Why Did It Take 15 Minutes for My Water to Boil?

[davon806]

Hi,
I noticed an interesting phenomenon when I was boiling the spaghetti yesterday.
Please refer to the attachments.
I poured about 200 mL of water into the pot and waited until it boiled.However,you know,it would only take you about 3 - 4 minutes to bring this amount of water into boil from room temperature.But I had been waiting for 15 minutes and it just didn't happen.I got really mad and so I put the spaghetti directly into the water and started the timer.The water didn't change into steam,and when there was about 3minutes left,I noticed that(as I was cooking with my brother,so I didn't see it at the beginning) the right fan of the exhaust hood was switched on,while the left one wasn't.Normally,I will switch both of them on.Thus,I thought the mystery stemmed from this.Subsequently,I pressed the button of the left fan.What really surprised me was that the water came to boil within 5 seconds!

Some additional information:
1.I turned on the right stove and right fan.Did the position of the stove matter?Would it happen if I turned on the left stove and the right fan?
2.At first,I didn't cover the pot.When I got more and more irritated,I covered it.A few gas bubbles seemed to evolve from the water surface,but it returned to be smooth after I had taken the cover away.I didn't think this was relevant because I seldom had the lid on while I was cooking.
3.I switched the gas stove to the maximum output throughout the whole process.

I guess it was related to the pressure of the surrounding instead of the temperature of water,because the rate of heat loss to surrounding will increase if both fans are switched on,and this will lower the temperature of the liquid further?Moreover,the water came to boil in an unbelievably short time,which suggested the water in the pot had probably exceeded 100 degrees Celsius.

I am not an engineering student,but I still want to know why this would occur.Hoping for someone to share their thoughts! Thx.

 

[bhillyard]

Was it a gas burner? At my local scout campsite the main gas cooker has had to be crosslinked to the exhaust fan because there was insufficient natural ventilation on the kitchen for the gas burners to have an adequate air supply.
This would fit with your experience of the heat output increasing with the increased ventilation.

 

[davon806]

Thx,but I didn't think it is the reason.I would either close all the fans or have all of them switched on.Yesterday was an exception.In fact I have had quite a lot experiences of heating with the gas stove without bothering the range hood,and eventually I was able to get everything sorted.

 

[mfb]

The air pressure is constant, you cannot change it with the exhaust hood - even if you would completely make your kitchen air-tight, the effect would be negligible.

The mechanism bhillyard suggested looks very reasonable - if the amount of gas available depends on the exhaust, it can explain all observations. The water was probably close to 100°, where relevant temperature differences become tiny - increasing the input heat can start visible boiling quickly.

 

[PJC01]

Hello,

Thank you for sharing your experience with boiling water and the interesting phenomenon you observed. It is not uncommon for water to take longer than expected to come to a boil, and there are a few factors that could have contributed to this in your situation.

Firstly, the position of the stove may have played a role. Gas stoves typically have a higher heat output in the center of the burner, so using the right stove instead of the left could have resulted in slower heating of the water.

Secondly, the exhaust hood fans being on or off can affect the pressure and airflow in the room. This can have an impact on the rate of heat loss from the pot of water, and ultimately, the time it takes for the water to reach boiling point. Additionally, covering the pot can also affect the pressure and heat loss, as you observed.

It is also important to note that the boiling point of water is not solely dependent on its temperature, but also on the surrounding pressure. By increasing the pressure in the room through the use of both exhaust hood fans, the boiling point of the water was likely lowered, allowing it to boil at a lower temperature and in a shorter amount of time.

Overall, it seems that a combination of factors, including the position of the stove, the use of exhaust hood fans, and covering the pot, all played a role in the longer boiling time you experienced. I hope this helps to explain the phenomenon you observed. Thank you for your curiosity and interest in understanding the science behind everyday experiences. Keep exploring and learning!