Drying Experiments

1
Drying Experiments Status

• Jack Bacon
• Chris Craw

2
Site Status

• Open space cleared of low branches, saplings,
  trunks, anthills, etc.
• Elevated mound under construction
• for dryness of system
• Allows expansion for potential heat reservoir
  system (TBD)
• North-south and east-west reference lines
  surveyed and staked

3
Dryer status

• Have elected townhouse architecture over
  high-rise after several design iterations
• Building a test-bed first, not a prototype
• Using an electric blower instead of intended
  turbine vent, to assure data consistency
  run-to-run
• Modular interface allows separate parallel
  development of heat collector design.
• Attempting a downdraft system for several reasons
• Updraft version possible, but not preferred.
• Screen size downsized to 21 square after heat
  load study.

4
Tests on Commercial Dryer

• Nesco 5-tray American Harvest borrowed for
  tests
• Many thanks to Adam McGinnis!
• Characterized flow rate, moisture removal rate,
  temperature, uniformity.
• All 4 fruit items plus simulant (water-logged
  pine bark nuggets) tested
• 3-of-4 fruits tested head-to-head in
  long-duration desiccation experiment

5
Commercial Dryer

• 0.5 m2 total area on 5 circular screens
• 500 Watt heater (more heat per unit area than is
  practical to absorb from the sun. Nlt1.
• 3 liters/sec (6.3 CFM) flow rate across, not
  through, screens
• Larger mesh size in screen than current vision of
  fine mesh substrate
• T rises at 4.7F/hour while dryer is full
• T ranges from 121 F - 171 F hotter than is
  trivial to do with solar
• Moisture still being lost from thin pineapple and
  papaya 12.5 hours after start, at high heat.
• May imply a 2-day dry cycle.
• Fruit shrinkage is significant, changing the
  screen open area dramatically over the course of
  time.

6
Fruit area shrinkage
7
Results

• Pineapple and Papaya are hard to dry
• 1 cm slices still drying after 12.5 hours
• Very thin slices needed for a 12-hour sun cycle
• Means lots of dryer area
• May need 2-day drying process
• Simulant drys much faster, has 2x dry matter
  compared to the fruits
• Paper has same dry weight fraction as fruit, but
  dries even faster than bark
• Great news for papermaking prospects!
• Simulant may need tenderizing or other
  substrate
• Papaya is pretty cheap and easy to handle.
• Availability is not guaranteed

8
Dryer Performance (same load on each tray)
9
Fruits and Simulant Weight History
10
Simulant Variant Test
11
Fraction of Max Drying
12
Temperature History
13
2011 Fruit Harvest by Month
Total fruit count
Approx Kg/day to be dried
14
Sizing
15
Humidity
16
(No Transcript)
17
Figure of Merit for Solar Sizing
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Collector Heat Flows
Convective Conductive
Radiated Spherical Wave Radiated Plane
Wave Forced Air Flow Heat Out
Tinfinity
T5
T1
T2
T3
T0
19
Collector Improvements
Rgt1
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Collector Improvements 2
21
Townhouse Concept
22
Townhouse Concept
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Townhouse Concept
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Heat Source Temps
25
Compost Option

• We will have a lot of compost
• Generation rate approximately 0.1 m3 per day from
  fruit operations
• Compost generates 200 W/m3 24x7
• 200 Watts necessary to dry 1 kg in 12 hours
• Temperature easily reaches 55C (130F)
• can rise above 65C (150F)
• At diminished heat rate decomposition slows down
• Full production of base load could be met with a
  pile measuring 1.5 x 3 x 20 meters
• 3 years to build/replenish on fruit operations
  alone.
• 40x dryer volume required for compost

26
Compost Heat Exchanger
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General layout
E
W
28
Conclusions so far

• Dec-April will be VERY challenging months for
  solar
• Its the rainy season with additional large mango
  harvest
• 172 Megajoules/day required
• Compost may be very useful, but probably not
  whole source
• Pasteurization/canning heat source may be useful
• Especially for mangoes, and rain-out days
• Canning Mangoes removes them from drying cycle,
  provides waste heat to dry base load Pineapples
  Papaya in rainy season
• Paraffin is a potential heat reservoir
• Significant excess capacity in March through
  September
• Avocados not a driver in July-August
• Paper-making, fruit leathers a potential use of
  system
• 2-day or overnight cycle may be necessary for
  base load of slow-drying Papaya Pineapple (90
  kg/day)
• Need 1.5 x base 1-day area (second day at 0.5
  residual fruit area)
• Ultimate dryer screen size 90 m2
• 6 x 16-Townhouse clusters, each cluster 0.6 x
  12 meters
• Pasteurization/canning option helps smooth out
  buffer from rain days