Journal of Research and Applications in Mechanical Engineering

Heat Transfer Characteristics of Filmwise and Dropwise Condensation on Vertical Tubes in the Presence of Air: An Experimental Study

Mohammad Sikindar Baba — 2026-09-20

Condensers are essential to many industrial processes, such as desalination, refrigeration, and power generation. The condenser performance largely depends on the mode of condensation (filmwise or dropwise) which significantly affects heat transfer rates. In this paper, An experimental investigation has been made on filmwise condensation (FWC) & dropwise condensation (DWC) to determine) the heat flux and heat transfer coefficient (HTC) for three steam temperatures of 100^oC, 80^oC and 60^oC. The results are compared with predicted values. It is observed that HTC of DWC is more than FWC. Experimental calculations of the influence of non-condensable gas (air) on heat flux and HTC have also been done and it was proved that the effect of air (1% and 2%) has a very detrimental effect on both FWC and DWC. The experimental values of HTC in presence of air are compared with predicted values obtained by two latest empirical correlations and deviation is identified in FWC. A satisfactory relation is obtained between actual and predicted values.

A Comparative Investigation on Friction and Wear Behavior of Green Lubricants

GURMEET SINGH GAHIR — 2026-09-20

Green lubricants are gaining increased attention due to the rising demand for environmentally friendly and sustainable solutions. To evaluate their suitability as base oils for lubricants in local automobile and power plant engines, the tribological performance of refined, bleached, and deodorized palm and jojoba oils was assessed and compared. The tests were conducted using a four-ball tester. The bio-based oils’ performance was evaluated under various load and temperature conditions using a tribological testing system. The results showed that unprocessed palm oil outperformed jojoba oil in terms of load-bearing capacity and friction reduction in its raw state. Additionally, palm oil exhibited wear protection performance similar to jojoba oil. With the radical incorporation of suitable anti-wear agents, palm oil can be transformed into a highly effective alternative to mineral oils, offering advantages in terms of tribology, environmental impact, and non-food competition.

A Digital Twin and Probabilistic Optimization Framework for Resistance Spot-Welded Joints in Automotive Applications

Prasad Padmakar kulkarni — 2026-09-20

This study formulates a digital twin–driven probabilistic model to forecast and optimize the tensile behavior of resistance spot-welded (RSW) galvanized steel auto-body joints. Experimental experimentation was performed on multi-spot cross-tension specimens by a Taguchi L27 design with the considerations of welding current (8959–9554 A), sheet thickness (0.19–0.30 mm), electrode force (350–497 N), weld spot number (2–8), and radial distance (12–16 mm). Tensile strength varied from 4.08 Kgf to 150.91 Kgf. A linear regression model accomplished ±5% prediction accuracy in this range, with thickness and number of welds as the most significant parameters, and radial distance as having a significantly negative effect on strength. To offset the weakness of regression, finite element analysis (FEA) was systematically incorporated, allowing for a mechanistic understanding of stress concentrations due to off-center weld placement and to confirm the observed empirical trends. The FEA also showed predictive validity, with calculations at an unseen parameter set (9554 A, 0.27 mm, 350 N, 8 spots) approximating tensile strength to 145.2 Kgf versus the tested 150.9 Kgf (3.7% error). Parameter uncertainty was quantified using Monte Carlo simulations with Latin Hypercube Sampling (170 runs), and Global Sensitivity Analysis indicated sheet thickness and weld radius as overall factors on strength variability. Dynamic tensile testing (1.32–2.00 m/min) validated the model's insensitivity to service-relevant strain rates. Together, the synergy from the combination of regression, FEA, and probabilistic simulations provides a predictive digital twin approach that is both statistically sound and mechanistically interpretable. The approach improves weld performance assessment reliability and provides scalable applicability towards lightweight and safe automotive structures.

Bionic Riblet Impeller for a Centrifugal Pump: CFD and Experimental Performance Analysis

Rajendra Pawar — 2026-09-20

This study adopts a novel bionic approach to evaluate the performance of a centrifugal pump using numerical simulations and validates the findings through experimental analysis. The centrifugal pump, featuring six backward-curved blades, was modeled by incorporating shark-skin-inspired riblet structures into the impeller design. The flow inside the pump was studied using k-epsilon (k-ε) turbulence models. The k-ε model gave results that were closest to the real experimental data. In most studies, only design parameters considered during computational fluid dynamics (CFD) analyses without consideration of experimental result. Here new bio inspired technique called bionics is applied to impeller of pump. The experiments were carried out using a computer-controlled pump testing setup. The pump's head, hydraulic efficiency, and power were analyzed using both CFD simulations and experimental tests on the duty point as per manufacturer’s catalog, having the revolution of 2,900 rpm, The bionic impeller achieves a best efficiency point (BEP) at a discharge rate of 12 m³/hr., with a head of 32.75 m and an efficiency of 39.21%. The CFD results closely matched the experimental results at the design flow rate and at all other tested flow rates as per duty points. In addition, by integrating nature-inspired design with testing, this study contributes to the development of high-performance, sustainable pumps. The results may help advance efficient industrial fluid transport systems. This research bridges biomimetic innovation with practical engineering, paving the way for future pump advancements.

Effect of Pouring and Mold Shell Temperatures on Porosity in Complex Investment Castings of Stainless Steel 304

Thanh Tan Nguyen — 2026-09-20

Investment casting offers a powerful combination of precision, design freedom, material versatility, and potential cost savings, making it an ideal choice for demanding applications across various industries. However, this technology also faces significant challenges that affect part quality, primarily due to the formation of porosity and air entrainment. These defects originate from inadequate solidification control and turbulent flow behavior during the mold filling process. This study aimed to investigate the effect of pouring and firing temperatures on the appearance of porosity in stainless steel 304 complex casting parts, to minimize casting defects. The casting geometry is characterized by intricate features and thin cross-sections, making it highly sensitive to thermal and flow behaviors. Six pouring temperatures (1580 °C, 1600 °C, 1620 °C, 1640 °C, 1660 °C and 1680 °C) and six firing temperatures (950 °C, 1000 °C, 1020 °C, 1040 °C, 1060 °C and 1080 °C) were evaluated. ProCAST software was used to analyze porosity formation and air entrainment, revealing that a pouring temperature of 1640 °C and shell temperature of 1040 °C achieved a minimal porosity (0.01 cm³) while reducing the air entrainment (0.5 mg/cm³). Additionally, the study also clarified that the relationship between pouring/shell temperature and casting defects is non-linear, with “trade-off” effects always happening in casting. Experimental validation via X-ray and microscopy inspection confirmed the simulation trends. The study recommends minimizing defects in thin-walled investment casting parts through precise thermal control, enhancing product quality and manufacturing efficiency.

Hydrodynamic Analysis of a Two-Lobe Bearing Lubricated with a non-Newtonian Fluid: Effects of Geometric and Rheological Parameters on Operating Characteristics

Hadjar Bennaceur — 2026-09-20

In the context of hydrodynamic lubrication, this paper investigates the contribution of the aspect ratio R/L to the static performance of two-lobe bearings, by incorporating the non-Newtonian rheological response of the lubricant modeled by the power law. The Reynolds equation is reformulated to incorporate fluid rheology and solved numerically using the finite difference method to determine the pressure profile within the lubricant film. The analysis focuses on the cross-impact of the aspect ratio, the power law index n, and the eccentricity ratio ε, on key parameters such as film thickness, pressure, load-carrying capacity, attitude angle, frictional force and coefficient, as well as the side leakage. The results indicate that film thickness is only marginally affected by the R/L ratio, but is highly sensitive to the lubricant's rheological properties, especially in high shear zones. A reduction of R/L or an increase of n improves the hydrodynamic support. Furthermore, shear-thickening fluids promote the load-carrying capacity and tribological efficiency, while long bearings exhibit increased sensitivity to leakage effects.

CFD and Experimental Study of Cavitation Behavior in Three-Lobe Journal Bearings Lubricated with TiO₂-Based Nanofluids

Nitin Ahire — 2026-09-20

Three-lobe journal bearings are widely used in high-speed rotating machinery due to their superior stability and load-carrying capacity. However, they are susceptible to vapor cavitation in the diverging region, which weakens the lubricant film and degrades performance. This study presents a combined numerical and experimental investigation of pressure distribution in three-lobe journal bearings under cavitating conditions, comparing a base oil (Mobil DTE 24) with a TiO₂-enhanced nanolubricant. Simulations were performed using the Zwart–Gerber–Belamri (ZGB) cavitation model within a multiphase CFD framework in ANSYS Workbench 2024R1 at operating speeds of 500- 1000 rpm. Results were validated against experimental pressure measurements at twelve angular positions using a custom-built test rig. For the base lubricant, CFD accurately predicted peak pressure near 210° and vapor cavitation between 240° and 330°, with deviations within ±0.06 MPa. The addition of TiO₂ nanoparticles increased peak pressure by up to 36% and raised the minimum pressure from –0.52 MPa to +0.50 MPa, indicating over 60% cavitation suppression. These improvements confirm enhanced film stability, greater load capacity, and close agreement between simulation and experiment. Furthermore, the TiO₂ nanolubricant reduced friction losses, minimized lubricant degradation, and supports the development of energy-efficient and sustainable tribological systems.

Energy Harvesting Using One-Way Bearing for Vehicle Suspension Applications

S. Chanayuth — 2026-09-20

Road degradation amplifies suspension energy dissipation due to factors like vehicle mass, speed, and surface roughness. Harvesting energy from suspension motion is challenging, requiring the conversion of irregular mechanical energy into electrical power. The energy harvesting device must operate effectively under ISO 8608 Class C and D conditions. An indirect-drive system converts linear motion into rotational motion to power a generator, with the 'two-leg mechanism' and one-way bearing rectifying motion direction. This research combines simulation and experimentation to assess power generation under sinusoidal wave conditions (10–20 mm amplitude, 1–3 Hz frequency). Maximum power occurs at 10–20 Ω resistance, increasing with frequency and amplitude. With 88.15% accuracy, the simulation model provides valuable insights for optimizing real-world performance.

Rotational Effects on Heat Transfer for In-Line Jet Impingement Array in a Mid-Span Turbine Channel: An Experimental Study

Chanon Sathiravorakul — 2026-09-20

This study examined heat transfer for a 3x11 inline impinging jet array within a rotating channel that simulates the turbine blade cooling in mid-span region. The heat transfer on the impingement surface was investigated using Thermochromic Liquid Crystals and a thin-foil heater under steady-state conditions. The influence of impingement distance (L/D=2, 4, 6) and Rotation number (Ro=0.0-0.0083) was examined at a constant Reynolds number of Re=10,000. Results indicate intricate relationships between impingement distance, Coriolis forces, and crossflow. Increased rotation numbers generally diminish heat transfer on both of leading and trailing sides relative to the stationary condition. At a small L/D of 2, crossflow effects predominated over rotational effects, resulting in gradual decrease in downstream region. In contrast to distances L/D=4 and 6, the Nusselt number declined rapidly in the upstream region, whereas the influence of rotation lessened in the downstream region.

Enhancing Energy Efficiency and Sustainability through Titanium Dioxide Enhanced Cool Roof Paints with Maximum Solar Reflectance

Ragupathi P — 2026-09-26

Cool roofs lower building temperatures by reflecting the sun, reducing cooling energy consumption. Their performance is solar reflectivity (SR) and infrared emissivity (IE) dependent. White ceramic tiles, white cement, and aluminium foil are normally used materials in India, but they lose performance over time. This research offers the addition of titanium dioxide (TiO₂) to paint for roof application to increase and maintain reflectivity. TiO₂, a white pigment, reflects infrared radiation, enhancing SR and prolonging roof longevity. Experimental data indicate indoor temperature decreases of 4.0–5.3°C, substantiating apparent cooling advantages. In contrast to conventional materials, TiO₂-based coatings remedy durability problems, presenting a cost-effective and environmentally friendly method for enhancing energy efficiency in warm regions. This novel method underscores TiO₂'s promise in revolutionizing cool roof technology for long-term use in India.

Design and Crash Safety Assessment of an Autonomous Electric Minibus Superstructure

Warot Usawiroj — 2026-09-26

This study presents the structural design and crash safety assessment of an autonomous electric minibus superstructure. A systematic approach combining material selection with simulation-based refinement enabled a balance of safety, efficiency, and manufacturability. ASTM A36 steel was selected for its favorable mechanical and practical properties. Targeted reinforcement of door pillars and floor cross-members improved lateral-impact resistance, reducing displacement by 65.9%, while front-end geometry adjustments enhanced pedestrian protection, keeping HIC and chest accelerations within safety limits. The final design also achieved a 7.7% reduction in structural mass without compromising integrity. These results demonstrate that combining material-informed design with parametric safety evaluation can guide the development of autonomous minibuses that are both safe and efficient for low-speed urban environments.

Numerical Study of heat transfer characteristics of Rectangular channel with combined roughness

Harvindra Singh — 2026-09-26

The study numerically investigates convective heat transfer enhancement in a solar air heater (SAH) duct using semi-circular roughness elements on the absorber plate. A three-dimensional, turbulent airflow model is analyzed with fixed heat flux and validated against the Dittus–Boelter correlation for smooth ducts. The flow in the rectangular channel is steady, incompressible, and turbulent, with constant properties throughout. Air properties such as density and viscosity remain uniform, and the solar radiation over the absorber plate is also uniform, facilitating calculations. The no-slip condition applies as a boundary condition in CFD simulations; minor heat losses to the environment can be neglected. It examined the influence of geometric configuration, particularly the p/e = 7, 8, 9, 10 and 11 relative pitch ratio between roughness elements, on the duct's thermal performance. These variables are investigated in turbulent flow conditions with Reynolds numbers (Re) between 3000 and 24,000. Results indicate that these roughness elements increase heat transfer rates by up to 262% compared to smooth ducts at a Reynolds number of 24,000, with optimal configurations yielding a Nusselt number approximately 2.3 times higher and a maximum thermal–hydraulic performance parameter of 1.61 at specific geometric conditions as under specific conditions at Re = 24,000, P = 22 mm, and P/e = 10.

Microstructure Evolution and Fatigue Behaviour of AA2099 Alloy Processed through Hybrid Multi-Axial Forging and Cryo-Rolling

Atul Bhatt — 2026-09-26

The effects of post-deformation annealing and hybrid severe plastic deformation (SPD)—multi-axial forging (MAF) followed by cryorolling (CR)—on the microstructural development and low-cycle fatigue (LCF) behavior of AA2099 Al-Cu-Li alloy were examined. After six MAF cycles (cumulative strain of 3.6), solution-treated specimens underwent cryo-rolling at −196 °C, leading to an overall thickness reduction of about 90%. Post-deformation heat treatment was then carried out at 150 °C and 200 °C. As a result of this processing route, the material developed an ultrafine-grained microstructure with an average grain size close to 0.42 µm, along with a high density of dislocations and a microstructure dominated by low-angle grain boundaries. were produced by the hybrid MAF+CR method. Grain size was increased to 0.84 μm after post-annealing at 150°C, which also improved texture intensity (~3.7 m.r.d.) and the high-angle grain boundary fraction. Because of the best precipitation strengthening, the MAF+CR+150°C condition demonstrated the best LCF performance, with the biggest hysteresis loops, maximum energy dissipation, and a peak cycle stress of about ±270 MPa. For MAF+CR+150°C, fracture analysis showed primarily ductile failure with fine equiaxed dimples, whereas MAF+CR+200°C displayed coarser features as a result of overaging. Progressive strain recovery with temperature was verified using Kernel Average Misorientation analysis. In ultrafine-grained Al-Cu-Li alloys intended for aerospace applications, this hybrid processing method successfully modifies microstructure to produce improved LCF resistance.

Hybrid ANN-GA Optimization of Burnishing Parameters for Improving Surface Finish and Hardness in 6061-T6 Aluminum Alloy

Amornsak Mayai — 2026-09-26

Improving surface finish and hardness in 6061-T6 aluminum is crucial for aerospace and automotive applications. This study presents a hybrid Artificial Neural Network–Genetic Algorithm (ANN-GA) model to optimize burnishing parameters—spindle speed, feed rate, and pressure. A full factorial design was used to analyze their effects on surface roughness and hardness. Experiments identified optimal conditions: 500 rpm, 0.3 m/min, and 2.0 GPa, achieving 0.372 µm roughness and 140.30 HV hardness. The ANN-GA model exhibited high predictive accuracy (R² = 0.9513, RMSE = 0.22), and proposed an alternative optimum at 799.02 rpm, 0.31 m/min, and 1.48 GPa. The findings confirm the effectiveness of the ANN-GA in capturing nonlinear interactions and reducing experimental trials. This integrated approach offers a robust tool for optimizing burnishing processes, particularly for high-performance components requiring superior surface integrity.

Optimization of Internal Rotor Cooling Using Variable Fan Configuration and Blade Angles in a Synchronous Reluctance Motor

Hoang Phuc Ngo — 2026-09-26

This study investigates the cooling efficiency of an internal rotor fan system integrated into a synchronous reluctance motor (SynRM), aiming to optimize key fan configuration parameters. The analysis focuses on the effects of fan blade angle, installation position (front, back, and both), and rotational speed on the motor’s thermal behaviour under various operating conditions. The experiment evaluated the cooling efficiency, while the simulation model was used to clarify the effects of air velocity and pressure on cooling performance. The results show that fan blade geometry and positioning influence the heat transfer coefficient. The 60^o fan blade configuration, when installed at the rear side, generates the highest cooling airflow through the rotor, reaching 11.31 m³/h at 2000 rpm, it achieves the lowest rotor temperature of 43°C after 10 minutes of cooling. Moreover, increasing the fan’s rotational speed from 1000 rpm to 3000 rpm enhances airflow, which improves heat transfer and further lowers rotor temperature. These findings contribute to improved thermal management strategies in SynRM design by demonstrating how integrated fan systems can enhance cooling efficiency through optimized configuration.