Fluid-particle Heat Transfer Research Articles

Measurement of local particle–fluid heat transfer coefficient in trickle-bed reactors

Particle–fluid heat transfer coefficient measurements are performed in a trickle-bed reactor using self-heated thermistor probes. Adding gas in a liquid flow always causes a decrease of the heat transfer while a further increase of gas load causes an acceleration of the liquid and an increase of heat transfer. Our values are badly predicted by mass transfer correlation combined to the Chilton–Colburn analogy. Radial variations of the heat transfer certainly indicate liquid flow non-uniformities.

Determination of fluid-particle convective heat transfer coefficient

Determination of fluid-particle convective heat transfer coefficient

Heat transfer to particles in shear flow: Application in aseptic processing

Convective heat transfer coefficients at the fluid-particle interface were obtained for shear flow in a holding tube to simulate aseptic processing of particulate-containing liquid foods. The particles were made of polymethyl methacrylate and were suspended in a solution of glycerin in water. The particle temperatures were monitored by placing at the particle center a melting point indicator that changed color at a specific temperature. The fluid-particle heat transfer coefficient varied between 58·3 and 1301·3 W/m 2 K for Reynold numbers of 73·1 and 369·4, and increased with increasing flow rate and particle to tube diameter ratio. The solid fraction enhanced heat transfer between 80 and 200% when the solid fraction was changed to 3·22% from a single particle suspension. The density difference between the particle and fluid was found to influence significantly the residence time of the particles within the holding tube.

Particle-fluid heat transfer and dispersion in fluidised beds

The dynamic response of a gas fluidised bed has been measured for a range of particle sizes of lead glass ballotini and a range of particle Reynolds numbers. A dispersion model has been formulated that includes the effects of gas and particle mixing, fluid-to-particle heat transfer and intraparticle thermal conductivity, and the dynamic thermal response in theory has been found by solving the partial differential equations in the Laplace transform domain. The coefficient of thermal dispersion, the particle-to-fluid heat transfer coefficient and the intraparticle thermal conductivity have been found for the experimental response by non-linear regression. The coefficient of axial dispersion was found to be large and the particle to fluid heat transfer coefficients agreed with an established correlation for fixed and fluidised beds. The intraparticle thermal conductivity agreed with literature values for lead glass, the estimates showed no trend with flowrate, and the standard deviation of the estimate was three times smaller than the deviation found from similar experiments in fixed beds.

Heat transfer and axial dispersion in packed beds

The thermal frequency response of beds packed with glass and metallic particles has been measured in the range of Reynolds numbers from 0·05 to 330. Values of the coefficients of axial dispersion of heat, intraparticle thermal conductivity and fluid-particle heat transfer coefficients have been found by non-linear regression. The experimental frequency response at Reynolds numbers less than one was found to be dominated by thermal dispersion and as the range of small Reynolds numbers was approached the values of particle Nusselt group became constant. The experimental values are compared with the results of other workers. The substantial differences at low Reynolds numbers are due to the inclusion of thermal dispersion in this investigation while others have omitted this effect.

Fluid—particle heat transfer in fixed and fluidized beds

Fluid-particle heat transfer in fixed and fluidized beds is re-examined. The heat transfer factor depends not only on the particle Reynolds number but also on the void fraction of the bed. The available experimental data has been correlated to yield a non-linear relationship between ϵ J h and the particle Reynolds number. The resulting expression is: ▪.