Study Of Nanofluids Heat Transfer Performance In High Temperature Condition Based On Vehicular Cooler

Following the specific power's enhancement of modern engines, conventionalengine coolants gradually can not meet the high heat loads of vehicle cooling systems.The appearance of nanofluids offers a new available approach for cooling systems andheat exchangers, and is becoming a new direction for engineering heat transfer.In this paper, over 300 varieties of nanofluids formulation have developed, andtheir suspension stability, thermal conductivity (k), specific heat capacity (C),dynamic viscosity (η) are all experimentally and theoretically studied in detail.Models of the k, C andηare respectively developed based on the micro-mechanism.These models are significant for designing nanofluids for special intents. The highboiling point & high thermal conductivity nanofluids have been selected from theformulations. Applying these nanofluids, the high temperature-low temperaturedifference (HTLTD) heat transfer tests have been done on certain vehicle oil cooler toverify the feasibility and validity of the nanofluids compared with water andconventional coolant.The suspension stability tests are based on the still layered and TEM figure, and theresults show that the suspension stability of nanofluids are seriously related to theproperties of nanoparticle, basefluid, dispersant and supersonic vibration. The generallaw is that low particle concentration, little particle dimension, high basefluidviscosity help to suspension stability.The transient-hot-wire technique systems were carefully self-designed to measurethe thermal conductivity of nanofluids. The results show that the thermal conductivityof nanofluids increases with the particle volume fraction and suspension situation,while decreases with the particle dimension. Based four micro-mechanisms: themicro-dimension effect, congregating of particles, micro-interface of solid-liquid andmicro-convective in the mixture system, the thermal conductivity model wasdiscovered for the low concentration nanofluids.The specific heat capacity of nanofluids has been investigated applying thecomparative heat capacity systems self-designed. The results show that nanofluidsheat capacity is lower than that of basefluid, and decrease with the particle volumefraction; meanwhile, the source of the decrease is concluded to develop the specificheat model for low concentration nanofluids.Applying the rotary viscometer, the viscosity of nanofluids is tested. The resultsshow that the viscosity is affected by the temperature, particle volume fraction andsuspension stability. Based on the Einstein solid-liquid mixture's viscosity equation,the nanofluids viscosity model was deduced from the test values.The heat conduction enhancement can be owing to two factors: static and dynamicmechanisms. The static one is from the optimization of thermal conductivity and thedynamic one is from the thermal dispersion and particle collision because of theparticle's Brownian motion in the nanofluids system. The collision between theparticles and the particle and the wall will lead to energy loss and conversion, whichis a fundamental factor to improve the thermal performance of nanofluids. Apply theFLUENT software to numerically simulate a vehicle oil cooler and the results show that nanofluids have a bigger heat flow, higher heat transfer coefficient than theirbasefluids.The high temperature, low temperature difference, low fluid flow, high precisionthermal performance test rig for nanofluids as the coolant is developed. Based on atypical oil cooler, the heat transfer and pressure performances of the water andanti-freeze fluid at low T-big T difference (max. T of 90 degree for coolant, while max.T of 120 degree for oil) and nanofluids and their basefluid (max. T of 120 degree forcoolant, while max. T of 135 degree for oil) are tested respectively. The results showthat the nanofluids with above 5% volume fraction could meet the heat transfer needsof the heat exchanger; the nanofluids have higher heat transfer coefficient than water,anti-freeze fluid and basefluid; and the heat transfer efficient is improved with thevolume fraction of nanofluids; nanofluids have higher boiling point and worktemperature that water and coolant, which makes it can work at a relative lowerpressure or none pressure circumstance.Nanofluids have excellent thermal performance compared with the conventionalcoolants. The organic high boiling point-high thermal conductivity nanofluids in thisstudy will cause bigger temperature differences to the cool fluid in the radiator—thesurrounding air, which is profitable to the whole vehicular cooling system's efficiency.The basefluid which is organic is good to prevent corrosion and frost and protectenvironment. These properties are significant to vehicular cooling system. The studyin this paper could direct to design the high compact and efficient heat exchangers.The nanofluids could be envisioned to have a wide application in the engineering heattransfer field.