Maximum Temperature Zone Research Articles

Experimental and numerical study of lean combustion of propane in divergent porous media burners

Porous inert media burners for industrial applications demand the utilization of flame front stabilization methods, among which the convective or cross-section variation technique stands out. In this work, combustion of lean premixed propane-air mixtures in cylindrical and divergent alumina packed-bed porous inert media burners was numerically and experimentally conducted. Three burners of 0°, 15° and 30° of divergence were used to study the variation of equivalence ratio and inlet velocity. A bidimensional transient mathematical model was developed and solved numerically, whose results show good agreement with experimental measurements. The maximum temperature along the central axis is location dependent, with upstream augmentation of up to 86 %, meaning an increase of ∼ 815 K in the case of the 30° burner. Combustion front propagation velocity of upstream regime flames show acceleration in both divergent burners due to heat transfer and increment of thermal power in relation to cross-sectional areas when reaching the inlet. In comparison to cylindrical burner, a concave shape of the combustion front and a stretch of the maximum temperature zone was obtained, due to the diffusive nature of the velocity field. Stabilized flames on both divergent burners were achieved in the equivalence ratio range from 0.4 to 0.6. Residence time of product gases is greatly prolonged with burner wall angle and the decrease in overall temperature towards the outlet.

Behaviour of bolted rigid joint with endplate under localised fire scenario

The bolted endplate rigid connections in steel structures are used due to their robustness in distributing forces between the connected members. Though numerous studies have been performed to investigate the response of endplate connections under conventional fires representing uniform temperatures throughout the members (ISO-834, ASTM E119, etc.), the response of the same in case of localised fire is still not explored fully. The present paper focuses on an investigation of the behaviour of a moment resisting frame (MRF) assembled with flush endplate connection with bolts as connecting medium under localised fire scenario using Finite Element (FE) technique. A series of cases with different magnitudes of applied loads was investigated. In all the cases, the frames were heated up to failure with the localised fire source underneath the beam midspan and the corresponding failure modes were investigated. Experiments were performed on the samples of material at high temperature to gather a firsthand information on material characteristics. The frames experienced member failure at the zone of maximum temperature in the beam (midspan) for load level up to 30% of its ultimate capacity, whereas for load level above this, the frame failed at the connecting bolts of grade 5.6, which were maintained at room temperature. Based on the numerical study, it was observed that the provisions of IS 800:2007 were conservative than EN 1993-1-8:2005 in evaluating the safety of bolts under localised fire scenarios. Finally, parametric studies with the variation in connection geometry and configurations were performed, and design suggestions were recommended.

Numerical investigation of the maximum temperature zone for liquid–vapour flow during reflooding

High-temperature deformation caused is a major problem during reflooding. To describe the heat transfer behaviour, relationship between the maximum temperature zone and influencing factors are investigated. Good agreement between the numerical predictions and experimental data is observed. The results are obtained. (1) The Euler number and Grashof number influence the maximum temperature zone, the Strouhal number has a greater influence. (2) There is no correlation between the maximum temperature zone and velocity distribution waveform. (3) The power distribution changes the flow and temperature field and shifts the position of the highest temperature from the middle to the top. (4) The change in initial temperature directly leads to PCT mutations and changes in the maximum temperature zone. An excessively large Grashof number initial power, a top-enhanced power distribution, and a linear power distribution leads to an excessively high PCT and the maximum temperature zone at higher positions, which requires significant attention.

JUSTIFICATION OF EXTRUDER PARAMETERS WITH FLEXIBLE SCREW ELEMENT

For dry grain extrusion, autogenous single-screw extruders are mostly used, in which more than 85% of the supplied energy is spent on overcoming frictional forces. This leads to heating of the body and screw of the extruder and uneven wear along their length. The greatest wear is observed in the zone of maximum pressure and temperature. The wear of the screw causes a decrease in the productivity of the extruder and a deterioration in the quality of the extrudate. In addition, in case of wear of the ridges, it is necessary to change the screw, that is, the costs associated with the repair and maintenance of the extruder increase. In order to increase productivity and reduce maintenance costs, a sectional design of the working part of the extruder is proposed, the characteristic feature of the screw of which is that grooves are cut on the outer surface of the section along the helical line, into which spring segments are inserted. The sections of the screw are installed close together, and their grooves form a continuous screw line. Moreover, the width of the grooves allows the springs, as a result of periodic pressure changes in the pre-matrix zone of the extruder, to move along the axis of the screw. Determination of rational parameters and modes of operation of the extruder with an elastic screw element was carried out using the method of planning multifactorial experiments. The specific performance of the extruder was chosen as the optimization criterion. It was found that with the diameter of the extruder screw 50 mm, the temperature of the extrusion process 142...145 0С, the moisture content of the grain mixture 18.0...18.6% and the diameter of the die 5.5 mm, the following values of the factors are rational from the point of view of the maximum specific productivity of the extruder: screw rotation frequency 330...480 rpm; the depth of the screw channel is 5.3...7.1 mm; screw pitch 20...21mm; the number of grooves cut on the inner surface of the extruder body is 7...9 pieces.

3-D modelling of the coaxial one-side resistance spot welding of AL5052/CFRP dissimilar material

Coaxial one-side resistance spot welding (COS-RSW) is an advanced technique for joining CFRP/metal dissimilar materials. In the present work, a three-dimensional model was developed based upon an in-house finite element code JWRIAN-SPOT to simulate the multi-physical process of the COS-RSW. The thermal cycle and joining strength of COS-RSW joints with different welding parameters were measured experimentally. The sensitivity of material properties of electrode couple and component of accumulated heat generation were discussed in detail. The predicted thermal cycles presented a reasonable agreement with measurements, which also explained the influence of welding parameters on temperature field. The joining strength of COS-RSW joints can be evaluated qualitatively via the area of effective molten zone, which reached about 20 MPa with a 4800 A welding current. The column and cylinder electrodes determined the peak value of interface temperature and molten zone area, respectively. The cylinder electrode was suggested to be fabricated by a high resistivity material to generate sufficient Joule heat. Moreover, the SUS304 electrode and its contact zone provided more than 70% of the entire heat generation. The materials of electrode couple should be determined carefully when employing COS-RSW for joining CFRP and other metals. • A 3-D model of COS-RSW was established based upon an in-house finite element code JWRIAN-SPOT • The joining strength of COS-RSW joints shows similar variation tendency to the area of effective molten zone • The column and cylinder electrodes determine the maximum interface temperature and molten zone area, respectively • The SUS304 electrode and SUS304-AL5052 interface generate more than 70% of the total Joule heat

Experimental Investigation of Green Roof Impact on Buildings Energy in Hot Climate

Green roofs are a layer that effectively working on blocks of solar radiation from entering the building's structure below partially. Its work as a passive cooling technique, and have the potential to reduce the high surface temperature of conventional roofs because of the soil thermal resistance, evapotranspiration, and several effects for foliage shading. This affects the heat flux flow of the roof that in turn influences the indoor thermal conditions and the building energy demand. The research goals are to test the influence of the green roof on reducing heat transfer to the interior of heavy structural buildings. The experimental part was done to examine the effect of the green roof and compare it with a standard roof under influence of ambient air temperature, solar radiation, and wind speed and test the effect of the green roof on reducing heat transfer inside the building. The model site was at the Diwanyah city (Latitude: 31.9868 and Longitude: 44.9215), the engineering college campus, Qadisiyah University. The experimental setup includes two cubicles, with equal internal volume values (163cm * 163cm * 105cm). The experimental results showed for the period 5-8 September 2019. The maximum zone temperature was 46.4 °C for traditional roof and 37.06 °C for the green roof at 3:24 p.m. The results showed that the maximum internal temperature was 46.97 °C and 36.42 °C for the traditional roof and green roof respectively at 3 p.m. Also, the results for period 18-21 July 2019 noted that the zone temperature decreased by 7.5 °C and the maximum temperature of the internal traditional standard roof’s surface is 45.66 °C and 37.41 °C for the green roof.

Investigation on the effect of electrode tip on formation of metal droplets and temperature profile in a vibrating electrode electroslag remelting process

AbstractIn the present work, a transient full-coupled modelling approach has been put forward to study the effect of electrode tip on formation of metal droplets and temperature profile in the electromagnetically-controlled electroslag-remelting furnace with vibrating electrode. The electromagnetic field, momentum and energy conservation equations are solved simultaneously based on the finite volume method. The interface of slag and metal is traced using the volume of fluid approach. The results show that in the case of cone tip electrode the average dimension of metal droplets is smaller compared to the flat tip electrode. In addition, the bigger and stretched metal droplets are not observed with the cone tip electrode. The temperature fields with the cone tip electrode are distributed in a prominent periodic pattern compared to the case with flat tip electrode. The maximum temperature zone with the cone tip electrode is located along the z axial in the upper part of slag, not in the lower part. When the frequency changes from 0.17 Hz to 1 Hz, the maximum temperature reduces from 2050 K to 1985 K and the peak value of velocity decreases from 0.20 m/s to 0.125 m/s. When the vibration amplitude varies from 3mm to 6mm, the maximum temperature in the slag cover drops by 3.9% and the peak value of velocity rises by 16.7%.

Numerical investigation of the process of low calcarium gas injection in the mixture air heater

Gas mixing air heaters are widely used for heating air in the systems of inflow ventilation of autonomous air heating and thermal curtains of industrial premises, drying installations, for heating of greenhouse farms. Mixing of air with products of combustion of gaseous fuel provides effective air heating. Air heaters are manufactured with a nominal thermal capacity of 0.15 to 6.3 MW. The coefficient of working regulation for thermal power, not less than 2,5. Air heating in the range of 30-80 ° C. The mathematical modeling of radiation - convective heat transfer in the gas tract of the boiler is executed on the basis of the averaged by the Reynolds number of the Navie - Stoks equations, taking into account gravity and with the neglect of compression. The model consists of the equation of continuity, impulse transfer, energy and chemical components of the gas mixture, recorded in a stationary form. The equations are closed by Newton's law for a pressure sensor.Fourier law for heat flux, the Fick's law for mass flow, the Clapeyron-Mendeleev law for the thermodynamic state of a gas mixture, the equations of the turbulence model k-ε Launder-Spalding and the model of turbulent combustion of Magnus-Hertgaher. The results of numerical simulation in the form of vectors of flow rates of gases, temperature, and concentration of O2, CH4, CO, H2O, CO2 in the characteristic sections of the flow part are presented. The aerodynamic structure of the torch, long range and maximum temperature zone are determined.The obtained results of theoretical research can be used to regulate the design parameters of gas mixing air heaters with the provision of specified concentrations of these gases depending on their need for growing crops in closed soils, as well as to achieve the necessary temperatures and velocities of the gases of the corresponding technologies. Maybe the basis for algorithmization of automation of the corresponding technological processes and cycles of elements of air (gas) systems of heat supply for various purposes. Calorie gas in mixing air heaters are presented

Research on Strategies and Methods Suppressing Permanent Magnet Demagnetization in Permanent Magnet Synchronous Motors Based on a Multi-Physical Field and Rotor Multi-Topology Structure

In this paper, a permanent magnet synchronous motor (PMSM) with sleeves on the rotor outer surface is investigated. The purpose of sleeves is to fix the permanent magnets and protect them from being destroyed by the large centrifugal force. However, the sleeve material characteristics have a great influence on the PMSM, and therewith, most of the rotor eddy-current losses are generated in the rotor sleeve, which could increase the device temperature and even cause thermal demagnetization of the magnets. Thus, a sleeve scheme design with low eddy-current losses is necessary, and a method suppressing the local temperature peak of permanent magnets is presented. The 3-D electromagnetic finite element model of a 12.5 kW, 2000 r/min PMSM with a segmented sleeve is established, and the electromagnetic field is calculated by using the finite element method. The results show the effectiveness of the presented method in reducing the eddy current losses in the rotor. Using the thermal method, it can be found that the maximum temperature position and zone of permanent magnet will change. Thus, some strategies are comparatively analyzed in order to obtain the change rule of the position and zone. The obtained conclusions may provide a useful reference for the design and research of PMSMs.

Three-zonal engineering method of heat calculation for fluidized bed furnaces based on data on commercial investigations of heat generation distribution during biomass combustion

A three-zonal method of heat calculation of furnaces for combustion of biomass and low-caloric fuel in the fluidized bed is described. The method is based on equations of thermal and material balances that account for heat generation by fuel in the zone, heat-and-mass transfer heat exchange between the furnace media and surfaces that bound the zone, and heat-and-mass transfer between furnace zones. The calculation procedure for heat generation by fuel in the fluidized bed (FB) using the heat generation portion by the fuel is proposed. Based on commercial investigations, the main factors that affect the average temperature in the FB and the portion of fuel heat that is released in the FB are determined. Results of commercial investigations showed that the airflow coefficient in the FB should be recognized as the main operation parameter that affects the average temperature in the FB and, consequently, heat generation in the FB. The gas flow rate in the FB can be marked out as the second factor that affects the consumption degree of oxidizer supplied in the FB. Commercial investigations revealed that mixing is affected by the gas flow rate in the FB and the bed material particle size, which may be changed during the boiler operation because of the agglomeration of particles of sand and ash. The calculation processing of commercial investigations on a KM-75-40M boiler of a CHP-3 of an Arkhangelsk Pulp and Paper Mill (APPM), which was carried out using the inverse problem procedure by means of a developed computer program, determined the range of the fuel heat release share in the FB, which was 0.26–0.45 at an excess air factor of 0.59–0.93 in the bed, and the heat release share in the maximum temperature zone in the total heat release in the superbed space. The heat release share in the bed is determined as an approximating function of the excess air factor in the bed and the fluidization number. The research results can be used during designing boilers with the fluidized bed on biomass.

Experimental and numerical study on combustion of baled biomass in cigar burners and effects of flue gas re-circulation

The paper presents results of experimental and numerical investigation addressing combustion of baled agricultural biomass in a 50 kW experimental furnace equipped with cigar burners. Experiments performed included measurements of all parameters deemed important for mass and energy balance, as well as parameters defining quality of the combustion process. Experimental results were compared with results of numerical simulations performed with previously developed CFD model. The model takes into account complex thermo mechanical combustion processes occurring in a porous layer of biomass bales and the surrounding fluid. The combustion process and the corresponding model were deemed stationary. Comparison of experimental and numerical results obtained through research presented in this paper showed satisfactory correspondence, leading to the conclusion that the model developed could be used for analysis of different effects associated with variations in process parameters and/or structural modifications in industrial biomass facilities. Mathematical model developed was also utilized to examine the impact of flue gas recirculation on maximum temperatures in the combustion chamber. Gas recirculation was found to have positive effect on the reduction of maximum temperature in the combustion chamber, as well as on the reduction of maximum temperature zone in the chamber. The conclusions made provided valuable inputs towards prevention of biomass ash sintering, which occurs at higher temperatures and negatively affects biomass combustion process.

Generation of carbon nanostructures with diverse morphologies by the catalytic aerosol-assisted vapor-phase synthesis method

The Fe catalyst-supported aerosol-assisted synthesis method was used to prepare carbon products of diverse morphologies from toluene. Aerosol mist generation was accomplished with an ultrasonic device. An open-ended quartz boat for powder collection was placed in the maximum temperature zone of the tube reactor (850 °C or 1000 °C). The morphology of the products was studied by SEM and TEM microscopy. Structural characterization was provided by powder XRD, whereas Raman spectroscopy was used to determine the structural quality/homogeneity of the products. The hydrogen gas sorption capacity of the product prepared at 850 °C was relatively high despite its rather moderate BET specific surface area.

Structure and reaction zones of hydrogen – Carbon-monoxide laminar jet diffusion flames

In this study, experimental and numerical investigations of laminar jet diffusion flames using carbon-monoxide – hydrogen mixtures are carried out. Using a simple experimental setup, high definition direct flame photographs and shadowgraphs are captured, and radial temperature profiles at two axial locations are measured. Numerical simulations of carbon-monoxide – hydrogen jet diffusion flames have been carried out using a comprehensive computational model, along with simplified detailed chemical kinetics mechanism having 14 species and 38 reactions, and an optically thin approximation based radiation sub-model. Validation of the numerical model is carried out by comparing the measured and predicted temperature profiles, and experimental shadowgraph images with second derivative of the predicted density field. Results from the numerical simulations provide insights to the structures, species and thermal fields of flames for varying hydrogen content in the fuel mixture. It is observed that the axial extent of the maximum temperature zone tends to move towards the burner exit as the percentage of hydrogen in the fuel increases. It is also observed that the maximum mass fraction of carbon-dioxide decreases and those of OH and water vapour increase with increasing percentage of hydrogen in the fuel. Radial distributions of important species are presented for varying hydrogen content in the fuel mixture, which clearly illustrate the structure of the flame. Radial profiles of net reaction rates of major species and net rates of few important reactions are presented. As hydrogen is added, the reaction zone moves out in the radial direction, increasing the radius of the flame.

Interlaminar resistive heating behavior of woven carbon fiber composite laminates modified with ZnO nanorods

Abstract Thermal heating in the interlaminar region of ZnO/woven carbon fiber composite laminates was investigated. In ZnO/woven carbon fiber composite laminates, the interlaminar region, composed of ZnO nanostructured arrays embedded on woven carbon fiber sheets, interacts with the thermoset vinyl ester resin. ZnO nanostructured arrays were formed into nanorods (NRs) using a hydrothermal process. To investigate the electrical resistive heating behavior of the interlaminar region, we analyzed the temperature profile as a function of time in three zones: a heating zone, a maximum temperature zone, and a cooling zone. The morphology of the ZnO NRs was investigated using scanning electron microscopy, and X-ray diffraction analysis was used to characterize the crystallinity and ZnO concentration. Differential scanning calorimetry was employed to analyze the specific heat capacity of ZnO/woven carbon fiber composite laminates. Electrical resistive heating was achieved in the interlaminar region through multiple junctions formed between the intrinsic woven carbon fiber tows and among the ZnO NRs. The contribution of the ZnO NRs to the thermal heat gain was interconnected with the woven carbon fiber and resin in the interlaminar regions. The interlaminar resistance between the upper and lower laminas of ZnO/woven carbon fiber composites increased with incremental increases in the ZnO concentration up to 110 mM. This effect was due to the interlaminar interface and the high surface density of ZnO NRs, which inhibit electron transport into the woven carbon fibers. Resistance decreased following electrical resistive heating due to an increase in the density of free electrons at high temperatures.

Thermo-Mechanical Coupled Analysis of Deformation Behavior in Friction Stir Welding Process of Aluminum 7075 Plate with Conical Pin

A 3D elastic-plastic and coupled thermo-mechanical FE model for friction stir welding(FSW) of aluminum 7075 plate with conical pin was developed based on the dynamic explicit code ABAQUS/explicit. Then temperature distribution and deformation behavior of 7075 aluminum alloy plate in FSW process were simulated and analyzed. The results show that the temperature is distributed in the plate with an approximate ellipse shape and decreases from the edge of the tool shoulder to the outer side of the plate. Furthermore, the maximum temperature zone decreases gradually from tool shoulder to the bottom of the plate. In the welding zone, the equivalent strain is also distributed with ring shapes, and it decreases from the edge of the tool shoulder to the outer side of the plate.

Phase change in the cathode side of a proton exchange membrane fuel cell

A three-dimensional steady state two-phase non-isothermal model which highly couples the water and thermal management has been developed to numerically investigate the spatial distribution of the interfacial mass transfer phase-change rate in the cathode side of a proton exchange membrane fuel cell (PEMFC). A non-equilibrium evaporation–condensation phase change rate was incorporated in the model which allowed supersaturation and undersaturation take place. The most significant effects of phase-change rate on liquid saturation and temperature distributions are highlighted. A parametric study was also carried out to investigate the effects of operating conditions; namely as the channel inlet humidity, cell operating temperature, and inlet mass flow rate on the phase-change rate. It was also found that liquid phase assumption for produced water in the cathode catalyst layer (CL) changed the local distribution of phase-change rate. The maximum evaporation rate zone (above the channel near the CL) coincided with the maximum temperature zone and resulted in lowering the liquid saturation level. Furthermore, reduction of the channel inlet humidity and an increase of the operation temperature and inlet mass flow rate increased the evaporation rate and allowed for dehydration process of the gas diffusion layer (GDL) to take place faster.

Hierarchical porosity of bentonite-based buffer and its modification due to increased temperature and hydration

The use of the hierarchical pore structure in a bentonite-based mixture as a part of a nuclear waste repository's engineering barrier is proposed. The pore structure was observed in an experimental mixture composed of milled Ca-bentonite (85 vol.%), quartz sand (10 vol.%), and graphite (5 vol.%), which had been subjected to long-term (44 months) combined effects of increased temperature (up to 90 °C) and hydration during the Mock-Up-CZ experiment. Although there were negligible changes in the mineralogical composition (a slight increase of illite content, and minor conversion of montmorillonite to beidellite), the studied material underwent significant changes in the hierarchical pore structure. The parameters of the pore space were examined by adsorption techniques (CO 2 and N 2), as well as by the intrusion technique (mercury porosimetry). Detectable pore radii ranged from about 0.4 nm to 58 μm (micro-, meso-, macropores, and coarse pores). The observed pore categories were attributed to the presence of solid particles and their arrangement. The smallest pores exhibited a typical radius of 0.65 nm (a range from 0.4 to 1.6 nm), a total specific surface area of 50 m 2/g for the initial material. Mesopores showing radii 10–20 times higher were found within aggregates of clay mineral particles. Their specific surface area was roughly similar to that of micropores. Simultaneous heating and hydration decreased the specific surface area of the micropores close to the source of heat (i.e. in the direction of increasing temperature). There was a slight increase of their volume in moderately heated areas (50–70 °C) and a decrease in both the less heated (30–40 °C) and highly heated areas (over 70 °C). The same process increased the specific surface area of mesopores by 1–18%. The maximum increase of this parameter was observed in the samples exposed to a lower temperature (30–40 °C). The volume and specific surface area of macropores and coarse pores significantly decreased (by 20 and 40% respectively) when compared to the pre-experimental material but the typical radius of macropores was increased by a factor of about 2 or 3 in the zone of maximum temperature. This fact contributed to increased hydraulic conductivity observed by Pusch et al. (2007).

Formation of alumina nanofibers in carbon-containing coflow laminar diffusion flames

Nano-fibrous materials have attracted continuing research interest because of potential applications due to their unique properties. We report, for the first time, formation of alumina nanofibers in carbon-containing coflow diffusion flames with pure oxygen support, using trimethylaluminum vapor as the precursor. The alumina nanofibers were non-crystalline, typically 2–10 nm in diameter and 20–210 nm in length. No alumina nanofiber formation was found in flames supported by air. Neither was alumina nanofiber formation found in flames with pure H 2 as fuel. Thermophoretic samples showed that the nanofibers were formed in the region past the maximum temperature zone of the flame. The experimental data suggest that the alumina nanofibers were formed from gas-phase aluminum-containing species in the flame. Gas-phase carbon-containing species such as CO were probably crucial to the formation of the alumina nanofibers.

Propagation rates of nonpremixed edge flames

The propagation rates ( U edge ) of nonpremixed ignition (advancing) fronts and extinction (retreating) edge flames were measured as a function of global strain rate ( σ), jet spacing ( d), mixture strength, stoichiometric mixture fraction ( Z st ), and Lewis number (Le) using a counterflow slot-jet burner in which edge flames propagated along its long dimension. Electrical heaters at both ends of the slot “anchored” the flames, allowing conditions resulting in negative values of U edge to be studied by triggering local extinction of anchored flames with an N 2 jet. Results are presented in terms of the effects of a dimensionless flame thickness ( ε) related to σ and a dimensionless heat loss ( κ) on a scaled U edge . Propagation rates were markedly enhanced/retarded in mixtures with low/high Le. Propagation rates and extinction conditions were highly asymmetric with respect to Z st = 0.5 despite the symmetry of flame location; mixtures with Z st greater/less than 0.5 behaved like stronger/weaker mixtures, apparently due to the relative locations of the radical production zone and maximum temperature zone for varying Z st . Two extinction limits were identified, corresponding to a high- σ strain-induced limit that was strongly dependent on Le but nearly independent of κ and a low- σ heat-loss-induced limit that was strongly dependent on κ but not Le. Most experimental findings were in good agreement with theoretical predictions; however, unlike predictions, “tailless” triple flames were not observed; instead standard triple flames and “short length” edge flames were found, and only for a very narrow range of experimental conditions. This is proposed to be due to the difference between the volumetric heat loss presumed in the models and the conductive transfer to the jet exits that dominates heat loss in the experiments.

Simulation of Transport Phenomena during Natural Convection Cooling of Bagged Potatoes in Cold Storage, Part I: Fluid Flow and Heat Transfer

Agricultural produce, such as potato, onion, etc. are packed in permeable gunny bags for cooling in a natural convective environment and subsequent long-term storage. Due to permeable boundaries, the heat and mass transfer within the bag is strongly affected by the flow characteristics, especially during the transient cooling process. Therefore, an attempt was made in this study to simulate the three-dimensional airflow and heat transfer in this system using the computational fluid dynamics technique. The mass transfer phenomenon is being modelled in Part II of this paper. It was found that air mainly penetrated through bottom and side surfaces of the bag and escaped from top surface. The velocity contours maintained symmetry about both the horizontal axes in horizontal plane and only about the vertical axis in the vertical plane. The same patterns were observed for isotherms as well. The average natural convective velocity in the bag at steady state was found to be 0·0016 m s−1. The temperature of the product in the bag decreased at a very fast rate during the initial cooling period and then dropped to comparatively slow rates. In the vertical plane, the zone of maximum temperature was observed below the top surface of the bag at the early stages of cooling and it proceeded towards the centre point as the cooling progressed. Steady-state average temperature in the bag was found to be 0·13 K higher than the surrounding air temperature at 274 K. The experimental product temperature at the centre of the bag was found to be higher than that of the simulated one. The maximum and minimum temperature deviation from the experimental values were 3·4 K at 287·1 K and 0·5 K at 279·1 K on 2nd and 16th day of cooling respectively when the measured initial and final temperatures of potato at the centre were 297·1 and 278·1 K, respectively for a total cooling period of 25 days.