Part of our background research was evaluating existing designs, with an emphasis on finding where our solution could provide something new.

This research motivates our requirements for some sensors to monitor autoclave cycle, as well as low cost and portability requirements.

 

Design 1:

https://www.engineeringforchange.org/solution/library/view/detail/Health/S00065

 

Steps of operation:

1. Open pressure vessel and load instruments.
2. Set timer temperature.
3. Empty and refill boiler with distilled water.
4. Align solar concentrator to the focal point.
5. Cycle begins once temperature is reached.

 

Pros	Cons
Affordable Portable Variable Temp Variable Timer Movable Solar-Concentrator Roof Top set-up	Small Volume

 

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Design 2: Prince-40 Concentrator

http://www.sciencedirect.com/science/article/pii/S0195670112000230

 

Requirement: Maintaining 134 °C for 60 min.

 

Even when the experiment was done in January, one of the coldest months in India, the required temperature was achieved in 45 min. After painting the surface of the stainless steel autoclave with black paint, this was achievable in 25 min. This was found to be energy saving in the long run, compared to electricity and liquified petroleum gas costs.

 

Pros	Cons
Affordable Efficient, even in the cold Can be deconstructed into boxes	Small Volume Not really portable Might take awhile to set up

 

Design ideas from the Prince-40 Concentrator: Use a reflective material underneath to bounce light into the pressure cooker and paint the pressure cooker with black paint if necessary.

 

Lessons learned: Make it more portable.

 

 

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Design 3:

Later iteration of Solarclave project, as presented by Anna Young in 2011: (covered on website as well)

 

Image taken from website as of Feb. 2013

 

 -121 C, 15 psi, 20 min  cited as CDC standard

 -field test measuring Temperatures inside  vessel > T on bottom of vessel

 -suspend vessel over array of reflectors -  array is constructed at site of use

 -under $200 and using local mat'ls

 -vessel is a pressure cooker, fiberglass insulation in plastic bucket housing, Al foil reflectors

 -duct below vessel traps air heated by mirrors

 -previous design: foil on satellite dish, wine bottle on dish holds water, 

      top tube feeds into top of pressure cooker

 

** desire stronger frame/vessel, better time/pressure/temperature indication 

 

 

Design 4: Ottoclave Project

- aims to add temperature, pressure sensors  and control to existing pressure 

 

Design 5:

Portable Solar Powered Autoclave

http://www.builditsolar.com/Projects/OddProjects/AutoClaveFirstplace_2.pdf

In this design, water contained in copper U-tubes, themselves enclosed in evacuated glass tubing, is heated under illumination, and the steam generated by the thermal exposure is piped into the sterilization chamber. 

 

The team came up with two designs: a large system, with an array of solar collection tubes; and a small system, with one solar collection tube.  

 

Large System: 

 

Large System Specifications

Processing Capacity	14 L
Sterilization Chamber Temperature	121-134 deg C
Sterilization Chamber Pressure	14.2 to 30.7 psig
Sterilization Cycle Time	55-80 min
Unit Cost	$1694

 

Large System Features

The entire collector array is mounted on a table which can pivot about an in-plane axis.  When tilted one way, the inlets from the U-tubes into the chamber are raised and steam will flow into the chamber; when tilted the other way, the inlets are lowered and sealed by condensed water and the steam is contained in the now elevated bottoms of the U-tubes.   The system is therefore capable of a modest degree of self regulating temperature and pressure.  Based on readings from temperature and pressure sensors, an electro-mechanical actuator (powered by a PV cell) will tilt the collectors into the configuration which will either increase T and P (the ON configuration) or decrease T and P (the OFF configuration) to reach values programmed by the user.  

 

Small System: 

 

Small System Specifications

Processing Capacity	1.5 L
Sterilization Chamber Temperature	121-134 deg C
Sterilization Chamber Pressure	14.2 to 30.7 psig
Sterilization Cycle Time	40-65 min
Unit Cost	$650

 

Small System Features

An Al sheet bent into a parabola is used as a reflecting mirror beneath the single collection tube.  

The small system is able to regulate its temperature and pressure by pulling a cover over the reflecting mirror and collection tube when either the temperature or pressure rises above a set value, and removing the cover when either the temperature or pressure drop too low.  As in the large system, the motors involved in this operation are powered by a PV cell mounted on the unit.   

 

Part Sources

Chambers	All American Autoclaves (Wisconsin Aluminum) The provided website cannot be found.
Collectors	Pre-manufactured collector arrays: Focus-solar www.focus-solar.com Powertech solar www.powertechsolar.co.uk/index.htm Solar design www.solar-design.demon.co.uk   Individual collector tubes: Himin solar energy www.himin.com/english/index.htm

 

Design 6: "Capteur Soleil"

Image from news article: http://www.thermablok.com/thermal-insulation/themablok-aerogel-insulates-solar-autoclave-press-release.htm

Journal article: http://www.ajtmh.org/content/87/4/602.long

• Steel A-frame spine 
• Bed of parabolic polished aluminium mirrors (2 m² each) directs sunlight onto steel tube containing water at apex of frame
• Water boils and the steam heats a custom hot plate on which a stovetop autoclave is placed 
• Autoclave is wrapped in a thin layer of Thermablok aerogel (highest thermal resistance of any known substance) and enclosed in plywood case 
• Back leg of frame can be ratcheted up to align mirrors with sun

 

Pros	Cons
Mirror position is adjustable Takes only ~40 min in good midday sun to begin significant heating of autoclave Good insulation Hot plate setup works for any stovetop autoclave	Expensive - initial setup costs ~$2100 Solar collector not portable  Autoclave temperature not adjustable Steam is used to heat a hot plate rather than being pumped directly into autoclave chamber - less efficient

 

Design 7: 'Salud del Sol'

Light Collector

•  Wooden frame covered with fiberboard
•  Outside lined with zinc
• Inside with printing laminate reflecting material
• Light is reflected onto a lens, that focuses the light on the chamber
• Two triangular prisms placed on the side of the solar cooker to direct the light even more
• This can get up to 140 degrees C, which is more than our needs

Chamber

• Used a pressure cooker painted black

Water

• No distilled water available
• Experimented with using wax instead

Pros	Cons
Seems relatively inexpensive Easy to construct, from basic materials	Light collector is not adjustable  Not portable

 

 

Design 8:

Michael Tyroller 2006