# NEW EQUATION CALCULATES THERMAL CONDUCTIVITIES OF C1-C4 GASES

April 18, 1994
Carl L. Yaws, Xiaoyan Lin, Li Bu, and Sachin Nijhawan Lamar University Beaumont, Tex. In the design of heat exchangers, heat-transfer coefficients are commonly calculated for individual items. These calculations require knowledge of the thermal conductivities of the species involved. The calculation of the overall heat-transfer coefficient for a heat exchanger also requires thermal conductivity data for the individual species. In fact, thermal conductivity is the fundamental property involved

Carl L. Yaws, Xiaoyan Lin, Li Bu, and Sachin Nijhawan
Lamar University
Beaumont, Tex.

In the design of heat exchangers, heat-transfer coefficients are commonly calculated for individual items.

These calculations require knowledge of the thermal conductivities of the species involved.

The calculation of the overall heat-transfer coefficient for a heat exchanger also requires thermal conductivity data for the individual species. In fact, thermal conductivity is the fundamental property involved in heat transfer.

Ordinarily thermal conductivities are either measured experimentally or estimated using, complex correlations and models. Engineers must search existing literature for the values needed.

Here, a compilation of thermal conductivity data for gases is presented for a wide temperature range. Using these data with the accompanying equation will enable engineers to quickly determine values at the desired temperatures.

The results are provided in an easy-to-use tabular format, which is especially helpful for rapid calculations using a personal computer or hand-held calculator.

### CORRELATION

The correlation for the thermal conductivity of a gas as a function of temperature is given by the equation:

[see equation]

where: [see equation] = thermal conductivity of gas, in w/m-K.; A, B, and C are regression coefficients specific to each compound (see Table 1); and T is the temperature, in K.

The constants to be used in this equation for determining gas thermal conductivity of 309 gases at low pressure are given in Table 1. The table contains data on a wide variety of substances, including:

• Hydrocarbons (alkanes, olefins, acetylenes, cycloalkanes)

• Oxygenates (alcohols, aldhydes, ketones, acids, ethers, glycols, anhydrides)

• Halogenates (chlorinated, brominated, fluorinated, and iodinated compounds)

• Nitrogenates (nitrites, amines, cyanates, amides)

• Sulfur compounds (mercaptans, sulfides, sulfates)

• Silicon compounds (silanes, chlorosilanes) and many other chemical types.

The tabulation is arranged by carbon number to enable engineers to locate data easily and quickly using the chemical formula. Also provided are the temperature range for which the data are accurate, and the thermal conductivity of each compound at 25 C.

A literature search was conducted to identify sources of thermal conductivity data. Both experimentally determined conductivities and estimated values were used to compile the table.

In the absence of experimental data, estimates were primarily based on the correlations of Roy and Thodos, Misic and Thodos, Stiel and Thodos, and modified Eucken models. Experimental data and estimates were then regressed to provide a single equation for all compounds.

Very little experimental data are available for highly polar and high-molecular-weight compounds. Also, very little experimental data are available for organic compounds at high temperatures (600 K.). Thus, the values for these compounds, and for high temperatures, should be considered rough approximations. A comparison of the correlation results and the actual data, for a representative chemical (CO2), is shown in Fig. 1. The graph shows good agreement between calculated and experimental values.

### EXAMPLE CALCULATION

The correlation results may be used for prediction and calculation of gas thermal conductivity. For example, to calculate the gas thermal conductivity of carbon dioxide at 550 K. (276.85 C.), substitute the appropriate coefficients A, B, and C from Table I into the correlation equation:

[see equation]

The calculated value (0.03344) and experimental value (0.03228) compare favorably (deviation = 3.59%).

The bibliography lists the sources of the experimentally determined thermal conductivities used to derive the equation and coefficients given here.

### BIBLIOGRAPHY

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Yaws, C.L., and Gallant, R.W., Physical Properties of Hydrocarbons, Vols. 1 (2nd ed.), 2 (3rd ed.), and 3 (1st ed.), Gulf Publishing Co., Houston, 1992, 1993, 1993.