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Science > Physics |
| User: |
"" |
| Date: |
01 Feb 2008 09:13:53 AM |
| Object: |
change in vicosity consumes energy? |
if a lubricating oil has a low Viscosity Index, this indeicates that
as the temperature rises, the viscosity decreases a (relatively) lot.
When that occurs, has energy been consumed?
If so, and we decrease the temperature, is the energy (in theory)
recoverable? (if not, it presumably means that entropy has
increased?)
If yes, it means that the lube oil is storing energy. What would be
the name of the parameter which indicates the energy-storage-density
of the substance?
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| User: "Paul O" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 09:27:47 AM |
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wrote:
if a lubricating oil has a low Viscosity Index, this indeicates that
as the temperature rises, the viscosity decreases a (relatively) lot.
When that occurs, has energy been consumed?
If so, and we decrease the temperature, is the energy (in theory)
recoverable? (if not, it presumably means that entropy has
increased?)
If yes, it means that the lube oil is storing energy. What would be
the name of the parameter which indicates the energy-storage-density
of the substance?
Look up "specific heat capacity". See:
http://en.wikipedia.org/wiki/Heat_capacity#Heat_capacity
I hope this helps.
--
Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
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| User: "" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 03:11:40 PM |
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Look up "specific heat capacity".
I hope this helps.
Not exactly. Some of the energy was consumed in making the oil
hotter; all of that is (in theory) recoverable. I want to ignore that
energy.
I'm talking about the energy that was used in changing the viscosity
of the oil After all, we can imagine (& maybe there really exists)
two different oils with the same specific-heat, but different
Viscosity Indexii
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| User: "dlzc" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 07:34:53 PM |
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Dear dances_with_barka...:
On Feb 1, 2:11 pm, wrote:
Look up "specific heat capacity".
I hope this helps.
Not exactly. Some of the energy was consumed
in making the oil hotter; all of that is (in theory)
recoverable. I want to ignore that energy.
I'm talking about the energy that was used in
changing the viscosity of the oil.
Which is completely recovered when the oil cools, because its
viscosity goes back up. Unless you "burn" the oil...
After all, we can imagine (& maybe there really
exists) two different oils with the same
specific-heat, but different Viscosity Indexii
"indexes". Doesn't matter, you get all the heat back. All you are
doing is changing the bonding between the molecules, when you consider
viscosity index, and this is not a permanent change unless you alter
the molecules themselves (oxidation, polmerization, scissioning).
David A. Smith
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| User: "Edward Green" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 05:09:24 PM |
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On Feb 1, 4:11=A0pm, wrote:
Look up "specific heat capacity".
I hope this helps.
Not exactly. =A0Some of the energy was consumed in making the oil
hotter; all of that is (in theory) recoverable. =A0I want to ignore that
energy.
I'm talking about the energy that was used in changing the viscosity
of the oil =A0After all, we can imagine (& maybe there really exists)
two different oils with the same specific-heat, but different
Viscosity Indexii
What makes you think the "energy used in changing the viscosity of the
oil" is different from the energy used in heating the oil?
The chief problem with your question is that it seems to put
"viscosity change" on an equal footing with a delta-E. Viscosity is a
property of the physical state of the oil. In general there is a
delta-E when the oil changes physical state, but no part of this is
specifically assignable to "viscosity change".
There is no reason two oils with identical specific heats in some
range could not undergo different changes in viscosity, even assuming
all physical changes in heating were reversible: the "explanation" for
this (which seems to presume it needs one), would presumably lie in
the details of their molecular structures.
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| User: "tadchem" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 04:11:30 PM |
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On Feb 1, 10:13 am, wrote:
if a lubricating oil has a low Viscosity Index, this indeicates that
as the temperature rises, the viscosity decreases a (relatively) lot.
When that occurs, has energy been consumed?
If so, and we decrease the temperature, is the energy (in theory)
recoverable? (if not, it presumably means that entropy has
increased?)
If yes, it means that the lube oil is storing energy. What would be
the name of the parameter which indicates the energy-storage-density
of the substance?
Viscosity is describable as the resistance to the transfer of momentum
between adjacent regions in a fluid.
In collisions between molecules, whether in liquids or in gases,
momentum and energy are conserved and bulk thermal equilibrium is
maintained. There is no storage or retrieval of energy in viscosity.
Changing the temperature of a fluid may store or retrieve energy
through some other process such as a phase change or some such, but
not through viscosity changes.
In general, raising the temperature will decrease the viscosity of
liquids, but increase the viscosity of gases. (Interestingly, the
viscosity of a mixture of gases is invariably higher than what might
be expected from an "ideal" mixture relationship. I suspect the same
is true of miscible liquids, for mechanistic reasons, but I have not
gathered the data to demonstrate this.)
FWIW, the reciprocal of viscosity is called the fluidity.
Tom Davidson
Richmond, VA
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| User: "Brian Whatcott" |
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| Title: Re: change in vicosity consumes energy? |
01 Feb 2008 09:43:55 PM |
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On Fri, 1 Feb 2008 07:13:53 -0800 (PST),
dances_with_barkadas@yahoo.com wrote:
if a lubricating oil has a low Viscosity Index, this indeicates that
as the temperature rises, the viscosity decreases a (relatively) lot.
Yes...
When that occurs, has energy been consumed?
Energy is consumed so to speak, in heating a liquid.
If so, and we decrease the temperature, is the energy (in theory)
recoverable? (if not, it presumably means that entropy has
increased?)
When a liquid cools, the energy associated with that temperature is
reduced, and it goes somewhere else.
If yes, it means that the lube oil is storing energy. What would be
the name of the parameter which indicates the energy-storage-density
of the substance?
It's just the same boring old parameter for many liquids, like water
for example - whose viscosity also varies with temperature.
It's called the Specific Heat capacity. For water it's around 4190
joules per kilogram. degree C Oils can have half that value.
Think of viscosity as the propensity to provide internal friction on
surfaces moving relative to each other in the fluid.
Brian Whatcott Altus OK
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