Aus Wissenschaft und Forschung 30 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 1 Introduction The vehicles of the future will require higher voltages of 400 volts than current models need of 12 volts and 40 volts. The global fluids market[1] for electric vehicles(EVs) encompasses three major types of electric vehicles which are hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). These vehicle types are present in the form of both passenger cars and commercial vehicles. Battery electric vehicle (BEV), is set to dominate the EV fluids market as it is powered solely by the battery systems in the vehicle, which makes it more crucial for automotive OEMs to ensure that the fluids in the EVs are able to optimize the thermal management and driving system. The prominent types of fluids which are being adapted for enhanced application in electric vehicles are greases, heat transfer fluids, driver system fluids, and brake fluids. The Heat transfer fluids market is anticipated to be the largest as the need for coolants in electric vehicles is very critical to cool the battery and increase its driving range. Many prominent EV manufacturers have adopted indirect liquid cooling for example Tesla, and GM in North America. Currently, shelf coolants used for ICE are being used in many EV vehicles for indirect cooling. One of the challenges is absence of ASTM test methods for evaluating EV coolants. This has led to many coolant manufacturers to use modified current ASTMD1384 methods and develop some in-house test methods. Moreover, these fluids need several other characteristics that distinguish them from products in ICE vehicles: compatibility with copper coiling, aluminum and polymer coating and ability to withstand electrical currents. These fluids must dissipate the large amounts of heat generated by EV batteries. The EV coolant formulation should also have electrical properties like electrical conductivity in certain range depending upon the battery configuration of particular EV. Author’s Lab, has been engaged in the unique and ongoing research current in engine coolant technology sin- Development of Next Generation EV Coolant Govind Khemchandani* Research indicates that there are two approaches to Electric Vehicle (EV) liquid cooling: direct and indirect. Direct liquid cooling involves direct contact between the coolant and the battery pack. Indirect liquid cooling requires a medium in between the battery pack and the coolant, preventing direct contact. Many prominent EV manufacturers have adopted indirect liquid cooling for example Tesla, and GM in North America. Currently, shelf coolants used for Internal Combustion Engines (ICE) are being used in many EV vehicles for indirect cooling. One of the challenges is absence of ASTM test methods for evaluating EV coolants. Some operators have used copper wires for generating deposits by employing voltage to test low conductivity EV coolants. Dober long ago realized that copper and aluminum will be the main components of EV engines hence used copper wire under high temp and pressure to show differentiation among coolants. The present paper focuses on Dober-in-house test Parr reactor methodology for comparing electrical conductivities, pH and additive depletion of various coolants thereby showing meaningful trends with time and temperature. This ultimately helps in developing new generation EV coolants. It is concluded that low electrical conductivity along with robust corrosion inhibition package is needed for optimum performance of EV coolants. Keywords Electric Vehicle, EV coolants, liquid cooling, shelf coolants, Combustion Engines Abstract * Govind Khemchandani, Ph. D. Dober Chemical, Woodridge, IL, USA https: / / www.dober.com/ performance-fluids Figure 1: Parr Set Up left & copper wire on cooling coil right ce last 30 years. Much of the work focuses on coolants suitable for engine coolant system components used in ICE [2] and EV engines. Dober in-house Parr Reactor method is used in this paper for comparing indirect EV coolants. 2 Experimental Five coolant samples were chosen which are currently being used in EV indirect cooling. These are coded as 1. D1 EG Premix50/ 50 2. G1 EG Premix50/ 50 3. J1 EG Premix50/ 50 4. V1 EG Premix50/ 50 5. D2 EG Premix50/ 50 Experimental set up is shown in Figure 1. The test conditions used are as below: • Temperature: 150 °C (302 °F) • Pre-charge of Air: 90 PSI • 10 feet copper wire • Duration: 2 weeks • Sample withdrawal intervals: 7,14, and 20 days • Measurement parameters: pH, conductivity, and color change These parameters were considered since earlier [2] authors from Fleetguard and Dober developed this method to model primarily the thermal stability of heavy-duty coolants in 300 K to 400 K miles of actual service. Three bench methods viz. Modified Reaction Kettle [3], ASTM D 2272 and Modified 4340 test [4] were chosen for comparison with Parr method. Parr tests were able to differentiate the quality of coolants and glycols. Results were consistent with field experiences and it was found to be the best of the four tests studied in this paper. Our aim is to study how corrosion inhibitor package used in these five coolants affect electrical conductivity and changes occurring in pH with time and temperature. 3 Description of the Method A total of 1,200 mL EG 50/ 50 Premix solution was added into the Parr reactor cylinder. A ten feet copper wire was wrapped around the cooling coils so that the copper wire would be in contact with the test solution. The reactor head was placed on top of the reactor cylinder and the reactor split ring collar was tightened. The type J thermocouple was placed into the reactor head’s thermowell. To start the test, the display, motor, and heater were turned on. The motor speed was set to 40 % maximum for good mixing and the temperature was set to 150 °C (302 °F). Air pressure is about 25 psi, generated from the heating of the coolant. The test lasted for 20 days. Samples were collected at 163, 331 and 482 hours. Samples were measured for pH per ASTM D 1287, electrical conductivity (CY) per ASTM D 1125, copper, and glycol degradation acids (formic and glycolic). After each sample collection, heat was stopped, and the test solution was cooled with cold water to 25 C. Subsequently, the reactor was refilled with air by pumping air through the reactor for 20 minutes before the heat was turned back on to continue the test. Measurement results of pH and CY are shown in Table1. Table 1 shows the experimental data collected during this investigation for the five coolants. During this investigation coolants J1 and D1 were also sent to an external lab for testing by so called copper wire test [5]. Both samples passed the copper wire precipitate test. However, J1 was claimed to be approved by OEM due to the lowest electrical conductivity of 116.3 µS/ cm while D1 is being used by buses successfully despite higher conductivity. It was reported that there were corrosion issues during the field trials of J1. Method used was as below: 1. Remove the rubber cover of electric wire 2. Put it in liquid to be tested 3. Apply 50V for 15 minutes 4. Check for precipitation on wire Both samples J1 and D1 were tested for glassware corrosion per ASTM D 1384. Comparison of the test results is shown in Table 2. Aus Wissenschaft und Forschung 31 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 D1 G1 J1 V1 D2 Hrs. CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH CY (μS/ cm) pH 0 3,370 8.22 3,540 8.00 116.3 7.33 2,667 8.79 1,967 8.33 163 3,470 6.40 3,530 7.13 239.0 3.99 2,767 6.70 2,042 5.99 331 3,560 5.97 3,610 6.43 290.1 3.70 2,998 6.01 2,119 5.26 482 3,690 5.74 3,720 5.98 636.0 3.63 3,130 6.01 2,275 4.76 Table 1: Electrical Conductivity & pH Aus Wissenschaft und Forschung 32 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 4 Results and Discussions Figure 3 and Figure 4 shows electrical conductivity and pH data of all the five samples. The electrical conductivity of the liquid coolant becomes important in a direct cooling application because of the contact between the coolant and the electronics [6]. However, in indirect cooling applications the electrical conductivity can be important if there are leaks and/ or spillage of the fluids onto the electronics. In the indirect cooling applications where water- Figure 2: Copper wire Deposit Test Type of Metal Sample J1 Sample D1 ASTM D Limits MAX Copper 35.47 1.27 10 Solder 50.20 0.88 30 Brass 56.72 2.07 10 Steel 329.33 -0.07 10 Cast Iron 686.67 -1.00 10 Cast Aluminum -4.72 9.27 30 Table 2: comparison Metal corrosion ASTM D 1384 -100,00% 0,00% 100,00% 200,00% 300,00% 400,00% 500,00% 0 100 200 300 400 500 Percent Change in Conductivity Hours Percent Change in Conductivity G1 D1 J1 V1 D2 Figure 3: Percent change in conductivity based fluids with corrosion inhibitors are generally used, the electrical conductivity of the liquid coolant mainly depends on the ion concentration in the fluid stream. Higher the ionic concentration, larger is the electrical conductivity of the fluid. The increase in the ion concentration in a closed loop fluid stream may occur due to ion leaching from metals and nonmetal components that the coolant fluid is in contact with. During operation, the electrical conductivity of the fluid may increase to a level which could be harmful for the cooling system. Comparison of J1 and D1: CY of J1 starts increasing immediately during the start of the Parr reactor test and by the end of 450 hours it attains the highest CY of 450 %. Under the same test conditions D1 and other coolants CY remains below 25 %. All these coolants are being used as indirect coolants and corrosion issues were reported by users of J1. It is interesting to note that initial pH of J1 is lower than all other coolants. However, after 482 hours it has the highest drop in pH. Simultaneously ASTM D 1384 test data for J1 show high failure rate with respect to copper, brass, solder, cast iron and steel. ICP analysis of J1 and D1 has shown differences in copper and iron wear indicators. Copper in J1 was found to be 206 mg/ l vs. D1 of 8.2 mg/ l. In D1 iron was absent while J1 showed 90 mg/ l. Parr reactor experiment clearly indicates that an increase in the electrical conductivity of the coolant fluid is contributed by ion leaching of both metals. On the other hand, G1 has the lowest drop in pH and lowest rise in CY. It can be hypothesized that there exists some correlation between pH and stability of CY besides the individual robust corrosion package quantity and quality used in these formulations. Authors lab has done further research using parr and developed lowest CY coolant for fuel cell application. These findings will be the part of next series of this project. References [1] Global Fluids and lubricants market for electric vehicles, BIS research,2020 [2] Yu-Sen Chen et al., Comparisio of bench test methods to evaluate heavy duty coolant thermal stability, Journal of Testing and Evaluation, May 2006, ASTM [3] Alkesei V. Gresham et al., Predictive tool for coolant development, ASTM STP 1335,R.E. Beal, ED. [4] Edward et al., A chemical base for engineering coolant/ antifreeze with improved thermal stability properties, SAE Technical Paper Series, 2001-01-1182 SAE,PA, 1996 [5] Internal communication, Chulwoo Park, Bullsone Co. [6] Bojanna Shantheyanda et al., Tech Brief - Low Electrical Conductivity Liquid Coolants for Electronics Cooling, www.electronics-cooling.com, 2015 Aus Wissenschaft und Forschung 33 Tribologie + Schmierungstechnik · 69. Jahrgang · eOnly Sonderausgabe 1/ 2022 DOI 10.24053/ TuS-2022-0029 -60,00% -50,00% -40,00% -30,00% -20,00% -10,00% 0,00% 0 100 200 300 400 500 Percent Change in pH Hours Percent Change in pH G1 D1 J1 V1 D2 Figure 4: Percent Change in pH