Thermal conductivity enhancement of the binary mixture (NH3 + LiNO3) by the addition of CNTs

• A relative transient hot-wire apparatus was designed and set up.
• Calibrated with water, toluene, dimethyl phthalate, ethylene glycol and H2O + LiNO3.
• Stable distribution of CNTs was achieved by chemical treatment.
• Thermal conductivity of NH3 + LiNO3 + CNTs has been measured.
• Concentrations of NH3 and CNTs have been the key parameters.

The objective of this paper is to experimentally investigate the enhancement of thermal conductivity in the binary working pair (NH3 + LiNO3) by adding carbon nanotubes (CNTs). A stable distribution of CNTs in the base fluid is achieved by surface modification of CNTs through oxidation. The key parameters are the concentrations of NH3 and CNTs in weight, ranging from 30% to 50% for NH3, and 0.005%–0.2% for CNTs. The thermal conductivity of the binary nanofluid was measured at 1.5 MPa, from 303.15 K to 353.15 K, using a relative transient hot-wire apparatus. Uncertainty in the measurements was estimated to be less than 0.025 W m−1 K−1. The highest thermal conductivity enhancement was obtained with the combination of 0.01 wt.% of CNTs in the base fluid of 40 wt.% NH3, where the maximum measured enhancements was 7.5% times than that of NH3 + LiNO3 solution.