INDUSTRIAL COOLING
t he chloride based solutions attack metal, and both potassium acetate and potassium formate attack zinc. Hence, any material containing zinc and zinc alloys, such as galvanised surfaces, should be avoided.
Maintenance
A full maintenance programme must be incorporated as part of the design in order to ensure that the concentration level as well as the fluid corrosion protection ability is maintained throughout the useful life of the fluid. Health and safety issues: For applications w here human contact is a possibility, or for food applications, it is best to consider non-toxic fluids such as organic salts, propylene glycol and glycerol.
Phase change secondary refrigeration applications like ice slurry (6) and carbon d ioxide have been successfully applied for both commercial and industrial applications but they are excluded from this paper which remained to cover only heat transfer system without any c hange of phase i.e. solid-liquid or liquid-gas. I t is clear that no single secondary refrigerant is i deal for every type of application, and therefore designers must find the best solution for the
application on a job by job basis based o n temperature range and application. A queous solutions generally require l ess volume flow rates in comparison with non-aqueous solutions, in order to transport the identical cooling capacity. However, they are relatively difficult to e liminate corrosion risks in particular with salt based solutions. It is vital t o achieve an air-free installation in order to avoid any potential corrosive problem.
Designers must compare the corrosivity, environmental pollution,
t oxicity, and flammability, site handling and cost i ssues along side the thermophysical properties of t he intended secondary refrigerants.
Practical applications in the field indicated that the new high performance salt based such as potassium acetate and potassium formate based solutions require very careful handling and the corrosion issues must be addressed very carefully. It is observed that some of the sites in particular with warm solution defrost systems suffered excessive and rapid corrosion problems less that a few months.
It is essential to keep a site record regarding
s tandard concentration and fluid quality reports as part of the regular maintenance checks and take the necessary modification works for major problems before they become a major problem. Finally, it is vital to establish a reliable supply chain for any new type of secondary refrigerants a nd some of the sites in Europe used imported fluids but suffered badly when there was a major leakage, hence, it is vital that both consultants and end-user ensure that a full charge of the system either kept on site or alternatively kept b y the supplier at all times for any critical refrigeration applications
DAPUK
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