Heat Transfer Re-visited Again!

[Everett Ogilvie]

Wow guys, great discussions earlier about heat transfer! I enjoyed it. I am another engineer trying to remember my heat transfer courses. Won't bring in any more equations, or unit analysis, just my own two cents worth, just because I enjoyed the discussions.

Whether or not the heat transfer is taking place in the block, or in the radiator, the process is a kinetic process, which implies a rate, which means time-dependence. Example: use BTU/sec as the heat transfer rate; the more seconds you multiply by, the more BTU transferred. Both heat transfer locations are related (the block and the radiator), and as the coolant temp approaches max, the differential is smaller, and the system should eventually reach steady state. I believe that when all parts in the system are new, the flow the water pump can deliver over its entire speed range will not be an issue. But on an aged system, even considering only the coating of the inside of the radiator with scale etc., the radiator's ability to transfer heat (it's efficiency) is reduced and the water jackets of the block become coated, limiting their heat transfer efficiency also. Consider this; if you filled your radiator with hot water, and it was not circulating and you blew air through the fins, the longer the water sits and the air blows, the cooler the water becomes until it reaches a steady state minimal temperature dependent on ambient conditions and the latent heat properties of the coolant. This seems to indicate that if water is going through a radiator "too fast" and it's efficiency is not "as new" you might encounter higher temperatures at higher circulation rates IF and only IF the original system's design specs are exceeded due to aging of any of the components. This is compounded by the coolant residence time in the block also, as someone previously mentioned.

Just my own thoughts based on a poor memory. And, just for fun!

[Tom B.]

Re: Heat Transfer Re-visited Again!

Everett,

Thanks, for joining in. If you'll notice there have been a couple postings as recent as last night and today, maybe there needs to be a unified location for the remainder of the discussion and an attempt at resolution, IF there can be either.

I'm understanding most, if not all information to the best of my ability, and for others like me that aren't engineers, I'm trying to understand things in simple terms, common sense, and the way the principles are "applied". Also, I'm not trying to confuse things with creative examples, they are just applied "ideas", hopefully not extreme.

It is difficult for me to understand the low factor or value being assigned to the rate of flow, the speed of coolant through the system. Two or three things APPEAR out of "balance". One is that the coolant is neither being "flash heated" (in the block) or "flash cooled" (in the radiator). The time, distance, surface area, or rate "element" is curious as to this example:

If someone enters a walk in freezer, from out of say a 100 degree day, how can they be sufficiently cooled in just a matter of seconds / minute? Is there not more of a time element, meaning the time at which they would stay, (generated by distance, --the "length" of the freezer (radiator), or surface area, or their speed -- slowness, fastness, etc.)?

As having been mentioned already, there are many things involved, the efficiency of the coolant, time / amount of heat absorbtion in the block, cooling efficiency of the radiatior, system components contributing to "wind chill", etc. I am assuming that the Reseach and Developement guys did more than design something and "tweak" it into place. Some common place questions come to my mind (and how they come into play) such as why / what would be the purpose of the having / not having the thermostat, the addition of a larger radiator for big blocks (providing more surface area, not necessarily to supply a larger source of coolant), and if the radiator design is adequate / not adaquate / marginal.

If this is just a "re-hashing" of all previous quieries and information, just say so, and it would be time for me to let go, ponder principles on my own, or just chip in the 7 bucks for a "flow reducer kit" and attempt some "observations". Thanks again, Everett, and everyone else involved. Tom #24014

[Tom B.]

Re: Heat Transfer Re-visited Again!

Everett,

Thanks, for joining in. If you'll notice there have been a couple postings as recent as last night and today, maybe there needs to be a unified location for the remainder of the discussion and an attempt at resolution, IF there can be either.

I'm understanding most, if not all information to the best of my ability, and for others like me that aren't engineers, I'm trying to understand things in simple terms, common sense, and the way the principles are "applied". Also, I'm not trying to confuse things with creative examples, they are just applied "ideas", hopefully not extreme.

It is difficult for me to understand the low factor or value being assigned to the rate of flow, the speed of coolant through the system. Two or three things APPEAR out of "balance". One is that the coolant is neither being "flash heated" (in the block) or "flash cooled" (in the radiator). The time, distance, surface area, or rate "element" is curious as to this example:

If someone enters a walk in freezer, from out of say a 100 degree day, how can they be sufficiently cooled in just a matter of seconds / minute? Is there not more of a time element, meaning the time at which they would stay, (generated by distance, --the "length" of the freezer (radiator), or surface area, or their speed -- slowness, fastness, etc.)?

As having been mentioned already, there are many things involved, the efficiency of the coolant, time / amount of heat absorbtion in the block, cooling efficiency of the radiatior, system components contributing to "wind chill", etc. I am assuming that the Reseach and Developement guys did more than design something and "tweak" it into place. Some common place questions come to my mind (and how they come into play) such as why / what would be the purpose of the having / not having the thermostat, the addition of a larger radiator for big blocks (providing more surface area, not necessarily to supply a larger source of coolant), and if the radiator design is adequate / not adaquate / marginal.

If this is just a "re-hashing" of all previous quieries and information, just say so, and it would be time for me to let go, ponder principles on my own, or just chip in the 7 bucks for a "flow reducer kit" and attempt some "observations". Thanks again, Everett, and everyone else involved. Tom #24014

[Tom B.]

Jerry: Exchange faster / Better?

Jerry,

Does the understanding I lack have to do with the "total volume" of the radiator, the "total volume" of coolant in the block and their rate of exchange? Are you trying to help me to understand that it is better to exchange the total volume of what is in the radiator faster / more often with what is in the block? Does the cooling system work better on that principle or with the principle I've been thinking, a slower exchange, retaining a volume of coolant in the block for more heat absorbtion, a slower rate of flow through the radiator which retains that volume for greater cooling and return to the block? I'm trying to clarify my terms of understanding. Tom #24014

[Tom B.]

Jerry: Exchange faster / Better?

Jerry,

Does the understanding I lack have to do with the "total volume" of the radiator, the "total volume" of coolant in the block and their rate of exchange? Are you trying to help me to understand that it is better to exchange the total volume of what is in the radiator faster / more often with what is in the block? Does the cooling system work better on that principle or with the principle I've been thinking, a slower exchange, retaining a volume of coolant in the block for more heat absorbtion, a slower rate of flow through the radiator which retains that volume for greater cooling and return to the block? I'm trying to clarify my terms of understanding. Tom #24014

[Tom B.]

PS

Evidently I can't tell: Are we "frying burgers" or "cooking a roast"? Same principles? Tom #24014

[Tom B.]

PS

Evidently I can't tell: Are we "frying burgers" or "cooking a roast"? Same principles? Tom #24014

[Everett Ogilvie]

Re: Heat Transfer Re-visited Again!

Hi Tom,

Just my own thoughts again, but I think that I am basically agreeing with you that the time the hot water spends in the radiator is a factor on how much heat is removed from the coolant by the radiator (my previous example of lettting water sit in the radiator while blowing air through it). I have personal experience with an old car that ran hotter at highway speeds (220 degress), and you could watch the temp gauge come down to about 200 degress as you pulled into a town and the engine speed, thus the coolant flowrate, slowed down. This of course is simplified and does not consider effects of the changing air flow through the radiator due to changing vehicle speed, although less air was more likely flowing through the radiator at lower vehicle speeds, unless some funny "ground affects" or something were happening to air flow. It used to be somewhat common to put larger pulleys on waterpumps to slow them down on racing engines, to lessen horsepower drag and to slow the coolant flow if the engine ran hot at high RPM. Of course we can't change pulleys on our Corvettes if we want correct configuration. I think that if the cooling sysem is operating near its limit, as in minimal effectiveness due to age, weather, air flow or anything else, then the coolant flow rate may be a big enough factor at high flowrates to cause the higher temperatures at higher engine speeds. Guess you will have to keep looking at all the components of the cooling system. If you still have no thermostat, or a high flow thermostat, you might try a standard thermostat just to see if it changes anything. Everett

[Everett Ogilvie]

Re: Heat Transfer Re-visited Again!

Hi Tom,

Just my own thoughts again, but I think that I am basically agreeing with you that the time the hot water spends in the radiator is a factor on how much heat is removed from the coolant by the radiator (my previous example of lettting water sit in the radiator while blowing air through it). I have personal experience with an old car that ran hotter at highway speeds (220 degress), and you could watch the temp gauge come down to about 200 degress as you pulled into a town and the engine speed, thus the coolant flowrate, slowed down. This of course is simplified and does not consider effects of the changing air flow through the radiator due to changing vehicle speed, although less air was more likely flowing through the radiator at lower vehicle speeds, unless some funny "ground affects" or something were happening to air flow. It used to be somewhat common to put larger pulleys on waterpumps to slow them down on racing engines, to lessen horsepower drag and to slow the coolant flow if the engine ran hot at high RPM. Of course we can't change pulleys on our Corvettes if we want correct configuration. I think that if the cooling sysem is operating near its limit, as in minimal effectiveness due to age, weather, air flow or anything else, then the coolant flow rate may be a big enough factor at high flowrates to cause the higher temperatures at higher engine speeds. Guess you will have to keep looking at all the components of the cooling system. If you still have no thermostat, or a high flow thermostat, you might try a standard thermostat just to see if it changes anything. Everett

[Tom B.]

Thanks Everett

Thanks again Everett. Also, I hope I didn't post up something while you were doing this in the meantime (I'll take a "no response" to mean it made no difference). Not trying to "argue" both sides, just clarify my thinking. Still leaning to the "slower is better" idea. Tom #24014

[Tom B.]

Thanks Everett

Thanks again Everett. Also, I hope I didn't post up something while you were doing this in the meantime (I'll take a "no response" to mean it made no difference). Not trying to "argue" both sides, just clarify my thinking. Still leaning to the "slower is better" idea. Tom #24014

[G B.]

YES! You've got it!

Consider the water in the radiator to be just an extension of the water in the block. You want the water in the radiator to be as hot as the water in the block for the greatest heat transfer from the radiator. Don't worry about how long it takes the heat to get into the water while in the block. It will get there just fine.

[G B.]

YES! You've got it!

Consider the water in the radiator to be just an extension of the water in the block. You want the water in the radiator to be as hot as the water in the block for the greatest heat transfer from the radiator. Don't worry about how long it takes the heat to get into the water while in the block. It will get there just fine.

[Tom B.]

Re: YES! You've got it!

Jerry,

You know, now that I have a better understanding of the "fast" principle and the "slow" principle, they both make so much common sense separately, I need to understand what the cooling system by design (or by happen-stance) does better. Either that or I'm still have an empty blank or two.

Is all of this (that we've discussed) just "opinion" or is there any verification (other than our own point of view) that we / I can reference? I would guess that this is where experience and application comes in. More thinking ahead. Tom #24014

[Tom B.]

Re: YES! You've got it!

Jerry,

You know, now that I have a better understanding of the "fast" principle and the "slow" principle, they both make so much common sense separately, I need to understand what the cooling system by design (or by happen-stance) does better. Either that or I'm still have an empty blank or two.

Is all of this (that we've discussed) just "opinion" or is there any verification (other than our own point of view) that we / I can reference? I would guess that this is where experience and application comes in. More thinking ahead. Tom #24014