Hydraulics & Pneumatics January/February 2023

HYDRAULICS 32 HYDRAULICS & PNEUMATICS January/February 2023 www.hpmag.co.uk One of the most common questions I am asked at training sessions and in sales meetings with clients is “Which is better – air-cooled or water-cooled?” The simple answer is that an adequately designed heat exchanger – be it water-cooled or air-cooled – is capable of removing the desired amount of heat. In my 30 years as a practicing industrial hydraulics engineer, I have used both extensively. To truly answer this question, we need to understand the basics and dig deeper. Why do machines heat up? No energy-consuming machine or system is 100% efficient. Though most of the energy consumed by a machine is used to do useful work, a part of the energy gets converted into heat. If this heat is not managed properly, the temperature of the equipment keeps increasing till it overheats. This causes irreparable damage, which in turn reduces efficiency further. The result is increased power consumption, reduced equipment life, breakdowns and increased maintenance costs. To help in managing the heat generated, most equipment – hydraulic systems, gearboxes, spindles, large electrical transformers, engines, compressors, turbines, vacuum pumps, generators, blowers – use industrial oils and coolants to lubricate, cool and keep the temperatures in check. This is done using heat exchangers or oil coolers. Oil coolers are used to cool these fluids by passing them over a cooler Heat exchangers – Water-cooled or air-cooled? fluid, separated by a barrier to prevent intermixing. They remove excess heat generated by energy losses in a system. In fact, oil coolers are essential for designing temperature-optimized machines or systems that keep oil temperatures within a limited range. They are basic prerequisites for cost-efficient operation, as they provide a number of performance enhancing, economic, and environmental benefits. In industry, various types of cooling media are used to transfer heat from cooling oils and lubricants e.g. water, air, refrigerants and hydrogen. Of these, we will discuss primarily the two types of cooling media that are most commonly used and readily available, with a relatively low cost viz. air and water. Air-cooled oil/fluid coolers In air cooled oil coolers the hot oil or fluid is passed in close proximity to a blast of ambient air. See Fig 1. The heat exchange takes place across a barrier between the hot oil and cool ambient air. There are predominantly two types of air-cooled coolers. tube fin-type and plate fin-type air-cooled oil coolers. Hot fluid enters the heat exchanger through an inlet header or tank via the inlet port. From the inlet header it is distributed through round or rectangular tubes, where the heat dissipation takes place. The cooled fluid is then collected in an outlet manifold called the outlet header or tank, finally exiting through the outlet port. Tube-fin oil coolers These are usually tubes with fins on the outer surface. The hot fluid flows through the round tubes transferring heat to the tube wall which in turn transfers heat to the fins attached to the outer surface of the tube. The fins are cooled by a draft of forced air. This type of oil cooler generally By Vineet Taneja, CEO, Ace Automation Engineers. Vineet Taneja: An adequately designed heat exchanger – be it water-cooled or air- cooled – is capable of removing the desired amount of heat. Fig 1: Air-based oil cooling system.