scholarly journals On the Vapour Pressure Gradient in the Layer near the Cooled Surface of a DewPoint Hygrometer

1961 ◽  
Vol 39 (3) ◽  
pp. 97-102
Author(s):  
M. Yoshitake
Keyword(s):  
Pressure Gradient ◽  
Vapour Pressure ◽  
Vapour Pressure Gradient

THE DIFFUSION OF WATER VAPOUR THROUGH VARIOUS BUILDING MATERIALS

1939 ◽  
Vol 17a (2) ◽  
pp. 15-32 ◽  
Author(s):  
J. D. Babbitt
Keyword(s):  
Diffusion Coefficient ◽  
Pressure Gradient ◽  
Water Vapour ◽  
Vapour Pressure ◽  
Building Materials ◽  
Building Construction ◽  
Materials Used ◽  
Vapour Pressure Gradient

A method of measuring the diffusion coefficient of water vapour through solids is outlined, and a table of the coefficients for various materials used in building construction is given. The method of employing these coefficients to calculate the vapour pressure gradient through a typical wall is shown, and this is applied to estimate the resistance to water vapour necessary to prevent condensation.

Evaporation from a large lowland reservoir – observed dynamics during a warm summer

2021 ◽  
Author(s):  
Femke A. Jansen ◽  
Adriaan J. Teuling ◽  
Remko Uijlenhoet ◽  
Cor M.J. Jacobs ◽  
Pieter Hazenberg
Keyword(s):  
Wind Speed ◽  
The Netherlands ◽  
Pressure Gradient ◽  
Vapour Pressure ◽  
Water Evaporation ◽  
High Temporal Resolution ◽  
Hydrological Models ◽  
Simple Regression Model ◽  
Lowland Reservoir ◽  
Vapour Pressure Gradient

<p>Distinct differences in surface characteristics between a water body and a land surface result in different drivers of evaporation and therefore its dynamics. It is essential to include and represent this difference in the parameterization of open water evaporation (E<sub>water</sub>) to improve operational hydrological models. Additionally, more accurate parameterization becomes even more crucial to predict potential changes in quantity and dynamics of E<sub>water</sub> in a changing climate in support of optimal water management now and in the future.</p><p>For this purpose, we performed a long-term measurement campaign to measure E<sub>water</sub> and related meteorological variables over a large lowland reservoir in the Netherlands. During the summer seasons of 2019 and 2020 eddy-covariance systems were applied at two locations at the border of lake IJsselmeer in the Netherlands. These high temporal resolution measurements gave us the opportunity to explore the dynamics and identify the underlying driving mechanisms of E<sub>water</sub>. Using the data collected during the summer of 2019 we were able to develop a simple regression model for both measurement locations. Combinations, both sums and products, of the following independent variables were considered: global radiation, wind speed, water skin temperature, vapour pressure deficit, and vertical vapour pressure gradient. The product of wind speed and vertical vapour pressure gradient best explained the observed hourly E<sub>water</sub> rates, which is consistent with the commonly used aerodynamic approach. The model was validated using the data of 2020. Additionally, we compared measured E<sub>water</sub> to E<sub>water</sub> computed with Makkink’s equation, which is currently used in the Dutch operational hydrological models to estimate E<sub>water</sub>. Although a correction factor is applied to account for the difference between land evaporation and E<sub>water</sub>, Makkink is not able to capture the dynamics of E<sub>water</sub>. This was reflected in the timing and shape of the evaporation peak at both daily and monthly scales. The disagreement of E<sub>water</sub> dynamics found between the measured and simulated E<sub>water</sub> even more demonstrates the value and need of a correct parameterization of E<sub>water</sub>.</p>

scholarly journals Water condensation and transport on bioinspired triangular patterns with heterogeneous wettability at a low temperature

2018 ◽  
Vol 377 (2138) ◽  
pp. 20180335 ◽  
Author(s):  
Dong Song ◽  
Bharat Bhushan
Keyword(s):  
Low Temperature ◽  
Pressure Gradient ◽  
Vapour Pressure ◽  
Arid Regions ◽  
Ambient Air ◽  
Theme Issue ◽  
Saturated Vapour Pressure ◽  
Saturated Vapour ◽  
Water Condensation ◽  
Condensed Water

Desert beetles and cactus plants collect water from fog in arid regions. The desert beetle uses heterogeneous wettability to transport water to its mouth. A cactus uses conical spines which provide Laplace pressure gradient to transport water to its base. In this study, bioinspired triangular patterns with various wettability and different from the surrounding regions were investigated to transport condensed water from ambient air. A low temperature of 5°C was used to decrease saturated vapour pressure to promote water condensation. Results from this study can be used to enhance the performance of water collection systems. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology’.

OBSERVATIONS ON THE PERMEABILITY OF HYGROSCOPIC MATERIALS TO WATER VAPOUR: I. OBSERVATIONS AT RELATIVE HUMIDITIES LESS THAN 75%

1940 ◽  
Vol 18a (6) ◽  
pp. 105-121 ◽  
Author(s):  
J. D. Babbitt
Keyword(s):  
Relative Humidity ◽  
Moisture Content ◽  
Vapour Pressure ◽  
Fick’S Law ◽  
Moisture Movement ◽  
Fick's Law ◽  
Vapour Pressure Difference ◽  
Moisture Content Gradient ◽  
Vapour Pressure Gradient

It is pointed out that experimental work has shown that for the transpiration of moisture through hygroscopic materials two distinct regions of relative humidity can be distinguished: (i) A region below some value between 70 and 80% where the moisture movement is proportional to the vapour pressure difference, and (ii) a region of high relative humidity where the moisture movement is not directly proportional to the vapour pressure. A theory is advanced that these two regions correspond to the two conditions in which water may be present in a hygroscopic material: (i) the water may be molecularly adsorbed, that is to say, the water is bound by the affinity of the molecules of water for those of the solid on which it is adsorbed; (ii) the water may be held in small fissures in the sub-microscopic structure of the sorbing material by capillary forces. The mechanism by which the moisture will move through the material would be different in the two cases and would result in the distinction between regions of high and of low relative humidity.A short discussion is given of Fick's law showing the form in which it might be expected to apply in the two cases. Measurements are given for fibreboards showing that below 75% relative humidity the resistance of the board to moisture transpiration is proportional to the thickness. The moisture content gradients through fibreboard samples have been determined. The diffusance through a board in which the moisture content gradient is opposed to the vapour pressure gradient shows that the latter is the important factor, and the determination of the moisture content gradient indicates that at these low humidities Fick's law is applicable.

Nanofibre Membrane Distillation for Brackish Water Treatment in Offshores and Small Islands

2020 ◽  
pp. 196-218
Keyword(s):  
Water Treatment ◽  
Pressure Gradient ◽  
Brackish Water ◽  
Vapour Pressure ◽  
Membrane Distillation ◽  
Volatile Components ◽  
Clean Water ◽  
Small Islands ◽  
Process Performance ◽  
Hydrophobic Membrane

Membrane distillation is a process driven by the vapour pressure gradient of water to allow the permeation of water vapours through the microporous hydrophobic membrane while retaining other non-volatile components present in the feed. In this chapter, the utilization of membrane distillation as promising membrane technology for the application of clean water production at offshores and small islands are discussed. One of the main challenges of membrane distillation is that the production rate is low compared to the membrane areas used as the process performance is mainly influenced by the membrane characteristics. Thus, the ideal membrane should possess distinct characteristics that are the most suitable exclusively for membrane distillation application. This chapter also highlights the nanofibre membrane as one of the excellent options as it can be fabricated to exhibit hydrophobic, thin, and open pores characteristics.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

An Attack on the Contamination Problem in the Electron Microscope

1967 ◽  
Vol 25 ◽  
pp. 368-368
Author(s):  
J. J. Kelsch ◽  
A. Holtz
Keyword(s):  
Electron Microscope ◽  
Pressure Gradient ◽  
Ionization Potential ◽  
Simple Solution ◽  
Specimen Surface ◽  
Contamination Rate ◽  
Local Pressure ◽  
High Ionization ◽  
Hydrocarbon Molecules ◽  
Contamination Problem

A simple solution to the serious problem of specimen contamination in the electron microscope is presented. This is accomplished by the introduction of clean helium into the vacuum exactly at the specimen position. The local pressure gradient thus established inhibits the migration of hydrocarbon molecules to the specimen surface. The high ionization potential of He permits the use of relatively large volumes of the gas, without interfering with gun stability. The contamination rate is reduced on metal samples by a factor of 10.

Hydration Chamber for Jeolco 200 Kv Microscope

1970 ◽  
Vol 28 ◽  
pp. 542-543
Author(s):  
V. R. Matricardi ◽  
G. G. Hausner ◽  
D. F. Parsons
Keyword(s):  
Electron Microscope ◽  
Water Vapor ◽  
Vapor Pressure ◽  
Pressure Gradient ◽  
Room Temperature ◽  
List Type ◽  
Type Number ◽  
Equilibrium Vapor Pressure

In order to observe room temperature hydrated specimens in an electron microscope, the following conditions should be satisfied: The specimen should be surrounded by water vapor as close as possible to the equilibrium vapor pressure corresponding to the temperature of the specimen.The specimen grid should be inserted, focused and photo graphed in the shortest possible time in order to minimize dehydration.The full area of the specimen grid should be visible in order to minimize the number of changes of specimen required.There should be no pressure gradient across the grid so that specimens can be straddled across holes.Leakage of water vapor to the column should be minimized.

Sign in / Sign up

Export Citation Format

Share Document