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Venting and drying for efficient sweating under PPE

To cool the worker under a PPE I propose to combine venting and drying to enable efficient sweating.

Photo of Rainer Winkler
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Update 7 December 2014

This is an old posting. See https://openideo.com/challenge/fighting-ebola/impact/scientific-support-to-gather-data-and-evaluate-designs for actual proposals. Actually I analyze options for secure filtered venting a PPE.

Original contribution:

Water has a Enthalpy of vaporization (heat of evaporation) of 2260 kJ/kg. Evaporating 1 kg of water per hour cools with an heat current of 630 W. A person at rest produces only about 100 W of heat.
It was proposed to used commercially availiable products for venting under cloth: https://openideo.com/challenge/fighting-ebola/ideas/equipping-and-empowering-the-care-community-to-fight-ebola (http://www.kuchofuku-products.com/index.html).
But connecting the air flow used for venting directly to the outside creates problems. Infectious material may enter the system and would be directly blown to the skin.
The moist that is created by evaoporation of the sweat has therefore to be removed. This can happen by:
a) Using silica gel or zeolite to dry the air. This may create problems, if the heat that is released duing the absorption heats the PPE too much
b) Pumping the air through a bottle with ice or cold water. This will dry the air. Problems are, that liquid water may leave accidentially the bootle and may cause problems under the PPE.

For venting a radial fan could be used. A small radial fan creates more pressure than the axial fans used in most (but not all) computers. So it will be easier to vent clothing that is not optimized for venting. The model I have makes 2 mbar overpressure.

The radial fan coupled with 100g of silica gel absorbed in a first test 0.5mg Water per second at 16°C and 60% humidity, this is equivalent to 1W of cooling. It heated itself to about 30°C, about 15°C higher than the ambient temperature. A working device might therefore require about 10kg of silica gel, to have a sufficient absorption rate. I am shure it should be possible to saturate the silica gel faster, in that case less gel would be required. But I gave here only the numbers I measured.

For cooling using ice I guess that about 1.5 kg of ice is needed to absorb 160g Water vapor per hour, leading to a cooling power of 100 W.

Update 03 October 2014: Systems like this may be realizable, but in the moment I doubt whether this can really be done in a few month with low technical effort. The fans required to vent the PPE are quite strong, and to have a cooling power that is better than a PCM vest, is probably not easy. So I am sceptical whether this problems can be solved in the short time frame.

Cooling and adsorbing humidity with ice has the disadvantage, that no adsorption heat has to be transfered out of the PPE.

Adsorbing humidity with silica gel has the disatvantage, that the silica has to be cooled. Here the latent heat plus the energy of wetting has to be transported to the outside of the PPE.

Please follow also the discussion on this very related post: https://openideo.com/challenge/fighting-ebola/ideas/desiccant-embedded-ppe-suit-to-keep-ppe-dry-and-bearable . Many ideas from the comments there can also here be applied.


 

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Photo of Deborah
Team

Hi Rainer, we'd like to share some guiding questions to help the development of your idea through engagement from our community and experts in their feedback.

Design - Is silica gel a viable option for PPE suits in West Africa? How do we dispose of the used gels and would this cause more inefficiencies and potential contamination? What issues do you see arising in the doffing and donning process? How can we make this more efficient?

Technology - What kind of wearable technology exists that is lightweight and powerful can we use to pump air through? Is there a natural way to pump air through using movement from the human body? How might we create a closed loop system that uses body heat to power the cooling system and that doesn’t require external power sources?

Adoption - what do we need to include in the suits that will help with training them how to use and follow safe protocol, especially in donning and doffing?

Distribution - how will these be distributed to remote communities that need them? What partners are needed for this?

Manufacturing - who can manufacture these suits? How much will it cost per suit and what would be the turn around for deployment in design and production time?

We're looking forward to seeing your idea build out as a result of expert knowledge. Feel free to update your idea and indicate what else you need to make this happen as you get more feedback. Good luck!

Photo of Rainer
Team

Hi Deborah,
thanks for your questions. My problem is that my time as volunteer is limited and some of this questions are hard to answer. Silica gel is cheap at least if it can be reused. But if it has to be disposed because of possible contamination, this would be a problem.

I have no solution for pumping the air that is simple and wearable. The silica gel might be placed on the outside of the cloth the worker wears. This cloth should be permeable to water vapor. The silica gel adsorbs the water fast, but only as fast as the water vapor is evaporated and transported to the gel. As the water is adsorbed, the silica gel becomes hotter. This decreases the water capacity it can hold (and may as a safety feature limit the rise in temperature if the cooling is insufficient).

Cooling machines with silica gel are in a bigger scale already in use, and the experiences from this may be used here.

Maybe this can be made to work, but this requires at least a few weeks of full time calculating and testing using thermal manikins, climate chambers and technical stuff. I tried as much as I can myself, so I tested a fan in PPE and also tried to cool with ice. But I am a volunteer who has to work and a family with children to care for. I might have a solution in a year or so if I proceed with the capacity I have, if there is one.

This openIDEO forum appears to me in the moment not optimal to develop a technical idea to a point where a workable prototype can be assessed. I would be happy if there would be more scientists and engineers active, that have the technical knowledge, experience and tools to design workable devices.

There are simple questions, that are to be answered in a structural way, and I do not know how to get them answered effectively.

- How strong has a fan to be to allow efficient sweating?
- Will this fan suck the PPE sheet to the skin and prevent venting without further means?
- How heavy will the batteries for the fan be? Can they be charged?
- How big is an efficient condensator to dry the air with ice?
- How big is an efficient adsorbing unit with silica gel?
- How can the heat the silica gel produces be kept away from the skin, at least so well, that the person is really cooled? Is this really a problem? Or do I just think so?
- Can the silica gel be sterilized after usage?
- Will workers believe, that it is sterilized?
- Can the design be made so small, that it fits under a PPE?
- Will it be reliable enough?
- ...
Too many questions for a single volunteer in such a short time.
With kind regards
Rainer

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