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Determination of the flow field downstream of an annular gap steam injector

Eklöf, Magdalena and Persson, Hanna (2008)
Department of Energy Sciences
Abstract (Swedish)
Background
Tetra Pak manufactures and distributes so called VTIS facilities for sterilization and
pasteurization of for example milk and ice-cream. These VTIS facilities uses a common
sterilization process called ultra high temperature (UHT) treatment. UHT treatment
involves heating the product to 130-150ºC for one to six seconds depending on type of
product. In the VTIS facility the temperature raise in the UHT treatment is obtained with
an annular gap steam injector. The annular gap steam injector injects high pressure steam
directly in to the product which is going to be sterilized, this raises the temperature of the
product almost instantaneously. When quickly raising the temperature of a product the
product can burn to the... (More)
Background
Tetra Pak manufactures and distributes so called VTIS facilities for sterilization and
pasteurization of for example milk and ice-cream. These VTIS facilities uses a common
sterilization process called ultra high temperature (UHT) treatment. UHT treatment
involves heating the product to 130-150ºC for one to six seconds depending on type of
product. In the VTIS facility the temperature raise in the UHT treatment is obtained with
an annular gap steam injector. The annular gap steam injector injects high pressure steam
directly in to the product which is going to be sterilized, this raises the temperature of the
product almost instantaneously. When quickly raising the temperature of a product the
product can burn to the walls of the facility and cause so called fouling (product burn-on
due to high temperatures). The fouling has been thoroughly investigated but it is still not
totally eliminated. The fouling changes character depending on flow, pressure and the
settings of the annular gap steam injector in the VTIS facility. On account of this it is
interesting to investigate if the flow field after the annular gap steam injector changes
when the flow, pressure and the settings of the annular gap steam injector changes and if
this can be connected to the fouling that occurs.
Methods
The flow field investigations has been made with the optical flow velocity measuring
technique Particle Image Velocimetry (PIV) which takes pictures of the flow field using a
camera, a high powered laser and particles in the flow. The PIV measurements took place
in a pilot plant build to mimic the annular gap injector part of the VTIS facility.
Measurements were done after the annular gap steam injector in a part of the VTIS
facility called the holding cell, 750 mm of approximately 4 000 mm of the holding cell, at
three different heights of the holding cell, was investigated. The pilot plant was run under
the same conditions as the VTIS facility in order to mimic the flow field in the VTIS
facility.
Results
When injecting high pressure steam in to the product a jet emerges from the annular gap
steam injector. Close to the annular gap steam injector the jet consists of steam but short
after the steam has condensed and the jet only consists of liquid. The diameter of the jet is
narrow close to the annular gap steam injector and then grows until it covers the whole
diameter of the holding cell. Before the jet has reached its full diameter a back flow is
present close to the walls of the holding cell. When the jet has reached its full diameter
and covers the whole diameter of the holding cell no more back flow can be detected (Less)
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author
Eklöf, Magdalena and Persson, Hanna
supervisor
organization
year
type
H1 - Master's Degree (One Year)
subject
keywords
steam injector, annular gap
language
English
id
1393063
date added to LUP
2009-05-05 15:35:21
date last changed
2009-05-05 15:35:21
@misc{1393063,
  abstract     = {Background
Tetra Pak manufactures and distributes so called VTIS facilities for sterilization and
pasteurization of for example milk and ice-cream. These VTIS facilities uses a common
sterilization process called ultra high temperature (UHT) treatment. UHT treatment
involves heating the product to 130-150ºC for one to six seconds depending on type of
product. In the VTIS facility the temperature raise in the UHT treatment is obtained with
an annular gap steam injector. The annular gap steam injector injects high pressure steam
directly in to the product which is going to be sterilized, this raises the temperature of the
product almost instantaneously. When quickly raising the temperature of a product the
product can burn to the walls of the facility and cause so called fouling (product burn-on
due to high temperatures). The fouling has been thoroughly investigated but it is still not
totally eliminated. The fouling changes character depending on flow, pressure and the
settings of the annular gap steam injector in the VTIS facility. On account of this it is
interesting to investigate if the flow field after the annular gap steam injector changes
when the flow, pressure and the settings of the annular gap steam injector changes and if
this can be connected to the fouling that occurs.
Methods
The flow field investigations has been made with the optical flow velocity measuring
technique Particle Image Velocimetry (PIV) which takes pictures of the flow field using a
camera, a high powered laser and particles in the flow. The PIV measurements took place
in a pilot plant build to mimic the annular gap injector part of the VTIS facility.
Measurements were done after the annular gap steam injector in a part of the VTIS
facility called the holding cell, 750 mm of approximately 4 000 mm of the holding cell, at
three different heights of the holding cell, was investigated. The pilot plant was run under
the same conditions as the VTIS facility in order to mimic the flow field in the VTIS
facility.
Results
When injecting high pressure steam in to the product a jet emerges from the annular gap
steam injector. Close to the annular gap steam injector the jet consists of steam but short
after the steam has condensed and the jet only consists of liquid. The diameter of the jet is
narrow close to the annular gap steam injector and then grows until it covers the whole
diameter of the holding cell. Before the jet has reached its full diameter a back flow is
present close to the walls of the holding cell. When the jet has reached its full diameter
and covers the whole diameter of the holding cell no more back flow can be detected},
  author       = {Eklöf, Magdalena and Persson, Hanna},
  keyword      = {steam injector,annular gap},
  language     = {eng},
  note         = {Student Paper},
  title        = {Determination of the flow field downstream of an annular gap steam injector},
  year         = {2008},
}