Dryers and how they work

[richnz]

So a dryer pumps hot air into the drum which holds clothes. The clothes tumble inside this drum and mix with the hot air. The hot air evaporates moisture inside the clothes and this leaves the drum at a cooler temperature.

Right?

So I have a Miele dryer and I always suspected it was HOT. When I first got it I recall putting my hand inside the stream of air flowing down to the condenser and thinking that was really hot.

I happen to own a diagnostic unit and have the software and have taken screenshots.

I was under the impression for example when you set the dryer to gentle, then warm air would be blown across the clothes.

Cottons with the Gentle option has air entering at 120 C (Target was 150 C) and leaving at 60 C (with a target of 66C).

My questions are:
What has happened to the difference?
What was the point of the low button when these temperatures are not low.

I have uploaded some screen shots from different loads.
The OPERATING STATE window shows the program and the additional function.

Thanks for any answers

Richard

 

[earthling177]

Richard:

Your general idea is right: hot air enters the drum tumbling the clothes, it warms up the clothes releasing moisture into the air and leaves the drum.

The difference in temperatures (air entering the drum and leaving the drum) is heat lost to warming up the clothes, the drum, the air etc. A lot of the heat/energy is applied not only to raise the temperature of the clothes and its moisture, but into evaporating the moisture to be held in the air.

If you look at a table that lists how much energy is necessary to raise a certain mass of whatever substance a number of degrees, you will quickly find out that water takes *much* more energy than clothes.

That's why at the start of a drying cycle the air leaving the dryer is much cooler than when the cycle is about to end.

The other thing to consider is that condenser dryers in general operate at higher temperatures than vented dryers. That having been said, older vented dryers frequently operated at much higher temps than you list, and to this day, some laundromat dryers operate at temps higher than 80C on *low* heat and reach over 100C on high.

I wouldn't doubt that gentle heat is lower than regular heat in your dryer.

Also, the high temp in the heater bank is to be expected, it is more or less like a blow dryer for your hair, the air in the vicinity of the heater bank is much hotter than when it mixes with the ambient air.

Another thing to keep in mind is that while newer vented dryers are now operating in lower temps, older domestic dryers often had a target temp above 60C to relax the wrinkles in permanent press clothes for example. It shouldn't be harmful for most real clothes (as opposed to plastic shower curtains) to tumble at that temperature.

Cheers,
   -- Paulo.

 

[yogitunes]

there were a select few dryers that offered 'modulating' heat temps.....in that meaning, like your gas stove, the temp could be selected by the turn of the dial, from a low simmer to a boiling high......

todays dryers mostly operate at HIGH temp all the time.....

by selecting a temp like "Low", doesn't offer that the max temp not go over 120 degrees, actually that's the minimum before the heat source comes back on....

lower temps are achieved by allowing a longer cycled 'heat off' time before it activates again....

this has always puzzled me of people who wash in cold water, for the reason of preventing shrinkage.....yet toss those items into a 160/180 degree dryer....way hotter than the temp of the water heater if they washed these same garments in hot water....

if anything, place a thermometer in the vent line, and by selecting temps, see how hot the air temps gets, and how low it gets before the heat comes back on, and how long of a time between the two....

there is of course the 'soft heat' feature of a Kenmore dryer....in that every time the heat cycles on, the temp is dropped/cut off by 5 degrees....basically as the clothes gets drier, the temp lowers down...if you ask me, the best system ever...other dryers operate at high temps across the whole cycle, until 'cool down' take place....

 

[henene4]

Air is a somewhat bad medium for heat-transfer as well.

Compare it to an oven: You select temperatures of 150-200C as well and still can put your hand in there, simply because the air transfers only a small amount of energy per time.

It would be interesting to know if the dryer possibly lowers these temperatures as the drying advances, adapting to the lower moisture content in the laundry.

 

[johnb300m]

It's my understanding that on some more recent Whirlpool made dryers in the US (at least), the Normal cycle will dry on HI and then step down to a more MEDIUM heat toward the end of the cycle.

I really like the results.

 

[panthera]

Condenser dryers

Which use water or air to provide the cooler side of the temperature gradient raise the temperature in the drum as high as possible to increase the effectiveness of the condensation process.

 

I, too, am puzzled by people who only wash in cold water in order to 'save their clothing' then use a tumble dryer or a heated iron to press their clothes.

 

They're not thinking rationally.

 

Of course, it's still best to wash clothes in the warmest water they can take. Ideally, the temperature of the water should be held at the most effective point for the various enzymes in use for a long enough period of time for them to do their work.

 

Sadly, cold water just isn't warm enough for enzymes to do a very good job. That's why detergents and dryer sheets and fabric softeners use stronger and stronger perfumes - to cover the filthy mess distributed over the clothes after they've been 'cleaned' in ice-cold water.

 

Unless the clothes are being damaged, I'd not worry about the dryer running too warm. This is the temperature range my Miele water-condensing dryer and my AEG air-condensing dryer used for all settings except special treatment (which took forever).

 

To my horror, the US government, back when they actually did consumer saftey, showed temperatures at the exhaust vent of the dryer of over 204C when the vent pipe was blocked before the internal safety thermostats turned the heat off. That's way above the auto-ignition point for dryer lint! Yikes! Time to recheck our dryer vents!

 

[kb0nes]

I've posted this before but it might be decent information in this thread too

This is a profile of the air temp of my gas Cabrio dryer and a load of towels. Thermocouple was in the airstream on the lint screen. Temps are degrees F

 

[launderess]

Have to remember

One reason why early tumble dryers ran very hot as did laudromat machines was the rather pitiful extraction of early washing machines.

For American homes top loaders and even wringer washers dominated the domestic market. None aside from a few machines like those offered by Frigidaire had very high spin speeds, and wringers equal at best about 200rpms. Either way you are putting basically sopping wet laundry into a dryer. You're going to need that high heat to "bake" out all that moisture.

In laundromats extraction from front loaders wasn't that much better, and top loading were what they were. Either way a place could "make money" on the dryers even if they ran hot (which many did), because customers tend to over dry. Some laundromats did offer separate Bock extractors to "cut down drying time", especially for heavier things.

On the commercial side of laundry it has long been recognized that the most efficient and effective way to remove moisture from the wash is via extraction. That is finally catching on with domestic machines as washers are able to offer faster final spin speeds. That in turn means less need for energy from dryers.

When using laundromat dryers always start off on "High" but will keep an eye on how load is progressing. Once things reach a certain stage of dryness will move the temp down to "Med" or even "Low". The last five minutes are always on "Delicates". Find the results are better than allowing laundry to bake dry, especially since the cool down period on these dryers is only one or two minutes. Not nearly long enough to reduce temps and prevent hard creases.

 

[tomturbomatic]

Phil, I am surprised at the 40 degree swing, fast as it is, with a thermister during the drying. I am spoiled by the steady drying temperatures of my gas dryer with the modulating burner that holds a steady 165F until cooldown.

 

[brucelucenta]

In laundromat machines that was why speed queen had a higher spin on their commercial machines back in the day of the solenoid machines with the fluid drive. No matter what speed you selected, it was always high for the spin speed. Frigidaire commercial machines had the rapid dry 1000 machines until the 70's and then they still had a fairly high spin speed.

 

[richnz]

Thank you

For your responses. I had it in my mind that the drying temperatures were more summer breeze like for the gentle option and not 8 degrees from regular (target wise).

It also brings home the thought that items won't shrivel should they be hot washed.
Cheers and keep up the good work.

Rich

 

[logixx]

The temps in my Bosch condenser dryer are also high. 75C for normal, 65C for gentle and 55C for extra gentle heat. Like virtually all European dryers, it has two heating elements that cycle individually or together for a more uniform heat output.

 

[kb0nes]

Tom, It would be interesting to do a thermal profile on a machine with a modulating burner. Of course it wouldn't oscillate like mine did. I bet there is a fair bit of variation there too.

Does anyone make a dryer with a modulated burner any longer? It is an interesting technique but the cost of the gas valve may have more then offset any possible advantage they could have had.