Thermophysical properties and heat transfer performance of Al2O3/R-134a nanorefrigerants.

(1)

Thermophysical properties and heat transfer performance of Al

₂

O

₃

/R-134a

nanorefrigerants

I.M. Mahbubul

a,⇑

_{, S.A. Fadhilah}

a,b

_{, R. Saidur}

a,c

_{, K.Y. Leong}

d

_{, M.A. Amalina}

a

Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

b

Department of Thermal-Fluids, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia

c

UM Power Energy Dedicated Advanced Centre (UMPEDAC), Level 4, Wisma R&D, University of Malaya, 59990 Kuala Lumpur, Malaysia

d

Department of Mechanical Engineering, Universiti Pertahanan Nasional Malaysia, Kem Sungai Besi, 57000 Kuala Lumpur, Malaysia

a r t i c l e

i n f o

Article history:

Received 26 January 2012

Received in revised form 18 September 2012 Accepted 2 October 2012

Available online 31 October 2012

Keywords:

Thermal conductivity Viscosity

Pressure drop Pumping power Heat transfer coefficient

a b s t r a c t

The past decade has seen the rapid development of nanofluids science in many aspects. In recent years, refrigerant-based nanofluids have been introduced as nanorefrigerants due to their significant effects over heat transfer performance. This study investigates the thermophysical properties, pressure drop and heat transfer performance of Al2O3nanoparticles suspended in 1, 1, 1, 2-tetrafluoroethane (R-134a). Suitable models from existing studies have been used to determine the thermal conductivity and viscosity of the nanorefrigerants for the nanoparticle concentrations of 1 to 5 vol.%. The pressure drop, pumping power and heat transfer coefficients of nanorefrigerant in a horizontal smooth tube have also been investigated with the same particle concentration at constant velocity of 5 m/s and uniform mass flux of 100 kg/m2_{s. In} this study, the thermal conductivity of Al2O3/R-134a nanorefrigerant increased with the augmentation of particle concentration and temperature however, decreased with particle size intensification. In addition, the results of viscosity, pressure drop, and heat transfer coefficients of the nanorefrigerant show a signif-icant increment with the increase of volume fractions. Therefore, optimal particle volume fraction is important to be considered in producing nanorefrigerants that can enhance the performance of refriger-ation systems.

1. Introduction

Nanofluids attracted many attentions of researchers around the world as a significant alternative to increase the heat transfer per-formance. Nanofluids, firstly, demonstrated by Choi[1]at Argonne National Laboratory that were defined as suspensions of nanopar-ticles into base fluids with the typical length scale of parnanopar-ticles is 1–100 nm. Recently (since 2005), nanorefrigerants have intro-duced as one kind of nanofluids that can enhance the performance of a refrigeration system[2]. By using nanoparticles in refrigeration system, three main advantages can be obtained[3]; (1) nanoparti-cle as an additive can increase the solubility between the lubricant and the refrigerant. (2) Thermal conductivity and heat transfer characteristics of the refrigerant can be increased. (3) Nanoparti-cles dispersion into lubricant may decrease the friction coefficient and wear rate. However, there are contradictory results as well available in literature. Henderson et al. [4] showed that direct dispersion of SiO2with R-134a decreases the boiling heat transfer

coefficient with the augmentation of nanoparticle concentrations. Moreover, they found that the heat transfer coefficient of

R-134a/POE/CuO increased accordingly with the nanoparticle volume concentrations.

Thermophysical properties are the fundamental properties that need to be investigated to gain the maximum output from nanore-frigerants. The thermal conductivity of a nanorefrigerant is propor-tional to the heat transfer coefficient. The heat transfer coefficient of higher thermal conductivity nanorefrigerant is larger than the fluids with lower thermal conductivity at same Nusselt number [5]. The nanorefrigerant thermal conductivity can be enhanced by increasing the volume fraction of nanoparticles suspended into refrigerant or by using nanoparticles with high thermal conductiv-ities[6–8]. Thermal conductivity can be varied due to the effects of particle volume fraction, nanoparticle types, refrigerants, particle sizes, and particle shapes. The interfacial layers developed in nano-fluids has been proven as the contributor to the enhancement of thermal conductivity[9–11]. Besides the interfacial layer, nanopar-ticle aggregation in nanofluids forms’s nanoparnanopar-ticles clustering around that enhances the thermal conductivity[6]. Brownian mo-tion due to nanoparticles suspension also has an indirect role in producing particle clustering[12]. Jiang et al.[6]investigated the thermal conductivity of nanorefrigerant experimentally by sus-pending different types of nanoparticles into R-113 refrigerant, and a model was developed by using resistance network method.

http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.10.007

⇑Corresponding author. Tel.: +60 3 7967 7611; fax: +60 3 7967 5317. E-mail address:[email protected](I.M. Mahbubul).

International Journal of Heat and Mass Transfer 57 (2013) 100–108

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