Using a Plate exchanger to cool a 175 Changfa

[veggie]

I am trying to determine if the plate exchanger I have will swap enough heat to keep my engine cool.
The engine is a small R175 Changfa being used in a mini-CHP project (See picture below).
The engine cooling system rejects approx 10K BTU'hr at 1800 rpm full load, and I expect it to be running at
75%+ load most of the time.

The heat will be exchanged to a 60 gallon tank with an initial temp of 65f.
With the engine coolant at 180f and the initial tank temp of 65f I expect the transfer of heat should be sufficient
to keep the engine cool. I have no idea of how to calculate the tank temperature point at which exchanger becomes incapable of
keeping the engine cool ?

The exchanger specs are as follows:

===============================
Dimensions:
Length:          7.52 inches
Width:          2.87 inches
Height:          1.33 inches
Weight:         About 1.75 lb

Port Fittings:          SS304 – ¾" NPTF
Efficiency:          44.4%
Heat Transfer Area:    0.014 m2/plate (.14 ft2/plate)
Plate Thickness:       0.3 mm (.012 inches)
Channel Capacities:    0.022 L/channel (.00582 gallons/channel)
Estimated Heat Transfer   1 to 5KW or 3500 -17,500 BTU/hour
Weld/Brazing Material:   99.99% Copper
Plate Material:      SS304

Note: These estimated heat transfers are based on a solar water heating application.
A typical application has about 110 deg F on the hot side and 65 deg F on the cold side (45 deg differential).
If your temperatures are colder or hotter, you will get more heat transfer.
If your flow rate is above ~ 1 gpm, you will get more heat transfer.

============================================

I know some of you have used plate exchangers on your engine cooling systems (Ronmar ??).
Perhaps I can get some "boots on the ground" experience with any issues associated with plate exchangers and their sizing.

cheers,
veggie

[Henry W]

Hi Veggie,

That is one beautiful setup. From reading the specs you might be ok with that cooler.

I always liked plate coolers to cool engine oil. They always did a very good job on my applications. I used one on my 2.3 Turbo Ranger and had no oil cooling issues.

Does the company make different sizes? If so what is the next size up?

Henry

[Ronmar]

Good specs, unfortunatly you are missing one key piece.  Well 3 pieces actually.
1. How many plates on your exchanger?
2. How is your primary loop circulated?
3. How is your secondary loop circulated?

Looks like the heat transfer spec they give is with those temps and 1GPM of flow?  Thru both loops?  That and temp difference will determine the thermal thruput.

I use a 5X12 exchanger with 10 plates, or right at 600 SQ/IN of surface ares.  It moves about 18,000 BTU/HR quite nicely, but my primary loop is thermosiphon.  WIth pumped flow it could move significantly more heat.  My secondary loop is pumped with the smallest taco pump they make, and I have a recirc valve on it to reduce the potential flow even further to keep it from burping with a 120F thermostat on the heatex secondary output.

IMO, flat plate heat exchangers are the best option for fluid to fluid heat transfer.  They have wonderfull turbulence even at low flows.  For thermosiphon, they have one disadvantage though.  They are so dense, they hold very little coolant mass, so they can have difficulty generating good flow as the volume cooled at any given time is small, compared to the volume heated in the cylinder and head of a 6/1.  I had to place my heatex about 30" above the head  of my 6/1 to get enough primary flow at full engine load. 

Without a good estimate of the flows thru the loops, it will be next to impossible to calculate the max allowable tank temp.  But I guess my last question would be why you need to?  For sustained operation, you need to remove as much heat as the engine generates, so that 60 gallon tank will eventually heat saturate and become useless as a place for the heat to go.  I run mine the same way, but with the slow flows thru the tank, the heat stays on the top, and drawing the coldest water from the bottom of the tank keeps that 65F supply constant for quite a while.  One way to deal with this is to inject cold water into the tank and purging some hot water from the top.  Another option is to put a fan coil/radiator unit on the tank outlet returning to the heatex.  This will cool the water leaving the tank to ambient air temp, keeping the heat dissipation constant as long as the air temp isn't too high.  By doing this, the tank can heat to full capacity storing all the heat. Beyond that it dissipates it to the air like a normal engine radiator.  This is how I set my system up so I maintain a full tank of hot water for domestic use.  It also allows the primary loop to be under 2 gallons with antifreeze in it, non toxic propolene glycol in my case:)  I also have it setup so I can put the radiator inside or outside depending on if I need heat in the house or not...   

[veggie]

Hi Veggie,

That is one beautiful setup. From reading the specs you might be ok with that cooler.

I always liked plate coolers to cool engine oil. They always did a very good job on my applications. I used one on my 2.3 Turbo Ranger and had no oil cooling issues.

Does the company make different sizes? If so what is the next size up?

Henry

Thanks Henry,

The exchanger was bought from DudaDiesel.
They have an Ebay store.
Many sizes.
http://stores.ebay.ca/DudaDiesel-Alternative-Energy?_trksid=p4340.l2563

veggie

[veggie]

Ronmar,

Sorry not to mention.....the exchanger is 15 plates.

My primary loop is very small so I want to keep the flow rate around 1/2 GPM.
I think the whole primary loop holds (engine block and exchanger loop) about 1 gallon.
I can circulate faster than 1/2 gpm if it would help.

Secondary loop can circulate at 1 gpm no problem.

I want to push as much heat as possible into the 60 gallon tank which is intended to give off it's heat through
the night in the greenhouse via a 5K BTU/hr fan coil.


Ideally I would like to bring the temp of the tank up to 160f but that may be difficult if the engine is at 180f (only 20f differential).

Perhaps one method of control is to build in a 190f shutdown and just let the engine run until it hits the temp limit

veggie

[Ronmar]

Well it looks like about 324 SQ/IN of transfer area.  You are right, 160 out to the tank from 180 will be more difficult.  Why such a low engine temp.  IF you ran a 195F thermostat, getting 160 out to the tank would be easier.  As to wether it will work or not, you won't know untill you try.  Both loops being pumped makes it a little easier to experiment with flows... 

How cold does it get where you are at? 60 gallons is 480 pounds at 160F cooled down to 80F = about 38KBTU.  About 7.5 hours at a 5KBTU rate?

[mobile_bob]

i see no reason that the 175 can't run substantially hotter than 180 degree's
it is afterall a hopper cooled engine by design which tells me it is made to operate
at boiling temperatures, or 212F at sea level.

me i would set it up with a 195 tstat and set the circulating pump to operate in such a manner as to keep the engine coolant as close to 212f as possible. its likely you will be running antifreeze of some sort so 212F is not an issue.

the engine will run cleaner and be a bit more efficient with fuel consumption the hotter you run it.

because it is water to water in the exchange, i see no reason why you can't harvest all the available heat from the engine, provided the exchanger is large enough to do the job.

whats to keep water on one side of the exchanger from being the same temp as the other side of the exchanger, when the medium is water?  i can see the rate of transfer dropping as you reach parity, but if the exchanger is large enough this rate of transfer is likely to be higher than the rate of btu production anyway?

what is a step up to the next size going to cost?  if it is acceptable i would go one size larger and go for it. put the pump on a temp switch that is set to about 205 or so, and let 'er rip.

bob g

[veggie]

Hi Bob,

I was planning on 180f because it allows me to run an "open" cooling system without pressure.
If I go to 190 or 200 (at my altitude of 3000 ft.) I would have to run a pressure system with a rad cap.
That should not be a problem assuming the Changfa can take some pressure.
What's your experience with the head gasket and cylinder sleeve o-rings when running coolant system pressure?


veggie

[mobile_bob]

the orings haven't been a problem, the head gasket likely won't be a problem either
unless you run the engine over its rated load capacity.

my s195 changfa, idi engine uses the stepped liner, wherein the liner contacts the head
and the gasket fits around that liner ledge or lip.

the engine as you know is rated at 13.2 hp (1 hour rating) at 2000rpm
so about 6.5kwe or so would be fine, however

in testing this engine with a block off plate, a 195 tstat, 10 lb rad cap, 50/50 coolant
bosch auxiliary pump,  and a thermostatically controlled fan on the radiator, with a total cooling capacity of right at 2 gallons.

it would run between 205 and 214F pulling 8kwe from the st7.5 head, however the oem changfa gskt could not hold this load level under these conditions, after every test run i would find that the engine had blown the fire ring and split the fire ring radially at the fold

i went to gaskets to go, and he supplied me with some s1100 head gaskets, of vastly superior materials, no more problems

in one test i forgot to turn the pump on and the coolant temp went all the way to 260F before i caught it!

the gasket did not fail and the o rings stood up just fine,

now i don't suggest 260F as anything one should do, but it is a testament to the quality of the orings with a closed system at 10psi and 260F, and also a testament to
the head gaskets ability to put up with the abuse while delivering 8.1kwe.

btw, the engine was singing along just fine, and with no smoke!

just hotter than hell!

so in my opinion, the orings can handle a 10 lb cap just fine and they certainly can handle the heat. 

what are your 175 gaskets made of? are they the sandwich copper type or the metal core fiber covered type?

either way, i can't see you having a problem with the engines gaskets or orings with a closed and pressurized system, as long as you are not running the engine at max output or exceeding the engines rating.  (which is doubtful that you have that in mind anyway)

fwiw
good luck
bob g

[mike90045]

Similar idea here, I've decided 35 gallons of 50/50 antifreeze (for it's anti-corrosion properties more than anything else) is not workable, and I'd like to reduce that to about 3 gallons with a heat exchanger on a 6/1. I'd like to stay with pure thermosiphon, and have seen the note about needing about 30" of elevation difference to get the flow started.
Would going to a oversized exchanger reduce the restrictions and allow usage without pumps on either side, be feasible, or is at least one pump needed with a exchanger  ?

at my 1500' elevation, boiling is 209F
according to these fellows:
http://www.engineeringtoolbox.com/boiling-points-water-altitude-d_1344.html

Antifreeze/coolant does little to raise the boiling point, it's the pressure cap on a radiator that gives the "250F" protection, so I'm not expecting anything there to change.

[veggie]

It should work.
I believe Ronmar has done what you are proposing.
Perhaps he can chime-in with a few tips....

[Ronmar]

Mike, I don't think it is so much the restrictions of the heatex, as the brazed flat plate heat exchangers flow really well.  The issue I ran into was I believe do to the very large differences in mass.  The cylinder and head on a 6/1 contain a gallon+ of coolant.  A 600 sq/in surface area brazed flat plate heatex contains ounces...  Thermosiphon is as much about the cold fluid flowing downward as it is about the hot fluid rising.  since there is so little mass in the heatex, it can't move all that much without some help. That is why radiators work well, they have hearly as much coolant in them as the cylinder and head.  By raising my heatex 30", I get a 1" pipe/hose running down out of the heatex that contains a much larger mass of chilled coolant,to help offset the larger mass inthe cylinder and help power the flow.  Even at the raised height, I am still running less than 2 gallons of coolant including what is in the expansion tank.  That is the lowest volume I have heard of, and it works pretty well at the heat output that the 6/1 is capable of.   

[Jens]

A little circulation pump takes about 40 Watts or so (by memory), there is very little reason not to run it when the engine runs. Run a second one in the secondary loop. You have a generator or alternator on the unit. Even if it is 12V, you can get a cheap 12V to 120V inverter from Canadian Tire and run the pump. You don't even need any control circuitry - when the engine runs you got power (well I guess if you are running 12V and a battery you need something to start up the pump when the engine runs). I ran my primary loop circulator straight off the generator.
If you have the room and your run time is less than the desired time to heat the 60 gallon storage tank, just add another old (used/free) electric hot water tank (remember I ran three in series).
There is (IMHO) very little chance of getting anywhere close to 160 degrees storage temperature with that small heat exchanger in a gravity feed mode.

Since you already have the heat exchanger, you could of course just try the gravity circulation setup and wait to add the pumps until the actual performance is known.

[mike90045]

Mike, I don't think it is so much the restrictions of the heatex, as the brazed flat plate heat exchangers flow really well.  The issue I ran into was I believe do to the very large differences in mass.  The cylinder and head on a 6/1 contain a gallon+ of coolant.  A 600 sq/in surface area brazed flat plate heatex contains ounces...  Thermosiphon is as much about the cold fluid flowing downward as it is about the hot fluid rising.  since there is so little mass in the heatex, it can't move all that much without some help. That is why radiators work well, they have hearly as much coolant in them as the cylinder and head.  By raising my heatex 30", I get a 1" pipe/hose running down out of the heatex that contains a much larger mass of chilled coolant,to help offset the larger mass inthe cylinder and help power the flow.  Even at the raised height, I am still running less than 2 gallons of coolant including what is in the expansion tank.  That is the lowest volume I have heard of, and it works pretty well at the heat output that the 6/1 is capable of.   

So the disadvantage I see to using a pair of pumps, is automatically powering them, and if I wired them to the ST head, wouldn't they stay wired when the motor winds down, and kill the residual magnetism ?  I don't have a 12V circuit, just the 250 out from the ST head.  I have 120Vac in the shed, but that's another switch to remember, both ON and OFF.  Would a snap disc thermostat be a feasible route to use ?  Attached to the engine side of the heatex, set for 180F ? 

[squarebob]

I have a 588 sq. in. Duda Diesel heatex 40" above my gm90 fed by 5/8" heater hose and flow controlled by a 195 t'stat with a small hole drilled in the base. It thermo siphons just fine. The secondary loop right now has a circ pump and a trans cooler radiator with fan to extract the heat. I am 195 in and 125 out of the primary loop. Works like a charm. I fashioned it after Ronmars avatar but have yet to put in the large storage tank. The secondary loop has only about 1 gallon of liquid and the flow is throttled back to maintain the 125 cool side on the primary loop.