Design of a Low Cost Solar Food Dryer
Design Team
Brian Arena, Nicholas Daggett
Andrew Gawlak, Joshua Gomes
Design Advisor
Prof. Mohammed Taslim
Email: [email protected]
Abstract
Spoiled food is a common problem that affects a wide variety of people, from those in
third world countries to local fruit and vegetable farmers. The simplest form of
preventing spoilage is to remove moisture from fruits and vegetables in order to extend
their storage lives. One simple and convenient solution to this problem is to make a
homemade dryer out of common materials such as wood, aluminum and glass. The
objective of this project is to find a more viable solution to this frequent do-it-yourself
project. The selected design is a self-contained, lightweight solution and is designed for
portability so the product can be taken wherever it is needed. The assembly of the
dehydrator is similar to that of a small tent, and features a removable food drying module.
The design uses a 360o solar collection surface, which is unique when compared with
other solar dryers on the market. This design brings increased efficiency compared to
current solar food dryers, all while staying within the $40 cost goal of the project.
The Need for Project
Solar drying provides a simple,
In many third world countries starvation threatens the wellbeing of
cost effective method to prevent
their citizens. While food shortage is a major factor in this starvation,
food spoilage.
another large contributor is due to the waste of excess food: spoilage.
In some countries, up to 50% of the food that is produced spoils before
it can be eaten. Some preventative measures can be taken through the
use of chemicals and other food additives. These methods are not
always readily available and often pose their own health risks. An
accessible, affordable, and reliable method of preserving food would
significantly reduce the food shortage issue in these developing
countries; solar drying devices provide a solution to this set of needs.
The Design Project Objectives and Requirements
The objective of this project is to
Design Objectives
design an effective, portable, low
The main objective of this project is to design a device that uses
cost solar fruit and vegetable
solar energy to dry fruits and vegetables. This device must be portable,
dryer.
self-contained, and rugged enough to withstand equatorial climates.
The device must be easy to assembly, disassemble, and use. The device
must be low cost so that it can be purchased by farmers in developing
countries, or a government organization to distribute to its citizens.
Design Requirements
Detailed requirements were established at the beginning of the
project based on the design objectives. The device must be an effective
dehydrator, drying its contents in 8 to 12 hours. The device must be
able to contain 5 pounds of fruit or 2 pounds of vegetables. The device
must be self-contained, meaning that the device is operational without
the need of additional parts. One of the most important, yet difficult
requirements is the production cost goal of $40 per unit.
Design Concepts Considered
Three candidate design concepts
Concept #1: Modified Through Pass Design
were developed as part of this
Common though-pass dryers have collection areas that only face
project of which one fully met
one direction (typically directed toward the equator). This severely
the requirements.
limits the effective area of dryer that is optimally positioned to the
sun’s radiation. By adding supplementary collectors to either side of
the original design, the collector screens will be normal to the sun for a
longer time over the course of the day as it travels from east to west.
Although this concept suggests improvements to both the efficiency
and portability over other through pass designs, it still presents
challenges in terms of cost and assembly.
Concept #2: Inflatable Half Dome
An inflatable dryer would utilize a single piece of flexible,
durable, PVC material that could be inflated through a single valve
using an air pump. Separate drying trays would be inserted into the
inflatable body. The solar collection area in this concept is a half dome
shape. Support cavities also inflate to allow for the product to hold the
weight of the drying food in its top chamber. When deflated, the device
could be rolled up and stored in a carrying bag. Although this design
presents ease of assembly and ultimate portability, there are many
disadvantages when it comes to manufacturability and durability.
Concept #3: Conical Tent
The conical tent idea involves the through pass design found in the
previous two concepts. The design is a complete 360o cone shape that
allows the solar collection area to be optimized from any angle that the
sun is positioned at, regardless of which way the user positions it. The
design uses a tent-like structure, with a light yet rugged frame, covered
with material that serves as the solar collection area. A flexible black
fabric serves as the collection plate, while an outer layer of transparent
PVC traps the thermal energy.
Based on performed research
performed by the team, no design like this has ever been constructed.
Three conceptual designs.
Recommended Design Concept
The conical tent design
After deliberation over the various concepts the team decided to
encompasses all the needs
select the conical tent design to move into detailed engineering
outlined in the project
analysis and production. This design encompasses all of the needs
requirements and objectives:
effective, low cost, durable, and
portable.
outlined in the problem statement.
This platform presents an
opportunity to experiment with never before used material
combinations and geometry.
Design Description
The design consists of a conical solar collector section and
modular bucket for easy insertion and removal of fruits and
vegetables. The frame of the system consists of a collapsible center
pole which will fit directly on top of a stake hammered into the
ground. The stake supports the center pole during assembly and
operation. The support cap is located on top of the center pole. The
support cap acts as both the base for the modular bucket and the
attachment point for the solar collecting materials. The way in which
the materials are attached to the cap is through a series of zippers in
order to create a seal and consistent geometry. The solar absorbing
material drapes onto the ground in order to better insulate the interior
Details of stakes and stand-off’s.
of the solar dryer. The transparent insulating layer is given a specified
height off of the ground in order to facilitate airflow.
Eight standoffs are located near the base of the solar collecting
materials. These standoffs allow for a consistent air gap and provide
an attachment point in order to stake the materials to the ground. Air
flows through the gap between the two layers and then through the
support cap and into the bucket. Tension created by a stake and line
system keeps the solar collecting materials taught, both creating a
well-defined air gap and making the structure stable. The final shape
provides optimal sun exposure and the use of standoffs has many
benefits including cheaper parts, lower profile, and easier assembly.
Analytical Investigations
The thermal system of a solar food dryer is relatively simple, and
can be modeled using common heat transfer relationships. The
primary resource for this data is the textbook Solar Engineering of
Thermal Processes by John Duffie. 47 different parameters of the
system were modeled using methods from this text, including flow
characteristics such as Rayleigh and Nusselt numbers, and
temperatures at each of the various layers in the device. This model
allowed the team to achieve correct drying temperatures by refining
the geometry of the design.
Additionally, multiple FLUENT analytical models were developed
to predict flow patterns. Simple 2-dimensional cross section models
evolved into 3-dimensional 1/8th sectional models, which finally were
used to make a full 3-dimensional model of the system.
The
FLUENT analyses supported the team’s ideas behind the conceptual
design, showing that natural convection patterns would form in the
Evolution of FLUENT analysis.
system.
Experimental Investigations
Once the prototype is complete (currently pending material
shipment), testing will be performed to check temperature increases
above ambient conditions. These results will be compared to the
analytical heat transfer models to check their validity.
Key Advantages of Recommended Design

Costs under $40 per unit
◦

Omnidirectional
◦


Food container can easily be removed for loading
Easy to assemble
◦
Detailed cross section of the
dryer.
Large collection area that can be used in any orientation
Modular
◦

Cost-effective materials drive price below other dryers
Simple assemble procedure, sets up in just minutes
Portable
◦
Entire device can fit back into the 5 gallon container
Financial Issues
The estimated cost of a production
The team constructed two prototypes, each costing roughly $150.
solar dryer is $38, which meets
Based on the two preliminary models, the following estimated
the project requirement of $40 per
unit.
production Bill of Materials was constructed:
•
5 Gallon Bucket and Drying Rack Assembly..…$8.00
•
Clear and Black Layers………………………….$12.00
•
Injection Molded Support Cap………………….$6.00
•
Pole and Stakes………………………………….$9.00
•
Nuts, Bolts, Grommets, Line…………………...$3.00
•
Total……………………………………………..$38.00
Recommended Improvements
While the prototype incorporates
There are many changes that will be incorporated into a
many of the core technologies of
production solar dryer that are not in the team’s prototype. The most
the final design, there are some
notable improvement is the drying racks.
The current system is
improvements that would be
cumbersome and less user friendly than desired. Another feature that
incorporated into a production
would be improved is the center pole. The prototype used PVC pipes
unit.
with connectors, whereas a production unit would use a telescoping
pole for increased portability.