| dc.description.abstract | In today’s day and age the search for more reliable, sustainable, energy efficient systems is a
constant. Over the last three decades large emphasis has been placed on vapour compression
cycles and making them as energy efficient as possible. To increase or decrease the temperature of
a controlled volume requires large amounts of shaft work [kW], however by developing and
conducting research into old technologies it could be possible to obtain a sustainable alternative
heating/cooling system. Aqua-ammonia absorption-desorption cycles are able to operate on
renewable energy, as this process removes the energy hungry compressor from the refrigeration
cycle and replaces it with a generator, absorber, rectifier, and regenerative heat exchanger.
Absorption-desorption cycles are the earliest form of refrigeration cycle, with the earliest dating back
to 1824. Pure ammonia refrigerant is one of only few alternative refrigerants with zero ODP (Ozone
Depletion Potential) and zero GWP (Global Warming Potential) accepted by all governments,
ASHRAE, UNEP, International Institution of Refrigeration, and almost all Institutes of Refrigeration
worldwide (ASHRAE, 1994).
In view of that, an investigation is required into alternative heating/cooling cycles, which can
be adapted and optimised to suit the limitations and requirements of alternative energy sources.
Contained within this dissertation are the thermodynamic and mechanical designs required for the
heat exchangers of an aqua-ammonia absorption-desorption cycle. The study includes an extensive
theoretical background and literature review, which led to the further investigation of the
thermophysical properties of aqua-ammonia refrigerant. Furthermore, the oeuvre includes the
verification and validation of the thermodynamic design and rating model for seven heat
exchangers, which are required to fully optimise the coefficient of performance of the aqua-ammonia
absorption-desorption cycle. The software package MS Excel was used to code the preliminary
thermodynamic design model, after which the software package EES was utilised to verify that the
preliminary thermodynamic design model had no mathematical errors. Validation of the
thermodynamic design models came in the form of predicted overall heat transfer coefficient values
versus typically expected overall heat transfer coefficient ranges. Where the typical Uc ranges have similar or near identical heat exchanger configuration to that of the thermodynamic design models in
this dissertation.
The mechanical design isn’t directly related to the main focus of this study, but does form an
integral part of the overall design of aqua-ammonia heat exchangers and is included in the scope of
work. The mechanical design includes the necessary first principle considerations to ensure the safe
operation of the heating and refrigeration package unit | en_US |
