Author Topic: Engine cooling: water tank vs. rad in tank vs:- water-water heat exchanger  (Read 12149 times)

0 Members and 1 Guest are viewing this topic.

Offline Sumner

  • Global Moderator
  • Hero Member
  • ***
  • Posts: 4078
  • Blanding, Ut..a small dot in the middle of nowhere
    • http://purplesagetradingpost.com/sumner/sumnerindex.html
.... Another thing I didn't think about was how much more efficient the radiator becomes when turned into a water to water unit. We can run a smaller radiator for better packaging....

We could of probably run a smaller radiator but this one wasn't that expensive and it is a 2 pass radiator which I also wanted to use.  Another advantage with the water in a separate tank besides moving the water past the rad. is that you can preheat the motor and not preheat any of the cooling water except what is in the tank around the rad.. 

Another obvious advantage over just a cooling tank, no rad-in-a-box, is that now you can run pressure in the engine side and none in the cooling side.  That sure helps with a lot of engines to help avoid steam pockets.

The driver turns the water pump on just before leaving the line, but the pump could also be activated by a switch on the shift linkage, say on the 1-2 shift.  I'd like to add that just in case the driver forgets to turn the water on.

Of course that never happens  :-o 8-) :oops: :oops: :cry: :cry:,

Sum

Offline manta22

  • Hero Member
  • *****
  • Posts: 4137
  • What, me worry?
Does anyone have a formula for amount of water needed in the tank vs horsepower? We are planning a system like this and will have up to 2500hp but most likely not more then 2000hp

It takes 1 BTU to heat water 1 degree F and then it takes 970 BTU more to convert it to steam. Water boils at 212F (not considering altitude) so if you raise 10 gallons of water (83.3 lbs (8.3 lbs/gal)) from 92F to 212F , it takes (212F - 92F) x 83.3 lbs = 9,996 BTU. Converting all of it to steam requires an additional 970 BTU/lb x 83.3 lb = 80,801 BTU. The total heat required to completely  boil away water whose starting temperature is 92F is 9,996 BTU+ 80,801 BTU = 90,797 BTU.

You need to convert horsepower to BTU transferred to the cooling system and that varies depending on each application. Maybe someone has already determined that for a typical (if there is one  :-) ) racing engine. Remember that most conversion charts are for horsepower to BTU per hour. A run on the long course is a lot shorter time-- far less BTUs.

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline Seldom Seen Slim

  • Nancy and me and the pit bike
  • Administrator
  • Hero Member
  • ***
  • Posts: 13158
  • Nancy -- 201.913 mph record on a production ZX15!
    • Nancy and Jon's personal website.
Nice maths, Neil.  And for what it's worth -- that 80.8k BTU is about what it takes to heat our house for one hour during a nasty blizzard.  That puts it in a different perspective, doesn't it - especially when thinking about that much heat generated for disposal in about 2 minutes.

Oh, yes -- by the way, I use the 80.8 figure because I allow the water to still be at about the boiling point after the run ends and the engine is shut down.  Good enough for this discussion. :-D
Jon E. Wennerberg
 a/k/a Seldom Seen Slim
 Skandia, Michigan
 (that's way up north)
2 Club member x2
Owner of landracing.com

Offline javajoe79

  • Sr. Member
  • ****
  • Posts: 618
Great info !! 
Coffey Fabrication and Race Prep
313 Wilhagan Rd Nashville, TN 37217
615-210-1605

https://www.facebook.com/CoffeyFabrication

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2625
  • Only time and money prevent completion!
A few things that you need to consider when using a plate liquid to liquid heat exchanger. One thing is that the BTUs that it is rated to adsorb are based upon several factors, the first of which is the differential temperature between the two fluids, obviously the greater the differential temp the more heat is transferred that is of course if you have the rated amount of fluid flow going through both sides of the heat exchanger. If you are not moving the fluid through the exchanger at a rate that is fast enough to ensure that the flow is turbulent then your heat exchange efficiency will suffer. Actually the faster the water flows the better. This brings up an additional potential problem. If the exchanger is rated at say 20 gpm flow don't think that you can just attach a 20 gpm nominally rated pump and have 20 gpm. As most if not all water pumps are centrifugal their flow rate drops as the out put pressure is increased, by such things as pressure drop across your plate heat exchanger so you will probably need a much larger pump just to ensure that you are getting enough water going through the exchanger, and that goes for both the engine cooling water and the water from your tank.  Neil is correct that the act of bringing water to boiling does require additional heat, the heat of transition, but if you are going to boil your tank water away that would require that your engine water be higher than boiling, not a good idea. I would much sooner go with your concept of a  closed tank system with lots of ice,which also requires additional heat to transition from ice to water and properly sized water pumps to insure good flow for both the cooling water and the engine water. I have applied plate heat exchangers a number of times and they can be very efficient and are of course very appealing because of their small size.  A liquid to liquid i.e. water to water in this case if properly designed, proper flow rates through both sides of the exchanger will typically be 7-8 times more efficient that an air to water exchanger, also assuming that its water flow rate and the rate of the air passing through it are correctly sized.

Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline tauruck

  • Hero Member
  • *****
  • Posts: 5126
This is what makes this forum what it is.

Thanks Rex.

I got schooled. :cheers: :cheers: :cheers:

Offline javajoe79

  • Sr. Member
  • ****
  • Posts: 618
A few things that you need to consider when using a plate liquid to liquid heat exchanger. One thing is that the BTUs that it is rated to adsorb are based upon several factors, the first of which is the differential temperature between the two fluids, obviously the greater the differential temp the more heat is transferred that is of course if you have the rated amount of fluid flow going through both sides of the heat exchanger. If you are not moving the fluid through the exchanger at a rate that is fast enough to ensure that the flow is turbulent then your heat exchange efficiency will suffer. Actually the faster the water flows the better. This brings up an additional potential problem. If the exchanger is rated at say 20 gpm flow don't think that you can just attach a 20 gpm nominally rated pump and have 20 gpm. As most if not all water pumps are centrifugal their flow rate drops as the out put pressure is increased, by such things as pressure drop across your plate heat exchanger so you will probably need a much larger pump just to ensure that you are getting enough water going through the exchanger, and that goes for both the engine cooling water and the water from your tank.  Neil is correct that the act of bringing water to boiling does require additional heat, the heat of transition, but if you are going to boil your tank water away that would require that your engine water be higher than boiling, not a good idea. I would much sooner go with your concept of a  closed tank system with lots of ice,which also requires additional heat to transition from ice to water and properly sized water pumps to insure good flow for both the cooling water and the engine water. I have applied plate heat exchangers a number of times and they can be very efficient and are of course very appealing because of their small size.  A liquid to liquid i.e. water to water in this case if properly designed, proper flow rates through both sides of the exchanger will typically be 7-8 times more efficient that an air to water exchanger, also assuming that its water flow rate and the rate of the air passing through it are correctly sized.

Rex
Great info Rex. The heat exchanger setup is one option I am considering for our build for packaging reasons.

 Can you elaborate as to why you don't want the engine water to be higher then boiling? I know that many forms of motorsport use high pressure cooling system and run engine coolant temps much higher then the average low pressure system. I understand that current nascar systems run near 300*F with no issues all day long. Of course you would build the engine with that in mind but...
Coffey Fabrication and Race Prep
313 Wilhagan Rd Nashville, TN 37217
615-210-1605

https://www.facebook.com/CoffeyFabrication

Offline Rex Schimmer

  • Hero Member
  • *****
  • Posts: 2625
  • Only time and money prevent completion!
There is nothing wrong with running the engine water at a temp higher than boiling, many race engines are designed for this, not uncommon for NASCAR, F1 etc to run water temps around 230 or even somewhat higher, but the engine needs to be designed for this operating temp, the right coatings, good oil cooling and lubrication and a cooling system that will operate at a pressure high enough to keep the water in liquid form at that temp. I think that NASCAR has set the water system max pressure at 20 PSI just to keep people from going to high. There are also some additional advantages to running high temps , the pressure required for high temp water will provide extra pressure in the block and this can provide additional support to the cylinder walls which on a super charged or turboed engine can be helpful.

As I read Neil's input it appeared to me that he was suggesting that you could uses the heat if transition for water turning to steam as part of your cooling scheme. The challenge with this is that would require that the engine water be significantly higher than boiling  and if you want to dissipate sufficient heat to keep the engine temp stable you would need the engine water temp high enough to provide the temperature differential to drive sufficient heat into the cooling water that you are trying to boil. A lot easier just to go with ice in the cooling water and run the engine at under 200 F.  Pretty easy to maintain a temp differential of 150 to 170 F and this will drive a lot of heat into your cooling tank water plus the heat of transformation of the ice to water.

Rex
Rex

Not much matters and the rest doesn't matter at all.