Iraqi journal of mechanical and material engineering

An approach to select the tube wall thickness distribution of streamlined tubes
intended for use in heat exchangers is developed in this study. The main goal is to
retain a streamlined outer profile (resist deformation) and to prevent strain failure due
to the applied internal pressure. The effect of the tube wall thickness distribution on
shaped tube efficiency is also considered. The strain is calculated as a function of
several dimensionless geometric ratios and the ratio of the internal pressure to elastic
material modulus. Using the finite element method, a set of dimensionless design
curves is created for elliptical tube geometries. From these curves, a range of possible
materials and tube geometries can be selected that meet a specific strain limit. To
illustrate the approach, structure-satisfied elliptical designs are selected and their
thermal performance is evaluated for an automotive charge air cooler made of
polymeric material.

This work presents a one dimensional modeling study for water movement through
the membrane of a hydrogen fuel cell. The model studies the effect of electro-osmotic
drag, pressure gradient and back diffusion on local water concentration through the
membrane. It is found that the current density increases the water movement due to
electro-osmotic drag while the pressure gradient increases the hydraulic permeation
and back diffusion. It is also found that after about 30 seconds both effects are
equalized and the water concentration throughout the membrane reaches equilibrium
state.

This research deals with a problem that exists during manufacturing of thermostone
blocks which are produced in a company for insulation building material.
Micro and macro cracks are some of those problems which reduce the resistance to
fracture under loads, or causing damage to the product during manufacturing
processes.
The research applies practical -theoretical method to determine the mechanism of
fracture, depending on taking two images, one is a stereo microscope with suitable
magnification, so that all different phases can be seen as possible, the second one is a
video image to show pores and cracks.
A numerical solution (finite element method) was applied on the images. Chemical
composition and percentage of elements and their effect on fracture behavior have
been studied also.

This research deals with the theoretical and experimental study of free convection
heat transfer between horizontal concentric pipes of constant inner and outer cylinders
temperature, respectively and (Ti>To). The finite elements method was used to solve
the numerical relations of momentum and energy equations. The numerical solution
has been included the calculation of the temperature and velocity values between the
cylinders by using ANSYS program (finite element analysis structural system).
Different models of concentric double pipes were created and tested with different
diametral ratios. Nusselt number was obtained for a range of temperature difference
(0T=Ti-To) of (6.01-120.42C0). The results also showed that the average heat
transfer coefficient values at the inner and outer radii respectively increased with the
increasing of Rayleigh number and the ratio of outer to inner radius. The theoretical
and experimental results were compared with some of researches that presented in the
literature to achieve the verification of the results obtained from the numerical
analysis and experimental modeling for the heat transfer between concentric double
pipes. The results are in good agreement.

This paper represents a numerical analysis intended for the selection and geometry
design of the capillary tubes used in the vapor compression refrigeration units. This
expansion component is usually selected for small home air conditioning units and
domestic refrigerators and freezers for their ease integration with the cooling units and
cheap prices. The numerical step by step model suggested in this work depends
mainly on the idea of the control volume theory for the conservation of mass, energy
and linear momentum of fluid refrigerants flowing inside the capillary tube. The flow
regime is divided into a number of increments for which the conservation expressions
were solved simultaneously for the physical characteristics parameters. These are
temperature, pressure, and vapor quality and mixture velocity along the capillary tube
from the entrance at the high pressure side to the exit at the low pressure side of the
refrigeration unit. The theoretical prediction for the profile of the characteristics
parameters showed a good agreement with available experimental data in the
literature and the ASHRAE published rating charts of the capillary tubes.

The aim of study is to understand the behavior of shrinkage cracks of cement mortar,
using different types of cement (O.P.C), (S.R.P.C) & (W.P.C) with mix proportion
(1:2.5) cement: sand by weight, and water /cement ratio (0.5) for all series. The
samples were cast in (I) shape steel moulds and had lateral restraint to resist volume
changes (shrinkage & creep) in cement mortar under wetting and drying cycles
(moisture content changes), the study consisted also determining compressive
strength and modulus of rapture for the cement mortar.
Experimental results showed that compressive strength of mortar of ( O.P.C) was
greater than of mortar with (S.R.P.C)&( W.P.C)by (23%,17%,16%) ,(35%,29%,28%)
at age (3,7,28) days respectively. The modulus of rapture of mortar with (O.P.C)was
greater than of mortar with (S.R.P.C)&( W.P.C) at age (28)days by (23%,25%)
respectively. The results showed that shrinkage cracks in samples occurred in mortar
with (O.P.C), (S.R.P.C) & (W.P.C) at age (21,24,28)days after casting respectively.
The crack width development of the sample with (O.P.C) was higher than the crack
width development of the sample with (S.R.P.C) until age of (66) days , and after that
decreased , but the crack width development of the sample with (W.P.C)stayed lower
than the crack width development of the sample with (O.P.C)& (S.R.P.C) at all ages

In this paper a numerical analysis is used to analyze the stresses due to thermal cycle
with different aluminum alloy of piston .Finite element method was used to evaluate
the coupling field (thermal –stress) on the piston .ANSYS5.4 Finite element code is
used to carry out the modeling process to determine the coupling stress .Two models
with three dimensions are created .The first is used to evaluate the temperature
distribution through the piston volume, and the second is used to evaluate the thermal
stress distribution due to heat gradient and the material different.
The result show the maximum range of temperatures is 4.3 °C and increases with
decreasing of material thermal conductivity .Thermal stress is concentrated on the
piston edges and depends on the material types.