scholarly journals The height limit of a siphon

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
A. Boatwright ◽  
S. Hughes ◽  
J. Barry
Keyword(s):  
Sea Level ◽  
Vapour Pressure ◽  
Ambient Pressure ◽  
Barometric Pressure ◽  
Low Pressure ◽  
Conclusive Evidence ◽  
Differential Pressure ◽  
Maximum Height ◽  
Reservoir Level ◽  
Pressure Region

Abstract The maximum height of a siphon is generally assumed to be dependent on barometric pressure—about 10 m at sea level. This limit arises because the pressure in a siphon above the upper reservoir level is below the ambient pressure and when the height of a siphon approaches 10 m, the pressure at the crown of the siphon falls below the vapour pressure of water causing water to boil breaking the column. After breaking, the columns on either side are supported by differential pressure between ambient and the low-pressure region at the top of the siphon. Here we report an experiment of a siphon operating at sea level at a height of 15 m, well above 10 m. Prior degassing of the water prevented cavitation. This experiment provides conclusive evidence that siphons operate through gravity and molecular cohesion.

Investigation of the Effect of Plume Number on Spray Collapse

2019 ◽  
Author(s):  
Panos Sphicas
Keyword(s):  
Ambient Temperature ◽  
High Velocity ◽  
Recirculation Zone ◽  
Ambient Pressure ◽  
Low Pressure ◽  
Ambient Conditions ◽  
Single Entity ◽  
Injection Duration ◽  
Pressure Region ◽  
Entrained Air

Abstract The plumes of a gasoline spray collapse into a single entity under the influence of ambient pressure, ambient temperature and injection duration. Previous work by the author studied experimentally [1] and numerically [2] the phenomenon of spray collapse. It was observed that the entrained air from every single plume, accumulatively creates a recirculation zone in the middle of the spray. The recirculation zone of high velocity, creates a low pressure region, which causes the collapse of the spray. In this paper, the influence of the number of plumes in the spray, is investigated numerically. The plume angle and ambient conditions matched Spray G, but the number of plumes was varied from two to eight. The effect of the plume number on the spray collapse was investigated numerically. It was evident that increased number of plumes in the spray promotes spray collapse.

Unprecedented CO2 adsorption behaviour by 5A-type zeolite discovered in lower pressure region and at 300 K

2021 ◽  
Author(s):  
Akira Oda ◽  
Suguru Hiraki ◽  
Eiji Harada ◽  
Ikuka Kobayashi ◽  
Takahiro Ohkubo ◽  
...  
Keyword(s):  
Pressure Range ◽  
Co2 Adsorption ◽  
Low Pressure ◽  
Lower Pressure ◽  
Dft Studies ◽  
Adsorption Behaviour ◽  
Zeolite Sample ◽  
Pressure Region ◽  
Type Zeolite ◽  
Efficient Adsorbent

The NaCaA-85 zeolite sample which works as an efficient adsorbent for CO2 at RT and in low pressure range was found and its specificity is nicely explained by the model composed of CO2 pinned by two types of Ca2+ ions through far-IR and DFT studies.

Exploration of Characteristics Governing Dynamics of Whirlwinds: Application to Dust Devils

2017 ◽  
Vol 72 (8) ◽  
pp. 763-778
Author(s):  
Sanjay Kumar Pandey ◽  
Jagdish Prasad Maurya
Keyword(s):  
Physical Phenomenon ◽  
Radial Pressure ◽  
Buffer Zone ◽  
Vertical Gradient ◽  
Azimuthal Velocity ◽  
Low Pressure ◽  
Dust Devils ◽  
Growth And Survival ◽  
Pressure Region ◽  
Upward Direction

AbstractIt is intended to model mathematically an ideal whirlwind which characterises this geo-physical phenomenon and eventually helps us decode the inherent dynamics. A dense cylindrical aerial mass is taken into consideration surrounding a rarer aerial region in order to keep a radial favourable gradient of pressure to sustain a rotational motion. It has been concluded that the whirlwind will survive as long as the low pressure region exists. The vertical pressure gradient also plays an equally important role. Since it is not connected to any cloud and the axial velocity is in the vertically upward direction, the momentary vertical gradient of pressure is required for its growth and survival. Horizontal ambient winds that rush towards low pressure zone, crush the air in the buffer zone, and turn vertically upward may also take the dust carried with them visibly to some height. It is considered that the angular azimuthal velocity varies within the annulus. An inference is that no whirlwind without a low pressure region within it can survive. This may be termed as the fundamental characteristic of whirlwind. It is further concluded that if the radial pressure difference between the outermost and innermost layers is larger, the whirlwind is thicker and consequently, it will last longer. Moreover, another conclusion arrived at is that the angular velocity will vanish if the inner radius is zero.

Improvement in lung diffusion by endothelin A receptor blockade at high altitude

2012 ◽  
Vol 112 (1) ◽  
pp. 20-25 ◽  
Author(s):  
Claire de Bisschop ◽  
Jean-Benoit Martinot ◽  
Gil Leurquin-Sterk ◽  
Vitalie Faoro ◽  
Hervé Guénard ◽  
...  
Keyword(s):  
High Altitude ◽  
Sea Level ◽  
Exercise Capacity ◽  
Barometric Pressure ◽  
Membrane Component ◽  
Alveolar Volume ◽  
Double Blind ◽  
Lung Diffusion ◽  
Endothelin A Receptor ◽  
Endothelin A

Lung diffusing capacity has been reported variably in high-altitude newcomers and may be in relation to different pulmonary vascular resistance (PVR). Twenty-two healthy volunteers were investigated at sea level and at 5,050 m before and after random double-blind intake of the endothelin A receptor blocker sitaxsentan (100 mg/day) vs. a placebo during 1 wk. PVR was estimated by Doppler echocardiography, and exercise capacity by maximal oxygen uptake (V̇o2 max). The diffusing capacities for nitric oxide (DLNO) and carbon monoxide (DLCO) were measured using a single-breath method before and 30 min after maximal exercise. The membrane component of DLCO (Dm) and capillary volume (Vc) was calculated with corrections for hemoglobin, alveolar volume, and barometric pressure. Altitude exposure was associated with unchanged DLCO, DLNO, and Dm but a slight decrease in Vc. Exercise at altitude decreased DLNO and Dm. Sitaxsentan intake improved V̇o2 max together with an increase in resting and postexercise DLNO and Dm. Sitaxsentan-induced decrease in PVR was inversely correlated to DLNO. Both DLCO and DLNO were correlated to V̇o2 max at sea level ( r = 0.41–0.42, P < 0.1) and more so at altitude ( r = 0.56–0.59, P < 0.05). Pharmacological pulmonary vasodilation improves the membrane component of lung diffusion in high-altitude newcomers, which may contribute to exercise capacity.

Analysis of the eastern Adriatic sea-level extremes

2021 ◽  
Author(s):  
Marija Pervan ◽  
Jadranka Šepić
Keyword(s):  
Sea Level ◽  
Adriatic Sea ◽  
Hot Spot ◽  
Storm Surges ◽  
Low Pressure ◽  
Long Period ◽  
Short Period ◽  
Sea Level Oscillations ◽  
Low Pass ◽  
Level Height

&lt;p&gt;The Adriatic Sea is known to be under a high flooding risk due to both storm surges and meteorological tsunamis, with the latter defined as short-period sea-level oscillations alike to tsunamis but generated by atmospheric processes. In June 2017, a tide-gauge station with a 1-min sampling resolution has been installed at Stari Grad (middle Adriatic Sea), the well-known meteotsunami hot-spot, which is, also, often hit by storm surges.&amp;#160;&lt;/p&gt;&lt;p&gt;Three years of corresponding sea-level measurements were analyzed, and 10 strongest episodes of each of the following extreme types were extracted from the residual series: (1) positive long-period (T &gt; 210 min) extremes; (2) negative long-period (T &gt; 210 min) extremes; (3) short-period (T &lt; 210) extremes. Long-period extremes were defined as situations during which sea level surpasses (is lower than) 99.7 (i.e. 2) percentile of sea level height, and short-period extremes as situations during which variance of short-period sea-level oscillations is higher than 99.4 percentile of total variance[J1]&amp;#160; of short-period series. A strong seasonal signal was detected for all extremes, with most of the positive long-period extremes appearing during November to February, and most of the negative long-period extremes during January to February. As for the short-period extremes, these appear evenly throughout the year, but strongest events seem to appear during May to July.&lt;/p&gt;&lt;p&gt;All events were associated to characteristic atmospheric situations, using both local measurements of the atmospheric variables, and ERA5 Reanalysis dataset. It was shown that positive low-pass extremes commonly appear during presence of low pressure over the Adriatic associated with strong SE winds (&amp;#8220;sirocco&amp;#8221;), and negative low-pass extremes are associated to the high atmospheric pressure over the area associated with either strong NE winds (&amp;#8220;bora&amp;#8221;), or no winds at all. On the other hand, high-pass sea level extremes are noticed during two distinct types of atmospheric situations corresponding to both &amp;#8220;bad&amp;#8221; (low pressure, strong SE wind) and &amp;#8220;nice&amp;#8221; (high pressure, no wind) weather.&lt;/p&gt;&lt;p&gt;It is particularly interesting that short-period extremes, of which strongest are meteotsunamis, are occasionally coincident with positive long-period extremes contributing with up to 50 percent to total sea level height &amp;#8211; thus implying existence of a double danger phenomena (meteotsunami + storm surge).&amp;#160;&lt;/p&gt;

Oxygen transport to exercising leg in chronic hypoxia

1988 ◽  
Vol 65 (6) ◽  
pp. 2592-2597 ◽  
Author(s):  
P. R. Bender ◽  
B. M. Groves ◽  
R. E. McCullough ◽  
R. G. McCullough ◽  
S. Y. Huang ◽  
...  
Keyword(s):  
Blood Flow ◽  
Sea Level ◽  
Chronic Hypoxia ◽  
Peripheral Resistance ◽  
Hemoglobin Concentration ◽  
Barometric Pressure ◽  
Ambient Air ◽  
Leg Blood Flow ◽  
State Cycle ◽  
O2 Delivery

Residence at high altitude could be accompanied by adaptations that alter the mechanisms of O2 delivery to exercising muscle. Seven sea level resident males, aged 22 +/- 1 yr, performed moderate to near-maximal steady-state cycle exercise at sea level in normoxia [inspired PO2 (PIO2) 150 Torr] and acute hypobaric hypoxia (barometric pressure, 445 Torr; PIO2, 83 Torr), and after 18 days' residence on Pikes Peak (4,300 m) while breathing ambient air (PIO2, 86 Torr) and air similar to that at sea level (35% O2, PIO2, 144 Torr). In both hypoxia and normoxia, after acclimatization the femoral arterial-iliac venous O2 content difference, hemoglobin concentration, and arterial O2 content, were higher than before acclimatization, but the venous PO2 (PVO2) was unchanged. Thermodilution leg blood flow was lower but calculated arterial O2 delivery and leg VO2 similar in hypoxia after vs. before acclimatization. Mean arterial pressure (MAP) and total peripheral resistance in hypoxia were greater after, than before, acclimatization. We concluded that acclimatization did not increase O2 delivery but rather maintained delivery via increased arterial oxygenation and decreased leg blood flow. The maintenance of PVO2 and the higher MAP after acclimatization suggested matching of O2 delivery to tissue O2 demands, with vasoconstriction possibly contributing to the decreased flow.

Cardiovascular adaptations in Andean natives after 6 wk of exposure to sea level

1991 ◽  
Vol 70 (6) ◽  
pp. 2650-2655 ◽  
Author(s):  
D. C. McKenzie ◽  
L. S. Goodman ◽  
C. Nath ◽  
B. Davidson ◽  
G. O. Matheson ◽  
...  
Keyword(s):  
Sea Level ◽  
Barometric Pressure ◽  
Cycle Ergometer ◽  
Left Ventricular ◽  
Structure And Function ◽  
Left Ventricular Ejection ◽  
Noninvasive Methods ◽  
Functional Changes ◽  
And Function ◽  
Quechua Indians

Six male Quechua Indians (34.0 +/- 1.1 yr, 159.5 +/- 2.1 cm, 60.5 +/- 1.6 kg), life-long residents of La Raya, Peru (4,350-m altitude with an average barometric pressure of 460 Torr), were studied using noninvasive methods to determine the structural and functional changes in the cardiovascular system in response to a 6-wk deacclimation period at sea level. Cardiac output, stroke volume, and left ventricular ejection fractions were determined using radionuclide angiographic techniques at rest and during exercise on a cycle ergometer at 40, 60, and 90% of a previously determined maximal O2 consumption. Subjects at rest were subjected to two-dimensional and M-mode echocardiograms and a standard 12-lead electrocardiogram. Hemoglobin and hematocrit were measured on arrival at sea level by use of a Coulter Stacker S+ analyzer. After a 6-wk deacclimation period, all variables were remeasured using the identical methodology. Hemoglobin values decreased significantly over the deacclimation period (15.7 +/- 1.1 to 13.5 +/- 1.2 g/dl; P less than 0.01). The results indicate that the removal of these high-altitude-adapted natives from 4,300 m to sea level for 6 wk results in only minor changes to the cardiac structure and function as measured by these noninvasive techniques.

scholarly journals Synthetically generated low-pressure systems to support studies of sea level extremes

2021 ◽  
Author(s):  
Mika Rantanen ◽  
Jani Särkkä ◽  
Jani Räihä ◽  
Matti Kämäräinen ◽  
Kirsti Jylhä
Keyword(s):  
Sea Level ◽  
Power Plants ◽  
Tide Gauge ◽  
Gaussian Function ◽  
Low Pressure ◽  
Tide Gauge Records ◽  
Pressure System ◽  
Sea Levels ◽  
Input Parameters ◽  
Low Pressure Systems

&lt;p&gt;Extremely high sea levels on the Finnish coast are typically caused by close passages of extratropical cyclones (ETCs), which raise the sea level with their associated extreme winds and lower air pressure. For coastal infrastructure, such as nuclear power plants, it is crucial to study physically possible sea level heights associated with ETCs. Such sea levels are not straightforward to determine from observational datasets only, because tide gauge records&amp;#160; cover about 100 years and do not necessarily capture the most extreme cases having return periods longer than 100 years.&lt;/p&gt;&lt;p&gt;In this study, a method for generating an ensemble of synthetic low-pressure systems is being developed to investigate the extreme sea level heights on the Finnish coast of Baltic sea. As input parameters for the method, the point of origin, velocity of the center of the cyclone and depth of the pressure anomaly need to be given. Based on the input parameters, the method forms an idealized low-pressure system using a two-dimensional Gaussian function. In order to find extreme, but still reasonable values for the input parameters, cyclone tracks from ERA5 reanalysis data will be analysed.&lt;/p&gt;&lt;p&gt;The ensemble of synthetic low pressure systems (i.e. the wind and pressure data) is used as an input to a numerical sea level model. As a result, we have an ensemble of simulated sea levels, from which we can determine the properties of the ETCs that induce the highest sea levels on a given location on the coast. The preliminary simulation results show that this method works well, forming a basis for studies on extreme sea levels.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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