Presenting Author- Mukul Sharma (Energy Centre, MANIT, Bhopal)
Co-author- Anil Kumar (Energy Centre, MANIT, Bhopal)
Co-author- Prashant Baredar (Energy Centre, MANIT, Bhopal)
Co-author- A. Palamanit (Energy Systems Research Institute, Prince of Songkla University, Hat Yai, Songkhla,
Co- author- V.P. Chandramohan (Mechanical Engineering Department, NIT, Warangal )
Basics of solar drying
Computational fluid dynamics (CFD) simulation
Description of domestic direct type multi-shelf solar dryer
Design of domestic direct type multi-shelf solar dryer
Assumptions for simulation
Boundary conditions for simulation
Results after simulation
Solar food drying is world wide known process which is adopted by
our ancestors from ancient era.
Open food drying is currently most preferred by the people of
developing nations like India.
There are some disadvantages of Open food drying such as
contamination by dust and insects , deterioration of food by rain,
birds, animals and human etc .
To overcome these disadvantages , Various dryers were developed
by the researchers. Some of them work on conventional power and
some works on Renewable Energy.
The devices works on conventional energy were used initially but
they were found to be costly and very energy intensive.
There are three types of solar dryers .
Direct Type Solar Dryer
Indirect Type Solar Dryer
Mixed Type Solar Dryer
Fig.1. Domestic direct type multi-
shelf solar dryer
Direct Type solar dryers uses direct solar radiation for food drying. They are of
two types viz. cabinet dryers and greenhouse dryers.
In Indirect type solar dryer, there are two separate parts: one is solar collector and
another is dryer.
The solar radiation’s heat is collected at solar collector and with the help of air , it
is transferred to drying chamber where drying of food takes place.
The mixed type solar dryers use both direct and indirect type technology
CFD is a branch of fluid mechanics that utilises the mathematical modelling and
numerical simulation algorithms to analyse and solve the problems that involve flow
of any fluid .
Various CFD simulation tools are:
• ANSYS- Fluent, COMSOL , OpenFOAM, Altair’s AcuSolve, Star-CCM+ , Autodesk
Simulation CFD and many more..
Some of the advantages of CFD simulation are as follows:
• The CFD analysis gives the exact result which empowers the researcher to analyse the
optimal design and overall performance of the model .
• CFD analysis software saves a significant time and money which would get wasted in
the experimental observations for performance validation of a model .
To Validate the design of domestic direct type multi-shelf solar dryer using
Computational fluid dynamics simulation.
To demonstrate the temperature distribution and radiation heat flux
distribution inside domestic direct type multi-shelf solar dryer.
A domestic direct type multi-shelf solar dryer (fig.1) was developed by
Singh et al. for Indian conditions.
The dryer has three perforated trays arranged one above other.
The air flows through the dryer by natural circulation.
It has variable inclination to capture more solar radiation. The
inclination was set as per the latitude of installed location of dryer. The
dryer was set up initially at Ludhiana, India (31oN).
The main parts of dryer were hot box, base frame, trays and shading
plates. The top, back, one side and gate of the box were insulated.
For air flow, 40 holes of 8mm diameter were given in bottom and 20
holes were given at the top.
A 4mm thick glass sheet was fixed as glazing in the front side of solar
The interior of dryer was painted with dull black paint for absorption
of solar rays.
Fig 1: Domestic direct type multi-
shelf solar dryer
The experiment at no load condition was carried out at Ludhiana(Punjab) on 21 November.
Initially, the inlet and outlet holes were blocked , so maximum stagnation temperature was
The dryer was placed facing to south direction at 9:30 am to 4:00 pm.
The average overall heat loss coefficient (U1) based on aperture area for dryer was calculated
𝐼 𝜏𝛼 = 𝑈1 (𝑇𝑆 − 𝑇𝑎) (1)
where, I = solar radiation intensity in W/m2, 𝜏 = transmissivity, α = absorptivity, 𝑇𝑆=
maximum stagnation temperature, 𝑇𝑎= ambient temperature.
The following experimental results were obtained at no load condition:
The maximum stagnation temperature attained by the dryer was observed
The corresponding solar radiation intensity and ambient temperature were 750
W/m2 and 30oC, respectively observed during mid-noon.
The overall heat loss coefficient U1 based on aperture area for dryer was found
to be 8.5 W/m2 K .
Fig.2: Wireframe model of domestic direct
type multi-shelf solar dryer
Fig.3: Meshed wireframe view of domestic
direct type multi-shelf solar dryer
Mass conservation equation :
+ 𝛻. 𝜌𝒗 = 0 (2)
where ρ is the fluid density and 𝒗 is the fluid velocity.
Momentum conservation equation :
𝜌𝒗 + 𝛻. 𝜌𝒗𝒗 = −𝛻p + ρ𝐠 + 𝐅 (3)
where, p is the static pressure,ρ𝐠 and 𝐅 are the gravitational and external forces, respectively.
Energy Conservation equation :
𝜌𝐸 + 𝛻. 𝑣 𝜌𝐸 + 𝑝 = 0 (4)
where, E is the total energy of fluid.
For simulation of temperature distribution, the little amount of air
flow is assumed from the lower and upper holes of 8 mm diameter.
To reduce the complexity of the simulation, the perforated tray mesh
size is considered of 2×2 cm2 and shading trays are neglected.
Lower holes are considered as inlet and upper holes are considered as
Total Elements- 2,88,343
Radiation model- Surface to surface, Solar Loading- Solar ray tracing
Latitude – 31o N , Longitude- 75o E (For Ludhiana), Fair weather Conditions
Date and time- 21 Nov. ,12:00 P.M.
Direct solar irradiance- 750 W/m2 , Diffused Solar irradiance- 200 W/m2
Inlet and outlet – openings
Fluid- Air with density 1.225 kg/m3 and specific heat -1006.43 j/kg-k, Thermal conductivity-
Ambient air temperature -300 K
Outer walls- insulated
near the trays can
be observed about
320 K. Further the
temperature rise can
be seen as air move
outlet to a range of
328 K which is
significant rise in
temperature as per
the design of dryer.
Fig. 4: Contour of static temperature of the trays inside
the dryer cabinet.
Fig. 5: Contour of static temperature of the dryer cabinet.
As the absorptivity of the
dryer is fixed to 0.9 as per
data used in experiments
due to this the most of the
radiation are absorbed
inside the dryer and this is
clearly seen in the
The maximum radiation is
incident on the trays and
this can be seen in Fig. 6.
This high heat flux helps in
increasing the circulating
continuously inside the
dryer to a significant level
which is required for food
Fig.6 : Heat radiation flux contour of trays inside the
An attempt has been made to carry out CFD based analysis using
ANSYS-FLUENT 14.0 software to get heat transfer and radiation
fluxes of Domestic direct type solar dryer at no load condition.
The temperature of the air inside the cabinet dryer increases to a
significant value of 326K with continuous flow of fresh air from the
atmosphere at natural circulation mode.
The major area inside the cabinet dryer such as trays, dryer walls gets
sufficient radiation flux which validates the design of the Domestic
direct type solar dryer. Hence, the design of the dryer formulated by
Singh et al. has been validated by this CFD simulation.
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