Yogurt Processing Case Study

Yogurt Processing Case Study
NT50M Plate and Frame Heat Exchanger
Optimal Plate Heat Exchanger selection for cooling sensitive products - Yogurt
Selecting the correct plate
heat exchanger for your dairy
products is critical to the
success of your operation.
GEA PHE System combines
over 100 years of experience
with technologically advanced
products to give optimal
solutions to your process
Britta Meier-Dinkel
needs. Based on the bachelor
Application Management Food & Sugar
GEA Ecoflex GmbH, Germany
thesis written by Ms. Britta
Meier-Dinkel, the following
summary provides a recommendation for designing yogurt plate
coolers. Ms. Meier-Dinkel investigated the influence of the shear rate on
the yogurt texture (viscosity) when cooled in a plate heat exchanger. This
evaluation was accomplished by choosing a variety of plate types and
corrugations, as well as comparing various gap velocities, which relate
to shear rate.
PHE models VT10, VT20 and NT50M were analyzed with high (H) and
low (V) heat transfer corrugation patterns. The VT10 and VT20 models
have conventionally been used for yogurt cooling and were tested in this
study. The newer NT50M model was also included in this testing to see
if it performs in a similar manner to conventionally used models.
The table below shows the properties of the different yogurt products
tested.
Product Specification
Test Sample
Protein
Yogurt
(thin viscosity)
Low Fat Product
Yogurt
(middle viscosity)
Standard Product
Yogurt
(thick viscosity)
High Fat Product
below 3%
3-3,5%
3,5-4,5%
0-2%
2-5%
Fat
5-10%
Density
1050 kg/m
1050 kg/m
1050 kg/m3
Heat capacity
3852 J/kgK
3852 J/kgK
3852 J/kgK
Thermal conductivity
3
3
0,465 W/mk
0,465 W/mk
0,465 W/mk
Dynamic viscosity (20°C)
150 mPas
210 mPas
300 mPas
Dynamic viscosity (50°C)
75 mPas
106 mPas
150 mPas
Please note: The protein content has a bigger influence on the viscosity than the fat content! Please ask your customer to give both media properties.
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Plates with both high (H) and low (V) heat transfer corrugations were
tested. It is assumed that the V-corrugation pattern is favorable due
to the lower stress effect to the yogurt texture and the resulting lower
pressure drops. The H-corrugation has the advantage of a higher
heat transfer rate, which leads to a reduced amount of required heat
transfer surface area. This will lower unit prices but may negatively
affect the final yogurt texture.
The VT20 is commonly used for yogurt cooling due to its large
plate gap. This study also included the newer NT50M model, with
a smaller plate gap, to determine the effects of a smaller gap on
yogurt texture. The obsolete VT10 was also included as it has been
successfully used for yogurt cooling and has a similar plate gap to the
NT50M. The comparison of the VT10 and NT50M can relate to the
overall processing differences between the VT and NT plate models.
Test Results and Conclusions
Optimal Product Series
Both plate types, VT and NT, showed almost identical results with
only minor observed differences in final viscosity. Both were
determined to be optimal for yogurt cooling. Given these results, it
can be concluded that the new NT plate series will perform as well
as the established VT series when properly applied under similar
process conditions.
this mal-distribution also occurred across each individual plate
further reducing the effective heat transfer area. Mal-distribution
and low flow across plates can result in erroneous heat transfer
calculations and sporadic outlet temperatures. In cases where low
velocities cannot be avoided a “Z-positioning” of the connections,
where the inlet and outlet connections are on the opposite sides of
the frame, will provide a more suitable product distribution.
Optimal Corrugation
It was proven that V-corrugation is more sensitive to the yogurt
viscosity than H-corrugation. V-corrugation provided reduced shear
stress on the product at similar velocities. Although the V-corrugation
requires additional surface area, in the form of one or two additional
passes, to fulfill the heat transfer task, the stress on the yogurt was
lower with less adverse effects on product texture and viscosity.
The results of this study indicate the plate with the optimal
V-corrugation should be chosen in regard to product requirements
(an improved yogurt texture) and not the higher heat transfer
H-corrugation plate.
Summary
The following table shows the tested operating conditions and
design recommendations for yogurt cooling.
Yogurt Design Recommendations
Optimal Yogurt Velocity
The test results showed that the shear stress on the yogurt and
its effect on final yogurt texture decrease if product velocities and
number of passes are reduced. A velocity of 0.07 to 0.08 m/s is
optimal in the VT or NT plates regarding viscosity loss and pressure
drop. The highest tested product velocity of 0.16 m/s caused a high
loss in viscosity and resulted in a high pressure drop.
A low test velocity of 0.03 m/s was problematic due to decreased
thermal performance and lower smoothing effect. Smoothing is
vital to get a uniform yogurt texture. Another problem with the low
velocity trials was that in plate packs with a single-pass-design, a maldistribution of product emerged. This mal-distribution across the
plate pack resulted in the rear section of the plate pack having little
product flow, reducing the effective heat transfer area. In addition,
GEA Heat Exchangers
GEA PHE Systems
GEA Heat Exchangers, Inc. PHE Division
100 GEA Drive, York, PA 17406, USA
Phone: +1 717 268 6200, Fax: +1 717 268 6162
[email protected], www.gea-phe.com/usa
Yogurt
Water
Inlet temperature
approx. 40°C
approx. 15°C
Outlet temperature
20 °C
x °C*
Pressure drop
up to 2,5 bar
up to 1,5 bar
Optimal velocity
0,07-0,08 m/s
up to 1 m/s
Velocity in connection
max. 1 m/s
max. 5 m/s
Number of passes
Preferred profile
Plate type
Product : Water flow
proportion
2 passes or more
V-profile
VT, NT
Minimum: 1 : 1
Optimum: 1 : 2
Maximum: 1 : 3
*Water outlet temperature depends on the ratio between water and yogurt volume
flow.
The specifications contained in this printing are intended only to serve the non-binding description of
our products and services and are not subject to guarantee. Binding specifications, especially pertaining
to performance data and suitability for specific operating purposes, are dependent upon the
individual circumstances at the operation location and can, therefore, only be made in terms of
precise requests.
About GEA:
GEA Heat Exchangers provides one of the most extensive product portfolios in the heat exchange
market worldwide for a wide range of applications. GEA Heat Exchangers manufactures plate,
shell and tube, air-cooled heat exchangers, air filter systems, synthetic fillings for numerous
areas of application, wet cooling towers and dry cooling systems, as well as air-conditioning
facilities. As a result, GEA Heat Exchangers provides reliable and comprehensive coverage of the
entire spectrum for heat exchange.
© GEA Heat Exchangers, Inc. Subject to modification XX – 3/14 PHE Division
Test Units and Background

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