Experimental investigation on TiO2 nanoparticle migration from refrigerant–oil mixture to lubricating oil during refrigerant dryout

The application of nanorefrigerant–oil mixture in refrigeration system requires continuous circulation of nanoparticles; however, only a small part of nanoparticles circulate by migration from the mixture to vapor within refrigerant dryout process. This study points out a more important nanoparticle circulation way by migration from bulk refrigerant–oil mixture to oil excess layer, and quantitatively evaluate the mixture-to-oil migration ratio affected by oil mass fraction, nanoparticle mass fraction and heat flux. The nanorefrigerant–oil mixture is TiO 2 /R141b/NM56; experimental conditions cover oil mass fraction of 5%–20%, nanoparticle mass fraction of 0.2%–1.0%, and heat flux of 10–100 kW m −2 ; the mixture-to-oil migration ratio is measured by absorbance method. The results show that mixture-to-oil migration ratio ranges within 0.388–0.969, and increases averagely by 51.8%, 28.3% and 8.0% with increasing oil mass fraction, reducing nanoparticle mass fraction and lowering heat flux over the whole range of present conditions, respectively.