Measurement Of Flow Resistance Research Articles

Evaluating the effects of soil grain roughness and rill cross‐section shape on flow resistance

AbstractThe knowledge of the hydraulic characteristics of rill flows is needed to improve the understanding and the accurate modelling of upland erosion processes. Flume investigations are developed to schematize conditions useful to analyze the influence of a unique variable significant for modelling rill hydraulics, while field investigations are used to simulate morphological and hydraulic conditions of natural cases. The main aim of this investigation is to compare flow resistance measurements carried out using a rectangular rill channel (flume data) and manually generated and naturally shaped rills (plot data) for the same soils and hydraulic conditions. The two data sets allowed for establishing how the soil grain roughness and rill cross‐section shape affect flow resistance using a theoretical equation deduced by applying dimensional analysis and self‐similarity theory. The analysis developed for a fixed‐bed channel with a rectangular cross‐section demonstrated that the influence of different soil roughness on the Darcy‐Weisbach friction factor is approximately equal to ±1%, while for a rill with an irregular cross‐section the same effect is almost equal to ±2%. Therefore, for an open‐channel flow on a fixed bed, the effect of the grain size roughness on the friction factor is limited. For each examined soil, the investigation also demonstrated that the rill cross‐section shape leads to a variability of the friction factor from −20% to +30%. This result highlights that, for a fixed‐bed channel, the effect of the cross‐section shape on the Darcy‐Weisbach friction factor is much greater than that due to the soil grain size roughness. The main implication of this work is that the results deduced by laboratory measurements with regular cross‐sections, thus neglecting a complex geometry, can be affected by relevant discrepancies from those obtained by the field measurements, which better simulate natural conditions.

Nasal Obstruction: Overview of Pathophysiology and Presentation of a Clinically Relevant Preoperative Plan for Rhino(Septo)plasty.

Impairment of nasal breathing is a highly prevalent and bothersome symptom that affects daily functioning and/or sleep quality. Those surgeons dealing with patients seeking rhinoplasty need to carefully analyze the preoperative nasal breathing capacity and predict the positive or even negative impact of rhino(septo)plasty on nasal breathing. Given the lack of correlation between the subjective feeling of suboptimal nasal breathing and the objective measurements of nasal flow and nasal resistance, a critical and mainly clinical evaluation of all anatomical, mucosal, and sensory mechanisms involved in nasal obstruction is mandatory. Indeed, thermo-, mechano-, and chemosensory receptors on the nasal mucosa, airflow, and respiratory dynamics might all contribute to the overall perception of nasal breathing capacity. In this review, we provide an overview of the factors determining suboptimal nasal breathing including different diagnostic and experimental tests that can be performed to evaluate nasal flow and nasal resistance and current limitations in our understanding of the problem of nasal breathing in an individual patient. An algorithm for the preoperative or diagnostic workup for nasal obstruction is included that might be useful as a guide for clinicians dealing with patients seeking nose surgery.

Investigation of the Porosity Gradient in Thickness Direction Formed by Cold Rolling in Porous Aluminum

To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication.

Pressure Drop Characteristics of the Reduced NGI Configuration with Several Common Glass Fiber Filters.

Background: Measurement of aerodynamic particle size distribution, a clinically relevant in vitro attribute of inhalable drug products, involves multistage cascade impactors and is tedious and expensive. A leading candidate for a quicker method is the reduced NGI™ (rNGI). This method involves placing glass fiber filters on top of the nozzles of a chosen NGI stage, selected often to collect all particles with an aerodynamic diameter smaller than approximately five microns. These filters contribute additional flow resistance that can alter the flow rate start-up curve, potentially affecting the size distribution and mass of the drug product dispensed by passive dry powder inhalers (DPIs). The magnitude of these additional flow resistance measurements is currently unreported in the literature. Materials and Methods: We placed glass fiber filters on top of the stage 3 nozzles of an NGI, along with the necessary support screen and hold-down ring. We measured the pressure drop across NGI stage 3 with the assistance of a delta P lid and a high-precision pressure transducer. With each filter material type and multiple individual filters, we gathered eight replicates at flow rates of 30, 45, and 60 L/min. Results: The filters typically doubled the total pressure drop through the NGI. For example, at a flow rate of 60 L/min, the Whatman 934-AH filters introduced a pressure drop of about 9800 Pa at stage 3, reducing the absolute pressure exiting the NGI to about 23 kPa below ambient, compared with a typical value of 10 kPa for the NGI alone at this flow rate. Conclusions: The pressure drop across typical filters is approximately equal to that through the NGI alone and therefore will affect the flow start-up rate intrinsic to compendial testing of passive DPIs. This change in start-up rate could cause differences between results of the rNGI configuration and those of the full NGI and will increase the required vacuum pump capacity.

Experimental measurements and CFD modelling of hydroxyapatite scaffolds in perfusion bioreactors for bone regeneration.

In the field of bone tissue engineering, particular interest is devoted to the development of 3D cultures to study bone cell proliferation under conditions similar to in vivo ones, e.g. by artificially producing mechanical stresses promoting a biological response (mechanotransduction). Of particular relevance in this context are the effects generated by the flow shear stress, which governs the nutrients delivery rate to the growing cells and which can be controlled in perfusion reactors. However, the introduction of 3D scaffolds complicates the direct measurement of the generated shear stress on the adhered cells inside the matrix, thus jeopardizing the potential of using multi-dimensional matrices. In this study, an anisotropic hydroxyapatite-based set of scaffolds is considered as a 3D biomimetic support for bone cells deposition and growth. Measurements of sample-specific flow resistance are carried out using a perfusion system, accompanied by a visual characterization of the material structure. From the obtained results, a subset of three samples is reproduced using 3D-Computational Fluid Dynamics (CFD) techniques and the models are validated by virtually replicating the flow resistance measurement. Once a good agreement is found, the analysis of flow-induced shear stress on the inner B-HA structure is carried out based on simulation results. Finally, a statistical analysis leads to a simplified expression to correlate the flow resistance with the entity and extensions of wall shear stress inside the scaffold. The study applies CFD to overcome the limitations of experiments, allowing for an advancement in multi-dimensional cell cultures by elucidating the flow conditions in 3D reactors.

Improving magnetic cooling efficiency and pulldown by varying flow profiles

Magnetic refrigeration systems are promising cooling solutions that employ the active magnetic regenerator refrigeration cycle to achieve practical temperature spans and environmental benefits. The hydraulic system that ensures a continuous flow of the heat transfer fluid through the system with a reciprocating flow in each regenerator bed is critical to the performance of the refrigeration cycle. Hence, we investigate the characteristics of the parallel flow circuit of a rotary active magnetic regenerator system, which consists of thirteen trapezoid-shaped regenerators, each filled with 295 g of gadolinium spheres. Fluid flow is controlled via electrically actuated solenoid valves (both piloted and direct-acting) connected to the regenerator hot side. By varying the percentage of opening of the control valves, different blow fractions (or fluid flow waveforms) could be investigated. The objective of the study is twofold: (i) assess whether flow imbalances of the heat transfer fluid exist in the cold-to-hot blow (cold blow) and hot-to-cold blow (hot blow) directions, and (ii) determine whether there is an optimal value of the blow fraction both to maximize the cooling performance and realize a rapid temperature pulldown. Flow resistance measurements demonstrate a symmetric flow circuit design and resistances that are similar in the cold and hot blow directions. Moreover, for the studied temperature spans of 6 K and 16 K, the best blow fraction was found to be about 41.6 %. For instance, at a 16 K span, a utilization of 0.32, and at 1.4 Hz, increasing the fluid blow fraction from 25.0 to 41.6 % enhanced the cooling capacity and second-law efficiency from 70 to 330 W and from 2.6 to 17.4 %, respectively. In turn, lower blow fractions favored a more rapid temperature pulldown. The magnetocaloric system was about 30 % faster in establishing approximately 14 K temperature span when the blow fraction was reduced from 41.6 to 30.6 %. Hence, magnetic refrigeration systems can benefit greatly from solenoid valves, which allow the system to operate either in a time-saving mode or an energy-saving mode.

Automation of intracoronary continuous thermodilution for absolute coronary flow and microvascular resistance measurements.

Microvascular resistance reserve (MRR) as derived from continuous intracoronary thermodilution specifically quantifies microvasculature function. As originally described, the technique necessitates reinstrumentation of the artery and manual reprogramming of the infusion pump when performing resting and hyperemic measurements. To simplify and to render this procedure operator-independent, we developed a fully automated method. The aim of the present study is to validate the automated procedure against the originally described one. For the automated procedure, an infusion pump was preprogrammed to allow paired resting-hyperemic thermodilution assessment without interruption. To validate the accuracy of this new approach, 20automated measurements were compared to those obtained in the same vessels with conventional paired resting-hyperemic thermodilution measurements (i.e., with a sensor pullback at each infusion rate and manual reprogramming of the infusion pump). A close correlation between the conventional and the automated measuring technique was found for resting flow (Qrest : r = 0.89, mean bias = 2.52; SD = 15.47), hyperemic flow (Qhyper : r = 0.88, mean bias = -2.65; SD = 27.96), resting microvascular resistance (Rμ-rest : r = 0.90, mean bias = 52.14; SD = 228.29), hyperemic microvascular resistance Rμ-hyper : r = 0.92, mean bias = 12.95; SD = 57.80), and MRR (MRR: r = 0.89, mean bias = 0.04, SD = 0.59). Procedural time was significantly shorter with the automated method (5'25″ ± 1'23″vs. 4'36″ ± 0'33″, p = 0.013). Continuous intracoronary thermodilution-derived measurements of absolute flow, absolute resistance, and MRR can be fully automated. This further shortens and simplifies the procedure when performing paired resting-hyperemic measurements.

Prognostic value of microvascular resistance and its association to fractional flow reserve: a DEFINE-FLOW substudy

ObjectiveThis study aimed to evaluate the prognostic value of hyperemic microvascular resistance (HMR) and its relationship with hyperemic stenosis resistance (HSR) index and fractional flow reserve (FFR) in stable coronary...

Practical Calculation of Sand-Bed River Flow Resistance

The dynamics of bed configurations and the effect of the bedforms on flow in sand-bed rivers are among the most challenging aspects of fluvial hydraulics to quantify. The big unknown is the resistance coefficient, without an accurate knowledge of which there is not much point in striving for overly precise numerical simulations of water-surface elevations and velocities. Two basic approaches have been used to account for the influence of bedforms on flow resistance. The first method divides the total resistance into two components: one related to impedance generated by the channel boundary without bedforms (grain resistance) and the other related to the opposing force produced by the bedforms (form resistance). The second tactic predicts the total resistance based on the overall flow and sediment parameters. It is the second approach that is followed in this study in which a neural network model is devised based on the evaluation of 941 measurements of reach-averaged flow resistance in small to large sand-bed rivers ranging from shallow to extremely deep. The model considers the influence of the several controlling variables, including water temperature and its effect on fluid viscosity, to make high-quality predictions of a resistance coefficient.

A computational fluid dynamics assessment of 3D printed ventilator splitters and restrictors for differential multi-patient ventilation

BackgroundThe global pandemic of novel coronavirus (SARS-CoV-2) has led to global shortages of ventilators and accessories. One solution to this problem is to split ventilators between multiple patients, which poses the difficulty of treating two patients with dissimilar ventilation needs. A proposed solution to this problem is the use of 3D-printed flow splitters and restrictors. There is little data available on the reliability of such devices and how the use of different 3D printing methods might affect their performance.MethodsWe performed flow resistance measurements on 30 different 3D-printed restrictor designs produced using a range of fused deposition modelling and stereolithography printers and materials, from consumer grade printers using polylactic acid filament to professional printers using surgical resin. We compared their performance to novel computational fluid dynamics models driven by empirical ventilator flow rate data. This indicates the ideal performance of a part that matches the computer model.ResultsThe 3D-printed restrictors varied considerably between printers and materials to a sufficient degree that would make them unsafe for clinical use without individual testing. This occurs because the interior surface of the restrictor is rough and has a reduced nominal average diameter when compared to the computer model. However, we have also shown that with careful calibration it is possible to tune the end-inspiratory (tidal) volume by titrating the inspiratory time on the ventilator.ConclusionsComputer simulations of differential multi patient ventilation indicate that the use of 3D-printed flow splitters is viable. However, in situ testing indicates that using 3D printers to produce flow restricting orifices is not recommended, as the flow resistance can deviate significantly from expected values depending on the type of printer used.Trial registrationNot applicable.

Measurement of Heat Transfer and Flow Resistance for a Packed Bed of Horticultural Products with the Implementation of a Single Blow Technique

This paper provides the practical implementation of the single blow technique as an effective approach of average convective heat transfer coefficient measurement for a packed bed of horticultural products. The measurement approach was positively validated for the case of a packed bed of balls. The presented results cover heat transfer coefficient results for carrots stored in packed beds for two various arrangements (regular and irregular) and bed of apples under conditions of various turbulent intensity at the inlet to the bed. The turbulent intensity (defined as the ratio of the root mean square of the turbulent fluctuation of the air velocity to the mean air velocity) varied from 0.02 to 0.14. The applied velocity ranges for the tests refers to the conventional storage conditions. The heat transfer correlations were proposed based on the obtained results for each arrangement. It was demonstrated that due to flow laminarization inside the bed, the turbulence intensity has no significant effect on heat transfer inside the bed. Heat transfer enhancement of up to 25% was demonstrated for the case of the irregular carrot arrangement in the tested bed. The flow resistance correlations were additionally proposed for the tested beds. It was demonstrated that the product arrangement does not produce an important effect on the pressure drop.

Toward mechanistic understanding the effect of aspect ratio of carbon nanotubes upon different properties of polyurethane/carbon nanotube nanocomposite foam

AbstractThis study investigated the carbon nanotube's aspect ratio's influence on the nanocomposite foams' cellular structure and mechanical, acoustic absorption characteristics. The free‐rising foaming process has been used for producing different flexible polyurethane (PU) foams embedded with other multi‐walled carbon nanotubes (MWCNT's). Dynamic mechanical and thermal analysis, flow resistivity, and compressive mechanical measurements were achieved on the prepared samples. The acoustic absorption coefficient in a wide range of frequencies was estimated for the prepared PU/CNT foamed nanocomposite samples. Results indicated that by increasing the aspect ratio of MWCNT, the absorption coefficient's peak shifts toward the lower frequencies and improved sound absorption characteristics of PU foam in the low‐frequency region. Moreover, the Young modulus of nanocomposite samples increases by increasing the aspect ratio of MWCNT's, whereas the stored strain energy or area under the stress–strain curve increases. Based on the obtained results, it is observed that the acoustic absorption coefficient of produced nanocomposite foams at the frequency of 800 Hz has been reported to have a 70% improvement in 2 cm samples and a 40% improvement in 3 cm samples compared to obtained results from pure PU foam.

Experimental investigation on effects of cross-flow Reynolds number and blowing ratios to film cooling performance of the Y-shaped hole

This paper presents an experimental investigation on effects of cross-flow Reynolds number and blowing ratios to film cooling performance of the Y-shaped hole. Flow resistance measurements were carried out to obtain the discharge coefficient. The film cooling effectiveness and heat transfer coefficient were measured by the transient liquid crystal measurement technique under three blowing ratios of 0.5, 1.0 and 2.0, respectively. The cross-flow Reynolds numbers of was fixed as 50,000 and 100,000, respectively. Numerical simulations with realizable k-ε turbulence model and enhanced wall treatment were performed to analyze the flow mechanism. Results demonstrate that the Y-shaped hole produces the higher film cooling performance than the cylindrical hole. For the Y-shaped hole, a reduction in the discharge coefficient with the increasing cross-flow Reynolds number is displayed. Meanwhile, the discharge coefficient increases with the increasing blowing ratio. It can be attributed to the enhancement of suction effect as well as the weakness of the blockage. The large blowing ratio results in better film coverage effect and higher film cooling effectiveness. The cross-flow Reynolds number has a significant effect on the film cooling effectiveness at the large blowing ratio. The heat transfer coefficient ratio increases with the increasing cross flow Reynolds number and the increasing blowing ratio. At all blowing ratio, the laterally averaged NHFR is valued between 0 and 0.6 in the hole downstream region, which means a positive effect of the film cooling performance. Under two different cross-flow Reynolds numbers, NHFR shows the trend of increasing firstly and then decreasing with the increasing blowing ratio. In the range of blowing ratio M< 1.4, the NHFR decreases with the increasing cross-flow Reynolds. In the range of blowing ratio M> 1.4, the NHFR increases with the increasing cross-flow Reynolds number. Compared with the cylindrical hole, under the same conditions, the Y-shaped hole have higher film cooling effectiveness, lower heat transfer coefficient, and higher discharge coefficient.

Basics of Coronary Thermodilution.

Coronary microvascular dysfunction is a highly prevalent condition in both obstructive and nonobstructive coronary artery disease. Intracoronary thermodilution is a promising technique to investigate coronary microvascular (dys)function invivo and to assess its most important metric: microvascular resistance. Here, the authors provide a practical review of bolus and continuous thermodilution for the measurement of coronary flow and microvascular resistance. The authors describe the basic principles of indicator-dilution theory and of coronary thermodilution and detail the practicalities of their application in the catheterization laboratory. Finally, the authors discuss contemporary clinical applications of coronary thermodilution-based microvascular assessment in humans and future perspectives.

Untangling the physics of water transport in boron nitride nanotubes.

Carbon nanotubes (CNTs) have long been heralded as the material of choice for next-generation membranes. Some studies have suggested that boron nitride nanotubes (BNNTs) may offer higher transport of pure water than CNTs, while others conclude otherwise. In this work, we use a combination of simulations and experimental data to uncover the causes of this discrepancy and investigate the flow resistance through BNNT membranes in detail. By dividing the resistance of the nanotube membranes into their contributing components, we study the effects of pore end configuration, membrane length, and BNNT atom partial charges. Most molecular simulation studies of BNNT membranes use short membranes connected to high and low pressure reservoirs. Here we find that flow resistances in these short membranes are dominated by the resistance at the pore ends, which can obscure the understanding of water transport performance through the nanotubes and comparison between different nanotube materials. In contrast, it is the flow resistance inside the nanotubes that dominates microscale-thick laboratory membranes, and end resistances tend to be negligible. Judged by the nanotube flow resistance alone, we therefore find that CNTs are likely to consistently outperform BNNTs. Furthermore, we find a large role played by the choice of partial charges on the BN atoms in the flow resistance measurements in our molecular simulations. This paper highlights a way forward for comparing molecular simulations and experimental results.

Thermodilution-Based Invasive Assessment of Absolute Coronary Blood Flow and Microvascular Resistance: Quantification of Microvascular (Dys)Function?

During the last two decades, there has been a sharp increase in both interest and knowledge about the coronary microcirculation. Since these small vessels are not visible by the human eye, physiologic measurements should be used to characterize their function. The invasive methods presently used (coronary flow reserve (CFR) and index of microvascular resistance (IMR)) are operator-dependent and mandate the use of adenosine to induce hyperemia. In recent years, a new thermodilution-based method for measurement of absolute coronary blood flow and microvascular resistance has been proposed and initial procedural problems have been overcome. Presently, the technique is easy to perform using the Rayflow infusion catheter and the Coroventis software. The method is accurate, reproducible, and completely operator-independent. This method has been validated noninvasively against the current golden standard for flow assessment: Positron Emission Tomography-Computed Tomography (PET-CT). In addition, absolute flow and resistance measurements have proved to be safe, both periprocedurally and at long-term follow-up. With an increasing number of studies being performed, this method has great potential for better understanding and quantification of microvascular disease.

Impact of entry–exit loss on the measurement of flow resistivity of porous materials

This study experimentally investigates the impact of low pore density and thickness on the flow resistivity, hence permeability, of periodic open porous materials. An experimental setup is developed to measure the flow resistivity of porous samples adhering to the guidelines provided by the International Standards Organization 9053 and American Society for Testing and Materials C522 standards. The flow resistivity of three different porous microlattices is considered. Two of the three lattices are obtained from a monospherical void subtraction method, while the third is the octet-truss lattice. The monospherical void geometries are body-centered-cubic and A15 lattices. The pore density, measured in terms of pores-per-inch (PPI), was varied from 1 PPI to 12 PPI for all three microlattices considered. At low PPIs, the pore sizes are on the order of macroscale thickness. Hence, the volume-averaging or homogenized equivalent fluid model may not be valid. The thickness variation for a fixed PPI is also considered over limits where traditional volume-averaging methods break down. It is shown that at extremely low PPIs and thicknesses, entrance and exit losses become dominant, and the flow resistivity measured as per standards ceases to be a constant with PPI or thickness. Furthermore, existing two-dimensional modeling approaches for losses due to flow in pipes are adopted to predict the entry and exit pressure loss coefficients for the considered microlattices with appropriate modifications.

Acoustic metamaterial for low frequency sound absorption in linear and nonlinear regimes

Acoustic metamaterial absorbers have been built and tested with focus on low frequency airborne sound absorption in linear and nonlinear regimes. The absorbers are made up of a series of piled up flat cavities, separated by thin walls and traversed by a perforation at their centre. A model for absorber effective properties is developed and compared with experimental data. The model is used to derive simple formulae for the frequency and the peak value of the absorption coefficient at the lowest frequency resonance, depending on the geometrical parameters of the structure. Different absorbers have been built with several cavity thicknesses to allow comprehensive comparisons with the model. Nonlinear properties of the absorbers are investigated experimentally using sine wave excitation around the resonance frequency with the amplitude of the incident wave up to 250 Pa. Flow resistivity measurements at low flow rates show that the periodic set of cavities does not modify resistivity significantly when compared to a simple perforated cylinder with same thickness. As flow rate increases, the flow resistivity grows linearly according to Forchheimer's law and has a significant dependence on the absorber thickness. A numerical model is developed accounting for the linear growth of flow resistivity with particle velocity amplitude in the central perforation and compared with the measurements at high amplitudes of the incident wave.

Absolute microvascular resistance by continuous thermodilution predicts microvascular dysfunction after ST-elevation myocardial infarction

AimsContinuous thermodilution using intracoronary saline infusion is a novel technique able to provide accurate measurements of absolute coronary blood flow and microvascular resistance (Rmicro). The aim of this study was to assess the ability of Rmicro, measured by continuous thermodilution, to predict microvascular dysfunction in patients with ST-elevation myocardial infarction. Methods and resultsIn this prospective observational study, continuous thermodilution was used to measure Rmicro in the culprit coronary artery of 32 patients with STEMI (mean age ± SD, 66 ± 10 years; 78% male) immediately post-primary percutaneous coronary intervention (PCI). Concomitant measurements of the index of microvascular resistance (IMR) and coronary flow reserve (CFR) were obtained by bolus thermodilution. Microvascular dysfunction was defined as an IMR > 40 or a CFR < 2. Rmicro was higher in patients with microvascular dysfunction based on the predefined thresholds; for IMR: 863 (IQR, 521–1079) vs 474 (IQR, 337–616) Wood units, p = .004 and for CFR: 633 (IQR, 455–1039) vs 474 (IQR, 271–579) Wood units, p = .02. Receiver-operator characteristic analysis demonstrated that Rmicro was predictive of microvascular dysfunction; area under curve (AUC) 0.800 (95% CI: 0.637–0.963, p = .005) for IMR-defined microvascular dysfunction and AUC 0.758 (95% CI: 0.593–0.924, p = .02) for CFR-defined microvascular dysfunction. An Rmicro threshold of greater than 552 Wood units was optimal for predicting microvascular dysfunction defined by IMR > 40. ConclusionsRmicro is able to identify STEMI patients in whom IMR and CFR measurements suggest significant microvascular dysfunction at the end of primary PCI.

Friction factor correlation for airflow through broken rocks and its applications in mine ventilation

The Atkinson equation along with its friction factor is commonly used to estimate pressure requirement in mine ventilation. However, friction factor correlation of flow through broken rock, typically found in blasted stope, gob, rock pit or block caving rock deposits, etc., is currently unavailable. Also, it is impractical to conduct direct measurements of flow resistance in an inaccessible broken rock zone. This paper aims to develop a new friction factor correlation of flow through broken rock that can be used directly in Atkinson equation. The proposed correlation is valid for broken rocks with diameter between 0.04 and 1.2 m and porosity ranging from 0.23 to 0.7.