Solar drying of drying agricultural product (Apricot)

Solar drying of drying agricultural product (Apricot)

Foued ChabaneDjamel Bensahal Abdelhafid Brima Noureddine Moummi 

Department of Mechanical Engineering, Faculty of Technology, University of Biskra 07000, Algeria

Laboratoire de Génie Mécanique (LGM), Faculty of Technology, University of Biskra 07000, Algeria

Department of Mechanical Engineering, Faculty of Technology, University of Laghouat 03000, Algeria

Corresponding Author Email:
27 October 2018
2 March 2019
31 March 2019
| Citation



This work allowed us to study the effects of some parameters on drying and specify the most influential. Drying is basically a phenomenon of removal of liquid by evaporation from an apricot. Solar drying is one of the processes that have found application in Algeria, because of the important quantities of solar irradiations that can be exploited in this country.Drying basically comprises of two fundamental and simultaneous processes: heat is transferred to evaporate liquid, and mass is transferred as a liquid or vapor within and the apricot as a vapor from the surface. The experimental study is investigated in the Biskra city of Algeria for drying Apricot in the drying room which it integrated with a solar air collector (new design) which the drying chamber receives the temperature from the solar collector which absorbed from sun. We have to spread the produce on a suitable surface and let it dry in the drying room and added the study of thermal performance of solar air collector and trying with three different airflow rates, namely, 0.018, 0.028 and 0.034 kg/s are conducted. Finally the results have been illustrated with mass water content, product temperature, drying room temperature, outlet temperature in both solar collector and drying room and enthalpy of solar collector and drying room which effect with increase the mass flow rate.


drying room, solar air collector, moisture content, mass flow rate, apricot, temperature

1. Introduction

The solar drying it’s the process which gives the free energy of hot air used in the drying room for evaporated the water into apricot. In this study we design the both of solar collector and the drying chamber which integrate with it, which give one system of drying, we are trying to test the apricot by it and the result talk about this design realized, it is the observation study.

An improved technology in utilizing solar energy for drying agricultural is the use of solar dryers where the air is heated in a solar collector and then passed through products. There are two basic types of solar dryer appropriate for use with agricultural: natural convection dryers where the air flow is induced by thermal gradients; and forced convection dryers wherein air is forced through a solar collector. In this study the drying solar with forced convection, The forced convection solar dryer can be considered as a conventional mechanical drying system in which air is forced through a dried product holder but the air is heated by a flat plate solar collector rather than by more conventional means.

Most developing countries are unable to solve their food problems for then tire population because of the rapidly increasing number of people in their respective territories.

Some research effort to design and develop a forced convection solar dryer using evacuated tube air collector. Their performance was compared with natural sun drying. The results of the present study show that the proposed solar dryer has been greater efficiency, and the moisture content of bitter gourd is reduced from 91% to 6.25% in 6 hours as compared to 10 hours in natural sun drying [1].

Another work studies an experimental study was conducted to investigate the performance of a solely solar drying system and a system equipped with an auxiliary heater as a supplement to the solar heat, [2]. The performances of both are compared to that of natural drying. Beans and peas are dehydrated in a system that consists of two flat plate collectors, a blower, and a drying chamber. Tests with four different airflow rates, namely, 0.0383, 0.05104, 0.0638, and 0.07655 m3/s were conducted. The efficiency of the mixed drying system was found to increase by 25% to 40% compared to the solely solar drying. A best fit to the experimental data of peas and beans was obtained by six exponential equations for the various systems with a correlation coefficient in the range 0.933 and 0.997.

Solar drying can be an effective means of food preservation since the product is completely protected during drying against rain, dust, insects and animals [3].

There is a great diversity of designs and modes of operation: forced convection, Ahmad et al., [4], Indirect forced convection, Bahlou et al., [5], Direct cabinet and indirect cabinet solar dryers, Banoult et al., [6], Solar-biomass hybrid dryer enhanced by the Co-Gen technique, Tadahmun and Hussai, [7]; Leon and Kumar, [8], Greenhouse solar dryers, Abdullah, [9]; Bechoff et al., [10], Direct solar dryer, Hii et al., [11], Heat pumps, Fadhel et al., [12]; Li et al., [13], Indirect natural convection solar dryer with chimney, solar dryer with greenhouse as collector, solar tunnel dryer (air collector), hybrid solar dryer assisted by evacuated tube collectors, Jairaj et al., [14]. F. Chabane & al [15-26], Presents a study of heat transfer in a solar air heater by using new design of solar collector. The collector efficiency in a single pass of solar air heater without, and with using fins attached under the absorbing plate has been investigated experimentally the maximum efficiency obtained for the 0.012 and 0.016 kg/s with, and without fins were 40.02, 51.50% and 34.92, 43.94%.

2. Characteristics of Wet Solids

The water-film solid adheres to its external surface by surface forces. A boundary layer at the periphery of the solid is constituted by air saturated with water, that is to say air containing water. Water vapor at a partial pressure equal to the vapor pressure of water that would be present in a chamber at the same temperature.

Let a mass Mh of wet material containing a mass Me of water and a mass Ms of dry matter:

Mh = Me + M (1)

2.1 Absolute humidity

Authoritarian humidity or moisture content or content (Kgav / Kgas) in dry-based water, where more simply moisture is expressed by liquid contained in the product in relation to its dry mass.

$X=\frac{{{M}_{e}}}{{{M}_{s}}}=\frac{{{M}_{h}}-{{M}_{s}}}{{{M}_{s}}}$  (2)

2.2 Moisture-based water content

Relative humidity where water content (%), or moisture-based water content is expressed by the mass of liquid contained in the product relative to its wet mass.

${{X}_{r}}=\frac{{{M}_{e}}}{{{M}_{e}}+{{M}_{s}}}$  (3)

2.3 Drying speed

The drying rate is the mass of evaporated water per unit of time and per unit area of evaporation of the material. The expression of the drying speed is then written:

$R=-\frac{d{{M}_{v}}}{s.dt}=\frac{{{M}_{s}}.dx}{s.dt}$ (4)

${{M}_{v}}={{M}_{s}}.dx$ (5)

$dx={{X}_{e}}-{{X}_{s}}$ (6)

3. Experimental Study

In this study, we focused on agro-food drying, using a solar collector and a drying chamber, which we manually performed in the technological hall of the Department of Mechanical Engineering of the University of Biskra, carried out in the period from February to May 2018.

Figure 1. Experimental setup (solar collector with drying chamber)

3.2 Description of the test bench

The experiment bench tests were carried out near the technological hall of the Department of mechanical engineering of the University of Biskra, which is located at the south-east of the Algerian Sahara at 34.5042 ° of latitude, at 5.4447 ° of longitude and at 105 meters of altitude. The experiment site is exposed to the sun.

In our case for the realization of the sensor we had recourse to the design of the following elements:

a. The box: is in the shape of wooden box of multiple type of thickness 15mm which will be used as base for the sensor, its dimensions are 153cm x 83cm x 10cm.

We placed holes 20 mm in diameter along the upper and lower front of the box to enter and exit the air. As can be seen Figure 2.

Figure 2. Holes of inlet solar collector

b. Insulation: Thermal insulation refers to all the techniques used to limit heat transfer between a hot environment and a cold environment, for this we used a good type of polystyrene with dimensions of 147cm x 77cm x 4cm.

c. Characteristic of polystyrene:

- The thickness of the polystyrene is 4 mm, which makes it solid and of high quality.

- It retains the temperature for a long time.

- It supports a temperature up to 100 ° C.

- It is flammable, with a self-ignition temperature of about 490 ° C.

d.Reflective Film: is a plywood type pad that separates the insulation from the absorber, to avoid affecting the insulation of sunlight concentrated in the absorber, its dimensions are 150cm x 80cm.

e. Characteristic of plywood:

- Good flexural strength and modulus of elasticity.

- Resist moisture.

- Resistant to high temperatures

f. The absorber: The solar absorber is the part of the solar heating system that captures the heat and transmits it to the air (for solar air heating). It acts as a heat exchanger that turns solar energy into heat. We made it in galvanized sheet with the same dimensions as the reflective film.

g. Glazing (Plexiglas): is a material with multiple applications. This thermoplastic, which can be molded by compression, injection, casting, blowing and extrusion, comes in many colors and in many forms (panels, blocks, pipes, bars). Feature of Plexiglas:

- This very clear material with a glossy appearance has a very high transparency and a higher light transmission than glass (its optical index is 1.49).

- It is resistant to UV rays, corrosion and atmospheric agents while being much lighter than glass (1.19 g/cm3 density).

- Finally, it’s very smooth and shiny surface appearance makes it an aesthetic material, even design, that can be used in the fields of construction and furnishing.

3.3 Manufacture of the drying chamber

The room is made of multiple type wood, protected on all sides with good quality insulation. Connect to the solar panel by a pipe, which passes air through holes to distribute this air on the dried product; its dimensions are 80cm x 50cm x 50cm.

Figure 3. Experimental setup of drying chamber

Figure 4. Orifices into drying chamber

Figure 5. Support of the product

-Orifices: We drilled holes in order to distribute the air on the product and avoid burning it. In our case, we put holes 10 mm in diameter in a square board, 30 cm by 30 cm. As show in Figure (4).

-The grate: Is a support on which the product is arranged, with holes for the removal of water, attached by four rods equilibrated to allow us to weigh the product without removing it (see Figure 5, This grid is characterized by its hardness and resistance to rust.

3.4 Flow measurement

To measure the flow, we used (the vacuum cleaner see Figure 6, the anemometer and the voltage regulator), to have a link between the voltage and the speed see Tab.1. Use of the debit law:

$\overset{.}{\mathop{m}}\,=\rho .V.S$  (7)

Table 1. Adjusting the flow in terms of voltage







Mass flow rate (kg/s)

























Figure 6. Vacuum cleaner for air circulation control

-Preparation for the test:

Experimental determination:

The dimensions of the collector are:

Dimensions (general): 1.53 m x 0.83 m.

-   Dimensions (specific): 1.50 m x 0.80 m.

Calculation of the collector surface:

-   Total area: 1.27

-   Area (specific): 1.20

•   Dimensions of the drying chamber:

-   Dimensions (general): 0.80 m x 0.50 m x0.50

-   Dimensions (specific): 0.73m x 0.42m x0.39

Calculation of the volume of the drying chamber:

-   Total volume: 0.20

-   Characteristics of the drying process:

We summarized the results of the drying process in the table 2 showing the state of the product before and after drying with a characteristic average, the results are as follows:

Table 2. Statistical results obtained from Apricot for different flows

4. Results and Discussion

Figure 7 show the variation of moisture content as a function to total time in minutes according to mass flow rate. We remark that variation its observation in the beginning operation to 200 min and then the curves it’s approaching together to when the dry is stable. The dry product of Acripot doesn’t depend of the total mass but relate of the time and the speed dry.

Figure 7. Moisture content of Apricot

Figure 8. Drying speed versus moisture content of the Apricot

Figure 8 show the variation of drying speed as a function of moisture content of the Apricot according to three mass flow rates with a different total mass of the Apricot used. We can see the drying speed begin with increase evolution to arrive in the point of deviation when the drying speed attains the values equal to ratio 0.005 and 0.0065 according to ratio moisture content 0.15 and 0.2, respectively the total mass of the Apricot 370 and 456 g. We conclude that mass flow rate of the air comes less versus the drying speed come fast.

The global solar radiation it’s begin with less power and increase to arrive a maximum value in median sun and then decrease to arrive a minimum value, see Fig.9. We can observe that the global solar radiation takes the maximum value with three days of the tests from 800 to 1050 W/m². This power used in the solar collector for heat air which gives the important temperature of drying chamber.

The figure 10 show, the evolution of relative humidity which goes to inlet solar collector, according to three days of the test, we can be seen the maximum variation is in the first days of the test and come minimum with approach in the second and last day.

Figure 9. Global solar radiation according to three days, respectively

Figure 10. Relative humidity in the inlet solar collector

Figure 11. Relative humidity in the outlet drying chamber

The figure 11 show, the progression of relative humidity which goes to outlet drying chamber, according to three days of the test, we can be remarked that values come much of the inlet solar collector which means the product out much the wet content and that what I needed to come. In the first days the relative humidity is going with a maximum values which begin with it 53 % and the median in the second day with 38.5 %, and a last variation in the last day with a minimum attain 35 %.

A during the heat air with solar collector which gives this temperature to drying chamber when the product put it inside on the support, under all this we create the source of distribution under the form of orifices in favor of homogenate the heat inside all chamber. In the figure 12, show the variation of temperature of the Apricot according to time of the day, we can see all the evolution curves begin with a less temperature and then take a more in the median sun time and for after that is stable with fixe temperature. When the mass flow rate take a much is associating that the product get a much the heat from air.

Figure 12. Temperature of the product of Apricot in the drying chamber

Figure 13. Temperature of the absorber plate of solar collector

In this study the heat air come from the absorber plate of a solar collector design see Figure 13, about this point we illustrate the curves of temperature an absorber plate for determinate the action with evacuated air in the streaming of collector to the drying chamber it’s necessity for this part. When the temperature an absorber is high implicate that the temperature enter of the drying chamber come much it is important in this test see Figure 14. The evolutions come parallel with variation of global solar radiation effect see Figure 9.

The drying chamber receives the temperature from the solar collector which absorbed from sun. The figure 14, show the variation of temperature of drying chamber sensor situated in the centre of the chamber. We remark that the temperature started with low temperature and finish with high temperature according to environment weather outside the experimental setup. The evolution come in versus varying with mass flow rate when lower implicate higher temperature in against come correct. About the last days we can be seen that irregular variation cause the solar radiation is irregular.

Figure 14. Temperature of the drying chamber

5. Conclusions

This work allowed us to study the effects of some parameters on drying and specify the most influential.

It is necessary to indicate that the results obtained and represented by the different curves according to the studied model, are built on real experiments.

For the capture surface, the increase of this factor makes it possible to increase the solar power captured. This leads to the elevation of the air temperature within the sensor allowing a short drying time. Thus, the drying air temperature, the flow rate, the mass of the product, and the solar radiation are important factors in increasing the efficiency of the dryer.

We are trying to test the apricot by it and the result talk about this design realized, it is the observation study.



Mass flow rate kg.s-1


Global solar radiation W.m-²


Velocity wind m. s-1


Ambient temperature °C


Inlet temperature of drying room °C


Outlet temperature of drying room °C


Temperature of product °C


Temperature of room °C


Different temperature °C


Total mass of procut g


dry anhydrous g


Water mass g


Moisture-based water content %


Absolute humidity kgav / kgas












Chamber or room








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