Flow and Heat Transfer Characteristics of Liquid–Solid Circulating Fluidized Beds

A series of experiments was conducted to investigate the flow and heat transfer characteristics of liquid–solid circulating fluidized beds. The experimental apparatus consisted of a single riser and a downcomer. Water at ambient conditions was used as the fluidizing fluid. Six kinds of particles were tested. First, particle holdup was measured, and a set of systematic data was acquired. By analyzing the experimental data, a simple predicting correlation was derived for the particle holdup. Next, pressure drop measurement was performed, and a predicting correlation was derived. Then heat transfer coefficient was measured, where two regions were identified, i.e., the “heat transfer enhanced region” and the “liquid single-phase heat transfer region.” On the basis of the experimental data, a predicting correlation was derived for each region, and a correlation was proposed for the entire region. Lastly, making use of the already-derived correlations, an analogy was investigated between the frictional pressure drop and the heat transfer coefficient.     

Heat transfer on tube bundles embedded horizontally in a liquid‐fluidized bed

Heat transfer on tube bundles embedded horizontally in a liquid‐fluidized bed was investigated experimentally. In the experiment, a total of 5 kinds of tube bundles in an equilateral triangular staggered arrangement, including a single tube, was used. Tested particles were of glass and ceramics, and their diameter range was from 2.1 to 6.0 mm. It was found that the distribution of local heat transfer coefficients around a tube depends not on the kind of particles, but on the tube pitch only, when a good fluidizing condition is maintained. Based on the experimental data, a new method was proposed to predict average heat transfer coefficient, which can be applicable for tube bundles having a tube pitch to diameter ratio of 1.2 to infinity (single tube). © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 85–98, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20048     

Particle holdup in a liquid–solid circulating fluidized bed

An experiment was conducted to acquire a set of systematic data of particle holdup in risers of a liquid–solid circulating fluidized bed. In the experiment, two kinds of riser were provided, their inner diameter being 24 mm and 36 mm, respectively. Tested particles were of glass and ceramics, having a diameter range from 2.10 to 4.95 mm. Water at ambient conditions was used as the fluidizing liquid. Particle holdup was measured using a shut‐off method. Based on the experimental data, a correlation for predicting the particle holdup was derived, which could reproduce almost all experimental data with an accuracy of ±15%. The effect of the wall was not recognized within the experimental range, i.e., the diameter ratio of particle to riser is less than 0.2. The independent parameters affecting the flow characteristics of liquid–solid circulating fluidized beds were identified. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(3): 184–196, 2008; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/htj.20194     

Heat transfer on tube bundles embedded horizontally in a liquid‐fluidized bed: 2nd report: On tube bundles of fundamental layouts including in‐line layouts

Heat transfer coefficients were measured on tube bundles of fundamental layouts including in‐line layouts embedded horizontally in a liquid‐fluidized bed. Tested tube layouts were single tubes, transverse single tube rows, longitudinal single tube rows, and in‐line arranged tube bundles. A total of 7 kinds of particles were used. Comparisons of the experimental data showed a good agreement with the heat transfer correlation developed for staggered layouts, when the average liquid velocity through each tube bundle was used as the reference velocity for the particle Reynolds number. Distribution of the local heat transfer coefficient was also investigated around tubes. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20245     

Heat transfer in liquid‐fluidized beds affected by column wall

Heat transfer from a column wall to liquid‐fluidized beds was investigated experimentally. The diameter ratio of particle to column was changed from 0.089 up to 0.332, using 11 sizes of particles and two sizes of columns. It was found from the experiment that the critical diameter ratio of particle to column is 0.2; below this value a good fluidizing condition is maintained for any flow rate and the heat transfer coefficient changes smoothly from the minimum fluidization to the liquid single‐phase flow. Based on the experimental data, a correlation was derived to predict heat transfer coefficients for the case affected by a column wall. © 2000 Scripta Technica, Heat Trans Asian Res, 29(7): 598–608, 2000     

Analogy between pressure drop and heat transfer in liquid–solid circulating fluidized beds

An analogy was found between the frictional pressure drop and the heat transfer in liquid–solid circulating fluidized beds. This investigation is based on the predicting correlations for the particle holdup, the heat transfer coefficient, and the pressure drop, which were all developed by the authors. When the heat transfer coefficients were expressed in terms of the modified j‐factor, then a close mutual relationship was observed between the modified j‐factor and the friction factor of the pressure drop due to liquid and particle flow. A correlation to express this mutual relationship was derived, which consists of the density ratio of particle to liquid and the non‐dimensional riser diameter. The heat transfer coefficient predicted from the derived correlation agreed well with the experimental data by the authors, and with existing data. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20246     

Influence of gas/liquid injection on two‐phase flow convective boiling of refrigerant mixtures

An analytical study on the influence of gas/liquid injection on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A and R‐407C in two‐phase flow boiling inside enhanced surface tubing. The data also revealed that gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the boiling point. It was also evident that the proposed correlations and the experimental data that the gas/liquid injection has significant impact on the heat transfer coefficient. In addition, the proposed correlations were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ±20, for the majority of data. Copyright © 2004 John Wiley & Sons, Ltd.     

Influence of liquid injection on two‐phase flow convective boiling of refrigerant mixtures

In this paper, an analytical study on the influence of liquid injection on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the liquid injection the thermophysical properties of refrigerant mixtures as well as the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. It was also evident that the proposed correlations and the experimental data that the liquid injection has significant impact on the heat transfer coefficient. In addition, the proposed correlations were applicable to the entire heat and mass flux, investigated in the present study under the liquid injection conditions. The deviation between the experimental and predicted under liquid injection were less than ±20, for the majority of data. Copyright © 2004 John Wiley & Sons, Ltd.     

Two‐phase flow convective condensation of refrigerant mixtures under gas/liquid injection

The influence of gas/liquid injection on two‐phase flow condensation heat transfer characteristics of some refrigerant mixtures in horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of the gas/liquid injection on the heat transfer characteristics such as average heat transfer coefficient of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow condensation inside enhanced surface tubing. The data also revealed that gas, liquid and gas/liquid injection is beneficial at certain gas/liquid injection ratios to the heat transfer coefficient depending upon the Reynolds number and the condensation point of the refrigerant mixtures in question. It was also evident that the proposed condensation correlations and the experimental data were applicable to the entire heat and mass flux, investigated in the present study under gas/liquid injection conditions. The deviation between the experimental and predicted under gas/liquid injection were less than ± 10, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Augmentation of boiling heat transfer from horizontal cylinder to liquid by movable particles

This paper presents a series of experimental results on a passive augmentation technique of boiling heat transfer by supplying solid particles in liquid. A cylindrical heater 0.88 mm in diameter is placed in saturated water, in which a lot of mobile particles exist, and the nucleate and film boiling heat transfer characteristics are measured. Particle materials used were alumina, glass, and porous alumina, and the diameter ranged from 0.3 mm to 2.5 mm. Particles are fluidized by the occurrence of boiling without any additive power, and the heat transfer is augmented. The maximum augmentation ratio obtained in this experiment reaches about ten times the heat transfer coefficient obtained in liquid alone. The augmentation ratio is mainly affected by the particle material, diameter, and the height of the particle bed set at no boiling condition. The augmentation mechanism is discussed on the basis of the experimental results. © 2001 Scripta Technica, Heat Trans Asian Res, 31(1): 28–41, 2002     

Pressure drop in liquid–solid circulating fluidized beds

An experiment was conducted to obtain data for pressure drop in risers of liquid–solid circulating fluidized beds, where two different risers (24 mm and 36 mm in diameter) were used. Tested particles were of glass and ceramics, and their diameter ranged from 2.10 to 4.95 mm. Water under ambient conditions was used as the fluidizing liquid. Pressure drop in the risers was measured using a reversed U‐tube manometer. Based on the experimental data, a calculation method was derived for predicting the pressure drop in the riser, which could reproduce almost all the data with an accuracy of ±20%. Furthermore, the effect of independent parameters was investigated on the pressure drop component ratios consisting of the total pressure drop. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20241     

Heat transfer on tube bundles embedded vertically in liquid‐fluidized beds

Bed voidage was measured in liquid‐fluidized beds having tube bundles embedded vertically in beds, and the heat transfer coefficient was measured on the outer surface of the tube. There were six kinds of test channels used, and a total of nine types of particles of glass and ceramics were tested. The measured bed voidage agreed well with those developed for in‐column fluidization, when the hydraulic equivalent diameter was used. Measured heat transfer coefficients on the vertically embedded tube bundles were higher than those on the vertically embedded single tubes, the calculated values for the in‐column fluidization, and the calculated values for the horizontally embedded tube bundles. Correlations for predicting the heat transfer coefficient were derived for the vertically embedded tube bundles and single tubes. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20267     

Prediction of heat transfer coefficient in the cyclone separator of a CFB

This paper deals with the study of heat transfer behaviour in the cyclone separator of a circulating fluidized bed (CFB) and how it is affected by relevant operating parameters. The experiments are conducted in a 140 mm diameter cyclone of a cold bed set‐up of 102 mm×102 mm bed cross‐section, 5.25 m height CFB. The cyclone separator is designed according to the high‐efficiency Lapple design and made to accommodate two identical heat transfer probes. From the experimental results, the heat transfer coefficient is found to increase with increase in solid circulation rate, as well as gas superficial velocity. The effect of bed inventory and heat flux on heat transfer coefficient has also been investigated. An empirical equation has been developed to predict the heat transfer coefficient in the cyclone separator based on dimensional analysis. The experimental results are compared with the predicted results and a good agreement has been observed. There is an optimal distance from the entry of the cyclone where the local heat transfer coefficient is maximum. The collection efficiency of the cyclone separator has been measured for all the operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.     

Diameter effect on supercritical heat transfer

The objective of this review is to assess and analyze the literature on the effect of tube diameter on heat transfer at super-critical (SC) pressures. The review is based on SC heat transfer data obtained in tubes with a diameter range of 3.18 to 38.1 mm, cooled by carbon dioxide, water, R-22, and R-12. The majority of experimental studies show that, for the same flow conditions, the heat transfer coefficient (HTC) in the ‘normal’ heat transfer mode increases with a decrease in tube diameter. Furthermore, it was found that at SC pressures, heat transfer is more prone to deteriorate in large tube diameters. In the “deteriorated” heat transfer mode, the HTC also appears to decrease with an increase in tube diameter.     

Prediction of two‐phase condensation characteristics of some alternatives to R‐22 inside air/refrigerant enhanced surface tubing

The results of an experimental study on the heat transfer characteristics of two‐phase flow condensation of some azeotropic refrigerant mixtures, proposed as alternatives to R‐22, on air/refrigerant horizontal enhanced surface tubing are presented. The condensation data indicated that the heat transfer coefficient of the blend R‐408A has the highest heat transfer rate among the blends under investigation. The condensation data also showed that R‐507 and R‐404A have similar heat transfer rates to that of R‐22 when plotted against the refrigerant mass flow rate. It can also be observed that, as the mass flux increases, the heat transfer coefficient increases. Correlations were proposed to predict the heat transfer characteristics such as average heat transfer coefficients as well as pressure drops of alternatives to R‐22 such as R‐507, R‐404A, R‐407C and R‐408A, as well as R‐410A in two‐phase flow condensation inside enhanced surface tubing. In addition, proposed correlations were found to fairly predict the two‐phase flow heat transfer condensation data. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of dynamic load on heat transfer characteristic of a two‐phase pipe boiling flow

An experimental investigation was performed to obtain the flow and heat transfer characteristics of a single‐phase water flow and a two‐phase pipe boiling water flow under dynamic load in the present work. By analyzing the fluid resistance, effective heat, flow pattern, and heat transfer coefficient of the experimental data, the effects of dynamic load on the flow and heat transfer characteristics of single‐phase water and two‐phase boiling water flow were investigated. The results show that the dynamic load significantly influences the flow characteristic and boiling heat transfer of the two‐phase pipe flow. It will enhance the fluid resistance and heat dissipation toward the ambient environment, and reduce the heat transferred to the two‐phase fluid. The impact mixing flow caused by the dynamic load breaks the uniform and varying principle of the wall temperatures. As a result of that, the greater the dynamic load, the lower the wall inner bottom temperature and the higher the wall inner top temperature in a certain extent. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20378     

Two-Phase Flow and Boiling Heat Transfer in Small-Diameter Tubes

For the development of a high-performance heat exchanger using small channels or minichannels for air-conditioning systems, it is necessary to clarify the characteristics of vapor‐liquid two-phase flow and heat transfer of refrigerants in small-diameter tubes. In this keynote paper, the related research works that have already been performed by the author and coworkers are introduced. Based on the observations and experiments of R410A flowing in small-diameter circular and noncircular tubes with hydraulic diameter of about 1 mm, the characteristics of vapor‐liquid two-phase flow pattern and boiling heat transfer were clarified. In low quality or mass flux and low heat flux condition, in which the flow was mainly slug, the “liquid film conduction evaporation” heat transfer peculiar to small-diameter tubes prevailed and exhibited considerably good heat transfer compared to nucleate boiling and forced convection evaporation heat transfer. The effects of the tube cross-sectional shape and flow direction on the heat transfer primarily appeared in the region of the “liquid film conduction evaporation” heat transfer. A new heat transfer correlation considering all of three contributions has been developed for small circular tubes.     

Influence of magnetic field on two‐phase flow convective boiling of some refrigerant mixtures

In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two‐phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R‐507, R‐404A, R‐410A, and R‐407C in two‐phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd.     

Heat transfer prediction of air‐to‐refrigerant two‐phase flow boiling of alternatives to HCFC‐22 inside air/refrigerant enhanced surface tubing

In this paper, an experimental study on the heat transfer characteristics of two‐phase flow boiling of some alternative refrigerants to HCFC‐22, on air/refrigerant horizontal enhanced surface tubing, is presented. Correlations have been proposed to predict the heat transfer characteristics such as average heat transfer coefficients, as well as pressure drops of alternatives to R‐22; such as R‐507, R‐404A, R‐407C, R‐410A and R‐408A in two‐phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was found that the correlations were applicable to the entire heat and mass flux, investigated in the present study, for the proposed blends under question. The deviation between the experimental and predicted values for the heat transfer coefficient and pressure drop were less than ±20, and ±35 per cent, respectively, for the majority of data. Copyright © 2000 John Wiley & Sons, Ltd.     

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity,liquid–liquid,strongly non-regular mixture

We report experimental evidence of a 20–40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid–liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone–hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid–liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid–liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved.