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Best endothermic reaction?

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LAN_403

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Tue Feb 10 2009, 10:03AM

Registered Member #561 Joined: Sat Mar 03 2007, 02:46AM
Location: Adelaide Australia
Posts: 230

What would be the best endothermic reaction? I've come up with an idea for an invention and it requires that 2L of water be cooled from 30-35c to 4-10c rather quickly through a coolant block. Without the use of electrical or mechanical means so it can be compact and fail proof

Any ideas?

Electroholic

Tue Feb 10 2009, 10:19AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

it would help if you can define "rather quickly".
2l of water 35C to 4C is about 260kJ.
Alos, knowing the ambient air temperature would help, assuming the whole rig is not submerge in some other fluid.

"Through a coolant block"? you mean a heat exchanger?

"no electrical or mechanical means"? not even to cycle the water or coolent?

aonomus

Tue Feb 10 2009, 12:13PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

I suppose a sufficiently large amount of ammonia nitrate, which is used in single-use cold packs could work, although you'd have to do the calculations based on the enthalpy of change of solution.

What is the use of this cooling method exactly? There may be other means to avoid having to use ammonia nitrate (seeing as how its also known as both a fertilizer and explosive, you could probably find a different compound to use).

Blitzorn

Thu Jun 11 2009, 12:27AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Hydrating Ammonium Nitrate can be used as a coolant but it's not a particularly rapid reaction (especially if you have no way to mix the fluids rapidly). Ammonium nitrate is used as an oxidizing agent in many homemade explosives and sometimes in types of explosive propellant. One thing to be aware of is that ammonium nitrate is capable of explosive decomposition and self-oxidation, so storing large amounts of it can be hazardous.

Proud Mary

Thu Jun 11 2009, 01:16AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Steady on the NH4NO3, boys - remember it's a controlled substance in many jurisdictions.

MinorityCarrier

Thu Jun 11 2009, 06:35AM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Like Electroholic asks, how fast?

Potassium chloride and ammonium chloride are two non-explosive salts that could be used in lieu of ammonium nitrate. Potassium chlorate and potassium permanganate have better heat of solution, but they, being very strong oxidizers, may also be subject to governmental regulation. Don't feel like calculating the enthalpy change, but I suspect it would take a lot of moles of salt, already in highly concentrated solution, mixing with the coolant block (exchanger?) water quickly, and it's a one-shot deal. You'd have to drain the coolant and recharge your solutions.

Release of a compressed liquid refrigerant throught the coolant block may work, but use one of the newer R-refrigerants that are less ozone-destructive.

You could blow compressed CO2 through the water itself, or use a block of dry ice, with lots of holes in it for increased surface area, to run the water through, just need to vent the CO2 gas. Also one-shot approaches.

However, without using any mechanical or electrical means, sort of severly limits how to activate the cooldown. Seems impossible without some kind of mechanical actuation.

I'm done blatheriing here.

john bunsenburner

Wed Jun 17 2009, 03:21PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

Well I would assume your invention is a chemical one,this means that dumping pounds and pounds of anything(especially an oxidizer) into it could become problematic to the invention's flawless function. UsingCO2 might also have the same effect as lots of it will dissolve in the water causing several problems including the weigt of the water to increase, along with the fact it will have a lower PH, this could affect your invention too. I would try and either use an iso-propanol alchohol and dry ice mix, where the iso-propanol is cooled down by the dry ice and then poured around a coil of soft copper(if that doesn't affect your reaction) through which the water flows. If you have acsses to it you could try using plain liquid nitrogen and either just pouring that into the water and stirring or doing the same thing as witht he iso propanol just with with the liquid Nitogen and flowing the water through at the right speed should give you the desired temperature(i am sure this can be figured out if you consider all the factors involved).

quicksilver

Mon Jan 25 2010, 09:44PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Dry ice and acetone....reusable and a wee bit cool.

MinorityCarrier's idea is a great one as the formation of dry ice could be controlled via a vessel of acetone; thereupon sealed for evaporation and you have you choice of temperatures depending upon distance from the medium material.

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