This doesn't explain anything. Why? Why is the heat transfer effected by how fast the coolant is moving? It's the same amount of coolant. It's the same amount of heat being generated by the engine. It's the same amount of radiator surface area. It's the same amount of air passing over the radiator. How fast the coolant is moving does NOT effect it's ability to conduct heat. That's a property of the material itself (or coolant mix) and the surface area.
Yes... the prpperties of the coolant will affect how it absorbs/releases heat but how much heat it absorbs or releases definately depends on coolant flow across the heated and cooled surfaces. Lets do an example.. If you task a heated pipe at a temperature of 300 degrees and put a stream of coolant (water) thru it and then thru a cooling pipe at 75 degrees. As you adjust the stream of water (to keep it from reaching boiling point).... The longer the water stays in the heated area the hotter it will get, depending on how long it spends in the cooled pipe is how much temperature is removed based on "time at temp" or cooling.. The faster you move the "coolant" acoross the surface the less heat the water picks up due to "time at temp" for heatiing. But soon you will reach a flow point that the water can no longer be cooled effectively by the "cooling" pipe due to "time at temp" under cooling. ..
yes. so it releases half the heat. It also picks up half the heat. BUT it does both twice as many times per minute. ==> same amount of heat moved. Your example is broken: How come the heating portion wasn't effected the same way? You're holding the coolant temp constant into the pipe regardless of how much time the coolant spends in contact with the heater. Try this: Steady state: Coolant exits engine and enters radiator at 200* Coolant exits radiator and enters engine at 100* Increase speed of circulation: Coolant exits engine and enters radiator at 175* Coolant exits radiator and enters engine at 125* The engine is still generating the same amount of heat. The radiator is still radiating the same amount of heat. The same amount of heat is being transfered out of the engine. The (average) block temperature is going to be the same. yes?
No it spends equal time in cooling as heating. Just that cooling has a limt that it can cool under a a certain flow rate under a heating source that is trying to get to a lot higher temperature. Yes. BUT The radiator cools against a certain flow rate range (think "time at temp"), remember it is only so big, and when you exceed that flow rate the radiator starts loosing effeciency. Or you can add more coils to the radiator. ..
I don't agree. The radiator's efficiency does not change. It holds x amount of coolant with x amount of internal surface area the coolant is in contact with and x amount of external surface area the air is in contact with. "Time at temp" is basically infinite because it's a closed system and the coolant is circulating. double the speed and the coolant spends half the time in the radiator twice as often.
Ok.. Normal flow example Water in to radiator 180 out is 110 Heat load increaeses temperature from 110 to 180. First pass under high flow 180 in 125 out (due to not enough time in radiator) Heat load now incraeses to higher outlet temperature due to higher 120 inlet temperature Second pass will be above 180 on inlet and so on. ? ..
Why? Why won't the temp be 175 on inlet for the exact same reason (due to not enough time in engine).
Engine temp will increase due to higher temp from radiator. Yes, you can design a system that will work with a higher flow rate...... but it will require more surface area on the radiator. ..
This might be the problem, the coolant does not CONDUCT heat, you're thinking of how a wire conducts electricity. The coolant has the ability to absorb heat by rising its temperature when IN CONTACT with a warmer surface and has the ability to disipate heat when in contact with a cooler surface. These are surface and TIME dependent transferes...you are not considering the time for the transfers to occur. NO...in this example, the radiator is NOT radiating the same amount of heat, it is only removing enough to lower the coolant 50 degrees when the speed is increased where it was lowering the coolant 100 degrees at the lower speed. NO..."Time at temp" is basically infinite is not true, you are assuming the transfer of energy from one material to another occurs instantaneously...it is not like electricity with near instantaneous transfer of electrons through a solid metal conductor. You're physics is faulty....
Also the water pump will flow more definately using more HP and possibly causing cavitation issues. ..
I'm going to have to go read up on this. I don't buy it right now. I believe the heat transfer starts instantly and continues at some rate that is relatively fixed. Naturally dependent on the temperature difference, yada, yada. You're saying there is some amount of time before the heat transfer starts? After the 2 materials come in contact? Are you saying that the transfer rate increases or decreases over time? Like it takes a while to get going and the transfer rate increases? I don't think so. Right. But you left out the rather important unit of volume. It's lowering TWICE the volume of coolant 50 degrees. The amount of BTUs transfered should be about the same. No, I'm not. See the above point. Entirely possible. but I'm not convinced of that yet.
Here is a example from back in the day, classic Mopar, one of the first tune up tips I learned. The old B and RB engines had two different water pumps from 1959 until into the 70's. Both used the same diameter drive pully, therefore turned at the same speed. The non a/c pump had a LARGER dimeter impeler with larger fins than the higher cooling capacity a/c water pump. The first go fast mod anyone did to a non a/c car was to go to the a/c pump, even mentioned in the Mopar tune up tips because it gave back a few horse power. The a/c pump moved less water and normally did not overheat in a non a/c car. The a/c pump moved the coolant slower and used a larger radiator...the coolant had more time to increase its heat intake in the engine and more dwell time in the larger radiator to transfer this heat through the metal and into the air flow to handle the higher heat load demand of the a/c and max cooling packages.
Quick it is a thermodynamics problem. You are treating the radiator as a single transfer which is not true as stated before (coolant-->metal-->air). First off there is a delay in the transfer since the temperature of the coolant cannot change instantly. There is a thermal resistance in the coolant as well as in the metal. This is the specific heat capacity of all of the pieces involved which simply put is the heat energy required to increase the temperature of a unit quantity of a substance by a unit of temperature. It takes time to transfer that energy which is exactly why flow rate is crucial to how an engine cooling system works.
Some basics: - Never run straight antifreeze; it's ability to absorb/shed heat is significantly less than a 50/50 mix with distilled water. In fact , not only does it lower the freezing point but also raises the boiling point of the mixture from 212F to 223F (@ sea level for this example, under pressure this value rises proportionally). Furthermore, water is required to activate various corrosion inhibiting chemicals present in the HOAT-type mixture that inhibit electrolysis/galvanic action, reduce corrosion, and prevent metalic consumption of the aluminum structures. - Water quality is critical; use distilled or di-ionized water (drugstores sell it by the gallon). Never(!) use tap water to create that 50/50 mixture; it is the very nature of the impurities within tap water that cause the mixture to actually become electrically conductive. Conduction allow galvanic action, in this case between the aluminum and metal components that are in physical contact with each other. Galvanic action is the process by-which unlike metals react and degrade each other as driect result of minute electrical activity. We actually break in hi-performance electric motor brushes by submerging them in distilled water - because it will not conduct electricity. Add to this tap water can cause scaling as the mineral content leaches out and chlorine used to reduce bacteria/germs significantly alters/degrades corrosion inhibitor performance. This discussion about thermal activity is more complicated than most realize; from an engineering perspective, a radiator varies from an ideal black body by a factor, ε, called the emissivity, which is a spectrum-dependent property of any material. Commonly, a fluid thermal mass (the coolant in this case), containing the heat to be rejected, is pumped from the heat source (the engine) to the radiator, where it conducts to the surface and radiates into the surrounding cooler medium. The rate of heat flow depends on the fluid properties, flow rate, conductance to the surface, and the surface area of the radiator. Watts per square metre are the SI units used for radiant emittance. If the system is not limited by the heat capacity of the fluid, or the thermal conductivity to the surface, then emittance, M is found by a fourth-power relation to the absolute temperature at the surface. The Stefan-Boltzmann constant is used to calculate it, as M = εσT4. Since heat may be absorbed as well as emitted, a radiator's ability to reject heat will depend on the difference in temperature between the surface and the surrounding environment. For particular operating temperatures, a system's overall heat flow may be given in thermal watts, abbreviated Wt. At this point it's guesswork to understand the efficiency of our (regular, severe duty, severe duty II) radiators, let alone the rate at which a HEMI generates (ever-changing) thermal energy. Suffice to say that thermostats prevent a time-out MIL code set as a result of producing a proper warm-up period. Running without a thermostat, what's the gain?? I don't see any gain...
Simply outstanding! :clap: One thing I was thinking about today (while I was winning my golf tournament) is this: Intuitively, I would think the rate is also dependent on the temperature difference from one side of a material to the other? Surely the rate of heat transfer through a radiator would be greater from 200* water to 50* air than the rate of heat transfer from 150* water to 100* air? Other thoughts were that an engine cooling system must be designed with some tolerances on the difference betweeen inlet temp and outlet temp? You don't want the difference to be too great right? Extreme case being when you crack your block by dumping cold water into an overheated system.
I think what you are refering to is shcok, which in the case we are discussing it would never occur. Essentially, the re-introduction of (lower temperature) coolant from the radiator back into the engine - at those junctions the surrounding material is already at a similar temperature value. make sense? Thanks for the compliment BTW
Ha! that's why I asked... for some reason, way back in my mind I started thinking (maybe it was a flashback from school) that might be the case. Another thought that came to mind while I was looking for my ball in the woods: If the transfer does take time and you continue to increase the rate of circulation then you would see the inlet and outlet temps converge. You might be seeing a reasonable coolant temp while burning up your engine... I assume that would be way out of the operating range of any water pump that could be used though. Now, for our practical case. I'm guessing the nominal increase in flow rate by removing the t-stat is going to have a negligable effect on cooling efficiency/capacity. The problems would be caused from operating the engine at too low of a temperature for too long.
For starters, there would be a significant increase in rate-of-flow if one removed the T-stat (cross sectional area has now been more than doubled - maybe even tripled). As Hemi31 pointed out, a restriction is a wise idea to allow more efficient thermal energy transfer, especially when an engine is working really hard (read hi-rpm under load - where the water pump would actually be moving fluid at the higherst rate).
So then I guess the last question would be: How slow is too slow? That would be when the coolant reaches (or within a couple of degrees) the air temp outside the radiator before it reaches the outlet of the radiator?
