Heat Transfer in Thermally Decomposing Ozone. Experimental Investigation

Abstract

The purpose o f this study was to investigate experimentally the effect of the homogeneous, gas phase thermal decomposition o f ozone upon heat transfer to ozone-oxygen mixtures in turbulent flow past a solid surface. Effluent from a silent discharge ozone generator passed through the 5/8-inch diameter, 1 0-inch long electrically heated glass test section. Seven inches from the test section inlet, local heat transfer coefficients were measured. Reynolds numbers in the test section were from 6000 to 13,000, and the wall temperatures investigated were from 623 O to 755" K. The experimental procedure consisted of measuring local heat transfer coefficients for both pure oxygen and ozone-oxygen mixtures (2.0 to 3.4% ozone b y volume) a t the some Reynolds number and temperature driving force. The chemical reaction reduced the heat transfer coefficient b y as much as 27%. A mathematical analysis based on the film theory model is in agreement with experimental results. HE transfer of heat between a solid surface and a fluid can be tion at the surface andl'or in the fluid. I n addition to a temperature gradient and the ordinary energy transport modes, concentration gradients are established as a result of the chemical reaction, and energy is also transported as chemical or configurational energy associated with the different diffusing molecules. At steady state, the reaction products and reactants diffuse in opposite directions. If there exists a significant difference in their chemical energies-i.e., if the heat of reaction is large-then a substantial net transport of energy results from the mass transfer.Heat transfer in a chemically reacting fluid is influenced by the usual physical properties and the fluid dynamics in the vicinity of the solid surface. However, the nature and rate of the chemical reaction itself are the key factors. If the reaction is sufficiently slow, its effect upon heat transfer can be neglected T .significantly affected by the occurrence of a chemical reac-and heat transfer coefficients computed by conventional methods. At the other extreme, for very fast reversible reactions, diffusion is the rate controlling mechanism, and chemical equilibrium can be assumed throughout the gas. The assumption of chemical equilibrium simplifies the general problem considerably in that the composition is a function of temperature and pressure, and the rate of the chemical reaction is not a factor in the analysis. I n this latter situation, the effect of the chemical reaction can be included as an additive contribution to the thermal conductivity and heat capacity of the fluid-that is, by considering effective thermal properties, the problem is equivalent to heat transfer in a nonreacting fluid with widely varying physical properties. The reversible dissociation of nitrogen tetroxide (N20&2N02) is an excellent example of a gas phase equilibrium reaction, and heat transfer i n this system has been thoroughly studied by many investigators (Brokaw,

Expression of the free β‐subunit of human chorionic gonadotropin in renal cell carcinoma: Prognostic study on tissue and serum

“…However, heat transfer and reaction engineering are currently out of favor as subjects of research in the laboratory. The only direct measurements of enhancement arising from a reaction that were identified are those Edwards and Ferguson13 for the gas‐phase decomposition of oxone in turbulent flow through a uniformly heated glass tube. Their observations of enhancements of up to 27% are consistent with the predictions of Eq.…”

Interaction of Chemical Reactions and Transport. 1. An Overview

“…They predict enhancements of the heat-transfer coefficient by as much as a factor of 10. The work of Edwards and Furgason is somewhat unique in that they carried out both experiments and finite-difference computations to determine the effect of the exothermic gas-phase decomposition of ozone on the heat-transfer coefficient. They found reductions of up to 27%.…”