Hi all. I'm a mechanical engineer working with issues related to vapor pressure in underground gasoline storage tanks. I have been trying to refresh myself on vapor pressure issues since I haven't really had to work with this since college. I am performing a pretty simple experiment and completely striking out in trying to understand the results. I am hoping that these are easily explained by someone who understands the physics here.
The experimental setup is as follows. I have placed 300 mL of gasoline (E10 unleaded) in a 1300 mL stainless steel vessel that is then placed in an environmental chamber kept at 20°C throughout. The lid of the vessel is tapped for a pressure transducer and a ball valve to vent pressure when desired. For initial conditions, the 300 mL of gasoline was placed in the vessel and the lid sealed. The remaining space is filled with air at 20°C and about 40% rh. Over time the pressure in the headspace rises as expected. I didn't let the vapor space reach saturated vapor pressure on the first rise as measuring that wasn't the subject of interest. After a time, the pressure in the vessel was vented through the ball valve, releasing a mixture of the gasoline vapors and the air from the initial conditions. This time I left the vessel undisturbed overnight and the pressure reached an equilibrium pressure roughly half of what it was when I vented. This was expected from prior experience. I thought that this might be explained by the fact that gasoline is a mixture of hydrocarbons with different volatilities and that I had been evaporating off the light ends of the mixture. This procedure of venting and waiting for the vapor pressure to rise was repeated several times with the equilibrium pressure in the headspace dropping each time. I have a graph of the pressure vs. time here. https://imgur.com/5c0mego. The two small upsets in pressure come from injecting a mall 45 mL of air into the chamber (1st upset) and then removing 45 mL of gasoline and replacing with 45 mL of air (2nd upset). The last thing that I did was to open the top of the vessel to allow an exchange of some of the gasoline vapors for air. After this venting and exchange, the vapor pressure again rises rapidly with the curve matching the original.
My reading on vapor pressure suggests that the saturation vapor pressure is an equilibrium between the liquid and vapor phase of the hydrocarbons in the gasoline. My understanding is that this should be
... keep reading on reddit ➡I am not a botanist and reading about VPD. I am trying to find a reference for VPD for cacti but all I find is general tables for plants at different maturities -aimed mostly at growing marijuana or other plants for consumption, which I am not interested in.
From my basic understanding, I would expect that VPD requirements would be a genetic adaptation (ie. arid plants would have different requirements to tropicals).
However, I don't know the fundamental stomata mechanism like you all would and unfamiliar if they behave similarly across all plant species or not.
Thank you in advance! Also if you have any references for various plants, it would be appreciated! I did a few Google scholar searches and came up empty handed, perhaps because I am not using the right search keywords.
I was solving material balance for an electrolyser during my final year project plant design. I am sure that during water electrolysis, hydrogen gas leaving the electrolyser entrains some water with it and I have to calculate what is the amount of that entrained water.
I found no equation for amount of entrained water yet but I got the idea that the leaving hydrogen gas will be saturated with water vapors. So if I am able to find the vapor pressure of water in that hydrogen water mixture, I will be able to calculate the composition. I am applying Raoult's law here. I know the total pressure and all I need is to find the saturation pressure of both water and hydrogen. The saturation pressure of water can be known but not of hydrogen at the give conditions. Is there a way to find? Of course hydrogen will be superheated at the conditions.
I'm sure this is a simple answer but it's one of those questions that's hard to Google. I noticed this most recently watching Smarter Every Day's baseball cannon footage and every time the cannon fires a huge white cloud that looks like smoke comes out of the barrel, but the only thing inside of it is pressurized air. Why does that air form vapor like that when it's released back out into the atmosphere?
I'm a bit confused about it.
A new post is up on my blog. I do these things when I feel it will add to someone's knowledge and when, frankly, I feel the need to reinforce my own understanding. And there's no better way to do that than trying to explain it.
Join me on the journey if you like. The more you know, the more you grow.
I just got a new eppendorf concentrator plus.
There are settings for aqueous, alchohol, and high vapor pressure.
Normally I am drying solvents like acetone. Sometimes I dry methanol or water.
My previous concentrator didn't have such settings; you simply set the temperature and turned it on. I'm wondering exactly what the different programs do differently and which I should use for what. Any ideas?
I have a wierd problem with vapors building up in my gas tank. If I run the A/C or it's a hot day out (usually both things seem to factor into this), the car will cut off and refuse to start til I unscrew the gas cap, and vent the vapor that's built up in there.
I'm not sure why it's not venting this vapor build up on it's own, I'm fairly sure it's supposed to, right?
What can I do to narrow down what's going on and fix it? Is this dangerous to my car/engine?
The car runs perfectly other than this one issue.
I recently replaced the tank on my 2003 Hugger 883 with a lowbrow frisco tank. It does not retain the stock overflow line and I’m using a gravity fed petcock. When the bike sits on hot days vapor is building up in the tank so when I open my petcock fuel in flooding my carb and dumping out onto the ground. Does this mean that my gas cap isn’t venting properly? I was under the impression vented caps only let air IN to prevent vapor lock or worse tank collapse. Do I just have to remember to pop my cap off to let the pressure out before I open the petcock? Any ideas would be greatly appreciated.
"The partial pressure of a vapor must be less than or equal to the vapor pressure if there is no liquid present. However, when both vapor and liquid are present and the system is in phase equilibrium, the partial pressure of the vapor must equal the vapor pressure, and the system is said to be saturated. The rate of evaporation from open water bodies such as lakes is controlled by the difference between the vapor pressure and the partial pressure."
Thank you. Edit: That’s why I love this community. Everyone is eager to have me understand the topic. I wish I could give awards to all of you.
Introduced: Sponsor: Sen. Deb Fischer [R-NE]
This bill was referred to the Senate Committee on Environment and Public Works which will consider it before sending it to the Senate floor for consideration.
2 cosponsors are on that committee.
This question my teacher gave us basically asks if there is a decrease in atmospheric pressure, will the vapor pressure of some substance A) Increase B) Decrease or C) Stay the same. Any help would be greatly appreciated!
I'm a bit confused about vapor pressure. I know when vapor pressure = ambient pressure, boiling occurs. But when a substances undergoes evaporation, the remaining solution loses energy so as to get the molecule in the gas phase. This would lower the temperature of the solution? while also increasing vapor pressure, as now there's more gas particles. But as there's increased gas particles it's increasing the pressure above the solution making it harder to evaporate/boil. So then as evaporation occurs, causing a vapor pressure increase, how does that make it closer to boiling as the solution has decreased in temperature and there's an increased pressure being exerted above the solution? Or is the increased vapor pressure just preventing evaporation in closed environments? Isn't this the premise of humid vs dry environments. Like sweating is harder in humid environments b/c there's a greater vapor pressure and so the sweat molecules can't evaporate? But this is an "open container"? Would love any clarification on this!
I just learned a lot about VPD. I’m relatively new to indoor growing. I’m currently on my second grow. My first time growing in an actual tent and I’m just now hearing about VPD. I just want any new growers to read this and do some research. Anyone with good resources, links, or just some helpful advice please share in the comments!!!
Hey guys,
What is a connection between phase change from liquid to gas and equality of vapor pressure with ambient pressure? Why should equality of vapor pressure above liquid and ambient pressure determine when boiling happens? I know that when ambient pressure is higher, molecules in liquid require more energy to spread out to form bubbles of vapor since vapor has lower density than liquid, so higher temperature is needed to reach this point. But, why should vapor pressure above liquid determine when this point happens?
Good day to you all. I am looking for a graph (and preferably a table with it) that shows the temperature and the percentage (weight or volumetric) of water and formic acid for different concentrations of formic acid in water.
r/chemistry helped me as a start of and suggested that combining antoine's law and raoults law might work but I ended up with a linear progression.
The problem I ran into so far is that formic acid doesn't behave like an ideal gas. As it has a negative azeotrope.
Anybody that can help me find this or help me calculate this.
how does vapor pressure relate to the rate of evaporation, boiling point temperature, and IMFs?
Salve jardineiros. Pra quem tem problemas com calor excessivo nesse país tropical, recomendo MUITO dar uma lida sobre o VPD. Existem várias fontes e artigos, mas esse achei bem completo e em PTBR: https://thepuffhub.wordpress.com/2020/03/02/vpd-vapor-pressure-deficit-deficit-de-pressao-de-vapor/
Fui juvenil no meu primeiro cultivo e não quis investir num termohigrômetro. Tive vários problemas como hermafroditismo, fungo, deficiência e excesso de nutrientes, etc. Tomei vergonha na cara e acabei comprando um medidor desses para o segundo ciclo de cultivo. Descobri que as vezes faz 34ºC na minha tenda, ou seja: considerando a temperatura recomendada para a vega, a plantinha estava sofrendo muito. Fiz o que pude em relação a exaustão mas as temps continuavam altas pois moro numa parte bem quente do BR. Depois que andei lendo sobre esse índice, descobri que posso manipular a umidade para além da faixa recomendada e proporcionar conforto para a plantinha mesmo em temperaturas extremas. Farei isso pois além da temperatura alta, o medidor também apontava baixa umidade (porém dentro da faixa geralmente recomendada), o que parece ser péssimo para o desenvolvimento das meninas.
Resumindo: COMPREM UM TERMOHIGRÔMETRO. E leiam sobre esse negócio aí. Sou leigo mas me parece ser essencial o entendimento dessa relação entre temperatura e umidade para um grow bem sucedido.
