As rarified gasses diffuse through pores, gas molecules interact with the pore walls. When pore diameter is on the order of the mean free path of the diffusing species, these molecule-wall interactions begin to retard the transport rate; the so-called Knudsen Effect. However, as pore diameter becomes much smaller than the mean free path, transport rates may again increase due to nano-scale effects. While this behavior has been demonstrated via computational models, it has not been verified experimentally at atmospheric pressure with working fluids relevant to practical engineering design (i.e., water vapor). In fact, initial experimental evidence suggests that water vapor diffusing through confined nano-pores may not behave as the computational models suggest. To understand how water vapor moves through pores less than 10 nm in diameter, the TFS Group @ UNT has developed an apparatus to probe water vapor transport processes in nano-porous membranes.

One of the most effective methods for removal of excess heat from surfaces is evaporative cooling. Porous membranes overlaid on hot, damp surfaces modulate the liquid-vapor evaporation front location with channels treated to be hydrophilic or hydrophobic. With proper design, porous membrane overlays can enhance evaporative cooling rates. The TFS Group @ UNT is researching hydrophilic pores to wick heat-carrying liquid away from hot surfaces faster than convection acting alone. This hot fluid then evaporates from the membrane surface, offering further cooling. We are also designing multi-functional systems that provide integrated cooling with some other useful property (i.e., blast protection, chemical-biological agent protection, structural rigidity). One potential application for our nano/micro-pore evaporative cooling research is self-cooling body armor for Soldiers.

The autogyro is an aircraft whose lifting mechanism is an un-powered rotor. Although similar in appearance to a helicopter rotor, the autogyro’s main rotor operates by a different aerodynamic principal: autorotation. Despite the autogyro’s robust flight stability against stall, this aircraft type has incurred a high accident rate, compared to other sport aircraft. Many accidents arise from nose-down pitching movements in low-speed forward flight, where a brief reduction in rotor through flow causes its speed to decay. The TFS Group @ UNT utilizes experimental autogyro models in a wind tunnel to recreate flight instabilities experiences by real aircraft. This research has led to improved aircraft design and enhanced flight safety.

Our data suggest that significant pitch control can be achieved for autogyros in low-speed forward flight by the addition of slip-stream-mounted elevators. These control surfaces could be used by a pilot for enhanced, delicate pitch control in the minimum straight-and-level speed flight regime, improving controllability.

A description of this research area is coming soon.

A description of this research area is coming soon.

Success in realizing miniaturized Brayton cycles is hampered by high RPM required to achieve efficient turbine operation. This problem can be eliminated by replacing MEMS axial turbines with Telsa turbines, which utilize fluid shear to generate torque and power. While inefficient in the macro-regime, Telsa turbines exhibit excellent performance at low Reynolds Number where fluid viscous forces dominate. We are using an analytical model to verify performance of tiny experimental Tesla turbines, fabricated using conventional machining processes. The project outcome, a successful micro-turbine design, will revolutionize portable energy for military, homeland security, portable electronics, and remote power applications.

Currently, solar photovoltaic (PV) installations are sized as large as economically possible, with inverters generating alternating current (AC) and surplus electrons fed to the grid. By eliminating the inverter and utilizing PV-generated direct current (DC) to drive DC loads, inversion inefficiencies are eliminated and economy is improved. Under this DC-to-DC paradigm, PV sizing rules change, favoring peak power matched to peak building load demand. However, economic benefit may arise by over-sizing a PV array peak output to exceed the building load. An optimization problem arises: is it advantageous to sacrifice a fraction of peak power to generate more electrons during off peak times? Simulation with experimental verification is ongoing to discover the PV sizing rules leading to optimized economics for DC-to-DC solar installations.