Miscellaneous research

Spray Cooling of Glass Fibers

Glass fibers are used as reinforcement in structural plastics, fabrics, printed circuit boards, and many other products. Such fibers typically have diameters in the range of 10 to 50 µm. These fibers are manufactured by drawing them in bundles of several hundred from a pool of molten glass at fiber speeds of up to 100 m/s. The fibers are sprayed with water to enhance their cooling rates and impart desirable physical properties. This project was aimed at characterizing the spray cooling process. The performance of the spray nozzles was one issue. Another was the interaction of the sprays with the airflow induced by the fiber bundle. The effect of spray on the temperature profile of the fiber boundary layer, and thus the fiber cooling rate, is of ultimate importance. Experimental studies of these processes were used in the development of analytical models that predict the fiber temperature. These results can be used to optimize fiber cooling and drying. This work was sponsored by PPG Industries, Inc.

D. Xiong and J.H. Lienhard V, “An Experimental Study of the Cooling of a Thin Glass Fiber During the Formation Process” Expt. Heat Transfer, 17(1):31–46, 2004. (doi) (preprint)
M. Sweetland and J.H. Lienhard V, “Evaporative Cooling of Continuously Drawn Fibers by Water Sprays,” Intl. J. Heat Mass Transfer, 43:777-790, 2000. (doi) (PDF file)

Thermal Control of a Planetary and Lunar Surface Exploration Micro-robot

A thermal control architecture design study was conducted for a novel robotic planetary and lunar surface exploration concept. The concept is based on the deployment of a large number of small spherical mobile robots over large areas, which employ hopping, bouncing and rolling as means of locomotion. The aim of the research is to prevent freezing and overheating of the robots, without compromising their mechanical and thermal reliability and stability. The proposed thermal control architecture relies on a low emissive silver surface coating and a low conductive silica aerogel insulation layer. This enables a single design to be used for several important potential explorations. The effects of a thermal control heat rejection mechanism, composed of a variable emittance coating and heat switch, are also studied in order to increase mission flexibility.

B.R. Burg, S. Dubowsky, J.H. Lienhard V, and D. Poulikakos, “Thermal Control Architecture for a Planetary and Lunar Surface Exploration Micro-robot,” 11th Conf. on Thermophysics Applications in Microgravity, Space Technology and Applications International Forum, Albuquerque, 11-15 Feb. 2007. (doi) (PDF file)

Laser Induced Fluorescence Measurements of Aerosol Deposition Rates

We have developed a laser-induced fluorescence technique for measuring the local deposition rates of aerosols of 0.5 to 100 µm diameter. This method uses liquid aerosols that are doped with a fluorescent dye; after deposition, the aerosol is excited and sampled via a focused fiber-optic probe. The LIF technique provides substantially better spatial resolution of the amount of deposition than can be obtained using more traditional methods. One focus of our work was on quantifying secondary factors that may confound the measurement, such as the slow statistical convergence of the deposited aerosols’ spatial distribution. For example,we developed analytical models for the statistical convergence which are in excellent agreement with measurements.

J.C. Moran and J.H. Lienhard V, “The Statistical Convergence of Aerosol Deposition Measurements,” Expts. Fluids, 22:375-379, 1997. (PDF file)

Thermal Control of Hydrostatic Bearings for Precision Machine Tools

This work investigated the frictional and thermal characteristics of radial hydrostatic bearings used in precision machine tool applications. The bearings considered were lubricated with water, rather than more viscous oils, leading to lower rotational friction and raising the lubricant heat capacity rate. Numerical and analytical models for bearing power consumption and temperature rise were developed. From these studies, bearings with highly optimized pockets and spindles were designed and tested; these bearings showed less than 3 K temperature rise at speeds exceeding 10,000 rpm. Related work involved temperature control of large tool-base structures.

K.L. Wasson, A.H. Slocum, and J.H. Lienhard V, R&D-100 Award for HydroSpindle development, 1996.
A.C. Pfahnl, J.H. Lienhard V, and A.H. Slocum, “Thermal Error Control of Precision Machine Structures,” Proc. 1996 NSF Design and Manufacturing Grantees Conf., Albuquerque, NM, January 3-5, 1996.
A.H. Slocum, J.H. Lienhard V, and P. Scagnetti, “Self-Compensated Water-Hydrostatic Bearings for Precision Machine Tools,” Proc. 1995 NSF Design and Manufacturing Grantees Conf., La Jolla, CA, January 4-6, 1995.

Vibrating Rubber Strings

The effect on vibrational frequency of the amount of stretch of different kinds of materials was examined. The effect of string inertia on the vibration of a point loaded string is examined theoretically, including exact and approximate results. Experimental results describing the response of loaded rubber cords were obtained and compared to a universal formula.

M.F. Beatty and J.H. Lienhard V, “Experimental investigation of the transverse vibrational frequency ratio of identical loaded and unloaded rubber strings,” Am. J. Physics, 50(2):113-119, 1982. (PDF file)