Air Flow Regimes Research Articles

Regional differences in the grain size characteristics of surface sediments from typical barchan dunes in arid zones

The grain size characteristics of aeolian sediments are the combined result of sand sources, regional airflow regimes, dune morphology, etc., and are essential for understanding the formation and evolution of barchan dunes. Based on field investigations and laboratory experimental data, in this paper, we explored differences in the grain size characteristics of the surface sediments of barchan dunes at the southeastern edge of the Taklimakan Desert (TKLM-SE), the western (QB-W) and southern parts of the Qaidam Basin Desert (QB-S), the sand belt connecting the Badain Jaran Desert and the Tengger Desert (BT-B), and their responses to sand sources, dune morphology, and wind regimes. The main results were as follows: (i) The mean grian size distribution patterns of the windward slope toe to the leeward slope toe through the dune crest/ridge varied with different transects of the barchan dunes and different deserts, showing four types including gradually fining (GF), gradually coarsening (GC), coarsening followed by fining (CF), and fining followed by coarsening (FC). The patterns were GF and CF in the TKLM-SE; GF, GC, and FC in the BT-B; GF, GC, and CF in the QB-W; and GF in the QB-S. (ii) The interdune sediments provided the source material for the formation and development of barchan dunes and their grain size varied in different deserts. The interdune sediments were composed of gravel and very fine sand in the TKLM-SE, while they were composed of medium and fine sand in the QB-W, QB-S, and BT-B. (iii) The windward side of the barchans varied with different wind directions, and dune height affected dune surface airflow velocity and direction, changing the pattern of grain size distribution on the dune surface. The wind regime over a ten-day or half-month scale could explain the variance in the grain size distribution patterns better than that on an annual scale. (iv) Grain size characteristics of dune surface sands changed with dune shape due to changes in the surface airflow velocity and direction and the sediment-carrying capacity of the airflow. With an increasing ratio of dune height to dune width, the grain size of the dune crest sands became coarser. These results help advance our understanding of the grain size characteristics of barchan dunes and regional variabilities in their patterns.

Identification of the Structure of Liquid–Gas Flow in a Horizontal Pipeline Using the Gamma-Ray Absorption and a Convolutional Neural Network

Knowledge of the liquid–gas flow regime is important for the proper control of many industrial processes (e.g., in the mining, nuclear, petrochemical, and environmental industries). The latest publications in this field concern the use of computational intelligence methods for flow structure recognition, which include, for example, expert systems and artificial neural networks. Generally, machine learning methods exploit various characteristics of sensors signals in the value, time, frequency, and time–frequency domain. In this work, the convolutional neural network (CNN) VGG-16 is applied for analysis of histogram images of signals obtained for water–air flow by using gamma-ray absorption. The experiments were carried out on the laboratory hydraulic installation fitted with a radiometric measurement system. The essential part of the hydraulic installation is a horizontal pipeline made of metalplex, 4.5 m long, with an internal diameter of 30 mm. The radiometric measurement set used in the investigation consists of a linear Am-241 radiation source with an energy of 59.5 keV and a scintillation detector with a NaI(Tl) crystal. In this work, four types of water–air flow regimes (plug, slug, bubble, and transitional plug–bubble) were studied. MATLAB 2022a software was used to analyze the measurement signal obtained from the detector. It was found that the CNN network correctly recognizes the flow regime in more than 90% of the cases.

THEORETICAL PERFORMANCE ASSESSMENT OF A PARABOLIC TROUGH HUMIDIFYING SOLAR COLLECTOR-BASED SOLAR STILL

In this paper, a parabolic trough humidifying solar collector-based solar still (PHSC-SS) is proposed. Its purpose is to apply some important performance improvement techniques to the flat plate humidifying solar collector-based solar still (flat plate HSC-SS), to significantly improve overall system performance. These included the use of parabolic trough solar concentrators and the design of humidifying solar collectors from evacuated tube collectors. The results reveal that, unlike flat plate HSC-SS, which must operate with a turbulent airflow regime to achieve optimum overall performance, PHSC-SS must operate with a laminar airflow regime and high inlet and outlet temperatures of air (at least 55 °C and less than 100 °C, at atmospheric pressure) in the heat collector element. For 900 W/m2 of incident solar irradiance, 2 m2 of solar collector area, and 0,00042 kg/s of air flow rate, the maximum energy efficiency, exergy efficiency and daily freshwater productivity of PHSC-SS were found to be 68,12%, 14,87% and 1,697 kg/h, respectively. Whereas for the same incident solar irradiance and solar collector area, and 0,1 kg/s of air flow rate, those of the flat plat HSC-SS were 72,9%, 1,12%, and between 1,07 – 2,923 kg/h (for inlet and outlet temperatures of air less than 30 °C, at atmospheric pressure), respectively. Although in some extreme cases freshwater productivity of flat plate HSC-SS can be higher than that of PHSC-SS, it should be noted that laminar airflow regime confers great advantages to PHSC-SS. These are higher air temperatures at condenser inlet (which ease water condensation process), no need of an auxiliary cooling device (needed in the flat plate HSC-SS), less mechanical vibrations of system, reduced condenser size, and less energy consumed by air blowers. Furthermore, the upper limit of the PHSC-SS is a PHSC-SS that operates without air flow, but rather by vaporization of water droplets at boiling point from absorber, followed by their suction to condenser, similarly to a flash evaporation.

The Study of Thermal Comfort in a Common Commercial Car Cabin: Looking at Malaysia’s Perspective

Assessing thermal comfort in vehicles poses unique challenges compared to buildings. The in-car environment is characterized by specific factors such as sunlight exposure, poor clothing insulation, non-uniform average radiant temperature, and limited time to establish comfort parameters. To address these challenges, this study aims to evaluate thermal comfort in different branded car cabins by analyzing temperature distribution, air velocity, relative humidity, and dew point temperature. A comprehensive review of literature was conducted, focusing on various aspects including airflow regimes, factors influencing thermal comfort, measuring instruments, and comfort indices. Understanding these factors is crucial for developing comprehensive methodologies to assess thermal comfort and indoor air quality in vehicle cabins. The results of the study indicate that MPV cars offer superior comfort levels within the optimal range of -1 to +1, surpassing sedans and compact cars. These findings are instrumental in guiding design and engineering decisions to improve passenger comfort in vehicles. Tailoring the design of different car types to meet the specific comfort requirements can lead to enhanced overall comfort and satisfaction. In conclusion, this study provides valuable insights into assessing thermal comfort and indoor air quality in vehicle cabins. By addressing the unique challenges posed by the in-car environment, it offers guidance for designing and engineering vehicles that prioritize passenger comfort and well-being.

A computational fluid dynamics study of the influence of sleeper shape and ballast depth on ballast flight during passage of a simplified train

The paper assesses the effect on the air flow regime underneath a simplified high-speed train of changing the ballast depth and the sleeper shape, with regard to its potential for causing ballast flight or pickup. The study was carried out numerically using the commercial Computational Fluid Dynamics (CFD) software AnSys Fluent. The flow profile beneath the underbody of the train was generated by means of a moving wall above the track. The Delayed Detached Eddy Simulation (DDES) with the SST [Formula: see text] turbulence model was used to simulate turbulent flow, and the ballast bed roughness was applied parametrically using the wall roughness feature when resolving the boundary layer. CFD simulations were validated for flow over a cube, showing good agreement with experimental results. Up to three different depths to the ballast surface and three different sleeper profiles were investigated. Velocity profiles and aerodynamic forces on cubes placed between or on top of the sleeper blocks were used to assess the propensity of individual ballast grains for movement. For a standard G44 sleeper, increasing the ballast depth and/or the ballast bed roughness was found to reduce aerodynamic loads on an individual ballast grain. A ballast grain on top of the sleeper is more prone to uplift than a grain on the surface of the ballast bed in the crib. A curved upper surface to the sleeper is beneficial in that it prevents ballast from settling on top, the most vulnerable position. However, the reduced flow separation associated with the curved top may increase the likelihood of ballast pickup from the crib. Hence new sleeper shapes intended to reduce the potential for ballast flight should not only prevent ballast from settling on top, but also increase flow separation through the provision of a sharp surface. A prismatic sleeper shape that achieves both is suggested.

Аэродинамика плохообтекаемых тел на примере конвективного теплообменного аппарата

Issues related to the research and study of regularities and features of external aerodynamics of various designs of thermal (including heat exchange) equipment, which are weakly streamlined bodies, remain uncovered and insufficiently studied. However, it is the control of the aerodynamic resistance of a design (aerodynamic imperfection) that can be a convenient criterion for both the thermal efficiency assessment and the optimisation of convective heat exchanger designs. The work is devoted to the study of the aerodynamics of poorly streamlined bodies using the example of a single section of a convective heat exchanger with a developed external surface. The single section is an assembly of two flat six-channel elements with non-standard external finning placed parallel to each other at a small distance, which leads to the formation of lattices in the inner space of the section. A numerical study of the influence of the structural parameters of the cross-section on the air flow regime and its local peculiarities has been carried out. The numerical solution is constructed in a quasi-stationary formulation based on the solution of the conservation equations of compressible continuous media by the control volume method. Due to the geometrically driven turbulence of the flow, the conservation equations were Favre and Reynolds averaged, followed by the closure of the averaged system of equations by the SST turbulence model. A counter-flow scheme of 2nd order accuracy is used to resolve non-viscous flows, and a central difference scheme of 2nd order accuracy is used for viscous flows. The conjugate gradient method is used to accelerate convergence. Significant non-uniformity of the flow both in the section channel and after the airflow exits to free space is shown, described and substantiated. The jet-like nature of the air flow after leaving the section is identified and shown. The essential non-uniformity and asymmetry of velocity and pressure profiles, and gradual pressure decrease along the length of the region are shown. At the same time, the peak values of the flow velocity maxima are 5 and more times higher than the velocity values in the middle section of the channel. It should also be noted that the formation of peripheral attached currents near symmetry planes with a local increase in the velocity modulus is observed. The analysis of the revealed peculiarities of the flow aerodynamics has allowed to designate constructive elements, the improvement of which will allow to optimise the design of the oil cooler in order to increase the efficiency of its operation. The possibility of the constructive optimisation of the external fin design is shown.

The Effect of Courtyard Geometry on Airflow Regimes for Ventilation in Tropical Nigerian Environment

Effective natural ventilation is subject to the ambient wind flow, as well as the conditions of the micro-climate and the geometry of the built structures in the environment. Architects and designers adopt the courtyard concepts for designs in hot tropical climates owing to its unique geometrical characteristics that enable the improvement of airflow required for natural ventilation. This paper presents a review of the airflow regimes within an urban settlement as well as flow regions cultivated when winds interface with courtyard buildings. The impacts of these winds are further studied against different courtyard configurations using schematic analysis based on the H/W ratios, to predict the natural ventilation potentials of various courtyard building types.

Meteoroid ablation simulations with ESA’s SCARAB software

We computed the ablation of different spherical artificial meteoroids entering from a low-Earth orbit in the context of the AllBert EinStein mission. AllBert EinStein is intended to reenter spheres of known size and material into the atmosphere to determine the percentage of kinetic energy converted to light. This paper models the reentry to predict magnitude curves for the different initial conditions. An emphasis is placed on determining the difference between the single body ablation model and ESA’s reentry software SCARAB. It is also shown how the CFD simulations can work in synergy with SCARAB results to increase detail in the airflow regime around. Our study shows that with few fixes the meteor method replicates with good accuracy the SCARAB results for different artificial meteoroids, showing the validity of both tools.

Plant-scale experiments of an air inflow accident under sub-atmospheric pressure by pipe break in an open-pool type research reactor

In an open-pool type research reactor with a downward forced flow in the core, pipes can be under sub-atmospheric pressure because of the large pressure drop at the reactor core in the atmospheric pool. Sub-atmospheric pressure can result in air inflow into the pipe from the pressure difference between the atmosphere and the inside of the pipe, which in a postulated pipe break scenario can lead to the breakdown of the cooling pump. In this study, a plant-scale experiment was conducted to study air inflow in large piping systems by considering the actual operational conditions of an advanced research reactor. The air inflow rate was measured, and the entrained air was visualized to investigate the behavior of air inflow and flow regime depending on the pipe break size. In addition, the developed drift-flux model for a large vertical pipe with a diameter of 600 mm was compared with other correlations. The flow regime transition in a large vertical pipe under downward flow was also studied using the newly developed drift-flux model. Consequently, the characteristics of two-phase flow in a large vertical pipe were found to differ from those in small vertical pipes where liquid recirculation was not dominant.

The connection between air flow regime and heat transfer in the boundary layer of the brake disc cooling unit

The boundary layer of the air flow blowing the surfaces of the brake mechanism prevents heat transfer from heated surfaces. The obtained analytical dependences of the velocities` and temperatures` distribution in the boundary layer represent the field of the boundary layer as a multilayer structural model, the laws of change in the velocities and temperatures of the air flow blowing depend on various sub layers of the boundary layer. According to these analytical dependencies, a thermal model “ventilated brake disc - external condition” was developed. The thicknesses of the boundary layers of the air flow blowing on the various surfaces of the brake disc are determined by various processes. For the working surfaces of the brake disc, the determining criterion is the thickness of the diffusion layer, while for the surfaces of the ventilation apparatus, the criterion for estimating the thickness of the boundary layer is thermal processes. In future, the developed thermal model “ventilated brake disc – external condition” should be the basis for thermal calculations in designing disc-shoe type brake mechanisms.

Numerical Analysis of the Rear Wind Influence on the Truck During Travel

Abstract Rear wind is the air flow that blows in the rear side of the truck. Also known as a tailwind, this aerodynamic force can cause stability issues during forward travel. The methodology of the study is CFD numerical analysis of vehicle aerodynamics. The results will be acquired for the influential aerodynamic parameters, which includes velocity, pressure, vortex, stress, that will explain the impact of rear wind on the truck body. This is achieved with the aid of design, modelling, and simulations using software Comsol Multiphysics. The simulations were performed with freestream velocity of rear wind on the back and around the truck body. Virtual Wind tunnel is modelled around the truck to simulate the wind blow and distribution. There are two airflow regimes analysed: laminar flow and turbulent flow. Simulations for the laminar air flow were implemented for Compressed air flow and the velocity limit Ma<0.3. Simulations for the turbulent air flow regime were implemented based on Reynolds-Averaged Navier-Stokes Equations (RANS) and K-ω model. Anemometer device is used for the experimental measurements of the wind velocity around the truck. The wind is a function of air velocity and atmospheric pressure. The paper is in the fields of Vehicle aerodynamics, Fluid Mechanics, and Transport safety.

THE INFLUENCE OF DIFFERENT FACTORS ON THE MAISOTSENKO CYCLE EFFECTIVENESS

An important problem in the heat industry is the significant cost of energy resources for air conditioning. Therefore, energy-efficient refrigeration systems based on renewable energy sources and evaporative air cooling, as well as air-conditioning systems according to the Maisotsenko cycle using psychrometric energy of the environment are of great importance. This paper presents the results of experimental and numerical research of the influence of various factors on the efficiency of indirect evaporative heat and mass transfer apparatus on the M-cycle on the basis of a new unit cell.
 An experimental stand of a heat and mass transfer apparatus with vertically arranged plate channels was developed for experimental research. Experimental studies of heat and mass transfer in the new unit cell were conducted in a wide range of Reynolds numbers 200…1200, temperature 16… 30 °С, relative humidity 30… 50 %. The calculated study was performed using a modified ε-NTU method. Studies have shown that the thermodynamic efficiency of a wet bulb thermometer at a Reynolds number below 500 exceeded one. According to the results of computational studies, the influence of cell length and surface intensification of dry channels on thermodynamic efficiency was determined. Shown the effect of changes in thermodynamic efficiency in the range of 86…94 % increase in efficiency by 1 % leads to an increase in cell length by 7 %. The value of the enhancement factor increases with increasing air flow regime, so when the heat and mass transfer surface area increases by 50 % and the Reynolds number 200, the thermodynamic efficiency increases by 14 %, and with the Reynolds number 800 – by 28 %. The dependence of the thermodynamic efficiency of the cells at the dew point on the relative humidity of the inlet air have a maximum, which with increasing Reynolds number shifts toward larger values of relative humidity.
 Unlike traditional air conditioning devices, the M-cycle heat and mass exchanger does not use a steam compression cycle, so energy costs are spent only on the operation of the fan to pump air, which is a more environmentally friendly and energy efficient way of air conditioning.

Evaluation of Heat Transfer Rates through Transparent Dividing Structures

In this paper, heat transfer and airflow in the gap between the panes of a central part of a double-glazed window were investigated using mathematical modeling. It has been shown that the cyclical airflow regime, in the form of ascending and descending boundary layers, loses stability and changes to a vortex regime under certain conditions depending on the gap width, transverse temperature gradient, inclination angle and window height, as in Rayleigh–Bernard convection cells. The study made it possible to determine the critical values of the Rayleigh number (Ra) at which the air flow regime in the gap between the panes of a window changes (in the range of values 6.07 × 103 < Ra < 6.7 × 103). As a result of the modeling, the values of the thermal resistance of a central part of double-glazed window were determined as a function of the width of the gap between the panes, the angle of inclination and the transverse temperature gradient.

Measurement of the water vapour permeability of earth plasters using small-scale wind tunnels under variable air flow regimes

To determine the water vapour permeability of porous building materials, the wet cup and dry cup tests are frequently performed. Those tests have shown to present high discrepancy. The water vapour permeability of building materials is an essential parameter to determine the hygrothermal behaviour of the material and its impact on indoor comfort. Several previous studies have aimed to improve the reproducibility of the tests, by improving the protocol, the analysis of the results, notably by taking into account the surface film resistance. Yet, it is commonly accepted with no evidence that this surface film resistance can be neglected for an air velocity above 2 m/s over the cup. This study aims at experimentally testing the influence of either the flow regime or the flow velocity on the robustness of the measured water vapour permeability. For this purpose, two mini wind tunnels were designed to produce a laminar or a turbulent flow above the cups with variable air velocity. Water vapour permeability tests were performed in the tunnels with varying air velocity and flow regime on earth plasters with different compositions. The results have shown that regardless of the air velocity and flow regime, the surface film resistance should not be neglected. Based on the presented results, to reach an optimal repeatability, the use of wind tunnels should be considered as they allow to precisely control the air flow above the samples.

Lung targeted liposomes for treating ARDS.

Acute Respiratory Distress Syndrome (ARDS), associated with Covid-19 infections, is characterized by diffuse lung damage, inflammation and alveolar collapse that impairs gas exchange, leading to hypoxemia and patient’ mortality rates above 40%. Here, we describe the development and assessment of 100-nm liposomes that are tailored for pulmonary delivery for treating ARDS, as a model for lung diseases. The liposomal lipid composition (primarily DPPC) was optimized to mimic the lung surfactant composition, and the drug loading process of both methylprednisolone (MPS), a steroid, and N-acetyl cysteine (NAC), a mucolytic agent, reached an encapsulation efficiency of 98% and 92%, respectively. In vitro, treating lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages with the liposomes decreased TNFα and nitric oxide (NO) secretion, while NAC increased the penetration of nanoparticles through the mucus. In vivo, we used LPS-induced lung inflammation model to assess the accumulation and therapeutic efficacy of the liposomes in C57BL/6 mice, either by intravenous (IV), endotracheal (ET) or IV plus ET nanoparticles administrations.Using both administration methods, liposomes exhibited an increased accumulation profile in the inflamed lungs over 48 h. Interestingly, while IV-administrated liposomes distributed widely throughout the lung, ET liposomes were present in lungs parenchyma but were not detected at some distal regions of the lungs, possibly due to imperfect airflow regimes. Twenty hours after the different treatments, lungs were assessed for markers of inflammation. We found that the nanoparticle treatment had a superior therapeutic effect compared to free drugs in treating ARDS, reducing inflammation and TNFα, IL-6 and IL-1β cytokine secretion in bronchoalveolar lavage (BAL), and that the combined treatment, delivering nanoparticles IV and ET simultaneously, had the best outcome of all treatments. Interestingly, also the DPPC lipid component alone played a therapeutic role in reducing inflammatory markers in the lungs. Collectively, we show that therapeutic nanoparticles accumulate in inflamed lungs holding potential for treating lung disorders.SignificanceIn this study we compare intravenous versus intratracheal delivery of nanoparticles for treating lung disorders, specifically, acute respiratory distress syndrome (ARDS). By co-loading two medications into lipid nanoparticles, we were able to reduce both inflammation and mucus secretion in the inflamed lungs. Both modes of delivery resulted in high nanoparticle accumulation in the lungs, intravenously administered nanoparticles reached lung endothelial while endotracheal delivery reached lung epithelial. Combining both delivery approaches simultaneously provided the best ARDS treatment outcome.

Numerical Investigation of Air Supply Distribution, Flow Regimes, and Thermal Patterns inside a Private Bus

Numerical Investigation of Air Supply Distribution, Flow Regimes, and Thermal Patterns inside a Private Bus

CFD modeling of a self-oscillatory airflow regime in the test ventilated room with plane supply opening

The current contribution presents the results of numerical simulation of the airflow and heat transfer in a model room of rectangular shape ventilated with a single plane jet under the conditions of the experiment by Mataoui et al. (2001). The 2D and 3D unsteady Reynolds-averaged Navier-Stokes approaches were used. Numerical solutions were obtained with the CFD package ANSYS Fluent based on the finite volume method with the cell-centered variable arrangement. The position of the air supply nozzle corresponds to the self-oscillatory experimental conditions. The results of the computational data validation are reported. Effects of the low-frequency velocity oscillations on the heat transfer parameters are discussed.

Surface Dielectric Barrier Discharge in a Cylindrical Configuration – Effect of Airflow Orientation to the Microdischarges

ABSTRACT This paper is devoted to studying the effect of airflow orientation on the microdischarges of the surface dielectric barrier discharge in cylindrical configuration through varying air input into the discharge chamber, the number of input nozzles, and the geometry of the active electrode. The air is supplied into the discharge chamber tangentially, radially, or axially through one or four input nozzles. Air input into the discharge chamber and the number of input nozzles determine the airflow regime. We used two active electrode geometries that are the axial strips or azimuthal rings. The change of active electrode geometry from rings to strips affects the orientation of microdischarges with respect to the airflow. For the discharge, the variation of air inputs and the number of input nozzles influences the flow regime in the discharge chamber, which, together with the active electrode geometry, affects the temperature field distribution in the chamber. These factors play an important role in plasmachemical processes leading to the discharge generation of various species, such as ozone. It is found that, for the maximum effect of airflow on discharge ozone generation, the streamlines should be uniformly distributed in the discharge chamber and predominantly oriented perpendicular to the majority of microdischarges.

HVAC system requirements for protection against epidemics similar to Covid-19

Tuberculosis and in some cases, flu, colds and other airborne diseases. Since research is one of the biggest concerns of causing influenza pandemics, most research surrounding aerosol contamination revolves around environmental influences on the influenza virus. Many literatures suggest that influenza is transmitted primarily through close contact, such as exposure to large respiratory droplets, direct mouth-to-mouth contact and short-term exposure to infectious aerosols. Diffusion can be accelerated or controlled by heating, ventilation and air conditioning (HVAC) systems. Researches continue that advances state of knowledge in the specific techniques that control airborne infectious disease transmission through HVAC systems, including ventilation rates, airflow regimes, filtration, and ultraviolet germicidal irradiation (UVGI). In this paper three methods of transmission of Airborne Infectious Diseases are discussed, namely through direct contact, large droplet contact, inhalation of droplet core. An extensive literature review of many papers was conducted infectious diseases spread in several different ways and the transmission of infectious viruses. This review targets direct and indirect contact as well as infectious viruses known to be transmitted from the air. And he focused on preventive ventilation systems for these targets. This paper will give idea to support further research on engineering controls to reduce infectious disease transmission.

Experimental study on laminar air flow and heat transfer through a spiral channel filled with steel balls

The demand in the industry for high heat transfer performance is increasing. Studies have been greatly carried out on the new emerging technologies and creating new arrangements in engineering design. Porous media or curved channel increases heat transfer. Studies have been carried out for many years in heat transfer in curved channels and porous media separately. However, in this study, the heat transfer in the case of both curved and porous media is investigated experimentally. The experiments are conducted at constant heat flux in laminar airflow regime. A total of 169 sets of experiments are carried out in 8 experimental groups, in two different radii of curvature, in the unfilled spiral channel and in spiral packed bed formed by locating 3 different ball diameters (2.00, 2.38 and 3.17 mm). Nusselt number (Nu) correlations are presented separately for both the inner surface, the outer surface and taking the average of the inner and outer surface temperatures in unfilled spiral channel. Nusselt numbers (Nui, Nuo, Nua) for inner surface, outer surface and the average of the inner and outer surface temperature are obtained as Nui=0.93De0.45, Nuo=0.50De0.58, Nua=1.16De0.44 respectively. Heat transfer in spiral packed beds has not been investigated or reported in the available literature. By defining a modified Dean number (Dem) to reveal the effect of curvature in spiral packed beds, a correlation between the modified Dean number (Dem) and the Nusselt number (Nup) based on ball diameter is given. Nusselt number for spiral packed beds are presented as Nup=0.19Dem0.81. This correlation is also suitable for straight packed beds when the curvature ratio is neglected.