Thermal conductivities of water

From 0 to 100 C, the thermal conductivity of water shows a linear relationship with temperature and can be expressed as 

Process engineering and design using Visual Basic 

---

Fig. 7. Thermal conductivity of water and steam as a function of temperature. Values given correspond to pressures in MPa. To convert MPa to psi,...

Molecular Nature of Steam. The molecular stmcture of steam is not as weU known as that of ice or water. During the water—steam phase change, rotation of molecules and vibration of atoms within the water molecules do not change considerably, but translation movement increases, accounting for the volume increase when water is evaporated at subcritical pressures. There are indications that even in the steam phase some H2O molecules are associated in small clusters of two or more molecules (4). Values for the dimerization enthalpy and entropy of water have been deterrnined from measurements of the pressure dependence of the thermal conductivity of water vapor at 358—386 K (85—112°C) and 13.3—133.3 kPa (100—1000 torr). These measurements yield the estimated upper limits of equiUbrium constants, for cluster formation in steam, where n is the number of molecules in a cluster. 

C hiilloner and Powell have measured the thermal conductivity of water trnm OT to K0 C Lawson and Co-workers conducted extensive studies on the thermal conductivity of water from 30 C to 130°C up to pressures of 114,000 psia.W These data are shown in Figure 44-13 Thciss and Thodos have developed a reduced state correlation for the viscosity and thermal conductivity of water and steam.101 They report the critical point transport properties as 0.043 centipoisc and 55.3 x 10 - calorics. cm-sec T... 

Frontas ev (59) observed an anomalous temperature dependence in the thermal conductivity of water around 30°-40°C. (Figure 2). (In this illustration the data points are those given by Frontasev, but I believe the curve shown gives a reasonable fit to the experimental data.) He stated specifically that an anomaly existed near 30°-40°C. and that it implies a fundamental modification in water structure in this temperature range. 

Figure 2. Thermal conductivity of water from data of Frontasyev (59). Curve redrawn by present author...

A pictorial summary of the relative thermal conductivities of water structures (water, ice, and hydrate), including those in sediment is presented in Figure 2.17 (Gupta, 2007). The large variation in composite thermal conductivity for water... 

There is little information about the influence of water on the thermal conductivity of coal, but since the thermal conductivity of water is markedly higher than that of coal (about three times), the thermal conductivity of coal could be expected to increase if water is present in the coal. 

For an aqueous solution with an electrical conductivity of 1 S/m (typical of cell culture media) and a field of 100 kV/m, the power density is 1010 W/m3. Without cooling this would be sufficient to take the liquid from room temperature to boiling point in 30 ms. Despite the low thermal conductivity of water (k=0.59 W/m°C at 15 °C), the steady state temperature rise at the centre of a 50 pm thick cooled film is only 5.3 °C. 

Table 4. Density, Viscosity, and Thermal Conductivity of Water 876...

Tem- perature, °F Density of liquid water, ib/ft3 Viscosity of water, centipoises Thermal conductivity of water, Btu/(h)(ft2)(°F/ft)... 

Example 2.10 Estimation of thermal conductivity of pure liquids Estimate the thermal conductivity of water at 300 K and latm. The density of liquid water at 300 K is 995.7 kg/m3, and its isothermal compressibility... 

Eqs. (8.66) - (8.68) show that thermal conductivity decreases with the increase in foam expansion ratio. Since the thermal conductivity of water (At = 0.63 V m 1 K1) is about 25 times higher than that of air (Ac = 0.024 V m 1 K 1), at n = 20-25 the thermal conductivity of a foam is mainly determined by that of the gas phase. 

Martin and Lang, by the parallel plate method, found for water at 7°-60 and 1 atm. kx 103=1 394(1+0 00230. The thermal conductivity of water was measured to 270° by Schmidt and Sellschopp it has a maximum at 130°. Mohanty connected k for water with the degree of association. 

Sengers, J. V. and J. T. R. Watson, Improved International Formulation for the Viscosity and Thermal Conductivity of Water Substance , J. Phys. Chem. Ref. Data, 15,1291 (1986). 

D. Bertolini and A. Tani, Thermal conductivity of water molecular dynamics and generalized hydrodynamics results, Phys. Rev. E, 56 (1997) 4135-4151. 

Figure 2-4. Thermal conductivity of water as a function of temperature.

CALL THE PROGRAM TO CALCULATE THE THERMAL CONDUCTIVITY OF WATER CALL PROG4 (TK, THER, N)... 

THIS PROGRAM CALCULATES THE THERMAL CONDUCTIVITY OF WATER ... 

At the other side of the temperature scale, water has a most peculiar property it expands as it freezes, contrary to most known substances. Anyone who has suffered the misfortune of frozen water pipes in the winter will be all too familiar with this property. Were it not for this anomalous expansion, ice would sink when it freezes and form a frozen reservoir at the bottom of the oceans. Because of the low thermal conductivity of water, the oceans would not thaw out in the summer. Year after year the ice would increase in winter and persist through the summer, until eventually all or much of the body of water, according to the locality, would be turned to ice (Henderson, 1913, p. 109). Henderson further stated that [t]his unique property of water [the anomalous expansion on freezing] is the most familiar instance of striking natural fitness of the environment, although its importance has perhaps been overestimated but he added that on the basis of its thermal properties alone. . . water is the one fit substance for its place in the process of universal evolution, when we regard that process biocentrically (1913, p. 107). 

The film coefficient of heat transfer in a water heater to heat water from 20 to 80 °C is 2300kcalh 1 m-2 °C 1. Calculate the heat flux and estimate the effective thickness of the water film. The thermal conductivity of water at 50 °C is 0.55 kcal h 1 m 1 °C 1. 

Sengers, J.V. and Watson, J.T.R., Improved international formulations for the viscosity and thermal conductivity of water substance, / Phys. Chem. Ref Data, 15,1291, 1986. 

---