No thermostat?

[larso1]

Egon wrote: "Are there not some types of graphs that show the fluid state versus pressure versus temperature???"

Yes, I think you're referring to the "Steam Tables", AKA "Thermodynamic Properties of Water at Saturation," and give characteristics such as specific volume, enthalpy, and entropy, all at a given temperature and corresponding absolute pressure. I'm sure there are graphs too, I just use the table because it's easy to use. HTH's.

Bill

 

[patrick_g]

Some engines run on a thermosiphon principle that does not include a water pump.

Perhaps do some googling and all will become clear.

There are simple low maint diesel gen sets and stationery engines that not only don't have a water pump, they don't have a radiator either. They just have a tank built around the cyl head(s) and you just top them off from time to time as when refueling.

Pat

 

[Egon]

At one time those were a very common type of engine Pat. Back before you were a young lad!!

Bill, I was referring to specific fluid charts in general. Not just tables/charts for steam.

 

[SPYDERLK]

Bill, did you turn on a light switch and put some illumination on the topic???

Said enuf ways, and from multiple sources, it sinks in.
larry

 

[patrick_g]

In otherwords, what you said was "not valid" (<to slow coolant down so that it spends enough time in radiator to effectively transfer liquid heat to air>) is indeed a valid statement IMHO.

Actually it is BALDERDASH!!!!

For years I have heard various shade tree mechanics talk about how if the water goes through the radiator toooooo fast it doesn't have time to lose the heat and it is not as effective.

This is JUNK SCIENCE and is totally bassackwards!!!!

Heat loss is the cumulative effect of many factors including the ambient temp, RH, Thermal conductivity of the radiator, coolant used and on and on and on but we can simplify the situation and consider two identical setups with one having slow flow and the other fast flow.

Delta T is the chief thing driving heat transfer in a radiator. This heat exchanger device (radiator) is actually poorly named as radiation is not the primary means of shedding heat in it. If all the radiator is hot then all of it is shedding the maximum amount of heat. If only part of the radiator is hot (near the water inlet) and the rest, especially near the water outlet is cool due to heat loss of the water then that part of the water sheds less heat and the net result is less heat is removed from the radiator. This assumes the same extant conditions of ambient air temp, RH, speed, etc and the same type of coolant and on and on.

Rather than drag calculus into the discussion lets simplify to make it totally obvious. Lets consider the argument that slower moving radiator flow cools better. If slower is better lets go really slow and see the results. Hot water enters the radiator and starts losing heat to the moving air. Since the water is flowing really slow the water is cooled really well before it reaches the outlet pipe (a good thing?) There is a lot of heat being generated in the engine and if the flow rate is reduced to say a teaspoon an hour there is no way for a teaspoon of water to transfer the heat generated in the engine in an hour! Ok this is too slow, agreed?

Lets speed up the flow and consider what happens. Faster flow moves more hot water into the radiator and it makes its way further across the radiator before being cooled "X" degrees. Now more of the radiator is hotter so it is more effectively shedding heat. Lets get magical and move the water through our imaginary radiator faster than the speed of light. Now the water makes it through the radiator before it can drop so much in temp as before. In this case the whole radiator is nearly uniformly hot (at the temp of the water coming into the radiator.) Now since the whole radiator is hot the whole radiator is shedding heat over all its area of contact with the air flow.

It should be clear that a radiator that is hot all over looses more heat to the air flow than a radiator that is only hot in a small area. Remember delta T. The hotter the average radiator temp is above ambient the more heat it can shed.

There is NO FLOW RATE that results in more heat transfer than a faster flow rate. Improvements in heat transfer with increasing flow rate run into the law of diminishing returns where additional increments in flow rate yield smaller and smaller increases in efficiency. Faster is always more effective at moving heat but at some point the additional gains are too small to justify the effort of getting them. In most instances rather than run a 40 HP water pump the engineers just put in a larger radiator (more frontal area) or a deeper radiator (more rows.) Each additional row of a radiator does less than the previous one because the last rows are receiving hotter air across them due to the hot rows in front of them. At some point it is way better to go larger in frontal area than more and more rows.

Pat

 

[3RRL]

Well then balderdash it is!
Spyderlik has been explaining this since post #7 and his subsequent posts have already made it clear to me.
School's out...

 

[patrick_g]

Whew, glad I didn't get a penalty for piling on!

Pat P.S. School may be out but this may be on the final exam so don't forget it!

 

[patrick_g]

At one time those were a very common type of engine Pat. Back before you were a young lad!!

Egon, Although not seen as often as in the olden days before the big rocks cooled when we were young but there are NEW diesel gensets with that sort of cooling system. No radiator, no fan, no fan belt, no water pump, just a water jacket (open to the atmosphere with no pressurization.) The idea is that you top off the cooling water when you refuel the generator. Some folks use larger fuel supply tanks and make a little gravity based "water minder" like a chicken waterer made with a Mason jar in function but with greater capacity. Then the low oil shutoff is the only thing to kill your backup electricity.

Pat

 

[Egon]

On the water jacket/evaporation cooling system I am not too familiar but whats new?

Now for radiators should we be thinking crossflow or vertical tubes? ehh

 

[woodchuckie]

Does it work the same with a heater core. Although the air is cooler on high speed,does it heat the car quicker or does the low air flow which is warmer heat the car faster. And how about the air conditioner on max and low speed.

 

[SPYDERLK]

Does it work the same with a heater core. Although the air is cooler on high speed,does it heat the car quicker or does the low air flow which is warmer heat the car faster. And how about the air conditioner on max and low speed.

Thats a hard one because some, and usually most, of the air coming thru the coil is fresh air. Already warmed air is leaving the car to make room for it. See the, at least partial, trade off? You are adding more heat [calories or BTU] per unit time to your space, but it is in the form of lower temperature at higher volume. When the air in the car is cold the hi fan is extemely more effective - and, i would think, less and less more effective than lo fan as the car warms.
larry
ps. missed AC part. It has some special considerations too. Later. gotta do something else right now.

 

[3RRL]

woodchuckie,
lol ... You have not been paying attention! You will have to stay after school and retake the final exam. I don't know about you guys, but I haven't done any calculus integrals or derivatives since like 1968.

 

[tallyho8]

Anyone who has ever been caught up in a traffic jam in bumper to bumper traffic on a hot day and has watched their temperature guage move to the red line as they wait almost motionless, knows that if they turn their heater on max temp and max fan speed, and open their windows, that it will cool their engine down fast at the expense of their own discomfort. It is worth the discomfort to avoid burning up your motor. Upon resuming normal speed you can turn off your heater and turn your a/c back on. If you try this with your heater on low fan speed, your temp guage may not even stop rising as I have had occasion to try this many times, so I say high air flow with less heat transfer will transfer more heat than low air flow with more heat transfer over a given period of time.

(Works for me)

 

[patrick_g]

On the water jacket/evaporation cooling system I am not too familiar but whats new?

Now for radiators should we be thinking crossflow or vertical tubes? ehh

Egon, cross flow or vertical means less and less as flow velocity increases. Thermal siphon aids low velocity vertical if the flow is bottom to top. High velocity water swamps out the differences.

Woodchuckie, If you are running your car's climate control in recirc mode then the fastest fan speed will give the best heating and cooling (with a proviso.) You will heat the car faster with max air flow but the high velocity air flow before the air coming out of the heater gets up to a satisfactory temp will not feel as comfortable as slower velocity air even though the temp in the car will rise faster. Good air flow supports evaporation of perspiration and aids the cooling effect of the A/C. A thermometer will show a faster drop if the fan is on high rather than low even though the air coming out of the vent is not as cold. In extremely humid circumstances slower air movement gives better dehumidification (per pass through the evaporator.) Humidity control is an important part of comfort.

If I missed anything my assistant, SPYDERLK will fill in the gaps.

If you are running in flow through ventilation mode then low fan speed can be a better deal as you will dehumidify better and lower the air temp more on the single pass than if you used hight fan. Even in recirc mode there is leakage (infiltration) and intentional makeup air so the air doesn't get stale (assuming no cigars.) In general for heating or cooling, recirc is way better performance. Flow though is good when the temp in the car is comfortable in flow though mode with little or no added heat or cooling and if you are having a tough time with fogging windows.

Pat

 

[tallyho8]

PS
This is also equivalent to the fan blade on your car going faster or slower while you are in that traffic jam. A slow moving blade pulls less air through the radiator but transfers more heat per cfm while a fan blade going faster moves more air through the radiator but transfering less heat per cfm, but I'll go with the faster moving fan blade to cool my motor off in this case anyday. No calculus integrals or derivatives, just plain ole fashioned experience.

 

[patrick_g]

When results are easily and correctly predicted by a casual observer it is not beneficial to invoke higher math. If concrete examples and simple thought experiments can lead someone to enlightenment, again higher math is not useful.

Pat

 

[Egon]

again higher math is not useful.

So now you tell me! Just after I got my shoes and socks off!

Just thinking of cooling systems brings back those memories of poplar fuzz and plugged radiators or frost and plugged radiators.

 

[3RRL]

How about those days when we drove around with water sacks hanging from our hoods for any long trip. At least out here in California. I can remember my Dad with his '49 Pontiac and the water sack when going on vacations. I didn't have to do that. I had a '55 and it ran pretty cool most of the time.

 

[woodchuckie]

Was the water sack for adding water to the radiator or what. I've never heard of that. Why was it hanging from the hood instead of being in the trunk or something.

 

[Egon]

They was for keeping the drinking water cool! cool