h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In Canada, we just call it dish soap but basically the common stuff one uses for hand-washing of dishes

We have a double sink in the kitchen. I fill one with rather hot water and the detergent, toss in the cutlery and first things that I would wash. The other sink gets straight hot(ter) water for suds rinsing.

Once it has cooled enough for my hands, still quite hot in fact, I proceed to wash the flatware, etc. And by then, the rinse side has cooled atleast a good 10C. Both sinks are of a single casting of stainless steel, identical in measures and capacity, and so neither side should dissipate more water heat than the other.

Why does the washing side remain hot so much longer? Is it something in the soap/liquid? I never fill it with much of anything material that would hold a lot of the 'heat'

Purely as a guess, the layer of bubbles may have an insulating effect, all that trapped air.

An idea, but at a very rough guess I would see the sudsy surface being well under 30% of the water edges and surface. And the remainder being metal, no insulating factors at all, ...

Even after 40 minutes of distracting phone calls, the sudsy side was comfortably warm and the rinse side about room temps

I would respectfully suggest that, in order to get a definitive answer you should approach the problem scientifically.

Take two thermometers and place one in each bowl (filled with equal volumes of water of equal temperature) and then proceed with the washing up as normal. Check the temperature of each bowl at regular intervals, say 1 or 2 minutes. Also observe the behaviour of the washer-up. How much is each bowl of water disturbed? Does one bowl receive water off the draining side of the sink or does this water drain elsewhere?

I will be interested to know the results.

t.

These are not bowls but the sinks that are built into the kitchen counter top. We do not use extra bowls of any sort, just the plugs that are built in ... I could purchase a few cheap thermometers and take 45-minute readings of one with suds and one without. But I also pay for the water to be heated and wasted. Fuel oil fired water heater, ya know

I don't think it's necessarily down to bubbles just being insulation against *convection*, but down to them also greatly reducing evaporation via a combination of effects - convective insulation slows down heat transport to the upper surface of the bubble layer, which results in lower rates of evaporation from the cooler surface.

Just look at the different amounts of of condensation in a cold bathroom between someone having a hot bath in plain water, and someone using bubble bath or similar to create a nice layer of bubbles and bathing for the same length of time in water of the same initial temperature.

Double sink.

Are the sinks the same dimensions, volume and made of the same material?

One cast, same material (stainless steel product) and same dimensions for width, depth, etc. 'Ambidextrious' so to speak ...

Measured, both sides are identical. With slight tapering towards the bottom, the mid level is 14" x 16", and while 7.25" of water could fit, I'd not guess more than 5.50" on the most generous days

(And I am leaning towards Potholer's concept ... a layer of bubbles and froth also makes for a lot of square-feet for temp dissipation. Not to mention that suds add to the tensile permeability of the surface of the water to evacuate steam and heat. (Perhaps the wrong words, I'm stretching a few decades, but soap does make the skin of water 'thicker')

Hmmm, OK. I guess that maybe a layer of bubbles is more like a layer of insulation just like the air pockets in your wooly jumper.

Interesting question.

I was thinking it was just a question of surface area or conductance of the sink material but your answer to my questions rules that out.

One thing I don't think is that the washing up liquid itself will make a significant difference. There is probably a maximum of 5% of it in the water and its heat capacity is not likely to make all that much difference to the overall heat capacity.

And yet that is the difference, one basin with washing up liquid at really-hot, one of just water as scaldy hot. And yet in 20 minutes, the suds are barely tolerable to the hands and the nekkid water is tepid.

Yes but how sudded - lots of bubbles?

Actually thinking about it - the soap does tend to sit of the surface and soaps/detergents are significantly organic in nature (i.e. carbon based compounds) which are very good insulators.
It may just be sitting on top and insulating the liquid below from the surroundings. I still think that a layer of bubbles is probably more significant to act as insulation though.

Later in the week, I will find a pair of 'toss-away' thermometers. And make a small record over an hour or so. I know it is not my imagination, so true numbers should tell. Say readings every 10 minutes or so, equal volume of water ... one common suds and one without

try doing it with frothy suds and without too. I.e. put the soap in but stir it in gently so it doesn't bubble up for the latter. I'm betting it's an air cushion inside the bubbles that is doing it.

For anyone thinking or experimenting, an evaporation block would be interesting - maybe a layer of clingfilm, if one could be placed on the water without getting bubbles underneath, or getting wet over too much of its upper surface.

Googling around, people who sell swimming pool covers seem to reckon that evaporation is responsible for about 60-70% of the heat loss, about twice as much as radiation, though that's coming from people who only seem to rate evaporation and radiation as serious ways of losing heat from the surface.

Whether they lump convection of warm air in with evaporation isn't clear (I suppose it's hard to separate the two in uncovered pools, since evaporation will presumably be constantly supplying warm vapour to participate in convection), though the fact that both plain and insulated covers are sold without huge claims being made for insulation being vital would rather point to evaporation being of large and maybe main importance.

Other data (from an RSPEC study) which did discriminate suggested that evaporation was responsible for slightly over twice the heat loss than convection was.

Have you swapped sinks?