CONVECTION DRYING

Date: 18th July, 2024

Moro Andy Samuel Nelson Ankrah Richmond Philip Prince Kyereme
Department of Chemical Engineering, Kwame Nkrumah University of Sci. and Tech.

REPORT INFO ABSTRACT

Keywords: Convective drying stands as a traditional method for
dehydrating materials. Numerous research endeavors,
1. Vaporization
both experimental and numerical, have significantly
2. Evaporation contributed to the understanding of convective drying,
3. Crystallization
benefiting researchers and industry professionals alike.
This investigation delves into the significance,
4. Convection techniques, uses, and statistical insights of convective
5. Radiation drying in the realm of food materials. The evaluation
also scrutinizes pivotal drying factors like shrinkage
6. Capillary and the impact of pre-treatments on the convective
7. Relative humidity drying process.The instrument used in the expirement
is CE 130 bowl dryer.In this research, the exploration
8. Enthalpy revolves around the dynamics of convective drying,
9. Drying rate with a particular emphasis on forced convection
mechanisms. To elaborate, the drying process entails
10. Vacuum Drying
extracting and evaporating water or any liquid from a
solution, suspension, or other solid-liquid blend to
produce a dry solid material.

1
 INTRODUCTION

Convection drying is an ancient technique used to dry moist materials. It involves the transfer
of heat through a fluid medium, such as air or gas, to remove moisture from a substance. This
method has been extensively studied through experimental and numerical research, enriching
the knowledge of researchers and industry professionals. Understanding the principles of
convection drying is crucial for various applications, from food processing to industrial
manufacturing. By exploring the mechanisms, historical significance, methods, and key
parameters of convection drying, we can enhance our understanding of this essential
process.In this experiment the CE 130 apparatus was used.When utilizing the CE 130
apparatus for convection drying, it's essential to understand the intricacies of this process.
Convection drying involves the transfer of heat through a fluid medium, typically air or gas,
to remove moisture from a material. The CE 130 apparatus provides a controlled environment
to study this phenomenon, allowing for precise measurements and observations. By analyzing
the behavior of the material undergoing convection drying with the CE 130 apparatus,
researchers can gain insights into drying kinetics, moisture removal rates, and the overall
efficiency of the drying process. This detailed introduction sets the stage for a comprehensive
exploration of convection drying using the CE 130 apparatus.There are two types of
convection: Natural convection occurs due to fluid motion from temperature differences,
which is slow in drying processes. Forced convection, on the other hand, uses devices like
fans to boost fluid movement, speeding up heat transfer. This method enhances the transfer
coefficient, expediting moisture removal and reducing drying time.The transfer coefficient
plays a vital role in convection drying by determining how effectively heat transfers between
the dryer (air) and the material's surface. A higher transfer coefficient results in more efficient
heat transfer, accelerating the evaporation of moisture from the material.Radiation drying
utilizes electromagnetic waves like infrared or microwave radiation to extract moisture from
a material by directly heating its surface. This method differs from convection drying, which
relies on fluid movement, as radiant drying heats the material's surface, leading to moisture
evaporation.Contact drying, also referred to as conductive drying, employs direct heat
transfer from a heated surface to the material undergoing drying. This method relies on
physical contact between the material and the heated surface. Contact drying may not be
suitable for all materials, particularly granular substances. Drying, a crucial process in
various industries like food, textiles, pharmaceuticals, and sewage plants, involves
eliminating water from a material before packaging. The end product of drying must be
completely dry, devoid of any moisture content. Industries utilize different types of drying
equipment tailored to specific products, including tray dryers, vacuum-shelf indirect dryers,
continuous tunnel dryers, rotary dryers, drum dryers, and spray dryers. Tray dryers are
commonly used in industrial drying processes.In the drying process, there are three main
types of drying: surface and capillary drying, pore drying, and dissociation of water of
crystallization. Initially, when heat is applied, surface moisture evaporates first, followed by
capillary moisture from small crevices. Pore drying involves moisture removal from holes
that don't open to the surface. Lastly, water of crystallization, bonded to material molecules,
requires the most energy to remove, resulting in the slowest drying

2
rate.

3
 1. Methodology
In the experiment, the setup included a CE 130 bowl dryer experiment stand, the sample to be
dried, a water source, a mass balance, and a stopwatch. The process began with removing the
drying plate from the support frame, taring the mass balance to zero, and measuring the mass
of the empty drying frame. The fan and heater were activated, and air flow and temperature
were adjusted accordingly. The dry sample was placed on the drying plates, water was added,
and measurements were taken. Observations such as mass of the moist sample, air
temperature, speed, and humidity were recorded at regular intervals until the material's mass
stabilized, indicating the completion of the drying

4
experiment.

1. DRYING CHANNEL 2.DRYING PLATES 3.TRANSPARENT DOOR

4.PROCESS SCHEMATIC 5.AIR VELOCITY SENSOR 6. MEASURING POINT FOR
HUMIDITY AND TEMPERATURE 7. DIGITAL BALANCE 8.BRACKET FOR
DRYING PLATES 9. MEASURING POINT WITH HUMIDITY AND TEMPERATURE
10.SWITCH CABINET WITH DIGITAL DISPLAYS 11. FAN
2. TABLE AND RESULT.

5
 Mass of
Mass of moisture
empty in
tray + Mass of sample/ Vr. g
dry moisture mass of change in water/ g Drying
sample + in the dry moisture dry mass rate, g
Time, s Temperature, Relative Humidity,
water,g %sample, g sample content .h water/h
0:00:00 67.3 13.3 1384.9 90.6 0.096599 0.00725 0.435014 408
0:01:00 67.2 13.4 1378.1 83.8 0.089349 0.007677 0.460603 432
0:02:00 67.2 13.5 1370.9 76.6 0.081672 0.007463 0.447809 420
0:03:00 67.1 13.5 1363.9 69.6 0.074208 0.007463 0.447809 420
0:04:00 67.1 13.5 1356.9 62.6 0.066745 0.005971 0.358247 336
0:05:00 67 13.6 1351.3 57 0.060774 0.005758 0.345453 324
0:06:00 67.1 13.6 1345.9 51.6 0.055017 0.005011 0.300672 282
0:07:00 67.1 13.6 1341.2 46.9 0.050005 0.004798 0.287877 270
0:08:00 67.1 13.6 1336.7 42.4 0.045207 0.004265 0.255891 240
0:09:00 67.1 13.5 1332.7 38.4 0.040943 0.004158 0.249494 234
0:10:00 67.1 13.6 1328.8 34.5 0.036784 0.004052 0.243096 228
0:11:00 67.1 13.5 1325 30.7 0.032733 0.004052 0.243096 228
0:12:00 67.1 13.5 1321.2 26.9 0.028681 0.003838 0.230302 216
0:13:00 67 13.6 1317.6 23.3 0.024843 0.002666 0.159932 150
0:14:00 67 13.6 1315.1 20.8 0.022177 0.001279 0.076767 72
0:15:00 67 13.6 1313.9 19.6 0.020898 0.001173 0.07037 66
0:16:00 67.1 13.5 1312.8 18.5 0.019725 0.001066 0.063973 60
0:17:00 67.1 13.5 1311.8 17.5 0.018659 0.001066 0.063973 60
0:18:00 67.1 13.5 1310.8 16.5 0.017592 0.000746 0.044781 42
0:19:00 67.1 13.6 1310.1 15.8 0.016846 0.000693 0.041582 39
0:20:00 67.1 13.6 1309.45 15.15 0.016153 0.000618 0.037104 34.8
0:21:00 67.1 13.6 1308.87 14.57 0.015535 0.000608 0.036464 34.2
0:22:00 67.1 13.5 1308.3 14 0.014927 0.000363 0.021751 20.4
0:23:00 67 13.5 1307.96 13.66 0.014564 0.000352 0.021111 19.8
0:24:00 67.1 13.5 1307.63 13.33 0.014213 0.000267 0.015993 15
0:25:00 67 13.5 1307.38 13.08 0.013946 0.000149 0.008956 8.4
0:26:00 67.1 13.5 1307.24 12.94 0.013797 0.000128 0.007677 7.2
0:27:00 67.1 13.5 1307.12 12.82 0.013669 3.2E-05 0.001919 1.8
0:28:00 67.2 13.6 1307.09 12.79 0.013637 0 0 0
0:29:00 67.1 13.5 1307.09 12.79 0.013637 0 0 0
0:30:00 67.2 13.5 1307.09 12.79 0.013637 0 0 0
0:31:00 67.2 13.5 1307.09 12.79 0.013637 0 0 0
Mass of empty tray = 356.4g

Mass of empty tray + dry sample = 1294.3g

Mass of dry sample = 1294.3g - 356.4g

6
Mass of dry sample = 937.9g

At time t = 0min

Mass of empty tray + dry sample + water = 1384.9g

Mass of moisture in sample = 1384.9g – 1294.3g

Mass of moisture in sample = 90.6g

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒

Moisture content, v =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

90.6 𝑔 𝑤𝑎𝑡𝑒𝑟
v = 937.9 𝑔 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

v = 0.09660 g water/ g dry sample

At time, t = 1 min

Mass of empty tray + dry sample + water = 1378.1g

Mass of moisture in sample = 1378.1g – 1294.3g

Mass of moisture in sample = 83.8g

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝑖𝑛 𝑠𝑎𝑚𝑝𝑙𝑒

Moisture content,v =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

83.8 𝑔 𝑤𝑎𝑡𝑒𝑟
v = 937.9 𝑔 𝑑𝑟𝑦 𝑠𝑎𝑚𝑝𝑙𝑒

v = 0.08935 g water/ g dry sample

The drying rate is given by:

∆𝑉 𝑉𝑥 − 𝑉𝑥+1 𝑔 𝑤𝑎𝑡𝑒𝑟
𝑉𝑟 = = ,
∆𝑡 𝑡𝑥+1 − 𝑡𝑥 𝑔 𝑑𝑟𝑦 𝑚𝑎𝑠𝑠. ℎ

Vr after 0 min:

7
 ∆𝑉 0.096599−0.089349
Vr = ∆𝑡
= 1
60

Vr = 0.435 g water/ g dry mass.h

Vr after 1 min:
∆𝑉 0.089349−0.081672
Vr = = 1
∆𝑡
60

Vr = 0.4606 g water/g dry mass.h

Drying rate after 0 min:

𝑑𝑚
= 0.435 × 937.9 = 407.987 g water/h
𝑑𝑡

Drying rate after 1 min:

𝑑𝑚
= 0.4606 × 937.9 = 431.997 g water/h
𝑑𝑡

7.1 POST-LAB

1. T1 = 25℃ Relative Humidity = 40% Velocity, v = 1.5m/s T2 = 48℃

Relative Humidity = 30%

There is no change in moisture content during the heating process,

hence X1 = X2 =X

Φ =30% P = 101.325 kPa

Mass flow rate of air in = mass flow rate of air out, therefore m1=m2=m

From the psychometric chart;

8
X1 = 5.9 g/kgDA

Specific volume, v = 0.853 m3 /kg

Inlet air enthalpy, Hi = 40.15 kJ/kg

Outlet air enthalpy, Ho = 122.66 kJ/kg Volumetric flow rate,

Vr = velocity × Area Area = (350 × 350) × 10−6 = 0.1225𝑚2

V = 1.5 × 0.1225 = 0.18375 𝑚3/s

Mass flow rate = m

𝑉 0.18375
m= = = 0.2154 kg/s
𝑣 0.853

q = m (H2 – H1) = 0.2154(122.66 – 40.15) = 17.773 kJ/s

2. Two industrial applications of convection drying;

1. Convection drying is used to extend the shelf life of perishable food items by removing

moisture, which opposes microbial growth.

2. Convection drying is used to remove solvents and moisture from APIs, ensuring their

stability and efficiency.

3. Two useful intensive properties of air in air conditioning processes;

1. Temperature. 2. Pressure.

9
CONCLUSION AND RECOMMENDATION

The CE 130 was used to track how wet samples dried. To determine moisture content, we
weighed the substrate with the wet sample every minute. The graphs revealed rapid drying at

10
the exposed surface, eventually reaching a point where the drying rate became constant at
zero. This indicated the presence of residual moisture, suggesting a need to raise the
temperature to eliminate excess moisture. Additionally, the graphs showed an inverse
relationship between wet mass, drying speed, and drying time. As time progressed, both the
moisture mass and drying rate decreased steadily.

3. References
1. WEBB,R.L, 1994. PRINCIPLES OF ENHANCED HEAT TARNSFER. JOHN WILEY,
NEW YORK.

2. KEEV.R.B. 1972. DRYING PRINCIPLES AND PRACTICE. PERGAMON PRESS,

LONDON

3. GEANKOPLIS,C.J.,2003. TRANSPORT PROCESS AND SEPARATION PROCESS

PRINCIPLES

4. CEGEL Y.A, 2019. HEAT AND MASS TRANSFER, FUNDAMENTALS AND

APPLICATION.

POST LAB ANSWERS

From the psychrometric app;

At Dry bulb temperature of 25 Degree celcuils and

Relative humidity 30% ; Humidity ratio = 0.00589 Kg/Kg DA Specific volume = 0.8518
m3/kg

Specific Enthalpy = 40.13 KJ/Kg DA

Area = 350×10-3 m × 350×10-3 m = 0.1225 m2

Volumetric flow rate = 1.5 m/s × 0.1225 m2 = 0.1838 m3 /s

Mass flow rate =Volumetric flowrate,(m3 /s)/Specific volume,( m3 /kg)

=0.1838/0.8518

=0.2158 kg\s

11
But the humidity ratio for both the inlet and outlet of the drying system are equal. Hence at
Humidity ratio of 0.00589 kg/kg DA and Dry bulb temperature of 48oC, the enthalpy of the
exiting air is 64.0 KJ/kg DA

Q = m (H2 −H1 )

Q = 0.2158 (64.0 - 40.13)

= 5.151 KJ/s

2. . i. It is for the processing and preservation of food in the food industry

ii. It is used in the removal of moisture from pharmaceutical products in order to convert
them into solids.

3. i. Density: The density regulates the airflow in an enclosure. Air density is inversely
proportional to its velocity.

ii. Humidity: it determines the amount of moisture in air. High humidity reduces temperatures
which is the mechanism used in air-conditioners

DECLARATION

I declare that:

 This report is my unaided work and is a true reflection of the lab I participated in.

 Large portions of it have not been submitted by another student for assessment.

 Significant portions of it were not copied from an internet source or a book.

 Significant portions of it were not written using chatgpt or any other AI tool.

12
  If any of the above statements turn out to be false, I forfeit the marks awarded to this

report.

NELSON ANKRAH RICHMOND. ………………. ………………….

Name Date Signature

MORO ANDY SAMUEL ………………. ………………….

Name Date Signature

PHILP KYEREME PRINCE ………………. ………………….

Name Date Signature

13
14
15