Focus Area 1: Frost and Ice Formation on Cold Surfaces
Dr. SA Sherif’s research group is the first in the world investigating frost and ice formation in supersaturated air employing psychrometric theory. This has a direct impact on preventing frost and ice formation in large walk-in freezers. They constructed a unique experimental facility in the Masur HVAC Laboratory at the University of Florida for that purpose. Several research contracts were funded by ASHRAE over a span of 10 years. Results of that research are seminal and were permanently included in the ASHRAE Handbook – Refrigeration. Dr. Sherif developed a procedure that refrigeration engineers and large walk-in freezer operators should follow to prevent the formation of ice crystals inside the freezer space and hence avoid the need to frequently defrost the coils inside the freezer. Another related area to frost formation is ice accretion on aircraft wings in supercooled clouds, especially when supercooled large droplets (SLDs) are present in the cloud. When dealing with the SLD regime, additional dynamical effects such as droplet splashing, droplet deformation, and droplet break up should be considered as they influence the local ice collection efficiency on the surface. During the breakup process, a large droplet is typically unstable and thus tends to break up into several smaller stable droplets due to the aerodynamic forces. Dr. Sherif’s group has developed sophisticated computer models that can capture these and other complex effects during the accretion process. The review paper at this link https://doi.org/10.1115/1.4070930 describes the important research issues in this focus area. In 2024, Dr. Sherif was invited by the Royal Society of London to guest edit a theme issue on Heat and Mass Transfer in Frost and Ice in Philosophical Transactions of the Royal Society – A. This is the oldest scientific journal in existence and is home to 17 of Isaac Newton’s papers. The theme issue was published on July 17, 2025, and the following links provide access to the relevant frost and ice work of Dr. Sherif and his research team that appeared in the theme issue: https://doi.org/10.1098/rsta.2024.0370 and https://doi.org/10.1098/rsta.2024.0367 and https://doi.org/10.1098/rsta.2024.0366 and https://doi.org/10.1098/rsta.2024.0368
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. Among the problems that Dr. Sherif and his team investigated are optimization of district heating systems using search methods https://doi.org/10.1002/(SICI)1099-114X(199703)21:3<233::AID-ER250>3.0.CO;2-H, optimization of roof spray cooling systems using the Transfer Function method https://doi.org/10.1002/(SICI)1099-114X(199812)22:15%3C1337::AID-ER433%3E3.0.CO;2-G, optimization of refrigerant mixtures for maximum refrigeration system coefficient of performance https://doi.org/10.1115/1.2906108, optimization of steam-jet refrigeration systems https://doi.org/10.1002/(SICI)1099-114X(199812)22:15%3C1323::AID-ER430%3E3.0.CO;2-W, the heat exchanger inventory problem https://doi.org/10.1115/1.2906108, optimization of swimming pool heating systems https://doi.org/10.1016/0360-5442(92)90005-K, optimization of air-conditioning systems of aquatic centers https://doi.org/10.1002/(SICI)1099-114X(199707)21:9<823::AID-ER303>3.0.CO;2-Q, performance of absorption chillers and heat pumps https://doi.org/10.1002/er.738, effect of refrigerant charge on the performance of air-conditioning systems https://doi.org/10.1002/er.719, and optimization of multi-stage vapor-compression refrigeration systems.
Focus Area 3: Two-Phase High-Speed Fluid Dynamics with Applications to Spacecraft Thermal Management
Dr. Sherif and Dr. Lear developed a thermal management system with no moving parts employing jet pumps based on a cycle that they invented called the Solar Integrated Thermal Management and Power (SITMAP). They and their team built and tested a laboratory-scale system and generated experimental data for the performance of the system under conditions like those found in space. A space-based thermal management system with no moving parts is needed to minimize the frequency of system maintenance. NASA-Glenn funded some of that work. They also worked closely with NASA-Marshall in developing the system. Examples of published work in this area includes the following: https://doi.org/10.2514/1.13824 and https://www.jstor.org/stable/44718486 and https://doi.org/10.2514/2.6074 and https://doi.org/10.2514/2.5778 and https://doi.org/10.2514/1.T4240 and https://doi.org/10.1243%2F0954406021525287 and https://doi.org/10.1002/1099-114X(200012)24:15%3C1373::AID-ER662%3E3.0.CO;2-M and https://doi.org/10.1016/S0020-7403(98)00123-4
Focus Area 4: High-Speed Impact Cleansers using a Mixture of Compressed Nitrogen and Compressed Water
Dr. Sherif and Dr. Lear helped develop two-phase high-speed impact cleansers employing a mixture of a gas (e.g., compressed nitrogen at 400psia) and a condensed phase substance (e.g., compressed water at 300psia) in a supersonic tube/nozzle assembly. The two-phase mixture exits the cleansing device at three-and-half times the speed of sound and impacts the surface to be cleansed, with the condensed phase particles acting as cleansing agents (like sandblasting). They developed mathematical models providing insights into the emulsification mechanism in surface cleansing of space shuttle and electronic components. They worked closely with NASA-Kennedy in developing that system. Examples of published research in this area includes the following: https://doi.org/10.1115/1.483240 and https://doi.org/10.1115/1.483221 and https://doi.org/10.1016/S0094-5765(99)00181-2 and https://doi.org/10.1016/S0094-5765(99)00183-6 and https://doi.org/10.1016/S0094-5765(97)00033-7 and https://doi.org/10.1016/S0094-5765(97)00032-5 and https://doi.org/10.1016/S0093-6413(98)00079-2
Focus Area 5: 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 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. Examples of research in this area can be found at the following links: https://doi.org/10.1115/1.4003075 and https://doi.org/10.1016/j.applthermaleng.2009.11.010 and https://doi.org/10.1115/1.2830854 and https://doi.org/10.1115/1.2906034 and https://doi.org/10.1115/1.4001567
Focus Area 6: 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. Examples of this research can be found at the following link: https://doi.org/10.1115/1.4001571
Focus Area 7: Energy Efficiency and Productivity Improvement of Manufacturing Facilities
The DOE-funded Industrial Training and Assessment center which Dr. Sherif directs is tasked with increasing the energy efficiency, improving productivity, and better managing waste of industrial and manufacturing facilities in Florida as well as training the next generation of energy engineers in these areas. Since its establishment, the UF Industrial Training and Assessment Center has completed 586 assessments and made 4936 recommendations that resulted in 15.63 Tera BTUs of energy savings and $186.74 million in cost savings for facilities in Florida. The Center has also trained and certified 202 students, many of whom have taken careers in the energy sector. Dr. Sherif and his students have also developed new performance indices for multigeneration systems, many of which are used on site in these facilities. Multigeneration systems are thermal systems that simultaneously produce more than one product (e.g., cooling, heating, power, water). They identified the issues and limitations related to the performance indices currently used to evaluate the efficacy of these systems and developed new and novel methods for their evaluation based on computing the relative saving ratios of energy and exergy. This has a direct impact on energy efficiency and energy pricing. A paper in the prestigious ASHRAE Journal appeared in January 2026 to addresses this issue. Examples of research aimed at improving the energy efficiency of systems and components in manufacturing facilities can be found at this link: https://doi.org/10.3390/en18195135
Focus Area 8: Hydrogen Energy
Dr. Sherif was among the first DOE-funded renewable hydrogen research group (four universities) in 1988 under the direction of the Solar Energy Research Institute, where he headed the team charged with liquid hydrogen production and storage. He and his students developed conventional and unconventional (magnetic and hybrid) hydrogen liquefiers (https://doi.org/10.1016/0360-3199(94)90135-X) including the Active Magnetic Regenerative (AMR) liquefier https://doi.org/10.1016/S0011-2275(00)00039-4. They worked on the first 0.1 ton/day AMR liquefier built by Astronautics Corporation of America. They also worked on liquid hydrogen storage (https://doi.org/10.1115/1.2905997) and (https://doi.org/10.1115/1.2905998) and https://doi.org/10.1016/0360-3199(92)90131-F. and on slush hydrogen storage https://doi.org/10.1016/0360-3199(94)90002-7. Dr. Sherif is the primary editor of the one-and-only Handbook of Hydrogen Energy, https://doi.org/10.1201/b17226. Dr. Sherif was among the first three Associate Editors for the International Journal of Hydrogen Energy, which now publishes 100 issues/year (https://www.sciencedirect.com/journal/international-journal-of-hydrogen-energy/issues).
Focus Area 9: Heat and Mass Transfer in Minichannels and Microchannels
Dr. Sherif and his group did fundamental studies of heat transfer characteristics of two-phase slug flow in microchannels. Despite the existence of many studies on two-phase flows in microchannels, most efforts seem to have failed in correctly capturing the flow physics, especially those pertaining to the slug flow regime characteristics. The presence of a thin liquid film in the order of 10 microns around the bubble is a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field and heat transfer characteristics. In the simulations reported by Dr. Sherif and his group, the film is successfully captured, and a very high local convective heat transfer coefficient is observed in the film region. A strong coupling between the conductive heat transfer in the solid wall and the convective heat transfer in the flow field is observed and characterized. Results showed that unsteady heat transfer through the solid wall in the axial direction is comparable to that in the radial direction. Results also showed that a fully developed condition could be achieved fairly quickly compared to single-phase flows. The fully developed condition is defined based on the Peclet number (Pe) and a dimensionless length of the liquid slug. Local and time averaged Nusselt numbers for slug flows are reported for the first time. Dr. Sherif and his group found that significant improvements in the heat transfer coefficient could be achieved by short slugs where the Nusselt number was found to be 610% higher than in single-phase flows. The work revealed new findings related to slug flow heat transfer in microchannels with constant wall heat flux. Examples of this work can be found at the following links: https://doi.org/10.1016/j.ijheatmasstransfer.2011.03.040 and https://doi.org/10.1615/ComputThermalScien.2024049784