Advances in Phytochemistry, Textile and Renewable Energy Research for
Industrial Growth – Nzila et al. (Eds)
© 2022 Copyright the Author(s), ISBN: 978-1-032-11871-0
Open Access: www.taylorfrancis.com, CC BY-NC-ND 4.0 license
The use of solar evacuated tubes as an alternative method of drying
Jepkosgei Joan ∗ , Isaiah Muchilwa & Jerry Ochola
School of Engineering, Moi University, Eldoret, Kenya
Owino George Omollo
School of Engineering, Egerton University, Nakuru, Kenya
David Tuigong
School of Engineering, Moi University, Eldoret, Kenya
ABSTRACT: Drying is one of the traditional methods of food preservation. It is performed in various ways
which include sun drying (natural sun) and forced convection (diesel heaters and solar evacuated tubes). The
sun drying method takes a long time and can be affected by seasons, thereby increasing the risk of spoilage of
the food being dried. This may be avoided by using more efficient methods of drying that enable quick drying
and can be used in all seasons. The aim of this study was to design and fabricate a heating system using solar
evacuated tubes to produce heat that could dry farm products. Fabrication was done using waste aluminium
sheets collected from Rivatex East Africa Limited. Tests were then carried out to determine the amount of heat
required for drying, the arrangement of the solar evacuated tubes housing, and the quantity of air necessary for
drying. Changes in temperature and relative humidity were also measured to determine the effectiveness of the
dryer. And the arrangement of the solar tubes was parallel. The solar heat collector was able to heat the air from
a temperature of 27.1 to 56.7
◦ C, and relative humidity dropped from 52.4% to 36.5%. Results show that the
designed solar dryer can be used as an alternative for natural sun drying.
Keywords: Drying, Solar Evacuated tubes, Solar Energy
1 INTRODUCTION
Maize drying is a process of removing moisture from
the grain to a definite value of operation, therefore
allowing ease of processing, storage of the product,
and reduced the growth of microorganisms. Maize drying includes heat and mass transfer with varying rate
processes that include physical or chemical transformation (Cengel, 2000). The typical maize dryers are
also used to dry farm produce such as coffee, corn, vegetables, milk products, and commercial fruits (Wang,
2005). When the grains are harvested, they have a
high moisture content of 25%–40% (Radhika, 2011)
that must be reduced for ease of storage or processing. Poor drying of the maize grain will lead to the
growth of mycotoxins, a low-molecular-weight natural product which is produced by filamentous fungi as
a secondary metabolite under suitable temperature and
humid conditions. Mycotoxins are poisonous chemical compounds, which when ingested by vertebrates
cause sickness or even death (Korir, 2012). To ensure
proper drying of high production capacity, an appropriate temperature should be used; if high temperature
is used for drying it will affect the quality of the grains,
∗ Corresponding author
and hence will affect consumers such as wet milling
industries.
1.1 Drying technique
Drying techniques vary among farmers from sun drying which is a natural method to the artificial methods
using forced hot air through the material. The various
ways of selecting the method of drying depend on the
cost and the production scale. Sun drying is the most
common method that is practiced by farmers because
it uses the sun as a source of energy which is abundant,
less costly, simple, and environmentally friendly (Akinola, 2006). Around the world there is encouragement
of the use of renewable energy due to the depletion of
fossil energy. Its use by farmers with advanced technology will result in an increase in farm productivity
(Weawsak, 2006).
Artificial forced hot air dryers are commonly used
to speed up the process of drying. The product is conditioned in a chamber (Ahmet., 2013). Maize stored
on a horizontal grid is dried by heat from a fire
that has been set below. The disadvantage of this
method is that the grain changes colour and produces an odour due to the effect of smoke from the
fire. To overcome this problem a hot air chamber/heat
exchanger unit and a chimney were developed, such
DOI 10.1201/9781003221968-13
103
Industrial Growth – Nzila et al. (Eds)
© 2022 Copyright the Author(s), ISBN: 978-1-032-11871-0
Open Access: www.taylorfrancis.com, CC BY-NC-ND 4.0 license
The use of solar evacuated tubes as an alternative method of drying
Jepkosgei Joan ∗ , Isaiah Muchilwa & Jerry Ochola
School of Engineering, Moi University, Eldoret, Kenya
Owino George Omollo
School of Engineering, Egerton University, Nakuru, Kenya
David Tuigong
School of Engineering, Moi University, Eldoret, Kenya
ABSTRACT: Drying is one of the traditional methods of food preservation. It is performed in various ways
which include sun drying (natural sun) and forced convection (diesel heaters and solar evacuated tubes). The
sun drying method takes a long time and can be affected by seasons, thereby increasing the risk of spoilage of
the food being dried. This may be avoided by using more efficient methods of drying that enable quick drying
and can be used in all seasons. The aim of this study was to design and fabricate a heating system using solar
evacuated tubes to produce heat that could dry farm products. Fabrication was done using waste aluminium
sheets collected from Rivatex East Africa Limited. Tests were then carried out to determine the amount of heat
required for drying, the arrangement of the solar evacuated tubes housing, and the quantity of air necessary for
drying. Changes in temperature and relative humidity were also measured to determine the effectiveness of the
dryer. And the arrangement of the solar tubes was parallel. The solar heat collector was able to heat the air from
a temperature of 27.1 to 56.7
◦ C, and relative humidity dropped from 52.4% to 36.5%. Results show that the
designed solar dryer can be used as an alternative for natural sun drying.
Keywords: Drying, Solar Evacuated tubes, Solar Energy
1 INTRODUCTION
Maize drying is a process of removing moisture from
the grain to a definite value of operation, therefore
allowing ease of processing, storage of the product,
and reduced the growth of microorganisms. Maize drying includes heat and mass transfer with varying rate
processes that include physical or chemical transformation (Cengel, 2000). The typical maize dryers are
also used to dry farm produce such as coffee, corn, vegetables, milk products, and commercial fruits (Wang,
2005). When the grains are harvested, they have a
high moisture content of 25%–40% (Radhika, 2011)
that must be reduced for ease of storage or processing. Poor drying of the maize grain will lead to the
growth of mycotoxins, a low-molecular-weight natural product which is produced by filamentous fungi as
a secondary metabolite under suitable temperature and
humid conditions. Mycotoxins are poisonous chemical compounds, which when ingested by vertebrates
cause sickness or even death (Korir, 2012). To ensure
proper drying of high production capacity, an appropriate temperature should be used; if high temperature
is used for drying it will affect the quality of the grains,
∗ Corresponding author
and hence will affect consumers such as wet milling
industries.
1.1 Drying technique
Drying techniques vary among farmers from sun drying which is a natural method to the artificial methods
using forced hot air through the material. The various
ways of selecting the method of drying depend on the
cost and the production scale. Sun drying is the most
common method that is practiced by farmers because
it uses the sun as a source of energy which is abundant,
less costly, simple, and environmentally friendly (Akinola, 2006). Around the world there is encouragement
of the use of renewable energy due to the depletion of
fossil energy. Its use by farmers with advanced technology will result in an increase in farm productivity
(Weawsak, 2006).
Artificial forced hot air dryers are commonly used
to speed up the process of drying. The product is conditioned in a chamber (Ahmet., 2013). Maize stored
on a horizontal grid is dried by heat from a fire
that has been set below. The disadvantage of this
method is that the grain changes colour and produces an odour due to the effect of smoke from the
fire. To overcome this problem a hot air chamber/heat
exchanger unit and a chimney were developed, such
DOI 10.1201/9781003221968-13
103