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Evaluation of Insulation and Absorber Materials in Solar Food Dehydrators

Evaluation of Insulation and Absorber Materials in Solar Food Dehydrators. Mitch Craib Spring 2002. Presentation outline. Introduction/history Earlier drying research at ASU Purpose & Hypotheses Research design/methods Results & Discussion Conclusions.

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Evaluation of Insulation and Absorber Materials in Solar Food Dehydrators

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  1. Evaluation of Insulation and Absorber Materials in Solar Food Dehydrators Mitch Craib Spring 2002

  2. Presentation outline • Introduction/history • Earlier drying research at ASU • Purpose & Hypotheses • Research design/methods • Results & Discussion • Conclusions

  3. Introduction: -History of drying • Grain, fruit, fish and meat sun drying performed for thousands of years • Military needs have advanced most food drying developments in the last 150 years • 1880s dehydration was mechanized -tunnel dryers (beef, carrots, & coffee) • Freeze drying developed during the Korean War • Shephard, S. (2000). Pickled, Potted and Canned: How the Art and Science of Food Preserving Changed the World. New York. Simon & Schuster. Figs and grapes Rice Rice Peppers

  4. They prevent contamination from dirt, fecal matter, and moisture (molds & fungi) They double or triple drying speed They shield food from direct sun helping to preserve nutritional content Solar food dryers have been promoted in the last 40 years. Why? Introduction:Solar Food Dryers & Their Importance Food dryers have been poorly studied, although many designs have been published

  5. Introduction: -Examples of Published Solar Dryer Designs (similar to the ASU dryer design)

  6. Introduction: -Dryer Studies at ASU (1997 & 1999) • ASU dryer developed • Tested dryers outside (with sun) & indoors (using halogen lights) with: • Reflectors, different glazing materials, absorber plate materials, venting strategies.. • Food moisture or temperatures were the variables of interest • Construction components that remained to be thoroughly tested • Expanded metal lathe or aluminum screen mesh absorber materials • Foam board insulation

  7. Findings from previous ASU studies • Outdoors: metal lathe produced hotter temperatures • Indoors: Aluminum screen produced hotter temperatures • No tests of insulation • Food, the best measure of performance, was not consistently assessed

  8. To compare the performance of expanded metal lathe and aluminum screen absorber plate materials in the ASU dryer To evaluate the efficacy of Celotex polyisocyanurate foam-board insulation in the ASU dryer Aluminum screen and expanded metal lathe would work equally well as heat absorbers Insulation would make little difference to dryer performance Investigation Purpose Hypotheses

  9. Method: Dryer Repair & Reconstruction • Dryers stored outside for 6 years • Moisture damaged • Needed to be rebuilt & modified

  10. Method: Dryer modification • Dryer a.) Insulation & Lathe (control) • Dryer b.) Insulation & Aluminum screen • Dryer c.) No Insulation & Lathe Dryer insulated and ready for absorber plate Aluminum screen installed Non-insulated dryer

  11. Test Dates: • 3/28/02, 3/29/02 • 4/1/02, 4/2/02 • 4/5/02, 4/6/02 • 4/7/02, 4/8/02 Method: -Test Site Location

  12. Method: Food processing • Food: Organic apples or potatoes • Sliced by hand • Weighed to the nearest gram • Divided evenly among the three dryers (4 trays per dryer) • Food safe screen

  13. Method: Measurement equipment • Temperature probes (below) placed in each dryer. One probe was used to monitor ambient air temperatures. • Humidity detector (right & below) was used to gauge moisture content of ambient air.

  14. Test Dates: • 3/28/02, 3/29/02 • 4/1/02, 4/2/02 • 4/5/02, 4/6/02 • 4/7/02, 4/8/02 Results: Mean Values for data collected on 4/1, 4/5, & 4/7

  15. Ambient °F Temperature Results: Food weight = moisture removal

  16. Results:Example of Temperature Data

  17. Discussion: • The bar graph suggests moisture removal was equivalent for the two insulated dryers. • The non insulated dryer performed slightly more poorly than insulated dryers in terms of moisture removal. • Oddly, the temperature graph & figure showed that the non-insulated dryer tended to experience higher drying temperatures. This finding, suggests there was something wrong with temperature probe placement or function. Higher temperatures should have resulted in greater moisture removal.

  18. Conclusions: • Aluminum screen mesh seems to work as well as metal lathe as an absorber material • Insulation appeared to increase moisture removed on the first day (about 7%) • This is a fairly small difference in performance • May only be important on cool drying days • Food weight (actual moisture removal) is the best measure of a food dryers performance. • Future studies need to: • Control for wind with a screen of some sort (note the huge temperature variability shown in the temperature figure) • Move dryers and temperature probes even more frequently • Conduct even more experiments to validate these findings.

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