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Study of conceptual design for flow-mixing stage of low-range humidity standard generator.

Bell, S A (1999) Study of conceptual design for flow-mixing stage of low-range humidity standard generator. NPL Report. CMAM 39

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Abstract

A study has been made of flow mixing as a method of generating gas of defined moisture content. The study was undertaken with a view to adding a flow mixing assembly to the existing NFL Low Frost-point Generator to extend its range downwards to -85 °C or below.
Implementations of flow mixing generators at other national humidity standards have been reviewed. Modelling has been carried out to examine how the desired range could be achieved, and to see how the uncertainties in input flow rates and moisture contents might propagate. Critical influences such as the source "dry" gas and the gas handling lines are also discussed, and the practical requirements stated. Other key issues are discussed, such as measuring instruments for trace moisture, and data for conversions between measured quantities of mole fraction and frost point.
The likely performance of a flow-mixing system is considered together with the performance of the existing NPL Low Frost-point Generator. It appears that the required range can be reached using the LFG alone, and the uncertainty in frost-point generation is likely to be equal to or better than that achieved by flow mixing. In this case, the addition of a flow mixing stage to the NPL Humidity Standard has only limited value.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CMAM 39
Subjects: Engineering Measurements
Engineering Measurements > Thermal
Last Modified: 02 Feb 2018 13:18
URI: http://eprintspublications.npl.co.uk/id/eprint/1263

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