A two-colour pyrometer was developed for measuring the temperature of single moving particles (typically 50 mu m in diameter, moving with a velocity of 3.8 m s-1) over the temperature range 1473-2773K. The rise and response times were 0.5 and 0.1 ms respectively; the accuracy was estimated to be +or-50K. The instrument has been used to study the combustion of single particles of sulphide minerals.

Two-colour pyrometer measurement of the temperature of individual combusting particles

Multi-phase flow measurements in powder processing

The temperatures of individual sulfide particles combusting in air have been measured with a two-wavelength radiation pyrometer. The pyrometer design allowed the temperature of the combusting particles to be measured for 15 to 30 ms; and the response of the system was sufficient to determine the heating rates of particles during reaction. The combustion of galena, pyrite, and pyrrhotite, in air, at 1130 K was investigated. The different minerals produced distinct combustion pulses which were recorded repeatedly. Galena particles reacted in air at a relatively constant apparent temperature of between 1400 and 1700 K. Reaction product fume was observed trailing behind the combusting particles. The pyrometer pulses recorded during the combustion of pyrite and pyrrhotite particles were similar; however, pyrite tended to ignite more rapidly than pyrrhotite. During combustion in air, the temperature of the iron sulfide particles increased at a constant rate up to a maximum of 2200 to 2600 K after which rapid cooling occurred; a sudden rise in combustion energy at peak temperature was likely due to an merease in the particle size resulting from the formation of cenospheres.

Two-wavelength pyrometry study of the combustion of sulfide minerals: Part I. Apparatus and general observations

An analysis was made of the rate of heat transfer by convection, radiation, and chemical reaction to a dispersion of particles in a non-absorbing gas The gas-solids suspension was subjected to co-gravitational flow at low Reynolds Numbers (50–500) through a cylindrical reactor, the wall of which was maintained at a uniform temperature (400–900°C) The rate of heat transfer by convection from the wall to the gas was determined experimentally The differential equations were solved on an IBM-650 digital computer, for the reduction of iron oxide particles (40 to 100 microns) by hydrogen The program output recorded the particle residence time and corresponding values of gas and particle temperatures, length of reactor travelled, percent reduction, and individual rates of heat transfer to the particle by convection, radiation and chemical reaction Experimental measurements in an electrically-heated, 44-in id × 85 ft long stainless steel reactor verified the calculated prediction that the particle temperature should at all time be nearly equal to that of the gas



Une analyse du taux de transfert de chaleur par convection, radiation et reaction chimique a une dispersion de particules dans un gaz non-absorbant a ete entreprise dans un reacteur cylindrique en acier inoxydable de 44”, diametre interieur, par 85 pi de longueur, dont les parois chauffees electriquement etaient maintenues a une temperature uniforme (400–900°C) La suspension de particules s'y ecoule de facon co-gravitationnelle a des nombres de Reynolds faibles (50–500) Le taux de transfert de chaleur par convection depuis la paroi au gaz a ete determine experimentalement Les equations differentielles pour la reduction des particules d'oxyde de fer (40 a 100 microns) par l'hydrogene ont ete resolues a l'aide de la calculatrice digitale IBM-650 Selon le temps de residence des particules il a ainsi ete determine les temperatures correspondantes du gaz et des particules, la longueur de la trajectoire dans le reacteur, le pourcentage d'oxydes reduit et les taux individuels de transfert de chaleur aux particules par convection, radiation et reaction chimique Les resultats experimentaux ont verifie l'hypothese que la temperature de la particule doit ětre en tout temps quasi egale a celle du gaz

Heat transfer to clouds of particles

Heat transfer in turbulent duct flow of a suspension of fine particles is examined. The flow is fully developed but the temperature profiles due to heat transfer are not. Two coupled similar equations define the system and illustrate the limitations which arise through describing heat transfer between the phases in terms of a particle heat transfer coefficient. In this case, however, the equations may be reduced to two equations of the Sturm-Liouville type. The solutions of these have eigenfunctions which are closely related and they share a common series of eigenvalues. The latter conclusions are expected to apply more readily to a transport reactor of large bore which circulates fine noncohesive particles.

Heat transfer in a gas borne suspension of fine particles in turbulent duct flow

The measurement of particle temperature in gas-solids suspensions by conventional pyrometric methods is complicated by a lack of knowledge of the particle emissivity and the absorption strength of the cloud. Further difficulties may be caused by background re-radiation, variations in geometrical factors and - if the particles are undergoing chemical reaction - rapid changes in the particle temperature. These difficulties can be eliminated if the radiant energies emitted by the particles at two different wavelengths (close in value) are measured simultaneously.



A pyrometer based on this principle was designed and constructed for measuring temperatures both in the infra-red (500–900 C.) and the visible (800–1200°C.) ranges. The radiation from the particles was passed through suitable pairs of monochromatic filters inserted in diametrical opposition into a metal disk rotating at speeds up to 8,000 r.p.m. The two alternating beams were focused on the cathode of a photoelectric cell, and the resulting voltages measured by means of a cathode-ray oscilloscope. The instrument was used successfully in an investigation of the rate of reduction of small iron oxide particles in the presence of hydrogen at temperatures ranging from 500 to 1100°C.



La mesure de la temperature des particules dans les suspensions gaz-solides, par les methodes pyrometriques conventionnelles, est compliquee en raison du manque de connaissances sur l'emissivitee des particules et sur le pouvoir d'absorption du nuage. D'autres difficultes peuvent provenir du re-rayonnement de l'arriere-plan, de variations dans les facteurs geometriques-si les particules sont soumises a une reaction chimique - et de changements rapides de temperature des particules. On peut eliminer ces difficultes en mesurant stimultanement les energies rayonnantes emises par les particules a deux longueurs d'onde differentes, mais rapporchees.



Les auteurs ont elabore et construit un pyrometre base sur ce principe pour les mesures de temperature a la fois dans l'infra-rouge (500–900 C) et aux longueurs d'onde visibles (800–1200 C). La radiation en provenance des particules passait par des paires de filtres monochromatiques appropries, places en opposition diametrale dans un disque de metal tournant a des vitesses allant jusqu'a 8000 r.p.m. On dirigeait les deux faisceaux alternes sur la cathode d'une cellule photo-electrique et on mesurait les voltages resultants au moyen d'un oscilloscope a rayons cathodiques. L'instrument s'est comporte de facon satisfaisante au cours d'une etude sur le taux de reduction de petites particules d'oxyde de fer en presence d'hydrogene a des temperatures allant de 500 a 1100 C.

N. J. Themelis

Papers

A two‐wavelength pyrometer for temperature measurements in gas‐solids systems