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tube styles and materials for testing simultaneously – typically laboratories only have small single tube testing facilities .
“ Through the windows located at the front and back of the unit , the high speed camera that forms part of the setup allows us to study various effects and factors , and we can understand the particular refrigerant ’ s boiling process and heat transfer dynamics . This rig is designed particularly for hydronic systems where the refrigerant cools a liquid and then the liquid gets dispersed to end points in the system . The rig simulates actual industry conditions very accurately . We can set exact temperatures , look at pressures and also measure flow rates . This all adds to the uniqueness of our system ,” Bock adds .
Big Betha is operated using the heated water and chilled glycol supplied by a rooftop heat pump and chiller system donated by a long list of industry collaborators , namely Satchtech , Danfoss , CIAT , KSB , Intramech and Tactical Fluid Industries .
“ Our university facility was particularly built with the intention of testing competing technology . Falling film evaporators are very similar to flooded evaporators , just with a simple modification in that we ‘ drizzle ’ refrigerant on the outside of the tubes . So now , instead of just boiling the refrigerant in a pool , like a pot of water , you have a thin layer of liquid on the outside of the tubes , and the boiling then happens in that thin film of liquid . Because you don ’ t have to fill the shell with refrigerant , you can reduce the refrigerant volume needed by 40 to 50 % in a system , and a lower refrigerant charge means you have less risk to both people and the environment . We can test various tube surfaces which allows us to determine the heat transfer coefficients of each type as well as the impact of changing any conditions ,” Bock continues .
Currently the rig is working with refrigerant R134a . The reason for this is that a significant amount of data already exists on this refrigerant , its properties and working conditions – to ensure the rig ’ s test results are within the same ranges as other reported tests . However , this unique equipment can accommodate many other refrigerants for testing , with plans afoot to begin testing with the next generation of HFO ( Hydrofluoroolefins ) refrigerants such as R1234ze or R1233zd ( E ), either by themselves or in blends such as R452A or R513A
This testing facility will allow for South Africa to stay up-todate with the latest in global refrigeration trends and ensure our local capabilities do not fall behind our overseas competitors .
“ If we can look at the heat transfer coefficients under all of the conditions , we can find the best possible parameters . Designers can then use the data we ’ ve produced using this facility to design refrigeration systems with the correct tubes and refrigerant conditions that provide the most efficient heat transfer possible ”, Bock notes .
A demonstration of the falling film technique – or drizzle of refrigerant over textured tube bank .
The University of Pretoria is very open to collaborate with industry on any research needs . “ This rig is designed for industry relevant testing , and perfectly suited to the full research and development spectrum that includes the commercialisation of products , rather than only studying the fundamentals . This technology will help industry to optimise their designs . So I encourage any role players interested in testing tubes or refrigerants to engage with us so that we can help solve their challenges while learning ourselves . Particularly for South Africa , having access to this type of technology is a big opportunity to potentially boost local industry by optimising designs and gaining competitiveness in the global arena .” concludes Bock .
Should you wish to engage with Dr Bock , please email bradley . bock @ up . ac . za for more information . RACA
" The University of Pretoria is very open to collaborate with industry on any research needs ."
www . refrigerationandaircon . co . za RACA Journal I October 2022 5