Mechanical Engineering Advances

The objective is to analyze the thermal and hydraulic performance in a Micro Channel Straight Printed Circuit Heat Exchanger. Counterflow and parallel flow configurations were analyzed for water cooling using ethylene glycol-based fluid and platelet-shaped non-spherical Boehmite alumina nanoparticles. The work presents results from applying a dimensionless theory that uses the concepts of thermal efficiency of heat exchangers and quantities associated with the second law of thermodynamics. Thermal efficiency, thermal effectiveness, thermal and viscous irreversibilities, thermodynamic Bejan number, and outlet water temperatures are presented in graph form. The data obtained allow us to conclude that the heat exchanger can work in a range of water and refrigerant flow rates below the design parameters. With the inclusion of nanoparticles with a volume fraction equal to 5.0%, the flow rates of the refrigerant fluid can be significantly reduced. The analysis performed shows that the use of nanoparticles improves the operational cost-benefit of the heat exchanger with a significant reduction in the hot water outlet temperature.

The objective is to use dimensionless analysis through the thermal efficiency method to determine the thermohydraulic performance of a spiral plate heat exchanger (SPHE) used to cool sunflower oil. The coolant consists of water as a base fluid and non-spherical Boehmite Alumina nanoparticles with a defined volume fraction. The concept of thermal efficiency for heat exchangers is used to determine the main quantities used in the analysis. Graphical results are presented for the number of thermal units (NTU), thermal efficiency, thermal effectiveness, hot fluid outlet temperature, thermal and viscous irreversibilities, and Bejan number. The analyzed heat exchanger provides excellent thermal performance for refrigerants consisting of water and non-spherical nanoparticles in platelets or cylindrical, with a volume fraction equal to 12%. Viscous dissipation significantly increases concerning the dissipation associated with pure water, but the cost-benefit is within reason for the proposed objective, within the flow rate under analysis.

The primary objective of this study is to quantify the rate of entropy generation within the Magnetohydrodynamic (MHD) slip flow system over the inclined needle. Entropy generation is a measure of the irreversibility and inefficiency in the flow process. The slip flow condition at the fluid interface can significantly impact the flow characteristics and heat transfer rates. In the hybrid nanofluid flow, which consists of non-magnetic and magnetic (Al₂O₃ and Fe₃O₄) are nanoparticles,  are considered as the base fluid. Furthermore, the effects of inclined magnetic fields are taken into interpretation. The PDE’s governing equations are converted into ODE’s using similarity transformations and solved by a numerical technique based on BVP4C. The results illustrate that crucial parameter such as the magnetic parameter, mixed convection parameter, nanoparticles of solid volume fractions, and Prandtl numbers are pointedly impacted by momentum and thermal profiles. The entropy and Bejan number also consider being various relationship combined parameters. These analyses protest that raising the magnetic parameter estates an increase in the hybrid nanofluid thermal profile under slip circumstances. Examined magnetic field impact on flow and entropy generation in MHD flows, revealing significant changes in entropy generation due to interaction between magnetic field and nanoparticles. This analysis understands the impact of MHD and slip effects on entropy generation, particularly in the context of the newly emerging 50:50 fluid mixture. Hybrid nanofluids have been shown to have improved thermal conductivity compared to traditional fluids, which can enhance the cooling or heating capabilities of the inclined needle.

The thermal efficiency of heat exchangers was applied for theoretical analysis of the thermal performance of a finned heat pipe heat exchanger (FHPHE) used as an auxiliary device to control the temperature and quality of the air conditioning in operating rooms. The theoretical analysis performed is punctual and distributed. It is divided into three aspects: analysis of the evaporator section, analysis of the condenser section, and analysis of the heat exchanger in terms of overall performance. The distributed procedure contrasts with the theoretical-experimental study, which uses the concept of thermal effectiveness (ε-NTU) for global heat exchanger analysis. The developed approach considers the number of heat pipes, the number of fins, and the flow rate variation at the inlet of the heat exchanger as fundamental parameters for determining the thermophysical quantities of interest. Theoretical values were determined for the average velocities, Nusselt numbers, thermal effectiveness, heat transfer rates, and exit temperatures. The localized theoretical-experimental comparisons are consistent, and the absolute relative error for the global heat transfer rate ranges from 0.5% to 35%.

The present study aims to investigate the vibration monitoring status in region three of gas transmission operations in Iran. Vibration monitoring is a strong tool for troubleshooting and protecting equipment (turbines). For this purpose, the vibration condition monitoring systems in a gas compression station have been studied. The number and location of vibration sensors, vibration signal transmission to the control room, alarm and stop command, and the ability to perform advanced vibration analysis for troubleshooting and data storage are taken into consideration. The favorable situation of vibration monitoring is provided for the purpose of comparison and conclusions about the status of vibration monitoring and needs have been made.

Polypyrrole/SnO₂ nanocomposites were created using in-situ polymerization techniques. The nanocomposites were described using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their thermal properties were studied using a Differential Scanning Calorimeter (DSC). The DC conductivity of the samples was measured as a function of temperature from 30 ℃ to 1900 ℃, and it was observed that increasing the concentration of tin oxide particles improves conductivity due to polaron hopping and composite chain length extension. The tensile strength of PPy nanocomposites doped in PVA thin film up to 6 wt% indicates 64.2 MPa, which may be related to the homogenous distribution of PPy nanocomposite in PVA. The study reveals that because 50 wt% of the nanocomposites have the highest conductivity and sensitivity, these nanocomposites may be useful in future applications.

The paper presents, the numerical investigation of point contact thermal elasto-hydrodynamic lubrication (EHL) with surface asperities are analyzed. The effect of temperature and surface roughness on fluid film thickness is studied in detail. The governing equations comprises Reynolds, film thickness, load balance and energy equations with appropriate boundary conditions. The second order finite difference approximation is used to discretize the governing equations and the resultant nonlinear system of algebraic equations is solved using Multigrid V-cycle with full approximation scheme (FAS) technique. Multi level multi integration (MLMI) technique is employed to solve the film thickness equation. The obtained results are illustrated in the form of graphs and tables which are comparable with earlier findings. The film thickness profiles shows dimple near to the outlet region due to temperature-viscosity wedge mechanism. Isothermal minimum film thickness is higher than the thermal minimum film thickness. Minimum film thickness is much smaller due to slide to roll ratio is positive ascompared to negative, whereas the behavior of central film thickness is contrast as that of minimum film thickness.

This work aims to apply a theoretical procedure to determine the performance of the heat exchanger of individually finned heat pipes used in an air conditioning system. The relevant physical quantities are defined and specified locally in the evaporator and condenser sections. The results obtained in the sections are associated with the theoretical determination of the global performance of the heat exchanger. Global theoretical results are compared with global experimental results. Thermal effectiveness, heat transfer rate, pressure drop, thermal and viscous irreversibilities, and thermodynamic Bejan number are determined at the evaporator, condenser, and heat exchanger. The relevant variables used to determine the results are the number of fins per heat pipe and rows of heat pipes. The theoretical-experimental comparison demonstrates that the localized model applied in the analysis is consistent and can be used as a design and comprehensive analysis tool for finned heat exchangers. The performance of the heat exchanger demonstrated exceptional when comparing irreversibilities through the Bejan number, indicating a favorable cost-benefit ratio for the fins less than 30 and the number of heat pipes equal to 49. Bejan’s thermodynamic number, which uses results related to thermal and viscous irreversibilities, demonstrated that one should look for the relationship between thermal irreversibility versus total irreversibility and that fin numbers between 10 and 20 for heat pipes equal to 49 provide a better cost-benefit ratio. The absolute percentage errors obtained between theoretical and experimental values, for an experimental number of fins equal to 30, for the overall heat transfer rate and overall thermal effectiveness range from 2.0% to 42.1%.

A review of the concepts of thermal efficiency and thermal and hydraulic irreversibilities is presented, applying the second law of thermodynamics and thermodynamic Bejan number. An example problem, typical of thermal heat exchange between two fluids, is given, with a dimensionless solution for parallel and counterflow flows. The quantities of interest presented through the example are thermal efficiency, thermal effectiveness, thermal irreversibility, the relationship between outlet and inlet temperatures versus the number of thermal units, and outlet temperature for hot fluid. The theory presented in this review has been applied to numerous problems related to heat exchangers over the last three years, as per references.