Master thesis proposal:
ALTERNATIVE SALT BASED SECONDARY FLUIDS FOR INDIRECT
REFRIGERATION SYSTEMS
Background:
Since the discovery of the negative effects caused by HFC refrigerants used in direct expansion
refrigeration systems, there is an increased interest in environmentally friendly refrigerants (low
GWP) and natural refrigerants (ammonia, hydrocarbons and carbon dioxide). European Union
has adopted two legislative acts with the objective of reducing the use of fluorinated gases (Fgases). This phasing down process requires new solutions and technologies as well as search for
alternative secondary fluids. Thus, the purpose of this work is to investigate different alternative
salt based secondary fluids that could be used together with new refrigerants in the indirect
refrigeration systems and geothermal heat pumps.
Introduction:
Secondary fluids are aqueous solutions of organic or inorganic salts, alcohols and glycols are
used as in the indirect refrigeration systems to transfer heat. Water is known for its corrosive
character and secondary fluids based on aqueous solutions have the same tendency. Potassium
organic salts like formates and acetates are known as environmentally friendly secondary fluids.
The most important advantages of salts compared to other aqueous solutions of alcohols and
glycols are good thermophysical properties, low toxicity and non-flammability. The purpose of
this work is to investigate properties of the different acetate salts in order to propose new blends
that could be used as secondary fluids for low temperature applications. Previous studies showed
that different alkali metal ions like sodium, cesium, lithium or ammonium are affecting the
solubility level, freezing point, thermal conductivity, viscosity and specific heat capacity in
different way. Among examined salts, ammonium formate showed the best performance among
all formate salts by giving the lowest freezing point as well as the highest specific heat capacity
and highest thermal conductivity and similar dynamic viscosity compared to potassium formate.
Instead, lithium formate salts had the highest dynamic viscosity among all samples and despite
high specific heat capacity and thermal conductivity values these salts cannot be recommended
for low temperature applications Both sodium formate and lithium formate were recrystallizing at
lower temperatures than 0 ºC when fast cooling rate was applied. Thus, the possible application
for these salts is rather limited to higher temperatures only. As seen, different type of cation
group in the formate salt can result in different properties, thus, further studies are recommended
to investigate different acetate salts.
Starting date: upon agreement
Project Partners:
Swedish Energy Agency, ADDCON NORDIC, Avantherm AB, Danfoss, Svensk Energi &
Kylanalys AB, Oy Granula Ltd, Grundfos, Gränges AB, ICT Ventilationkyl, Industri
Laboratoriekyl AB, Kemetyl AB, NIBE, Nowab AB, Swed Handling AB, Stainless Engineering
AB, TEO-KYL Sweden AB, Temper Technology AB, WILO Sverige
KTH Supervisor: Monika Ignatowicz, PhD student
Applied Thermodynamics and Refrigeration Div.
Dept. of Energy Technology, Royal Institute of Technology, KTH,
Brinellvägen 68, Stockholm, 100 44, Sweden
[email protected]