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close this bookAppropriate Community Technology - A Training Manual (Peace Corps; 1982; 685 pages)
View the documentThe Farallones Institute Rural Center
View the documentCHP International, INC.
View the documentPreface
View the documentAcknowledgments
View the documentIntroduction
Open this folder and view contentsPhase I: Introduction to training
Open this folder and view contentsPhase II: Earthen construction and fuel-saving cookstoves
Open this folder and view contentsPhase III: Pedal/treadle power
Open this folder and view contentsPhase IV: Solar water heaters
close this folderPhase V: Solar agricultural dryers
View the documentPhase V Calendar
View the documentSession 1. Introduction to agricultural dryers
View the documentSession 2. Tour of solar dryers
View the documentSession 3. Solar agricultural dryer design procedures and rules of thumb
View the documentSession 4. Two-hour dryer construction
View the documentSession 5. Review of existing solar dryer plans
View the documentSession 6. Smoke testing solar dryers
View the documentSession 7. Introducing new technologies: solar dryers
View the documentSession 8. Design of solar agricultural dryers
View the documentSession 9. Site selection and preparation
View the documentSession 10. Construction of solar agricultural dryers
View the documentSession 11. Issues and methods in development and diffusion of appropriate technology
View the documentSession 12. Natural cooling
View the documentSession 13. Approaches to health systems
View the documentSession 14. Nutritional gardening
View the documentSession 15. Practical drying tips
View the documentSession 16. Cardiopulmonary resuscitation
View the documentSession 17. Dryer assessment and modification
View the documentSession 18. Introduction to cost benefit analysis (cba)
View the documentSession 19. Presentation of solar dryers
View the documentSession 20. Introduction to the final phase of the training program
Open this folder and view contentsPhase VI: Concluding the program: The energy fair
Open this folder and view contentsAppendices

Session 6. Smoke testing solar dryers

Total time:

2 hours


* To design and carry out experiments to determine the air flow through solar dryers


* To discuss the effects of vent size, chimney height, temperature and convective air flow on dryer design


* Attachment V-6-A, "Guidelines for Two-Hour Dryer Experiment"


* Attachment V-6-B, ''Data Collection Sheet',


Thermometers, stopwatch or wristwatch, smoke source (bee smoker, cigar, etc.), two-hour solar dryers (from Session 4)


Step 1. (5 minutes)
Present the session objectives and outline the activities.

Step 2. (10 minutes)
Distribute and review Attachments V-6-A and V-6-B.

Step 3. (55 minutes)
Have the participants form their construction groups, design and carry out the smoke test experiments on their two-hour dryers.

Trainer Notes

* Emphasize the need to determine objectives for the experiments.

* Stress the importance of repeating each experiment several times to average the effects of uncontrolled variables, such as a breeze or a passing cloud.

* Explain that they will be presenting their experiment and its results later in the session.

* Have the groups chart their experiment results on a graph.

Step 3. (15 minutes)
Have the groups prepare their graphs and presentations.

Step 4. (20 minutes)
Have the groups give their presentations.

Trainer Notes

After each presentation, encourage questions and discussion about how vent size, chimney size, temperature and convective air flow affect dryer design.

Step 5. (15 minutes)
Conclude the session by having the participants identify general conclusions which can be drawn from their experiments.

Trainer Notes

You should point out that the conclusions from these experiments will be useful later in the phase when participants are designing and building their solar dryers.


The two-hour solar dryers illustrate the variables involved in the design of solar dryers: vent size, vertical height (measured between air vents), temperature and convective air flow. The flow may be measured by releasing into the cylinder light, airborne matter, e.g., feathers, smoke or dust particles, and timing the ascent with a watch from the point of entry until the material emerges at the top. The volume of the cylinder, divided by the time elapsed, will indicate the estimated air flow.

Using a thermometer, the temperature is measured at the outlet, which is the hottest point. Two variables may be introduced to affect the air flow and temperature: the air vents may be left unobstructed or made progressively smaller by taping or otherwise blocking the opening; or the dryer may be tilted from horizontal (no flow) to vertical (maximum flow).

Through conducting such experiments, information is gained regarding the interrelationships of various factors -venting, height, temperature and air flow. Examples of two experiments are:

1. Temperature and air flow are measured in one section of the dryer placed in various positions (including vertical and horizontal).

2. Temperature and air flow are measured after one, or both, ends of the dryer are partially closed, while it is in various degrees of tilt.

Guidelines for conducting the experiments:

1. Record all observations.
2. Attempt to be as accurate as possible.
3. Keep the dryer in the sun to avoid any cooling between experiments.
4. Maintain the dryer's position (either horizontal or vertical) so that it is as perpendicular to the sun as possible, in order to maximize insolation.
5. Keep track of the ambient air temperature.
6. Do not place the thermometer in direct sunlight.
7. Change only one variable at a time during the experiments, and maintain all other factors constant, e.g., record all temperatures and air flow data, changing only the vent size or the height, not both simultaneously.

If desired, graphs may be prepared to describe height vs. airflow, height vs. temperature, vent size vs. air flow or vent size vs. temperature. Data may be recorded on Attachment V-6-B, "Data Collection Sheet."


Ambient air temperature: 20°C

Model Description and Configuration

Air Flow (None, Low, High)

Outlet Air Temperature

One section, vertical


Four sections, vertical


One section, horizontal


One section, 45° tilt, small inlet


One section, vertical, small outlet


Four sections, 60° tilt, 5 mall outlet

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