Thesis-2004-Al-Hakim.pdf (29.28 MB)
An investigation of spray-freezing and spray-freeze-dryings.
thesis
posted on 2013-08-13, 13:33 authored by Kassem Al-HakimDrying is an important process for a variety of industries such as pharmaceuticals,
food, and chemicals, and produce products with low bulk density, good shelf
stability, economical storage and transport, and in some cases unique structural
qualities. Of the various drying methods available, freeze-drying is the most
beneficial for heat sensitive products that susceptible to thermal degradation. Freezedrying
also confers a porous structure on the material result from the voids left after
subliming the ice crystals. Freeze-drying however is used mainly for high value
products due to the high capital and operational costs. The cycle time of such a drier
may take several hours.
The spray-freeze-drying process has evolved in an attempt to shorten the freezedrying
process time. The process atomises a liquid feed to increase the heat and mass
transfer surface area. The spray is then frozen in a very cold gas or a cryogenic liquid
to form solid particles, which are then freeze-dried. Some processes incorporate a
- fluidised bed freeze-drier to reduce the drying time by forced convection heat and
mass transfer.
This project aim to develop the Spray Freeze- Drying process and examine the effect
of the process on the drying entities and resulting product quality, followed by
modelling of the spray freezing operation in an attempt to optimise the operation.
This thesis is divided into two main areas of investigations;
Spray freezing investigation as an influential on the resulting product size and
structure. The experiments performed using Phase Doppler Anemometry technique
to measure the particle size distributions and velocities in a specially constructed
spray freezing chamber with incorporated windows. A spray freeze-drying chamber
was constructed composed of three parts co-current spray freezing, gas - particle
separation, and fluidisation freeze-drying unites. Successfully spray characterisation
measurement was carried in both ambient and sub-ambient temperatures, producing
data of the drop size distribution and velocities from refractive scattered laser PDA
measurement. The technique produced valuable information about the spray size
distribution and velocity, the application of this technique appear was a novel
approach in the spray freezing process measurement. The result were used in the
established spray freezing model derived from Pham (1984) freezing model
incorporating with a recalescence stage from the Hindmarsh (2003) spray freezing
model. The current model predicted the droplet freezing time, which is influenced by
the droplet diameter, velocity and freezing gas temperature. The results also shows
an agreement between the freezing time predicted and the PDA recognition of bursts
rejected due to their possible phase change.
The spray-freezing-drying chamber was operated in vacuum conditions to produce
freeze-dried whey protein powder. The powder characteristic results shows an
physical properties such as density, solubility and particle sizes in comparison to
spray drying and cryo-spray freeze-drying. The morphology of the spray freeze-dried
whey powder is substantially different to that produced by spray drying and displays
a porous microstructure. The operation of the freeze-drying unites requires an further
investigation for temperature, pressure, and flow control to maintain the freezedrying.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Chemical Engineering
Publisher
© Kassem Al-HakimPublication date
2004Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough UniversityEThOS Persistent ID
uk.bl.ethos.416932Language
- en