Engineering topics

Fowlis, William W.

Publications and source records attributed to Fowlis, William W..

3 records

NASA NTRS1991

Particle orbits in a rotating liquid

The motion of small spherical particles under gravity, in a viscous fluid rotating uniformly about a horizontal axis, is investigated. Formulations and solutions are obtained for the particle orbit problem and the rotation rate optimization problem. It was found that the rotation rate which maximizes the fraction of the reactor cross-section area containing particles that will not spiral out to the wall in the experimental time (for heavy particles), or that have spiraled inward without hitting the wall (for light particles) is close to 1 rpm.

Roberts, Glyn O.↗

NASA NTRS1988

Experimental and theoretical analysis of the rate of solvent equilibration in the hanging drop method of protein crystal growth

The principles of the hanging-drop method of crystal growth are discussed, and the rate of water evaporation in a water droplet (containing protein, buffer, and a precipitating agent) suspended above a well containing a double concentration of precipitating agent is investigated theoretically. It is shown that, on earth, the rate of evaporation may be determined from diffusion theory and the colligative properties of solutions. The parameters affecting the rate of evaporation include the temperature, the vapor pressure of water, the ionization constant of the salt, the volume of the drop, the contact angle between the droplet and the coverslip, the number of moles of salt in the droplet, the number of moles of water and salt in the well, the molar volumes of water and salt, the distance from the droplet to the well, and the coefficient of diffusion of water vapor through air. To test the theoretical equations, hanging-drop experiments were conducted using various reagent concentrations in 25-microliter droplets and measuring the evaporation times at 4 C and 25 C. The results showed good agreement with the theory.

Fowlis, William W.↗

NASA NTRS1987

A comparison of the reduction of convection by a magnetic field and a microgravity environment

The relative effectiveness of magnetic damping and the microgravity environment of space for suppressing buoyancy driven convection in semiconductor crystal melts was analyzed using flow estimates based on the convection driven by a single vertical heated plate. The results show that convection can be more than a factor of 10 weaker in space. If a strong magnetic field is applied in space, the convection can be reduced by a factor of 1000 over similarly magnetically damped convection in an earth-bound laboratory. The heated plate estimates were checked by comparing them with exact boundary layer theory for the nonmagnetic problem in the same configuration and they were found to be accurate.

Fowlis, William W.↗