: Frost and Ice Formation on Cold Surfaces

This involves frost and ice formation in the supersaturated zone and other meta-stable states at low temperatures. A unique experimental facility has been constructed in the Masur HVAC Laboratory. Several research contracts were funded by ASHRAE in this area.

Focus Area 2: Thermodynamic Design Optimization of Thermal Systems

Research in this area requires a mix of second law thermodynamic analysis, economics, and mathematical optimization tools.  Typically, the problem involves maximizing either the first and second law performance of thermal systems under economic constraints employing calculus-based optimization or a discrete optimization method. This area is referred to as “exergoeconomics,” implying a mix of exergy or availability analysis and economics.

Focus Area 3: Two-Phase High-Speed Fluid Dynamics with Applications to Spacecraft Thermal Management

The thermal management part relates to space environmental control problems involving two-phase jet pumps and ejectors This topic also has relevance to two-phase high-speed impact cleansers. These employ a mixture of a gas and a condensed phase substance in a supersonic tube/nozzle assembly. The two-phase mixture exits the cleansing device at about four Mach and impacts the surface to be cleansed, with the condensed phase particles acting as cleansing agents. Drs. Lear and Sherif have developed mathematical models providing insights into the emulsification mechanism in surface cleansing of space shuttle and electronic components.  Both the space thermal management and the industrial cleansing problem are of interest to NASA (Kennedy, Marshall, and Glenn) which have funded several projects in these areas. Also, because NASA Kennedy is developing a niche in cryogenic applications in space, Drs. Lear and Sherif have adapted the space thermal management models that they have developed to space cryogenic applications.  Dr. Sherif’s background in cryogenic heat transfer (which he has developed through research on several DOE contracts early in his career) is relevant to this effort.

Focus Area 4: Distributed Power and CHP Systems

Drs. Lear and Sherif are co-inventors of a machine that employs a gas turbine coupled with an absorption refrigeration system. The invention (US Patent 7,472,550) has resulted in several research contracts. With a machine fully operational at the laboratory scale, the Florida Department of Environmental Protection awarded the University of Florida a multi-million dollar grant to build a demonstration model at the UF Energy Research and Education Park. The machine produces power, refrigeration, and water and is versatile enough to use a variety of liquid fuels.

Focus Area 5: Refrigeration and Air Conditioning with Rotary-Vane Expanders

Drs. Sherif and Lear have worked on modifying the design of heat pumps to incorporate rotary-vane expanders in place of conventional expansion valves. The Air Force Research Laboratory (ARL) has funded such an effort with the deliverable being a working deployable heat pump that the Air Force could further develop and use in the battlefield. For a typical air conditioning application, extraction of power during the expansion process allows an increase of about 10% in the coefficient of performance (COP) and a reduction of 1% in the refrigerant flow rate, for a fixed cooling load. The reduced flow would translate to a size/weight reduction of about 1.5%, which, coupled with a reduction in required power of 10%, makes this an attractive option. The idea of using a rotary-vane expander for work recovery is especially attractive if accompanied by the use of a rotary-vane compressor mounted on the same shaft.  These compressors are typically suited for refrigerating capacities up to 350 kW and pressure ratios up to 7. They are also suitable for use as booster compressors in low-level, double-stage large refrigeration systems with a compression ratio less than 3. Certain challenges remain in handling the two-phase fluid as it goes through the expander in addition to the problems associated with internal leakages that occur in tiny clearance spaces similar in nature to the flow in microchannels.