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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

TWO PHASE FLOW BOILING HEAT TRANSFER COEFFICIENT AND PRESSURE DROP OF REFRIGERANT AND γ-Al2O3 BASED NANOLUBRICANT MIXTURES IN A 9.5 MM SMOOTH TUBE.

Lorenzo Cremaschi
Auburn University, Department of Mechanical Engineering, Auburn, AL 36830, USA

Pratik S. Deokar
Auburn University, Department of Mechanical Engineering, Auburn, AL 36830, USA

Andrea A. M. Bigi
Auburn University, Department of Mechanical Engineering, Auburn, AL 36830, USA

Abstract

Driven by higher energy efficiency targets, there is a critical need for major heat transfer enhancements in heat exchangers. Nanolubricants, that is, nanoparticles dispersed in the non-volatile component of a refrigerant and lubricant liquid mixture and working as thermal energy transport vectors within the liquid mixture, have the potential to bring major improvements to the heat transfer processes in the energy industry, space-conditioning, refrigeration, the transportation and chemical sectors.
This paper presents new experimental heat transfer coefficient and pressure drop data of refrigerant R410A and nanolubricants mixtures two phase flow boiling. Spherical Alumina (γ-Al2O3) nanoparticles with 40 nm nominal particles diameter were dispersed and stabilized in polyolester (POE) lubricant at mass concentration of 20 wt.%. These highly concentrated nanolubricants were mixed with refrigerant R410A during two phase flow boiling at saturation temperature of 4.4°C.
The effect on the heat transfer coefficient and pressure drop was systematically investigated in laboratory for horizontal 9.5 mm smooth inner wall copper evaporator tube and for a broad range of mass flux and two heat flux conditions. The increased thermal conductivity of the nanolubricants with respect to the base POE oil did not augmented the heat transfer coefficient at the low heat flux. The nanoparticles remained in suspension neutrally buoyant in the liquid phase of the mixture and did not actively participate to the heat transfer process. However, when the heat flux was increased from 15 to 21 kW/m2, a sudden significant increase of heat transfer coefficient was observed while the pressure drops were marginally affected.

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