Heat Transfer in Canned Heat Transfer in Canned Liquid/Particle Mixtures Subjected To Liquid/Particle Mixtures Subjected To

Axial Agitation Thermal ProcessingAxial Agitation Thermal Processing

Department of Food Science and Agricultural ChemistryMcGill University

July 15 , 2008

CSBE Conference

Mritunjay Dwivedi & H.S. Ramaswamy

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

IntroductionIntroduction

Thermal ProcessingThermal Processing

Today the Consumer demands more than safe and self stable product

High Quality Convenience in end use

Introduction

Processors demand technology which is More efficient Cost effectiveHigh speed in natureHTST process is designed to meet the aforementioned processors and consumers demand

Minimizing the severity of heat treatmentPromoting product quality

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)

Three Major developments in HTST processing

Two Different Modes of Rotation in Agitation retorts

mg

mg

mg

mgmg

Axial Rotation (Continuous Operation) End over end rotation (Batch Operation)

Rotational Modes

Several Studies Conducted in End Over End Agitation

Processing

But very little information is available on axial agitation

processing

U and hfp

are commonly used

to quantify the heat

transfer process.

U : Overall heat transfer coefficient

hfp: Fluid to particle heat transfer coefficient

U

hfp

RetortLiquid

Particle

Process Parameters

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 ObjectiveOverall 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

CAGE

Attachments

RETORT SHELL

CAN

Detail – Attaching Cans in Axial Mode of Rotation

Modification of Stock RetortModification of Stock Retort

MethodologyMethodology

SUS Attachment

shellCage

32 Circuit HUB

S-28 NR rotating thermocouple

Tl

TlTl

Placement of cans in EOE and Axial Mode

EOE vs Free vs Fixed Axial

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

To data

logger

S-28 Ecklund Thermocouple

Results and Discussions

Development of a suitable methodology to measure

convective heat transfer coefficients in free axial mode

Ufixed hfpfixed Ufree hfpfree

273 575 491 759

146 245 564 947

152 316 462 697

256 476 563 875

136 227 356 572

145 259 474 790

279 589 360 496

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

Models (U & hfp Vs for free axial mode)

+Liquid temperature Data from wireless sensors (Free Axial)

Overall energy balance equation

22 123.903.2

875.446.3394.32776.00159.281

RC

RCRCTU ModeAxialFixed

22

......

78.582.1

581.5546.5575.2489.461

RC

RCRCTh ModeAxialfixed

U & hU & hfp (Free axial Mode)(Free axial Mode)Methodology to U & hfp

Results and Discussions

Evaluation of the effects of system parameters on heat transfer

coefficients with Newtonian fluids during axial rotation

Free Vs. Fixed Axial ModeEffect on hfp

Free Vs. Fixed Axial ModeEffect on hfp

0

100

200

300

400

500

600

700

800

900

1000

20 30 40

Particle Concentration (%)

hfp

(W/m

2K)

φ19 mm φ 22.25 mm φ 25 mm

Free Axial ModeEffect of Particle size and Conc. on U & hfp

Free Axial ModeEffect of Particle size and Conc. on U & hfp

0

100

200

300

400

500

600

700

800

900

20 30 40

Particle Concentration (%)

hfp

(W

/m2 K

)

Polypropylene Nylon Teflon

Free Axial ModeEffect of Particle density and Conc. on U & hfp

Free Axial ModeEffect of Particle density and Conc. on U & hfp

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

Dimensionless correlations set up

Neural network models set up

Parameters Experimental range

Retort Temperature

Rotation speed

Can headspace

Test liquids

Test particles

Particle Size

Particle concentration

111.6,115,120, 125,128.40C

4,8,14,20,24 rpm

5 mm and 10 mm

Newtonian: 80,84,90,96,100 % glycerin solution

Polypropylene, Nylon and Teflon

0.019, 0.02225 and 0.254 meters

20 %, 30 % and 40 %

Dimensionless GroupsDimensionless Groups

Description Relationship Significance

Reynolds number

Visualize the flow characteristics of a liquid

Prandtl number Thickness of hydrodynamic to thermal

boundary layer (ν/α)

Nusset Number Heat transfer caused by convection

Froude number Resistance of an object

moving through liquid Grashof Number Flow characteristics over

an object

k

cP pr

k

hdNu ch

g

NdFr ch

2

2

3)(

chs dTTg

Gr

chud

Re

Regression Analysis usedRegression Analysis usedRegression Analysis usedRegression 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

Description Pure Forced Mixed Convection

R2 SS R2 SS

Free Axial U, with particle

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

Free Axial U, without particle 0.96 39132

EOE, U without particle 0.81 577.57 0.97 224

Nu = A1 ( GrPr) A2 + A3 (ρp/pl )A5, (dp/Dc)A6, Re A7, Fr A8, PrA9, PCA10

Free Convection

Forced Convection

Fixed Axial Mode - With particles Free Axial Mode - With particles

hfp 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

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

Comparisons of errors for ANN models vs. Dimensionless correlations for liquid with particulates

Comparisons of errors for ANN models vs. Dimensionless correlations for liquid without particulates

Modification of the existing cage of the pilot stock rotomat was successful

Conclusions

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

T-Test showed no significant difference between the performance of standard thermocouples and wireless sensors.

Conclusions

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 YouThank You