Water, properties Prandtl number

The Prandtl number depends on the thermophysical properties of the fluid only. Typical values of the Prandtl number are 0.001-0.03 for liquid metals, 0.2-1 for gases, 1-10 for water. 

This book contains tables of the properties of water and steam from 0 to 800 and from 0 to 1000 bar which have been calculated using a set of equations accepted by the members of the Sixth International Conference on the Properties of Steam in 1967. Properties which are tabulated include the pressure, specific volume, density, specific enthalpy, specific heat of evaporation, specific entropy, specific isobaric heat capacity, dynamic viscosity, thermal conductivity, the Prandtl number, the ion-product of water, the dielectric constant, the isentropic exponent, the surface tension and Laplace coefficient. Also see items [43] and [70]. 

The Prandtl number depends on the thermophysical properties of the fluid only. Typical values of the Prandtl number are 0.001-0.03 for liquid metals, 0.2-1 for gases, 1-10 for water, 5-50 for organic liquids and 50 - 2000 for oils. The Prandlt number depends on the bulk temperature of the fluid since the viscosity is a strong function of temperature for this reason, especially in very narrow microchannels in which the viscous heating effects are not negligible (see viscous heating and viscous dissipation), the Prandlt number cannot be considered as a constant along the channel. 

Generally speaking, the conventional numerical analysis with a k-e turbulence model and accurate treatment of thermophysical properties can successfully explain the unusual heat transfer phenomena of supercritical water. Heat transfer deterioration occurs due to two mechanisms depending on the flow rate. When the flow rate is large, viscosity increases locally near the wall by heating. This makes the viscous sublayer thicker and the Prandtl number smaller. Both effects reduce the heat transfer. When the flow rate is small, buoyancy force accelerates the flow velocity near the wall. This makes the flow velocity distribution flat and generation of turbulence energy is reduced. This type of heat transfer deterioration appears at the boundary between forced and natural convection. As the heat flux increases above the deterioration heat flux, a violent oscillation of wall temperature is observed. It is explained by the unstable characteristics of the steep boundary layer of temperature. 

The local Reynolds number Re = 2rU/v used in the studies of EPRs varies between 100 and 2 000, so that one often takes n = 1/3, m = 1/2, and C = 0.6. The Prandtl and Schmidt criteria express the properties of interacting substances. For the systems heat in air and water vapour in air , they are Pr = (vp1cp)/A 0.7 and Sc = v/D 0.6 [60], Having transformed these basic empirical relations, Berman [60] suggested a relation for spraying systems aE = 3 U/2r, provided the local velocity U is taken in m/s and the droplet diameter 2r in m. The latter was used in the following performance ofSCSs. 

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