Liquid Solid Fluidized Bed Heat Research Articles

A model for the prediction of thermal resistance of calcium sulfate crystallization fouling in a liquid–solid fluidized bed heat exchanger with cylindrical particles

Calcium sulfate fouling was determined experimentally in a heat exchanger during liquid–solid fluidized bed with cylindrical particles and forced convective (without particles) heat transfer. Then a model to predict the fouling resistance during the solid–liquid fluidized bed heating system was proposed. According to the proposed model and experimental data, a correlation is presented for the prediction of fouling resistances of calcium sulfate during liquid–solid fluidized bed heating at any time. Finally, the prediction of the presented correlation for performed fouling is compared with measured data. Results show that the absolute average percent relative error between experimental data and those obtained by the proposed model vary between 0.6 and 22.8.

Modification of heat transfer correlations in a liquid–solid fluidized bed heat exchanger with cylindrical particles in aggregative fluidization

Most correlations presented for the heat transfer coefficient of liquid–solid fluidized bed heat exchangers are based on experiments with glass bead particles in particulate fluidization which usually under-predict the heat transfer coefficient. The present study used experimental data from previous studies for the heat transfer coefficient in liquid–solid fluidized bed heating systems using cylindrical metal particles and five heat transfer correlations based on experiments with spherical glass beads to approximate the behavior of the cylindrical metal particles under aggregative conditions. The results show that modifying the correlations significantly improved the prediction of heat transfer coefficients and the average relative error decreased in comparison with those for the original correlations.

The effect of particle properties on the heat transfer characteristics of a liquid–solid fluidized bed heat exchanger

The dominant parameters of a liquid–solid fluidized bed heat exchanger are studied both numerically and experimentally. The numerical simulations have been validated using a laboratory scale fluidized bed heat exchanger filled with stainless steel spherical particles as the particulate medium. In addition, the effect of particle properties such as the particle density, specific heat, thermal conductivity and size on the heat transfer characteristics of the fluidized bed heat exchanger have been studied using the strong tool of computational fluid dynamics. The results show that the heat transfer rate can be maximized for an optimum particle size. Moreover, the study on different materials has been conducted comparing stainless steel, aluminum and copper as the particulate phase. The obtained results of different particle properties are discussed considering the hydrodynamics and heat transfer aspects of changing the particle properties.

Numerical investigation on prevention of fouling in the horizontal tube heat exchanger: Particle distribution and pressure drop

To improve the performance of fouling prevention in liquid–solid fluidized bed heat exchanger with the horizontal tube bundle, parametric study of particle distribution and pressure drop in the heat exchanger was numerically conducted. Eulerian multiphase fluid model was used to calculate the flow of liquid–solid two phase in heat exchanger by means of the commercial software Fluent. In the simulation result, it was demonstrated that more particles occurred in the lower tubes of the horizontal tube bundle in low velocity due to the lack of full fluidization. Relative to that in low velocity, uniformity distribution of particle was obtained in high velocity which was accompanied with greater dynamic pressure drop. The particle with the greater density and diameter was inclined to sediment in the lower tubes due to larger sediment velocity and difficulty in the realization of full fluidization. Meanwhile an increase in size and density of particle would bring about greater pressure drop originating from more particle kinetic energy consumed. Effect of volume fraction of solid phase on particle distribution and pressure was discussed. It showed that an increase in volume fraction of solid phase led to significant rise of pressure drop. It was because consumed kinetic energy and collision energy of particles were greatly amplified with the increasing volume fraction of solid phase. Therefore greater volume fraction of solid phase, especially for the particle with the greater diameter and density, would not be recommended in the performance of fouling prevention in the horizontal tube bundle heat exchanger.

Mitigation of ice crystallization fouling in stationary and circulating liquid–solid fluidized bed heat exchangers

Liquid–solid fluidized bed heat exchangers are attractive ice crystallizers since they are able to mitigate ice crystallization fouling and exhibit high heat transfer coefficients. Experiments show that the fouling removal ability of stationary fluidized beds increases with decreasing bed voidage (95–80%) and increasing particle size (2–4 mm). The removal of ice crystallization fouling appears to be more effective in circulating fluidized beds, especially at high circulation rates. Fouling removal is realized by both particle–wall collisions and pressure fronts induced by particle–particle collisions. A comparison between ice crystallization experiments and impact characteristics shows that the removal rate is proportional to the impulse exerted on the wall. A model based on these phenomena is discussed and predicts the transition temperature difference for ice crystallization fouling in both stationary and circulating fluidized beds with an average absolute error of 9.2%.

Prevention of fouling and scaling in stationary and circulating liquid–solid fluidized bed heat exchangers: Particle impact measurements and analysis

Fluidized particles in liquid–solid fluidized bed heat exchangers are able to remove deposits from the walls and thus to prevent fouling or scaling. This fouling prevention ability is believed to depend strongly on the frequency and force of particle–wall collisions. This paper presents piezoelectric measurements of impacts on the wall in both stationary and circulating fluidized beds of various particle sizes and bed voidages. Two types of impacts were measured, namely by collisions of particles on the sensor and by liquid pressure fronts induced by particle–particle collisions close to the sensor. The characteristics of both impact types are used to analyze the total impulse and energy exerted by impacts on the wall for various fluidized beds.

Heat transfer and operating conditions for freeze concentration in a liquid–solid fluidized bed heat exchanger

Freeze concentration involves concentrating liquids partially by freezing water out of the solution thus leaving behind a concentrate rich in its solutes. It is an expensive process that could benefit from alternative approaches that are more cost-effective. In this paper, freeze concentration is studied inside a fluidized bed heat exchanger (FBHE), which is a cheaper alternative to the conventionally used scraped surface heat exchanger (SSHE) in a freeze concentration process. A pilot scale vertical fluidized bed heat exchanger was designed and constructed in the University of Auckland to test the feasibility of this process using stainless steel (SS) particles for ice removal. Experiments were conducted with NaCl solutions to determine the effect of NaCl concentration and bed porosity on the stability of operation. Operating stability improved with increasing NaCl concentration and decreasing bed porosity proving the feasibility of this equipment to freeze concentrate liquid solutions at certain conditions in the range of parameters tested. A long-term freeze concentration experiment was carried out in which freeze concentration in the solution was confirmed via freezing point depression (FPD). FBHE can be used to freeze concentrate NaCl liquids more cost-effectively than SSHE at stable conditions within the range of tested parameters.

Bed Voidage and Heat Transfer in Non-Newtonian Liquid-Solid Fluidized Bed

The presence of particles in liquid-solid fluidized beds enhances the bed heat transfer, because the movement of the particles leads to an increased turbulence in the system. Moreover, the violent movement of the particles has a positive effect on fouling of the heat transfer surface. The aim of this investigation was to perform systematic measurements of bed voidage and heat transfer coefficient for solid-liquid fluidization in a cylindrical tube and to study the effect of process parameters such as particle size and density, flow velocity, and liquid viscosity on these subjects. A large number of experiments were performed using different cylindrical and spherical particles fluidized in aqueous CMC solution with different concentrations. Using the experimental results, a new correlation for predicting heat transfer coefficient in non-Newtonian liquid-solid fluidized bed heat exchanger was introduced.