Total Air Flow Rate Research Articles

A Study of an Integrated Analysis Model with Secondary Flow for Assessing the Performance of a Micro Turbojet Engine

The objective of this study is to implement a more realistic integrated analysis model for micro gas turbines by incorporating secondary flow and combustion efficiency into the existing model, which includes main engine components such as the compressor and turbine, and to validate this model by comparing it with test results. The study was based on the JetCat P300-RX, which has a maximum thrust level of 300 N. Simulations were performed using ANSYS CFX, employing the κ-ω SST turbulence model and a mixing plane interface between individual components. The eddy dissipation model (EDM), with a combustion efficiency of 90%, was used as the combustion model. A user subroutine was also applied for the power matching of the compressor and turbine to calculate the fuel flow rate in each iteration. For secondary flow, it was assumed that 3% of the total air flow rate would flow through the secondary path and be applied to the compressor and turbine. Simulations were conducted over a range of 30,000 to 104,000 RPM, with ground conditions evaluated, including altitude-simulated conditions. To validate the analysis model, engine performance metrics such as pressure ratio, air flow rate, fuel flow rate, and exhaust gas temperature (EGT) were compared with test results. The results demonstrated that errors were less than 5% for most engine performance metrics, except for EGT and fuel flow. The discrepancy in EGT was attributed to differences in the sensing methods, while the variation in fuel flow was found to be due to the lubrication system and losses due to the secondary air flow. Consequently, this study confirmed that the integrated simulation model accurately predicts engine performance. The results indicate that the integrated simulation model provides a more realistic prediction of overall engine performance compared to previous studies. Therefore, it can evaluate detailed thermo-fluid properties without the need for component performance maps, enhancing performance evaluation and analysis.

Innovative Design of Cooling System for a High-Torque Electric Machine Integrated with Power Electronics

The growth of electrical machine applications in high-torque environments such as marine propulsion and wind energy is encouraging the development of higher-power-density machines at ever higher efficiencies and under competitive pressure to meet higher demands. In this study, numerical simulations are performed to investigate the characteristics of air cooling applied to a 3 MW high-torque internal permanent magnet electric machine with integrated power electronics. The whole system of the main machine and two converters at either end are modelled with all details. Effects of different parameters on the total pressure drop and air flow rate to the machine and converters are examined. Results show that by changing the converter outlet hole size, the air flow rate to the machine and converter can be adjusted. Air guides and pin vents reveal excellent performance in the distribution of air to laminations and windings with a penalty of some increase in pressure drop, which is more pronounced when using smaller outlet holes. Furthermore, the air return manifold increases the pressure drop and causes a reduction in air flow rate to the converter. Insulation between compression plate and laminations is an unavoidable component used in electric machines and acts as a thermal insulator. However, it can also significantly augment pressure drop, especially in combination with smaller outlet holes. Thermal studies of the integrated power electronics illustrate that components’ temperatures are less than the temperature limit, confirming enough air through the converter. Analysis of power electronics in the case of fan failure provides the operational time window for the operators to respond.

A hybrid cooling tower model for plume abatement and performance analysis

A one-dimensional model of a hybrid cooling tower and its atmospheric plume is presented with the aim of studying plume abatement, water consumption and cooling performance. To achieve this goal, a counter-flow wet cooling tower model is integrated with an effectiveness-NTU model for the dry cooling section, and, a turbulent plume model. To estimate fan power requirements, a draft equation is also included to predict the pressure drop and damper requirements in the dry and wet sections. The proposed model is used to study the effect of environmental and operating conditions on hybrid cooling tower plume visibility and cooling performance. In particular, and for the hybrid cooling tower examined in this study, a visible plume can be suppressed by approximately 10%–40% and 80%–90% hybridization, i.e., dry section to total air flow rate ratio, when the ambient air temperature is 5°C and −20°C, respectively. Results highlight the inherent trade-offs between cooling capacity, plume abatement, water consumption and fan power. Parametric studies identify the range of operating conditions for which satisfying outlet water temperature and plume abatement requirements may prove especially challenging.

Transitions of thermoacoustic modes and flame dynamics in a centrally-staged swirl combustor

In the start-up process of practical gas turbine applications, the modulation of operating condition, especially the variation of global equivalence ratios (ϕglo), could cause the variations of stability regimes. The above process is accompanied by the increase of total air flow rates (ṁair) when approaching the stable operation condition, and thus the effect of this parameter should also be considered in the operating condition modulation process. This work presents an experimental investigation into the transitions of thermoacoustic modes and flame dynamics in a centrally-staged swirl combustor over a range of ϕglo and ṁair. The present thermoacoustic system exhibits two transitions of thermoacoustic modes with ϕglo variation, showing distinct characteristics of pressure oscillation (p′) and flame structures. To further explore the detailed variation of p′ characteristics and its link to flame dynamics during two transitions, a nonlinear dynamic analysis of p′ including its phase and recurrence plots as well as a proper orthogonal decomposition (POD) study have been conducted. The thermoacoustic network analysis and local Rayleigh index analysis have clarified the mode transition mechanism with varying ϕglo and ṁair. The present results can provide a guideline for quantifying the stability regimes of fuel-flexible combustors during the operating condition modulation processes.

Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

In staged fixed bed biomass combustion, primary air is supplied beneath the fuel bed with secondary air then provided above in the freeboard region. For fixed bed configurations, the freeboard is further divided into a primary freeboard length (LI), which is upstream of the secondary air and a secondary freeboard length (LII), measured from the secondary air all the way to the exhaust port. Despite extensive research into fixed bed configurations, no work has been successfully completed that resolves the effects of changing LI on fuel conversion, both in the fuel bed and within the freeboard of batch-type biomass combustors. In this study, experiments on a 202 mm diameter and 1500 mm long batch-type combustor have been conducted to determine the effects of changing primary freeboard length over three secondary to total air ratios (Qs/Qt) and two total air flow rates (Qt). The impact of these conditions has been studied on (i) intra-bed fuel conversion, measured through burning rate (kg/m−2 s−1), fuel bed temperature (°C) and ignition front velocity (mm-s−1), as well as (ii) post-bed fuel conversion in the freeboard, expressed through freeboard temperatures and emissions (NOx ppm, CO2%, CO ppm, O2%). The fuel used throughout the above experiments was Australian hardwood pelletised biomass. Results show that changes to primary freeboard length over LI = 200 mm, 300 mm and 550 mm, or LI/D = 1.00, 1.48 and 2.72, respectively, affect both intra-bed and freeboard (post-bed) performance indicators. The highest values of burning rate, ignition front velocity and fuel bed temperature were observed for interim values of LI/D = 1.48 at Qs/Qt = 0.25 and Qt = 0.358 kg/m−2 s−1. Primary freeboard lengths of LI/D = 1.00 and 1.48 were found to have higher freeboard temperatures, NOx and CO2 as well as lower CO and O2 values as compared to LI/D = 2.72 at Qs/Qt = 0.50 and 0.75. Increasing Qs/Qt from 0.25 to 0.50 for LI/D = 1.00 and 1.48 initially increased freeboard temperatures, with an accompanying increase in NOx and CO2 as well as decrease in CO values. However, further increase in Qs/Qt to 0.75 lead to lower freeboard temperatures for all primary freeboard lengths.

Numerical simulation of the effect of air-intake on the indoor flow field of a dedusting equipment cabin used in tunnel construction

There is a significant amount of dust during tunnel construction. As a comprehensive prevention method for tunnel dust, dust collector technology has been widely used in tunnel construction. The flow field distribution in a dedusting equipment cabin directly affects the treatment efficiency of tunnel dust. In this study, using a dedusting equipment compartment with 5 (in row) × 20 (in column) filter cartridges (FCs, diameter of 0.35 m) as the research object, the effects of air-intake mode, position, and other parameters on the airflow rate of FCs inside the cabin, and indoor air distribution characteristics were studied using a numerical calculation method, which was verified by an experiment. The results indicated that for the cabin with only an end air-intake, the length of the cabin cannot be too long, as this would cause a low airflow rate of the FCs located at the center of the cabin. Furthermore, the effects of setting a baffle and grille on the total airflow rate of the FCs inside the cabin with only an end air-intake was more significant than that with both an end air-intake and side air-intakes, the difference of the total airflow rate among them can be up to 59%. Setting a baffle at the end of an air-intake significantly reduced the total airflow rate of the FCs about 59%, which was significantly increased about 5% by setting grilles. Additionally, the side air-intakes improved the total airflow rate of the FCs more than the end air-intake by about 24%, but the intake efficiency of the former was lower than that of latter by about 61%. Finally, based on cabins with only an end air-intake, setting the side air-intakes on the cabin where the airflow rate of FCs is low, can significantly improve the total airflow rate of FCs in the cabin, particularly the FCs around the side air-intakes, the increase here can reach 36% compared with other locations.

Identification of air leakage in a household heat pump tumble dryer

Leakage of air in tumble dryers is an important parameter regarding the energy efficiency of the drying process. In general, tumble dryers are prone to leakage, therefore further investigation and optimization in this field is of great interest. This study investigates and quantifies leakage of air within the closed-loop system of an in-situ household heat pump tumble dryer. Each potential leakage location was characterized by leakage curve obtained either by isolated or cumulative measurements using system pressurization method. Based on the static pressure distribution within the closed-loop system, the leakage outflow and inflow were quantified. The leakage of air at the rear and front drum seal was evaluated with and without drum movement. The results indicated the highest leakage outflow rate at the heat pump housing, which represents 12,6% of the total drying air flow rate within the closed-loop system. Sealing heat pump housing improved the condensation efficiency from B to A class according to the IEC 61121.

Experimental Investigation of Air Bubble Curtain Effects on Water Wave Field

This paper studies the effects of an air bubble curtain on surface water waves. Water particle velocities and free surface elevations were measured simultaneously at two cross-shore locations downstream of the air bubble curtain. Measurements were carried out for regular waves using different air bubble curtain configurations. Free surface elevations were measured using resistive gauges and the instantaneous velocities were acquired using an Acoustic Doppler Velocimeter (ADV). The characteristics of the free surface elevation time series, velocity field and turbulence are analyzed and discussed. The free surface elevation was found to be attenuated by the air bubble curtains. The phase averaged velocity profiles also depict the effect of the air bubbles in the flow field by generating milder longitudinal velocities (u) and by increasing the transverse component of the velocity (w). The increase in the turbulence intensity and the different energy spectrum produced by the air bubble curtain is also observed. The experimental results indicate that the thickness of the air bubble curtain and the total air flow rate affects the wave field.

Respiratory infection risk-based ventilation design method

A new design method is proposed to calculate outdoor air ventilation rates to control respiratory infection risk in indoor spaces. We propose to use this method in future ventilation standards to complement existing ventilation criteria based on the perceived air quality and pollutant removal. The proposed method makes it possible to calculate the required ventilation rate at a given probability of infection and quanta emission rate. Present work used quanta emission rates for SARS-CoV-2 and consequently the method can be applied for other respiratory viruses with available quanta data. The method was applied to case studies representing typical rooms in public buildings. To reduce the probability of infection, the total airflow rate per infectious person revealed to be the most important parameter to reduce the infection risk. Category I ventilation rate prescribed in the EN 16798-1 standard satisfied many but not all type of spaces examined. The required ventilation rates started from about 80 L/s per room. Large variations between the results for the selected case studies made it impossible to provide a simple rule for estimating the required ventilation rates. Consequently, we conclude that to design rooms with a low infection risk the newly developed ventilation design method must be used.

Parametric analysis of an air-based radiative cooling system coupled to a thermal storage wall for a low-income household

Research on natural cooling of buildings has produced an extensive scientific bibliography since 1980s. Nevertheless, few examples of complete experimental systems are registered, and rigorous procedures for their dimensioning are currently not available. This work analyses the performance of an air-based low energy radiative cooling system in Chile. The system is composed of a series of specialized radiative air collectors, a mechanical ventilation system, and a thermal storage wall, which is part of the indoor environment. The design has been tested in an experimental prototype where external and internal environmental conditions have been monitored during a full week in midsummer conditions. The data obtained is used to validate an analytical model designed to study the behavior of each component and the system’s performance. This work studies the relationship between the radiator surface, the air volume flow rate, and the thermal storage wall volume that serves to neutralize the thermal loads, maintaining comfortable temperature conditions throughout the day. Comparison of the simulations with and without thermal conditioning has been conducted. In term of the system sizing, a thermal wall of 2.55 m3 and a total air flow rate of 48 m3/h is required to reach the optimal operating point of the first floor of the house. A sensibility analysis indicated that increasing the number of collectors slightly reduces the wall’s size. Based on these conditions, the work concludes with the proposal of a simple procedure for the sizing of passive cooling systems installed in social housing developments.

Numerical Investigation of Latent Thermal Storage in a Compact Heat Exchanger Using Mini-Channels

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with dh = 1.6 mm and channel-2 with dh = 2.3 mm) are oriented vertically in a cuboid of 0.15 × 0.15 × 0.1 m3 with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15–31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41–53% and increasing the mean UA values within melting by 19–52% for a packing factor range of 77.4–86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation.

Simulation and analysis of air cooling configurations for a lithium-ion battery pack

Lithium-ion batteries are widely used in electric vehicles (EVs) and hybrid electric vehicles (HEVs), in which proper measures have to be taken to ensure the batteries working with in a suitable temperature range. The air-cooling battery thermal management system (BTMS) is still a widely used solution for this purpose. Based on modeling and numerical simulation method, this paper aims to analyze and improve the cooling effect of the battery cells by optimizing the airflow configuration and layout employed in the U-type air-cooling BTMS. It is found that, for eighteen selected designs in the current study, the best cooling performance can be achieved when the number of both inlet and outlet manifolds is increased to be three. Further analysis is also carried out for the obtained optimum design to confirm its applicability in a wider range of total inlet airflow rates and temperatures.

A Control Strategy of the Air Flow Rate of Coal-Fired Utility Boilers Based on the Load Demand.

An analysis was conducted on the relationship between the calorific value of different types of coal and the theoretical air requirement. It was found that the theoretical air volume required for generating the same amount of heat during combustion is the same for different types of coal. The concept of the air/coal ratio was improved by proposing the concept of the air/carbon ratio, which refers to the ratio of the mass of air to the mass of carbon during complete combustion; the ratio is approximately 11.5 kg/kg (mass ratio), being roughly constant for different types of coal, unlike the air/coal ratio showing a significant change with coal types. The total air flow rate in a boiler changed with load demand, and the influence of different fuel types can be neglected at the same load level. On this basis, an air flow rate control strategy for coal-fired utility boilers was proposed and implemented in the boiler in which the air flow rate required to the furnace is a function of the unit load. Experiments conducted in a 300 MWe coal-fired utility boiler confirm that the use of the control strategy of the air flow rate for the combustion optimization improves the stability of the main steam pressure and mitigates the fluctuations of the coal flow. These results provide a foundation for the implementation of a new strategy of air/coal decoupling and independent control of boiler combustion.

Development of a virtual fan airflow meter for electronically commutated motor fan systems

Airflow measurement is essential to efficiently operate air handling units (AHUs) in commercial buildings. Due to the space and cost limitations for physical meters, many virtual airflow meters have been developed for induction motor driven fan systems. On the other hand, electronically commutated motor (ECM) fans have been widely applied in AHUs. However, the applicability of virtual airflow meters to ECM fan systems remains unclear. The purpose of this paper is to develop and validate a virtual airflow meter for ECM fan systems using measured fan head and motor input power and speed. First, a virtual airflow meter model is developed by referring to an ECM fan energy model and the corresponding calibration procedure is established, then the developed model is calibrated using the manufacturer data of a 7,865 m3/h ECM fan, including fan airflow rate, head and motor input power at different motor speeds, and validated in a test AHU with an array of four calibrated ECM fans. The validation result shows that the developed meter can accurately calculate the total AHU airflow rate with the root mean squared error of 660 m3/h and the normalized root mean squared error of 4%.

Image-Based Feedback Control for a Coaxial Spray

Abstract Optimization of jet engine sprays has the potential to improve efficiency and reduce environmental impact. Sprays can be continually optimized in multivariate scenarios using real-time feedback control, but a method of controlling the sprays based on physical properties must first be established. In this study, a spray controller was developed to optimize the spray angle obtained from shadowgraphs, with the assumption that the largest angle is desired. The spray angle was used as an example, as it is a physically important parameter which is easily found through shadowgraph imaging. Varying ratios of swirled air to straight air, determined by the image-based feedback controller were introduced into the air portion of a coaxial airblast nozzle while keeping the total air flow rate constant. A golden section search converged on the swirled air ratio that provided the largest angle and was validated from the distribution of spray angle versus swirled air ratio. The ratio that produced a spray with the greatest angle of 25.8 ± 2 deg was found at a swirled air ratio of 0.66 ± 0.03 for a spray with a momentum ratio of 6. The successful design and implementation of this image-based feedback controller is intended to provide a foundation for developing real-time active feedback controllers for sprays.

Technology for Monitoring and Control of Air Flows Inside Metal Silos during Grain Storage

Introduction. Preservation of grain crops in flat-bottomed metal silos is not possible without monitoring and control of air flows in the internal volume. In the silos with uncontrolled air flows, there is a redistribution of moisture and additional moistening of the grain surface layer that leads to losses of about 2% of grain. The aim of this work is to develop a technology for preventing the grain surface layer from humidifying during storage in metal silos. Materials and Methods. Under laboratory conditions, aerodynamic parameters of wheat and soybean grains were determined in the range of filtration rates less than 0.15 m/s. In metal silos, with a capacity of 2,000, 3,000 and 10,000 t, the temperature and relative humidity of the air inside at the top of the silos and outside were measured simultaneously. The temperature and relative humidity measurement period was 30 min for two and five months. Autonomous recorders were used for measurement. Results. A new objective standard of grain ventilation is proposed ‒ minimum (critical) filtration rate, which ensures moisture removal outside the silo. The analytical studies produced an equation for calculating the weighted average filtration rate of air leaving the grain mass. The total air flow rate corresponding to the weighted average filtration rate will provide a filtration rate of at least critical over the entire surface and will exclude moisture settling. The periods of air saturation with moisture up to 100% in the supervisory space under the roof of the silo have been determined experimentally. The mechanism of heat emission up to the silo roof space from the depth of grain mass during storage has been clarified. Discussion and Conclusion. The algorithm for safe active ventilation of grain and roof space in metal silos is proposed. Limit values of relative humidity of atmospheric air are recommended, the use of which will exclude humidification of grain mass when ventilating actively in the range of temperature difference between grain and atmosphere up to 30 °С and more. The obtained data can be used by mechanical engineers in the manufacture of metal silos and by grain producers in the operation of the said silos.

An experimental investigation on the operational characteristics of a novel direct expansion based air conditioning system with a two-sectioned cooling coil

Abstract For controlling indoor thermal environment, only indoor air temperature is usually considered when using conventional direct expansion (DX) based air conditioning (A/C) systems. Therefore, based on the previous experiences in developing novel A/C units to provide an enhanced moisture removal capacity, a novel constant speed DX A/C system with a two-sectioned cooling coil (TS-DXAC) has been proposed. In the proposed TS-DXAC system, to reduce its size, the two sections were arranged in parallel with their respective matching variable speed supply fans, and the mass flow rates for both refrigerant and air to each section could be adjusted. The total air flow rate of the system remained however constant, so as not to affect indoor air flow distribution and occupants’ thermal comfort. The inherent operational characteristics of a prototype experimental TS-DXAC system have been experimentally studied. The study results showed that the variations in the mass flow rates of refrigerant and air to the two sections would result in different combinations of the output total cooling capacity (TCC) and equipment sensible heat ratio (E SHR) from the prototype, and that the TCC – E SHR relationship was constrained within an irregular area. Furthermore, different inlet air temperatures and humidity levels would also influence its inherent operational characteristics as reflected by the changes in the positions and shapes of the irregular areas, with the latter influencing more on the operational characteristics.

Experimental and numerical studies for applying hybrid solar chimney and photovoltaic system to the solar-assisted air cleaning system

Under the background of global energy shortage and environment deterioration, researchers of the world pay high attention to develop renewable energy. This paper proposes a hybrid solar chimney and photovoltaic system for the novel solar-assisted air cleaning system. Small-scale laboratory setups are designed and fabricated. Experimental results reveal that replacing 50.60% acrylic glass of the collector top with photovoltaic panels will reduce the thermal air flow rate only by 14%, but generate significant electric power output. A three-dimensional numerical simulation model is established and validated by experimental results (air flow rate, temperature distribution). The model includes solar ray tracing model, surface to surface radiation model, buoyancy-driven flow and heat transfer model and power generation model. Then, this model is used to predict a large-scale system based on the Manzanares pilot power plant in Spain. For the large-scale system, the electrical energy generated by the photovoltaic panels can be used to drive suction fans to increase air input. Covering the entire top surface of the collector by photovoltaic panels (113-meter-wide), the total air flow rate would increase to 2.21 times compared with the system without photovoltaic panels. And setting photovoltaic panels on the collector bottom with 113-meter-wide, the total air flow rate would increase to 2.42 times. Thus, adding photovoltaic panels for the collector can greatly improve the utilization of solar energy. It can increase the amount of air purification, or reduce land requirement for the same flow rate.

Operating a Commercial Building HVAC Load as a Virtual Battery Through Airflow Control

Virtual battery (VB) is an innovative method to model flexibility of building loads and effectively coordinate them with other resources at a system level. Unlike a real battery with a dedicated power conversion system for charging control, methods are required for operating building loads to deviate from the baseline to respond to grid signals. This article presents a VB control for a commercial heating, ventilation, and air conditioning (HVAC) system to follow the desired power consumption in real-time by adjusting zonal airflow rates. The proposed method consists of two parts. At the system level, a mixed feedforward and feedback control is used to estimate the desired total airflow rate. At the zone level, two priority-based algorithms are then proposed to distribute the total airflow rate to individual zones. In particular, a zonal airflow limit estimation method is proposed using machine-learning techniques, in contrast to physics-based thermal models in existing studies, to more accurately capture zonal thermal dynamics and improve temperature control performance. An office building on the Pacific Northwest National Laboratory campus is implemented in EnergyPlus, and used to illustrate and validate the proposed control.

Performance evaluation of a retrofitted multi-cyclone using computational fluid dynamic

Multi-cyclone is widely used in industries as air pollution control device due to several advantages over other available separation units such as its low capital, operating, and maintenance cost and as well as its usability under a wide range of operational conditions. However, it is merely a pre-cleaner as it is inefficient in collecting fine particulate especially, particulate matter with size less than 10 µm (PM10) and below. Hence a simple, cost-effective retrofit on a Conventional Multi-cyclone (CMC) with the motivation of increasing its overall performance on fine particulate emission control was carried out. The retrofit was performed by creating higher negative pressure inside the dust hopper of the CMC by extracting 10% and 24% from the total volumetric airflow rate of the unit with the means of an external Induced Draft Fan. The Computational Fluid Dynamics (CFD) with Reynold Stress Model (RSM) turbulence model was performed and validated using experimental data to gain a better understanding in pressure distribution, velocity profile and particulate movement between the CMC and the Retrofitted Multi-cyclone (RMC). The CFD results show deviation between 0% to 8% for pressure at inlet and outlet of cyclone compared to the experimental results. In addition, CFD results depict that the RMC has higher pressure at the inlet and lower pressure inside dust hopper of CMC, which cause the finer particle to be pulled in through suction outlet. Also, the emission of fine particulate is reduced in RMC by 9% to 16%. compared to the CMC. Moreover, the phenomena at the suction duct can be clearly explained with the usage of CFD. The finding suggests that a simple, cost-effective retrofit at the multi-cyclone has increased the overall performance in the fine particulate collection, and the understanding of the phenomena could be enhanced by the CFD.