A 32-year MAE veteran, Professor S.A. Sherif stays at the cutting edge of thermal, fluid, and energy sciences

The proudest moment of Dr. S.A. Sherif’s career came in 2001. 

After receiving his bachelor’s and master’s degrees from Alexandria University in Egypt, coming to the United States in 1978, earning his Ph.D. from Iowa State University, and being a professor at Northern Illinois University, the University of Miami, and eventually UF, he was honored with the Kuwait Prize for applied sciences. This is one of five categories in which Arab scientists are recognized.  

However, to find the moment he cites as his happiest, you’d have to rewind 10 years back to 1991, when his long and winding whirlwind of a journey finally landed him at the place he’s now called home for over three decades.

“My happiest moment was when I joined the faculty of the University of Florida,” he said. “I continue to be proud, serving on the MAE faculty at the University of Florida. I especially enjoy working with so many capable MAE staff members who make performing my teaching and research duties so much easier than otherwise.”

Sherif’s research has seven main areas of focus in the fields of thermal, fluid, and energy sciences: frost formation, aircraft icing, thermodynamic design optimization, two-phase high-speed fluid dynamics, heat pumps employing expansion devices with output work, hydrogen energy, and solar energy. 

Sherif’s research group was the first in the world to use large walk-in freezers with supersaturated air to experimentally investigate frost and ice formation, and couple that with the theory of applied psychrometrics. Air becomes supersaturated when it is unable to carry the amount of moisture present in a confined space at the current temperature. When this happens in a freezer, it enables the formation of airborne ice crystals, which accelerates frost formation on the walls and ceiling. This is bad because it increases the frequency at which it’s necessary to defrost the freezer coils, and it’s a common problem for walk-in freezers due to warmer outside air being frequently introduced with in-and-out traffic. Funded by several ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) research contracts over a 10-year period, Sherif’s group built a unique experimental facility in the UF HVAC Laboratory to study this issue. The seminal research they conducted there on the psychrometrics of frost formation in freezers, including a procedure they developed to prevent frost formation in supersaturated conditions, was published in the ASHRAE Handbook—Refrigeration and in the International Journal of Refrigeration. His group continues to research frost formation on multi-row deep freezer coils, studying both supersaturated and subsaturated air.

The area of aircraft icing focuses on ice accumulation on the wings of aircraft in supercooled clouds, especially in the presence of supercooled large droplets (SLDs). Sherif’s group is developing computer models to capture the effects of SLDs and ice crystals on a variety of different aircraft wing designs. Understanding the physics and aerodynamics of this is crucial to preventing ice accumulation on aircraft wings when the aircraft is flying through clouds. Sherif was inspired to pursue this area of study after spending the summer of 1994 on the Arnold Air Force Base in Tennessee, which houses the largest and most advanced complex of flight simulation test facilities in the world.

Thermodynamic design optimization of thermal systems requires a mix of second-law thermodynamic analysis, economics, and mathematical optimization tools to maximize the performance of thermal systems under certain constraints. This is typically approached through calculus-based optimization or discrete optimization methods. Research in this area helps the development of techniques to design thermal systems in the most efficient ways (for example, designing them to be as cheap, small, fast, or energy-efficient as possible). Practical uses of this type of research range from roof-spray cooling systems to solar energy collection to heating and air conditioning to the optimal allocation problem in designing heat exchangers.

The study of two-phase high-speed fluid dynamics is relevant to many real-world applications, such as the design of spacecraft environmental control systems with no moving parts and the design of high-speed impact cleansers that clean space shuttle components with minimal water consumption. Spacecraft environmental control systems are space-based and use jet pumps and ejectors to produce power and cooling with solar energy. High-speed impact cleansers use a mix of compressed nitrogen and compressed liquid water through a converging-diverging nozzle to impact the target surface at supersonic speeds (like a sandblaster, but with small amounts of water). Sherif’s interest in this field was sparked during his experiences working at the Kennedy Space Center in 1993 and the Marshall Space Flight Center in 1996 and 1997, both of which are NASA facilities. 

Sherif began working with heat pumps employing expansion devices with output work in 2004, when he acquired a research contract from the Air Force Research Laboratory to design and build a laboratory-scale heat pump unit with a rotary-vane expander in place of the expansion valve. The Air Force invests in the development of portable and deployable heat pump units with vane expanders because they are lighter and more efficient than conventional heat pumps, and are thus better for use in battle.

Sherif’s work with hydrogen energy focuses on the production of hydrogen using solar energy and on storing it in liquid form. Funded largely by NASA and the US Department of Energy (DOE), he has also done extensive work on liquid hydrogen storage and gas liquefaction involving both conventional and magnetic liquefiers. The DOE is emphasizing hydrogen as a priority as it explores alternate sources of energy for the US, as the idea of a “hydrogen economy” is gaining prominence worldwide. Sherif was part of the first renewable hydrogen energy research program in the country, where he worked on a DOE grant as a faculty member at the University of Miami in 1988. Since then, he has served as a subject editor for the International Journal of Hydrogen Energy, is currently a member of the Advisory Board of Directors of the International Association for Hydrogen Energy and was the primary editor of the Handbook of Hydrogen Energy.

In the area of solar energy, Sherif’s group studies the heat transfer and thermodynamics of solar-powered multi-generation systems. The group has developed systems with optimized heat transfer enhancements in parabolic trough collectors with optical enhancements and secondary reflectors, as well as novel multi-generation systems with adjustable cooling-to-power ratios. Sherif’s group has also succeeded in highlighting issues and limitations of the performance indices used to evaluate the efficacy of multi-generation systems, and has worked to develop methods for computing the relative saving ratios of energy and exergy, which are better metrics for system effectiveness.

In addition to all his research, Sherif underscores his relationships with students, Ph.D. candidates and undergrads alike, as being among the most gratifying aspects of his job.

“I love working with and guiding my Ph.D. students,” he said. “I also love teaching large undergraduate classes, especially in heat transfer and in thermodynamics.”

Helping students prosper and setting the foundations for their future accomplishments is one of Sherif’s primary aims at this point in his career.

“My goal is to see my many Ph.D. students successfully complete their degree requirements and start successful and productive careers in academia, industry, and national labs,” he said.