International comparison of a NIST primary standard with an NRLM transfer standard for small mass flow rates of nitrogen gas

The history of the creation of the State primary standard of gas volumetric and mass flow rate units GET 118-2017 is presented. The significant role of international comparisons was noted at various stages of the creation of GET 118-2017: the comparisons results confirmed and made it possible to include in the KCDB the calibration and measurement capabilities of the Russian Federation in the field of gas volumetric flow measurements, and also helped to determine the direction and list of measures to improve the standard. A patented comparison method for calibrating critical nozzles, implemented in GET 118-2017 for transfer the units of volumetric and mass flow rates of gas to working standards, is described. The design, composition and characteristics of GET 118-2017 are presented. Currently, more than 700 working standards of gas volumetric and mass flow rates used in the Russian Federation and some KOOMET member countries are traced to GET 118-2017, the total number of calls to GET 118-2017 for the transfer of measurement units exceeds 3500 per year.

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Experimental investigation on the heat transfer characteristics of supercritical CO2 at various mass flow rates in heated vertical-flow tube

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2019.04.097 ◽

2019 ◽

Vol 157 ◽

pp. 113687 ◽

Cited By ~ 9

Author(s):

Shijie Zhang ◽

Xiaoxiao Xu ◽

Chao Liu ◽

Xinxin Liu ◽

Chaobin Dang

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Mass Flow ◽

Supercritical Co2 ◽

Vertical Flow ◽

Heat Transfer Characteristics ◽

Flow Tube ◽

Flow Rates ◽

Transfer Characteristics ◽

Mass Flow Rates

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Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

Geothermal Energy ◽

10.1186/s40517-021-00201-3 ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Tobias Blanke ◽

Markus Hagenkamp ◽

Bernd Döring ◽

Joachim Göttsche ◽

Vitali Reger ◽

...

Keyword(s):

Reynolds Number ◽

Laminar Flow ◽

Mass Flow ◽

Flow Rate ◽

Heat Exchangers ◽

Circular Ring ◽

Flow Conditions ◽

Flow Rates ◽

Mass Flow Rates ◽

Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

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