Heat transfer analysis when using Al2O3–water nanofluid in a double pipe heat exchanger with parallel flow arrangement

Abstract

Heat exchangers are thermal devices used in several industrial applications. Parallel flow arrangement means that both fluids flow stream is in the same direction. Low thermal conductivity of traditional fluids affects in a negative manner the efficiency of heat exchangers. In order to overcome this drawback, literature recommends the use of nanofluids. This paper deals with a theoretical study of performance enhancement of a double pipe heat exchange with parallel flow arrangement. The analysis consists in a comparison between the situations in which the water and the water base nanofluid (Al₂O₃-water) are the cooling fluids. The cold fluid is a nanofluid (NF)- represented by Al₂O₃ nanoparticles added to water. The diameter of nanoparticles is 25 nm and the considered volume concentration is of 0.25%. The hot fluid is water. The nanofluid flows in the outer pipe, while the water flows in the inner pipe; fluids flow with constant inlet temperature: 32°C – for the nanofluid and 58°C – for the water. The volumetric flow rate varies in the range: 0.5÷1.9 L/min. The obtained results show that the average values of the following: heat transfer rate, effectiveness, inner and outer heat transfer coefficients, all for the nanofluid, are about 16%, 10%, 16% and respectively 17% higher in comparison to the base fluid. The analysis will reveal the fact that a better performance of the heat exchanger it is achieved when using Al₂O₃-water nanofluid as a cooling medium than when using the base fluid (water), due to the higher thermal conductivity of the nanofluid.