HR: 1340h
AN: H53F-1477    [Abstracts]
TI: Improving Heat Pulse Probe Sensitivity without Changing its Geometry
AU: * Saito, H
EM: hiros@cc.tuat.ac.jp
AF: Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho Fuchu, Tokyo, 183-8509, Japan
AU: Simunek, J
EM: Jiri.Simunek@ucr.edu
AF: University of California, Riverside, Department of Environmental Sciences, Riverside, CA 92521, United States
AU: Tuli, A
EM: atuli@ucdavis.edu
AF: University of California, Davis, Department of Land, Air & Water Resources, Davis, CA 95616, United States
AU: Hopmans, J W
EM: jwhopmans@ucdavis.edu
AF: University of California, Davis, Department of Land, Air & Water Resources, Davis, CA 95616, United States
AB: The heat pulse probe (HPP) has recently received increased attention as it allows in-situ, simultaneous, and automated measurements of soil hydraulic and thermal properties, as well as soil water fluxes. Although the currently-used design allows many applications, changes in HPP design and analysis are needed to increase its sensitivity to smaller water fluxes. In our previous study, we showed that significantly different temperature responses are obtained depending on the axial location of thermistors and that only temperature measurements near the middle of the 33-mm long heater fulfill the assumption of an infinite line heat source. It was also demonstrated that larger heater needle diameters allow larger heat pulses, leading to larger temperature differences between upstream and downstream thermistor needles and thus a higher sensitivity to water flux measurements. Both approaches, however, require changing the physical geometry of HPP, which is not favored by practitioners. In this study, we numerically evaluate the impact of alternating heat pulse durations, rather than changing the HPP geometry, on improving sensitivity of HPP under different conditions. For example, for a standard 1-mm diameter heater needle, five times greater sensitivity was achieved by using eight times longer heat pulse duration, while increasing the maximum temperature at the heater by only 8 degree C. If a standard heat pulse duration of 8 seconds is used, five times greater sensitivity can be achieved only by applying eight times greater heat pulse, which leads to the maximum temperature at the heater exceeding 100 degree C. Longer heat pulse durations are beneficial for the estimation of smaller liquid fluxes. All numerical experiments were conducted using the HYDRUS-2D code.
DE: 1866 Soil moisture
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting