Luca Viscito

Flow boiling of R32 in a horizontal smooth tube of 6.0 mm internal diameter: heat transfer coefficient and pressure drop

This paper presents a series of experiments on flow boiling heat transfer coefficient and pressure drop using refrigerant R32. Tests were performed in a smooth horizontal stainless steel tube with an internal diameter of 6.00 mm, with the heat directly applied on the test section tube through DC current. Trends of the heat transfer coefficient and pressure drop data are displayed for different operating conditions. Specifically, the saturation temperature was fixed to 25 and 35 °C, the heat flux varied from 5 to 50 kW/m2 and the mass velocity was fixed to the low values of 150 and 250 kg/m2 s. The effects of the operating parameters on the heat transfer results are also shown.

Critical heat flux in a multi-minichannel heat sink. Effect of the heated length-on-diameter ratio

This paper exhibits saturated CHF experimental values obtained with R134a and R1234yf, working at saturation temperatures from 25 °C up to 65 °C (i.e. reduced pressures from 0.16, 0.20 and up to 0.46, 0.54, respectively). The mass flux was let to vary from 150 up to 350 kg/m2 s. All tests were performed with an aluminum multi-minichannel heat sink, made up of seven rectangular ducts, each of them 2 mm wide, 1 mm high and 35 mm long. Two heated lengths of 25 and 35 mm were structured, in order to study two different Lh/Deq ratios. The results show that critical heat flux is enhanced with increasing the mass flux and decreasing the saturation temperature. A greater Lh/Deq ratio leads instead to lower CHF values.