A. That equation always holds true for single phase (liquid only) heat transfer. If you have two phase (boiling), then you have an additional term due to the latent heat of vaporization (energy removed by boiling). That equation is the heat removed by the radiator (or the heat gained by the engine). These will always balance (at least try to) due to the radiator and the rest of the cooling system. There will only be an imbalance if the radiator is maxed out and cannot dissipate the heat that the engine is putting out. At this point, the coolant temperature will increase until overheating occurs.

Now, let's say you are maxed out and you kicked on additional flow. This is what would happen:
- temperature difference across the radiator will still decrease (above equation)
- the pump does adds some heat to the coolant (waste heat by the pump, extra load on the alternator running the pump). The amount is small, though.
- as flow continues to increase, the delta T will continue to decrease to a point where the delta T cannot be measured. The energy is still being removed at the same rate (perhaps enhanced some from the increased flow)

Basically, as the flow increases towards infinity, the temperature everywhere in the system becomes equal (say 180* everywhere). Really, the ability of the coolant system is determined by the radiator:
- air flow (convection) through the radiator
- surface area of radiator
- material of rad (high conductive material like aluminum can enhance heat transfer)
- average temperature of the coolant system
- ambient temperature

The max energy removed by the rad is:

Q= h (convective heat transfer coefficient) * A (area) * (Tcool-Tamb)

h- depends on fin design, air flow through rad
A - surface area of all the fins
Tcool - average coolant temp
Tamb - ambient temperature

If Qengine > Q rad, the coolant temp will increase using the above equation until there is a balance. If you didn't have to worry about localized boiling and such, T coolant will just keep increasing with engine load to make the heat balance. If the rad is larger, better flow through the rad, or lower ambient temp, the radiator can remove the same amount of energy with less increase of Tcoolant.

Q. OK so that is all real good.

So lets say you are at the upper echelon of heat conduction.....then just increase the flow of water. this is where the T-outlet increases?

A. Energy removed by the rad is:

Q=Cp(specific heat) [kJ/kg*C]*mass flowrate [kg/s] *delta T [C]

So with nothing else changing, an increase in flowrate will just mean a lower temperature difference between the inlet/outlet of radiator. This is the heat that is removed by the radiator. Since you are not changing waste heat of the car (still idle or whatever), the energy needed to remove from the engine to keep it cool stays the same. Presumably, you have a T-stat regulating the temperature at the inlet of the radiator (say 180*). Say you need a 30* delta T to start out with (outlet temp of 150*). Now, let's say you double the flow rate. Now, your outlet temp will be 165* (15* delta T).

Now as flow increases, there are some other advantages. The radiator will be more efficient (up to a point), because of better convective heat transfer. Similar for the engine. The faster flow would allow a smaller radiator, less air flow through the rad, or be able to handle a higher load (more power, work better in summer). There is a limit. At a certain point, no matter how good your convective heat transfer is you are still limited on how fast the heat can transfer through the radiator fins or through the block of the engine. This is referred to as being conduction limited.

So from the other day...and I didn't want to clutter up the other guys thread any further.

And the Ground rules with me are, I am just talking and thinking out loud. I DO NOT KNOW IT ALL and even though I come off that way sometimes.....anyone is free to tell me I am wrong and please please please show me how I am wrong. This way I learn and that is what I am really all about....learning and getting to the truth of things that I don't quite understand.

Thermal conductance

Q. The story goes like this. if you are sitting in traffic. and somehow you increase the flow of coolant into your radiator, will you see a drop in temps exiting the bottom or outlet of the radiator.

Guys,

Gotta get an answer here. I am having to step up my knowledge on Thermal Conductance and Thermal properties for a new product line we've taken on.

And of course, none of the "homework" is fun unless it is car related.

Start thinking about your radiator.

Here is the question.

If you do nothing else to your cooling system....meaning no other variables enter the equation, save one.

The story goes like this. if you are sitting in traffic. and somehow you increase the flow of coolant into your radiator, will you see a drop in temps exiting the bottom or outlet of the radiator.

The discussion came from someone using an electric water pump vs. a belt driven water pump.

From what I can find, the Temperature Difference (or Delta T) will not change. The radiator can only dissipate "X" amount of heat so lets say the Delta T is 30° F

If you increase the amount of coolant entering the radiator all you are going to do is raise the over all temps of the Delta T.....not INCREASE the amount of Delta T.

So if the water coming in is "X" gpm(gallons per minute) 200° and leaving at 170°. increasing the GPM is only going to increase the........


And that is where I stop and scratch my beard and check the point on top of my head....look in the mirror at my pencil neck.......and also wring my hands.....but only after I straighten my pocket protector.

If the radiator is already cooling to its capacity, adding volume of coolant for it to cool is only going to increase the load which means the Delta T would be affected by the increased load.

Understand, we are not factoring in increased windflow on the OUTSIDE of the radiator.

I won't blame my wife or GF.

I was late to work and I threw the front wheel on my 914 and off I went. I made it about a mile before it rattled and then flew off. It bounced down the road about 300 yards and fell over in someones yard.

I walked over there and retrieved the wheel. Then I stole one lug "bolt" (remember it was a VW product....they used big bolts) from each of the other three wheels and put it back on. No Damage however...like many others the car was light up there and really didn't come down until the car stopped.

Case!! I am so confused.

Please tell me what you are trying to say......type slowly as I don't read real well.

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Oh that is loosely used.

Good stuff Gary.

about this coilover mod. Does the products you make address the coil over debate for the lower rear mount?

*puts flame suit on*

that made me laugh

Welcome and tell us about the products.

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"They/Them/you" are starting to catch up with my procrastination.

yeah, I've been putting a lot of stuff off. I don't feel bad about it though. I've been busy and the car does run really good. I'd give it a 80%.

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dammit, I have to do mine one day soon.

I personally don't know where the distributor cap is located on an 85. On my 84 it is right next to the firewall.....this could lead to a grounding issue with the hood being closed.

Honestly....I am just throwing crap out as popping the hood to get the car to start is so odd.

I'll bet you guys dollars to donuts that the heater core fins are blocked with dust build up.

Does the A/C blow hard or is it just heat?

Logic is that the A/C fins would be clogged with dust from the condensation build up, and that is why I ask.

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So wait, they work fine now?

And before they would just stop rotating.....no grinding noise associated?

Voltage....had to be voltage or binding. The stop switch on these headlights basically is a Volt meter. When it senses a voltage spike from the light hitting the limiter it stops sending power to the motor. Yours had to be binding up or the switch is getting old or the connection was gummed up...

Yes, I have been eyeballing that area for a light as well.

I'll think about it for a while then my shower is over and the thought runs down the drain when I turn the water off. Reality of an actual work day quickly fills that vacated gray matter......

I'd like a light for the dash area. It sucks when you turn on the lights and the Center console is still as dark as it was before. I am not sure whey they didn't put a over head dome on the "roll bar" section of the top. They figured out how to put a third brake light in there......

And as far as using LEDs in the Digital Dash, I am in agreement with you CC. I can't see using anything else in there. Especially a focused LED.

no no, not the windows the Mirror adjust button.

That one kills me, I hit the button...Nothing happens.....I panic and start the OD diagnosis process......until I figure out what I have done...

I know you have this new problem...but just to be sure.

Did your starting problem get solved with the new battery?

Honestly, if you have the money you'll like that tranny much better.

I get sick of that push button Overdrive. It is a pain in the ass having to check the button all the time.....by that, I mean like after slowing down on the Freeway when you hit a traffic jam. Then you forget the button is pushed, you start grabbing gears and they seem way off....the damn button is pushed which basically makes 2 into 3rd and 3rd into 4th.......dumb as hell idea.

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Doh!

Horse power? I am not referring to any increase or decrease. We are just discussing thermal dynamics for the purpose of getting the truth out in the open about how a radiator cools. And understand, I am not a "know it all". I have to work this out just like the rest of us. With Qacks very well thought out questions and very inquisitive curiosity, I think we can all learn something here.

I was correct previously. Temperature Delta is where it is all at.

Ok Heat dissipation through a given surface area can be calculated and a maximum number of watts transferred can be determined.

Again, if you are at the maximum watt transference and you increase the flow of heated fluid into the inlet.

Here is a good write up. You'll need to familiarize yourself with the nomenclature but in essence the Delta-T does not increase with added temps. The Delta-T remains a constant.

http://www.energy-based.nrct.go.th/Ar ... utomobile%20radiators.pdf

Correct. Delta T So if the temp....that is a good question why is that??


Let's see, if the function is Delta T and you have a maximum Temp Delta of say 70°C and the outside temp stays at 70° F Then if the Delta T makes the difference then why would added flow change what I said. The outside temps stayed at 70° so why wouldn't you still get 70°C delta-T?

I'll have to pose the question to the guys, cause you bring up a good point.

^^I've been thinking on this for a day.

If the heat transfer rate maximum has already been reached, adding more heat, via added coolant flow, can in no way increase the watts transferred. The Temps in the Radiator outlet will only increase unless something else changes.

The only way to increase the wattage transfer is to decrease the external temps that the Radiator is subject to. Either by dropping the room temperature or increasing air flow.

I understand what you are saying, you are thinking that once the coolant travels through the fins.......it is going to cool down to the same temps due to the length of travel....But my point is this.

As the coolant travels down the radiator passages the temps drop. IF YOU start flowing more coolant the temps at the lower area are going to increase with the taxation of added energy from the added coolant flow. The bottom of the radiator will begin to rise in temps.

[quote="Qack"]Quote:
I see how I said it wrong, Let me try again, the Heat exchanger wattage transfer will not diminish.....

because a larger amount of heated fluid is entering the heat exchanger. The heat exchanger can only transfer so many watts of energy while it is sitting in an ambient room with no air flow.

More coolant equates to more heated or excited molecules entering the heat exchanger. The Heat exchanger is transferring the same amount of energy as it did before but the added energy from the added fluid raises the over all temps. We see a rise in over all temps. But saying the radiator is not cooling is wrong thinking....it is doing the same job it did before we raised the bar by increasing the amount of fluid.

Again, we are dealing with Temperature "Delta's" or temperature "differences".

We can change the Temperature delta by adding air flow over the fins, once we do this the heated fluid is exposed to cooler temps at the heat exchanger thereby removing more energy or watts from the coolant. Temperature delta is what it is all about.

C'mon CC you know this is the typical 4x3 scam from a "Vette" shop.

You don't take a 4x3 in that is running just fine, change the fluids and then both trannies are all the sudden junk.

OP, There is something fishy here, and I just hope the dealer and that shop work it out without involving you.

IF you want, CC know exactly the steps to accurately trouble shoot the 4x3. I'll bet you a donut it is something minor.

Your problem may lie with the rest of the vacuum hose. It may be dry and brittle and cracked somewhere along the route. That would be my next step.

The fact that your control unit changes settings leads right back to a vacuum issue. OR the gate is simply stuck in one place.

Do you hear the "hiss" when you punch up different settings on the control unit?

Qack!!

You aren't helping me at all. You are supposed to tell me just what I want to hear and forget about all those facts you keep posting.

My self esteem has dropped dramatically and My Sliver Metallic car is not getting painted in my garage.....and it is all your fault!!

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yes I agree you need both. But in thermal solutions as CC pointed out Temperature delta at the point of heat exchange is crucial.

The Colder the radiator is to begin with will dictate how much cooling you get from running fluid through it.

If the radiator has no air flow you can calculate how many Watts is it will transfer sitting in an ambient room. The wattage transfer will actually diminish by running more heated fluid though it without changing any other parameter.

That calculation moves once air flow is passing across the fins.

Here is the company I work for as an engineer.

http://www.ferrotec.com/products/thermal/

well, you have to have a water pump.

But then you continue with things that prove my point. Once a certain level of temp is reached, the only thing that cools the system down is airflow over the radiator.

By increasing fan speed
By fans turning on

By increasing coolant flow the radiator is only going to remove "X" amount of energy with stagnant air.

[quote="CentralCoaster"]Quote:
that is a little extreme for us daily drivers.

OK for all out there that drives their car around town and to and from work......

I could see getting a device if I had to bleed brakes on that frequency. But for most of us that will have to do this once every two years or so......

oh and believe me 14 year olds are perfectly capable of pushing a brake pedal.

How interesting.

So these newer guns are only spraying at 10psi??

why then are so many people saying you have to have an ~8cfm capacity compressor??

If a gun is only using 10psi then surely a smaller compressor could keep up with it.........correct?

Would you attribute the "Fisheye" effect to water rather than dust?

Another thing that I could never get a straight answer is.......if you look at a C4, it is really chopped up into sections. If you had a way of mixing the exact color over and over, would you really need a "Big Gun" to spray large areas??? The Clamshell is the only thing that bothers me it is a huge area...but the rest of the car is small touch up style areas with lots of breaks for masking off. If you are not changing colors and only restoring the paint, could you not paint section at a time???

What is an HVLP gun?

What is a Turbine Gun?

And if we get down to 4. CFM level what now?

I also would like to point out.

If you are worried about your pedal going all the way to the floor and "Damaging" something..........maybe that Master Cylinder is not the thing you want your life Dependant upon....I'm just sayin'....

Maybe now would be a good time to swap out such a critical piece of equipment rather than babying it.

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Dude, I couldn't agree with you more.

I am at a loss with all these recommendations for gadgets to help you do a 20 minute job.

14 year old in the driver seat. Make sure they understand that they cannot let off the brake pedal until you give the "release" command.

Take a wrench and go to the furthest wheel from the MC. Stick a piece of vacuum hose over the valve and run the other end into a coke bottle. Open the bleeder valve and tell the kid to "push"......all the way down. Then before his foot reaches the floor board you close the bleeder. then tell him to release.

Now repeat this procedure until the fluid coming into the coke bottle is nice and clear without any bubbles. Then move to the next closest wheel. The pedal won't get firm until you have finished the very last wheel.

If I have to warn you not to let the fill cup run dry then maybe you shouldn't be working on brakes by yourself.

20 minutes.....tops and the only special thing needed is a Coke bottle and a piece of tubing. The uncomfortable thing will be listening to your wife or son repeating "are we finished yet?"

Anyone mentioning better coolant flow equating to better cooling is off the mark entirely.

The Heat exchange occurs in the radiator and the ability of the radiator to dissipate the energy of the water flowing through it.

To prove my point, go out and get in a traffic jam, watch as the heat builds in the coolant system and then when it is good and hot, rev your motor and see if the added coolant flow cools the system........it won't

The only thing that will change the temperature is airflow over the radiator....not coolant passing through the inside. The slightest forward movement will bring the temps down almost 10°.

Second, I'd like to point out that only CC has even mentioned using Deionized water when refilling. Understand that even though we have mostly Steel components, Electrolysis is occuring in our cars and that is the reason that your aluminum heater core turns to mush.

You've taken an internal water source.....added minerals (by way of using tap water) so that it will carry a good charge, then you've hooked up a DC power supply to it, ensuring that the electrical charge starts to eat away at the walls of whatever metal source they come in contact with.

I know it is not real prevalent in C4s but all the newer aluminum component motor builders (including GM later years) have all accepted this fact and recommend that you use Dei water in the system.

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we're not talking about the area where the spare tire is located. Look in the back area just behind your seat. There, you'll find two small doors that lift up. These are what is referred to as the Storage bins. Look on the lid of one of them and you'll see the build sheet stuck to it.

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All of that is great info for sure. Thanks.

CC have done anything just yet?

You'll have to get the red one running first..........

I think that was my thread!! Wow someone remembered me.....

http://www.theforumlounge.com/1984-corvette-4x3-t8555.html?t=8555

[img]http://www.theforumlounge.com/attachment.php?attachmentid=1945&stc=1&d=1169923552[/img]

New Member over here!! Lotsa familiar faces I see.