Thermal Boundary Layers in Critical Flow Venturis

Published

July 30, 2021

Author(s)

John D. Wright, Aaron Johnson, Michael R. Moldover, Woong Kang, Liang Zhang, Bodo Mickan

Abstract

We improve the usefulness of small (diameter < 10 mm) critical flow venturis (CFVs) as transfer standards for gas flow by measuring and explaining how their discharge coefficients depend on the temperature T of their environment. At Reynolds numbers Re < 2.5 x 10⁵ (e.g., a 2 mm diameter throat; inlet: air at 1 MPa), CFVs exhibit sensitivity to the environmental temperature of approximately 0.02 % K^-1 due to biased measurements of the stagnation temperature T₀ (temperature "sampling" error) and from ignoring the low-density, annular, thermal boundary layer generated by heat transfer from the CFV's body to the gas flowing through the CFV. To reduce temperature sampling errors, we used a non-metallic approach pipe and a temperature sensor with a low stem-conduction error. To correct for thermal boundary layer effects on the flow, we used Geropp's functional form: C_T = 1+K_T Re^-1/2 [Δ}T⁄T₀] where Δ}T is the difference between the CFV's inner wall temperature and the stagnation temperature. For CFVs made of stainless steel and copper with diameters of 0.56 mm, 1.1 mm, and 3.2 mm we measured K_T ≅ -7 while Geropp's theory predicts K_tbl ≅ 2.

Citation

Flow Measurement and Instrumentation

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.flowmeasinst.2021.102025

Local Download

Keywords

critical, flow, venturi, boundary layer

Citation

Wright, J. , Johnson, A. , Moldover, M. , Kang, W. , Zhang, L. and Mickan, B. (2021), Thermal Boundary Layers in Critical Flow Venturis, Flow Measurement and Instrumentation, [online], https://doi.org/10.1016/j.flowmeasinst.2021.102025, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=927458 (Accessed December 15, 2024)