Effect of Nanofluid Thermophysical Properties on the Performance Prediction of Single-Phase Natural Circulation Loops

Nur Çobanoğlu,Ziya Haktan Karadeniz

doi:10.3390/en13102523

Nur Çobanoğlu, Ziya Haktan Karadeniz

Open Access

https://doi.org/10.3390/en13102523

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Journal: Energies	Publication Date: May 15, 2020
Citations: 6	License type: CC BY 4.0

Affiliation: Izmir Kâtip Çelebi University

Abstract

Specifying nanofluids’ thermophysical properties correctly is crucial for correct interpretation of a system’s thermo-hydraulic performance and faster market-uptake of nanofluids. Although, experimental and theoretical studies have been conducted on nanofluids’ thermophysical properties; their order-of-magnitude change is still a matter of debate. This numerical study aims to reveal the sensitivity of single phase natural circulation loops (SPNCL), which are the passive systems widely used in solar thermal and nuclear applications, to thermophysical property inputs by evaluating the effects of measured and predicted nanofluid thermophysical properties on the SPNCL characteristics and performance for the first time. Performance and characteristics of an SPNCL working with water-based-Al2O3 nanofluid (1–3 vol.%) for heating applications is evaluated for different pipe diameters (3–6 mm). The thermal conductivity effect on SPNCL characteristics is found to be limited. However, viscosity affects the SPNCL characteristics significantly for the investigated cases. In this study, Grm ranges are 1.93 × 107–9.45 × 108 for measured thermophysical properties and 1.93 × 107–9.45 × 108 for predicted thermophysical properties. Thermo-hydraulic performance is evaluated by dimensionless heat transfer coefficients which is predicted within an error band of ±7% for both the predicted and measured thermophysical properties of the data. A Nu correlation is introduced for the investigated SPNCL model, which is useful for implementing the SPNCL into a thermal system.

Highlights

In a general sense, an increase in thermal conductivity by addition of nanoparticles into a base fluid (distilled water (DIW), ethylene glycol (EG), etc.), producing a nanofluid, results in higher heat transfer performance
Enhanced thermal conductivity is the main reason for the improved heat transfer performance, but the change in other thermophysical properties may reduce the overall efficiency of the system
The correct interpretation of the convective heat transfer and overall efficiency is crucial for nanofluid applications to obtain a realistic conclusion [1,2]

Summary

Introduction

An increase in thermal conductivity by addition of nanoparticles into a base fluid (distilled water (DIW), ethylene glycol (EG), etc.), producing a nanofluid, results in higher heat transfer performance. Enhanced thermal conductivity is the main reason for the improved heat transfer performance, but the change in other thermophysical properties (especially viscosity) may reduce the overall efficiency of the system. The measurement of the thermophysical properties of nanofluids involves some difficulties due to the complex physical interaction between fluid and nano-particles [3]. The thermal conductivity and viscosity of nanofluids are the most studied properties since they highly influence the performance of the system [4,5,6,7,8,9,10]. Measurements by commercial devices that are tuned for Energies 2020, 13, 2523; doi:10.3390/en13102523 www.mdpi.com/journal/energies

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