International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
Experimental Studies on an Evaporative
Cooler as an option to mitigate post-harvest
losses experienced by commercial producers
of vegetables in Ghana
Sekyere C. K. K#1, Forson F.K *2, Amo-Aidoo A#3, Afriyie J.K#4
1
Department of Mechanical and Manufacturing Engineering, UENR, Sunyani
2
Department of Mechanical Engineering, KNUST, Kumasi
3,4
Department of Mechanical Engineering, Kumasi Polytechnic
Corresponding author: University of Energy and Natural Resources (UENR), Mechanical and Manufacturing
Eng. Dept., P.O. BOX 214, Sunyani, Ghana.
Abstract. This paper presents experimental studies
on a proposed evaporative cooler as part of a
project intended to develop an effective technology
for preserving fresh horticultural produce in order
to overcome high postharvest loses among
commercial farmers in Ghana. The proposed cooler
was made out of block board, flexible wire mesh,
jute fibre and a water feeding mechanism. Two
categories of test were conducted namely; test under
no load conditions and test under loaded conditions.
The cooler was located at the test site in Kumasi
(6o41'28"N 1o36'36"W). The test under loaded
conditions was run by loading the cooler with 68
grammes of fresh tomatoes. Parameters measured
include cold space temperature and the relative
humidity at four different locations designated as
C1, C2, C3, and C4. Under no load conditions, the
evaporative cooler recorded a minimum cold space
temperature of 18oC in an ambient of 28oC and 62%
RH for an air flow rate of 2.91 m3/s. Under load
conditions, a value of 21 oC was recorded as the
minimum product surface temperature for an air
flow rate of 3.53 m3/s. Results showed that cooling
effect
increases
with
decreasing
ambient
temperature and increased bulk air velocity.
Keywords: Evaporative cooler, cold space, relative
humidity, jute fibre
I. INTRODUCTION
Storage of fresh horticultural produce after
harvest is one of the most pressing problems of a
tropical country like Ghana. Due to their high
moisture content, fruits and vegetables have very
short life and are liable to spoil. Moreover, they are
living entities and carry out transpiration, respiration
and ripening even after harvest. Metabolism in fresh
horticultural produce continues even after harvest
and the deterioration rate increases due to ripening,
ISSN: 2231-5381
senescence and unfavorable environmental factors.
Hence, preserving these types of foods in their fresh
form demands that the chemical, bio-chemical and
physiological changes are restricted to a minimum
by close control of space temperature and humidity
(Chandra et al., 1999). Loss estimates for tropical
fruits vary from 10% to 80% with reported losses in
underdeveloped Countries toward the upper end of
this range (Food and Agriculture Organization,
2005). In Côte d’Ivoire, postharvest loss of
agricultural produce due to Spoilage associated with
a lack of storage facilities has been estimated at 20
% to 30 % overall (Dissa et. al, 2007). The
corresponding postharvest loss value for Burkina
Faso was estimated at 50% of the national
production annually. The postharvest loss figure for
Ghana was estimates between 20% and 50% of total
fruits and vegetables production. The fruits and
vegetables, being perishable, need immediate postharvest attention to reduce the microbial load and
increase their shelf life, which can be achieved by
storing them at low temperature and high relative
humidity conditions. These conditions are usually
achieved in cold storages.
In the warm plains of Ghana, fruits and
vegetables are stored in pits or cool dry rooms with
proper ventilation on the floor or on bamboo racks.
Inside the hut, fruits and vegetables are kept on floor
or over racks and covered with straw or plant leaves
to avoid exposure to the atmosphere. By this
method, fruits and vegetables can be stored for few
days without much damage and commercial
producers sell these products in local villages
weekly market according to their financial needs.
Several simple practices are useful for cooling and
enhancing storage system efficiency wherever they
are used, and especially in developing countries,
where energy savings may be critical. Mechanical
refrigeration is, however, energy intensive and
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
expensive. It involves considerable initial capital
investment, and requires uninterrupted supplies of
MOMENCLATURE
et. al., 2015). Appropriate cold storage technologies
are therefore required in Ghana for on-farm storage
of fresh horticultural produce in remote and
inaccessible areas, to reduce losses. The use of lowcost, low-energy, environmentally friendly cold
chambers made from locally available materials, and
which utilize the principles of evaporative cooling,
are considered to be a viable option for solving the
problem of post-harvest loses.
A
surface area, m2
c
specific heat capacity, kJ/kg.K
C1 cold space chamber 1
C2 cold space chamber 2
Evaporative cooling is an environmentally
friendly air conditioning system that operates using
induced processes of heat and mass transfer where
moisture and air are working fluids (Camargo,
2007). Such a system provides an inexpensive,
energy efficient, environmentally benign (not
requiring ozone-damaging gas as in active systems)
and potentially attractive cooling system (Zahra and
John, 1996).
C3 cold space chamber 3
C4 cold space chamber 4
hfg latent heat of vaporization, kJ/kg
L
length, m
m
mass, kg
Q
quantity of heat, kJ
R
thermal resistance, K/W
t time, s
T
temperature, oC
U
overall heat transfer coefficient, W/(m2K)
 velocity, m/s
V
II. DESCRIPTION
OF
EVAPORATIVE COOLER
volume, m3
V volum/*- flow rate, m3/s
m mass flow rate, kg/s
W humidity ratio, kg moisture/kg dry air
ΔT temperature difference, oC
Greek symbols

relative humidity, %

thermal conductivity, W mK

mass density, kg m
3
Subscripts
a
air
bb blockboard
i
initial
f
final
jf jute fibre
tot total
X inlet to evaporative cooler
Y outlet to evaporative cooler
electricity which are not always readily available,
and cannot be quickly and easily installed (prabodh
ISSN: 2231-5381
The main objective of this project is to
investigate the possibility of using evaporative
cooling system for food preservation in remote areas
of Ghana where grid electricity is not available.
THE
The proposed evaporative cooler is
principally made of wooden frames at the supports,
the top, base, doors and the shelves. The vertical
sides of the structure with the exception of the front
part are made of flexible wire mesh. The cooler has
four identical rectangular chambers which serve as
the cold space for food storage (see Fig. 1). A
fabricated metal container of trapezoidal crosssection with base dimension equal to` the top
horizontal part of the cooler serves as the water bath
from which water is fed to the jute fibre. The
trapezoidal inner shape was adopted in order to
enhance water uptake by the jute fibre for effective
evaporation.
Fig. 1 The proposed evaporative cooling system
The middle area of the jute fibre is immersed into
the water with the water bath being filled to the brim
with water. The jute fibre is held to the bottom of the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
water bath by its own weight in a wet state. The
parts of the jute fibre external to the water bath cover
the four vertical sides of the cooler with the cooler
facing southwards. This was done to ensure adequate
air drive through the cooler from the back side.
Where RT is the total thermal resistance of the wall
of the evaporative cooler (including blockboard and
jute fibre). Using the components of the wall, jute
fibre (thickness 2 mm and thermal conductivity
0.046 W/m.K) and blockboard (thickness 2 cm and
thermal conductivity 0.13 W/m.K), the total thermal
resistance of the cooler wall can be calculated as
RT 
Fig. 2 Achitectural structure of the evaporative
cooler
Water wets the entire jute fibre medium by flowing
outwardly from the water bath via capillary action.
Cooling is achieved through evaporation of water
from the jute fibre as ambient air flows over the jute
fibre through natural circulation. Figure 2 shows the
architectural structure of the evaporative cooler
without flexible wire mesh and jute fibre. The
structure measures 969 mm × 500 mm (high) ×562
mm external and was constructed of a 2 cm thick
blockboard. The structure houses four identical
shelves as shown in Fig. 2. Each shelf dimension is
454.5 mm × 230 mm (high) × 261 mm. The
trapezoidal shaped water bath measures 987 mm and
969 mm on the top and bottom sides respectively,
and 194 mm high.
To cool 68 grammes of fresh tomatoes from an entry
temperature of 30 oC to a final desired temperature
of 18 oC, the amount of heat to be removed can
calculated using by
Q  mc(Ti Tf )
1.1
where m is the mass of tomatoes, c the specific heat
L jf Lbb

 jf bb
1.4
,
where Ljf and Lbb are the thicknesses of jute fibre
and blockboard and λjf and λbb denote the thermal
conductivities of jute fibre and blockboard,
respectively. Using the given parameters, the total
thermal resistance and the overall hear transfer
coefficient are 0.1973 K/W and 5.07 W/m2.K,
respectively, giving a wall transmission heat gain of
159.41 kJ.
The amount of water to be evaporated from the jute
fibre in order to achieve the needed cooling can be
calculated by
1.5
Q  mwhfg
,
where mw is the mass of water to be evaporated and
hfg is the latent heat of evaporation of water at an
annual average ambient temperature of 30oC (hfg =
2430 kJ/kg). With a total heat load of 191.89 kJ, the
required mass of water is 0.0850 kg. Having
determined the mass of water required, the water
bath size can be determined by calculating the
volume of water as
V
mw

1.6
,
where  is the density of water (103 kg/m3) and V
is the required water bath volume. Assuming cooling
to the desired final temperature can occur in eight
hours, the rate of evaporation of water
can be calculated by
capacity of tomatoes at temperatures above freezing
(3.98 kJ/(kg.K), Ti is the initial temperature of
tomatoes and Tf is the desired final temperature of
tomatoes. This gives a product load of 32.48 kJ. The
wall heat gain by wall transmission can be calculated
by
1.2
,
where A is the total area available for heat transfer
(m2), U is the overall heat transfer coefficient
(W/m2.K) and T is the difference in temperature
between the cold space and the ambient. The overall
heat transfer coefficient is given by
QT  AU T
U
1
RT
1.3
m w 
mw
t
1.7 ,
where t is the cooling time. This yields 1.77×10 -4
kg/min. If ambient air at an average temperature of
30 oC and relative humidity of 75% (average values
in June for Kumasi) comes into contact with the wet
jute fibre and leaves saturated (100% RH), then the
air leaving the wet material would have a
temperature of 26.8 °C (tdb = twb=tdp). The process
which is essentially a constant wet bulb temperature
process would occur at constant specific enthalpy of
approximately 82.5 kJ/kg dry air (see Fig. 3).
Performing an energy balance on the evaporative
cooler,
 m   m
s
in
s

 sX
,where m
,
ISSN: 2231-5381
1.8
m sX  m w  m sY
out
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 sY represent the moisture
and m
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
contents of air before and after the evaporative
cooling process respectively. Equation (1.8) implies
m w  m a WY  WX 
m
w
1.9 
WY WX 
where WX and WY are the humidity ratio values of
air before and after the evaporative cooling process
 a is the mass flow rate of dry air
receptively, and m
 m a 
as depicted in Fig. 2. Reading from the psychrmetric
chart, WX = 0.0205 kg moisture/kg dry air and W Y =
0.022 kg moisture/kg dry air, thus, the required mass
flow rate of air, m
 a  0.116 kg min . The
corresponding volume flow rate of air,
Fig. 3 Psychrometric representation of evaporative
cooling process
1.10
Va  m a  vX
,Where v X is the specific volume of air at inlet to
the evaporative cooling unit ( v X
This
gives
a
volume
III. METHOD
 0.89 m 3 min ).
flow
rate
value
The test performed using the experimental
evaporative cooler can be categorized as: (a) test
under no load conditions and (b) Test under load
conditions. In each case, the average cold space
temperature values, relative humidity and ambient
air velocity were measured for each of the four
compartments of the cold space at hourly intervals.
The cold space temperature and relative humidity
were
measured
using
Quartz
clock
Humidity/temperature probe (model 5168s) whereas
the ambient air velocity was measured using weather
station
(model
PCE-FWS
20)
of
0.1032 m3 min .
Table I. Test results for day one: no load condition
C.2
T/
(°C)
ϕ/
(%)
5:00 PM
6:00 PM
7:00 PM
C.1
T/
ϕ/
(%)
(°C)
25
56
20
62
20
62
26
22
19
58
62
58
(°C)
26
20
19
60
60
62
(°C)
25
20
19
64
64
65
AMBIENT
T/
υ/(
m/s)
(°C)
32
0.3
27
0.3
26
0.7
8:00 PM
21
20
57
20
61
19
65
25
TIME OF
DAY
(GMT)
62
C.3
Under no load condition, the performance of the
cooler was investigated by placing thermometer and
humidity probe in each of the four (4) chambers as
well as the ambient. The temperature and humidity
values were measured at hourly intervals. The
amount of water used was determined by checking
the level of water in the container. The top and
bottom chambers on the right were designated C1
and C2 whereas the corresponding top and bottom
chambers on the left half of the cooler are designated
C3 and C4, respectively. Under load conditions, the
IV. RESULTS AND DISCUSSIONS
Tables I to IV show results for tests covering
loaded conditions and no load conditions. The no
load test was extended over a three day period in
order to understand the characteristics of the
ISSN: 2231-5381
T/
ϕ/
(%)
C.4
T/
ϕ/
(%)
0.7
ϕ/
(%)
45
56
58
60
evaporative cooler was loaded with 68 grammes of
fresh tomatoes and temperature, humidity and
velocity values were measured over the test period.
The fresh tomatoes were purchased from the local
Asafo market, located about 0.7 km from the test
site, weighed with an electronic balance and gently
placed in the four chambers (C1, C2, C3 and C4) of
the cold space. Equal amounts of 17 grammes were
placed in each chamber of the cold space in order to
ensure an even distribution of the cooling load for
comparative studies. It was ensured that the
tomatoes purchased were without defects.
evaporative cooler. In each case the ambient
temperature and ambient relative humidity were also
monitored in order to determine the extent of
temperature and humidity moderation activities
going on in the evaporative cooler. Tables I, II and
IV show test results under no load conditions
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
The first day of testing under no load conditions
was commenced at 5:00 PM (GMT) with average
ambient temperature at 32 oC which steadily
decreased to 25 oC at about 8:00 PM (GMT) when
the first day of experimentation was terminated. The
intention was to examine the performance of the
proposed cooler during that period of day. The
average ambient relative humidity also increased
progressively from 45% to 60% during the first day
test period. The evaporative cooler exhibited
significant decreases in cold space temperature for
the chambers C1, C2, C3 and C4 with temperature
ranges of 25 to 20 oC, 26 to 19 oC, 26 to 19 oC and
25 to 19 oC for C1, C2, C3 and C4, respectively.
Comparing with the ambient temperature within the
test period, the minimum and maximum effective
temperature differences (ΔT = Tamb – Tc) available
for cooling for C1, C2, C3, and C4 are 4 oC
minimum and 7 oC maximum; 5 oC minimum and 7
o
C maximum; 5 oC minimum and 7 oC maximum;
and 6 oC minimum and 7 oC maximum, respectively.
relative humidity values indicate that the cold space
air for the various chambers has undergone some
amount of cooling. Air volume low rate ranged
between 0.62 and 1.45 m3/s.
Table II shows results for day two under no
load conditions. Day two (2) of the test under no
load conditions commenced at 10:00 AM (GMT)
and proceeded till 5:00 PM (GMT) with ambient
temperature values ranging between 27 and 37 oC
while the ambient air relative humidity values
recorded a range of 44% to 58%. Cold space
temperature range of values recorded for chambers
C1, C2, C3, and C4 are 26 oC (initial temperature) to
19 oC (final temperature), 24 oC to 20 oC, 24 oC to 19
o
C, and 25 oC to 18 oC, respectively. This compare
fairly well with the findings of Chouksey, 1985, who
recorded cold space temperature within the range
21–25 °C with 80–90% RH when the outside
temperature and RH were 40–42 °C and 30–35%,
respectively. In comparison with prevailing ambient
conditions, the maximum average effective
temperature difference values obtained for C1, C2,
C3, and C4 are 16 oC (which occurred at 2:00 PM,
GMT), 14 oC (which occurred at 3:00 PM, GMT), 17
o
C (which occurred at 3:00 PM, GMT), and 14 oC
(which occurred at 2:00 PM and also at 3:00PM,
GMT), respectively. These maximum effective
temperature difference values occurred at air volume
flow rate of 2.08 m3/s for C1 and C4, and 1.45 m3/s
This temperature differences show that an
appreciable level of cooling can be attained when the
cooler is loaded with products. Relative humidity
range of values recorded for C1, C2, C3 and C4 are
56 to 62%, 57 to 62%, 60 to 62%, and 64 to 65%,
respectively. The slight increases in cold space
relative humidity values with respect to ambient
Table II. Test result for day two: no load conditions
C.1
TIME OF
DAY
(GMT)
T/
(°C)
C.2
C.3
C.4
AMBIENT
ϕ/
(%)
T/
(°C)
ϕ/
(%)
T/
(°C)
ϕ/
(%)
T/
(°C)
ϕ/
(%)
T/
(°C)
υ
/(m/s)
ϕ/
(%)
10:00 AM
19
60
20
58
19
59
18
61
27
1.4
56
11:00 AM
12:00 PM
19
23
58
64
22
23
57
58
20
20
57
64
21
22
58
64
30
32
1.4
0.7
55
58
1:00 PM
22
65
24
62
23
64
23
66
33
0.3
45
2:00 PM
21
62
24
64
21
62
23
64
37
1.0
52
3:00 PM
24
57
24
62
21
60
24
62
38
0.7
54
4:00 PM
5:00 PM
24
26
60
60
23
24
61
62
21
24
62
56
23
25
54
54
36
32
0.7
0.3
44
44
for C2 and C3. For effective heat transfer with reasonable heat exchanger surface area, a minimum of 10 oC
effective temperature difference is required. Clearly, the temperature difference values recorded suggest that the
evaporative cooler would serve as an effective preservation technology for most vegetables. The relative
humidity range of values recorded were 57% to 65%, 57% to 64%, 56% to 64%, and 54% to 66% for C1, C2,
C3, and C4, respectively. In comparison with the ambient relative humidity values recorded at the test site for
day two, it can be concluded that significant air cooling occurs in the cold space chambers of the proposed dryer.
Table III shows results for day three under no
load conditions. The third day of the tests run also
started at 10:00 AM (GMT) and ended at 5:00 PM
(GMT). Ambient temperature values obtained were
within the range 28 oC to 39 oC with a corresponding
range of ambient relative humidity values of 51% to
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62%. The maximum average effective temperature
difference values for cold space chambers C1, C2,
C3, and C4 are respectively, 14 oC (at 3:00 PM,
GMT), 16 oC (AT 4:00 PM, GMT), 15 oC (at 3:00
PM, GMT), and 19 oC (at 3:00 PM, GMT). Air
volume flow rate ranged between 0.62 to 4.98 m3/s.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
For all three test conducted under no load conditions
it can be seen that in periods of low ambient
temperatures the cold space chamber temperatures
are lower. Results obtained for the tests conducted
under no load conditions compare fairly well with
the findings of Kulkarni et. al, 2014, who obtained
cold space temperature values of 14 to 27 oC, 17 to
27 oC, and 16 to 22 oC for Jaipur, Ahmadabad, and
Bangalore, respectively.
Results for cooling 68 grammes of fresh
tomatoes are shown in table IV. Within the test
period, ambient temperature and relative humidity
values recorded ranged between 28 oC to 42 oC and
32% to 58% (see columns 15 and 16 of table IV),
respectively. The minimum and maximum effective
temperature difference values for chambers C1, C2,
C3, and C5 relative to ambient conditions are 5 oC
(at 10:00 AM) and 18 oC (at 3:00 PM); 1 oC (at
10:00 AM) and 18 oC ( at 3:00 PM); 2 oC (at 10:00
AM) and 18oC (at 3:00 PM); and 2oC (at 10:00 AM)
and 18 oC (at 3:00 PM), respectively. There were
significant increases in cold space relative humidity
for the four chambers (see columns 4, 7, 10, and 13
of table IV) due to the appreciable levels of
established that evaporative coolers cause cold space
temperature drop and increase in cold space
humidity. An initial product surface temperature of
26 oC was recorded for all chambers. Cold space
chambers C1, C3, and C4 recorded minimum
product surface temperature of 21 oC at an air flow
rate of 3.53 m3/s (Volume flow rate, V  A  v ,
where A is the wetted jute fibre surface area and v is
air velocity) from 12:00 PM to 1:00 PM. This could
be attributed to an increase in air bulk velocity
within the period leading to increased evaporation
rate from the jute fibre covering. Based on the initial
product surface temperature, the maximum drop in
temperature for cold space chambers C1, C2, and C4
is 5 oC whereas C3 recorded 3 oC.
Figures 4, 5 and 6, show graphs of chamber
temperatures (Tc1, Tc2, Tc3, and Tc4) and ambient
temperature (Tamb) versus time of day for the three
no load tests and one load test conducted whereas
figure 7 show graph of product surface temperatures
(Tp1, Tp2, Tp3, and Tp4) and ambient temperature
versus time of day for the test under load conditions.
The usual periodic character and the time
dependence of the wind resources is made evident
by the variations depicted in the Tamb curves of
figures 4, 5, 6 and 7. Therefore, the influence of
seasonal variations in wind activity on the
performance of an evaporative cooler cannot be
overlooked.
humidification of cold space air involved in the
cooling process due to respiration of the fresh
products as well as addition of moisture through
evaporation of water in the jute fibre material. This
confirms the findings of Jha and Aleksha, 2006, who
Table III. Test results for day three: no load conditions
C.1
TIME OF
DAY(GMT)
10:00 AM
11:00 AM
12:00 PM
1:00 PM
2:00 PM
3:00 PM
4:00 PM
5:00 PM
C.2
C.3
AMBIENT
T/
ϕ/
T/
ϕ/
T/
ϕ/
T/
ϕ/
T/
(°C)
18
18
23
24
24
25
21
22
(%)
62
62
64
60
60
62
56
65
(°C)
17
18
20
25
23
25
23
22
(%)
66
66
62
58
54
58
56
58
(°C)
18
20
22
24
22
24
20
22
(%)
64
64
64
62
58
60
57
61
(°C)
20
18
20
21
21
20
22
23
(%)
61
66
65
62
62
64
57
52
(°C)
28
29
34
34
34
39
29
31
Under no load conditions on days one and three, the
cold space chamber temperature (Tc4) recorded
relatively lower temperatures with respect to Tc1,
Tc2 and Tc3whereas Tc2 and Tc1 were slightly
higher for days one and three respectively(see
figures 4 and 4.6). The scenario for day two of the
no load test was slightly different as chamber three
recorded relatively lower temperatures. The
minimum product surface temperature of 21 oC
occurred at chambers 1, 3, and 4. However, product
surface temperature values were comparatively
ISSN: 2231-5381
C.4
/υ
(m/s)
2.4
2.2
1.4
0.7
0.7
0.3
1.7
1.0
ϕ/
(%)
58
62
60
52
56
54
51
58
lower for chamber 4 whereas chamber 2 recorded
slightly higher temperatures. The variations
observed for chamber temperatures under no load
conditions and product surfaces temperatures for the
loaded test could be attributed to the periodic nature
of the available wind resources and the random
change in direction of air giving rise to non-uniform
rate of evaporation across the entire jute fibre
surface. It is worth noting that the periodic character
of the wind resource can be fully understood by
extending the test across all seasons.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
Table IV. Test results for Day four: test with a load of 68 grammes of fresh tomatoes
C.1
TIME
OF DAY
(GMT)
C.2
C.3
C.4
AMBIENT
Tp
T/
ϕ/
Ttp/
T/
ϕ(
Tpt
T/
ϕ(
Tpt
T/
ϕ(
T/
υ
ϕ(
t
(°
(%
(°C)
(°C)
%)
/
(°
%)
/
(°
%)
(°
/(m/s)
%)
(°
C)
)
(°C)
C)
(°C)
C)
C)
C)
10:00 AM
26
23
61
26
27
60
26
26
59
26
26
62
28
0.7
58
11:00 AM
24
24
65
24
25
61
24
24
62
24
24
64
31
0.7
52
12:00 PM
21
21
62
24
24
60
21
23
60
21
21
64
30
1.7
58
1:00 PM
21
21
62
23
24
62
22
23
60
21
22
63
35
1.7
42
2:00 PM
23
23
64
24
25
59
23
23
58
23
24
62
37
1.4
42
3:00 PM
24
24
63
23
24
60
24
25
58
23
24
63
42
1.0
38
4:00 PM
24
24
62
25
26
59
24
24
55
24
24
61
34
0.7
32
5:00 PM
24
25
60
24
25
60
23
23
58
24
24
60
40
0.7
41
Graph of Tc1, Tc2, Tc3, Tc4, and Tamb vs Time of day
(day 1)
40
Tc1
32
26
30
20
27
22
26
19
Tc2
25
20
Tc3
10
Tc4
0
5:00 PM
6:00 PM
7:00 PM
Tamb
8:00 PM
Fig. 4 Graph of Tc1, Tc2, Tc3, Tc4 and Tamb vs Time of day: no-load test, day 1
Graph of Tc1, Tc2, Tc3, Tc4, and Tamb vs time of day
(day 2)
40
30
20
27
30
32
38
37
33
36
32
Tc1
Tc2
Tc3
10
Tc4
0
10:00 11:00 12:00 1:00
AM
AM
PM
PM
2:00
PM
3:00
PM
4:00
PM
5:00
PM
Tamb
Fig.5 Graph of Tc1, Tc2, Tc3, Tc4 and Tamb vs Time of day: no-load test, day 2
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
Graph of Tc1, Tc2, Tc3, T4, Tamb vs Time of day
(day 3)
60
Tc1
40
34
29
28
20
34
39
34
Tc2
31
29
Tc3
0
10:00 11:00 12:00 1:00
AM AM PM PM
2:00
PM
3:00
PM
4:00
PM
Tc4
5:00
PM
Tamb
Fig. 6 Graph of Tc1, Tc2, Tc3, Tc4 and Tamb vs Time of day: no-load test, day 3
Graph of Tp1, Tp2, Tp3, Tp4, and T amb vs Time of day
(day 4)
60
Tp1
40
20
28
26
31
24
30
21
35
21
37
23
42
34
24
23
40
24
0
10:00 11:00 12:00 1:00
AM AM PM PM
2:00
PM
3:00
PM
4:00
PM
5:00
PM
Tp2
Tp3
Tp4
Tamb
Fig. 7 Graph of Tp1, Tp2, Tp3, Tp4 and Tamb vs Time of day: test with load test, day 4
V. CONCLUSIONS
A typical experimental type evaporative cooler was
designed and constructed. Two categories of
experiment were carried out on the cooler. The first
category of test was conducted under no load
conditions as part of a general cooling characteristic
study. The second category of test was conducted
using 68 grammes of tomatoes to determine the
performance of the evaporative cooler under load
conditions. Considering the result of the study, the
following conditions be drawn:
(1) Average maximum effective temperature
difference values recorded for cold space
chambers C1, C2, C3, and C4 are
respectively, 14 oC, 16 oC , 15 oC, and 19 oC
on day three of the no load test whereas the
corresponding values for day two are 16 oC,
14 oC, 17 oC, and 14 oC for C1, C2, C3, and
C4, respectively. An average maximum
effective temperature difference value of 7
o
C was recorded for all chambers on day
one of the no load test. The improved
effective temperature difference values
recorded indicate that the evaporative
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cooler can serve as an effective
preservation technology for vegetables if
properly configured.
(2) A maximum drop in product surface
temperature of 5 oC was recorded for
chambers C1, C3, and C4 with a minimum
product surface temperature of 21 oC at
3.53 m3/s between 12:00 PM and 1:00 PM
(GMT).
(3) Results show that cooling increases with
increased bulk air velocity and decreasing
ambient temperature. Following this
observation, it can be concluded that the
proposed evaporative cooler design can be
used to preserve fresh vegetables at the
coastal belt of Ghana and places like
Aplaku, Mankoadze, Warabeba and
Oshiyier where annual mean wind speeds
range between 3.88 m/s and 4.75 m/s.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 9- March 2016
VI. RECOMMENDATIONS
Following the results of the studies, the following
recommendations are made in order to improve the
performance of the proposed evaporative cooler:
(a)
Considering the limited period within
which the tests was conducted, it is
recommended that further tests be
conducted across all seasons in order to
fully understand the cooling characteristics
of the evaporative cooler
(b)
It is also recommended that the
orientation and location of the cooler be
varied in order to determine the effect of
orientation on performance.
ACKNOWLEDGEMENT
The material support offered by the Department of
Mechanical Engineering, Kumasi Polytechnic, in the
form of instruments and the technical support from
Yankey and Mensah, final year students of the
2014/2015 year group for the successful completion
of this study are gratefully acknowledged.
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