Maximum Linear Preheating Temperature

Flow Velocity and Compressibility Effects on Vibrational Relaxation Kinetics During Plasma-Chemical CO2 Dissociation Maximum Linear Preheating Temperature 

The CO2 flow velocity and compressibility were not taken into account in the purely kinetic equation (5-45). Taking into account the fluid mechanics effects leads to the following correction of formula (5-50) for characteristic VT-relaxation time (Fridman, 1986)  

After the time interval exceeds the critical one (t tvt), the translational temperature growth becomes explosive (see Fig. 5-18). The explosion of To is due to the strong exponential dependence of the VT-relaxation rate on temperature (see Chapter 2, Landau-Teller formula). VT-relaxation deterMnes gas heating and increase of translational temperature, which then leads to an exponential acceleration of the VT relaxation and further and faster gas heating. A linear growth of translational temperature is limited by the characteristic time Tvt and, hence, by the maximum linear preheating before the explosion  

the translational temperature grows linearly due to VT relaxation from the initial temperature (which is usually room temperature) to the maximum one T° + A To.vt 

If the ionization degree is sufficient (5 8), the stationary vibrational temperature Tf is established after a necessary time interval of about /ks n. The stationary vibrational temperature T - in the active discharge zone canbe found from the energy balance equation (5-44), taking the CO2 dissociation rate in the framework of the one-temperatuie approximation (compare to (5 6))  

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Flow Velocity and Compressibility Effects on CO2 Vibrational Relaxation Kinetics. Analyze the characteristic VT -relaxation time (5-51) and the maximum linear preheating temperature (5-53) during CO2 dissociation in plasma stimulated by vibrational excitation, taking into account the gas compressibility. Describe the qualitative difference of the systems performed in subsonic flows (M 1), supersonic flows (M 1), and near the speed of sound. 

Example 7.5.3 A fluidized bed using 200-jum sand particles is being used to preheat hydrogen used in a direct reduction unit. The solids and the gas are in a cross flow arrangement the solids may be regarded as completely mixed and at a temperature of 1000°C. If the linear gas velocity is 10 times the minimum fluidization velocity and the bubbles are half the maximum stable size, estimate the bed depth required to preheat the gas to 900°C from 25°C inlet temperature. 

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