Print ISSN: 1813-0526

Online ISSN: 2220-1270

Main Subjects : Mechanical Engineering


A Review of Solar Air Heaters: Techniques for Thermal Performance Enhancement

Omar Mohammad Hamdoon

Al-Rafidain Engineering Journal (AREJ), 2020, Volume 25, Issue 2, Pages 46-59
DOI: 10.33899/rengj.2020.128374.1065

The solar air heater is a simple device which captures solar energy. Producing hot air by using a solar air heater is a renewable energy heating technology used to process heat generation for space heating. Such systems produce heat at a minimum initial and running cost. Minimum maintenance like cleaning of collectors only is required. Many studies have studied the possibility of improving the performance of solar collectors and raising their thermal efficiency through additions and improvements that were added to the solar heater. Among these improvements are: Adding the extended surfaces to the upper or lower  channels, or both,  attaching baffles to the absorber plate surface, using corrugated absorber plate, and storing the extra thermal energy and releasing it during sunset. The objective of the present paper is to review the various studies dealing with previous improvements, to present the design modifications, in addition to summarizing their most important results. Based on the review, it is found that: Adding the fins and baffles together to the absorber plate surface of the single or double pass solar air heater has a great effect on improving the thermal efficiency. The use of a corrugated absorber plate leads to a significant increase in the efficiency of the solar air heater. The heat stored in the solar air heater can be used to produce useful heat for several hours after the absence of solar radiation and raise daily efficiency.

Improving the Performance of A Flat Plate Solar Collector Using Nanofluid as Working Fluid

Omar Mohammed Hamdoon

Al-Rafidain Engineering Journal (AREJ), 2020, Volume 25, Issue 2, Pages 37-45
DOI: 10.33899/rengj.2020.127218.1041

Solar energy is the best alternative to limited fossil fuels. The foremost important means of utilizing solar energy are solar collectors. The most common types of solar collectors are flat plate solar collectors. A great deal of theoretical research has been conducted to enhance the flat plate solar collector efficiency. One effective way to increase the efficiency is by using an improved thermal properties fluid as nanofluid. In this paper, a numerical study has been made to enhance the efficiency and improve the performance of solar collector via the use of (Multi-Wall Carbon Nano Tube-water) MWCNT-H2O nanofluid instead of traditional fluid like water as working fluid under the weather of Mosul city / Iraq (36.3489° N, 43.1577° E). One dimensional dynamic model using implicit finite difference method was used. Solving energy conservation equations through the various layers of the solar system is the basis upon which the current model was based. Effects of nanoparticle volume fraction and mass flow rate on the working fluid stream temperature differences, and the thermal efficiency were studied. The mass flow rate was varied from 0.004 kg/s to 0.03 kg/s, while the volume fraction was varied from 0% to 6%. The results of "Nanofluid Based Flat Plate Solar Collector" were compared with the experimental results presented by [1]. The comparison established a good match between the current results and experimental results. The results showed an increase in the working fluid outlet and inlet temperature difference and collector thermal efficiency due to the addition of MWCNT nanoparticles. The temperature difference of "Nanofluid Based Flat Plate Solar Collector" was found 28.8⁰C at 0.014 kg/s and 6% in April, while it was 25 ⁰C at the same condition in the "Water Based Flat Plate Solar Collector case". Also, the thermal efficiency of "Nanofluid Based Flat Plate Solar Collector" was found 2.41% to 6.68% more than the "Water Based Flat Plate Solar Collector case".

Effect of Impact Velocity and Angle on Erosion Behavior for Polymeric Composite Materials

Ahmed W. Khalid; Abdullhaqq A. Hamid

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 2, Pages 101-114
DOI: 10.33899/rengj.2019.164326

Due to significant effect of the phenomenon of erosion and its entry in many engineering and industrial applications, hence the importance of the study of erosion, especially the key factors of impingement velocity and impingement angle, because of their high effect on the phenomenon of erosion. The erosion testing device was manufactured according to ASTM G76 specifications, and devices rotating molds casting and vacuum equipment were manufactured, and unsaturated polyester specimens and its composites were reinforced with two types of reinforcing materials silicon carbide particles (SiC) and fiberglass (5 wt. %) and (44%. wt. %) respectively.  The impingement velocity (25.2, 33 m / s) and impingement angles (30°, 60° and 90°) affecting erosion were studied. From the results obtained, it is noted that the behavior of polyester was brittle behavior and the composites behaves semi-ductile. And that the maximum erosion rate of polyester is at an impingement angle (90°) and the maximum erosion rate of polyester composites is at an impingement angle (60°). Silicon carbide particles improved erosion resistance at the impingement angles (90°, 30°), but at an angle (60°) they reduced pure polyester resistance to erosion, while fibers increased the rate of erosion. It was noted that the relationship between the impingement velocity and the rate of erosion is a direct relationship and that the effect of increasing the impingement velocity on the angle of impingement (60°) is greater than its impingement on the angles (90°, 30°).

Effect of magnetic field on mixed convection in superposed Nanofluid and porous layers inside lid-driven cavity

Ehab Abudlaziez Hamza; Abbas Saeed Hussain

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 2, Pages 1-11
DOI: 10.33899/rengj.2019.164323

In the present research the effect of magnetic field on the mixed convection was carried numerically in lid driven composite two dimensional square cavity ,this cavity composed of two layers : a Cu-water nanofluid layer superposed a porous media ,the porous media saturated with the same nanofuid  The left and right walls are thermally insulated ,However the bottom wall which is in contact with porous media is isothermally hot while the top wall which is in contact with nanofluid layer is isothermally cold and being lid driven in constant velocity to right.
        The governing equations in this study were normalized and solved numerically by finite difference method. The convection term of the momentum and energy equations were treated by upwind scheme, while the diffusion and source terms were treated by central difference. Gauss-siedel iteration method were used for solution vorticity and energy equations and Successive Over Relaxation method were used for solution of stream function equation.. In this study the following parameters were considered:
Hartman number (Ha) from (0 to 60), nanoparticles volume fraction (0.01, 0.03, 0.05), Richardson number (Ri) (0.1, 1, 5), Darcy number (Da) (10-3, 10-4, 10-5) and porous layer thickness (Wp) (0.3, 0.5, 0.7) at constant Reynolds number (Re=100) and Prandtl number (Pr=6.24). The results show that increasing Hartman number causes a reduction in mixed convection heat transfer and this effect reduced by increased the porous layer thickness. In increased of Hartman number from 0 to 60 with Wp (0.3, 0.5, 0.7) a reduction in convection heat transfer. Moreover an increase in Richardson number ( Ri ) enhanced the convection heat transfer for all Hartman number , Also the increase of nanoparticles  volume fraction improve the heat transfer and this effect reduced as Hartman number increased. It is noticed that increasing Hartman number to 30 gives highest value of Nusselt number at lower thickness of porous layer.

Simulation of Cold Forming of Spur Gears using DEFORM 3D

Zainab Mohammed T. Rasheed; Mohammed Najeeb Abdullah

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 2, Pages 74-80
DOI: 10.33899/rengj.2019.164324

In the current study, the DEFORM3D program was used to simulation of cold forming of spur gears using lead metal. Three different forms of billets were used to forming the spur gear and the choose of the size of billets was determined according to the size of suggested gear in this study. Analyzes were performed such as effect of stress, strain, average stress, total distance and speed during the formation process. Through the results of the values ​​of the average stresses for the three billets, it was observed that the lowest value is obtained when using a solid billet. As indicated by the results of the study of the maximum stress occurs when the use of hollow billet with a diameter of 4 mm. In the study of effective stress, it was observed that there was a convergence in the stress values ​​for all work pieces; these values ​​in the age zone are greater than the center area. The results obtained from numerical modeling showed that the minimum effective strain occurs when using a hollow billet with a diameter of 4 mm and the highest value when using a solid billet. The velocity of the metal flow is proportional with the shape of the billet, it is noted that the value of the velocity in the case of hollow billets (4 mm and 6 mm) was close together and higher than the value of the metal flow velocity when using a solid billet. The speed of the metal flow is proportional with the amount of the billet cavity; in the case of the hard solid billet the speed is low. Peak load is affected during the formation of the spur gear with the shape of billet; it was observed that the peak load values ​​of the 4 mm hollow billet were less than the peak load of the other two cases.

Manufacturing of Erosion Measuring Rig for Polymers and Their Composites with some Experimental Results

Ahmed W. Khalid; Abdullhaqq A. Hamid

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 2, Pages 115-129
DOI: 10.33899/rengj.2019.164327

Solid Particle Erosion System was manufactured as a laboratory and according to the ASTM G76 specifications in a horizontal position with a feeder screw, as the system consists of the main parts: air compressor, voltage regulator, and rubber connection hoses. And the main parts of the rig: nozzle, screw, DC motor, transmission pipes, and Installation platform. The nozzle was made of low alloy steel and hardened by water-quenching, and the conical nozzle cavity was made to insert sand into the nozzle barrel. Tolerance was chosen between the screw and cylinder in practice, with a tolerance of (4 mm) out of two experiments that were tried (2, 4 mm). So, the tolerance was chosen based on the used particles (erodent) in different ranges (150-350 µm), (350-500) µm) and (500-710 µm), preferably a tolerance that gives a smooth spin rotation. One of the things to consider is the stability of the sand flow rate and the issue of overflow or vice versa is the occurrence of a stop flow, and taking into consideration the calibration between the spin rotation and the pressure of the air. Also, the sizes of sand particles used can determine several things, including tolerance, the diameter of the nozzle barrel, and the velocity of particles that can be taken. The rig was tested for specimens of unsaturated polyester (UP) and its composites reinforced with (5 wt. %) of silicon carbide, where the experiment was carried out at an impingement velocity (25.2 m / s) and impingement angles (30°, 60°, 90°) and the size of the erodent from sand Silica has a size of (350-500 µm), so the results showed that the polyester gave the highest erosion rate at the angle (90°), which indicates its brittle behavior, while its composites gave the highest erosion rate at the angle (60°), which indicates its semi-ductile behavior. It is comparing the results obtained with previous research that shows that the rig gave positive results, and it can measure the rate of erosion of polymeric materials and their composites.
 

Numerical Analysis of Effect of Nano-particles on Fluid Flow and Heat Transfer by Forced Convection in Channel with different traingle configuration

Ammar A. Mahmood; Amir S. Dawood

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 2, Pages 56-64
DOI: 10.33899/rengj.2019.164321

This research presents a numerical analysis of the three-dimensional simulation of heat transfer and fluid flow incloded forced convection through a square-section channel with different ribs and the effect of addition of nanoparticles with constant heat flux up and down the channel. The single-phase approach of Nano-fluid is employed; it is assumed that the base fluid (water) and nanoparticles (Al2O3) are treated as a homogeneous mixture. The study assumes that the Nano-fluid incompressible, steady and laminar. The nanoparticles used in 25 nanometers and with volumetric concentration (1-5) %. ANSYS 18.1 FLUENT is a computational fluid dynamics (CFD) program. The finite volume method was used to solve the ruling equations. To ensure accuracy of the results, the validity was performed with previous studies of the channel and under the same boundary conditions and the result was Compatible. By using ribs at the top and bottom of the channel in two alignment inline and staggered, and five ribs per surface, and in tow shapes (triangle A and triangle B). The aspect ratio is equal to (2(. with five different values for Reynolds numbers (300, 500, 700, 900 and 1200). The results showed that triangular ribs type (A) with staggered alignment represent the optimal state of the all studied shapes and at all Reynolds numbers. The maximum value of the performance evaluation criteria (PEC) was 1.8561 and the use of Nano-fluid at a concentration of 5% compared to 1.5991 for the same channel using water only, and at Reynolds number 1200. At 5% volume concentration, the heat transfer coefficient (h) was 29.78% higher than the thermal conductivity increase of 16.48% when using only the Nano-fluid. When adding the triangular ribs type (A), the increase in heat transfer coefficient (h) is equal to (143.03%). Actually, other factors such as dispersion, Brownian motion, hermophoresis, vortex generator, and nanoparticles migration also are responsible for the enhancement of convective heat transfer.

Theoretical Stress Analysis of Gas Turbine Blade Made From Different Alloys

Suha Hashim Ahmed; Ghaidaa Husain; Majeed Ali Abdulrazaq

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 1, Pages 10-18
DOI: 10.33899/rengj.2019.163122

Blades may be considered to be the heart of turbine without blade there would be no power and the slightest fault in blade would mean a reduction in efficiency and costly repairs.
The centrifugal force is one of the problems faced by the designer of blades especially at the first stages. The designer aims at reducing the stresses with in the allowed limit.
The ANSYS 15 software was used as far as it is the most effective in analyzing the different numerous cases of stresses, the blades with limited root in all direction (X,Y,Z) were taken into consideration . The centrifugal forces were applied on the rotor blades at running speed of 6000 r.p.m., The finite element models of the blade were constructed using D3-10-noded Tetrahedron elements shape, SOLID 187,  mesh of the entire blade 23406 Node,136575element. The average of normal stress, Von misses, Maximum principle stress, Minimum principle stress were calculated according to ANSYS 15  program,  these stresses are as the result of the effect of centrifugal force for all planes along the blades and then values of stresses were compared to the curves for each  alloy.The current research concluded that the Titanium alloy is the best alloy used in terms of reducing stresses due to centrifugal force, that is because density of Titanium alloy used is less than that of other used alloys, leading a reduction in centrifugal forcess that are directly proportional to mass.

Buckling Analysis of Hybrid Laminated Composite Beam Analytically and Numerically

Omar A. Mohamed

Al-Rafidain Engineering Journal (AREJ), 2019, Volume 24, Issue 1, Pages 19-25
DOI: 10.33899/rengj.2019.163123

Composite materials become more attractive for researches because of higher strength to weight ratio. As a result, many papers have recently published in this field. The current study deals with improving the resistance of hybrid laminated composite beam under critical buckling load. A number of carbon layers under various orientation angle and positions of hybrid fiber coupled with glass epoxy layers have been studied analytically and numerically. Firstly, an analytical model is presented by using Euler's theory to determine critical buckling load. Then, a 3D finite element models for the composite beams have been simulated by using ANSYS commercial program. The results show a very good agreement between theoretical and FEM (finite volume method). The critical buckling load, shows a proportional with increase the carbon layers number as same time the critical buckling load value shows a valuable decrease when the position of carbon layer insert towards the mid-plane more ever, this value various with orientation angle changing.