Confirmation of a lower psychrometer constant

Schurer, K.

doi:10.1088/0022-3735/14/10/014

Cited by 6 publications

(3 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There are, however, studies that challenge this formulation (Schurer 1981;Fan 1987;Visscher 1995), and empirical estimates of g (g e ) ranging from 0.00054 to 0.0007 K 21 were found using a fixed, steady-state T db and T wb of 308 and 138C, respectively (Visscher 1995). We alternatively estimated g e by rearranging the psychrometric equation g e 5 e s (wb) À e s (dp)…”

Section: A Theoretical Considerationsmentioning

confidence: 99%

The Psychrometric Constant Is Not Constant: A Novel Approach to Enhance the Accuracy and Precision of Latent Energy Fluxes through Automated Water Vapor Calibrations

Loescher

Hanson

Ocheltree

2009

Journal of Hydrometeorology

View full text Add to dashboard Cite

Numerous agencies, programs, and national networks are focused on improving understanding of water and energy fluxes across temporal and spatial scales and on enhancing confidence to synthesize data across multiple sites. Enhancing the accuracy and precision in the surface energy balance and the latent energy (lE) flux lies, in part, with being able to uniformly calibrate water vapor measurements at and among sites to traceable standards. This paper examines (i) the traceable physical controls on field applications of chilledmirror hygrometers and (ii) an automated means to accurately and precisely calibrate infrared gas analyzers for water vapor concentrations and eddy covariance (lE) data. The environmental physics and gas handling were examined in a theoretical and applied manner that found that chilled-mirror technologies can be a robust measure of dewpoint temperatures and ambient water vapor only if the unit conversions are accounted for between inlet and body temperatures. Psychrometers were also examined and a functional relationship (exponential) was developed for the psychrometric constant against the wet-bulb temperature depression (T db 2 T wb ), g 5 (5.71 3 10 À5 ) 1 (5.48 3 10 À4 )(1 À 0.66 T db ÀT wb ) across a wider range of temperature depressions than previously reported. These empirical estimates of the psychrometer constant for small temperature depressions are much lower than other reported values-that is, ;0.000 52 K 21 for a wet-bulb temperature depression (T db 2 T wb ) of 4.3 K.

show abstract

Section: A Theoretical Considerationsmentioning

confidence: 99%

The Psychrometric Constant Is Not Constant: A Novel Approach to Enhance the Accuracy and Precision of Latent Energy Fluxes through Automated Water Vapor Calibrations

Loescher

Hanson

Ocheltree

2009

Journal of Hydrometeorology

View full text Add to dashboard Cite

show abstract

“…The origin of the instrument itself goes back to the latter part of the 18th century (Wylie 1979). A value of A around 6.70 × 10 −4 • C −1 is generally accepted and psychrometer tables were constructed on the basis of that value (Schurer 1981), but other values are also in current use, depending on the psychrometer construction principle and operating conditions. Manufacturers also have their own psychrometer constants.…”

Section: Introductionmentioning

confidence: 99%

“…The literature includes many experimental and theoretical works dealing with the problem and new claims are constantly being made. Wylie (1979) and Wylie andLalas (1981a, b, 1992) have concluded that the conventional value for A was 8% too high, a conclusion that was also shared by Schurer (1981) and Fan (1987). The World Meteorological Organization (WMO) reference psychrometer (Wylie andLalas 1981a, 1992) is based on Wylie and Lalas' lower constant values.…”

Section: Introductionmentioning

confidence: 99%

A thermodynamic formulation of the psychrometer constant

Simões-Moreira¹

1999

Meas. Sci. Technol.

View full text Add to dashboard Cite

This work aimed to present an exact formulation of the psychrometer constant based on thermodynamics reasoning, rather than the usual empirical approach. Such a thermodynamic psychrometer constant sets a common ground for expected values independently of the type of construction and operating conditions of a psychrometer. The assumption that one is dealing with a perfect gas mixture conveys the exact solution to a simpler expression for the thermodynamic psychrometer constant with a relative deviation within -2% for a thermodynamic wet-bulb temperature less than 60 °C and standard pressure, which suffices for field applications. It has also been found that the thermodynamic psychrometer constant is strongly dependent on the thermodynamic wet-bulb temperature, weakly dependent on the dry-bulb temperature and pressure dependent too. The formulation is compared with experimental data and reproduces very closely the results for an adiabatic saturation psychrometer. Experimental data on constants of several psychrometer types tend to scatter around the exact solution, except for the World Meteorological Organization psychrometer, which gives consistently lower values than the ones from the present formulation. In addition, an analysis of the error introduced when one mistakes the temperature reading of a regular psychrometer for the thermodynamic property is carried out. A typical difference between these two temperatures is around ±0.4 °C for air at room temperature. Finally, speculations regarding means of improving psychrometer design in order to obtain the thermodynamic wet-bulb temperature directly from the instrument are presented. Keywords: psychrometry, psychrometer, moist air, humidity, wet-bulb temperature

show abstract

Water and Plants

Schurer¹

1986

Advanced Agricultural Instrumentation

View full text Add to dashboard Cite

Confirmation of a lower psychrometer constant

Cited by 6 publications

References 1 publication

The Psychrometric Constant Is Not Constant: A Novel Approach to Enhance the Accuracy and Precision of Latent Energy Fluxes through Automated Water Vapor Calibrations

The Psychrometric Constant Is Not Constant: A Novel Approach to Enhance the Accuracy and Precision of Latent Energy Fluxes through Automated Water Vapor Calibrations

A thermodynamic formulation of the psychrometer constant

Water and Plants

Contact Info

Product

Resources

About