[Mb-hair] Re- Fw- Nuking Water

[John Zuehlke]

Yes, the phenomena of "superheated" liquids does exist, and they can rather explosively change state (into gas) as described.

Though the reasons behind this is quite well explained in the material you quoted, I still would be cautious with some of the suggested protective measures.

What is happening is that the water (or other liquid) has absorbed enough energy to change it from the liquid stare into a gas (steam), but nothing has triggered the change to occur yet. Any mechanical disturbance of the water can trigger the change, and, once it gets going, the resulting disturbance is adequate to trigger the rest of the liquid to change state. This will continue (with great, explosive, rapidity) until the remaining liquid has been so depleted of energy that it cannot change to gas.

In chemistry labs, it is common practice to place inert "boiling chips" into a liquid to prevent such explosions. They typically are sharp pieces of glass, the sharp edges of which form a "nucleus" around which gas bubbles will form. Thus the liquid will start turning to gas as it is heated and thereby not become significantly "superheated".

Your science teacher is right-on, but the other responses leave something to be desired. Several things to be cautious of: 

1) A "two minute per cup" limit on heating water is not very meaningful. It is the amount of energy that goes into the water that matters, not how long it is in the oven. The amount of energy is dependent on the size (Wattage) of the microwave, the setting (duty cycle), and the amount of water in the cup. Since these are all variables, the amount of time needed to achieve "superheated" status is also variable. 

2) Superheating is not a phenomena limited only to heating by microwaves. It can occur even in a conventional stove-top tea kettle. It usually doesn't occur because most vessels used for heating on stove tops have enough sharp edges to trigger gas bubble formation.

3) Placing something into the liquid when heating it does not stop superheating by "diffus(ing) the energy." The added items simply provide additional nuclei (either mechanical or chemical) to trigger bubble formation.


4) The wait 30-seconds rule is also not foolproof. Liquids can remain superheated for quite some time before something occurs to trigger bubble formation.

A interesting fact is that this phenomenon can happen IN REVERSE and is quite commonly seen. A gas may be "supercooled" below the temperature at which it would normally turn into a liquid. This is commonly seen in the formation of clouds and fog, which are suspended droplets of water that have condensed out of gaseous water in the atmosphere. Scientists used this from the early days of the atomic era to visualize nuclear radiation. Water vapor was supercooled delicately so that it wouldn't condense into liquid. When a charged nuclear particle, such as an Alpha or Beta "ray" passed through the gas it would leave a trail of minute liquid water droplets that represented the path the particle took.

On a different, but related, subject, there is a special danger to heating by microwave or other High frequency radiation: Thew "skin" effect. I learned about this "the hard way" when, years ago, I decided to heat a small carton of milk in my college's new microwave oven. I warmed the milk just to drinking temperature and then drank it down. After I had swallowed the last satisfying gulp, I discovered that the entire inside of my mouth (and, therefore, esophagus, etc.) was coated in a thick layer of wax from the inside of the carton! Microwaves penetrate, and thus, supply heat, to varying depths depending on the electrical conductivity of the material heated. In the case of my milk, apparently the outer surface of the milk reached a high enough temperature to melt the wax coating on the carton while the rest of the mile that was closer to the center received relatively little heat. When I drank it, the milk was mixed and seemed only pleasantly warm, but it carried the melted wax from the carton along with it!

Hope that this proves helpful.



Blessed be with love, peace, and happiness,

John

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----- Original Message -----

Date: Sun, 1 May 2005 06:49:31 -0400
From: "ROBERT CLARKE" <CLARKE445566 at msn.com>
Subject: [Mb-hair] Fw: Nuking Water
To: "Virginia Campbell" <vghc_ginny at yahoo.com>, "Terence Clarke"
<tclarke at rdwgroup.com>, "monty clarke" <montyclarke1965 at hotmail.com>,
"Skip Rothrock" <SROCKNJ at worldnet.att.net>, "Robert Ferrante"
<theworld at pri.org>, "Michael Butler" <michael at michaelbutler.com>,
"Clarke Young" <clarkelyoung at yahoo.com>, "christopher clarke"
<kilap at hotmail.com>, "Chip Clarke" <chipp2269 at yahoo.com>, "Brad
Marshall" <Marshall.edwin at Progidy.net>, "Barbara Clarke"
<Bclarke167 at aol.com>
Message-ID: <200505011347.j41DltS3008340 at dune.islandtechnologies.net>
Content-Type: text/plain; charset="iso-8859-1"



----- Original Message -----

Subject: Nuking Water


I checked Snopes and this is true.

Microwaving Water!

(I did not know this, did you?)

A 26-year old man decided to have a cup of coffee. He took a cup of water and put it in the microwave to heat it up (something that he had done numerous times before). I am not sure how long he set the timer for, but he wanted to bring the water to a boil. When the timer shut the oven off, he removed the cup from the oven. As he looked into the cup, he noted that the! water was not boiling, but suddenly the water in the cup "blew up" into his face. The cup remained intact until he threw it out of his hand, but all the water had flown out into his face due to the build up of energy. His whole face is blistered and he has 1st and 2nd degree burns to his face which may leave scarring.

He also may have lost partial sight in his left eye. While at the hospital, the doctor who was attending to him stated that this is a fairly common occurrence and water (alone) should never be heated in a microwave oven If water is heated in this manner, something should be placed in the cup to diffuse the energy such as a wooden stir stick, tea bag, etc., (nothing metal).

It is however a much safer choice to boil the water in a tea kettle.

General Electric's Response:

Thanks for contacting us, I will be happy to assist you. The e-mail that you received is correct. Microwaved water and other liquids do not always bubble when they reach the boiling point. They can actually get superheated and not bubble at all. The superheated liquid will bubble up out of the cup when it is moved or when something like a spoon or tea bag is put into it.

To prevent this from happening and causing injury, do not heat any liquid for more than two minutes per cup. After heating, let the cup stand in the microwave for thirty seconds! before moving it or adding anything into it.

Here is what our local science teacher had to say on the matter: "Thanks for the microwave warning. I have seen this happen before. It is caused by a phenomenon known as super heating. It can occur anytime water is heated and will particularly occur if the vessel that the water is heated in is new, or when heating a small amount of water (less than half a cup).

What happens is that the water heats faster than the vapor bubbles can form. If the cup is very new then it is unlikely to have small surface scratches inside it that provide a place for the bubbles to form. As the bubbles cannot form and release some of the heat has built up, the liquid does not boil, and the liquid continues to heat up well past its boiling point.

What then usually happens is that the liquid is bumped or jarred, which is just enough of a shock to cause the bubbles to rapidly form and expel the hot liquid. The rapid formation of bubbles is also why a carbonated beverage spews when opened after having been shaken."

If you pass this on you could very well save someone from a lot of pain and suffering.

Thank You Very Much.

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