Performance improvement in automotive cooling system

Abstract

Due to the increasing power requirement and the limited available space in the vehicles, it is extremely difficult to increase the size of the radiator, placed in the front of the vehicles. A good engine cooling system can reduce the time of the engine start and warm up processes, in which the engine reaches its optimal working temperature and also reduces the hydrocarbon (HC) and carbon monoxide (CO), which are produced during the starting and warming up period. Improvements in the performance of the automotive radiator can be done by using alternative coolants of better heat transfer and pressure drop characteristics, various improved heat transfer fin surfaces, high thermal conductivity fin materials and by changing the position and orientation of the radiator. Hence, the present investigation focuses the detailed theoretical and experimental studies on the performance improvement of automotive radiator using alternative coolants (including proposed new coolant, optimum propylene glycol (PG) brine, fin surfaces, fin materials, radiator position and orientation. In this study, three types of alternative coolants i.e base fluids (water, PG, ethylene glycol (EG), sugarcane juice), nanofluids (Al2O3/PG brine, Ag Al2O3/EG brine) and hybrid nanofluids (0.5%Al2O3 +0.5%TiO2/PG brine and 0.5% Al2O3+0.5%CuO/PG brine) have been considered. Considered alternative coolants have been prepared and their thermophysical properties have been measured in laboratory and then compared with the theoretically predicted or the literature data. Among the base fluids, sugarcane juice exhibits better properties and 25% PG exhibits similar properties as water at higher temperature. Hence, 25% PG has been proposed as new emerging coolant and extensive theoretical, experimental and numerical studies have been discussed. xvi Theoretical performance enhancements of automotive radiator with considered alternative coolants, considered fin surfaces (rectangular, wavy and louvered), alternative fin materials (foam materials) and orientations have been presented. Theoretical results show that, the new proposed coolant optimum PG brine (25% PG) exhibits similar performance as water at higher temperature. However, among all the studied coolants, sugarcane juice as base fluid, PG brine based Ag nanofluids and PG brine based hybrid nanofluid have higher heat transfer rate, effectiveness and lower pumping power in louvered fin as compared to wavy and rectangular fin radiator for the theoretical analysis. However, carbon and graphite foam as radiator fin materials, result in higher heat transfer rate and effectiveness as compared to conventional radiator fin materials With respect to the radiator position configuration, CCFC (combination of cross and counter flow configuration) results in better performance from conventional and counter flow configurations for heavy vehicles. Experimentation for radiator performance on a wind tunnel based radiator set up shows that the heat transfer coefficient, heat transfer rate and effectiveness for water and optimum PG brine are nearly same. Also, the performance evaluation of cooling system with engine assembly using various coolants shows that the heat transfer rate and effectiveness are higher for PG brine based (0.5%Al2O3+0.5%TiO2) hybrid nanofluid coolant at engine full load. Fuel energy distribution analysis for the same full load of engine results in 33.2% enhancement in heat transfer to PG brine hybrid nanofluid. As compared to conventional coolant (25% EG brine) radiator core volume size deceases by 10% for PG brine based hybrid nanofluid. CFD simulations prove that the predicted 25%EG brine based silver nanofluid, possess higher pressure drop as compared to validated results of PG brine based radiator coolant.Use of nanofluids and hybrid nanofluids lead to reduction in radiator size, weight and cost, engine fuel consumption.