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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Soil, Water & Air Resources Research » Research » Publications at this Location » Publication #219100

Title: Evaluation of a new, perforated heat flux plate design

item Sauer, Thomas - Tom

Submitted to: International Communications in Heat and Mass Transfer
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2008
Publication Date: 7/29/2008
Citation: Sauer, T.J., Akinyemi, O.D., Thery, P., Heitman, J.L., Desutter, T.M., Horton, R. 2008. Evaluation of a new, perforated heat flux plate design. International Communications in Heat and Mass Transfer. 35:800-804.

Interpretive Summary: The amount of energy moving through soil is typically measured with a sensor called a flux plate, which involves measurement of a temperature difference across a thin disk of known thermal properties. However, when it rains or when the soil dries due to evaporation, these flux plates block the flow of liquid water and water vapor. This error can be large as the water and water vapor also transfer energy. A new flux plate design that includes holes in the plate to allow liquid water and water vapor to pass through the plate was tested. Measurements in the laboratory with dry and saturated sand and clay indicated that the new design was as accurate as standard plates for measuring heat flux for all conditions except saturated sand. Additional tests showed that the new plate did not disrupt the flow of water as much as the standard design. Field tests in a loam soil showed that the new plates were accurate and durable as they performed well for several weeks. The results of this study are important to scientists seeking to obtain more accurate estimates of soil heat flux for studies of surface energy balance and soil thermal regimes.

Technical Abstract: Accurate measurement of heat flux is essential to optimize structural and process design and to improve understanding of energy transfer in natural systems. Laboratory and field experiments evaluated the performance of a new, perforated heat flux plate designed for environmental applications. Laboratory tests involving dry and saturated sand show that performance of the new CAPTEC plate is comparable to a solid REBS plate. Very low temperature gradients may have led to poor performance of the CAPTEC plate in saturated sand. Water infiltration and redistribution experiments using clayey and sandy soils showed an apparent reduced disruption of liquid water and vapor in the soil surrounding the CAPTEC plate as compared to a solid Hukseflux plate. Field tests in a loam soil indicated that the CAPTEC plates were durable and produced daily total flux values within ~ 0.15 MJ m–2 of independent estimates.