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DOI: 10.14738/aivp.92.9435
Publication Date: 13th February, 2021
URL: http://dx.doi.org/10.14738/aivp.92.9435
Design, Fabrication and Evaluation of a Bobloon Vacuum
Dryer
*Uhiara N S3
, Anosike E M1
, Abodenyi V2 A, Ahmed U3
, Anayo G3
. Adesanya T D4
, Eduzor E3
1
Dept. of Electrical electronic Engr. Federal Polytechnic Bauchi.
2
Dept. of Agric. And Bio-Env. Engr. Federal Polytechnic Bauchi.
3
Dept. of Food science and Technology Federal Polytechnic Bauchi 4
Dept. of Nutrition and Dietetics, Federal Polytechnic Bauchi.
*uhiarazi@yahoo.com
ABSTRACT
The bobloon vacuum, a device that employs a deflating and inflating bobloon to create vacuum inside
a drying chamber was fabricated according to the design shown in Figure 1. To evaluate the
performance of the device, samples arranged in a basket, were introduced into the drying / vacuum
chamber before the chamber was made air tight by means of a screw cap. The magnitude of vacuum
is read off the vacuum meter (operation pressure -1.5kp), while an incooperated industrial
thermometer helped to ensure a working temperature of 500C. The samples (10g each) of carrot, hot
pepper and guava after eight hours of vacuum drying reported new weights of 3.7, 4.3 and 5.5g
respectively. Equal weights of same produce (samples), dried under the sun (inside a glass covered
cabinet dryer) for 8 hours had the following weights respectively: 1.8, 2.2 and 2.8g. Results showed
that Vitamin A in the carrot samples reduced from 213μg/100g in fresh sample to 146μg/100g in
vacuum dried and 16.5μg/100g for sun dried samples respectively. The sensory evaluation (color
comparison) between fresh, vacuum dried and sundried carrot, showed no significant difference
between the fresh and vacuum dried samples (p≤0.05).
Key words: vacuum drying, nutrients, consistency preservation, bobloon.
1 Introduction
Most dryers are classified as direct dryers where hot air (at near atmospheric pressure) is used to
supply the heat to evaporate water or other solvents from the product (samples). Vacuum drying of
samples, involves the exposure of the samples to an environment of pressure lower than that of the
atmosphere during the process of evaporation or drying. Drying is among the most energy intensive
unit operations, due to the high latent heat of vaporization of water and the inherent inefficiency of
using hot air as the (most common) drying medium (Brennan et al 1990, Viboon et al. 2007). According
to Brennan et al (1990), when dried by convection at high temperatures, these heat sensitive products
are degraded (change color/appearance and have lower vitamin or nutrient content).
Vacuum and freeze drying which offer alternative paths tend to be more expensive than dryers that
operate at near atmospheric pressure. With vacuum drying, ventilation does not occur and personnel
working near the dryers are safer. It is also possible to recover the precipitated moisture collected
during the drying operation for further use. Drying temperature can be carefully controlled and for
the major part of the drying operation, the samples remain at temperatures below 700C. Duration of
drying is about 12 to 48 hours.
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Uhiara N S, Anosike E M, Abodenyi V A, Ahmed U, Anayo G. Adesanya T D, Eduzor E; Design, Fabrication and
Evaluation of a Bobloon Vacuum Dryer. European Journal of Applied Sciences, Volume 9 No 2, April 2021; pp:
45-48
URL: http://dx.doi.org/10.14738/aivp.92.9435 46
To understand how vapour operation can aid drying, consider the following equation which represents
a simple drying theory.
Q = UA∆T Q = total heat (in British thermal units- BTU or joule)
U = overall heat transfer coefficient (BTU)/ (ft2/oF or M2/oC)
A = the effective heat transfer surface area (ft2 or M2)
∆T = the temperature difference between the (wetting) liquid’s boiling temperature and
the heating mediums temperature in0F or oC.
The process goal is to achieve an effective heat transfer (Q) to the material so that its liquid content is
vaporized. Most often the material properties and the dryer type effectively establish the U and A
values for the process. So the process efficiency objective should be to maximize the ∆T value. By
controlling atmospheric pressure, the vacuum dryer increases the effective ∆T for a given process. It
reduces the boiling point (vapourization temp.) required for removing the liquid (Youngsawatdigul et
al 1996, Brennan et al 1990).
2 Materials and methods
The device was fabricated according to the design shown in Figure 1. When the bobloon was
connected to the drying chamber via the stop cork and valves and then pulled apart, the volume of
gas in the drying chamber decreases resulting in decrease in pressure. This is because pressure (p) is
inversely proportional to (v) gas volume (v α 1/p). On demarcation of the two compartments, using
stopper cork (locking cork 1) the pressure distribution between the drying chamber (dc) and bobloon
(b) is given by –pdc(-vdc) = pbvb .
The samples (10g each of carrot, hot pepper and guava) contained in baskets were introduced into
the drying chamber which is made air tight by means of the screw cap – X, before the connection to
the bobloon.
The methods of Morris Jacobs (1999) were employed in assessing the vitamin A and vitamin C contents
of fresh and sundried samples of carrots, red pepper and guava. The tests were carried out equally on
samples of same product, dried using the bobloon vacuum dryer. Employing a 20 man trained panelist,
the samples were subjected to comparative sensory evaluation (color, flavor/ aroma) with analysis of
variance at p ≤ 0.05.
Figure 1: Bobloon vacuum dryer.
C:\Users\my computer\Desktop\BOOBLON VACUM DRYER.JPG
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European Journal of Applied Sciences, Volume 9 No. 2, April 2021
Services for Science and Education, United Kingdom 47
3 Results and discussions
Conventional vacuum dryers are powered by rotor driven suction fans. Bobloon facilitated vacuum
dryer (Figure 1) is novel in vacuum drying technology. This device therefore though of 80% local
content, above 60% efficiency hence cheaper, still exhibit some problems associated with novelty
including non existence of precision spare parts with resultant hike in cost of fabrication (following
repeated parts condemnation). The problems of acceptable finishing and occasional pressure leakages
will only get better after subsequent budgetary allocations.
Assessment of (fabricated) bobloon vacuum dryer; comparison of dried Agricultural commodities
The loss in vitamin A between the fresh carrot and sundried samples was 196/213 multiplied by 100
which give 92%, while between the fresh and vacuum dried samples it was 67/231 multiplied by 100
which equal 31% (Table 1). The vitamin C of the sundried guava was 1.76mg/100g while that of the
vacuum dried sample had 3.19mg/100g (Table 1)
4 Sensory evaluation result
The result of sensory evaluation carried out to compare the raw agricultural commodities after (drying
by the stipulated processes and storing on shelf for thirty days) with the various treatments, showed
that 70% and above of the color and aroma/flavor of the vacuum dried samples were retained (not
lost) compared to below 25% retained (not lost) in the sundried samples (Tables 2 and 3).
Table 1: Assessment of effectiveness of a novel (bobloon) Vacuum Dryer; comparison of vacuum and
sundried Agricultural commodities
Sample Treatment Impact of Nutrients
Vit.A (mg/100g) Vit.C (mg/100g Weight/Water
Lost (g)
Carrot: Fresh
V/dried
S/dried
213± 1.0a
146.09± 1.5b
16.5± 1.0c
7.6± 1.2a
1.76± 0.9b
1.73± 0.5c
10±0.5a
3.7± 0.1b
1.8±0.3c
Guava: Fresh
V/dried
S/dried
62.4± 0.5a
31.27± 0.1b
16.18± 10c
22.8± 0.7a
3.19± 1.0b
1.76± 1.1c
10± 0.5a
5.52 ± 0.4b
2.84± 0.2c
Pepper: Fresh
V/dried
V/dried
80± 2.0a
15.2± 1.0b
6.56± 1.5c
5.00± 0.1a
1.99± 0.15b
0.414± 0.2c
10± 0.6a
4.3± 0.3d
2.2± 0.4e
Means ± standard deviation for same sample on same column with different super scrip, is significantly
not different (P ≤ 0.05).
V= Vacuum dried S= Sun dried.
Table 2: sensory (flavor/aroma) evaluation result of fruit samples from Drying operations
Samples Carrot Pepper Guava
un-dried (control) 9± 0.1a 10± 0.3c 9± 0.6e
Vacuum Dried 8± 0.3a 8± 0.4c 7± 0.1e
Sun dried 4± 0.1b 3± 0.4d 2± 0.2f
Means ± SD on same column, with same super scripts are not significantly different (P≤ 0.05)