Analysis of Heat Transfer Characteristics of a GnP Aqueous Nanofluid through a Double-Tube Heat Exchanger.

Uxía Calviño,Luis Lugo,José Fernández-Seara,Matthias H Buschmann,Javier P Vallejo

doi:10.3390/nano11040844

Abstract

The thermal properties of graphene have proved to be exceptional and are partly maintained in its multi-layered form, graphene nanoplatelets (GnP). Since these carbon-based nanostructures are hydrophobic, functionalization is needed in order to assess their long-term stability in aqueous suspensions. In this study, the convective heat transfer performance of a polycarboxylate chemically modified GnP dispersion in water at 0.50 wt% is experimentally analyzed. After designing the nanofluid, dynamic viscosity, thermal conductivity, isobaric heat capacity and density are measured using rotational rheometry, the transient hot-wire technique, differential scanning calorimetry and vibrating U-tube methods, respectively, in a wide temperature range. The whole analysis of thermophysical and rheological properties is validated by two laboratories. Afterward, an experimental facility is used to evaluate the heat transfer performance in a turbulent regime. Convective heat transfer coefficients are obtained using the thermal resistances method, reaching enhancements for the nanofluid of up to 13%. The reported improvements are achieved without clear enhancements in the nanofluid thermal conductivity. Finally, dimensionless analyses are carried out by employing the Nusselt and Péclet numbers and Darcy friction factor.

Highlights

Published: 25 March 2021Over the past decade, energy has become an essential resource; demand for it is continuously increasing due to the rising population, industrialization and urbanization.According to the Current Policies Scenario in the World Energy Outlook [1], energy demand rises by 1.3% each year up to 2040
The thermophysical and rheological properties for a new polycarboxylate chemically modified graphene nanoplatelets (GnP) 0.50 wt% aqueous nanofluid were experimentally determined by two laboratories, showing a good agreement
Enhancements of up to 13% for the coefficients and moderate pressure drop increases of less than 6% were achieved for the proposed nanofluid

Summary

Introduction

Published: 25 March 2021Over the past decade, energy has become an essential resource; demand for it is continuously increasing due to the rising population, industrialization and urbanization.According to the Current Policies Scenario in the World Energy Outlook [1], energy demand rises by 1.3% each year up to 2040. A significant advance in heat transfer systems has been with passive methods that involve no direct external power application, and active schemes, which entail the application of external power [2]. Some of the passive methods used to enhance the performance of heat transfer devices are twisted tape inserts [3], or the inclusion of fins [4] or baffles [5], while some of the active methods are the use of ultrasounds [6] or the application of electrodynamic techniques [7]. The use of nanofluids to enhance heat transfer processes has proved to be a promising line of research [8]

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