# Enhancement of Heat Dissipation from the Hydraulic System Using a Finned Adaptive Heat Exchanger
## 3 Results and Discussion  
The experimental research was focused on determining the efficiency of heat removal from the hydraulic circuit using a new design type of adaptive heat exchanger (AHE). The distribution of oil temperatures at the inlet and outlet of the AHE during cooling process is shown in Figure 4. A comparison was realised for hydraulic circuit with AHE, without AHE, and AHE with contact surfaces covered with copper-based thermal conductive paste for the inlet oil temperatures \(T_{in}\) (Figure 4a) and outlet oil temperatures \(T_{out}\) (Figure 4b). In addition, the effect of oil flow through the hydraulic circuit was also evaluated. Oil circulated in the hydraulic circuit from 0 to 5 min, followed by cooling without forced oil circulation from 5 to 10 min. From the distribution of the inlet and outlet oil temperatures the significance of the AHE used in the circuit can be observed. The inlet oil temperatures for hydraulic circuit without AHE achieved values 1.98% to 6.86% higher compared to a circuit with AHE, and 0.59% to 7.39% higher compared to AHE with copper-based thermal conductive paste. The outlet oil temperatures for hydraulic circuit without AHE achieved values 0.17% to 8.87% higher compared to a circuit with AHE, and 0.74% to 10.78% higher compared to AHE with copper-based thermal conductive paste. The differences between AHE with and without thermal conductive paste were minimal in the range of values 0.14% to 1.75% and 0% to 3.79% for \(T_{in}\) and \(T_{out}\) depending on oil flow, respectively. With the oil pump on (0 to 5 min), AHE with thermal conductive paste achieved higher values by 0.14% to 5.63% and 0% to 3.79% for \(T_{in}\) and \(T_{out}\) compared to AHE without paste, respectively. However, without forced oil flow (oil pump off) the effect was the opposite; AHE without thermal conductive paste achieved higher values by 0.5% to 1.75% and 0.04% to 2.58% for \(T_{in}\) and \(T_{out}\) compared to AHE with paste. Figure 3: Installation of an additional heat exchanger in the experimental hydraulic circuit. 1—additional heat exchanger, 2—hydraulic pipe, 3—hydraulic oil filter, 4—hydraulic oil reservoir, 5—heating spiral, 6—gear pump, 7—power supply, 8—pipe surface temperature sensor, 9—oil temperature sensor at the inlet to the AHE, 10—oil temperature sensor at the outlet of the AHE, 11—flow meter, 12—data-logger. The distributions of temperature difference during the cooling process for oil pump on (Figure 5a) and oil pump off (Figure 5b) had a decreasing character from 0 to 5 min and increasing character from 5 to 10 min with cooling time. At the beginning of the cooling process, between 0 min and 1 min 20 s, the process gradually settled to a steady state. From 1 min and 20 s onwards, the temperature differences reached approximately the same values until 5 min, when the oil pump was in operation (Figure 5a). From Figure 5a it can be observed that the temperature differences \(\Delta T\) in the range of 1.79 \({}^{\circ}\)C to 1.09 \({}^{\circ}\)C, 1.76 \({}^{\circ}\)C to 0.97 \({}^{\circ}\)C, and 1.87 \({}^{\circ}\)C to 1.35 \({}^{\circ}\)C, for the hydraulic circuit with AHE, without AHE, and AHE with thermal conductive paste. In addition, the oil pump generated heat and pressure on the oil by its action, which increased the temperature in the circuit. After switching off the oil pump from 5 to 7 min, a gradual steady-state condition was reached, from which point the temperature differences no longer varied significantly within 10 min. From Figure 5b a steady state \(\Delta T\) can be observed from 7 to 10 min in the range of 4.59 \({}^{\circ}\)C to 4.24 \({}^{\circ}\)C, 3.88 \({}^{\circ}\)C to 3.48 \({}^{\circ}\)C, and 4.77 \({}^{\circ}\)C to 4.48 \({}^{\circ}\)C, for the hydraulic circuit with AHE, without AHE, and AHE with thermal conductive paste. Figure 4: Oil temperature distribution during the cooling process with oil pump on (0 to 5 min) and oil pump off (5 to 10 min).