Iraqi journal of mechanical and material engineering

Double pipe heat exchangers (DPHEs) are widely used in various industries due to their
simple design and high heat transfer efficiency. This review paper comprehensively examines
methods to enhance heat transfer performance in DPHEs, categorizing them into active, passive,
and compound methods. Active methods explored include rotating the inner tube, while passive
methods cover twisted tapes, finned surfaces, wire coils, and nanofluids. Each method is analyzed
for its impact on heat transfer rate, pressure drop, and overall thermal performance. The novelty
of this paper lies in its detailed comparative analysis of these methods, providing insights into the
optimal design and operating conditions for maximizing thermal-hydraulic performance. The
review highlights that while methods like using nanofluids and twisted tapes significantly improve
heat transfer, they also increase pressure drops, necessitating a careful balance to optimize
efficiency. These findings serve as a valuable resource for researchers and engineers developing
efficient DPHE systems.

different cooling media for a set of researches, where will be mentioned to the change
that happen of the metal in order to obtain new properties according to the required
applications. The water and oil were used as the two main media of quenching most
often to obtain rapid quenching after heating to austenitic temperature in most studies,
but two these media were used in various forms such as the use of salt solution or
cooled and hot water in addition to that can used engines oil, vegetable oil, various
polymeric fluids and others. From previous studies and types of quenching media
mentioned in this review, some of mechanical properties such as hardness and tensile
strength improved when using water rather than oils while toughness property
increase at cooling in polymer fluid. However, the goal of quenching were obtained
an increase in the value of hardness, impact strength, tensile strength, wear resistance
and improved other required properties according to the certain manufacturability and
industry requirements.

The paper present some main experimental results on fatigue crack detection using
Electrical Potential Drop technique (EPD) under constant stress amplitude. The potential
drop electrical circuit was designed and manufactured as well as tested using the flat
fatigue specimens of aluminum alloy 7075-T6. The experimental analysis showed that the
electrical potential drop circuit capable for detecting the fatigue crack during the test and it
gave satisfactory crack length results observation compared to the actual lengths for
fatigue long cracks.

The primary vibrating system of the supported beam type, employed in numerous places
such as bridges and double-beam constructions, has its theoretical natural frequencies and
Mode shape specified. It is possible to lessen beam vibration and assess the efficiency of
tuned vibration absorbers on a beam structure by determining the location and quantity of
dynamic vibration absorbers (DVA) on a supported beam. When DVAs are present, the
vibration amplitude lowers; the reduction amount depends on the number and location of
DVAs. Additionally, the Vibration of the structural beam can be affected by the connected
DVAs. Connecting the DVA at the optimal location of the vibrational peak is crucial, and
it depends on the vibration modes. Harmonic analysis determines the harmonic response
for external excitation. Finally, the operating conditions of the primary structure or
equipment can affect the performance of the DVA. For instance, if the immediate structure
experiences varying loads or forces, the DVA must be designed to accommodate these
changes.

In the current work, multi-layers were manufactured based on epoxy polymer using Nano Graphine and aramid (Kevlar) fiber as fillers.
Nano Graphine was added by 1, 2, 3 wt% to the epoxy matrix and the Kevlar sheets were embedded within these composites. The die casting process is used to prepare the composite plate with thickness of 3mm.
To improve the performance of Kevlar fibers, these fibers impregnated in the shear thickening fluid (STF), which is composed of fumed Nano silica and polyethylene glycol (PEG). By using ultrasonic dispersion method to dispersion nano particles into the composite and then preparation the sample ,some mechanical (tensile strength, impact strength, and hardness test) According to our findings, the best result was for (2%wt Gnps) the tensile, impact strength, and hardness values 260.2 MPa, 51.194 kJ/m2, and 69.5 MPa, respectively, by soaking these fabrics with shear thickening fluids we observe improve the mechanical properties for the composite materials for the 2%wt Gnps percentage (tensile strength, impact strength, and hardness ) are (290.9 MPa, 77.82 kJ/m2, and 72.22 MPa) respectively