Feature
even means that fewer plates are required per pack without losing out on performance .
New designs also incorporate asymmetric channels that optimize thermal efficiency , resulting in up to 30 % higher efficiency and reduced fouling . In other words , it helps provide long-term , cost-effective , and quality performance .
Further innovations come in the form of plate patterns which improves flow and distribution , so the risk of fouling and unplanned downtime is considerably reduced . This saves customers on time , energy and maintenance costs . Moreover , new welding techniques and flow assistance designs have been developed . RACA
CO2 SYSTEMS IN HEX INDUSTRY By Marius La Grange
In the last 10 years the “ CO 2
Equator ” has shrunk dramatically thanks to ever increasing operating pressures and new components becoming freely available to the commercial refrigeration sector . The “ CO 2
Equator ” is significantly smaller than before with trans-critical systems capable of operation in extremely warm ambient temperatures at the cost of a lower COP .
The operating COP thus being a deciding factor and much ongoing development going towards improving all important COPs at extreme ambient conditions . The competitive COP ’ s trans-critical systems being a driving factor towards the rapid application rate . Fewer discussions revolve around COP , but the installation cost remains higher for R744 trans-critical systems when compared to similar HFC applications .
Many retailers in SA have made the switch to trans-critical systems for new installation and this clearly indicates that the operational benefits outweigh the premium in most applications . The very competitive retail sector being a fertile soil for innovation and application trails , and of course a big consumer of energy .
To newcomers , we first need to answer the question “ what is a trans-critical ” refrigeration system ?” Figure 1 will assist in order to get a better grasp of these applications . CO 2 or R744 has a comparably low critical temperature of 31 ° C . The critical temperature for most HCFC & HFC refrigerants being 30 to 60 ° C warmer . R22 has critical temperature of 96 ° C and for R404A if is 72 ° C . So , what does this mean ? If you needed to condense the discharge gas from a R404A system and the ambient air available ( the cooling medium ) was 48 ° C ( much lower than the critical temperature for R404A of 72 ° C ) it is hopefully immediately apparent that it is feasible since the ambient air is very warm to any human but significantly cooler than the refrigerant ’ s critical temperature . The same would not be true for an R744 system .
ARTICLE SOURCES : 1 . Alfa Laval 2 . Danfoss 3 . Evapco 4 . Food Processing History 5 . HC Heat Exchangers
Figure 1 - Ph-chart
Rejecting heat energy and condensing the R744 would not be possible with ambient air of 48 ° C in a similar process . This is the great problem solved in the last 20 years with the development of trans-critical technologies . One being that traditional air-cooled condenser was developed into a device capable of much higher operating pressures . Hence from a distance they seem very similar to traditional air-cooled condensers .
In case you are not familiar with concept of the critical point – it is the temperature above which it is not possible to liquefy ( condense ) the refrigerant . Why is this relevant ? The short answer is that a refrigeration expansion process requires the refrigerant at high pressures and in a liquid state . Heat absorption / cooling ( with the refrigerant gaining enthalpy / boiling off ) takes place with the liquid refrigerant changing phase and “ evaporating ” as the main purpose for having a refrigeration installation offering the required cooling effect with vapour drawn back the system ’ s compressor .
The aspect of CO 2 gas cooler design , function and installation will be covered in a technical article in the following issue of RACA Journal .
6 . Johnson Controls 7 . Market Reports 8 . Oak Ridge National Laboratory 9 . Science Direct 10 . Thermocoil https :// www . ohio . edu / mechanical / thermo / property _ tables / CO2 / ph _ CO2 . html
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RACA Journal I January 2023 www . refrigerationandaircon . co . za