Thermal conductivity of liquid

Filippov, Tarzimanov, and Totsldy, Thermal Conductivity of Liquids ana Gases (in Russian), Standartov, Moscow, 1978, now published in English translation by CRC Press, Miami, FL. 

Thermal Methods Level-measuring systems may be based on the difference in thermal characteristics oetween the fluids, such as temperature or thermal conductivity. A fixed-point level sensor based on the difference in thermal conductivity between two fluids consists of an electrically heated thermistor inserted into the vessel. The temperature of the thermistor and consequently its electrical resistance increase as the thermal conductivity of the fluid in which it is immersed decreases. Since the thermal conductivity of liquids is markedly higher than that of vapors, such a device can be used as a point level detector for liquid-vapor interface. 

Bretsznajder (1971) gives a group contribution method for estimating the thermal conductivity of liquids. 

In general, the thermal conductivities of liquid mixtures, and gas mixtures, are not simple functions of composition and the thermal conductivity of the components. Bretsznajder (1971) discusses the methods that are available for estimating the thermal conductivities of mixtures from a knowledge of the thermal conductivity of the components. 

Specific heat of liquid = 2.78 kJkg loC thermal conductivity of liquid = 0.12 Wnrl0C 1. 

The gas-phase wall heat-transfer coefficient can be evaluated by using the gas-phase Reynolds number and Prandtl number in Eq. (33). The thermal conductivities of liquids are usually two orders of magnitude larger than the thermal conductivities of gases therefore, the liquid-phase wall heat-transfer coefficient should be much larger than the gas-phase wall heat-transfer coefficient, and Eq. (34) simplifies to... 

Fig. 2.12. Thermal conductivity of liquid helium and helium gas. Data from [41]. 

Thermal Conductivities of Liquids. As was the case with viscosity, it is difficult to derive useful relationships that allow us to estimate thermal conductivities for liquids from molecular parameters. There is a theoretical development by Bridgman, the details of which are presented elsewhere [11], which assumes that the liquid molecules are arranged in a cubic lattice, in which energy is transferred from one lattice plane to the next at sonic velocity, v. This development is a reinterpretation of the kinetic theory model used in the last section, and with some minor modifications to improve the fit with experimental data, the following equation results ... 

Temp., °F Absolute pressure, Ib/sq in. Latent heat of evaporation, Btu/lb Specific volume of steam, cu ft/lb Density of liquid water, Ib/cu ft Viscosity of liquid water, tentipoisea Thermal conductivity of liquid water, (Btu)(ft)/ (°F)(ft2)(hr)... 

In Fig. 8 we show a comparison of the thermal conductivity for liquid HMX obtained from our NEMD simulations with measured values for crystalline HMX [54] as well as values used in combustion models for HMX [55]. Despite being weak, the temperature dependence of the thermal conductivity of liquid HMX is not featureless. The thermal conductivity exhibits a sharp drop in the temperature interval from the melting point (550 K) up to 650 K. At higher temperatures the thermal conductivity exhibits almost no temperature dependence. The predicted value at 550 K is consistent with the HMX crystal data [54]. The thermal conductivity used in some combustion models [55] agrees to within about 25% with our NEMD predictions over the entire temperature interval. 

The minimum information covers chemical formula, molecular weight, normal boiling point, freezing point, liquid density, water solubility and critical properties. Additional properties are enthalpies of phase transitions, heat capacity of ideal gas, heat capacity of liquid, viscosity and thermal conductivity of liquid. Computer simulation can estimate missing values. The use of graphs and tables of properties offers a wider view and is strongly recommended. 

Bridgman [Proc. Am. Acad. Arts Set., 59, 141 (1923)] showed that the thermal conductivity of liquids is increased by only a few percent under a pressure of 100,330 kPa (1000 atm). The thermal conductivity of some liquids varies with temperature through a maximum. It is often necessary for the engineer to estimate thermal conductivities methods are indicated in Sec. 2. 

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