EXPERIMENT 14: CAMPHOR BALLS
CHEMICAL ENGINEERING LABORATORY
Determination of mass transfer coefficients for the sublimation of camphor and naphthalene
Parth V or a1 , Chet Chetan Pand Pandere 2 , A shi shi ma C hop hopra 3 , Shraa Shraavya R ao4 ,Aj ay V erma 5 , A di tya Upa Upasani sani 6 1:14CHE1010 2:14CH E 102 1022 2
3:14CHE1042 4:14CH E 105 1058 8
A R T R T I C L E I N F O Mass transfer coefficient, camphor, naphthalene
5:17CHE201 6:17CH E 202
A B S T R A R A C T
In this paper, experiments were were performed to study the variation of mass transfer coefficient as a function of flow rate of air for sublimation for a laminar regime Camphor-air system and Naphthalene-air system were considered. considered. Variation of mass transfer transfer factor with Re and mass transfer coefficient with gas flow rate rate was determined for both systems.
1. Introduction
In this report, we have attempted to find the mass transfer coefficient for a sublimation process. We have also attempted to determine its variation with gas flow rate. Gas-liquid mass transfer coefficients come into play in industrial gas-solid catalytic processes. The rate of mass transfer between a solid phase and a gaseous phase depends largely on astagnant gas film at the interface. The film thickness is dependent on the degree of turbulence at the solid gas interface, ie. the gas velocity at the interface. The film thickness typically decreases with increase in turbulence. The mass transfer coefficients
depend similarly upon the film thickness and upon the degree of turbulence at the solid gas interface. In this experiment, we have selected camphor or naphthalene as the phase change material and will attempt to determine the influence of gas velocity on the mass transfer coefficient at a constant gas temperature, for a fixed initial particle mass. Nomenclature
K g Ps Re Sc Ms Jd G
Mass Transfer Coefficient Vapor Pressure of Camphor Reynolds Number Schmidt Number Molecular Weight Mass transfer Factor Gas Flow Rate
2
Experiment 14: Camphor Balls
2. Theory
Mass Transfer Coefficient is the ratio of the flux to a concentration (or composition) difference. Thus,
……..(1)
These coefficients generally represent rates of transfer that are much greater than those that occur by diffusion alone, as a result of convection or turbulence at the interface where mass transfer occurs. To find k g by correlations, Mass transfer coefficient kg depends principally upon the transport properties of the fluid (Sc) and the hydrodynamics of the particular system involved(Re)
packed bed. A schematic diagram of the test apparatus is shown in Figure 1. A column, 6.8 cm in diameter and 2.2 cm in height is packed with camphor balls. Dimensions of the camphor balls are measured using a screw gauge having least count 0.01 mm, at the start of recording observations. 3.2. Procedure
The dimensions and number of the camphor balls are noted using the vernier callipers. They are weighed and packed in the column. Metered air is passed for a known time until a measurable difference in weight is observed. The loss in weight of the balls is found and the flow rate of air. The experiment is repeated for different flow rates for air, different bed height and particle diameter.
…….(2) …….(3 )
Mass transfer factor j d is given by ..…..(4)
The experimental jd is compared with the correlations available:
..…..(5) .…..(6)
Both correlations are applicable for laminar flow only. Equation 5 is taken from the lab manual, while equation 6 is taken from Perry’s Chemical Engineering Handbook. 3. Materials and Methods:
3.1. Materi als and Setup
Camphor balls from were used. A series of experiments were used to determine the mass transfer coefficient in a camphor/naphthalene
Fig. 1 – Set Up
4. Results and Discussion:
4.1. Camphor-Air System:
For camphor – air system, variation of mass transfer coefficient with gas flow rate was plotted in figure 2. (in terms of logarithm). Table1 shows the values of gas flow rates and mass transfer coefficients. The expected trend was observed:
EXPERIMENT 14: CAMPHOR BALLS
mass transfer coefficient increases with increase in gas flow rate. The equation obtained was ……(7) It must be noted that this equation is only valid for the system in the range of gas flow rates 250 ml/min to 600 ml/min. Table 1: Gas Flow Rates and Mass Transfer Coefficients
G(ml/min)
kg (m/s)
273.87 375.03 591.33 282.33 405.93
0.13 0.15 0.22 0.13 0.16
% Error in G 5.00 3.08 2.00 4.00 2.86
4.33
3.09
0.49
5.37
4.78
2.03
0.41
4.83
4.04
4.01
0.62
4.87
4.33
2.88
0.50
3.99
1.00 0.00 3.00
% Error in Kg
4.00
5.00 Exptl
-1.00
0.01 0.01 0.01 0.01 0.01
Eqn 5 -2.00
Eqn 6
-3.00 -4.00
-8.80
-8.40
-8.00
y = 0.7133x + 3.7662 R² = 0.9885
-7.60
-7.20 -1.50
-1.70
-1.90
-2.10
In addition, variation of mass transfer factor with Reynolds number was plotted and compared with the correlations given by equations 5 and 6. While the general trend of idecrease in mass transfer factor with increase in Reynolds number is followed, it was observed that both the correlations significantly underpredicted the mass transfer factor values. Figure 3 shows the comparison of predicted and experimental values. Table 2: Mass Transfer Factor and Re
4.01
% Error in Re 5.01
ln(jd)
The experimental correlation obtained is shown in figure 4. The lines indicate a 95% confidence interval. 0.70 0.60 0.50
Fig. 2: lnk g vs lnG
ln(Re)
Fig 3:lnJD vs lnRe
% Error in Jd 0.63 6.66
y = -0.2872x + 1.7643 R² = 0.9142
0.40 0.30 3.90
4.40
Fig 4: lnJD vs lnRe
The equation obtained was:
…….(9 )
4
Experiment 14: Camphor Balls
4.2. Naphthalene-Air System:
0.00
Time constraints prevented us from taking more than 3 readings. A plot of mass transfer coefficient versus gas flow rate was plotted, as shown in figure 5. The expected trend was followed : mass transfer coefficient increased with increase in flow rate Table 3: Mass Transfer Coefficients and Gas Flow Rates lnG
-9.00
% Error in G -8.75
6.67
-3.66
% Error in kg 4.01
-7.97
3.33
-3.50
3.34
-7.67
2.50
-3.32
3.13
-8.50
lnkg
-8.00
-3.00 -7.50 -7.00
-4.20
Fig 4: lnk g vs lnG
Similarly, mass transfer factor was plotted against Reynolds Number. The same trend was observed, that of decreasing mass transfer factor with increase in Reynolds No. Table 4: Mass transfer Factors and re ln(jd)
6.00
-0.50 Series1 -1.00
-1.50
We have not attempted to fit these values to a line, as we have only three data points. However, with further data points, we will be able to fit lines and get correlations for naphthalene, similar to camphor.
-3.80
% Error in Re
5.00
Fig 4: lnjd vs lnRe
-3.40
ln(Re)
4.00
% Error in Jd
4.62
6.67
-0.43
6.96
5.40
3.34
-1.05
3.93
5.64
2.51
-1.17
3.25
5. Conclusion
Experiments were conducted to find the variation of mass transfer coefficient and mass transfer factor with air flow rate for the sublimation of camphor and naphthalene within the laminar regime. It was observed that mass transfer coefficient increased with increase in gas flow rates in both cases. Mass transfer factor decreased with Reynolds Number in both cases. Correlations were obtained for these variations in case of camphorair system. Further on, more data points are required before similar correlations can be obtained for naphthalene. 6. References:
1. Perry’s Chemical Engineering Handbook 2. Shivkumar Bale, et al, Spatially resolved mass transfer coefficient for moderate reynolds number flows in packed beds: Wall Effects, International Journal of Heat and Mass Transfer 110 (2017)406-415, 16 March . 2017
EXPERIMENT 14: CAMPHOR BALLS
.
6
7. Annexure 1: Observations
8. Annexure 2:
Experiment 14: Camphor Balls
EXPERIMENT 14: CAMPHOR BALLS
Sample Calculations Observations: Rotameter Reading: 16000 Gas Flow Rate : 16000*0.927-1600=274 ml/min Dball =0.00690 m H= 0.00556 m Bed Ht=2.3 cm Bed Diameter =6.54 cm Weight Change Δ W=1.01 gm. N =100 A=π(dballh+0.5dball2 )N =2.05 x10-2 m2 Volume V ball=πr2hN=2.18 x 10-5 m3 Voidage Ε= V ball/Bed Volume=0.72 Velocity Vel=G/( πr2 )=0.08 m/s Re =Dball Velρ/μ=55.4
Time=20 min K g =0.13 m/s Sc= μ/ρD Jd = k g Sc2/3/vel=1.87 Error Analysis: If R=f(X 1, X 2, X 3 ) Then
So for example, given A=π(dballh+0.5dball2 )N =2.05 x10-2 m2 dball =0.69 cm h=0.556 cm Δdball =0.002 cm Δh =0.002 cm
=0.46 % 9. Annexure 3: Calculation Tables 1. Camphor Flow Rate
Wt Change gm 16000.00 1.01
Dia cm
Ht cm
N
0.01
0.01
105.00
A Volume sq cu m m 0.02 2.18E05
Bd Ht 0.02
Voidage
G(ml/min)
0.72
273.87
G(cu V(m/s) m/s) 0.00
0.08
8
Experiment 14: Camphor Balls
26000.00
1.20
0.01
0.01
105.00
0.02
40000.00
1.75
0.01
0.01
105.00
0.02
20000.00
1.15
0.01
0.01
100.00
0.02
28000.00
0.92
0.01
0.01
100.00
0.02
Re
Kg (m/s)
2.18E05 2.18E05 2.44E05 2.72E05
Sc
0.02
0.72
375.03
0.00
0.11
0.02
0.72
591.33
0.00
0.18
0.04
0.80
282.33
0.00
0.08
0.04
0.78
405.93
0.00
0.12
jd
lnjd
ln(Re)
55.39
0.13
2.67
2.97
1.09
4.01
75.86
0.15
2.67
2.58
0.95
4.33
119.61
0.22
2.67
2.39
0.87
4.78
57.11
0.14
2.67
3.12
1.14
4.04
82.11
0.13
2.67
2.15
0.77
4.41
2. Naphthalene Flow Rate
Wt A sq Volume Voidage Change m cu m gm 12000.00 0.25 0.04 0.00 0.39 24000.00 32000.00
0.30 0.32
0.04 0.04
0.00 0.00
0.33 0.43
G(cu m/s)
ln G
V(m/s)
Re kg
0.00 0.00 0.00
8.75 7.97 7.67
0.05 0.10 0.14
jd
101.44 0.03
0.65
0.03
0.35
0.04
0.31
221.08 280.67
lnjd 0.43 1.05 1.17
