جستجوی مقالات مرتبط با کلیدواژه « computational fluid dynamics » در نشریات گروه « مکانیزاسیون کشاورزی »

Greenhouse drying is one of the drying methods that can dry large amounts of agricultural products simultaneously. All greenhouse dryer models use solar radiation energy. Greenhouse dryers are very similar in appearance to a greenhouse in that the air inside is  heated by solar radiation, and the desiccants are dried inside. Because a large part of Isfahan province has a dry climate and has 300 sunny days a year, there is a high potential for using this type of dryer. The performance of this dryer depends on the airflow characteristics and the geometry of the dryer chamber. Therefore, this study aims to predict the behavior of airflow inside the chamber of greenhouse dryers using computational fluid dynamics (CFD) for the climate of Isfahan. For this purpose, the effect of sunlight intensity and external geometry of the dryer on the speed, temperature, and air pressure inside the chamber was investigated by Ansys Fluent 18 software. This study evaluated four common types of geometries for greenhouse dryers. These four types of geometry include a greenhouse with a convex roof, a one-sided sloping roof, a double-sided sloping roof, and a greenhouse with a convex roof and vertical walls, respectively. The simulation results were validated by comparison with experimental results obtained from other researchers. The results showed that the greenhouse with a convex roof and vertical walls had the best performance in the uniformity of airflow velocity inside the dryer. Also, the best performance in the uniform air temperature distribution inside the dryer was related to the double-sided sloping roof and the greenhouse with a convex roof and vertical walls. The lowest air pressure inside the dryer chamber was associated with the geometry of the greenhouse with the convex roof.

The porous materials in hot water dryers are used in industry because they increase heat transfer. In these cases, the thermal performance of the heat channels is greatly influenced by the arrangement of the porous material inside the duct. Therefore, the aim of this study, which was performed by simulation method by Ansys Fluent 16 software, is to improve heat transfer in hot water dryers using new geometries of porous materials. For this purpose, the effect of 5 different types of geometry for porous material (with equal volumes) at 5 different dimensional heights of metal foam (1, 0.8, 0.6, 0.4, and 0.2) and the effect of two different pore diameters (0.1 and 0.05 cm) were evaluated on the  hydrodynamic and heat transfer indices including average Nu number and performance evaluation criteria (PEC). The porous material was considered aluminum alloy with a thermal conductivity of 40 W / m2K and a porosity of 0.95 throws a thermal sink. The results showed that using porous materials in the heat channel increased the Nu number and heat transfer. Also, increasing the pore diameter in porous materials increased the Nu number. The highest PEC number was related to the case where the pore diameter and the height of the porous material are equal to 0.1 and 0.2 cm, respectively.

Cyclone separators use the centrifugal force generated by the gas flow stream to separate the particles from their carrier gas. Simple design, low capital, and easy maintenance make them ideal for use as a valuable pre-refining or sedimentation device. The cause of the particles moving towards the wall and separating from the fluid phase is the centrifugal force created by the rotational flow in a cyclone.Computational fluid dynamics (CFD) is one of the most well-known and widely used advanced modeling methods used for a variety of applications, including separation processes, thermal processes such as dryers, as well as a wide range of engineering and agricultural applications. The numerical solution of Navier-Stokes equations is the basis of all CFD techniques, which is the result of the rapid progress of computers and a deep understanding of the numerical solution of turbulence phenomena.

The measurement system of experimental data includes a cyclone separator, feeder, piping, and fan. Measurements of velocity and pressure were carried out using a hot wire air flow rate, (Model 8465-TSI with a resolution of 0.07 m.s-1 and a working range of 0.125 to 150 m.s-1), as well as a differential pressure gauge (CPE310s- KIMO, with an accuracy of 0.1 Pa), respectively. To investigate the effect of the output flow regulator plate on the cyclone performance, five different positions in addition to the base position (zero degree angle or fully open) including angles of 15, 30, 45, 60, and 75 degrees were evaluated.The conservation laws governing the various flows and geometries in the CFD include the conservation law of mass, conservation law of momentum, and conservation law of energy.According to the Mach number value, the pressure base solver was selected. Also, the Reynolds stress model (RSM) was applied to model the flow turbulence. In the discrete phase model (DPM), the fluid phase is solved continuously by solving averaged time equations, while the dispersed phase is calculated by tracing a large number of particles through the flow field.The boundary conditions used in this study include the inlet velocity boundary condition at the inlet of the cyclone, the outlet pressure boundary condition in the upper and lower outlet sections, and the non-slip wall boundary condition for other surfaces. The particle collision to the wall was also defined as reflective. In the mesh section of the cyclone simulation, five mesh levels were used to check the mesh independence test. The numbers of mesh cells in the five levels were 196810, 283120, 427890, 634940, and 1045290. The selected mesh was 427890 level regarding time consideration.

In the first section, the validation of simulation results with experimental results is discussed. The value of the velocity magnitude decreased with increasing the angle of the plate, which is probably due to the reduction of the inlet level as well as thereduction of the exhaust airflow in the cyclone air outlet.The maximum value of velocity magnitude occurred according to the direction of the air inlet in the cyclone inlet, which is gradually reduced due to the rotational motion inside the cyclone.The collection efficiency in the cyclone at different levels of regulating plate has values of 85.1% to 95.3%, with maximum collection efficiency at 30° which was 95.3%. The turbulent intensity contours show that turbulence intensity decreases to an angle of 30 °, and then reaches an almost constant value for the 30, 45, and 60 ° angles.

As the angle of the output current regulator plate increased, the magnitude of velocity decreased significantly.The separation efficiency showed an increasing-decreasing trend for different values of the regulator plate such that up to a 30° angle of the plate had a positive effect on the separation efficiency.In general, considering the compromise between separation efficiency and pressure drop as two key parameters affecting the performance of the cyclone, an angle of 30 degrees was selected as the best angle among the studied angles for application.

In livestock and specifically poultry houses, controlling the internal environment conditions is a key factor to increase animal productivity and prevent their casualties. Controlling the atmospheric conditions like the air temperature and gas concentration in semi-enclosed spaces like poultry houses can improve the living conditions. Experimental tests on the atmospheric conditions of livestock and poultry houses are challengeable and due to limitation of measurement points, unstable climate conditions and experimental errors. Simulation of the air temperature and momentum conditions is used unlimitedly with computer resources by Computational Fluid Dynamics (CFD) methods to overcome the limitations of experimental tests. This method has vast abilities of parametric analysis and predicting the optimum range of functional parameters. So in this research, the air temperature and velocity distribution of a poultry house were simulated using CFD to achieve the best condition for the air ventilation and uniform temperature distribution.   

In the present study, the geometrical model of poultry house was created using Gambit software and meshed. The mesh independence study was also performed. According to the results, 166550 elements were enough to solve the problem with an acceptable accuracy.The Reynolds-averaged Navier-Stokes (RANS) equation was selected to simulate the momentum transfer inside the poultry house. The k-ε model is one of the most used turbulence models for industrial applications. The main assumption in this model is that the flow is incompressible and that the fluid is Newtonian. A transient heat transfer equation within the fluid domain was selected to predict the air temperature that describes a time-dependent process that includes the conduction and convection terms. All the boundary condition was measured experimentally during 24 hours and their temperature was modeled using the proper mathematical models and applied to the developed model. The mathematical models were solved simultaneously in ANSYS- FLUENT software. The developed simulator was validated experimentally by measuring the air temperature of some specified locations (13 points).

The results demonstrate that the model enjoyed satisfactory accuracy so that the RMSE value between the measured and predicted air temperature was in the range of 0.405 to 1.29 and the simulator could predict the air temperature with the accuracy of 0.6 degrees. Therefore, it is possible to use the validated simulator for the real-time controlling of poultry houses to optimize the ventilation process. According to the results, the high heterogeneity in the air temperature and about an 18-degree difference was observed in the air temperature distribution at various locations of poultry houses. In addition, the air velocity was not uniform at the different plans of poultry house; especially in the central points of poultry house, it was higher than 1 m/s that is higher than the recommended value. Therefore, the simulator was used to improve the ventilation of the poultry house. The results of various simulations carried out indicated that the angle of the air inlets vents affects the air turbulence. Also, the air temperature and velocity distribution were more uniform when the air inlet vents were across each other. Therefore, some new gates were opened and the angle of the existing gates was changed to improve the ventilation condition of the poultry house. By such modification, the ventilation condition of the poultry house was improved and the air velocity and temperature distribution in the optimized house were more uniform than that observed in the primary one. The air temperature and velocity were in the range of 291 to 297 K (18 to 24 °C) and 0.23 and 0.46 m s-1, respectively. These values are at the recommended condition for poultry houses.

The opening angle of the vents had a significant effect on the air distribution. Application of across vents in the  side-walls of poultry house led to uniform distribution of air velocity and temperature. The developed simulator has good performance and accuracy to design and construct poultry houses.

One way of improving the thermal performance of greenhouses is using thermal insulators (thermal shading). In this study, the behavior of a novel dynamic shading system made of two-layer polycarbonate plates containing fluid was investigated by numerical method. In this system, according to the cooling and heating requirements also to control the incoming or outgoing radiation from the greenhouse, the appropriate fluid was pumped into the ducts between the polycarbonate plates by a hydraulic pump. Studying the hydraulic parameters, including intra-duct pressure and fluid velocity between plates, can be very useful for the proper design of the shading to minimize the energy required and run the system. The computational fluid dynamics (CFD) method and standard k-ε turbulence model simulated turbulent flow inside the shading ducts. Validation between experimental and numerical data showed an average difference of less than 5 percent between the experimental and numerical pressure drop data. The maximum velocity value of 0.96 ms-1 was obtained for the ducts inside. In comparison, the system pressure drops in single (series) and triple modes (parallel) it was 3793 Pa for the latter and 3439 Pa for the former, which indicates 9.3% decrease in pressure drop for the innovative and proposed design.

Cyclones are widely used to separate solid particles from the fluid phase. Due to the ease of construction, low running costs, and hard-working conditions at high temperatures, people's interest in using cyclones is increasing day by day. Engineers are generally interested in two parameters to perform a complete evaluation of the design and operation of a cyclone. These parameters are the particle collecting efficiency and the pressure drop inside the cyclone. The precise prediction of the pressure drop in cyclone is very important which it is directly related to operating costs.Computational Fluid Dynamics (CFD) is a diversified tool for predicting flow behavior in a wide range of design and operational conditions. Numerical solution of Navier-Stokes equations is the basis of all CFD techniques, which is the result of fast computer upgrades and a better understanding of the numerical resolution of turbulence.

Regarding preliminary experimental tests and understanding the fluid flow, the flow rate of 0.08 kg s-1 was selected as the flow rate. Six levels of inlet velocities 10, 12, 14, 16, 18, and 20 m s-1 were selected for understanding the effect of inlet velocity on the cyclone performance. The measurements were carried out using a hot-air anemometer (TSI-8484model with a resolution of 0.07 m s-1 and an operating range of 0.125 to 50 m s-1), and a pressure differential meter instrument (CPE310s-KIMO model) with an accuracy of 0.1 Pa.The region is discretized as a finite volume in a set, called the region grid or mesh after discretization. For incompressible fluids, pressure-based and density-based solvers are used, respectively. Regarding the velocity of the material entering the cyclone and low Mach number, a pressure-based solver could be used in this study.The shear stress transport model (SST) is a modified version of the k-ω 2-equation model. This model combines the two turbulence k-ω and k-ε models. The Lagrangian discrete phase model in Ansys Fluent follows to the Euler-Lagrangian model.Defining the best type of boundary condition is important for solving the problem and extracting solving fields. The boundary conditions used in this study include the inlet velocity in the entrance of cyclone and output pressure in both the upper and lower output sections.

In the results section, the results are initially validated by experimental results. Then, the parameters relating to separation efficiency and pressure drop are discussed. Finally, the tangential and axial velocities are considered as important parameters in the cyclone performance.One of the important issues in the cyclones is the static pressure because it completely affects the phenomenon of separation in the cyclone. The velocities of 16 m s-1 and 18 m s-1 have a good potential for use as the base velocity of the inlet fluid to the cyclone. The velocity of 20 m s-1 is not suitable for separation due to high-pressure drop related to high static pressure.The separation efficiency in the cyclone was 92 to 99% at all levels, the highest separation efficiency of 99% occurred at the velocity of 16 m s-1 and the lowest separation efficiency of 9% happened at the velocity of 20 m s-1.An increasing trend in axial and radial velocities occurred and the highest tangential velocity occurring in the input section. Considering the working conditions, the inlet velocities of 10 m s-1 to 16 m s-1 are appropriate for the turbulence intensity viewpoint.

(1): The speeds 16 m s-1 and 18 m s-1 showed a good potential for use as a base velocity of the fluid to the cyclone.(2): The highest separation efficiency for the velocity of 16 m s-1 (99%) and lower isolation efficiency was obtained at velocity of 20 m s-1 (92%).(3): The velocities of 10 m s-1 to 16 m s-1 are suitable input rates from the point of view of turbulence intensity.(4): It is concluded that from the point of view of wear to the velocity of 10 to 16 m s-1, practical use is possible, and the velocity of 18 m s-1 and 20 m s-1 require the reinforcement of the relevant sections.

Computational Fluid Dynamics (CFD) was used to study airflow and temperature distribution in cold storage and finding temperature levels. Total sugar, reducing sugar and sucrose of potato tubers cv Sante stored at 5 °C and relative humidity of 80%, were extracted. The results showed that there was a significant difference between the concentration of total sugars, reducing sugar and sucrose due to temperature distribution heterogeneity.It led to a 2 °C difference between the warmest and coldest points in product mass. Changes in the content of sugars were matched with simulated temperature contours. The rate of increase in soluble sugars was predicted by reducing 1 °C air temperature. Total sugars, sucrose, and reducing sugar were 4.27, 3.15 and 0.67 mg/g dry matter, respectively. Computational fluid dynamics, by analyzing fluid flow and distributing temperature and detected critical areas, leads to improving packaging and product placement, and improve airflow in the stack.

Greenhouse structure is one of the most important factors in the greenhouse industry; enhancing its strength and decreasing the cost of its manufacturing have always been among manufacturers consideration. The aims of this study were to design an octagonal greenhouse with square cross-sectional components with enough resistance to standard loads applied by structure stress analysis methods. Design and optimization of this greenhouse involved selecting the minimum thickness of the profiles and columns. In addition, the layout of the trusses is led to minimum weight of structures per square meter. This greenhouse was designed to have nessecary structure standards and could be used in different climate conditions of Iran. In design process, initially the effects of wind load with 120 km/h were determined by using fluid dynamics calculations. Afterward, the main frame of the structure including columns, horizontal beams and trusses, were designed according to wind, snow and pendant loads. The results showed that the wieght of metal to be  used to build the structure of greenhouse was less than 8.5 Kg/m2 ,  very lower than that in similar stuctures (20 kg/m2).

The sedimentation chambers are used in various agricultural systems. In this study, an innovative design of the chickpea sedimentation chamber including the chamber with the flow path deviation blade are considered and the effect of this blade on the sedimentation efficiency, required flow, distribution of air flow and chamber erosion were investigated experimentally and numerically. The computational fluids dynamics for numerical simulations was used. A laboratory setup equipped with a hot wire anemometer and differential pressure meter was used to obtain the velocity and pressure data and model validation. The results showed that the use of the flow path diversion blade has an 11.4% increase in sedimentation efficiency, reduction of 6.67% of the required airflow and cause the reduction of erosion in chamber.

The issue of noise pollution is one of the concerns of most societies and industries because of their relationship to the environmental comfort of life or work of people are paying attention. The Aero-acoustics not only because of government regulations on the noise pollution, but also due to the increasing demand of the people's living standards and create a safe environment for farm animals is considered important. At the same time, products with high aero-acoustic performance will attract a lot of customers, which is in the interest of the global economy. Reducing current noise is often accompanied by a reduction in energy costs, resulting in durability of structures and improved product quality.

Sound measurements were carried out at the wind tunnel in Tabriz Tractor Engineers Company. Using the measurements performed by the instrument, the sound levels were measured at different periods of the fan. In many practical applications that include turbulent flow, no noise has any specific tone and the sound energy is continuously distributed over a wide range of frequencies. In cases where broadband noise is present, statistical disturbance values easily calculated from the RANS equations can be used in conjunction with semi-experimental correlations and audio coordination to reveal some broadband noise sources.
Based on the problem, the boundary condition is the type of "input velocity" for the input and "output pressure" for the output. It was also used to move the mesh to apply the rotary motion of the fan. The thermodynamic conditions at these boundaries should be considered.

The accuracy of the simulation results data was verified with the measured data. In the laboratory results, the audio level is accompanied by an audio environment and an inverter and a belt that is about 15 db. With this in mind, the simulation results had a good agreement with experimental results.The velocity is a critical parameter in fan-related discussions. In the upper part of the fan, the speed of the air increases as the fan sucks, and this speed will increase as the fan approaches. In the second part, which includes the fan, for speeding objects, the speed will increase as the radius increases (due to the constant rotational speed), so the maximum speed will be at the tip of the blades. In the lower part of the fan, the speed will decrease as the fan impact decreases on the air molecules as well as the boundary layer behavior near the walls.As the speed and intensity of the turbulence are higher at the tip of the blades, hence the kinetic energy of these regions must also be higher. The kinetic energy of the turbulence in these areas is the highest. At the bottom of the fan, it is also observed that the kinetic energy of the turbulence has been relatively high, due to the existence of flow vortices that emerge from the fan period and the presence of positive and negative pressure (negative pressure due to suction of the fan center). The high pressure difference on both sides of the fluid particles causes a rotating flow in the particles, which affects the adjacent particles and causes vortex formation.

The results showed that the numerical acoustic evaluation simulates the performance of the broadband band with good results and has good agreement with the effects of the current on the noise. Increasing the recognition of the factors and their effects on the fan noise level can help to reduce the noise effects of turbo-machines. Using numerical simulations in predicting and reducing noise, in addition to time saving, dramatically reduces costs by using direct methods and mechanical design physically. With regard to all aspects and calculations, it can be concluded that acoustic numerical simulation and broadband noise model have a good ability to analyze noise in fans and rotary machines.

Large industrial factories often discharge significant quantities of low-pressure steam (dead steam) into the atmosphere, which causes energy losses. Retaining low-pressure steam content reduces boiler load, resulting in energy savings and lower costs for the fuel consumption (for example, gas consumption bill in a factory). The boosted-pressure steam is used in processes such as distillation, hot water production, space heating or vacuum generation. If the vapor pressure for the intended application is low, a thermo-compressor is able to increase the pressure and temperature to the required level. Thermo-compressors are a special type of gas compressor that uses an actuator to compress secondary fluid and does not have any blades or moving parts. The accurate prediction of the thermo-compressor performance improves the reliability of this process and increases its efficiency.

Two important characteristics for the current thermo-compressors are entrainment ratio (ER) and compression ratio (CR). The first is the dimensionless mass flow rate, and the second is the dimensionless pressure. The wet steam theory as a classic theory is used by Wolmer-Frankel-Zeldovich to calculate the amount of liquid particles. In order to select the best geometry for the thermo-compressor among all possible geometries, the performance of each model must be compared with other models. In following, the case that includes characteristic parameters associated with the target values has been selected.The commercial Ansys Fluent Versions 15, based on the finite volume method (FVM) was used to simulate and monitoring the flow behavior inside the thermo-compressor. The governing partial differential equations (PDE) were solved implicitly using a density-based solution. The convective heat transfer terms were discriminated based on the second-order upwind scheme. The non-linear governing equations were solved using the implicit coupling solver and the standard wall function was used near the wall. Given the three-dimensional flow for steam, the equations of mass conservation, momentum, and energy were written. The Realizable  model was used to simulate turbulences in the flow.

A summary of the results is presented in terms of the results of pressure, velocity magnitude, Mach number and temperature. A general understanding of this characteristic for a thermo-compressor is extremely important for recognizing the fluid flow inside it, and it is very useful for practical use. Pressure is the most important factor in the recharge section of a thermo-compressor. Increasing the recharge vapor pressure in a thermos-compressor revival the dead steam and increases the steam efficiency. The revival steam can be used in other parts because of their high thermal content. Another important factor in the study of flow behavior inside the thermocouple is velocity magnitude. This quantity, which is closely related to the concept of momentum inside the thermocouple, had high influences from high pressure inputs as well as the thermo-compressor geometry. The highest amount of velocity occurs after the initial nozzle and had a very high magnitude (1000 ms-1), which was also remarkably high in Monnet's terms. Another important characteristic of a flow is the temperature of the stream. The high input temperature associated with motive vapor at the outlet of the primary nozzle was sharply reduced, even in some section reached to 110 °Kelvin. Due to the very high flow momentum in this section, the fluid phase remained gas and it can be justified from the point of view of the fluid dynamics.

Considering the importance of thermodynamic properties of steam in conversion and industries, it would be extremely beneficial to fully understand the interactions inside the thermocouple compressor. The importance of the discussed characteristics is more specific when there is a close relationship between each of these factors and energy consumption in a factory or in any industrial production unit. It was observed that the designed thermos-compressor was able to increase the velocity and temperature in a desirable range for the conversion of non-consumable vapor to the pressure and temperature. It was concluded that the Realizable  model due to the prediction of the jet characteristics appearing in the flow regimes for axial symmetry had a high ability to simulate fluid flows inside the thermos-compressor.

Long drying time and high energy consumption are the big problems in paddy drying using conventional batch type dryer. Besides, non-uniformity occurs in paddy rice dried and low milling quality. Paddy is over dried in lower layers and broken kernel chance increased in milling process. Using of a new pattern for warm air causes to better air passing through the paddy bulk and uniformity of drying. Computational fluid dynamics (CFD) is a good method for modeling of air passing in dryers in order to find better air condition in paddy drying process. The aim of this research was investigation on common and porch patterns applied for air entrance to paddy bulk in a dryer in order to optimize air channel conditions in a conventional paddy dryer. In this study, optimization of air flow was investigated in a batch type paddy dryer using computational fluid dynamics (CFD). Two patterns as conventional and porch (reverse V type) patterns were applied for air entrance to paddy bulk in the dryer as conventional and porch (reverse V type) patterns. Experimental examination were done using a laboratory batch type dryer with chargeable air flow pattern in 50 °C for drying paddy (Tarom-Hashmei Var.). Numerical simulation of air velocity and pressure drop in porous media of paddy in the dryer was achieved by employing computational fluid dynamics method and Fluent software. Air velocity pattern and temperature changes in bulk of paddy were investigated in different time of solution including 20, 100, 1000, 1800, 3600 and 7200 seconds for both patterns. Considering air flow and temperature as constant, the results showed the porch type pattern has better performance than the conventional pattern for air passing in the dryer. The velocity vortex was higher in all parts of the channel in the porch scheme. Air velocity uniformed decreased from beginning to end area in the conventional pattern, but in the porch type pattern, air velocity was more in the end of the duct than beginning area. Pressure drop was about 10 percent in the conventional pattern than porch pattern. At the end of the air channel, this variation inversed due to contact of the air with the end wall and pressure drop in this part of the chamber of porch scheme was higher than the conventional one. Improvement of air flow in paddy occurred in low and middle layers in the porch type pattern and there was no difference between two air passing patterns in top layers. Validation of modeling showed that temperature disturbance of the porch model was more uniform than the conventional model and difference between temperatures of model and experiments was about 2 to 3 °C. The research concluded that using of the porch type pattern had better performance than the conventional pattern for air passing in the dryer but it is needs to more supplementary research to find the best height and angle in the paddy dryer. Porch type pattern causes to more speed and uniformity of air among of paddy than the conventional pattern. This improvement observed in low and middle layers of the paddy bulk. Validation of temperature data showed that the difference between experimental and modeled data was 4 to 6 percent and this difference was higher in the conventional pattern than the porch pattern. According to the results of this research, Porch pattern can be recommended to use in the conventional batch type dryer.

One of the ways to use solar energy is to use a solar dryer. But these kind of dryers have low efficiency that optimizes their absorbent plate to increase efficiency and save energy. For this purpose, the air flow inside the compartment of the adsorbent plate of the solar dryer was simulated using the computational fluid dynamics modeling and the heat transfer process, flow distribution and air velocity inside the compartment were analyzed and finally, the plates were compared in vitro. In this research, three different modes of the page with the same input and three different output modes (circular, conventional and perforated) were investigated. In a porous sheet with porosity, the plate was used with a coefficient of 0.0314. The results showed that between analytical and empirical data, the explanatory factor (R2) was above 97%. There are circular and conventional heat accumulation in the corners, which, by changing the type of output and converting it to the perforated output state, Heat and heat accumulation are prevented.

The significant of solar energy as a renewable energy source, clean and without damage to the environment, for the production of electricity and heat is of great importance. Furthermore, due to the oil crisis as well as reducing the cost of home heating by 70%, solar energy in the past two decades has been a favorite of many researchers. Solar collectors are devices for collecting solar radiant energy through which this energy is converted into heat and then heat is transferred to a fluid (usually air or water). Therefore, a key component in performance improvement of solar heating system is a solar collector optimization under different testing conditions. However, estimation of output parameters under different testing conditions is costly, time consuming and mostly impossible. As a result, smart use of neural networks as well as CFD (computational fluid dynamics) to predict the properties with which desired output would have been acquired is valuable. To the best of our knowledge, there are no any studies that compare experimental results with CFD and ANN.
A corrugated galvanized iron sheet of 2 m length, 1 m wide and 0.5 mm in thickness was used as an absorber plate for absorbing the incident solar radiation (Fig. 1 and 2). Corrugations in absorber were caused turbulent air and improved heat transfer coefficient.
Computational fluid dynamics:K-ε turbulence model was used for simulation. The following assumptions are made in the analysis.
(1) Air is a continuous medium and incompressible.
(2) The flow is steady and possesses have turbulent flow characteristics, due to the high velocity of flow.
(3) The thermal-physical properties of the absorber sheet and the absorber tube are constant with respect to the operating temperature.
(4) The bottom side of the absorber tube and the absorber plate are assumed to be adiabatic.
Artificial neural network: In this research a one-hidden-layer feed-forward network based on the back propagation learning rule was used to simulate the output temperature of a solar collector. The number of neurons within the hidden layer varied from 1 to 20. The hyperbolic tan- sigmoid and pure-line were used as the transfer function in the hidden layer and output layer, respectively. Minimization of error was achieved using the Levenberg-Marquardt algorithm. To carry out the aforementioned steps, the dataset (105 observations) was split into training (70 observations), and test (35 observations) data. Training sets used to develop models included air velocity, solar radiation, time of the day, ambient moisture and temperature values as inputs with an associated temperature of the collector as outputs. The aim of every training algorithm is to reduce this global error by adjusting the weights and biases.
Compare experimental results with ANN
The performance of the three-layer ANN for the prediction of output temperature of flat-plate solar collector by the Levenberg–Marquardt training algorithm was illustrated in Fig. 4. ANN predicted output temperatures with R2 and RMSE of 0.92 and 1.23, respectively. Furthermore, the maximum error in prediction of output temperature of solar collector was 3.3 K. These results are in agreement with Tripathy and Kumar, (2009) those who have predicted the output temperatures of food product in the solar drier using ANN with and RMSE of 0.95 and 0.77, respectively.
Compare experimental results with CFD simulation: Fig. 6 shows that over the starting length of the absorber plate, there is a variation of the velocity profile which is caused by sharp geometry and it leads to some recirculation of the air in this part of absorber plate. After this part of boundary layers, flow is fully developed and velocity profile becomes smoother and constant.
Fig. 8 shows that the predicted temperature was within the experimentally measured temperature. The highest differences between simulated and experimental temperatures were around -2.4K to 4.6K for different time periods. The temperature differences of 4K were reported by Selmi et al. (2008). This disagreement is due possibly to the fact that there are unknown experimental inputs such as turbulence intensity, radiative heat loss from the absorber sheet to the surroundings, Leakage, and measurement tool errors which were not accounted in the model simulations. These losses by radiation are significant at high irradiation levels. This result agrees with studies done in Badache et al. (2012).
Thickness of absorber plate and radiation loss, in CFD model, does not take into consideration. For this reason maximum output temperature is seen in maximum radiation which is 12 p.m. While in real condition, it takes some time for absorber plate to get to its maximum temperature.
Moreover, the numerical temperature is smaller than the real temperature after 12 p.m. This may occur because of the thickness of metal which keeping the absorbed heat and losing it after awhile. Generally there is a time step hysteresis for the numerical temperature.
According to this study it can be concluded that the ANN operates better than CFD to predict the output temperature operation. However, ANN method does not give any information about the prediction of temperature distribution and velocity profiles in the solar collector. Although prediction accuracy of the CFD method is less than ANN method, but the provided information on the velocity and temperature profile of the solar collector is still valuable.

Concentration decreases the amount of water in liquid food and increases shelf life. Several types of evaporators are used for concentration, thus, it is necessary to simulate the process before design to control efficiency. The flow of pomegranate juice was simulated in a forward-feed flat plate evaporator at concentrations of 18 to 50 Brix in a two-phase mixture model using computational fluid dynamics. The results show that a vacuum developed in the evaporator column causing a slight drop in pressure at the inlet. Temperature increased at high intensities at the flow entrance zone. The magnitude of the velocity of the vapor increased as the flow increased from the inlet toward the outlet of the evaporator. Radial velocity was at a maximum in the middle of the flow medium and decreased gradually toward the boundary layer. The volume fraction of the pomegranate juice decreased and the volume fraction of the steam increased gradually from the inlet toward the outlet of the evaporator. This model can be applied for other liquids, but it is first necessary to define the thermo-physical properties of the liquid at different concentrations.