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In modern days, refrigeration systems are important for industrial and domestic applications. The systems consume more electricity as compared to other appliances. The refrigeration systems have been investigated thoroughly in many ways to reduce the energy consumption. Hence, nanorefrigerant which is one kind of nanofluids has been introduced as a superior properties refrigerant that increased the heat transfer rate in the refrigeration system. Many types of materials could be used as the nanoparticles to be suspended into the conventional refrigerants. In this study, the effect of the suspended copper oxide (CuO) nanoparticles into the 1,1,1,2-tetrafluoroethane, R-134a is investigated by using mathematical modeling. The investigation includes the thermal conductivity, dynamic viscosity, and heat transfer rate of the nanorefrigerant in a tube of evaporator. The results show enhanced thermophysical properties of nanorefrigerant compared to the conventional refrigerant. These advanced thermophysical properties increased the heat transfer rate in the tube. The nanorefrigerant could be a potential working fluid to be used in the refrigeration system to increase the heat transfer characteristics and save the energy usage.

A new emerging heat transfer fluid called nanofluid has been introduced in many applications nowadays such as electronic, nuclear reactor, biomedical, automotive, and industrial cooling. In recent years, refrigerant-based nanofluids and nanorefrigerants have been introduced as significant effects of nanoparticles in heat transfer performance and energy consumption reduction [

Many studies have been conducted to investigate the thermal conductivity of the nanofluids. However, there are limited literatures on the nanorefrigerants thermal conductivity [_{2}O_{3 }nanoparticle volume fraction on the heat transfer and pressure drop of R141b refrigerants under constant mass flux, temperature, and pressure [_{2}O_{3} nanoparticles in R-134 refrigerant has reduced the energy consumption about 10.32% with only 0.2% of nanoparticles suspension [_{2}-R600a reduced 5.94% and 9.60% energy consumption in domestic refrigerator, respectively [_{2}O_{3} nanoparticles reduced power consumption about 25% compared the conventional oil [_{2}O_{3}/R600a nanolubricant reduced power consumption of the compressor about 11.5% compared to the conventional POE oil and the coefficient of performance of the refrigeration system enhanced about 19.6% because of the nanolubricant [_{2}O_{3 }nanorefrigerant thermal conductivity can be enhanced by increasing the volume fraction of nanoparticles suspended into the R-134a refrigerant [_{2}O_{3}/R141b nanorefrigerant increased with 0.5–2 vol.% concentrations and temperature range of 5–20°C, meanwhile the viscosity of the nanorefrigerant increased with the nanoparticle concentration but decreased with temperature [

The viscosity of nanorefrigerant with different type of refrigerant, R-134a also could be enhanced with nanoparticle concentration of 1 to 5 vol.% theoretically [_{2}O_{3} nanoparticles influenced the pressure drop, pumping power, and heat transfer coefficient of the nanorefrigerant in a horizontal smooth tube. Heat transfer coefficient influenced the heat transfer rate in the cooling system. The enhancement of the heat-transfer coefficient due to Al_{2}O_{3} nanoparticle concentration is obtained for single-phase laminar flow in microchannel, although there are surface deposition, nanoparticles clustering, and agglomeration in the two-phase regime [

In this study, the thermophysical properties of nanorefrigerant are investigated by considering the CuO nanoparticles and the conventional refrigerant, R-134a. Table

Physical properties of CuO nanoparticle.

Nanoparticles and Conventional refrigerant | Thermal conductivity (W/m·K) | Density ^{3}) |
Diameter |
Viscosity |
---|---|---|---|---|

CuO (Copper Oxide) | 32.9 | 6320 | 40 | — |

R-134a | 0.0139 | 1202.6 | — | 0.00019336 |

Specification values in determining nanorefrigerant properties.

Constant parameter | Value |
---|---|

Refrigerant velocity, |
1.2 m/s |

Diameter of nanoparticles, |
40 nm |

Thermal conductivity of copper, |
401 W/m·K |

Heat transfer coefficient for air, |
50/m^{2}·K |

Temperature inlet, |
26°C |

Temperature outlet, |
−10°C |

A tube of evaporator with CuO/R-134a nanorefrigerant.

The thermal conductivity of nanorefrigerant is calculated by using data from Table

Mahbubul et al. (2013) introduced the Brinkman formula to determine the viscosity of nanorefrigerant, as in (

Figure

Nanorefrigerant thermal conductivity enhancement.

Nanoparticle volume fraction, Ø (%) | Thermal conductivity efficiency, ( |
Nanorefrigerant thermal conductivity enhancement (%) | Nanorefrigerant viscosity enhancement (%) | Heat transfer rate enhancement (%) |
---|---|---|---|---|

0.01 | 32.21 | 3121 | 44.45 | 5.1098 |

0.02 | 33.35 | 3234 | 99.58 | 5.4936 |

0.03 | 34.02 | 3302 | 165.38 | 5.7763 |

0.04 | 34.52 | 3352 | 241.86 | 6.0011 |

0.05 | 34.91 | 3390 | 329.025 | 6.1739 |

Thermal conductivity as a function of nanoparticle volume fraction.

The nanoparticle is suspended into the conventional refrigerant with 1% volume fraction which causes an increase in the thermal conductivity about 3121% enhancement from 0.0139 W/m·K to 0.4477 W/m·K. The significant enhancement occurred due to interfacial layer consideration in the mathematical modeling. It created equivalent particles with no overlapping between particles. The use of nanoparticle volume fraction up to 5% increased the thermal conductivity of nanorefrigerant more than 100% as the conventional refrigerant, R-134a, itself has higher thermal conductivity compared to other types of base fluid such as water and ethylene glycol.

Basically, with more addition of nanoparticles concentration into the nanorefrigerant, the thermal conductivity of the nanorefrigerant will be increased accordingly. However, the viscosity of the nanorefrigerant must also be considered since it may affect the overall performance of refrigeration system. The increments of nanorefrigerant viscosity due to nanoparticle suspension are shown in Figure

Viscosity as a function of nanoparticle volume fraction.

Heat transfer rate as a function of nanoparticle volume fraction.

The thermal conductivity of refrigerant-134a is 0.0139 W/m·K at temperature of 26°C. Suspending 1% vol. fraction of nanoparticles into the refrigerant has increased the thermal conductivity about 3121.05% enhancements. Additional 1% vol. fraction has increased the thermal conductivity in range of 3.53–8.38% up to 5% vol. fraction. The viscosity of nanorefrigerant is also showing great percentage of enhancement which is about 44.45% once compared to the conventional refrigerant with only 1% of nanoparticles volume fraction. The heat transfer rate of a tube of nanorefrigerant with 5% vol. fraction is about 1% enhancement. This study introduced trends to other researchers to investigate the thermophysical properties of nanorefrigerant experimentally. It is important to have superior thermal properties of the nanorefrigerant that could withstand the variation of temperature and pressures and the nanoparticles would not cause the clogging, corrosion, or pressure drop in the overall performance of refrigeration system.

The authors declare that there is no conflict of interests regarding the publication of this paper.

Support of this research through a Grant from Universiti Teknikal Malaysia Melaka, Malaysia, for Project no. PJP/2012/FKM(10A)/S0185, is greatly acknowledged.

_{2}O

_{3}/R-134a nanorefrigerants

_{2}O

_{3}-R134a nano refrigerant in refrigeration system

_{2}-R600a nano-refrigerant as working fluid

_{2}O

_{3}/R141b nanorefrigerant

_{2}O

_{3}-R141b nanorefrigerant in horizontal smooth circular tube

_{2}O

_{3}as working fluid