The effect of method for thermo-physical characteristics determining of gaseous fuel combustion products on the heat transfer coefficient computation at convective thermal exchange

Аuthors

Kurnakova N. Y.^*, Nuzhdin A. V.^**

Platov South-Russian State Polytechnic University (NPI), 132, Prosvesheniya str., Novocherkassk, 346428, Russia

*e-mail: kurnatalya82@mail.ru
**e-mail: a.nugdin@yandex.ru

Abstract

While a heat exchanger designing, it is necessary to determine the heat transfer coefficient from the coolant to the heat exchange surface or vice versa applying the criterion equations adduced in the article.

The theoretical part of the article presents the thermo-physical parameters computingof the mixture of gases according to the rule of additivity, using mass or volume fractions of the combustion products components and the Wilkie method. The thermal conductivity coefficient of a multicomponent gas mixture is being determined by the Mason and Saxen equation. The calculation was performed with the combustion products temperature changing from 200 °C to 400 °C in increments of 50 °C. The excess air coefficient varied from α_т = 1.05 to α_т = 1.4 in increments of 0.05. Calculated by the rule of additivity using the volume fractions of the components of the combustion products, the dynamic viscosity coefficient is less than the one calculated by the Wilkie method for any coefficients of excess air and temperature of the combustion products. When using the mass fractions of the components of the combustion products, the dynamic viscosity coefficient is greater than that calculated by the Wilkie method. Calculated by the additivity rule using the volume and mass fractions of the combustion products components, the thermal conductivity coefficient is greater than that calculated by the Mason and Saxen equation for any coefficients of excess air and temperature of the combustion products.

The result of determining the error of criteria calculated by a simplified method with volume fractions in the temperature range 200 °C — 400 °C gives the following:

— for Reynolds criteria, the error increases to minus 0.46 % — minus 0.92 %;

— for Nusselt criteria, the error decreases to 1.77 % — 0.92 %;

— for Prandtl criteria, the error decreases to 5.5 % — 4.23 %.

When using mass fractions:

— for Reynolds criteria, the error decreases to 1.18 % — 0.26 %,

— for Nusselt criteria, the error decreases to 2.03 % — 1.07 %,

— for Prandtl criteria, the error decreases to 4.16 % — 2.46 %.

The error in determining the heat transfer coefficient calculated by a simplified method using volume fractions in the temperature range 200 °C ÷ 400 °C, the error decreases to minus 3.73 % — minus 2.69 %, and when using mass fractions decreases from minus 3.15 % — minus 1.82 %. A similar pattern persists for natural gases and industrial gas from coke ovens. For blast furnace gas, the error of the heat transfer coefficient increases to minus 1.78 % — minus 2.08 %, and increases to minus 0.75 % — minus 1.81 % when using mass fractions.

Keywords:

combustion products, heat transfer coefficient, dynamic viscosity coefficient, thermal conductivity coefficient, Wilkie method, Mason and Saxen equation

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