Insulation R value

[Mjone77]

For a science project that I am doing, I am testing different types of insulation in between the walls of cups and how well they keep the water warm or cool. I've done some research on insulation, but I can not find anything that breaks it down into easy terms. Could you please break down R value into easy terms and maybe, if you know, which type(s) of housing insulation would be best to put between the walls of a regular sized cup so that it is the most effective to keep the water cool or warm.

[michel123456]

For a specific thickness of a specific material, R expresses the resistance of transmission of heat. When R is high, the material provides good thermal insulation.

If you don't grasp easily it's units (K·m²/W), it is maybe easier to grasp its reciprocal (W/m².K): the quantity of heat (in Watts) that passes through a square meter of material for one degree Kelvin.

[Enthalpy]

The best material is vacuum, and then you've made a Thermos cup.

 

Aid it if needed (not for a cup) by several layers of sheet with low infrared emissivity, in which case it's a multiplayer insulation (MLI).

 

Other possibilities are less efficient. Avoid metals, choose the plastic or ceramic properly, but the good ones are nearly identical. No magic through the material, only the shape.

 

An intermediate method, neither solid nor vacuum, is a foam. Choose a rigid non-toxic one that withstands heat (dishwasher), enclose it between hard protective layers. Something like microballoons in a ceramic might work.

[CaptainPanic]

I agree with michel123456: the easiest term is the Heat Transfer Coefficient, U, expressed in (W/m².K)

 

If you transfer some heat from A to B, you express this in Watts (power). Watts are Joules per second: how much energy you transfer per unit of time.

 

This heat is transported through a surface area. Like the outside of the cup, in which you hold your hot or cold drink.

And if you have a larger temperature difference between the cup and the air (or your hand which is holding the cup), this transfer will go quicker.

 

So, that means you arrive at a formula to calculate how much energy is transferred (lost or gained) by or from that cup:

 

[math]P = U\cdot{A\cdot{\Delta{T}}}[/math]

in which:

[math]P[/math] = power (Watts)

[math]U[/math] = heat transfer coefficient (W/m².K)

[math]A[/math] = surface area (m²)

[math]\Delta{T}[/math] = temperature difference between object and outside (K)

 

The next question would be: is there any way to predict the heat transfer coefficient U? And the answer is: yes. But it's pretty damned complicated. If you want to know anyway, please specifically ask for it, and we'll explain.

[michel123456]

The best material is vacuum, and then you've made a Thermos cup.

 

Aid it if needed (not for a cup) by several layers of sheet with low infrared emissivity, in which case it's a multiplayer insulation (MLI).

 

Other possibilities are less efficient. Avoid metals, choose the plastic or ceramic properly, but the good ones are nearly identical. No magic through the material, only the shape.

 

An intermediate method, neither solid nor vacuum, is a foam. Choose a rigid non-toxic one that withstands heat (dishwasher), enclose it between hard protective layers. Something like microballoons in a ceramic might work.

I don't know about void, but most if not all methods use air.

Air is a good insulator under the condition to avoid convection current.

For avoiding convection current, you need to enclose the air in small partitions, in practice less than half an inch (that is approx. the distance between 2 glasses in a double glass window)

 

 

Some materials you can find commonly are wool, fur, cotton. Then you go to expanded polystyrene, mineral wool, glass wool. All materials are based on the same principle.

 

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edit

 

You must also insulate against radiation. that's why most insulations have multiple layers.

Edited November 6, 2012 by michel123456

[alpha2cen]

For a science project that I am doing, I am testing different types of insulation in between the walls of cups and how well they keep the water warm or cool. I've done some research on insulation, but I can not find anything that breaks it down into easy terms. Could you please break down R value into easy terms and maybe, if you know, which type(s) of housing insulation would be best to put between the walls of a regular sized cup so that it is the most effective to keep the water cool or warm.

 

This is non-steady state heat transfer problem.

Other factors are also important.