Iraqi journal of mechanical and material engineering

Analysis of airflow and thermal characteristics of attics of bobtail-shaped pitched roofs heated through a horizontally suspended ceiling is numerically carried out in this study. Pitch angles of 14o, 18o, 30o, and 45o within the standard pitch roof range are selected. The configuration falls within Rayleigh number 3.19 x 105  Ra  2.04 x 107. A finite-volume CFD code was used to solve the mass, momentum, and energy conservation equations governing the problem. The results obtained indicate a strong influence on the shape and angle of the roof. At lower roof pitches, the flow field is characterized by multiple counter-rotating vortices asymmetrically arranged within the enclosures. Eight cells in the 14o enclosure were reduced to five in the 45o roof pitch. The size and rotating strength of a vortex increase from the left corner to the middle of the enclosures. At higher pitch angles, the vertical wall obstructed the flow leading to a number of distorted cells. The maximum velocity within the aerodynamic boundary layer along the base wall occurs at Y=0.02 with the values U=0.013 and U=0.028 in the 14o and 45o enclosures respectively. The thermal field portrays a convection system of rising hot plumes from the base wall and descending cold jets from the inclined walls; all enclosed by thin boundary layers along the walls. Graphical plots of velocity and temperature variations along some cross-sections within the enclosures enable the prediction of some important heat and flow parameters.

PMMA (poly-methyl methacrylate) acrylic resin is commonly utilized in the manufacture of denture bases. However, its mechanical characteristics may be inadequate for this purpose. The purpose of this research is to look at the mechanical characteristics (flexural strength, flexural modulus, impact strength, fracture toughness) of PMMA composite by adding two kinds of synthetic fibers Polypropylene (PP) and Polyacrylonitrile (PAN). Numbers of PMMA composite samples were generated at specified weight ratios of (1.5, 3.5, 5.5, and 7.5 wt.%) in this study. Research results showed that during fibers ratio increased until max. point (7.5wt. %), a decrease in flexural strength value was observed. Notably, PMMA/PAN composite sample has more influence than PMMA/ PP composite. Also, a decrease in the flexural modulus during fibers ratio increases until maximum (7.5wt. %), flexural modulus for PMMA/PAN composite were higher than the values PMMA/PP composite specimens. When it came to I.S, it was discovered that when the fiber ratios were raised, the impact strength rose at a ratio (7.5wt. %). Finally, the results of fracture toughness showed an improvement for the composite specimen (PMMA/7.5 wt. % PAN fiber). In contrast to (the PMMA/7.5wt.% PP fiber) composite specimen, there was a decrease compared to the neat sample.

The characteristics of self-healing related to N-type cement mortars, the addition of human pathological bacteria to enhance mortar durability, and compressive strength thus reducing maintenance cost and manpower after crack initiation. Bacteria have been examined by using two types of biological agents: Proteus mirabilis and E. Coli bacteria. Mortars are formed from a combination of Portland cement and ordinary sand, treated by Proteus mirabilis and E. Coli bacteria with different concentrations. The mechanical properties of the treated mortars are measured and the mortars were characterized by means of Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and electron energy dispersive spectroscopy (EDX). This study shows that Proteus mirabilis and E. Coli assist the formation of calcium carbonate inside the mortar micro-pores leading to enhancement of the compressive strength and hardness of the mortar specimen. This emphasizes the possibility of activating the self-healing characteristic of the cement mortar and its utilization for cracks treatment and repair.

In this work, the effect of electromagnetic field on thermal performance of concentrated parabolic trough solar collector is studied experimentally. A two-axis tracking parabolic trough collector formed of a reflector (mirror tapes matrix), of (2m *1m), and an absorber copper tube (receiver) is designed. Water and water-based magnetic iron oxide (Fe3O4) nanofluid are used as heat transfer fluid in the collector. Three volume concentrations (0.3%, 0.5%, and 0.9%) of nanoparticles are investigated under a magnetic flux of (3.2, 4.3, 6.2, and 7.9*103 Gauss), which is installed at absorber inlet, middle, and exit. The three coils are connected to a DC-generator to control the electromagnetic field. The electromagnetic field effect on water flow in the absorber is found weak. A significant thermal improvement is figured when utilizing ferrofluid as a heat transfer fluid in the absorber. It is represented by higher temperature distributions in the absorber and higher solar collector efficiency compared with base fluid.

Different types of dynamic instability of the system occur when the flow velocity exceeds a specific value; thereby the problem of dynamic instability of the pipe conveyed flow became shining. Several effective parameters play an important role in ingstabiliz the system, such as stiffness addition. In this search, dynamic analysis of pipe conveying fluid stiffened by linear spring was studied using the finite element method. The effect of stiffness addition (linear spring) and the effect of spring location was deeply studied. Also, the effect of flow velocity on the dynamic stability of the system was taken into the consideration. It was observed that there is a critical flow velocity after which the system loses its stability. There is a critical spring constant at which the dynamic behavior becomes more sensitive. Also, there is a specific spring location (effective location) so the spring offers the best results for the frequency of the system. Effective spring locations depend on the flow velocity and spring constant itself. The effective spring location was found to be arranged from x/l= 0.7 to 1.

The simulation of electrochemical deposition is developed by using a non-isothermal model. The model consists of two parts; the first is a continuum part that simulates the transport of heat and mass and the voltage distributions, and the second is a stochastic noncontinuum part that simulates the bulk diffusion, surface diffusion, and adsorption of the particles. The finite element method is used to solve the differential-algebraic governing equations of the continuum part whereas the Kinetic Monte Carlo method is used to simulate the particle actions in the non-continuum part. The model is applied to the electrodeposition of Zn in ZnSO4 additive-free electrolyte. A comparison is made between the experimental and the simulated results including the surface morphology and the temperature distributions. The results indicated that the simulation model is very promising to be used for such a complicated process.