Overview of the effect of pressure on fluid viscosity
Effect of pressure on fluid viscosity

Figure 1 shows the viscosity of water along isobars as a function of temperature. The critical coordinates for water are T_c = 647.14 K and P_c = 22.064 MPa. Pressure ranges from 0.1 MPa to 1,000 MPa, and temperature from 273.15 to 1,300 K. In some ranges T > 1,000 K (or more generally for all fluids: T_r > 1.5 with T_r reduced temperature, $T_r=\frac{T}{T_c}$), pressure has little effect on viscosity. But when T < 1,000 K (T_r < 1.5) and when P > P_c (for water P_c = 22.064 MPa), pressure has a significant effect on viscosity, as can...