This experimental study defines heat transfer characteristics of four different nanorefrigerants (Cu, CuO, Al, and Al2O3-R141b) flowing inside horizontal smooth and internal thread tubes. Tests were conducted within a mass fraction range of 0.1 wt%, 0.2 wt%, and 0.3 wt%. The flow flux range was from 9.4 to 25.9 kg.s(-1) under a constant heat flux condition. Based on the experimental results, the effect of the flow flux, mass fraction, and types of nanoparticles were analyzed and discussed. The results show that the heat transfer effect of nanorefrigerants in an internal thread tube is superior to a smooth tube. For Cu-R141b with a 0.2 wt%, G1 = 9.4 kg.s(-1) condition, comparing its heat transfer performance in a smooth tube with that in an internal thread tube, the heat transfer enhancement increased by 4.50% in the internal thread tube. With a G2 = 16.5 kg.s(-1) condition, the same nanorefrigerant undergoing the same test had a heat transfer enhancement increase in the internal thread tube of 5.17%. For Al-R141b with a 0.2 wt%, G2 = 16.5 kg.s(-1) condition, the smooth tube vs. internal threat tube test yielded a heat transfer enhancement increase in the internal thread tube of 4.15%. For Al2O3-R141b with 0.2 wt% and a G2 = 16.5 kg.s(-1) condition, the test showed a heat transfer enhancement increase in the internal thread tube of 4.07%. (C) 2017 Elsevier Ltd. All rights reserved.