Hydraulics & Pneumatics January/February 2023

HYDRAULICS 34 HYDRAULICS & PNEUMATICS January/February 2023 www.hpmag.co.uk evident that we have a total loss of efficiency of 20% + 20%. In comparison if we look at an air- cooled oil cooling system, we have only one process. Again, assuming we have a well-designed process with an overall efficiency of 80%, there is a direct benefit of 20% in improved efficiency while using an air-cooled oil cooling system in comparison to a water based one. There are other important nuances that need to be considered. For instance, the cost of energy required to pump cooling water for the entire usable life of the equipment. There is also the cost of plumbing in the initial setup, coupled with the hidden cost of maintenance of the water pump and the plumbing. It is also noteworthy that the water needs to be treated to remove salts and minerals to achieve consistent heat exchange. Untreated cooling water is more often than not laden with salts and minerals. These too add their bit to a maintenance engineer’s woes. The salts and minerals present in the water deposit on the barrier between the two fluids, commonly known as scaling. Fig.4 shows scaling in shell – tube and gasket plate-type heat exchangers. Water scaling results in bad heat conduction. Therefore, the ability of the oil cooler to transfer heat reduces considerably over time, due to scaling. Water-based oil coolers therefore need to be descaled. As the water flows through the oil cooler, salts start depositing on the surface of the tube or plate barrier between the two fluids, through which the heat is being transferred. These salt or chemical deposits called scale (usually white or off- white in colour) build up over time. As a result, heat exchange reduces considerably. Water cooled heat exchangers therefore need to be serviced or descaled from time to time. The performance reduces with respect to usage time. The extent of loss in efficiency is dependent on the quality of water available at the site of usage. The amount and type of dissolved salts and minerals in the water determines the frequency of descaling (or servicing in case of gasket plate heat exchangers). These cost heavily, not only in terms of maintenance cost, but also the cost of gaskets/descaling chemicals, time, money and production loss due to repeated maintenance shutdowns. Air-based oil cooling system On the other hand, let’s look at an air- based oil cooling system. Here too there is a drop in efficiency with time, as dust and pollutants from the atmosphere deposit on the fin surface. The fins too need to be cleaned, but the cleaning process is simple and effective. A compressed air blast done regularly is enough to remove the dust build up. This cleaning can be carried out while the system is still operative and does not require a shut-down. Besides the above, an obvious advantage of an air-cooled oil cooler is that it does not require water, which means that equipment requiring cooling need not be near a cooling water connection or source. The machine can therefore be stand-alone. Just plug in the electrical power and we are good to go. On the contrary, every time a machine with a water-based oil cooling needs to be shifted or relocated, the water supply plumbing needs to be redone. Further, the problems associated with treatment and disposal of water have become more costly with government regulations and environmental concerns. Air-cooled or air blast or fan cooled oil coolers as they are commonly called provide means of transferring the heat from the fluid directly into ambient air, without environmental concerns and at a nominal running cost. Traditionally, water has been used for centuries as a cooling medium. However, annual water consumption in the world has reached astronomical figures. The increasing scarcity of fresh water resulted in the need for its recirculation. For it to be recirculated for cooling, the water needs to be cooled, which is done by cooling it with air. Newer technologies therefore evolved to increasingly use air directly as a cooling medium. Air-cooled systems dissipate heat with flowing air. These not only have the advantage of easy availability, higher reliability and lower running cost but are simpler to maintain. They also eliminate the problem of water contamination and minimise corrosion. www.aircooledoilcoolers.com Fig 4: Left and Right – Scale formation inside a water-cooled oil cooler.