Zeolite retains heat indefinitely, absorbs 4x more heat than water • Hacker News Board

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#41

Post by ars » Wed, Jun 06, 2012, 9:54 PM UTC

hexagonal wrote: post #20

jerf wrote: post #8

Earlier quoted context omitted.

I'd like to see some energy density numbers in units I can understand before I would jump up and down about this use. (I'm not saying you're wrong so much as saying I can't provide evidence you're right, and I'm hoping someone else can. Or at least tell us what exactly "the heat storage capability of water" is such that something can have 4 times as much. Please hold wild-assed guesses, please, I can compute the ener…

The term of art you're looking for is "specific heat". https://en.wikipedia.org/wiki/Specific_heat The relevant number for water at 25C is 4.184 joules per gram. But this isn't a strict apples to apples comparison: if you heat and cool zeolite in a vacuum chamber, it'll have a pathetic specific heat. (Like perlite, another foamed mineral, which has a specific heat of something like 0.1) That's because there's a chemi…

Someone downmodded you because you messed up your units.

It's 4.184 joules per gram Kelvin. Meaning it stores that much energy for each dress of heat you add to it. If you take water from near freezing to boiling that's 100 degrees of storage - meaning 418.4 joules per gram - which is much more reasonable.

And there is no reason you have to stop at boiling. Storing something at 500 degrees is not impractical, so assuming starting at 20 degrees (room temperature) you can store over 2000 joules per gram. And there are plenty of materials that can handle even higher temperatures.

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#42

Post by nottwo » Wed, Jun 06, 2012, 9:54 PM UTC

This reminds me of zeolite-water solar adsorption refrigeration:

This paper presents some of the experimental evaluations of a prototype solar refrigerator, based on an intermittent thermodynamic cycle of adsorption, using water as refrigerant and the mineral zeolite as adsorber. This system uses a mobile adsorber, which is regenerated out of the refrigeration cycle and no condenser is applied, because the solar regeneration is made in the ambient air For the regeneration, a SK14 solar cooker is considered. The cold chamber, with a capacity of 44 liters, is aimed for food and vaccine conservation. The objective is to analyze the advantages and disadvantages of the eventual use of this refrigerator in rural regions of Peru, where no electricity is available. On the bases of the results obtained, a new prototype of refrigerator for rural regions is designed, based on the same thermodynamic cycle, but including changes in design and operation.

http://fc.uni.edu.pe/mhorn/ISES2003%20(solar%20refrigeration...

During the day, solar energy is used to drive water out of the zeolite. The dry zeolite is exposed to water under low-pressure causing the water to evaporate and be adsorbed into the zeolite. The evaporative cooling can be used to refrigerate food without electricity.

A German company with various zeolite refrigeration applications:

http://www.zeo-tech.de/index_en.html

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#43

Post by ComputerGuru » Wed, Jun 06, 2012, 10:12 PM UTC

Is this the same Fraunhofer Institute that owns the patents on MP3?

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#44

Post by gte910h » Wed, Jun 06, 2012, 10:23 PM UTC

excuse-me wrote: post #16

rcthompson wrote: post #3

Short version of the science: The heat is released via an exothermic chemical reaction between the Zeolite and water. However, unlike the one-time-use chemical-reaction heating pads you can buy in a pharmacy, this reaction is reversible, so you can "recharge" the Zeolite by heating it and removing the water as it is released in order to force the reaction to reverse itself. The reaction goes something like this: Zeol…

Recharging it isn't that simple We use zeolite as a water scavenger in high vacuum systems, it's tremendously good at grabbing onto water BUT because it's so porous and very low thermal conductivity it's a real pain to heat it enough to get all the water out again. We have a heater resistor at the bottom of a small can of this and the top of the pellets a few cm away is cool enough to touch. You might do better with…

A drum dryer like you use for clothing sounds built to take water out of these things (with grates smaller than the pellets of course).

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#45

Post by ck2 » Wed, Jun 06, 2012, 10:31 PM UTC

Solar power storage for night/clouds - solved?

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#46

Post by olefoo » Wed, Jun 06, 2012, 10:39 PM UTC

Zaak wrote: post #25

excuse-me wrote: post #16

Earlier quoted context omitted.

Recharging it isn't that simple We use zeolite as a water scavenger in high vacuum systems, it's tremendously good at grabbing onto water BUT because it's so porous and very low thermal conductivity it's a real pain to heat it enough to get all the water out again. We have a heater resistor at the bottom of a small can of this and the top of the pellets a few cm away is cool enough to touch. You might do better with…

I wonder if you could incorporate a wire mesh into the zeolite to improve the heat distribution.

If you could figure out a good way to integrate the heating element and the the zeolite on a surface like a menger sponge you would have a very high surface area and good thermal response characteristics.

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#47

Post by phn » Wed, Jun 06, 2012, 10:45 PM UTC

deelowe wrote: post #38

mtmcannon wrote: post #30

Earlier quoted context omitted.

You can heat Zeolite using solar power during the day and release the energy at night. Current thermal energy storage techniques use stuff like molten salt ( http://en.wikipedia.org/wiki/Thermal_energy_storage ), which is a lot harder to work with than pellets.

Yeah, but once you do that, how do you get the water back out? It sounds like this stuff doesn't do that very easily.

From what I understood, the water comes out when you heat it.

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#48

Post by ktizo » Wed, Jun 06, 2012, 10:46 PM UTC

quantumstate wrote: post #32

hexagonal wrote: post #20

Earlier quoted context omitted.

The term of art you're looking for is "specific heat". https://en.wikipedia.org/wiki/Specific_heat The relevant number for water at 25C is 4.184 joules per gram. But this isn't a strict apples to apples comparison: if you heat and cool zeolite in a vacuum chamber, it'll have a pathetic specific heat. (Like perlite, another foamed mineral, which has a specific heat of something like 0.1) That's because there's a chemi…

The specific heat is the energy needed to raise the temperature per mass. So for water it takes 4.184 joules per gram to raise the temperature by 1 kelvin. So if you heated water to 75 degrees you would have put in about 205 joules per gram. You then have to deal with conductive losses and the efficiency of a heat engine. This is not directly comparable to the energy density of gasoline or a lithium ion battery which…

0. you must play the game

1. you can never win

2. you can only break even on a very cold day

3. it never gets that cold

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#49

Post by olefoo » Wed, Jun 06, 2012, 10:50 PM UTC

debacle wrote: post #37

> retains heat indefinitely What are the physics behind that, because it sounds like it violates the laws of thermodynamics.

No, your conversion of ambient heat to drying the zeolite and the inverse release of heat when adding water; are both less than perfectly efficient. Entropy grows at each step. The retention of heat in the dried zeolite is not a conversion step, and the total entropy of the system doesn't change during that time.

Re: Zeolite retains heat indefinitely, absorbs 4x more heat than water

#50

Post by DanBC2 » Wed, Jun 06, 2012, 10:52 PM UTC

gte910h wrote: post #44

excuse-me wrote: post #16

Earlier quoted context omitted.

Recharging it isn't that simple We use zeolite as a water scavenger in high vacuum systems, it's tremendously good at grabbing onto water BUT because it's so porous and very low thermal conductivity it's a real pain to heat it enough to get all the water out again. We have a heater resistor at the bottom of a small can of this and the top of the pellets a few cm away is cool enough to touch. You might do better with…

A drum dryer like you use for clothing sounds built to take water out of these things (with grates smaller than the pellets of course).

Noisy as hell though. Also, how robust are the pellets? Tumbling them may create a lot of dust. Damp dust would be tricky to control.

I used to have to dry silica gel bags. We'd put them in a temperature controlled oven for a few hours, it'd ramp the heat up and fans would pull air through. That worked quite well, but was only for small quantities.

I guess you could have many mesh racks with heating at the base (or even through the mesh) and fans at the top to extract moist air. Drying that air and re-using it would handy.