Thermo-fluid modeling and thermodynamic analysis of low-temperature parabolic trough systems with multi-walled carbon nanotubes/water nanofluids

Abstract

Numerical thermodynamic analysis for low-temperature parabolic trough receivers with Multi-walled carbon nanotubes/water (MWCNT/water) nanofluids as a heat transfer fluid is presented. Numerical modeling is carried out using developed in-house software and is based on a coupled 3D thermo-fluid mathematical model that combines Monte Carlo ray tracing method and finite volume method. Experimental thermophysical properties of the MWCNT/water nanofluids with 0.05%, 0.1%, and 0.3% nanoparticles volume fraction are approximated in the temperature range of 25 °C−70 °C. Created nonlinear mathematical model and numerical algorithm are validated through comparison with analytical and experimental data. It was discovered that the optimal correlation between MWCNT/water thermal conductivity and heat capacity plays a key role in the heat transfer enhancement and increased energy efficiency of the low-temperature parabolic trough collectors. Impact of the inner tube surface roughness and MWCNT/water viscosity on pressure drop inside tube receiver are studied. It was found that only the MWCNT/water nanofluid with 0.05% nanoparticles volume fraction at laminar flow regime in long tube receivers enhances convective heat transfer and guarantees temperature growth by 3% in comparison with pure water. MWCNT/water nanofluid with 0.05% nanoparticles volume fraction also increases energy and exergy efficiencies by 10% and has low pressure drops, and therefore is recommended as promising heat transfer fluid for different types of low-temperature parabolic trough collectors.