[John Chapman (OP)]

 
When I was in my twenties I once had a hot date. 20 minutes before my new girlfriend came round I realised I had no clean underwear. That was when I had a brainwave. Using one of those new microwave oven thingies and I could quickly wash my underpants and dry them in the microwave. I’d read that microwaves work by heating up the water within an object but articles without water, such as crockery, wouldn’t get hot. So.... the water should boil off and leave the underwear dry and, what with the fan inside, cool. So just enough time to rinse out my pants, bung them in the microwave, and quickly jump in the shower while they dry.

That was my second mistake - leaving my underpants cooking while I had a shower, I mean. 5 minutes before my girlfriend arrived I got out the shower and smelled the smoke.

To cut a long story short my new girlfriend arrived to find me running around the house wet and naked using my towel to try and flap all the smoke out of windows. And her Mum was with her, having dropped her off!

So where did I go wrong? I’d read that microwave ovens work because water molecules are polarized and boomerang shaped and flip backwards and forwards as they try to align themselves with the alternating electric field of the microwaves. Vibrating atoms = heat. I think. But my nylon cooking bowls don’t set alight. So why did my nylon underpants?
 

[Chemistry4me]

As you have learned, microwaves don't dry clothes effectively. They are good at making water hot, and if the water becomes hot enough, it will boil, leaving the clothing dry, but the thing is, there is nowhere for that water to go because there is no airflow. So if you had gotten out of your shower a bit earlier, and taken your underwear out, you probably would have found that it was piping hot but still wet! What you should have done was to heat it for a few minutes, take it out (carefully! With gloves on) and fan it around a bit, put it back in and repeat the process.

[neilep]

How did the date go ?


What ewe of course should have done is bung a load of talc in there too..that would have sorted it !..or stuck one of those mini battery powered hand fans in there to create a nice air flow. The microwave would have done the job good and proper then !!


This reminds me when years ago wifey was away and one of my kids dirtied a towel real bad with mud and stuff..I could not be arsed to put it in the washing machine so,having just filled the dishwasher, I just chucked it in there.

To my disbelief the dishwasher did not clean the towel at all !...hmmmpth !!..I was well miffed because it meant I had to use the washing machine after all and that's girlies stuff !!

[John Chapman (OP)]

Hi Chem

I still don't understand why, since water can only reach 100c (at normal atmospheric pressure) and water is the only thing that would have heated up, why did my underpants reach combustion temperature. Wet or dry they shouldn't have exceeded 100c.

Hi Neil

How did the date go ?
 

Many years later I married her.
 

[Chemistry4me]

Did you have any metal in there? Buttons with metal? Keys???

[John Chapman (OP)]

Wot, in my underpants?!

Actually, I think they were probably made from cotton rather than nylon. I don't know if that's significant, what with cotton being organic and all.

[lyner]

I think the reason has to do with insulation. You can burn bread, too, because the temperature in hot spots can get very high if the heat can't flow easily to the cooler bits.
They use turntables and 'mode stirrers' to keep hotspots from forming but they don't always work well enough. Liquids work best becaust they convect the heat around inside.

[Herman Melville]

How did the date go ?

Yes, I'd like to know about that too. Did you have to explain the smoke? Are you still in touch?

[Chemistry4me]

Hint: []

How did the date go ?
 

Many years later I married her.
 

[Don_1]

Hi Chem

I still don't understand why, since water can only reach 100c (at normal atmospheric pressure) and water is the only thing that would have heated up, why did my underpants reach combustion temperature. Wet or dry they shouldn't have exceeded 100c.

Hi Neil

How did the date go ?
 

Many years later I married her.
 

I had a disaterous date like that!!!

[neilep]

LOL..Don beat me to it !!....

[Bored chemist]

How terribly sweet and romantic.
Anyway, I think that cotton is polar enough to absorb microwaves and heat up.

[techmind]

A microwave oven, when switched on, pumps 700 watts of microwave energy into the oven cavity. That energy has to go somewhere! If the cavity/oven is empty, then most of it will be dissipated in the magnetron, causing that to overheat.
But anything which is damp or otherwise has "dielectric losses" will potentially get hot - especially if it's the only thing in there.