Viscosity related problems in winter

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liquid soap dispenser on basin

There are a couple of problems you have to face in winter. The problems I’m talking about are due to viscosity. The idea of writing about it came into my mind when I was refilling liquid soap this morning. Although the hole in the packet was big enough, the liquid would not come out. The thing is liquids are more viscous in winter due to low temperature. The relation between viscosity and absolute (Kelvin) temperature of a liquid is:

η = A + B/T

Here, η is the viscosity and T is the absolute (aka Kelvin) temperature of the liquid; A and B are constants. These constants take different values for different liquids. When the temperature is low, the quantity B/T is of high value. In such a case, η has a high value since A and B are positive constants. This is why in low temperatures, specially in winter liquids have high viscosity, be it liquid soap or condensed milk. Watch the following video to see how condensed milk is heated to lower down its viscosity.

Do coconut oil and low quality edible oil face the same problem?

These oils face the above-mentioned problem to some extent indeed, but they face another bigger problem. These oils have low melting and freezing points. Which is why they get frozen in the winter low temperatures of countries like India and Bangladesh. As a result, it is quite inconvenient to use these oils in the winter. High quality edible oils are hydrogenated, that’s why they have higher freezing points and don’t get frozen in the winter low temperatures.

Heat can be used to melt these frozen oils, but the amount of heat mustn’t be minimum only to make the oil melt. Because even if the oil is melted, it could still be very viscous due to having a low temperature. So, it would not roll. That’s why a big amount of heat is applied to raise the temperature enough. As a result viscosity lowers down to a great extent.

How viscosity of gases change with change in temperature?

Interestingly enough, viscosity of gases increase with increase in temperature. If viscosity is denoted by η and T is the absolute temperature, the following relation applies for gases:

η ∝ √T

It means that cold gases can flow pretty fast and hot gases can’t flow fast enough, due to high viscosity. Now you surely understand why winter cold breezes are so capable of flowing and making your bones shiver. Those who sit opposite to air conditioners in offices have first-hand experiences about it.

Why there has to be two holes in a condensed milk can?

can food being heated beside fire

Do you see two holes on the condensed milk can in the above image? A housewife was asked about it. She replied it was done so that air can enter the can and milk remains okay, which is not the real case. If there was only one hole, the milk would not want to come out, due to air pressure. When a bottle filled with water is upside down, the water doesn’t come out constantly (in a stream). A little bit of water comes down, then air enters, then a little more water comes down, then a little more air enters the bottle, and so on and so forth. This is why at this time you get to hear a gurgle sound.

This is possible because water has a low value for coefficient of viscosity. But this coefficient has quite a high value for condensed milk. That’s why this sort of milk would not want to come down when there’s only one hole in the can. Because of this there has to be two holes in a condensed milk can. Air enters through one hole and milk comes out through the other hole. As a result vacuum isn’t created inside the can.


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