An indirect forced convection solar dryer integrated with porous sensible heat storage medium was developed. The effect of porous thermal storage and mass flow rate of air on the performance of the ...system for drying bitter gourd was studied. The experimental setup consists of a blower, solar flat plate collector with corrugated absorber plate (2m2) and a drying chamber. The thermal storage medium (pebble) is placed below the corrugated absorber plate, in the air passage as a porous medium. The experiments have been carried out with various mass flow rates of air and different drying models have been used for explaining the drying behaviour of sliced bitter gourd. The result shows that, (i) the initial moisture content 92% (w.b) of bitter gourd was reduced to 9% (w.b) in 7h in the proposed drying system, while it was 10h for open sun drying, (ii) the maximum specific moisture extraction rate was observed as 0.215kg/kWh at the mass flow rate of 0.0636kg/s and the corresponding specific energy consumption was 4.44kWh/kg, (iii) the collector and drying efficiency of the system were 22% and 19% respectively. The two term model and Midilli–Kucuk model are most suitable for indirect solar dryer and open sun drying in terms of statistical parameter respectively. The drying inside sensible heat storage based indirect dryer was more consistent and produced better quality product as compared to open sun drying.
•Every year post harvest losses are increasing rapidly due to the lack of storage facilities.•Solar dryers are the most suitable technology that can be easily availed at low cost and in small scale and it can be used as an income generation option for farmers and women in rural areas.•The role of solar dryers in food processing industries is significant especially in developing countries in the following areasoFor preserving fruits and vegetablesoDairy industriesoAgricultural crop dryingoTimber dryingoIndustrial waste drying•The utilization of thermal storage medium in the solar dryers is being focused much for the reasons of extending the availability of the system for operation and to achieve better quality of the products.
•Performance of the sensible heat storage based indirect solar dryer was studied for drying bitter gourd slices.•The thin layer drying behaviour explained with drying models for the indirect solar dryer and under open sun drying.•Probably, first time, the drying models were reported for bitter gourd drying in the indirect solar dryer.
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•Oscillatory diffusion results from flow oscillation plus random particle hindering.•Enhances nanoparticle transport in biofilm mitigation and targeted drug delivery.•A stochastic ...model of oscillatory diffusion was investigated.•Parametric sensitivity study was performed for various model parameters.•Stochastic model predictions agreed with CTRW theory with restrictions.
Colloidal particles in the pore spaces within a packed bed move back and forth in response to an imposed oscillatory flow, such as that associated with an acoustic field. The diffusive motion of the particles results from intermittent hindering of the oscillatory motion, which we assume to result from particle filtration by the packed bed pore spaces. We consider an experimentally-validated stochastic model that entails a series of transitions between an oscillatory state, where the particle oscillates with the fluid flow, and a captured state, where the particle is held fixed in the bed. The paper examines sensitivity of this stochastic model to different parameters and compares the stochastic model predictions for diffusion coefficient with predictions of an analytical solution based on continuous-time random walk (CTRW) theory. The results are relevant to applications such as nanoparticle penetration into biofilms, drug capsule penetration into human tissue, and microplastic transport within saturated soil.
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•Oscillating flow enhances particle diffusion in a porous media.•Diffusion results from oscillation plus random hindering.•Experiments exhibit statistical measures similar to random ...walk diffusion.•Particle hold-up duration exhibits log-normal distribution.•Stochastic model displays similar characteristics as experiments.
An experimental study was conducted of particle diffusion within a porous bed when exposed to oscillatory flow. The particle oscillates up and down within the porous bed in response to the oscillatory flow, but also becomes intermittently stuck for time intervals of varying duration. The combination of oscillating flow and random hindering of the particle motion by the porous bed leads to a diffusive process called oscillatory diffusion. A variety of statistical measures are used to characterize the particle diffusion under the oscillatory flow. These measures show that the experimental data exhibit characteristics of both classical diffusive processes as well as oscillatory processes. The particle hold-up time duration was found to be well fit by a log-normal distribution for all experimental cases examined. A simple stochastic model that captures the key features of the oscillatory diffusion process is shown to yield statistical measures that compare well with experimental data.
A hydrodynamic model, with incorporation of porosity, is considered to investigate oblique water wave scattering by two fully submerged parallel porous plates with the wave propagating over a porous ...bed in a homogeneous fluid flow with the upper surface exposed to atmosphere. The porous plates are assumed to follow the theory of thin plates and the wave propagation through the porous structure follows porous wave-maker theory. The behavior and properties of the roots of the dispersion relation are analyzed by adopting counting argument and contour plot. Time-harmonic propagating waves propagate with exactly one wavenumber along the free surface for any given frequency. Methods of eigenfunction expansion and least square are employed to acquire the complete analytical solution for interaction of water waves with submerged porous plates. Subsequently the reflection and transmission coefficients as well as the energy loss are computed. Then those are examined corresponding to various values of parameters such as porous-effect parameter, the submergence depth of plates from free surface, angle of incidence, porosity of the sea-bed. Present investigation clearly demonstrates that the wave reflection is of oscillatory nature. It further shows that the occurrence of minima in wave reflection is due to an increase in the inertial effect of the porous plates which dissipate a significant portion of the wave energy. The effect of the porous bed under consideration on surface gravity waves is carried out by introducing various numerical values to the hydrodynamic wave characteristics and it is noticed that a reasonable change in porosity of the sea-bed has a significant impact when the propagating wave encounters the submerged structure. The present approach is expected to be of great significance in designing and construction of different types of effective wave absorbers utilized in sea for studying reflection as well as dissipation of wave energy in coastal regions and hence for the purpose of coastal as well as offshore engineering. The present model is validated by comparing it with some established result.
Experimental investigation of gasification of oil shale dust in a counterflow moving bed filtration combustion reactor was carried out. The process was implemented similar to filtration combustion of ...gases: pulverized solid fuel supplied simultaneously with oxidizer. For a controlled supply of fuel dust a new rotating dispenser was used. Characteristics of process depending on the equivalence ratio were obtained. The absence of a rise in pressure drop over time indicates the lack of fuel accumulation and ash inside the porous bed, all ash was carried out from the reactor with a gas stream. It is shown that an increase in the flow rate of a gaseous oxidizer leads to an increase in both temperature and the inert velocity. The inert velocity, the calorific value of gaseous products, and the efficiency of gasification increase almost linearly with the equivalence ratio. Proposed method allows producing combustible gaseous products without a noticeable concentration of pyrolysis tars and calorific value up to 4 MJ/m3, gasification efficiency was ~85%.
•A method for a controlled supply of fuel dust was proposed.•No increase in the pressure drop in the reactor over time is shown.•A method allows obtaining gaseous products free of pyrolysis tar.
A method to calculate a two-phase flow and to find the dryout region in a volumetrically heat-generating porous bed using computational fluid dynamics (CFD) is developed. It is assumed that the ...structure of the porous bed, cooling water and water vapor are at all saturation temperature in the boiling zone, and all the generated energy is transferred to the water by boiling where the water fraction is above a certain value. Lipinski model is used for the drag between two-phase flow and porous media. The CFD results are compared with the axis-symmetry COOLOCE tests. If a critical water fraction of 0.0025 is set as the threshold value, below which no boiling occurs in the porous bed, the error of the dryout power densities between the calculations and the measurement that causes the detection of the dryout in the conical bed is 4.2 – 32% depending on the system pressure.
•A 3D transient model for the simulation of fixed bed biomass combustion was developed.•The thermal conversion of solid wood was modelled by solving transport equations of several variables.•A ...compaction model was introduced to account for the local shrinkage of the bed.•The model predictions was compared with experimental data.
CFD codes are well equipped in the resolution of the gas phase combustion, however the solid phase modelling still needs to be developed. The aim of this work is to implement several submodels of thermal conversion of solid fuels and the interaction with the gas phase in a commercial CFD code. For this, a set of submodels taken from literature is proposed for simulating the combustion of solid biomass in packed beds. The modelling method implements several variables that represent the main parameters of the solid mass in the framework of a commercial CFD code. The transport equations of the solid phase are used to predict the transient evolution of the bed and the interaction with the gas phase within the bed and the area surrounding it. The radiative heat transfer is modelled by modifying the standard Discrete Ordinates model to consider the temperature difference between the solid and gas phases and the high absorptivity of the medium. A compaction model is introduced to account for the local shrinkage of the bed due to the collapse of regions weakened by their combustion. The results of the model are presented and discussed by the contrast of the model through the simulation of an experimental burner whose ignition rates, maximum temperatures, and drying, devolatilisation, and char thicknesses are known. The model shows a reasonably accuracy in the predictions of some variables as ignition rates, maximum temperatures and the bed height transient evolution. The comparison of the drying, devolatilisation, and char thicknesses for different air mass fluxes shows reasonably good tendencies even thought the values are excessively high. Compared with previous works done by the authors and by others, it can be seen that the introduction of a bed compaction submodel, as the one presented here, can help in the realistic estimation of the processes involved in packed be combustion of biomass and point to particle shrinkage and bed’s mechanics as an important process to be considered.
•Developed a solar air heater with corrugated absorber plate integrated with porous bed.•Energy efficiency with packed bed varies from 20.35% to 50.92.%•Exergy efficiency with packed bed +3.97% to ...−2.81% for the mass flow rates 0.0141 kg/s to 0.0872 kg/s.•Solar collector with packed bed capable to deliver the hot air in the range of 45 to 60 °C –suitable for drying.•Energy efficiency of the packed bed collector is 3 to 8% higher than the collector without packed bed.
The thermal performance of the solar collector for air heating purpose is investigated with and without packed bed through experimental and theoretical methods. A simple flat plate solar air heater was developed with 2m2 corrugated absorber plate and integrated with porous pebble bed in the airflow path to act as a sensible heat storage medium. The experimental studies were carried out for different mass flow rates of air from 0.014 to 0.087 kg/s with the increment of 0.0095 kg/s. Steady-state theoretical models have been established to predict the thermal performance of the air heaters and the results indicated that they are well enough to predict the outlet air temperature with acceptable error percentage. The collector with packed bed storage medium is more efficient than without packed bed in terms of energy efficiency as well as in reducing temperature fluctuation of air at the outlet of the collector. The energy and exergy efficiency of the collector with packed bed veried from 20.35% to 50.92% and +3.97% to −2.807% for the airflow rates 0.014 kg/s to 0.087 kg/s respectively. Solar collectors with packed bed are capable to deliver the hot air in the range of 45 to 60 °C for a longer period and which can be preferred for achieving a better quality of the dried products as well as for space heating applications.
To better understand the evolution characteristics of bed porous structure during iron ore sintering, X-ray computed tomography scanning technology was used to analyze the pore parameters in ...different areas of the sintering bed. A pore skeleton structure model was established to study the characteristics of the airflow channels in different zones. The absolute permeability of different areas was calculated through simulation, and the corresponding streamline and pressure drop distribution were analyzed. The results show that the porosity of raw material zone, high-temperature zone, and sintered zone increases gradually, which are 37.69%, 46.41%, and 55.57%, respectively. The absolute permeability calculation results of the raw material zone and sintered zones are 792.49 μm2 and 20560.80 μm2, while the tortuosity is 1.77 and 1.45, respectively. Compared with the raw material zone, the flow streamline in the sintered zone is thicker and denser, the airflow resistance and the pressure drop are minor.
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•X-ray computed tomography technology was used to analyze pore parameters.•Pore skeleton structure model was established.•Absolute permeability of different areas was calculated through simulation.•Streamline and pressure drop distribution were calculated and analyzed.•Evolution characteristics of pore structures were analyzed.
•The coolability of debris bed formed in APR1400 pre-flooded reactor cavity is analyzed.•The shape of debris bed is assumed considering the geometry of APR1400 reactor cavity.•Multi-phase flows in ...heat-generating porous bed are calculated using CFD.•The ratio of dryout region of debris bed is calculated according to system pressure, effective diameter of particles, and repose angle of debris bed.
This study evaluates how large a debris bed becomes dryout during ex-vessel cooling in a pre-flooded reactor cavity if a postulated severe accident occurs. It is assumed that all generated energy is transferred to water liquid by boiling if the water liquid fraction is more than assumed critical liquid fraction. Heap-like debris beds with a repose angle of 25°, 35° and 45° are analyzed, and the effective particle diameters are assumed to be 0.65 mm, 0.9 mm and 1.65 mm with 0.37 porosity, respectively. The system pressures are considered from 1 bar to 5 bar. In all cases, dryout occurs in the debris beds and the proportion of dryout region accounts for 29.2 % to 92.2 %. The larger the effective diameter, the smaller the dryout region; and the larger the system pressure, the smaller the dryout region. It is also evaluated that as the repose angle increases, the dryout region decreases. As the repose angle increases, the angle at which flowing water faces the debris bed becomes steep, so more coolant can be injected into the debris bed and less coolant flows along the slope of the debris bed.
