heat transfer device for off-grid medical sterilization william dunk david luker samuel majordaniel...

Heat Transfer Device For Off-Grid Medical SterilizationWilliam Dunk David Luker Samuel Major Daniel Rist

Mechanical Engineeringteam.sterilize@gmail.com

The Problem:

Unsterile Medical Equipment in Off-Grid Developing Countries

• 1/5 of humanity lacks access to electricity (International Energy Agency 2009)

• Off-grid medical clinics unable to sterilize tools

• Infectious diseases spread rapidly throughout communities

• Rural Pakistani clinic: 94% observed injections involved unsterile syringe…44% of these patients tested positive for Hepatitis C (World Health Organization 2000)

• We have designed a thermally powered heat transfer device that will be able to operate an autoclave to sterilize medical tools in off-grid locations

Our Solution

Production of Thermal Power

• Curved mirrors reflect sunlight on to water filled pipe to produce steam at up to 165°C and 6 bar

• Proven deployable system: currently utilized in Haiti for cooking

• Can be expanded to increase capacity (greater steam output)

Acknowledgements

Our Design

Testing and Results

Design 1 Design 2

*Design Inverted to Show Details

Heat Transfer DeviceDesign Criteria

• Heat transfer device must be able to power an unmodified, commercially available autoclave

o All-American 1915x autoclave

• Heat transfer device must be powerful enough to meet Centers for Disease Control steam sterilization standards

o Autoclave must maintain an internal temperature of 121°C for 30 minutes

• System (power source + heat transfer device) must be completely self-sustainable

o Thermal power requires only the sun

• Heat transfer device must be economical and practical for deployment to developing countries

o Total cost of device must be less than $200

Design 1

• Maintains 121°C for 30 minutes

• Biological test results: negative

o Biological spores neutralized

o Effective steam sterilization

Conclusions• Our heat transfer device is able to sterilize medical instruments

with an unmodified autoclave per CDC requirements

• Our system is completely self-sustainable requiring only the sun and water

• Our heat transfer device is economical with a total cost of $175

• Our system is a promising solution to the medical sterilization problem currently affecting the 1/5 of humanity who currently live in off-grid locations

• Steam from Capteur Soleil enters aluminum plate at “steam inlet”

• Steam travels through grooves, heating aluminum plate by convection

• Autoclave rests on top aluminum plate, heated by conduction

• Autoclave and plate are insulated by combination of aerogel, foam and wood with total R-value = 3.45 m2K/W = R-20

Front view of Capteur Soleil, designed by Jean Boubour

Aramid fiber gasket with SBR rubber binder for steam (0.4/1.6 mm)

Bottom aluminum plate (9.5 mm)

Top aluminum plate (9.5 mm)

Power Results• Power testing was conducted using an electric steam generator to maintain a

constant pressure

• Plate designs 1 and 2 were tested with gaskets of 0.4 mm and 1.6 mm thickness

• Global F Test conducted at significance level of 0.05

• F statistic: 11.64; .0001 < critical-value < .001

• Data provides sufficient evidence to conclude there is a difference among plate design and gasket thickness with respect to mean power output

• t test conducted at significance level of 0.05 between gasket thicknesses

o t statistic: 6.05; critical value < .001

o Data provides sufficient evidence at the .05 level of significance to conclude that the .4 mm and 1.6 mm gaskets differ in their mean power output

o 1.6 mm gasket yields 95% greater power output

ANOVA Table for Power OutputSource df SS MSBetween

plates and gaskets

3 54144.23 18048.08

Within plates and

gaskets16 24811.09 1550.69

Total 19 78955.31  

• t test conducted at significance level of 0.05 between plate designs

o t statistic: .305; critical value < .40

o Data does not provide sufficient evidence at the .05 level of significance to conclude that design 1 and design 2 differ in their mean power output

o Plate designs 1 and 2 have equal mean power outputs

Sterilization Results

Groove dimensions: 6 mm deep x 4.75 mm wide

Groove dimensions: 4 mm deep x 3 mm wide

GETINGE 24 hour biological test pack

Medical tools not properly sterilized

All-American 1915x autoclave

Insulation container (43 cm x 43 cm)

Dr. Douglas SchulerJoe GesenhuesJean Boubour

Attempt at sterilization: sunlight exposure

Photo courtesy: Dr. Fischer-Hoch, UTH, Brownsville