H. Rahmanian- Koushkaki; S. H. Karparvarfard
Abstract
Introduction Pneumatic conveying is a continuous and flexible material handling method which uses positive or negative air pressure to convey materials in pipe. This conveying system is generally divided into two groups of dilute and dense phase. The purpose of this research was to create spiral grooves ...
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Introduction Pneumatic conveying is a continuous and flexible material handling method which uses positive or negative air pressure to convey materials in pipe. This conveying system is generally divided into two groups of dilute and dense phase. The purpose of this research was to create spiral grooves inside horizontal pipes which transfer granular materials under dense phase. Also, the performance of these pipes was compared with control pipes. Finally, friction factors obtained in this research were compared to the previous study. Materials and Methods To create spiral grooves inside the pipes, a broaching machine was designed and developed. Then, by connecting the broached pipes to a pneumatic conveying test- rig of granular materials, the performance of these pipes was compared with control pipes. The specifications of the broaching machine and test-rig were as follow. Broaching machine: The machine included chassis, an electromotor with one hp power, a reduction gearbox, a ball screw for converting rotational motion to linear motion, a spiral shaft, a guide with three bolls, broaches and inverter. Cutting operations and creating grooves inside the pipes were done using broaches. These broaches had two angles, attack angle of 15 degrees and a clearance angle of 10 degrees. The spiral angle of broaches was 30 degrees, the spiral pitch was 260 mm, the width of each groove was 1.5 mm, and a number of teeth were 20. Test- rig: The main components of the test- rig were the air compressor, blow tank, conveying pipes, solid discharge control valve (SDCV), receiving hopper, orifice plate flow meter, pressure transducers, and single point load cell. The compressor was a piston- type, the air flow rate was 405 L min-1 and maximum pressure was 12 bar. For a continuous flow of air and material mixture into conveying pipes, a blow tank was used. To transfer material from blow tank to pipes, a 90-degree bend with a radius of 250 mm and an inner diameter of 40 mm was used. The inner diameter of pips was 40 mm, the thickness was 5 mm and was selected from ABS. In order to measure static pressure of air along the pipes, 10 holes of one mm diameter were drilled on the surroundings of the pipes at intervals of one meter. Then, on each of these holes, a polyethylene bushing was placed. Pressure transducers were threaded on the top of these bushings. A solid discharge control valve was placed at the end of the flow line to control the flow of materials in a dense and continuous phase and to prevent material acceleration. The materials were introduced into the receiving hopper after leaving the valve. To measure the volume flow rate of air, an orifice plate with D and D/2 tapping was used. The pressure transducers were Hogller. For measuring the mass of the materials entering the receiving hopper, a single point load cell (Zemic L6G) was installed under the hopper. A data acquisition system based on ARM microcontroller was used to record output signals from transducers. The treatments were four levels of groove depth (0, 0.35, 0.55 and 0.9 mm), three levels of air pressure (1, 2 and 3 bar) and three levels of pipe length (3, 6 and 9 m). The transferred material was considered as mung bean. Results and Discussion The results of ANOVA showed that the main effects of groove depth, pipe length, and air pressure were significant on the mass flow rate of transmitted mung bean and solid friction factor at 1% probability level. The results indicated that the maximum mass flow rate and minimum friction factor were observed at a pipe length of 3 m, the groove depth of 0.90 mm and air pressure of 3 bar. Minimum mass flow rate and maximum friction factor were observed at pipe length of 9 m, the groove depth of 0 mm (smooth pipe) and air pressure of 1 bar. Conclusion The results showed that the existence of spiral grooves within horizontal conveying pipes would increase the mass flow rate of the mung bean and reduce the solid friction factor of the mung bean and inner wall of pipes.
Design and Construction
H. Rahmati Aidinlou; A. M. Nikbakht
Abstract
Introduction Increasing the area of absorber plate between the flowed air through the duct can be accomplished by corrugating the absorber plate or by using the artificial roughness underside of the absorber plate as the commercial methods for enhancing the thermohydraulic performance of the flat plate ...
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Introduction Increasing the area of absorber plate between the flowed air through the duct can be accomplished by corrugating the absorber plate or by using the artificial roughness underside of the absorber plate as the commercial methods for enhancing the thermohydraulic performance of the flat plate solar air heaters. Evaluation of this requires the construction of separated solar air heater which is costly and time consuming. The constructed solar flat-plate collector simulator can be a sufficient solution for obtaining the heat transfer and thermodynamic parameters for evaluating the absorber plate. The inclined broken roughness was chosen as the optimum roughness which is surrounded by three aluminum smooth walls. Materials and Methods The duct for both smooth and roughened plate have been constructed based on the ASHRAE 93-2010 standard. In order to achieve a fully thermal and hydraulic developed flow, the plenum is constructed. The centrifugal fan is considered by applying the required air volume at the pressure drop obtained by the duct, plenum and the orifice meter. The TSI velocity-meter 8355 is used to measure the velocity of air crossing through the pipe connected to the centrifugal fan. The micro manometer Kimo CPE310-s with the resolution of 0.1 Pa is used to measure the pressure drop across the test section of the smooth and roughened duct. The LM35 sensors are used to measure the absorber plate and air temperature through the test section. Obtained parameters are used to calculate the Nusselt number and friction factor across the test section for smooth and roughened absorber plate. The Nusselt number and friction factor parameters which is obtained for smooth absorber plate based on experimental set-up, is compared with Dittus-Bolter and Blasius equations, respectively, for validating the simulator. By calculating the Nusselt number and friction factor, Stanton number is obtained based on the equation (6), and thermohydraulic coefficient is calculated by the equation (5) for the desired roughness. Results and Discussion Pressure drop for smooth duct is obtained to be 20 Pa. Maximum velocity crossed through the plenum is calculated by the equation (8). Thereafter, pressure drop for plenum by considering the maximum velocity in equation (7), is obtained to be 1.16 Pa. The same procedure for maximum velocity which is crossed through the orifice meter is obtained by the equation (10) and then the pressure drop for orifice meter is calculated equal to 243 Pa by considering the velocity in equation (9). Total pressure is given by the equation (11) to be 246.16 Pa. The required power for centrifugal fan is obtained equal to 105 W from equations (12), (13) and (14), respectively. Both aforementioned Nusselt number variations with Reynolds number were monotonously increased by increasing the Reynolds number. The gained RMSE and coefficient of determination between the Nusselt numbers are 0.0566 and 0.6944, respectively. The obtained RMSE and coefficient of determination between the friction factors are 0.0004 and 0.6814, respectively. The low value of the RSME and high value of the R2 analysis for both Nusselt number and friction factor shows that there is a good agreement between the experimental data and empirical correlations. Fig. 8 demonstrates that the thermohydraulic coefficient is decreasing as the Reynolds number increased. The effect of friction factor related to the Stanton number is shown up more effective by increasing the Reynolds number. It should be noted that the same procedure is conducted for Han's experiment where the thermohydraulic performance is decreased as the Reynolds number increased. The maximum magnitude of the thermohydraulic performance was achieved at minimum 3149 Reynolds number. Conclusion The flat-plate solar collector simulator was designed based on the ASHRAE 93-2010 standard which consists of the centrifugal fan, chosen based on the required air volume by considering the pressure drop in the duct, plenum and orifice meter. The experiment was conducted between 3149 to 19247 Reynolds numbers. The good agreement between the comparison of the Nusselt number and friction factor obtained by the experiment for smooth duct was achieved by the Dittus-Bolter and Blasius equations, respectively, to validate the simulator. The obtained thermohydraulic coefficient for optimized roughness surrounded by three smooth walls was lower than the former investigated roughnesses at each Reynolds number
