Car Cooling Challenge

I would tell you but you wouldn't learn anything and your teacher would be angry with me.

You are forgetting speed of flow.....

In series, the flow rate will be twice as high as in parallel......

GA from me.

Thanks! This is an interesting concept. I might think about this if I ever move back to the farm in the woods.

Lynch

I agree, but would run the hottest water into the radiator exposed to the outside air the most.

I'd say that the two radiators combined in parallel would give you the higher heat transfer capacity, while the two radiators combined in series would give you the lower coolant temperature.

Is your question correct? What matters, heat transfer capacity or coolant temperature?

Most likely series, but you can't say for sure without specifics. The big fly in the ointment will be the efficiency vs flowrate curve.

Since this is posted in the automotive section I would say the radiator under the vehicle bonnet directly in front of the airflow will be cooler than the second radiator located behind it, irrespective of whether or not the radiators are series or parallel connected. This assumes natural forced-air cooling due to the vehicle moving, and forced-air fan cooling when the vehicle is stationary.

All bets are off if the second radiator is mounted on the roof.

Hello, If you want to lower you're coolant temperature, I would recommend using one radiator and purchasing a lower temperature thermostat. However, I would not recommend running you're coolant at a lower temperature than what is specified. Hope this helps.

Now you have me in a blond moment. Is the air flow or the coolant flow in parallel or series?

Air flow is constant. Coolant flow is series or parallel.

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Ran some simulations. If I include radiation, series and parallel work about equally well in my ideal radiator. If I don't include radiation, series does better. Maybe we could have some details??? I'm just guessing here.

Well, some interesting comments. This is not quite an automotive question, but it does involve auto radiators. I'm designing a home cooling system that will circulate lake water thru auto radiator(s) and blow the air thru the house. My grandfather did this in the 1930's to cool a movie theater. When I started to think about multiple radiators, I got stuck on the series/parallel question. It's just one area of uncertainty. I have no idea how to size the system, how much water and air flow will be needed, should I use thin or thick radiators, etc. Any ideas where to look would be most appreciated.

To start with this question should have been posted in Mechanical Engineering, as you want to cool your house (HVAC). Chilled water systems have been around for years. Try Googling "chilled water systems", you'll find a lot of information on the subject. And being your in Texas, where you don't need to run antifreeze in your vehicles, whats the ambient temp. of the lake you want to use. And if your going to use the lake for cooling your house, your going to have to use a closed loop system, due to the EPA, which wasn't around in the '30s!

The heat exchanger in the lake is going have to be a substantial size to extract enough heat to make worth while your efforts. And your going have figure out a way to protect your under water system from boat anchors and fishing hooks.

As far as the cooling coil(s) for inside the house, you could use an "A" frame coil in your central furnace, like an A/C evaporator coil, but being you want to use a lake for your cooling, I think you'll find that using a 'zone' circuit would be more efficient. I would start here:

http://www.google.com/search?sourceid=navclient&aq=0&oq=chilled+water+&ie=UTF-8&rlz=1T4GFRD_en___US341&q=chilled+water+system

dj

Hi SSCpal,

I'd like to ask you what the average water temperature, at the inlet of the suction foot, vs average air temperature will be when in operation. Relative humidity will be an issue, as well.

Really, the water temperature is the most important missing part of the puzzle. Then one of the number crunchers can model it.

This would not work in Arkansas, unless you had a stream within pumping distance.

BTW, not so smart,

I checked his previous posts before jumping in with my answer. ^{_{parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel parallel}}

Cheers to you both!

Lyn

I use a system like this to cool my house with. I use the water that I water my lawn to cool the house with, then it is sprinkles on the lawn. I use an evaporator from a thermo king refer trailer as the heat exchanger, since the coils will stand a very high pressure. When you are working with something like this, you do not have much difference between the inlet and outlet temperatures of your water. Use the radiators in parallel with each other. Since you are only be able to drop the temperature of the water not more than 5 or 6 degrees, you need as much cold water exposed to the air stream as you can get. If you use the radiators in series, the water will be staying in the system too long, and the efficiency will suffer.

If the flow of coolant is slow enough to bring the air temperature to the same temperature as the coolant coming out of the first radiator, sending it through a second radiator will not reduce the air temperature any further.

IMHO running the radiators in parallel with a larger volume water pump would cool more air. I can't prove it. My mind is made up now, try not to confuse me with facts.

Wait! we are not removing heat from an engine we are removing heat from a room.

Using lake water. So, we need the temperature of the incoming water etc, etc

Flow rate, etc

I need a diagram. Good night.

I need sleeeppppppppppppppp.

Its a trick question. Either way all your numbers are the same. running the radiators in series or parallel does not increase there capacity or surface area. and since all your other values are constant then it doesn't make a bit of difference. One reason for this is because as your water cools and approaches the ambient air temp. the more difficult it becomes for the air to extract heat from it. its that whole T1/T2 thing in thermodynamics. (You can not make cold. You can only extract heat.)

Now if your initial radiator is excessively restrictive then adding another in series would enhance that restriction (assuming identical radiators) and at that point a parallel system would be preferential as it would reduce resistance to flow ther-by decreasing the likely hood of premature pump ware, hose fatigue, and excessive losses in horsepower trying to push that fluid.

That should keep your teacher happy. Confused works also.

You should use the radiators in series.

Anant.

If your cooling a structure then you must go parallel "if" you are doing zones (cooling rooms separately). However, It is important that you try to balance your system as much as is practical. I figure you'd probably be trying to save a few bucks and go with a simple pumping station with flow and pressure as constant as practicable. If so then some type of zoning valve should be considered. Also consider that your lake water will have debris and sediment in it and will require filtration. To help you keep your costs down you may want to consider recycling a pool filter and back flush valve system. Since this will most likely be running constantly it would be a good idea to get one that either operates electrically on differential pressure or on a percentage timer. This will help keep your system from clogging up. I don't know how to help you calculate thermal exchange rates. If you really want to get simple you could do a whole house system in which all your radiators are in one group with a large fan blowing across them and then duct that throughout your house. In such a system then a series setup would work well. keeping the unit/s with the coldest water furthest from the fan and work toward it in passes. This is the proper way to use a heat exchanger which is essentially what you'd be constructing in this instance. You will also need to consider how you will deal with condensation, protecting your incoming/outgoing lines from freezing during winter when your system is shut down if you live in such a climate. (draining works well.) You might also want to check to make sure your not violating any environmental impact legislation in your area. Cold water in & warm water out might affect the fishes.

I hope this has helped some.

Crimich13 - "Cold water in & warm water out might affect the fishes." That depends on the size of the lake :P

Getting back to the original question, my advice would be to get a radiator twice the size, otherwise paralell, as mentioned before the greater the difference in temperature between the coolant and the airflow the more heat will be transferred, in paralell the coolant will enter both radiators at its hottest temperature, you may need to up the flow rate for greater efficiency.

You wrote:-

you may need to up the flow rate for greater efficiency.

If the water in the engine, where the temp sensor is (or better said, should be!), gets too hot, then upping the flow rate is a possibility, but I would imagine that the water pump has been sized to allow enough cooling under almost all circumstances of outside temperature. Or at least it should be......

That is why a thermostat is needed/used, to block the flow partially (under control of the temperature of the water flowing past it) to allow the engine to remain at one good working/correct temperature all the time its running......

Only in conditions of extreme outside temperatures and a marginally sized radiator (or one that is partially blocked or where the cooling fan is inoperable etc etc), will the thermostat open fully to allow a full flow of water at water pump speeds....because the water has exceeded its designed temperature.

Having two rads in parallel does not change the water throughput through the pump/engine, it just allows the water to run slower through the two rads, giving it more time to cool, thus probably letting the thermostat close/block even more water as the water it is getting supplied with from the rad, should be significantly cooler than before with one rad.....

The only down side to two rads is that as there is a small hole in the thermostat to allow a small quantity of water through, even when fully closed, it could be that the motor takes a "tick" longer to warm up in a very cold winter, theoretically at least. In practise, I doubt if anyone would notice!!

If the water pump has been sized for adequate cooling, why hasn't the radiator?

This isn't about engines anyway.

That was not the question posed!!!

But maybe he lives in a very hot climate and he has a vehicle that was not fully and correctly designed for that climate. I am sure that he is not alone with such problems!!

Also, some car manufacturers supply a fitted radiator sized for the country where it is to be sold. If a cold region car is exported to a hot region, then such problems can arise......

That is the good point of driving a Japanese car in Germany or most of Europe, they always have very generously sized radiators.....overheating on one of these only happens when something else goes seriously wrong first!!

!! WAKE-UP !! The discussion has changed! There is NO motor involved (except the electric pump motor to drive the lake water through piping through the radiators in the house/cabin.

As such / no thermostat either

I was referring to the immediate discharge area. And the potential cumulative effects upon such areas. If a municipality allows one citizen around a lake to do this then they have to allow all of them. And municipality's love to get into anything different like this. They will ask about intake and discharge flow rates. They will raise questions about discharge temp, location, elevation, tidal flows in that location. They will have questions about intake location, suction screening, etc.. They may want the applicant to have some form of environmental study done by a qualified company. They may want a wild life study done to see if there are any endangered species that nest or breed in that specific area or immediate path of the discharge stream as this may effect there chances of survival. Raising the fluid temp too close to the bottom or top could conceivably change growth patterns in algae and other aquatic plant life and disrupt the food chain in such an instance. They will definitely say something about flushing lake water through those recycled radiators that are soldered together with lead and used to hold antifreeze. Even discharging above ground raises issues as fertilisers, pesticides and other such contaminants are likely to be picked up some where along the flow as the water naturally seeks to re-enter the lake. I haven't even approached the question of whether or not this might be a reservoir.

I agree that the likely hood of causing a rise in temp of the entire body of water from the discharge of just one dwelling is nil. But there most certainly are environmental effects at the point of discharge. It used to be that people living around lakes would discharge all sorts of things into them (rivers also) such as waste water. Take a good look at the lasting cumulative effects of that.

unless the person building this lives in an underdeveloped country that has little or no regulation over such systems then all of these are very real topics that will need to be addressed.

There is a delicate ecological system in most lake systems. It does not take much to disrupt there natural balance. This is why we see abnormal algae blooms, experience e-coli out breaks , etc... When we introduce changes to a body of water beyond its natural capability to absorb and correct such changes. Much of which is occurring on a biological level.

So please forgive my oversimplification when I said cold water in & warm water out may affect the fishes.

My previous response was academic. Yes. Such a system is, from a mechanical stand point, feasible. However it is fraught with problems that may effect others. This is why we have building codes, environmental studies, etc.. To keep us from doing harm to ourselves, each other and the environment. Small impacts are still impacts. Even if it is within acceptable limits we should at least pose it to ourselves on a moral level.

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Woodsy the Owl says. Give a Hoot, Don't Pollute

An intelligent, studious and well written response, keep on hooting Woodsey!

Looking at the way a radiator is constructed, I would say parallel is better.The incoming water is applied to all vertical coils simultaneously, in parallel.If series was more efficient, they would be one continuos loop.Resistance to flow becomes an issue when in series, as well as an efficiency drop off due to decreasing differential temperature.If they are in parallel, do not place them one in front of the other, this will reduce efficiency also.

Condensor and evaporator coils are also in parallel.Take a clue from the experts that design heat exchangers.

I use two radiators to cool drilling fluid in a Gun Drill operation. As the oil approaches 130 degrees one radiator comes on line with a 3 hp fan directing ambient air across the cooling fins. If the oil continues to rise in temp the other comes on line and removes additional BTU's from the oil stream going to the filtering sump. The radiators are in series for the oil flow and in parallel for air flow. ( 2" lines at 160 gpm).

These are old WWII Gun Drills 2 spindles each drill unit two units in operation. We drill 446 SS with a 1" bore to a depth of 48" in a 2 5/8 blank. It takes about 40 minutes to drill one piece. Production is 4 pieces per hour with cleaning and bore gauging units.

Have you ever tried having the rads in parallel for the oil? I am sure you would notice a difference for the better in the temperature of the oil.....it would be measurably cooler...

Also, the resistance to liquid flow would be dramatically improved eg. reduced.

Stan, very interesting stuff! Thanks for your work. Doesn't water flow rate come into the equation? In parallel, the flow rate will be half that of the series.

I am going to rewrite my question and post it in the General section, under the title "water/air heat exchangers: series or parallel?" for those who want to follow it there. Sorry if I misled anyone; the original 1930's system used auto radiators and that's where my head was.

SSCpal, when you re post this, please give some more details like approx. water temp. at the depth you plan on using, size of pond or lake, approx avg. ambient air temp., how far is the pipe run from the house to the water, etc.

True, the flow rate in the parallel case is half per exchanger compared to the series case. But remember, there are two exchanger flow paths, so the total mass flow of water in the overall system is the same in either case. Again, it comes back to analysing the heat transfer efficiency of the second exchanger, where the effect of LMTD in the second exchanger will dominate the overall system performance, all other things being equal (such as film transfer efficiency inside the radiators at 50% or 100% flow).

In reality, the parallel arrangement would actually have greater total system mass flow on the water side because of the lower pressure drop associated with the reduced flow per exchanger. Again, this effect favours parallel arrangement over series for overall heat transfer efficiency.

Regards,

Stan

we can't answer. The mass flow and reynolds number could kill you in either parallel or series.

It's been a while, but I think this might interest those who participated in the discussion. I have a friend who built his house on a small lake. He has a well and pumps cool water from it thru his HVAC and then the water runs out a hose into the lake. He didn't bother with any EPA or other govt nonsense. He's outside city limits and the only inspection needed was by the county of his septic system.