Document Type

Thesis - University Access Only

Award Date

1996

Degree Name

Master of Science (MS)

Department / School

Electrical Engineering

First Advisor

David W. Galipeau

Abstract

The purpose of this work was to develop a better understanding of the dew point measurement process and to investigate several issues that are critical for the development of a commercially viable surface acoustic wave (SAW) based dew point hygrometer. Optical dew point hygrometers, most widely used instrument used to measure dew point have several drawbacks including limited resolution, long term instability, self heating from resistive temperature devices (RTDs), and high cost. An important innovation in this work was SAW microsensor measurements of both condensation and temperature which improves measurement resolution at potentially lower cost. A theoretical description of dew point and the dew point measurement process was developed. Including such issues as nucleation and growth, liquid-solid phase transitions, and surface energy and wettability. Several sources of dew point measurement error were also described. The critical issues that were experimentally investigated included: the ability of the SAW microsensor to precisely measure condensation density as compared to an optical reflection technique; the resolution of SAW temperature measurements; the effects of surface contamination on SAW and optical dew point measurements; the ability to measure the buildup of contamination with the SAW microsensor; the ability to detect the frost point transition and the stability of SAW and optical sensors at the frost point transition; the effects of the condensing surface on dew point measurements; and the resolution and stability of the SAW micro sensor as compared to a commercial optical sensor. It was found that the SAW microsensor can measure dew point when its surface contaminated without significant measurement error, while the optical sensor loses stability. The high sensitivity of the SAW microsensor allowed for precise control of condensation density which increased dew point measurement resolution. It also reduced ripening and coalescing of the condensate, eliminating the need for a dry-off cycle. By comparison the optical technique could not maintain a constant condensation density over an extended period of time without a dry-off cycle. The SAW microsensor could also detected the frost point transition temperature. During the frost point transition, SAW amplitude was used to provide continuous dew point measurements. This is a significant advantage over the optical method which could not provide continuous measurements through the frost point transition. Finally, it was found that the energy of the condensing surface had a significant effect on dew point measurement accuracy at low condensation densities. This may provide a new technique for measuring surface energy.

Library of Congress Subject Headings

Condensation
Dew point
Acoustic surface wave devices

Format

application/pdf

Publisher

South Dakota State University

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Rights Statement

In Copyright