ArticlePDF Available

Evaluation the effectiveness of an indirect solar dryer under Aswan governorate conditions

December 2023
Aswan University Journal of Environmental Studies

DOI:10.21608/aujes.2023.214979.1159

Authors:

Mostafa Omar Hassan

Aswan University

Content uploaded by Mostafa Omar Hassan

Content may be subject to copyright.

Content uploaded by Mostafa Omar Hassan

Content may be subject to copyright.

Page 315 Hassan et al., 2023

`Vol. 4, No. 5, pp. 315-332, (December 2023)

DOI: 10.21608/aujes.2023.214979.1159

Aswan University Journal of Environmental Studies (AUJES)

Online ISSN: 2735-4237, Print ISSN: 2735-4229

Journal homepage: https://aujes.journals.ekb.eg/ E-mail: AUJES@aswu.edu.eg

Original research

Evaluation the effectiveness of an indirect solar dryer under Aswan

governorate conditions

Mostafa O. Hassan a *, Loai Nasrat b, Wael A. Mahmoud c and Taraby H.H.H.a

a Department of Agricultural Engineering and Biosystems, Faculty of Agriculture and Natural

Resources, Aswan University, Egypt.

b Electrical Engineering Department, Faculty of Engineering, Aswan University, Aswan,

Egypt.

c Faculty of Agricultural Engineering, Al-Azhar University (Assiut Branch), Assiut, Egypt.

Received: 4/6/2023 Accepted: 26/9/2023

Abstract:

This paper presents an evaluation of an indirect solar dryer consisting of a solar collector,

trays located in the drying chamber, and an air outlet opening above the drying chamber. The

solar collector consists of a Corrugated galvanized steel panel painted black and covered with

sheets of transparent glass, 3 mm thick from the top, and with dimensions of 2400 x 1100 mm.

The side walls of the solar collector are made of wood, are the insulation is thermal wool with a

50 mm thickness and are painted black from the outside. The drying room measures 1100 x 1200

mm, is made of wood, is thermally insulated from the inside, and contains a number of shelves.

The solar dryer was tested with a load of henna leaves, it was exposed to solar radiation from

8:00 a.m. to 3:00 p.m. A leaves of henna drying test is used to evaluate solar dryers, with a

maximum average temperature of 56.2 °C for the load test. 3000 g of henna leaves were used in

the load test to gauge how well the solar dryer worked. For the solar drying test, 3000 g of henna

leaves were dried from a starting moisture content of 74% W.b to a final moisture content of

8.4% in 7 hours of sunlight. The drying rate was calculated to be 306.7 g/h for the load test. The

drying efficiency was calculated to be 19.5%. The average collector efficiency was also

discovered to be 79.7% for the load test.

Keywords: Performance Evaluation, Drying, Solar Radiation, leaves of Henna.

1- Introduction

The biggest problem now facing humanity is energy. Nonrenewable and

renewable energy sources are the two main categories (Perlin, 1999). Energy research has

been rapidly progressing toward clean, sustainable, and renewable energy systems, such

wind, geothermal, and solar energy technologies, over the last few decades. These devices

were created for a number of uses, such as drying and heating (Chang and Kim, 2001;

Moummi et al., 2004; Battisti and Corrado, 2005).

_____________________________

Corresponding author*: E-mail address: mostafaomar@agr.aswu.edu.eg

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 316 Hassan et al., 2023

Egypt's solar atlas, published in 1991, shows that it has a technical solar-thermal

electricity generating potential of 73.6 Peta watt hour, an annual direct normal energy

density of 1970–3200 kWh/m2, and 2900–3200 hours of sunshine (Comsan,2010).

Henna thrives in heavy, fertile clay soils that are completely drained. It thrives in

soils with a pH range of 4.3 to 8.0 and an annual precipitation of 0.2 to 4.2 meters. Henna

is exported in excess of 10,000 t annually. The top exporting nations are Pakistan, Iran,

Sudan, India, and Egypt, while the top importing nations are the Middle East and North

Africa, Western Europe, and North America. About 1000 t of henna herbs are exported

from Sudan annually. The United States (500-600 t/year), France (250 t/year), Saudi

Arabia (3000 t/year), and Great Britain (100 t/year) are the top four importers (Rehmat et

al.,2020).

Although it is generally agreed that properly designed forced-convection (active)

solar dryers are more selective and controllable than the natural-circulation (passive)

types, the latter are clearly inappropriate for remote rural village farm application in the

majority of developing countries due to the need for electricity or fossil-fuel driven fans

and/or the use of auxiliary heating sources, which makes both their capital, maintenance,

and operational costs prohibitive. The ''ventilated greenhouse dryer'' has the benefit of low

cost and simplicity in both on-site construction and operation for large scale applications

in rural areas (Ekechukwu and Norton,1999).

Drying is the process of removing moisture from a product, such as by lowering

water activity, which can slow down the rate of deterioration and retain the quality.

Agricultural products can be securely kept for several days if they are dried to eliminate

the maximum amount of moisture while retaining their active ingredients. Additionally,

the amount of free water in the meal is greatly reduced during this procedure, which

results in a concentration of dry matter without compromising the food's tissue,

wholesomeness, or outward appearance. This drying process involves the material's

internal mass and heat transfers (Lamidi et al., 2019).

The literature may show a variety of solar dryer kinds or designs. In light of the

ongoing advancements in solar dryer design, it should be developed to consistently update

the classifications of solar dryers. Additionally, other methods may be used to group solar

dryers. In fact, there are many different categories of solar dryers that have been

published in the literature (Chaudhari and Salve, 2014; Tiwari et al., 2016). In this

study, solar dryers are categorized based on the way air flows, how the sun heats the

product, and the type of drying chamber Figure (1.1) demonstrates the many types of

solar dryers.

Lawsonia inermis L., sometimes known as henna bushes, is a member of the

Lythraceae family of plants and is a shrub with both decorative and medicinal uses.

Henna is a perennial plant that may live for up to 10 years in the ground after being

planted. The stem, which contains colorful components, has simple, leathery leaves on

either side that become brown when the branches reach maturity. From the Babylonians

and the Pharaohs employed the henna plant in their religious rites, it is regarded as one of

the medicinal, aromatic, and cosmetic plants that man has known since the dawn of the

earliest civilizations. It is a tropical plant that presumably originated in South America,

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 317 Hassan et al., 2023

Iran, or India. Cultivation of the plant has since expanded to Australia, North Africa, and

southwest Asia (Ghani et al., 2021).

Figure (1): Classifications of solar dryers

Drying requires a lot of energy to do. The use of conventional and fossil fuel heating is

expensive, inefficient for drying, and emits unwanted CO2.Since it causes erosion and

desertification, burning biomass is not a wise choice for heating. Drying typically involves the

use of expensive energy sources like electricity or a mix of solar energy and another type of

energy. Harnessing solar energy for heating agricultural goods is a low-cost solution in terms of

both capital and operating expenditures (Akuffo et al., 2003). Solar energy is abundant in these

remote areas of Egypt, where the amount of sunshine hours is around 3500 h/year (Ahmad and

Schmid, 2002).

2. Materials and Methods

The performance assessment test was conducted using an indirect solar dryer. The indirect

solar dryer was constructed in the workshop and tested on the campus of the College of

Agriculture and Natural Resources at Aswan University, Egypt.

2.1. Components of the solar dryer

An indirect solar dryer consisting of a solar collector (SC), trays located in the drying

chamber and exhaust fan.

2.1.1 Solar collector SC

The primary goal in building the solar collector was to use locally available materials to

collect as much solar energy as possible at the lowest possible cost. SC performance evaluations

were carried out in Egypt's governorate of Aswan. Latitude and longitude are 24.06° and 32.45°,

respectively, with 14 hours of daylight and I = 8.2 KWh/m2 per day for a 24.06° solar declination

angle. It is painted black to keep the heat inside and is thermally insulated with thermal wool that

has a thickness of 50 mm. Three main parts make up the solar collector: The glass cover is 2400

mm long, 1100 mm wide, and 3 mm thick. The cover is fastened to a 100 mm-thick wooden

frame. Corrugated galvanized steel black plate is used to create the absorber plate, the height

between them was 10 cm. Thermal wool with a 50 mm thickness serves as shown figure (2).

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 318 Hassan et al., 2023

Figure(2): solar collector “SC”.

2.1.1.1. Solar collector absorber plate

The air fluid receives the collected energy through the energy absorber plate. For effective

heat absorption, the absorber plate was constructed from a Corrugated galvanized steel plate that

was one millimeter thick and black-coated. 50° is the rib angle, and 5 cm is the top height.

2.1.1.2. Transparent glass cover.

In order to increase the temperature of the absorbent surface, the transparent glass plate absorbs

the solar radiation that is directed towards it and allows it to enter the interior. The glass cover is

3 mm thick, 2400 mm long, and 1100 mm wide. Table (1) dimensions solar collector absorber

plate and transparent glass cover.

Table (1) dimensions solar collector absorber plate and transparent glass cover.

Properties of cover material –glass

Solar spectrum refractive index:

1.52

Transmittance:

0.89

Number of covers:

Cover-plate air spacing:

150 mm

solar collector glass cover dimensions length

2400mm

SC width

1100 mm

SC absorber area

2.256m2

Properties of absorber plate

Conductivity Iron:

60.50 W/m k0

Thickness:

1 mm

Solar spectrum absorbance:

0.88

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 319 Hassan et al., 2023

Properties of cover material –glass

Long-wave emittance:

0.15

top height

50 mm

Ribbing angle

50o

solar collector absorber dimensions length

2400mm

SC width

940 mm

SC absorber area

2.256 mm

2.2. The drying chamber.

The drying chamber is made of wood with a thickness of 30 mm. It is thermally insulated

by thermal wool with a thickness of 5 cm and painted black to trap the heat inside. The

manufactured drying chamber can accommodate three or more trays and has an exhaust hole. The

drying chamber has a length of 1100 mm, width of 0.65 m and height of 1200 mm. It is equipped

with a two-piece door in the front. It is about 800 mm above the ground and carried on 4 legs.

2.3. Exhaust Fan/Ventilation Fan.

DC 12V exhaust fan, Material Plastic, with a diameter of 16 cm, a size of 150 mm, a

capacity of 20 watts, and a frequency of 50 Hz. It is installed inside a circular hole; axial fan was

used to draw hot air to the chamber Dryer.

Table (2) Ventilation Fan specifications

speed

Diameter

capacity

frequency

type

volt

Material

15 cm

20 watts

50 Hz

12V

Plastic

2.4 Measuring instruments

2.4.1. Solar intensity device

System temperatures were recorded by the digital thermometer and the different measured

point of a prototype using thermocouple type K, Ranged from -200 to 1250 oC, with accuracy of

± 1%+3. A Pyranometer model PSP was used to measure the solar radiation sensitive to 9 µV per

W/m2. The Pyranometer readings were linear to ±0.5% in measurement ranged from 0 to 2800

W/m2.

2.4.2 Anemometer.

The anemometer apparatus is used for measuring air speed their specifications are shown in

Table (3). Table (3): Specifications of the anemometer.

Air Velocity

Range

Resolution

Accuracy

meters per sec

0 - 30m/s m/s

0. 1 m/s

± (3% + 0.20 m/s)

Air Flow

Range

Resolution

Area

cubic meters/min

0-9999 m3/min

0 to 9.999 m2

Air Temperature

Range

Resolution

Accuracy

10 - 50 Deg.C

0.1 oF/c

4.0 oF (2.0 oC)

⁎ Model UT363.

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 320 Hassan et al., 2023

24.3 Electronic balance.

Model DT2000, Capacity(g) 2000, Readability(mg) 0.5, Linearity error(g) ≤±1, Plan size

173x135mm, Dimension 230x178x66mm and Voltage AC 220V.The initial weight of the henna

leaves to be dried was determined with an electronic balance Sensitive scale with three decimal

digitsbefore being inserted in the dryer. The weight was determined at every one-hour interval

during the drying process.

2.4.4. Electronic circuit.

Table (4): Specifications of the Electronic circuit.

Parameter

Specification

Job

Figures

Adriano Uno

(ATmega328)

Operating Voltage

5V. DC Current

for 3.3V Pin: 50

mA. Flash

Memory: 32 KB.

SRAM: 2

KB(ATmega328P)

Data storage

Precision

Digital

Temperature

and Humidity

Sensor

Module

(DHT22))

3 to 5V power and

I/O. 2.5mA max

current use during

conversion (while

requesting data).

Good for 0-100%

humidity readings

with 2-5%

accuracy.

Good for -40 to

25°C temperature

readings±0.5°C

accuracy.0.5Hz

sampling rate.

A digital

temperature

and humidity

sensor.

Digital

Temperature

Sensor

Module

(DS18B20)

Unique1-Wire

interface requires

only one port pin

for

communication.

Each device has a

unique 64-bit

serial code stored

in an onboard

ROM.

Can be powered

from data line.

Power supply

range is 3.0V to

provides 9-bit

to12-bit

temperature

measurements

and has an

alarm

function with

on volatile

user-

programmable

upper and

lower trigger

points.

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 321 Hassan et al., 2023

Parameter

Specification

Job

Figures

5.5V.

Measures

temperatures from

–55°C to +125°C.

Thermometer

resolution is user-

selectable from 9

to 12 bits.

User-definable

nonvolatile (NV)

alarm settings

with Alarm search

command.

identifies devices

whose temperature

is outside of

programmed

limits.

A device for measuring temperature and humidity is shown in the following figure (3):

Figure (3): The circuit diagram

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 322 Hassan et al., 2023

2.5. Performance evaluation of the solar dryer:

2.5.1 Solar collector efficiency

The solar collector was built on the presumption that it operates in a steady state, so the

system analysis techniques described here can be used to use the thermal performance analysis to

maximize system efficiency by Duffie and Beckman (1991); Kalogirou (2004); and ASHREA

(2005) as follows:

 

 ................................................................... 1

Where; I is the solar radiation flux incident on the tilted surface of the SC W/m2, Qu is the

useful energy gain per time a solar collector "W".

   󰇛󰇜  ....................................................... 2

where Qi is the absorbed solar energy, and A is the surface area of collector (m2),  is the

transmittance of the SC covers, and  is the absorptance of the SC plate.

Overall heat transfer coefficient (Awady, 1999).

󰇛 󰇜 ................................................. 3

   󰇛󰇜-󰇛 󰇜

󰇛 󰇜 .............................................. 4

where  is the collector heat input “W”,  is the solar collector overall heat losses “W”, m is

the fluid mass ﬂow rate (Kg/s),  is the temperature of cold air “oK”,  is the temperature of hot

air “oK”, Ta is the SC average temperature “oK”, Tm is the temperature of ambient still air “oK”,

and  is the air ﬂuid heat capacity “kJ/kg °K”.

2.5.1.1 solar collector thermal losses

Because of the various layers and components, each of which has a different set of thermal

characteristics, it is challenging to measure the average solar collector temperature. as shown in

figure (4).

Figure 4: Heat transfer through layers of air, wood, glass wool and absorber plate.

  

 



  



 ................. 6

      ................................. 7

R overall = R glass wool+ R wood ....................................... 8

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 323 Hassan et al., 2023

  

 .......................................................... 9

where R is the thermal resistance of insulation “°K/W”, R1 is the thermal resistance of

inner layer of insulation “°K/W”, R2 is the thermal resistance of second layer of insulation

“°K/W”, Rn is the thermal resistance of nth layer of insulation “°K/W”, RS is the thermal

resistance of outer surface of insulation “°K/W”, hb is the surface coefficient of outer surface

“W/m2 °K”, ha is the surface coefficient of inner surface “W/m2 °K”, kI is the thermal

conductivity of inner layer of insulation “W/m °K”, k2 is the thermal conductivity of second layer

of insulation “W/m° K”, and kn is the thermal conductivity of nth layer of insulation “W/m °K”.

According to earlier equations, a wooden frame and glass-wool layers were used to cover the

collector's back and sides in order to reduce heat losses from the FPC. The sum of the values for

the conductivity of air, wood, glass wool, and absorber layers will determine the heat transfer's

overall thermal conductivity (Awady, 1999).

2.5.2 Drying efficiency.

The ratio of energy used to heat the sample and evaporate its moisture to the total energy

consumed is known as drying efficiency. This gauges the dryer's overall efficacy.

(Forson et al., 2007; Drew, 2011 quoted from Brenndorfer et al, 1987).



………………………………………… (10)

Where;

Mw = Mass of moisture removed by dryer (kg)

T = total area of collectors (m2)

T = Average solar insolation (W/m2)

L = Latent heat of evaporation of water (kJ/kg)

Td = Overall drying time, (seconds)

2.5.3 Average drying rate.

The mass of moisture extracted by the drier, Mw, and drying time are used to calculate

the average drying rate, Mdr, the amount of moisture that was taken out of the meal over the

course of drying was given by (Tonui et al., 2014).

 

……………………………………………… (11)

Where,

dr = Average drying rate (kg/h)

Mw = Mass of moisture removed by dryer (kg)

Td = Overall drying time (h)

2.5.4 Moisture content.

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 324 Hassan et al., 2023

The amount of water in the produce is its moisture content. There are two methods for

calculating the moisture content of produce: on a wet basis and on a dry basis, the amount of

moisture in a material's original mass can be represented on a wet basis and expressed According

to (Mohanraj and Chandrasekar, 2009).

On wet basis

 󰇛󰇜

…………………………………… (12)

On dry basis, moisture

 

…………………..……………………………… (13)

Where,

wb= moisture content on wet basis (%)

db= moisture content on dry basis (%)

i = Initial mass of the product before drying (kg)

f = Final mass of the product after drying (kg)

2.5.4 Moisture gain or loss.

This is the percentage increase or decrease in moisture during the night period. A negative

value indicates further moisture loss while a positive value indicates moisture gain (Mohanraj

and Chandrasekar, 2009). It can be calculated as;



………………………………… (14)

Where;

sr = Mass at sunrise (kg)

ss = Mass at sunset (kg)

i = Initial mass of sample (kg)

2.6. Henna.

Lawsonia inermis L., sometimes known as henna bushes, is a member of the Lythraceae

family of plants, annual or perennial, with a lifespan of about three years and may extend to ten,

evergreen, abundantly branching, up to three meters long, and has roots and a red stake. henna

was obtained from one of the local fields in Aswan. Its stem has many branches and lateral

branches, and it is green in color. The shrub's height ranged from 2 to 3 meters, and the flower

color was Miniata with purple flowers. Leaves are dark oval, 1.5-5 cm long, and 0.5-2 cm wide.

Henna leaves contain different glycoside substances, the most important of which is the main

substance known as (Lawson) and its chemical molecule of the type 2-hydroxy-1,4-

naphthoquinone or 1,4-naphthoquinone. This substance is responsible for the biological effect in

medicine as well as the red dye.

Henna consists of the following compounds: Dyes of type 41-naphthoquinone, including

1% Lawson (2-hydroxy-41-naphthoquinone), hydroxylated naphthalene derivatives such as 4-

glucosyl and oxy-21-dihydroxy, cumarine,xanthon, flavonoids, 5-10% tannin,gallic acid, and a

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 325 Hassan et al., 2023

low amount of steroid like sitosterol The flowers contain a volatile oil that has a sweet and strong

smell, and its most important constituents are phobita ionones (A, B, and Ionone). The amount of

active substances, especially lawson (which is the colouring matter), increases in henna leaves as

the plant grows older, and young leaves contain small amounts of these substances compared to

their aged counterparts. Besides that, they contain gallic acid and tannins in a ratio of 5–10 And

sugary and resinous materials, at a rate of about 1%.

2.7 Experimental Procedures and Dryer Evaluation.

Fresh leaves of henna were obtained from one of the local fields in Aswan. The

extraneous elements, such as weeds and damaged or discolored plants, and the initial

moisture content of the henna leaves were determined by oven drying. The test was

conducted on September 13, 2022. Relative humidity, the temperature, the initial and final

mass of the henna leaves, and the speed of the wind were measured at various points

during the experiment.

2.7.1 Load test.

Under the solar drying test, 3000 g of henna leaves were used for the test. Each

tray was covered in a single layer of 1000g henna leaves. Additionally, the dryer's

evaluation criteria were noted. The original moisture content of henna leaves was

determined via oven drying, and the average value was 74%wb. The weight of the henna

leaves spread out on each tray was then calculated using the formula: [Tray + henna

leaves] - Tray = henna leaf weight. Trays containing the henna leaves were placed in the

drying chamber. Based on the established initial moisture content, the decrease in weight

of the henna leaves was measured and used to assess the moisture loss of the leaves

during the drying process. Wet basis calculations were used to determine the moisture

content at each point during the drying process. The henna leaves were dried further until

there was no discernible loss of weight or moisture. Based on the drying rate, drying

efficiency, and dryer's performance. Temperature and humidity are measured through a

humidity and temperature sensor.

3. Results and discussion.

3.1. Test.

The solar drying test was conducted on September 13, 2022, using the solar dryer to dry

the henna leaves. In this test, 3000 g of henna leaves in the form of two layers —1000 g in each

tray—were dried over the course of nearly 7 daylight hours, going from a moisture content of

74.0% wb to a moisture content of 8.4% wb. A safe moisture content for storage is less than 10%

(Sengar et al., 2018).

3.1. Variation of Temperature with time.

Where the Temperatures with time were recorded, represented graphically as in Fig (5).

The plate of collector attained a maximum temperature of 70 °C, tray 1 in the drying

chamber recorded a temperature of 56.2 °C, and the ambint's average temperature was 42.21 °C

at 14 h. The ambient temperature and the dryer's average temperature were 37.2 and 43.84 °C,

respectively. A temperature increases of 5.01 o C above ambient resulted from this. The collector

attained a minimum temperature of 55 °C, tray 3's drying chamber recorded 39.5 °C, and the

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 326 Hassan et al., 2023

outside air temperature was measured at 28.08 °C at 8:00 a.m. It is also noted that the

temperatures on the first shelf are higher than on the second and third shelves, and on the second

shelf, they are higher than on the third shelf.

Figure (5). Variation of Temperature with time.

3.2. Variation of Moisture Content with time.

Where the Moisture Content with time were recorded, represented graphically as in Fig

(6). The experiment began with a moisture content of 74.0% w.b and ended with a moisture

content of 8.5% w.b in less than seven sunshine hours.

Figure (6). Variation of Moisture Content with time.

8 : A M 9 : A M 10A M 11AM 12P M 1 PM 2PM 3PM

temperature (0c)

time (hr)

tray 1 tray 2 tray 3 ambient T-plate

8AM 9AM 10AM 11AM 12PM 1PM 2PM 3PM 4PM

moisture content (%)

time (hr)

tray 1 tray 2 tray 3

Aswan University Journal of Environmental Studies (AUJES) 4 (5), pp. 315-332, (2023).

Online ISSN: 2735-4237, Print: ISSN 2735-4229. https://aujes.journals.ekb.eg/

Page 327 Hassan et al., 2023

As observed in the graph, tray 1's sample lost water more quickly than trays 2 and 3's

samples did. It was noted that the moisture content steadily decreased over time after starting out

strongly. The correlation between drying rate and time-varying moisture content. the drying rate

gradually decreased from its initial high level as the moisture content decreased (Sengar et al.,

2018).

3.3. Variation of relative humidity with time.

Where the relative humidity with time were recorded, represented graphically as in Fig (7).

Figure (7). Variation of relative humidity with time.

Relative humidity vs time was plotted on the graph at three sections, at collector, ambient

air and in chamber of dryer from 8:00 a.m. to 3:00 P.M. at one-hour interval. Figure (7) shows at

first, it appeared that the relative humidity was nearly the same throughout. The relative humidity

started to drop as the air heated up in the solar collector, and it was typically around 8.6%. At

8:00 a.m., the relative humidity at the chamber outlet started to rise as a result of the hot air from

the collector entering the drying chamber evaporating moisture from the henna leaves. The

relative humidity starts to fall as the henna leaves start to dry, which means that the rate of

evaporation is slowing down with time. It is also noted that the relative humidity in the third shelf

is higher than in the first and second, and in the second shelf is higher than in the first shelf.

Thermal performance analysis of the solar collector system

1. Load

Table 5. Thermal performance analysis of the solar collector system.

Time

Solar energy

available

Absorbed

solar energy

Useful heaty

Solar collector

losses w