Questions tagged [humidity]

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Why is sound attenuation greater in dry air than humid air?

I have just learned the surprising fact that the attenuation coefficient of sound in air depends strongly on relative humidity: at any given frequency, it can be several times larger in very dry air (...
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16 views

Evaporation rate vs. volume relative humidity

I have a certain volume (V, in cubic centimeters) of air with a given temperature (Ta in Celsius) and relative humidity (RH %). Inside it I have a glass of water with a free surface with the same Ta. ...
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39 views

Estimation of relative humidity

Assume that we have a box of $1\ \mathrm{m^3}$ with a constant wall temperature of $15\ \mathrm{^\circ C}$. The box was filled with air. The temperature of the air was $30\ \mathrm{^\circ C}$ and the ...
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1answer
46 views

Heating outside air - how much humidity can it take?

I am trying to figure out this problem - maybe it is simple for someone of you but I can't figure it out. I have known variables of outside air temperature and relative humidity (RH), I am taking ...
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1answer
51 views

How does sweat evaporate even when the relative humidity is 100%

Recently I entered a room at my workplace with sweaty clothes.The thermostat read 5°C and the humidity was 100%.The outside temperature was close to 20°C.Also the AC was switched off.In about ten ...
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26 views

Vacuum test in the laboratory

If I put some water in a plastic container and apply a vacuum pressure of -0.20bar the water comes out of plastic container which should not as per design and material of container. This is called ...
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3answers
31 views

Warm or cold air

Which air can be used to dry out food or clothes? Warm or cold air? I've read that keeping food in the fridge makes it dry out. Blowing hot air to the hair also dries the hair out. I'm confused.
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1answer
98 views

How does my body temperature stay lower than ambient air temperature if it goes over 37°C?

I know it's because of sweat, but why should the sweat over my skin get heat from the body, cooling it under the ambient temperature, instead of getting it from the hotter air all around me? If I ...
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37 views

Doubts on conductor and insulator

I read on Stephen Gray's discovery of conductor and insulator. From that I came across a question that how cork, wood, rope can act as conductor being an insulator but then I got the answer that it is ...
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1answer
90 views

How does an ultrasonic humidifier / atomizer affect temperature?

Evaporative cooling is a technique used to cool air by using the evaporation of a liquid. My google research on evaporative cooling shows a ubiquitous concept of forcing air through a pad/membrane/...
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1answer
90 views

(Why) does wet air contain more oxygen?

I've heard the fact wet air contains more oxygen is the reason experts recommend to humidify the air. Intuitively, I'd say wet air should contain water of a greater density and thus, make less space ...
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3answers
54 views

Blowing smoke out of the clean air - can someone explain?

Yesterday my wife and I were out walking. The weather was cloudy and humid (it had been raining a few hours before). Around 15 C. Suddenly, with no apparent reason, both of us had smoke coming out ...
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18 views

Is there an effect on condensation when the elevation is changed?

So, I'm working on a test for a project and we want to see if any condensation occurs. The relative humidity temperature are fixed. From this we can find the dew point, which will give us a good ...
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24 views

Understanding relative humidity

I am having some trouble understanding relative humidity. If I have a vacuum chamber in which I place a hygrometer to measure relative humidity. In case I am able to achieve full vacuum, will the ...
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2answers
28 views

How to achieve a desired relative humidity in a sealed environment

I need to find out how much water to add (in milliliters) to a sealed test tube (which has a volume of 53 milliliters) to achieve a relative humidity of 60% when the temperature is heated 80 degrees ...
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34 views

Is there an influence of the air humidity on the air expansion by a temperature change?

I have found the following formula to calculate the expansion of air by a temperature change, if the pressure stays at the same level: ΔV = ​ɣ * V0 * ΔT This would give me an expansion of 46.96m3 in ...
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2answers
151 views

Relative humidity, definition and its dependence on state variables

Relative humidity ($RH$) is defined by the following equation: $$ RH = \frac{p_{vap}}{p_{sat}} $$ Where $p_{vap}$ is the vapour pressure and $p_{sat}$ is the saturation vapour pressure. VAPOUR ...
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38 views

Pinch point for heat and mass exchanger devices (like cooling towers)

As you know, there is a pinch point for heat exchangers... But can we introduce a pinch point for heat and mass exchanger devices (like cooling towers)? At cooling towers, the outlet water ...
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1answer
115 views

The minimum temperature that water can reach at a cooling tower

I have read this sentences at a paper and I can't understand the reason: Consider a cooling tower and read the following sentence: "When the water enters hotter than the air, the ideal condition ...
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1answer
227 views

Why do we sweat on a hot and humid day but the clothes are able to dry?

I know that on a humid day,water vapour content is high in air and as a result evaporation of sweat is lesser and hence we feel hotter. What I am not able to get is, if water vapour content is high,...
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1answer
22 views

How is steam affected by a fan?

Scenario Consider a humidifier with a fan behind it. Assume same room, moderate temperature, low fan speed. ...
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3answers
786 views

Will water in a vacuum evaporate continously?

Will a vacuum chamber that is maintained at 0.1 Atmospheres with an open water container inside ever reach 100% humidity of the remaining air, so that no more water evaporates or will water ...
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1answer
38 views

Diminished receptivity of paper to pencil during periods of humidity

Why does paper become less receptive to pencil when it is humid out? I have generally experienced this with a 4B pencil.
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2answers
53 views

Why Does Charging and Discharging Happen in Low Humidity, but not High?

If one rubs a neutral glass rod with cat fur will cause it to have excess negative charge in low humidity, but not in highly humid conditions. Why not? How does the water neutralise the rod? Why ...
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67 views

Closed System Pressure Rise due to temperature & relative humidity

Consider a closed system E.g. a lighting wellglass equipment like this: (Why this is a closed system? Because it is made air-tight through use of sealants - which seals the two components - an ...
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1answer
1k views

How to add the relative humidity percentage to molar mass of air

The higher the relative humidity percentage, the higher the molar mass of air, right? So then how do I add the higher amount of water in the air to the molar mass of air? For example, let's take a ...
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2answers
164 views

Can water boil at 100% absolute humidity?

The definition of absolute humidity is the amount of water that can exist in solution with air as a gas. My question is, in a closed vessel that contains a flask and a burner or heat source below it ...
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44 views

how to influence RH and air presure to resistance of air

For example higher RH (relative humidity of air) provide lower air electrical resistance. But how I can calculate with this relation? Moreover air pressure (between 1500 and 500 hpa) can influence ...
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2answers
114 views

Does air have to be oversaturated in order to make resublimation possible?

I am writing a pre-scientific work about the chemtrail conspiracy theory. A part of that is the exact process of contrail formation. There is one more puzzle piece missing. Hopefully the answer to ...
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3answers
180 views

Where is humidity?

During hot and humid weather, we sweat incessantly due to high humidity. But when we sit under a fan, we feel cold and comfortable. Why do we feel cold and chilled? Why don’t we feel the humidity?
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3answers
2k views

Why doesn't the moisture freeze out of the air when the air temperature is below freezing?

I would think that there would be zero humidity outside right now and it's 21 degrees. The weather site says there is 71% humidity.
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2answers
61 views

Propagation speed of air humidity

I'm currently playing with relative air humidity and temperature sensor that makes measurements in my living room once every 60s. When plotted the data on a chart I noticed that spikes and dips of ...
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0answers
81 views

Efficiency of a dehumidifier with respect to temperature [closed]

I have just bought a dehumidifier to decrease humidity in my bedroom. I'm wondering if it takes more energy to work (assuming same liters of water condensed) in winter with cold temperatures or in ...
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3answers
669 views

What law or formula discusses the relationship between pressure and dew point?

A lot of times, dew point is focused primarily upon temperature and relative humidity. However, that same point of saturation is affected by the pressure, but I can't find a formula, or law even, that ...
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3answers
561 views

Does Humid Air Rise (neglecting the effects of weather turbulence-for example in a closed environment like a sealed room)

An internet search will find many people claiming that Humid Air (water vapor) rises. However, I am skeptical because if lighter molecules rose then, it follows that the air would be stratified by ...
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1answer
381 views

Does fog clean the air of fine dust

When fog forms, the air is usually saturated with moisture. Thus, small droplets form and creates fog. Suspended fine dust can serve as condensation nuclei during the formation of fog. So my question ...
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4answers
5k views

Why is it hot before raining?

What causes the temperature hike before a rain? I have heard explanations like one that says as the moisture rises, you sweat more. Can somebody provide a more scientific explanation for this.
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1answer
540 views

Air-drying a dishwasher: door cracked or wide open?

My dishwasher's design is focused on noise, so there is no air vent which would allow noise to escape. When the dishes are done, I always open the dishwasher to fully dry the still-hot dishes. But, ...
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1answer
521 views

Explanation of cooling and dehumidifcation process on psychometric chart

I've got the same problem while trying to understand air cooling and heating. My textbook shows a picture like the following: In this Mollier chart we s that for air cooling we have too cool down ...
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2answers
97 views

What does absolute humidity do in a large space with a temperature gradient?

What does absolute humidity do in a large space with a temperature gradient? Situation: Enclosed space, approximately 8 meters in height. The space is nearly leak-proof, essentially no air being ...
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2answers
525 views

Effect of humidity on temperature

When temperature changes, relative humidity changes. Imagine I have a closed room at a certain temperature; then, I blow water vapor at a similar temperature. Can a change in relative humidity induce ...
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1answer
136 views

Which is the same between two connected rooms, relative or absolute humidity?

Question: Consider two glass bottles filled with humid air, connected with a tube. One of the glasses is hot (heated), the other is cold (cooled) and the situation is steady state. How will humidity ...
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2answers
564 views

Dependence of relative humidity on temperature and pressure

How is relative humidity determined by temperature and pressure? What is the equation and its derivation? The following is a specific scenario. Suppose a cubic container encloses a solution consists ...
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1answer
551 views

Can Humid air ever be heavier than dry air?

I understand that humid air is generally lighter than dry air, as water vapor molecules are lighter than nitrogen or oxygen molecules. But... my issue is that when I test RH in a closed container (a ...
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1answer
634 views

How does relative humidity affect the rate of water evaporation?

How does the relative humidity of the air affect the speed at which water evaporates? I know there are other parameters that affect it, so I made this assumptions: We have a plain metal plate of $1m^...
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466 views

Calculating amount of water needed to increase humidity to target Humidity

We are currently working on a greenhouse startup project. And we want to be able to maintain the humidity inside our greenhouse. Given we know the outside temperature and humidity. And also the ...
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91 views

How many water molecules in the air - is my calculation correct?

I want to know how many water molecules are in one cubic meter of air (Relative humidity=20%, Temperature=293K) This is my calculation: $p=2.3kPa$ (because of vapor pressure at 20C is 2.3 kPa (as on ...
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1answer
169 views

How tall would a chimney have to be to form rain?

The Caribbean often has temperatures over $30 \sideset{^{\circ}}{}{\mathrm{C}}$ with 100% humidity. If I were to build a chimney there, how tall would it have to be before rain formed inside it? ...
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1answer
119 views

What Causes Slanting Pointed Ice Spikes to Form? [duplicate]

Ice spikes are fairly rare but there is a general consensus about how they form from extruded pressurized water in containers subjected to below freezing conditions. This morning as I fed my dogs I ...
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1answer
419 views

How does a humidifier save on heating?

I have heard that using a humidifier in the winter can help you save money in heating costs. If this is true, I was curious about the physics behind why this is. My thoughts were that since water has ...