Synthetics- Heat Transfer

[cryptokid]

so why is it that mercury transfers heat many times better than even water, yet is so thin at 40c that it would be way lower than even a zero weight oil.

mercury at 40C is 0.12 cst.

i dont understand this.

 

[buster]

What is Amsoil refering too here? Some claim S2k is great at reducing temps.

quote:

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AMSOIL Series 2000 20W-50 Synthetic Racing Oil is specially formulated to carry the oil's wear reducing and heat transferring agents to the engine's surfaces and hold them there. By positioning vital agents where they are most needed, Series 2000 provides a degree of engine protection unavailable with any other oil.

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[jason07-1zzfe]

cryptokid:

quote:

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...using viscosity as the only variable.

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[S2000driver]

I think Amsoil's marketing is trying to say something technical in everday terms, and really messing it up. I know what they are trying to say; the oil wets to surfaces instead of the opposite.

If you take exactly what they say, it doesn't make sense from a heat transfer point of view.

You can't take a heat transferring agent, put it on something and hold it there, and expect it to take heat away. It rapidly approaches the temperature of the medium it sticks to, then there is no heat transfer... no matter what the "heat transferring agent's" properties are (in the absence of a phase change).

There has to be a constant physical mechanism for the heat to be carried away, which is by constantly replacing the oil on the surface of the metal, not just by "holding" it there.

quote:

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Originally posted by buster:
What is Amsoil refering too here? Some claim S2k is great at reducing temps.

quote:

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AMSOIL Series 2000 20W-50 Synthetic Racing Oil is specially formulated to carry the oil's wear reducing and heat transferring agents to the engine's surfaces and hold them there. By positioning vital agents where they are most needed, Series 2000 provides a degree of engine protection unavailable with any other oil.

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[toyvwbenz]

I guess I don't understand. If the sump temp of a 20W-50 is hotter than a 10W-30 under the same conditions, wouldn't this show the 20W-50 to be pulling more heat away from the crank, for example, and depositing it in the sump. If the 50 weight is hotter, what heated it up? Or is it not transfering its heat to the oil pan or oil cooler as efficiently as the 30 weight.

I think the phenomenon of lower sump temps with lighter viscosity oils is more the result of less internal friction within the oil itself and less the result of heat transfer properties.

 

[MolaKule]

quote:

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I guess I don't understand. If the sump temp of a 20W-50 is hotter than a 10W-30 under the same conditions, wouldn't this show the 20W-50 to be pulling more heat away from the crank, for example, and depositing it in the sump. If the 50 weight is hotter, what heated it up? Or is it not transfering its heat to the oil pan or oil cooler as efficiently as the 30 weight.

I think the phenomenon of lower sump temps with lighter viscosity oils is more the result of less internal friction within the oil itself and less the result of heat transfer properties.

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Heat movement or heat transfer can only be possible if one body is cooler than another body, or if one body is hotter than another.

Place a hot slab of iron (300 F)on the left and call it SLAB A, another cold slab (0 F) on the right and call it SLAB B. Both Slabs have the same mass. Place a short round solid brass cylinder between the two slabs and heat will move from SLAB A to SLAB B until the slabs are at the same temperature, called "Equilibrium."

If the oil is cooler than say the bearing, heat will flow from the bearing to the oil. If the oil is hotter than the bearing, heat will flow back to the bearing. Hopefully, the oil will always be cooler than the bearing or say the piston.

The bulk oil temp is always higher than the coolant temp AFTER the engine gets to operating temperature. See this article in which a computer model of sump and oil temperatures was verified by dyno:

https://bobistheoilguy.com/forums/posts/196/

The oil has two primary heat sources:
1. Viscous Friction. Your engine is always putting some of its Hp into the oil by moving it, but the thicker oils require more energy to churn and to move, so some of oil's heating is due to the oil overcoming it's own internal friction, or "viscous" friction in the oil itself.
2. Engine parts, such as bearings, pistons, valve stems, and cylinder liners, contribute directly to the oil's heating by convection and conduction.

The oil's heat in turn is transferred by conduction, convection and radiation. The coolant takes most of the heat away from the oil. And some heat is rejected by the oil conducting its heat to the oil pan and in turn, the oil pan being cooled by air convection and by radiation. Very little heat from the oil is radiated.

[ March 11, 2004, 01:15 AM: Message edited by: MolaKule ]

 

[MolaKule]

cryptokid,

Mercury is much more dense than oil or water, and due to its electronic structure, it conducts heat better.

The difference in densities between engine oils of differing viscosities is such a small percentage that it is insignificant.

[ March 11, 2004, 01:22 AM: Message edited by: MolaKule ]

 

[Brio]

I'm still not convinced thinner runs cooler "in mot cases?" My oil changes are done the same way(@10^C ambient), run bike till it reaches 100^C-fan kicks in drops to 95,I shut bike off.10W 40 comes out almost hot.15W 50 comes out warm. Any other Real World Experiences. This is almost like comparing 2 oils on there specs,1 looks superior to the other-BUT UOA's verify similar.

 

[Brio]

Can this be seen as 10W 40 getting hotter OR carring more heat to the pan.

 

[BrentB]

I think Brio has it - the thinner oil is hotter because it picked up more heat.

The heat carrying ability of a liquid is related to it's Prandtl Number - the ratio of heat capacity times viscosity divided by thermal conductivity. The lower the number, the more heat that can be "carried". Liquid metals have very low Pr numbers, BTW.

Motor oils will have similar heat capacity and thermal conductivity. That leaves viscosity, then. The lower the viscosity, the better able it will be to move heat.

 

[MolaKule]

Excellent point, Brent.

Adding to this is the fact that the Reynolds number (the ratio of inertia and viscous forces) of the oil in most machines is in the turbulent regime, and the thinner oil is more likely to become "turbulent" as well.

This is based on the fact that turbulent boundary layer fluctuations enhance the transfer of momentum and energy, and this case, it would be the enhancement of the transfer of heat energy.

[ March 13, 2004, 09:43 PM: Message edited by: MolaKule ]

 

[S2000driver]

When isn't fluid flow in an engine turbulent?

The Reynolds number is used for predicting laminar vs. turbulent flow in pipes, not for flowing inside combusion engines which are constantly bombarded with shock waves. There is a huge "gray zone" in the Reynolds number for laminar flow to be sustained, and it's almost always changed to turbulent when an external disturbance is present.

For the small range of viscosities in automotive lubricants, I find it hard to believe a measureable difference turbulence exists.

Most of the difference in heat rate would come from a higher viscosity's resistance to flow from an equal input from the oil pump. With a higher resistance to flow, less volume will be transferred through the lubrication system per unit of time, leading to a lower heat transfer rate.

[ March 14, 2004, 02:30 AM: Message edited by: S2000driver ]

 

[BrentB]

But oil pumps are positive displacement so the flow rate of a thick and thin oil will be the same (a thinner oil will have slightly higher internal leak-back in the pump, so will flow slightly less). The resistance to flow from the higher viscosity oil shows up as higher oil pressure.

 

[S2000driver]

I agree that an automotive oil pump with positive displacement is constant volume instead of constant energy input. It would demand more power to pump a thicker viscosity oil, and the additional heat of work would be disspated into the oil.

quote:

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Originally posted by BrentB:
But oil pumps are positive displacement so the flow rate of a thick and thin oil will be the same (a thinner oil will have slightly higher internal leak-back in the pump, so will flow slightly less). The resistance to flow from the higher viscosity oil shows up as higher oil pressure.

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[MolaKule]

quote:

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When isn't fluid flow in an engine turbulent?

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Most likely when its cold (low viscosity) and at startup.

 

[Terry]

I wanted to share some Dyson Analysis ideas we use to affect cooling using lubricant fluid flow dynamics in automotive and race applications.

You engineers can ruminate on these a bit.

Remember I am not a theorist but care more about affectation and racing performance than proofing on the old chalk board.

Forms of turbulence in a lubricant that can increase performance through turbulent flow and resultant heat diminishing effect:

Convection

Mechanical

Gravity wave 1) Breaking shearing waves
2) Buoyancy or density waves

If one studies these and can formulate or create the environment in an engine that allows the proper use of these observations we can increase HP, reduce heat, and run longer.


Enjoy.

Terry

 

[Primus]

Hope the link suits to the present topic:


http://new.minimania.com/nmm/LUBRICATION__Temperature_critical_1005.htm