# Enhancement of Heat Dissipation from the Hydraulic System Using a Finned Adaptive Heat Exchanger
## 3 Results and Discussion
(**a**) At the inlet of the adaptive heat exchanger; (**b**) at the outlet of the adaptive heat exchanger. The non-steady state in the 5 to 7 min time period was caused by inertial flow after pump shutdown and pressure changes in the system. A longer time (more than 5 min) after pump shutdown would result in a gradual equalization of the inlet and outlet temperatures of the AHE. In practice, a circulating flow system is used in which heat increases due to the influence of the hydraulic equipment connected to it. The heat flow distribution, calculated from the Equation (1), during the cooling process with and without oil flow through the circuit is shown in Figure 6. The AHE installed in the circuit caused an increase in heat flow of 0.85% to 46.53% compared to the circuit without AHE at forced flow. On average, there was an improvement of 19.79% from the second minute of the cooling process at forced flow. At the same time, the AHE with the thermal conductive paste achieved a higher heat flow by 0.67% to 50.75% and 1.39% to 50.50% compared to the AHE without the thermal conductive paste, and the circuit without the AHE at forced flow. On average, there was an improvement of 24.93% and 20.49% at forced flow (Figure 6a). Although the hydraulic circuit without oil flow achieved higher heat flow values (Figure 6b), in practice we cannot consider a hydraulic system without oil flow. The extended heat exchange surface of the AHE ensured a more intensive heat dissipation from the hydraulic pipe surface compared to a system without AHE. Figure 5: Temperature differences distribution during the cooling process. (**a**) Oil pump on (0 to 5 min); (**b**) oil pump off (5 to 10 min). Surface temperatures on the pipes at the inlet and outlet of the AHE, \(T_{s,in}\) and \(T_{s,out}\), are shown in Figure 7. The temperature differences of the inlet and outlet surface temperatures for the hydraulic circuit without AHE reached low values of 0.5 \({}^{\circ}\)C to 1.9 \({}^{\circ}\)C. In contrast, installing AHE in the hydraulic circuit resulted in an increase in \(\Delta T_{s}\) to values of 2.3 \({}^{\circ}\)C to 8.1 \({}^{\circ}\)C. The AHE with thermal conductive paste achieved \(\Delta T_{s}\) in the range of 2.5 \({}^{\circ}\)C to 8.3 \({}^{\circ}\)C, which represents only a slight increase compared to AHE without thermal conductive paste. From the distribution of the inlet and outlet surface temperatures, it is evident that heat transfer is improved by AHE and AHE with thermal conductive paste compared to the hydraulic circuit without AHE. The distribution of the overall heat transfer coefficient, \(U\), calculated according to Equation (2) is shown in Figure 8. At the beginning of the cooling process, the hydraulic system without AHE achieved the highest value of the overall heat transfer coefficient (\(U=721.66\) W/(m\({}^{2}\cdot\)K)). In contrast, the hydraulic system with AHE reached the lowest value (\(U=448.31\) W/(m\({}^{2}\cdot\)K)). With the increase in cooling time, there was a gradual decrease in \(U\) for the hydraulic system without AHE. From the cooling time of 0:03:00, the cooling process can be considered as a steady state, and the hydraulic system with AHE achieved 1.3 times and 2.2 times higher the overall heat transfer coefficient at 0:05:00 compared to the AHE with thermal conductive paste and the system without AHE, respectively. Figure 6: Heat flow distribution during the cooling process. (a) Oil pump on (0 to 5 min); (b) oil pump off (5 to 10 min). The practical benefits of the AHE design and research include the possibility of additional heat removal from the hydraulic circuit, which has a wide range of positive effects on the operation of hydraulic systems. The working fluid (oil) is protected from degradation due to increased heat dissipation from the circuit because of the increased heat exchange surface. The AHE can be effectively used in systems where working fluids overheat due to high pressure or friction.