Help me size a tank for thermo siphon!

[Horsepoor]

Here is an excellent link for coolant specifications:

http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html

The below illustrates about 90% of the heat transfer results from water evaporating from the open surface of a hot water cooling tank. I remember reading an extremely interesting post 2 or 3 years ago by ROMAR and considered using a horse watering tank for cooling. I ended up with a small radiator and a home heating recirculating pump (extremely reliable). Here is the link for open tank heat transfer.

http://www.engineeringtoolbox.com/heat-loss-open-water-tanks-d_286.html

[XYZER]

One of my secret dreams (don't tell anyone) was to use a Model T brass radiator.  A born natural.
Casey

Model T radiators are designed specifically for thermo siphon. They have a large upper tank so it can loose some water and not loose the thermo siphon. That is the main problem with a modern radiator and the need for a large reservoir so the upper tank does not go dry and halt the thermo siphon. This is a basic layout of how I do mine. I have one with a Metro radiator and fan. The other is using a larger Saturn radiator. Neither needs a fan in cool weather or if it is out in the wind. The larger the radiator the less fan you will need.

[Randybee1]

XYZER, You keep your radiator cap loose, do you have a coolant recover tank for the radiator? If not.. why? I'm guessing if the system is not pressurized it won't develop a vacuum when it cools down. I decided to go with a Plymouth Horizon radiator with fan system. I have not run it longer than 15 minutes because the NEW fan sensor/switch I bought is defective and the fan stays on all the time.

Thanks, Randy B

[Henry W]

I was actually thinking I might just hook up a fan. The problem with adding a thermostat is my coolant lines are only 5/8 diameter. Its a little 14 hp engine. Not sure why they are so small!  Randy B

If the coolant lines are only 5/8" dia it is a good chance that the engine was used for marine application.
It most likely used a raw water rotory vane pump. The pumps are very effective to suck water up a few feet when coolant lines are dry.Standard automotive style circulator pumps would become airlocked under these conditions. The coolant lines are kept to a smaller dia so the pump can overcome an airlock condition. By reducing the Dia. of the tube from say 1-1/2 or 2" to 5/8 the pump needs much less suction. The reason is, the pump has much less volume/mass to suck up in a smaller dia line.

A 5/8 dia. suction line is large enough with a raw water rotory vane pump setup to cool a 50+ hp inboard engine with no problem in raw water applications.

The only problem with rotory vane pump setup is it should not be used directly in a closed loop system where it is subjected to hot water. The rubber impeller cannot withstand heat. But they are used in fresh water applications with heat exchangers all the time. But that would require two pumps for the engine. One circulator for the closed loop part of the system and one rotory vane pump for raw raw water part of the system.

Henry

[mobile_bob]

my 195 is cooled with a bosch auxillary heater pump, the ones used to provide for heaters in MB,VW, Audi and others
it is coupled to the engine with 5/8 and 3/4 heater hose and pushes water into the drain port at the bottom of the cylinder
that being a 3/8" pipe port.

the 195 will pull over 7kwatts and the pump and cooling system will handle that with no problems

i am using an '87 nissan sentra radiator, electric fan and fan temp switch and am thermostatically controlled with a late '80s
honda t/stat and housing with a bypass hose that is 1/2" with a 1/8" orifice and an 1/8" hole drilled in the stat.

the system is ran with a 7lb cap and 50/50 antifreeze mix, the temps cycle between 205 and 215F at full engine load.

and i use a recovery tank, which picks up the expansion overflow and returns it on cool down.

it works exceptionally well

my control system starts the pump before startup, and maintains its operation after shutdown for a programmed period of time
to allow for system cooldown and limit heat soak which can lead to unnecessary overflow.

it is my belief that the little bosch pump probably could provide enough flow to cool 20 plus hp

bob g

[Henry W]

Bob, I feel you are right on your belief that the little bosch pump probably could provide enough flow to cool 20 plus hp engine. Also a closed loop cooling system is much more desirable over a raw water cooled system because once the water is warmed up the incoming water that cools the engine is only 10 or 20 deg. cooler than the water that is leaving the thermostat. A raw water cooled engines at times could get a dose chilled water to the engine and temperature differance can be 150 deg. or more.

Henry

[Randybee1]

I have my little Kubota up and running with the radiator/fan/thermosiphon method. I went to the junk yard today to look for a coolant recovery tank (got one for $3.00) and for a Bosch water pump. I forgot all about the pump because I saw 2 really nice looking 18 gallon fuel tanks ( came out of a boat) .They were just setting in a bathtub.  The tanks had the sender unit and the metal straps. They are a nice rectangular shape, very thick plastic. I paid $25.00 for one. I'm gonna go back tomorrow and get the other one...maybe I'll remember to look for that pump this time

I'll probably hook up the water pump when I get it because today I ran my engine with generator attached for about 40 minutes. The radiator fan kicked on at 8 minutes after start up and did not shut off. The ambient temp is about 50 degrees f. I went back out after 30 minutes, turned the key and the fan did not come on so I know its working correctly. I do not have a temp gauge hooked up yet so I don't know what my water temp is running at yet.

Randy B

[Ronmar]

I would reccomend you go get a little IR thermometer.  Very handy device for setting up and troubleshooting a cooling system.  You just need to remember to always measure from something with the same emissivity for consistent readings.  Bare copper will give you some wild variations:)  The easiest way to do this is to take a can of flat black spraypaint and paint a small spot at every area you want to take temperature measurements from. 

[Shipo]

my 195 is cooled with a bosch auxillary heater pump, the ones used to provide for heaters in MB,VW, Audi and others
it is coupled to the engine with 5/8 and 3/4 heater hose and pushes water into the drain port at the bottom of the cylinder
that being a 3/8" pipe port.

the 195 will pull over 7kwatts and the pump and cooling system will handle that with no problems

i am using an '87 nissan sentra radiator, electric fan and fan temp switch and am thermostatically controlled with a late '80s
honda t/stat and housing with a bypass hose that is 1/2" with a 1/8" orifice and an 1/8" hole drilled in the stat.

the system is ran with a 7lb cap and 50/50 antifreeze mix, the temps cycle between 205 and 215F at full engine load.

and i use a recovery tank, which picks up the expansion overflow and returns it on cool down.

it works exceptionally well

my control system starts the pump before startup, and maintains its operation after shutdown for a programmed period of time
to allow for system cooldown and limit heat soak which can lead to unnecessary overflow.

it is my belief that the little bosch pump probably could provide enough flow to cool 20 plus hp

bob g

Hey bob I like your settings and I want to do it in my 195, but I don't understand from where you are getting the coolant to supply the pump unless you have only one entry in the top plate. I have George plate with two entry in the top and I don't see how can I use the bottom entry with the pump. Unless I use a "T" in the cool side to supply the button with the pump. Do you think that will work?

[mobile_bob]

i only use one of the two top holes, and that is for the t/stat extension housing, the bypass hose comes off the extension housing
the other port i just put my mechanical temp gauge bulb into so i can read the temp right above the cylinder

the water goes from the pump to the drain port on the cylinder,


the suction side of the pump is attached to the lower radiator hose, the nissan sentra has a ~1.25 lower hose, with a T which
was meant for the car heater return.  i blocked the bigger and attached the pump the the heater port of the radiator.

the top hose coming off the tstat goes to the top radiator port via a section of 1" emt tubing

the bypass is a half inch line that i put a rubber orifice into and then feed it back into a T going into the pump intake side.
this keeps the engine loop circulating, and when the t stat opens the water flows back to the radiator for cooling.

i have to redo this system to include a heat exchanger for the coolant loop, but haven't done that yet.

i picked up a second pump at the salvage yard, and will be using it with the exhaust heat exchanger because the one i am using
for testing moves way too much water and runs off of 120vac, if i slow down the coolant flow to the exchanger i will likely increase
its ability to transfer heat.  the 120 vac pump moves about 5 gallons per minute, i think i would like it better at maybe a gallon per minute which i think is about what these little bosch pumps are good for.

i will try to get a couple pictures posted this weekend, if everyone bears in mind that this is a prototype and not in finished form.

really need to take the time to tear it all down for final welding, sand blast and paint, the unit in rust looks rather,,, rusty!

bob g

[Randybee1]

I would reccomend you go get a little IR thermometer.  Very handy device for setting up and troubleshooting a cooling system.  You just need to remember to always measure from something with the same emissivity for consistent readings.  Bare copper will give you some wild variations:)  The easiest way to do this is to take a can of flat black spraypaint and paint a small spot at every area you want to take temperature measurements from. 

Funny.. I was going to do just that yesterday! I left the junkyard and was thinking of going to Harbor Freight to get a remote IR thermometer.. but then I thought.. not on Black Friday!.. maybe next week

Randy B