Multiphysics Brings Vaccines
to the Developing World
COMSOL Multiphysics provides resources to deliver vaccines to areas of the
world with limited electricity.
In many areas of the developing world, there’s limited access to electricity, and many places have never had any type of power infrastructure.
This presents a challenge for aid workers and
doctors. In the recent past, vaccines that needed to
be stored at cold, relatively constant temperatures
couldn’t be taken into the remote areas where they
were needed most. As part of the Global Good
program at Intellectual Venture Labs (IVL), a
team of innovators invented a thermos-like container called the Passive Vaccine Storage Device
(PVSD) that uses high-performance insulation to
completely change the way vaccines are stored in
areas with little or no electricity.
Meeting strict safety requirements
If not kept within the necessary temperature
range at all times, vaccines can spoil and become unusable. Global Good’s researchers were
tasked with following the parameters dictated by the World Health Organization. To be
delivered safely, the vaccines are required to stay
within a narrow window of 0 to 10 C.
The first prototype that the researchers designed was based on a cryogenic dewar, a device
that relies on vacuum and multi-layer insulation technology to store extremely cold liquids.
Dewars that can normally hold liquid nitrogen
or liquid oxygen for extended periods of time
were only able to hold ice for a few days before
Global Good’s researchers used experimentation along with thermal and vacuum system
modeling with COMSOL Multiphysics in order
to identify materials and designs that would
allow the PVSD to maintain high vacuum levels
at high temperatures. Like a cryogenic dewar,
the PVSD relies on multi-layer insulation within
a vacuum space to minimize heat transfer.
The high-quality vacuum virtually eliminates
convective and gas conduction heat transfer,
while the multi-layer insulation cuts down on
radiative heat transfer. The multi-layer insula-
tion, made of reflective, extremely thin sheets
of aluminum and a low-conductivity spacer, is
similar to materials used in spacecraft.
Simulating vaccine storage in
Researchers for Intellectual Ventures’ Global
Good program used an environmental chamber
to recreate conditions similar to the climate in
Sub-Saharan Africa in order to rigorously test
and understand the performance of their prototypes. However, building a quality prototype
of a vacuum dewar is an involved effort. To explore different design directions more efficiently
before building prototypes, the team turned to
COMSOL Multiphysics and its Heat Transfer
Module and Molecular Flow Module, among
others. Their challenges included optimizing the
internal geometry for maximum cold storage
time, maintaining higher vacuum capacity and
managing outgassing in the vacuum space. The
minimization of outgassing is critical, as even
moderate amounts of residual outgassing within
the vacuum space over the life of the PVSD can
cause the vacuum to lose its integrity, increasing
heat transfer into the device.
The geometry of the device is optimized to
maximize vaccine hold time and to be as accessible as possible for health workers in the field.
As a first line of defense against the elements, the
outside of the device consists of a metal enclosure padded with protective rubber bumpers,
while the inner part of the PVSD consists of a
smaller shell connected at the very top to the
outside with a cantilever neck. Because of this
design, conductive heat transfer can only happen
at the connection point. In addition, a composite
neck maintains the vacuum space so that there is
no gas permeation from ambient air.
Improving storage device design for
As a result of the experimental and theoretical
work that went into the PVSD, the device is capa-
ble of making a significant impact on the vaccine
cold chain in the developing world, allowing
vaccines to travel into more remote regions and
to be stored for longer periods of time without
the need for power. Down the road, Intellectual
Ventures will improve their storage device de-
signs to keep vaccines cold for extended periods
with even more efficiency. The team will continue
working to create groundbreaking tools with the
ability to save lives around the world.
( Top): Thermal simulation of the PVSD shortly after loading;
the process of melting ice blocks is modeled using the phase
change feature in COMSOL Multiphysics. (Bottom): The
PVSD uses similar temperature control storage methods to
a cryogenic dewar. With a single batch of ice, it can store
vaccines for extended periods of time. Image: COMSOL