Experimental investigation into pool boiling heat transfer performance of TIO2-R141b nanofluid for horizontal low-finned U-tube.

An experimental investigation was performed into the pool boiling heat transfer performance of a low-finned U-tube immersed in TiO2-R141b nanofluid. Nanofluids with four different nanoparticle loadings (i.e., 0 vol%, 0.0001 vol%, 0.001 vol%, and 0.01 vol%) were prepared using a two-step method. The heat transfer performance of the low-finned U-tube was compared with that of a plain U-tube for all four working fluids. The results showed that the heat transfer performance of the finned tube was around 40-120% higher than that of the plain tube. However, the Energy-Dispersive X-ray Spectrometry (EDS) results revealed that some of the TiO2 nanoparticles adhered to the heated surface during boiling, and therefore increased the thermal resistance. As a result, the heat transfer performance obtained using the nanofluids was lower than that obtained using pure R141b refrigerant. Accordingly, an ultrasonic vibration crusher was used to inhibit the formation of the nano-sorption layer on the U-tube surface. The vibration crusher was found to improve the heat transfer performance of the nanofluids by around 30%. Moreover, of the four working fluids, the nanofluid with a particle loading of 0.0001 vol% yielded the optimal heat transfer performance.