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rover67
02-08-2011, 11:27 AM
Can anybody help me calculate what size heat exchanger I'd need for the following:

Hot side:

Liquid = Engine Coolant. Mix of anti-freeze and water
Flow Rate = 2 gallons per minute (guess)
Temp at inlet = 190 degrees F

Cold side:

Liquid = water
flow rate = 4 gallons per minute
inlet temp = 40 degrees F
outlet temp = 104 degrees F

I am wondering if something like this would work:

http://cgi.ebay.com/Stainless-Steel-Brazed-Plate-Heat-Exchanger-8x3x1-5-/350396390423?pt=LH_DefaultDomain_0&hash=item5195409c17#ht_1122wt_1088

or if i'd have to go bigger like this:

http://cgi.ebay.com/20-plate-Copper-Brazed-Heat-Exchanger-3-x7-6-WVO-SVO-/150551721122?pt=LH_DefaultDomain_0&hash=item230d94f4a2#ht_2271wt_855

basically they give a number of plates and a overall size on them... I guess I could get a few of the cheaper used ones and try it.

DaveInDenver
02-08-2011, 12:08 PM
Assuming 50/50 ethylene glycol at 190*F, it has cp (specific heat) of 0.86 Btu/lb*F, e.g. 3.63 kJ/kgK. You'll also need to know the pressures and calculate the mass flow per unit time. I'll work on it tonight if you want, but you could probably figure this out faster than me. Pretty sure this was on my thermodynamics final 10 years ago. :-/

rover67
02-08-2011, 12:12 PM
Assuming 50/50 ethylene glycol at 190*F, it has cp (specific heat) of 0.86 Btu/lb*F, e.g. 3.63 kJ/kgK. You'll also need to know the pressures and calculate the mass flow per unit time. I'll work on it tonight if you want, but you could probably figure this out faster than me.

Yeah don't mess with it if it is going to take you a while, I was just kinda avoiding getting the books out.... I was thinking maybe somebody dealt with this stuff more than me. Didn't know if somebody had some sort of a program they worked with at work. Last time I messed with this kind of stuff was also many moons ago in school.

I'd say the hot side runs at 13psi (radiator cap) and the cold side probably only a few PSI

Jacket
02-08-2011, 12:16 PM
Thinking about a shower system? :cool:

I've only done a small amount of research on heat exchangers, but most of the systems distinguish between shower temp water and true "hot water", which could be painfully hot to shower in (which is probably why you are trying to figure out the calculation).

Kurt has done a number of installs, so you could give him a ring as an option. I don't see that Helton publishes any specs other than the size of the exchanger.

http://www.cruiseroutfitters.com/helton_install.html

rover67
02-08-2011, 12:29 PM
Yeah, I want to basically make sure that it will get hot enough with a decent flow for an all out long nice hot shower. I'll plumb it in the same circuit as the heater controls in the truck, so adjusting the hot water temp should be as easy as limiting the coolant flow by shutting off the heater control valve with the temp lever in the truck. I think.

And the heat exchangers on ebay are a good enough deal that I want to try it.

The one on Kurt's site is a lot smaller than I was envisioning.

SteveH
02-08-2011, 12:47 PM
Liquid = water
flow rate = 4 gallons per minute
inlet temp = 40 degrees F
outlet temp = 104 degrees F

For reference, my brother just installed a household instant hot water heater (natural gas fired) and it's rated at 165K BTU. It can heat 2.5 gal of water/min about that much (from 60-120 or so) - barely. You need a TON of energy to heat 4 gal/minute from 40-104F. That might be about all the waste heat that a 2F generates, assuming you can capture it.

Some of the onboard shower users have told me that real-time temperature control is so tricky that they just heat a large bucket of water, and shower out of the bucket to avoid burns.

rover67
02-08-2011, 01:45 PM
Liquid = water
flow rate = 4 gallons per minute
inlet temp = 40 degrees F
outlet temp = 104 degrees F

For reference, my brother just installed a household instant hot water heater (natural gas fired) and it's rated at 165K BTU. It can heat 2.5 gal of water/min about that much (from 60-120 or so) - barely. You need a TON of energy to heat 4 gal/minute from 40-104F. That might be about all the waste heat that a 2F generates, assuming you can capture it.

Some of the onboard shower users have told me that real-time temperature control is so tricky that they just heat a large bucket of water, and shower out of the bucket to avoid burns.

maybe I need to lower my requirements!

Now that you mention it I had a tank-less water heater in my old place, and it worked for a shower, but not terribly well. Dang.

AxleIke
02-08-2011, 01:45 PM
Yeah, I'm gonna have to agree with Steve here Marco. I don't think you are going to be able to heat 4 gal per minute with the coolant system on the truck. Air is just over a quarter specific heat of Ethylene Glycol, but water is double. You'll have to run the calcs, but I'd be suprised that you could heat that much water that quickly with just the engine coolant, especially running through the heater.

I may be wrong though.

Best of luck.

rover67
02-08-2011, 02:16 PM
This is a cool link:

http://classicbroncos.com/shower.shtml

BreckBJ44
02-08-2011, 04:01 PM
Marco, I'd do something similar to the plumbing in your house with the installation of a mixing valve.

Put your pump before the heat exchanger (cold side) and Y it off so one cold water source goes through the exchanger and the other bypasses it. Join the two at a mixing valve that lets you adjust the ratio of hot to unheated water. I remember seeing a few ambitions guys mount the outlet permanently to the fender of the truck. All they have to do is plug the shower hose into it, flip the pump switch and shower time...

rover67
02-08-2011, 04:10 PM
Marco, I'd do something similar to the plumbing in your house with the installation of a mixing valve.

Put your pump before the heat exchanger (cold side) and Y it off so one cold water source goes through the exchanger and the other bypasses it. Join the two at a mixing valve that lets you adjust the ratio of hot to unheated water. I remember seeing a few ambitions guys mount the outlet permanently to the fender of the truck. All they have to do is plug the shower hose into it, flip the pump switch and shower time...

That's a good idea.... i need to look up those valves.

subzali
02-08-2011, 04:21 PM
So the HVAC control adjusts hot/cold water in an FJ60? I would have assumed it regulates hot/cold air to get the vent temperature where you want it :confused:

I like Kraig's idea :thumb:

rover67
02-08-2011, 04:48 PM
yeah, it basically works a water valve on the fire wall just like the FJ40's.. so moving it to cold would slow the flow through the heater core and heat exchanger.

Check this thing out though:

http://media.wattswater.com/es-70a.pdf

satchel
02-08-2011, 05:04 PM
That tempering valve is pretty cool. So are you planning on having this thing running continuously or a lather, rinse, lather kind of thing? I would think if you are not running the water continuously that the heat being built up in the water sitting in the heat exchanger waiting to be released would be so hot that the tempering valve would not move fast enough from hot to cold before scolding you when you do turn the water on again. Really interesting to see if it would be able to or not. Guess you could just do like others say and point it away from you for a second when you turn it back on to be sure, but that would be great if that valve could automatically adjust it fast enough for you.

So are you just always going to assume you will be near a river or something, or are you planning on having a water tank as well? I've thought about permanently mounting a water tank under the truck and just have a thermostat on it so that a pump constantly circulates the water through an exchanger until the entire tank reaches the desired temp, then the pump turns off. never ending supply of hot water from a river would be cool though.

Air Randy
02-08-2011, 05:04 PM
I had a cabin cruiser boat that had a small hot water heater (2 gal?) that was heated using the engine cooling water from a GM 305 V8. It was an open system that took in cold lake water and returned the heated coolant water to the lake. It made for a pretty nice shower but I'm sure thats because the engine had time to heat the 2 gallons of water first. I never ran it out so I don't know what the recovery time is.

You may want to check some of the marine manufacturers websites, there may be some info there thats useful to you.