Saturated steam, thermal properties

All of the chemical evidence that can be marshalled indicates that wood fiberboard manufacture exploits the thermoplastic properties of lignin. Defibering is effected by the thermal softening of lignin in the middle lamella at saturated steam pressures above 130C. Interfelted fiber mats are consolidated with or without densification pressure by the thermoplastic fusion of lignin-rich fiber surfaces at high board conversion temperatures. 

The Thermal Properties of Saturated Water Vapour (Steam)... 

A power-law solution of a polymer (density 1000kg/m ) is flowing through a 3 m long 25 mm inside diameter tube at a mean velocity of 1 m/s. Saturated steam at a pressure of 0.46 bar and a temperature of 353 K is to be condensed in the annulus. If the polymer solution enters the heater at 318 K, at what temperature will it leave Neglect the heat loss to the surroundings. The thermo-physical properties of the solution are heat capacity = 4180 J/kg K thermal conductivity = 0.59 W/mK flow behaviour index, n = 0.3. 

Coefficients of the equadon of state and of the equation for transport properties are stored for each substance. Parameters of the critical point and coefficients of equations for calculadon of the ideal-gas functions, the saturated vapor pressure and the melting pressure are kept also. The thermal properties in the single-phase region and on the phase-equilibrium lines can be calculated on the basis of well-known relations with use of these coefficients. The system contains data for 30 reference substances monatomic and diatomic gases, air, water and steam, carbon dioxide, ammonia, paraffin hydrocarbons (up to octane), ethylene (ethene), propylene (propene), benzene and toluene. The system can calculate the thermophysical properties of poorly investigated gases and liquids and of multicomponent mixtures also on the basis of data for reference substances. 

Extensive tables of the viscosity and thermal conductivity of air and of water or steam for various pressures and temperatures are given with the thermodynamic-property tables. The thermal conductivity and the viscosity for the saturated-liquid state are also tabulated for many fluids along with the thermodynamic-property tables earlier in this section. 

Fig. 4.7 illustrates (4.24). As we can see from the graph, the temperature dependence of the dynamic viscosity and the thermal conductivity can have a marked influence on the heat transfer, as far as they change starkly with the temperature. In condensing steam, for a temperature difference between the saturation and wall temperatures of s — i o < 50 K, the material properties vary for As/Ao between 0.6 and 1.2 and for Vs/vo between 1 and 1.3. This region is hatched in Fig. 4.7. It is clear that within this region the deviations from Nusselt s film condensation theory are less than 3%.

The following property data are given for water at the saturation temperature of 100 °C liquid density gL = 958.1 kg/m3, vapour density go = 0.5974kg/m3, enthalpy of vaporization Ahv = 2257.3 kJ/kg, liquid thermal conductivity Al = 0.677 W/K m, dynamic viscosity of the liquid pl = 0.2822 10 3 kg/s m, specific heat capacity of the steam-air mixture cpg = 1.93kJ/kgK. Further, the heat transfer coefficient between the steam-air mixture and the condensate film is = 30W/m2K. 

NIST/ASME Steam Properties Database versiou 2.21 http //www.nist.gov/srd/nistlO.cfm (accessed November 10, 2010) (purchase required). Thermophysical properties include in the STEAM Database temperature, Helmholtz energy, thermodynamic derivatives, pressure, Gibbs energy, density, fugacity, thermal conductivity, volume, isothermal compressibility, viscosity, dielectric constant, enthalpy, volume expansivity, dielectric derivatives, internal energy, speed of sound, Debye-Hlickel slopes, entropy, Joule-Thomson coefficient, refractive index, heat capacity, surface tension. The STEAM database generates tables and plots of property values. Vapor-liquid-solid saturation calculations with either temperature or pressure specified are available. 

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