Trickle Flow Regime Research Articles

CFD and experimental studies of reactive pulsing flow in environmentally-based trickle-bed reactors

Pulsing flow in trickle-bed reactors (TBRs) has been claimed to promote the averaged heat and mass transfer rates, thereby enhancing the overall conversion and productivity. In this work, we focused on the mineralization of organic matter by catalytic wet oxidation at different liquid flow modulations. The convective nature of the disturbances that lead to pulsing was simulated by an Eulerian Computational Fluid Dynamics (CFD) model and validated with experimental data. In order to evaluate the predicted effects of pulsing on reaction outcome, first the multiphase flow governing equations were detailed with the computational methodology used in the simulation procedure. Prominent numerical parameters were optimized in terms of mesh aperture and time step. Second, to enable objective assessments of the merits of the different cyclic strategies, several computational runs were performed addressing the effect of nominal gas and liquid flow rates as well as the oxidation temperature. Here, we found that the concentration profile computed by the CFD model for pulsing flow conditions demonstrated superior oxidation performance over the trickling flow regime, which has been further corroborated by experimental evidences. Afterwards, the normalized concentration series close to the top of the TBR exhibited sharp fronts and gradually become less intense as they travel downward that reflected the nonisolated nature of the traveling liquid pulsations. Finally, these computational and experimental findings enabled us to intensify the detoxification of high-strength wastewaters and can be further exploited due to advantageous dispersive and convective heat/mass transfer phenomena under pulsing flow conditions.

Hydrodynamic Simulation of Pulsing-Flow Regime in High-Pressure Trickle-Bed Reactors

In the present study, attention is focused on the CFD simulation of trickle-bed reactors when the trickling-flow regime changes into the pulsing-flow regime, along with the parameters that characterize this latter regime. These parameters include the velocity at which the pulse front travels along the bed, the frequency of pulsations, and the structure of pulses being formed (i.e., the sizes of the liquid-rich and gas-rich zones). Results are presented for a three-phase reactor operating at an elevated pressure in the pulsing-flow regime. Several parameters that characterize the pulsing flow, namely, the velocity of pulses traveling along the bed, the frequency of pulsations and their structure, the length of the pulses, and the length of the liquid-rich zone, were examined at high pressure by means of an Eulerian CFD model.

Cyclic Operation Strategies in Trickle Beds and Electrical Capacitance Tomography Imaging of Filtration Dynamics

The dynamics of propagating liquid pulsations generated via various cyclic operation strategies in trickle beds was monitored through electrical capacitance tomography (ECT) for gas and liquid superficial velocities in the range of trickle flow regime. The characteristics of ON−OFF liquid, ON−OFF gas, and gas/liquid alternating cyclic operations were compared in terms of mean liquid holdup, pressure drop, pulsation intensity, pulsation propagation velocity, and spatial maldistribution maps of liquid holdup and liquid pulsation propagation velocity. The morphological features of liquid holdup pulsations as a function of cycle frequency were characterized in terms of breakthrough, plateau, and decay times. Gas/liquid alternating cyclic strategy was shown to produce long-lived liquid pulsations under the applied operating conditions and thus could be viewed as a new process intensification means to achieve uniform phase holdup and velocity distributions. In ON−OFF liquid cyclic operation, pulsation velocity ...

CFD modelling of multiphase flow distribution in trickle beds

Abstract Multiphase flow in trickle-bed reactors (TBR) is known to be extremely complex and depends on a multitude of effects including the physico-chemical properties of both gas, liquid and solid phases, the ratio of column diameter to particle diameter and most importantly the gas and liquid superficial velocities. Despite several works devoted to the experimental investigation of liquid distribution, there is yet no universal agreement on the influence of interstitial phenomena on overall TBR hydrodynamics. Consequently, a Eulerian multiphase model was developed to predict the liquid holdup and pressure drop in the trickling flow regime with a 3D computational grid. The multiphase model was optimized in terms of mesh density and time step for the successful hydrodynamic validation activities. The model predictions correctly handled the effect of different numerical solution parameters. Afterwards, particular attention is paid to the consequences on flow development and hydrodynamic parameters of imposing liquid maldistribution at the bed top with three types of liquid distributors. Several computational runs were carried out querying the effect of gas and liquid flow rate on overall hydrodynamics. Computational fluid dynamics (CFD) predictions demonstrated that liquid flow rate had a prominent effect on radial pressure drop profiles at the higher values whereas the gas flow rates had it major outcome at lower regimes. Regarding the liquid holdup predictions, several time averaged for radial and axial profiles illustrated that a five times increase on liquid flow rate cannot be matched by an equivalent change on gas flow rate. The increase in both flow rates was found to smooth the oscillatory behaviour of local phenomena, but the gas flow rate had an outstanding consequence on both hydrodynamic parameters. Finally, CFD simulations at atmospheric conditions were compared with the pressurized ones. Liquid holdup fluctuations of about 25% between the liquid-rich and the gas-rich zone can be smoothened as long as the operating pressure is increased until 30 bar.

Trickle flow hydrodynamic multiplicity: Experimental observations and pore-scale capillary mechanism

Trickle bed reactors are encountered throughout the process industry. Considerable attention has been given to the study of the hydrodynamics of this type reactor. It has been identified that, in the trickle flow regime, the hydrodynamic parameters (e.g. pressure drop and liquid holdup) are not unique functions of the operating and system conditions, but depend on the flow history. This study reviews the experimental trends identified in literature on the basis of a limiting cases framework and then evaluates the three-dimensional pore-scale liquid distribution using computed tomography (CT) data. This leads to the identification of 20 phenomenological trends that characterize hydrodynamic multiplicity, including hydrodynamic flow hysteresis as well as the effects of pre-wetting. The CT study yields additional experimental insight into the role of capillary pressure and ultimately leads to the proposal of a capillary gate mechanism based on contact angle hysteresis as the root cause of multiplicity. The mechanism is incorporated into a simple pore-network model. It is shown that the qualitative performance of the model corresponds closely to the majority of phenomenological trends and is capable of explaining the observed experimental behaviour.

Comparison of different reactor types for low temperature Fischer–Tropsch synthesis: A simulation study

The commercially established slurry bubble column and fixed-bed reactors for low temperature Fischer–Tropsch synthesis were compared with novel micro- and monolith-reactors by mathematical modeling. Special attention was paid to the influence of catalytic activity on the reactor efficiency and the losses by mass and heat transfer resistances. The simulation results show that a micro-structured reactor exhibits the highest productivity per unit of catalyst volume followed by slurry bubble column reactor and monolith reactor. The fixed-bed reactor that was assumed to operate in the trickle-flow regime has a particularly low catalyst specific productivity due to severe mass transfer resistances. However, caused by a very low ratio of catalyst and reactor volume the micro-reactor has only a similarly low productivity per unit of reactor volume as the fixed-bed reactor. In contrast, the reactor specific productivity of slurry bubble column reactor and monolith reactor is up to one order of magnitude higher.

Effect of Particle Porosity on Hysteresis in Trickle-Bed Reactors

Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs.

Structure of trickle-to-pulse flow regime transition and pulse dynamics at elevated temperature in slow-mode cyclic operation

The effects of temperature and pressure on the structure of the trickle-to-pulse flow regime transition in slow-mode cyclic operation in trickle-bed reactors were reported. The relationship between liquid holdup and liquid velocities at the trickle-to-pulse flow transition in cyclic operation, the shock wave behavior as a function of bed depth, as well as the pulsing flow regime properties were investigated for Newtonian (air–water) and non-Newtonian (air–0.25% carboxymethylcellulose (CMC)) liquids. At a given temperature, the breakthrough, plateau and decay times of the shock wave were found to decrease with bed depth. The pulse velocity and pulse frequency for pulsing flow regime both in cyclic operation and in natural pulsing (constant-throughput operation) were observed to increase with temperature. However, increasing the reactor pressure led to increased pulse frequency and decreased pulse velocity. Analysis of the transition liquid holdups for natural pulse flow and cyclic operation revealed that the liquid holdup decreased with temperature and pressure. The transition liquid holdups and superficial liquid pulse velocities in symmetric peak-base cyclic operation surpassed those in constant-throughput operation for given temperature, pressure and gas velocity, giving rise to wider trickle flow regime area in cyclic operation. The behavior of both Newtonian and power-law non-Newtonian fluids was similar regarding the effect of temperature, pressure and gas velocity.

Lateral mixing in trickle bed reactors

Knowledge of lateral mixing is essential to understand heat and momentum transfer parameters in both single-phase liquid and two-phase gas–liquid co-current down flow through packed bed columns. The reactors through which gas and liquid concurrently flow downwards through a bed of catalytic packing are called trickle bed reactors. Experimental data on lateral mixing coefficients from both the heat transfer and radial liquid distribution studies are obtained over a wide range of flow rates of gas ( 0.01 – 0.898 kg / m 2 s ) and liquid ( 3.16 – 71.05 kg / m 2 s ) using glass spheres (4.05 and 6.75 mm), ceramic spheres (2.59 mm), and ceramic raschig rings (4 and 6.75 mm) as packing materials covering trickle flow, pulse flow, and dispersed bubble flow regimes. In the present work, an expression for estimation of lateral mixing coefficient ( α β ) L is derived using the data on radial liquid distribution studies. The agreement between the values of ( α β ) L obtained from heat transfer studies and from radial liquid distribution studies using the experimental data shows that there exists an analogy between the heat transfer and radial liquid distribution in packed beds. Since ( α β ) L is an important variable for estimation of various heat and mass transfer parameters, a correlation for ( α β ) L based on present heat transfer study is proposed. The agreement between the ( α β ) L values estimated from the proposed correlation and experimental values is satisfactory with a standard deviation (s.d.) of 0.119.

RTD IN TRICKLE BED REACTORS: EXPERIMENTAL STUDY

Axial dispersion has been measured in a laboratory-scale model trickle bed reactor at different liquid and gas flow rates under co-current down-flow condition. Air was used as gas phase and water or aqueous polyethylene glycol solution was used as liquid phase, covering the Reynolds number range of 0–164 for gas phase and 4–86 for liquid phase. Liquid phase residence time distribution was measured using a 1 M KCl pulse tracer. The axial dispersion model was used to simulate the observed RTD, and liquid phase PeL and BoL were estimated as model parameters. Based on the results, it was observed that under low interaction flow regime (trickle flow), liquid phase Bodenstein number, BoL, increased gradually with liquid phase Reynolds number, ReL, and was found to be nearly independent of gas phase Reynolds number, ReG. Near the flow transition point, BoL or PeL decreased, and in the high interaction regime it showed an oscillatory response. In the trickle flow regime .

Prediction of pressure drop and liquid holdup in trickle bed reactor using relative permeability concept in CFD

A Computational Fluid Dynamics (CFD) model based on porous media concept is presented to model the hydrodynamics of two-phase flow in trickle-bed reactors (TBRs). The aim of this study is to develop a comprehensive CFD based model for predicting hydrodynamic parameters in trickle-bed reactors under cold-flow conditions. The two-phase Eulerian model describing the flow domain as a porous region has been used to simulate the macroscale multiphase flow in trickle beds operating under trickle flow regime using FLUENT 6.2 software. The closure terms for phase interactions have been addressed by adopting the relative permeability concept [Sàez, A.E., Carbonell, R.G., 1985. Hydrodynamic parameters for gas–liquid cocurrent flow in packed beds. A.I.Ch.E. Journal 31, 52–62]. The model has been evaluated by comparing predictions with the data (collected under a varied set of laboratory conditions) available in the open literature. It is shown that while being relatively simple in structure, this CFD model is flexible and predictive for a large body of experimental data presented in the open literature.

Catalytic and non-catalytic wet air oxidation of sodium dodecylbenzene sulfonate: Kinetics and biodegradability enhancement

Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) were investigated as suitable precursors for the biological treatment of industrial wastewater containing sodium dodecylbenzene sulfonate (DBS). Two hours WAO semi-batch experiments were conducted at 15 bar of oxygen partial pressure ( P O 2 ) and at 180, 200 and 220 °C. It was found that the highest temperature provides appreciable total organic carbon (TOC) and chemical oxygen demand (COD) abatement of about 42 and 47%, correspondingly. Based on the main identified intermediates (acetic acid and sulfobenzoic acid) a reaction pathway for DBS and a kinetic model in WAO were proposed. In the case of CWAO experiments, seventy-two hours tests were done in a fixed bed reactor in continuous trickle flow regime, using a commercial activated carbon (AC) as catalyst. The temperature and P O 2 were 140–160 °C and 2–9 bar, respectively. The influence of the operating conditions on the DBS oxidation, the occurrence of oxidative coupling reactions over the AC, and the catalytic activity (in terms of substrate removal) were established. The results show that the AC without any supported active metal behaves bi-functional as adsorbent and catalyst, giving TOC conversions up to 52% at 160 °C and 2 bar of P O 2 , which were comparable to those obtained in WAO experiments. Respirometric tests were completed before and after CWAO and to the main intermediates identified through the WAO and CWAO oxidation route. Then, the readily biodegradable COD (COD RB) of the CWAO and WAO effluents were found. Taking into account these results it was possible to compare whether or not the CWAO or WAO effluents were suitable for a conventional activated sludge plant inoculated with non adapted culture.

Catalytic wet air oxidation of substituted phenols: Temperature and pressure effect on the pollutant removal, the catalyst preservation and the biodegradability enhancement

The influence of temperature (140 and 160 ◦ C) and oxygen partial pressure (2 and 9 bar) on the continuous catalytic wet air oxidation (CWAO) over activated carbon (AC) has been investigated for the removal of phenol, o-cresol and 2-chlorophenol in aqueous solutions. Seventy-twohour tests were performed in a fixed bed reactor in trickle flow regime. A commercial AC was employed as catalyst. The pollutant elimination effectiveness, the distribution of major reaction products and the AC behaviour were studied for each compound. Also, respirometric screening tests were completed to the effluents before and after each CWAO experiment to assess the biodegradability enhancement. The results show that pollutant disappearance, chemical oxygen demand (COD) removal, total organic carbon (TOC) abatement and biodegradability enhancement (fraction of COD readily biodegradable, %CODRB) were very sensitive to temperature but rather independent of the oxygen partial pressure (PO2 ). On the contrary, AC catalyst preservation was strongly influenced by both temperature and pressure. For instance, for phenol CWAO at 2 bar of PO2 ,a s temperature increased from 140 to 160 ◦ C, phenol conversion increased from 45% to 78%, COD removal from 33% to 65%, TOC abatement from 21% to 62% and %CODRB from 4% to 36%. Similar behaviour was found for the other model compounds tested, although the level of refractoriness was rather different. © 2007 Elsevier B.V. All rights reserved.

Solid Foam Packings for Multiphase Reactors: Modelling of Liquid Holdup and Mass Transfer

In this paper, experimental and modeling results are presented of the liquid holdup and gas–liquid mass transfer characteristics of solid foam packings. Experiments were done in a semi-2D transparent bubble column with solid foam packings of aluminum in the range of 5–40 pores per inch (ppi). The relative permeability model described by Saez and Carbonell (1985) is used to describe the liquid holdup data for solid foam packings of 5, 20 and 40 ppi. The investigated system variables are the superficial gas and liquid velocities, using counter-current flow with maximum gas velocities and liquid velocities of 0.8 m s−1 and 0.03 m s−1, respectively. The relative permeability model is able to describe the liquid holdup in the low liquid holdup or trickle flow regime as well as in the high liquid holdup regime, which resembles flow in a packed bubble column. Gas-to-liquid mass transfer is modelled using the penetration theory. Mass transfer coefficients up to 6 s−1 are predicted; these high values are largely due to the high specific surface area of the solid foam packings.

A study of local liquid/solid mass transfer in packed beds under trickling and induced pulsing flow

Induced pulsing flow (by cyclic liquid feeding) in packed beds, operated in the trickling flow regime, is studied as a method of overall improvement of catalytic reactor operation. In this paper results are reported of experiments aimed at determining local and global liquid/solid mass transfer rates, mainly for the so-called fast mode of ON–OFF periodic liquid feeding, with frequencies of order 0.1 Hz. Such mass transfer data for the fast mode of induced pulsing are not available in the literature. Uniform 6 mm glass spheres and alumina cylindrical extrudates, of 1.5 mm diameter and a narrow distribution of lengths, are employed in the tests. For completeness, results are also reported for single-phase (liquid) and trickling flow through the same packed beds. A well-known electrochemical technique is employed to measure instantaneous local mass transfer coefficients by means of quite a few probes distributed throughout the bed. The hydrodynamic characteristics under the above conditions, reported in companion papers, are helpful in interpreting the new mass transfer data. There is a wide spread of the time-averaged local mass transfer rates, in all cases tested, apparently due to packing and flow non-uniformities. This spread is much smaller in the case of packed uniform spheres. In general, the benefits of cyclic liquid feeding are more evident in the packed bed of spheres than in that of cylindrical extrudates; for instance, with increasing mean liquid rate, induced pulsing tends to reduce the spread of local mass transfer coefficients, which suggests that more uniform fluids distribution is promoted. The imposed liquid pulses are reflected in the observed periodic variation of local mass transfer coefficients; the latter appear to decay along the bed in the same manner as the liquid pulses. Other trends of local mass transfer rates are identified and discussed in relation to measured variation of liquid holdup, under the same conditions. For packed spheres, the measured global mass transfer rates are in fair agreement with literature correlations obtained for the trickling flow regime, unlike the case of packed extrudates where significant deviation is observed.

Flow Regime Transition in a Trickle Bed Reactor

ABSTRACT Hydrodynamic behavior of a trickle bed reactor is dependent on the flow regime that arises when gas and liquid flow concurrently downward in the reactor. Empirical or semi-analytical models available in the literature do not predict to satisfaction the transition between the trickle and pulse flow regimes in cocurrent down flow in a TBR. In the present study, flow transition between trickle flow (low-interaction) and pulse flow (high-interaction) regimes was experimentally observed for different non-foaming Newtonian and non-Newtonian liquid phases under concurrent down flow conditions with air in a packed bed using different bed configurations. The effect of bed geometry along with fluid phase properties has been considered to modify the flow map coordinates, so as to collapse the data corresponding to different bed configurations and Newtonian liquid-phase properties onto a single curve (within±20%). An empirical correlation for the prediction of Newtonian liquid-phase mass velocity at the transition between high interaction and low interaction regimes was developed, which assumes the form: The correlation was found to be in good agreement with the experimental data available in the literature for different Newtonian liquid-phase systems including data on nonspherical particles. This correlation is found to predict the transition satisfactorily when liquid-phase viscosity was replaced by apparent viscosity in the case of viscoinelastic liquid-phase systems. The correlation was further extended to predict the transition for a viscoelastic liquid-phase system with the introduction of the Weissenberg number as:

Trickle bed hydrodynamics and flow regime transition at elevated temperature for a Newtonian and a non-Newtonian liquid

Despite the hydrodynamics of trickle beds experiencing high pressures has become largely documented in the recent literature, trickle bed hydrodynamic behavior at elevated temperatures, on the contrary, largely remains terra incognita. This study's aim was to demonstrate experimentally the temperature shift of trickle-to-pulse flow regime transition, pulse velocity, two-phase pressure drop, liquid holdup and liquid axial dispersion coefficient. These parameters were determined for Newtonian (air–water) and non-Newtonian (air–0.25% Carboxymethylcellulose (CMC)) liquids, and the various experimental results were compared to available literature models and correlations for confrontation and recommendations. The trickle-to-pulse flow transition boundary shifted towards higher gas and liquid superficial velocities with increasingly temperatures, aligning with the findings on pressure effects which likewise were confirmed to broaden the trickle flow domain. The Larachi-Charpentier-Favier diagram [Larachi et al., 1993, The Canadian Journal of Chemical Engineering 71, 319–321] provided good predictions of the transition locus at elevated temperature for Newtonian liquids. Conversely, everything else being kept identical, increasingly temperatures occasioned a decrease in both two-phase pressure drop and liquid holdup; whereas pulse velocity was observed to increase with temperature. The Iliuta and Larachi slit model for non-Newtonian fluids [Iliuta and Larachi, 2002, Chemical Engineering Science 46, 1233–1246] predicted with very good accuracy both the pressure drops and the liquid holdups regardless of pressure and temperature without requiring any adjustable parameter. The Burghardt et al. [2004, Industrial and Engineering Chemistry Research 43, 4511–4521] pulse velocity correlation can be recommended for preliminary engineering calculations of pulse velocity at elevated temperature, pressure, Newtonian and non-Newtonian liquids. The liquid axial dispersion coefficient ( D ax ) extracted from the axial dispersion RTD model revealed that temperatures did not affect in a substantial manner this parameter. Both Newtonian and power-law non-Newtonian fluids behaved qualitatively similarly regarding the effect of temperature.

Estimation of trickle-to-pulse flow regime transition and pressure drop in high-pressure trickle bed reactors with organic liquids

Flow regime boundaries and pressure drop in trickle bed reactors are crucial for design, scale-up and operation of such reactors. The flow map experiments are performed in a pilot plant reactor of 0.051 m diameter and 1.2 m height, with cumene–hydrogen system. A new technique – the acoustic signal measurement – is used for distinguishing between trickle and pulse flow regimes. The effect of operating pressure was investigated in the pressure range of 0.14–2.0 MPa. For higher operating pressures, the trickle-to-pulse transition boundary moves towards higher flow rates of both liquid and gas phases. The pressure drop over the reactor bed is increasing with increasing operating pressure and gas/liquid throughputs. The pressure drop results obtained with hydrogen at higher operation pressures match reasonably well the results obtained with air–water at atmospheric pressure. This comparison is made using a new developed pressure drop correlation and illustrates the influence of increased gas density (high operating pressure effect). The Trickle Bed Simulator of University Laval [F. Larachi, B. Grandjean, I. Iliuta, Z. Bensetiti, A. André, G. Wild, M. Chen, Excel Worksheet Simulator for Trickle-Bed Reactors, http://www.gch.ulaval.ca/bgrandjean/pbrsimul/pbrsimul.html, 1999] was found to match reasonably well our pilot plant measured values for low and high operating pressures.

Characterization of Multiple Flow Morphologies within the Trickle Flow Regime

The existence of multiple hydrodynamic states in the trickle flow regime is a well documented, but as yet poorly quantified phenomenon. The prewetting procedure is known to drastically impact the hydrodynamic state and morphology of the liquid flow. In this work, three limiting cases for the case of no gas flow are identified: Nonprewetted, Levec-prewetted, and pseudo-Kan-prewetted. For the quiescent air-distilled water-3 mm glass spheres system, it is shown that bed-scale maldistribution exists in all three modes of operation, but is more severe in the Levec- and nonprewetted modes. The incorporation of a novel volumetric utilization coefficient into an existing momentum balance-based holdup model is sufficient to accurately model the holdup in all prewetted modes (AARE = 9.2%). This results in the first holdup model that takes the prewetting procedure into account. Present results support the notion that Kan-type prewetting results in film flow, while Levec- and nonprewetted modes are dominated by rivulet flow.

Induced pulsing in trickle beds—characteristics and attenuation of pulses

Gas/liquid down-flow in packed beds is studied, under periodic liquid feeding (at sufficiently high frequencies to be classified as “ fast” mode of pulsing), in a range of mean liquid and gas flow rates within the steady “trickling flow regime”. The aim is to identify periodic feeding conditions resulting in improved fluid-mechanical characteristics (e.g. uniform fluids distribution) and possibly enhanced transport rates in this flow regime, which is common in industrial processes. From instantaneous, cross-sectionally averaged holdup measurements, at various locations along the packed bed, quantitative information is obtained on the axial propagation and attenuation of induced pulses. A phenomenological treatment of the pulse decay process facilitates data interpretation and leads to the determination of a characteristic attenuation factor for the various conditions tested. Key parameters of the process studied include, in addition to dynamic holdup, pressure drop, pulse celerity and intensity, as a function of fluid feed rates ( G , L ) and liquid cyclic frequency. Under the conditions of these tests, and for fixed mean rates G , L , the time averaged holdup and the pulse celerity are practically constant along the bed; furthermore, these quantities as well as the pressure drop do not seem to be affected by the imposed cyclic liquid feeding frequency. An expression to tentatively correlate pulse celerity data is recommended. The computed attenuation factors indicate that there is a rather narrow band of mean gas and liquid rates (along the so-called “pseudo-transition” boundary to pulsing flow) where pulse decay is at a minimum. Based on these results as well as on pulse intensity vs. bed length data, recommendations are made on preferred conditions for induced pulsing (from the fluid-mechanical standpoint) which would maximize expected benefits.