Engineering Quandry

"HammerheadFistpunch" (hammerheadfistpunch)
06/12/2014 at 16:29 • Filed to: nerd talk

So, I'm learning about !!!error: Indecipherable SUB-paragraph formatting!!! , mostly because I now have a fridge that uses it and I'm a nerd.

The basic principles (that totally is amazing to me) is that you use heat to to boil ammonia and water that then cycles through an evaporator, mixing with with hydrogen to reduce its partial pressure then magic [Boyles law] happens and heat is drawn out of the medium where the evaporator is the Ammonia gas cools, and mixes with water and the hydrogen returns to the loop and it starts all over again. Its refrigeration without a compressor and only a heat source to drive the cycle. Its often used commercially to use waste heat and either chill fridges or power AC system.

After reading up on its use for AC systems I came across something interesting. The trouble with getting AC from Solar heat (blows my mind) is that you need 190 degree water or higher for the cycle to work. Then it occurred to me...what has an abundance of waste heat in the form of 190 degree water? a radiator for a car!

So here's my question: Aside from complexity and cost, why aren't we using that waste heat to drive our ac? granted the SOP is 1/4 of a compressor but the advantages are too cool (sorry) to not consider.

1. smaller radiator means less frontal area means more aerodynamic

2. FREE AC! its waste heat anyway, you would be putting that gas back to good use

3. No AC compressor sucking up my precious Horse Powers. Also, more MPG

4. If you used a air to liquid heat exchanger you could store cold air performance and send it BACK to the cooling cycle if needed OR cool other components like transmissions or differentials

5. its all driven by heat, nothing else, no electronics, no belts, nothing. (aside from blowing the cold air)

I Don't know the engineering behind the Cooling tonnage required for a car, but it seems that in a world of electrically decoupled accessories, this would be an area worth investigating.

DISCUSSION (26)

JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t > HammerheadFistpunch
06/12/2014 at 16:35

Kinja'd!!!

HammerheadFistpunch > JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t
06/12/2014 at 16:37

its safe enough for thousands of RV fridges.

JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t > HammerheadFistpunch
06/12/2014 at 16:39

I didn't actually know they were still using it in RV fridges, somehow I thought it had been outlawed for vehicular use...

HammerheadFistpunch > JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t
06/12/2014 at 16:41

mot sure if they are still using Ammonia, but you can also use lithium bromide or, as rumor has it, other solutions that supposedly quadruple the principles efficiency (in Einstein fridges).

Denver Is Stuck In The 90s > HammerheadFistpunch
06/12/2014 at 16:42

Grammar quanrdy

HammerheadFistpunch > Denver Is Stuck In The 90s
06/12/2014 at 16:43

nope. Aint care. Science is happenin' and if all you have to contribute is a dig at the dyslexic guy then maybe there are other posts you'll enjoy more.

Denver Is Stuck In The 90s > HammerheadFistpunch
06/12/2014 at 16:48

I was simply trying to alert you in a creative way to a typo you may have not noticed. I understand dyslexia is something that is very hard to deal with I am an LD student as well. (not dyslexia)

Racescort666 > HammerheadFistpunch
06/12/2014 at 16:50

Leakage has always been the biggest issue with mobile A/C systems. How well will this system stand up to jarring and the beating that automotive systems take?

Stationary (houses and refrigerators) usually use different refrigerant than automotive systems for specifically this reason.

I'm not saying it can't be done, I'm just saying that these are things to think about. If cost and complexity weren't issues, more environmentally friendly refrigerants would be used and better seals would be used as well.

HammerheadFistpunch > Denver Is Stuck In The 90s
06/12/2014 at 16:50

Sorry, sensitive to grammar criticism.

Denver Is Stuck In The 90s > HammerheadFistpunch
06/12/2014 at 16:53

Just be glad your not dyscalculic, That would not be good if you are into engineering.

Roberto G. > HammerheadFistpunch
06/12/2014 at 16:56

As far as I know the absorption system has not a big performance , and therefore it's presently only used for refrigerators of small capacity. Moreover, to correctly work a refrigeration absorption system must be perfectly leveled, which would be quite difficult in a moving car. Eventually I doubt very much that the system you suggest would be able to provide the necessary amount of BTU that are required by an efficient car AC.

You can tell a Finn but you can't tell him much > HammerheadFistpunch
06/12/2014 at 16:58

I think to get enough cooling tonnage to get a car cooled off on a hot sunny day would make this a prohibitively large system. Plus they have to be vertically oriented to work because they rely on convective heat transfer to drive the cycle. The weight and packaging space required to make a system that would effectively cool a car are most likely prohibitive. Throw in the fact that when people get in a hot car they want it to cool off NOW and not after they've driven for 5-10 minutes and the coolant has heated up.

Plus evaporative cooling is black magic and there aren't enough automotive engineers who are willing to sell their souls to the devil to keep them running.

HammerheadFistpunch > Roberto G.
06/12/2014 at 16:59

Well the tiny loop in my fridge is about 600 btu/hr, so a radiator sized loop seems like it would be able to hit the 2-3 tons capacity (36000 btu). At the worst case you could add a smaller, electrically driver compressor to compensate and that would free up drive hp.

A 1 ton Absorption system and a 1.5 ton electric compressor. I mean, its just waste heat anyway, might as well do something with it.

HammerheadFistpunch > You can tell a Finn but you can't tell him much
06/12/2014 at 17:01

There is defintly some work to be done here, and I seem to recall this system was being considered for commercial trucks driven off the exhaust stacks, so it seems like it could work. Just daydreaming.

Roberto G. > HammerheadFistpunch
06/12/2014 at 17:06

Sorry... I was updating my reply with a forgotten, important info: to correctly work an absorption refrigeration system must be perfectly leveled, which would be quite difficult in a moving car!

You can tell a Finn but you can't tell him much > HammerheadFistpunch
06/12/2014 at 17:28

That I can see making sense. Packaging isn't such a constraint on a commercial truck, and they have enough height that one of these systems likely wouldn't effect bodywork height.

The other thing that just popped in my head is that you want the heat applied at a specific point in the cycle. It probably wouldn't work well to have the whole loop stuffed into a hot engine bay which is where it would likely end up on a car. On a semi or commercial truck you could hang it on the back of the cab, especially if you were using exhaust gas to supply the needed heat.

HammerheadFistpunch > You can tell a Finn but you can't tell him much
06/12/2014 at 17:30

hmmm, good point.

505Turbeaux > HammerheadFistpunch
06/12/2014 at 17:32

an engine likely produces enough waste heat to cool a car interior with absorption. I have thought of this a few times and why it wouldnt work and only ran into efficiency. Ford experimented with electric compressors a while back too which removes the load from the engine (except for additional charging requirements for the battery), which can certainly drive a small auxillary compressor for Max Cool. You have now occupied my brain for the next hour

HammerheadFistpunch > 505Turbeaux
06/12/2014 at 17:34

Even with a COP of .3-.5 it seems like there would be more than enough waste BTU's in the rad to make it work. Of course there are issues, but I feel like it would be of enough benefit to make it work.

HammerheadFistpunch > Denver Is Stuck In The 90s
06/12/2014 at 17:37

No, that describes me quite well actually. Which is why I produce videos. It's a curse that I love engineering (literally all my friends and my father are/were engineers) but I can't math.

Difficulty reading analog clocks

Inability to comprehend financial planning or budgeting

Difficulty reading musical notation

Difficulty navigating or mentally "turning" the map to face the current direction rather than the common North=Top usage

Often unable to grasp and remember mathematical concepts, rules, formulae, and sequences

Mistaken recollection of names. Poor name/face retrieval. May substitute names beginning with same letter

Yup, thats me!

Denver Is Stuck In The 90s > HammerheadFistpunch
06/12/2014 at 17:41

Man, that sucks, I am the same way. I'm not dyscalculic, but Math escapes me, thats why I am studying to be an industrial designer and not an engineer or an architect. I would have loved to be able to do those things, But I cant handle the math.

HammerheadFistpunch > Denver Is Stuck In The 90s
06/12/2014 at 17:45

I was in the Mech Eng program for a year and decided It wasn't going to work out. Hate it because i LOVE this sciencey nerdy stuff. My good friends are:

Mechanical Engineer

Electrical Engineer

Aerospace Engineer

and my father was a mechanical engineer

I get the concepts perfectly, but I wouldn't be able to do the math to save my life. I can even see the concepts working in my head...but I couldn't give you the specifics needed to make it work without trial and error.

Arch Duke Maxyenko, Shit Talk Extraordinaire > HammerheadFistpunch
06/12/2014 at 17:50

Thermodynamics

HammerheadFistpunch > Arch Duke Maxyenko, Shit Talk Extraordinaire
06/12/2014 at 17:51

Radio elephant.

Denver Is Stuck In The 90s > HammerheadFistpunch
06/12/2014 at 17:52

"I get the concepts perfectly, but I wouldn't be able to do the math to save my life. I can even see the concepts working in my head...but I couldn't give you the specifics needed to make it work without trial and error."

This explains my process for everything in a nutshell. My dad is a Civil Engineer and my brother is going to UC Boulder in the fall in the mechanical engineering program. It kinda runs in my family.

Drakkon- Most Glorious and Upright Person of Genius > HammerheadFistpunch
06/12/2014 at 19:44

how about a reservoir of super cooled air to use as chemical intercooling? My turbo LOVES 5 degree mornings.