# Enhancement of Heat Dissipation from the Hydraulic System Using a Finned Adaptive Heat Exchanger
## 2 Materials and Methods  
The designed adaptive heat exchanger (AHE) installed in the hydraulic circuit is shown in Figure 1. The heated working fluid (hydraulic oil) flowing through the hydraulic pipes (1) is cooled by the AHE. The main part of the AHE is a pair of flanges (2, 4) that encircle the outer wall of the pipe. The upper flange (2) is ribbed on the sides and in the centre and ensures continuous heat dissipation from the surface of the AHE. The lower flange (4) without ribbing was enclosed to the upper flange (2) from the opposite side. The fixing of the flanges to the pipe was secured by means of a clamping joint, which was formed after tightening the M6 (3) tightening screws. Due to the length of the hydraulic pipe on which the AHE was mounted, it was also possible to vary the number of heat exchange segments. The individual segments were connected to each other by means of hinges with opposing pins (5), into which brass connecting pins (6) were inserted. When a change in the design length of the AHE was required, the connecting pins (6) must be pushed outwards from the hinges (5). After the flow of the working fluid through the pipeline with the fitted heat exchange segments, the cooled fluid exits further into the hydraulic circuit (to the pump, tank...). The fluid in the hydraulic circuit was heated continuously during the operation of the machine or equipment to an operating temperature that varied depending on the load. The optimum working temperature of hydraulic oil used in construction machinery is in the range of 40 \({}^{\circ}\)C to 70 \({}^{\circ}\)C. The optimal operating temperature is 50 \({}^{\circ}\)C. When the hydraulic oil is heated above 90 \({}^{\circ}\)C, the negative hygroscopic properties of the oil are greatly increased, causing degradation. In addition to oil degradation, most of the polymers contained in hydraulic seals and hoses also degrade (loss of elasticity). The quality of the hydraulic oil and the condition of the cooling system play an important role. The hot oil reduces the efficiency of the hydraulic system and causes leaks (damage to rubber seals, loss of sealing effect), which also reduces the working pressure and causes the oil to heat up more. The chemical reactions that take place in hydraulic oils are oxidation due to the presence of air, and hydrolysis due to the presence of water. For this reason, an important factor is the chemical stability of the oil, which is determined in terms of resistance to the oxidation in which oil molecules and oxygen combine, which also results in a visual change through the oil \"darkening\" [21]. Oxidation also results in a change in acidity, viscosity, and the disappearance of additives, causing, for example, a decrease in operating pressure and a change in machine operation [22]. If the hydraulic oil is continuously subjected to high heat loads, oxidation products are formed in a short time, which stress the pump. If they are not removed (e.g., filling change), these products will start to settle on metal surfaces (pipe walls, tanks) and will build up additional layers of dirt which will restrict the flow of the fluid. According to  
Figure 1: The adaptive heat exchanger mounted on the hydraulic pipe (dimensions are in mm). (a) Assembly of six heat exchange segments; (b) cross-section of the heat exchange segment. A—inlet of the oil, B—outlet of the oil, 1—hydraulic pipe, 2—upper finned flange, 3—tightening screw, 4—bottom flange, 5—hinge, 6—connecting pin. studies, 70-85% of hydraulic system failures are due to unfavourable oil conditions [23]. This percentage is mainly made up of soft contaminants and water, i.e., oxidation products of the oil and reaction products of oil additives. A smaller part is made up of hard dirt, which includes, for example, metal, dust, or abrasives. In the machines and equipment there is lack of assembly space around the individual components.