Air Temperature

[Lagonda]

My engine runs best between 5° and 20° C. Around 12° being optimal. I really notice a drop in performance with temperatures above 30° C.*

*rough estimates

[hightower99]

My engine runs best between 5° and 20° C. Around 12° being optimal. I really notice a drop in performance with temperatures above 30° C.*

*rough estimates

I'm guessing you are talking about ambient temp right?

[Lagonda]

Yep, outside temperature.

[Alastor]

Also you are kinda right about ICs but it isn't the physical size or internal volume that really matters. What matters is the mass of metal used to make it and how much surface area there is between that mass and the mass of the air traveling through it.

Adding more material to a heat exchanger is very lazy way to design one, especially for a high performance car. The better approach is to minimize the material while maximising both interior and exterior surface area.

It is better to transfer the heat to the cooling medium as quickly as possible, rather than storing it in the heat exchanger.

[Quiggs]

Adding more material to a heat exchanger is very lazy way to design one, especially for a high performance car. The better approach is to minimize the material while maximising both interior and exterior surface area.

It is better to transfer the heat to the cooling medium as quickly as possible, rather than storing it in the heat exchanger.

I'm with stupid. (Who's not so stupid.)

[hightower99]

Adding more material to a heat exchanger is very lazy way to design one, especially for a high performance car. The better approach is to minimize the material while maximising both interior and exterior surface area.

It is better to transfer the heat to the cooling medium as quickly as possible, rather than storing it in the heat exchanger.

I didn't say to add material to the IC to make it better. I said in current ICs what matters is the mass of the IC AND the surface area between that and the air running through it (both internal surface area for the intake air and external surface area for the air that cools the IC).

Minimizing the material isn't overly bright either. It does have the advantage of making a lighter IC but it won't cool the intake air as much. With less material the IC will heat up quickly and it won't be able to transfer all that heat only to the outside air so the intake air will not be cooled as much compared to an IC designed with the correct amount of mass (not too much not too little). remember in an air/air IC the cooling medium and the source medium have the same thermal properties.

Read my post about air/water ICs Notice I said the same thing as you there? Because you are right when the cooling medium has different thermal properties then the source medium.

[Alastor]

I didn't say to add material to the IC to make it better. I said in current ICs what matters is the mass of the IC AND the surface area between that and the air running through it (both internal surface area for the intake air and external surface area for the air that cools the IC).

But it is not just simply the mass, it is the mass and the specific heat of the mass.

Minimizing the material isn't overly bright either. It does have the advantage of making a lighter IC but it won't cool the intake air as much. With less material the IC will heat up quickly and it won't be able to transfer all that heat only to the outside air so the intake air will not be cooled as much compared to an IC designed with the correct amount of mass (not too much not too little). remember in an air/air IC the cooling medium and the source medium have the same thermal properties.

The mass only affects the transient temperature response. So you could have a very massive IC that would have fairly low average temperature because it is so massive, and it takes a long time to warm up. Or the surface area can be increased to increase the heat transfer rate. The heat transfer rate will determine the steady state or maximum temperature that IC will reach.

So both approaches could result in the same IC performance, except one will be lighter than the other.

[hightower99]

But it is not just simply the mass, it is the mass and the specific heat of the mass.

Exactly. Consider that in a air/air IC the coolant and the source material have the same thermal properties.

The mass only affects the transient temperature response. So you could have a very massive IC that would have fairly low average temperature because it is so massive, and it takes a long time to warm up. Or the surface area can be increased to increase the heat transfer rate. The heat transfer rate will determine the steady state or maximum temperature that IC will reach.

Yes the mass effects the transient temperature response but think about it. You have two basic states. When the car isn't moving (or only slowly) when the highest flow is occuring in the IC and when you are driving fast when the cooling air flow is higher than the flow in the IC. During the first state you want to have a certain amount of mass so that it will cool the intake air, during the second state you really want to minimise the mass so that the heat is transferred out as fast and as efficiently as possible. Now think about what happens when the states are reversed. With the high mass IC the temperature on the outside surface will not reach a high temperature and it won't effectively harness the extra cooling from the increased cooling flow. With the low mass IC coming down from high speed it will be hot and therefor it will not absorb heat from the hot intake air and because of the low coolant flow it will take some time to cool (much less than the high mass IC but still some time) and when it does cool enough to absorb heat from the intake air the air around the outside of the IC will also be hot and it will hit an equalibrium point at a relatively high temperature. Thus there is an optimal mass for an air/air IC depending on how you drive. Spend most of your time at speed then opt for the lower mass IC. Spend any significant time standing still and you will want some mass.

So both approaches could result in the same IC performance, except one will be lighter than the other.

They don't achieve the same performance in all conditions. It all depends on how you drive.

[Alastor]

Exactly. Consider that in a air/air IC the coolant and the source material have the same thermal properties.

That is true.

But the heat flow path is from air -> aluminum -> air. In your previous post when you were referring to the IC mass, I assumed you were talking about the aluminum. I will continue to assume that until you tell me otherwise.

Yes the mass effects the transient temperature response but think about it. You have two basic states. When the car isn't moving (or only slowly) when the highest flow is occuring in the IC and when you are driving fast when the cooling air flow is higher than the flow in the IC.

I guess this goes back to how the car is being used. But if the engine is under load at a stop, then IC mass (aluminum) will help to keep the intake temperatures down until the car begins to move.

During the first state you want to have a certain amount of mass so that it will cool the intake air, during the second state you really want to minimise the mass so that the heat is transferred out as fast and as efficiently as possible.

I agree, but for the first state you still want just enough IC mass to keep the IAT from going out of control.

Now think about what happens when the states are reversed. With the high mass IC the temperature on the outside surface will not reach a high temperature and it won't effectively harness the extra cooling from the increased cooling flow.

The high mass IC can still reach the same high temperature is just takes longer.

With the low mass IC coming down from high speed it will be hot and therefor it will not absorb heat from the hot intake air and because of the low coolant flow it will take some time to cool (much less than the high mass IC but still some time) and when it does cool enough to absorb heat from the intake air the air around the outside of the IC will also be hot and it will hit an equalibrium point at a relatively high temperature. Thus there is an optimal mass for an air/air IC depending on how you drive. Spend most of your time at speed then opt for the lower mass IC. Spend any significant time standing still and you will want some mass.

First, an IC can be designed to work effectively at a variety of speeds so the high speed / low speed is relative. An IC could work effectively at 100 MPH or 30 MPH.

Secondly, the low mass IC will cool down faster than the high mass IC . It doesn’t make sense that the high mass IC will warm up slower and cool down faster.

They don't achieve the same performance in all conditions.

That is certainly true, but I think for any given application mass can still be minimized.

It all depends on how you drive.

You mean if not moving is considered driving :P

[hightower99]

That is true.

But the heat flow path is from air -> aluminum -> air. In your previous post when you were referring to the IC mass, I assumed you were talking about the aluminum. I will continue to assume that until you tell me otherwise.

Yes but Air is on both sides and the path of heat can go both ways depending on certain conditions. Yes I am talking about the mass of the IC (the metal bits).

I guess this goes back to how the car is being used. But if the engine is under load at a stop, then IC mass (aluminum) will help to keep the intake temperatures down until the car begins to move.

Exactly glad to see you agree

I agree, but for the first state you still want just enough IC mass to keep the IAT from going out of control.

Yes my point is not to add mass to an IC or to say that ICs should have alot of mass, simply that a certain amount is needed for effective use.

The high mass IC can still reach the same high temperature is just takes longer.

Actually with the higher mass IC at speed, the whole mass of the metal will not reach as high a temperature as a lower mass IC. The fast moving coolant air will cool the outside surface and the hot intake air will heat the inside creating a heat gradient through the actual material of the IC. This is the problem with having too much mass as the inside will stay hot and the outside will stay cool lowering efficiency on both sides. Think about it. Given the same amount of energy flowing though the material of the IC the one with more mass will stay at a lower temperature.

First, an IC can be designed to work effectively at a variety of speeds so the high speed / low speed is relative. An IC could work effectively at 100 MPH or 30 MPH.

I tend to make the division between moving and stationary as opposed to between different speeds.

Secondly, the low mass IC will cool down faster than the high mass IC . It doesn’t make sense that the high mass IC will warm up slower and cool down faster.

You are correct. The higher mass IC will heat up and cool down the slowest. However this can be an advantage (maintaining the heat in the aluminium will cause no damage to the engine). whereas cooling down too quickly means dumping some heat back into the already hot intake air (and that could lead to damage).

That is certainly true, but I think for any given application mass can still be minimized.

Probably But I would still caution against over-zealous minimising of the mass. You do need some.

[Alastor]

Actually with the higher mass IC at speed, the whole mass of the metal will not reach as high a temperature as a lower mass IC.

This would depend on the application. If the engine is going to run under load for any significant amount of time then the IC will likely reach a near steady state temperature.

The fast moving coolant air will cool the outside surface and the hot intake air will heat the inside creating a heat gradient through the actual material of the IC.

Just to make sure we are on the same page, I believe what you are referring to is the temperature gradient between the hot and cold sides of the IC. It is this difference in temperature that drives the heat from the hot side to the cold side, where temperature and heat are two different quantities.

This is the problem with having too much mass as the inside will stay hot and the outside will stay cool lowering efficiency on both sides.

First, isn’t this a negative comment against having more mass?

Secondly, the thermal gradient will only be affected transiently by the mass. The magnitude of the gradient will depended on the thermal resistance of the heat path. The thermal resistance is dependent on the heat path length and the thermal conductivity of the material.

Think about it. Given the same amount of energy flowing though the material of the IC the one with more mass will stay at a lower temperature.

Temporarily, all else being equal eventually both the low mass and high mass ICs will reach the same temperature.

You are correct. The higher mass IC will heat up and cool down the slowest. However this can be an advantage (maintaining the heat in the aluminium will cause no damage to the engine). whereas cooling down too quickly means dumping some heat back into the already hot intake air (and that could lead to damage).

If the IC cools down more quickly and the IAT is hot, the heat cannot be transfered in to the intake air. Heat by itself can only move from hot to cold.

[hightower99]

Just to make sure we are on the same page, I believe what you are referring to is the temperature gradient between the hot and cold sides of the IC. It is this difference in temperature that drives the heat from the hot side to the cold side, where temperature and heat are two different quantities.

First, isn’t this a negative comment against having more mass?

Secondly, the thermal gradient will only be affected transiently by the mass. The magnitude of the gradient will depended on the thermal resistance of the heat path. The thermal resistance is dependent on the heat path length and the thermal conductivity of the material.

Yes I meant temperature gradient. Also this gradient will pump heat through the metal it will be hampered by the fact that the surface that is getting heat from the IA is hot (therefore a lower rate of transfer) and the side that is giving the heat to the coolant is cold (also less transfer). BTW the transfer I am referring from the IA to the aluminium and from the aluminium to the AA (Ambient Air). It certainly is a negative comment that is opposed to having too much mass. Also I am assuming that the hig and low mass ICs we are thinking about to share all the same physical measurements except for mass therefore I assume the thickness to be increased on the high mass version therefore higher thermal resistance and a higher magnitude of gradient.

Temporarily, all else being equal eventually both the low mass and high mass ICs will reach the same temperature.

Why? in order for that to happen more heat energy must pass through the higher mass IC and the comparison wouldn't be fair. Given the same heat energy the higher mass IC will stay cooler.

If the IC cools down more quickly and the IAT is hot, the heat cannot be transfered in to the intake air. Heat by itself can only move from hot to cold.

Yes but when the IC was hot it would have been very hot and when you slow down/stop the intake air will be cooler (because the charger is not flowing as much at such a high pressure) and some of the heat that will leave the IC will be dumped into the relatively cooler IA. Also the LMIC will stay hot anyways as long as there is heat from the IA. I am not arguing that you shouldn't minimise mass or that you should only have a HMIC simply that you shouldn't go overboard either way. There is an optimal mass for air/air ICs. However with air/liquid ICs I would agree with you 100% totally minimise the mass of the aluminium. The best water IC would have direct contact between the air and the water.

[Alastor]

Also I am assuming that the hig and low mass ICs we are thinking about to share all the same physical measurements except for mass therefore I assume the thickness to be increased on the high mass version therefore higher thermal resistance and a higher magnitude of gradient.

I am not sure changing thickness is valid in this context. I think to compare the low mass and high mass ICs the material density must be changed. If the thickness of the IC walls are changed it will change the thermal resistance through the wall.

So in the case of the larger mass IC, if the wall thickness is increased the temperature gradient through the cross-section will also increase. The result will be either higher operating temperature and/or less overall heat transfer.

Why? in order for that to happen more heat energy must pass through the higher mass IC and the comparison wouldn't be fair. Given the same heat energy the higher mass IC will stay cooler.

If both IC’s are identical other than mass (i.e. different densities) and some amount of heat is applied, they will both reach the same steady state temperature. The difference is that the one with more mass will take longer to reach the steady state temperature.

There is an optimal mass for air/air ICs. However with air/liquid ICs I would agree with you 100% totally minimise the mass of the aluminium. The best water IC would have direct contact between the air and the water.

What difference does it make if the cooling medium is water or air? If is ideal to have air and water in direct contact, why wouldn’t this be true for air and air?

[hightower99]

I am not sure changing thickness is valid in this context. I think to compare the low mass and high mass ICs the material density must be changed. If the thickness of the IC walls are changed it will change the thermal resistance through the wall.

So in the case of the larger mass IC, if the wall thickness is increased the temperature gradient through the cross-section will also increase. The result will be either higher operating temperature and/or less overall heat transfer.

Changing the density is something I would have a problem with as that would imply a change in the thermal properties of the material used and we haven't discussed that at all. (In fact I thought we agreed that the material is aluminium?) Changing the thickness is valid IMO because it is normally the main variable changed when mass is increased or decreased in ICs in the real world. My whole POV has been based on changing only the mass (through thickness, which changes thermal resistance). Also the increased temperature gradient might lead to less overall heat transfer to ambient air but roughly the same amount of heat will be taken from the IA and stored in the mass of the IC.




[QUOTE=Alastor]If both IC’s are identical other than mass (i.e. different densities) and some amount of heat is applied, they will both reach the same steady state temperature. The difference is that the one with more mass will take longer to reach the steady state temperature.[{QUOTE] I beg to differ. If you have two masses that share all thermal properties and spacial volume and differ only in density, and if you supply the same amount of energy to both than the lesser mass will achieve a higher final temperature than the greater mass. the temperature increase due to increased internal energy (heat) is proportional to the mass. The greater the mass the less of a temperature change per unit energy gained. Also I would think you would have a hard time to find two otherwise identicle materials that differ solely in density (i.e. without them having different thermal properties).

What difference does it make if the cooling medium is water or air? If is ideal to have air and water in direct contact, why wouldn’t this be true for air and air?

Again this is due to the thermal properties of water and air. When the source (intake air) has the same thermal qualities as the coolant (like in an air/air IC) then you need to seperate them. Think about this. If you blow cold air and hot air into a container and close it the hot air will stay hot for some time and the cold air will stay cold. Why? because of the fact that air doesn't like to gain or loose heat to air (thats one of the contributing factors for weather). However if you blow hot air at an aluminium plate and blow cold air against the other side of said aluminium plate then you will notice that the hot air is cooled and the cold air is heated when they come into contact with the aluminium plate. Now in a air/water IC the coolant already has different thermal properties from the source therefore you don't need anything between them.

[Alastor]

Also the increased temperature gradient might lead to less overall heat transfer to ambient air but roughly the same amount of heat will be taken from the IA and stored in the mass of the IC.

But the more heat that is stored in the mass the higher it’s temperature will become which will reduce overall effectiveness.

I beg to differ. If you have two masses that share all thermal properties and spacial volume and differ only in density, and if you supply the same amount of energy to both than the lesser mass will achieve a higher final temperature than the greater mass. the temperature increase due to increased internal energy (heat) is proportional to the mass. The greater the mass the less of a temperature change per unit energy gained.

I have been assuming that for both cases the heat transfer into and out of the IC has been the same. Since the cold and hot side areas are the same, for both the low and high mass ICs, then the surface temperature must also be the same. This would imply that the IC will reach the same steady state temperature.

Also I would think you would have a hard time to find two otherwise identical materials that differ solely in density (i.e. without them having different thermal properties).

True, but since we are only talking hypothetically/theoretically it doesn’t seem unreasonable as it helps isolate the affects of the change. As apposed to changing mass and wall thickness which will result in coupled effects.

Again this is due to the thermal properties of water and air. When the source (intake air) has the same thermal qualities as the coolant (like in an air/air IC) then you need to seperate them. Think about this. If you blow cold air and hot air into a container and close it the hot air will stay hot for some time and the cold air will stay cold. Why? because of the fact that air doesn't like to gain or loose heat to air (thats one of the contributing factors for weather). However if you blow hot air at an aluminium plate and blow cold air against the other side of said aluminium plate then you will notice that the hot air is cooled and the cold air is heated when they come into contact with the aluminium plate.

Air doesn’t transfer heat well to air, because of its very poor thermal properties. Generally speaking air can be considered a thermal insulator. Nevertheless, you won’t get better heat transfer from hot air to cold air by putting aluminum in the middle. Regardless of how good it’s thermal properties, the aluminum will only serve to increase the thermal resistance between the hot and cold sources.