Abstract
The heat loads on electronic systems of an unmanned air vehicle are a significant problem. So enhancing heat transfer is a critical key to solve these thermal problems. This study is focused on increasing heat transfer rate in a crossflow heat exchanger by using nanofluids numerically. Effects of different Reynolds number of hot fluid (Re= 6000, 8000, 10000, 12000), different inlet velocity (Vair,inlet=30, 45, 60, 90 m/s) of cooling fluid, temperature of cooling air at different altitude (Tair,inlet=15, 10, 4, -17℃) and different types of nanofluids (Cu-H2O, CuO-H2O, TiO2-H2O, H2O) on heat transfer were studied numerically. Realizable k-ε turbulence model of ANSYS FLUENT computational fluid dynamics code was used for numerical analysis. It was obtained that increasing Reynolds number from Re=6000 to 12000 causes an increase of 44.65% on average Nusselt Number. Increasing inlet velocity of cooling air from 30 m/s to 90 m/s causes an increase of 6.96% on average Nusselt number. Increasing or decreasing air inlet temperature at different attitude does not cause any significant change on average Nusselt number. Using Cu-H2O nanofluid, which shows the best performance, causes an increase of 6.63% on average Nusselt number according H2O. Numerical results were also compared with experimental results at literature. It was obtained that numerical model can represent experimental results in a good level.
Highlights
Unmanned aerial vehicles (UAVs) are frequently used to collect data in the fields of real estate photography, mapping & surveying, agriculture, atmospheric studies and so on
This study focused on enhancing heat transfer by using nanofluids for a cross flow heat exchanger of an Unmanned Air Vehicle
Effect of Re number of hot fluid on Nu number Effect of inlet velocity of the hot fluid as Reynolds number for Cu-H2O nanofluid on heat transfer is investigated
Summary
Unmanned aerial vehicles (UAVs) are frequently used to collect data in the fields of real estate photography, mapping & surveying, agriculture, atmospheric studies and so on. Due to compact size of UAVs, thermal management holds a unique and important position UAV design. The procedure of thermal management generally involves circulation of coolant which would collect heat from distributed parts in the UAV and transfer it either to the fuel or to a heat exchanger. Thermal management of electronics in a UAV is generally achieved by forced convection of external air. With increased complexity, it becomes important that thermal management systems are carefully designed system based on air-moving devices [2]. A major bottleneck which poses problems in efficient heat transfer is low thermal conductivity of process fluids [3]. This constraint limits the compactness and effectiveness of heat exchangers. It is expected that the thermal conductivities of fluids having metallic, non-metallic or polymeric suspended particles will be higher than those of ordinary process fluids
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