Heat Transfer to Liquid/Particulate Mixtures in Can

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Transcript Heat Transfer to Liquid/Particulate Mixtures in Can

Heat Transfer in Canned
Liquid/Particle Mixtures Subjected To
Axial Agitation Thermal Processing
Mritunjay Dwivedi & H.S. Ramaswamy
Department of Food Science and Agricultural Chemistry
McGill University
July 15 , 2008
CSBE Conference
Introduction
Thermal Processing
 Most efficient method of food preservation
 Principles of thermal processing:
Safety and shelf stability
Reduce the number of microorganisms of public health
concern
Create an environment to suppress the growth of
spoilage microorganisms
Introduction
Today the Consumer demands more than safe and self stable product
 High Quality
Processors demand
technology which
 Convenience
in end isuse
More efficient
Cost effective
High
in nature
HTSTspeed
process
is designed to meet the aforementioned processors
and consumers demand
Minimizing the severity of heat treatment
Promoting product quality
Three Major developments
in HTST processing
Aseptic
processing and
Packaging (1)
Three Major developments
in HTST processing
Thin Profile
Packaging and
Processing (2)
Three Major developments
in HTST processing
Rotational
retorts
Processing (3)
Two Different Modes of Rotation
in Agitation retorts
Rotational Modes
mg
mg
mg
mg
mg
Axial Rotation (Continuous Operation)
End over end rotation
(Batch Operation)
Several Studies Conducted in
End Over End Agitation
Processing
But very little information is
available on axial agitation
processing
Process Parameters
U and hfp
are commonly used
to quantify the heat
Particle
hfp
Liquid
U
transfer process.
U:
Overall heat transfer coefficient
hfp:
Fluid to particle heat transfer
coefficient
Retort
Heat transfer in free axial agitation is it
difficult
Attaching temperature sensors
 Collection of data
Knowledge of U and hfp is important in
predicting the particle center lethality
Overall Objective
The overall objective of this presentation is to
carry out a detailed evaluation of heat transfer
to canned particulate fluids under rotary
processing
Heat transfer studies of particle-liquid mixtures canned foods in free axial mode
Modification of Stock rotomat similar to FMC steritort
Modification of Stock Retort
RETORT SHELL
CAGE
Attachments
CAN
Detail – Attaching Cans in Axial Mode of Rotation
Methodology
EOE vs Free vs Fixed Axial
shell
Cage
Tl
Tl
SUS Attachment
32 Circuit HUB
Tl
S-28 NR rotating
thermocouple
Placement of cans in EOE and Axial Mode
Heat transfer studies of particle-liquid mixtures canned foods in free axial mode
Modification of Stock rotomat similar to FMC steritort
Compare heat transfer rates between Axial and EOE mode
S-28 Ecklund
Thermocouple
To
data
logger
Results and Discussions
Development of a suitable methodology to measure
convective heat transfer coefficients in free axial mode
Methodology to U & hfp
Models (U & hfp Vs for free axial mode)
U & hfp (Free axial Mode)
Ufixed
hfpfixed
Ufree
hfpfree
273
575
491
759
146
245
564
947
152
316
462
697
U FixedAxialMode  281.0159 0.776 T  32.94 C  33.46 R  4.875 C  R 
256
476
563
875
2.03 C 2  9.123 R 2
136
227
356
572
145
259
474
790
h fixed...Axial...Mode  461.89  24.75 T  55.46 C  55.81 R  5  C  R 
279
589
360
496
1.82 C 2  5.78 R 2
142
243
478
706
210
390
581
945
345
719
395
653
191
314
455
777
199
405
458
629
344
632
343
637
189
307
527
886
198
348
450
759
381
797
450
788
201
337
454
726
246
449
452
785
185
298
445
779
81
115
448
761
+
Liquid temperature Data from
wireless sensors (Free Axial)
Overall energy balance equation
Results and Discussions
Evaluation of the effects of system parameters on heat transfer
coefficients with Newtonian fluids during axial rotation
Free Vs. Fixed Axial Mode
Effect on hfp
Free Axial Mode
Effect of Particle size and Conc. on U & hfp
φ19 mm
φ 22.25 mm
φ 25 mm
1000
900
800
hfp (W/m2K)
700
600
500
400
300
200
100
0
20
30
Particle Concentration (%)
40
Free Axial Mode
Effect of Particle density and Conc. on U & hfp
Polypropylene
Nylon
Teflon
900
800
hfp (W/m 2K)
700
600
500
400
300
200
100
0
20
30
Particle Concentration (%)
40
Results and Discussions
Dimensionless correlations for convective heat transfer
to canned liquid particulate mixture subjected to axial and
end-over-end rotations under natural and forced convection
Parameters
Experimental range
Retort Temperature
111.6,115,120, 125,128.40C
Rotation speed
4,8,14,20,24 rpm
Can headspace
Test liquids
5 mm and 10 mm
Newtonian: 80,84,90,96,100 % glycerin
solution
Test particles
Polypropylene, Nylon and Teflon
Particle Size
0.019, 0.02225 and 0.254 meters
Particle concentration
20 %, 30 % and 40 %
Dimensionless
correlations set up
Neural network
models set up
Dimensionless Groups
Description
Reynolds number
Relationship
udch
Re 

Visualize the flow
characteristics of a liquid
c p
Thickness of
hydrodynamic to thermal
boundary layer (ν/α)
Prandtl number
Pr 
Nusset Number
Froude number
Grashof Number
Significance
k
hd ch
k
Heat transfer caused by
convection
d ch N 2
Fr 
g
Resistance of an object
Nu 
Gr 
g (Ts  T )d ch
2
moving through liquid
3
Flow characteristics over
an object
Regression Analysis used
A multiple linear regression analysis for
developing forced convection correlations
A step-wise multiple non-linear regression analysis was
used to develop the mixed convection dimensionless correlations
Nu = A1 ( GrPr) A2 + A3 (ρp/pl )A5, (dp/Dc)A6, Re A7, Fr A8, PrA9, PCA10
Free
Convection
Forced Convection
Description
Pure Forced
Mixed Convection
R2
SS
R2
SS
0.85
213947
0.92
175873
Fixed Axial U, with particle
0.84
115585
0.93
84388
Free Axial hfp, with particle
0.80
180504
0.90
99453
Fixed Axial hfp, with particle
0.81
247587
0.95
126434
0.96
39132
0.97
224
Free Axial U, with particle
Free Axial U, without particle
EOE, U without particle
0.81
577.57
Comparisons of errors for ANN models vs. Dimensionless correlations
for liquid with particulates
Fixed Axial Mode - With particles
hfp
Free Axial Mode - With particles
U
hfp
U
DC
ANN
DC
ANN
DC
ANN
DC
ANN
MRE
(%)
10.24
2.6
8.62
2.9
8.3
1.85
7.35
2.5
R2
0.92
0.98
0.92
0.97
0.95
0.99
0.95
0.98
Comparisons of errors for ANN models vs. Dimensionless correlations
for liquid without particulates
End over end mode
Free Axial Mode
U
U
DC
ANN
DC
ANN
MRE (%)
6.05
3.81
8.34
2.06
R2
0.97
0.98
0.95
0.99
Conclusions
Modification of the existing cage of the pilot stock rotomat was successful
U was significantly higher in case of axial
mode than in EOE mode of agitation, contrary to study made
by Naveh and Kopleman (1980)
A methodology was developed for the measurement of U and hfp
subjected to free axial agitation.
With an increase in rotational speed, particle density and retort temperature,
there was an increase in the associated hfp and U values
Conclusions
T-Test showed no significant difference between the performance of standard
thermocouples and wireless sensors.
Dimensionless correlations for mixed and pure forced convection were developed
with and without particulates in Newtonian fluids during all modes of agitation
Higher coefficients of correlations showed that in all forced convection situations,
the natural convection phenomenon continues to operate because of buoyant forces.
ANN models yielded better results those from the dimensionless correlations.
Thank You