This study develops a novel mathematical model to examine blood flow dynamics in a catheterized, inclined artery with overlapping stenoses, accounting for mild stenotic conditions. The analysis incorporates the combined influences of body acceleration, slip velocity, and viscous dissipation, while heat transfer is modeled via the Cattaneo-Christov framework to capture non-Fourier thermal effects. The coupled momentum and energy equations are solved analytically using a perturbation approach, yielding the expressions for wall shear stress, flow rate, velocity, and impedance. Parametric analysis reveals that higher body acceleration, slip velocity, and arterial inclination enhance both velocity and flow rate, whereas larger catheter radii reduce velocity. Wall shear stress intensifies in converging arterial segments due to elevated forces on the vessel wall. These results provide valuable insights into the coupled hemodynamic-thermal behavior of catheterized stenotic arteries, supporting improved clinical strategies for managing pathological arterial conditions and optimizing interventional procedures.

An infrared suppression system (IRS) is used in modern vessels to mitigate the heat of the engine's exhaust. A converging-diverging funnel system is examined, with a nozzle positioned just before the exhaust pipe to enhance the device's efficiency. The thermo-fluid study of the proposed system involves resolving transport equations related to continuity, momentum, energy, and turbulence via the finite volume solver in ANSYS FLUENT. The research contrasts the IRS device in both nozzle and non-nozzle conditions. The nozzle enhances the device's mass entrainment, ultimately reducing the exit temperature. The maximum velocity and back pressure impose limitations on the nozzle's application to meet incompressibility and back pressure standards. The influence of the nozzle diameter ratio on output parameters, such as mass entrainment and outlet temperature, is examined. The characteristics are analyzed at various exhaust inlets, ranging from 7.5 kg/s to 31 kg/s. The current study examines three distinct diameter ratios: 0.625, 0.5, and 0.375. A lower diameter ratio exhibits more mass entrainment than a higher diameter ratio. The outlet temperature decreases as the diameter ratio increases. Nonetheless, the maximum velocity and back pressure limit the application of the nozzle. The nozzle, with diameter ratios of 0.625 and 0.5, meets the requirements for incompressibility and back pressure for all studied mass inlets. Nonetheless, a nozzle with a 0.375 diameter ratio can accommodate these circumstances only up to an input mass of 15 kg/s.

In the present study, the performance of an inclined microchannel-incorporated heat sink (MCHS) attached to a heat source, mimicking a microelectronic device, has been investigated through computational approach. Three different coolants are used: DI water and aqueous nanofluids of copper oxide (CuO) and carbon nanotube (CNT), respectively. The microchannel of dimension 10 mm × 180 μm × 57 μm is designed with a preset inclination (0°, 0.33°, 0.66°, and 1°). At first, the overall thermal behavior of the MCHS with water as coolant, flowing through the heated microchannel, is evaluated based on the local temperature distribution, local heat transfer coefficient (HTC), and pumping power to assign the performance index for optimization of a specific inclination. In the subsequent part, the optimized geometry is rendered more efficient with nanofluids and modified flow parameters. It is observed that Nusselt number increases by 2.4% for mere 1° inclination as compared to a straight microchannel with water as a coolant and further increases by 2.3% with water + CNT. The efficiency index (<i>h</i>), a parameter governed by flow and thermal resistance, is shown to be highest for 1° inclination with water + CNT as coolant for inlet temperature of 298 K and velocity of 1.312 m/s. The primary reason for efficient cooling with inclination and high velocity is induced pumping arising from gravitational drainage and better thermal transport at channel wall due to proximity between channel wall and base. Physically, this additional cooling can get augmented due to uniaxial elongation like flow of CNT-based nanofluid due to its high aspect ratio.

We compare the efficacy of R513a, a refrigerant blend comprising hydrofluorocarbon/hydrofluoroolefin, with R134a, a commonplace refrigerant having a higher global warming potential, in the context of low-temperature heat pipe applications. Tests were conducted considering both helically grooved heat pipes and also smooth heat pipes (i.e., thermosyphons) to ascertain performance differences under a variety of operating conditions. Our laboratory measurements reveal that, in most cases, R513a may be employed as a one-to-one substitute for R134a, exhibiting better performance and enhanced heat transfer capacity. A detailed strategy is crucial for transitioning from one refrigerant to the other in those parametric regimes where R134a outperforms R513a. This involves adjusting either the fill mass or design parameters, such as the groove dimensions or internal diameter, to achieve comparable performance. Our study contextualizes the strategy for transitioning to alternative heat pipe refrigerants and provides a valuable confirmation of the fact that eco-friendly alternatives can rival, and sometimes even outperform conventional refrigerants.

In the convective drying of a wet porous medium by hot air, the medium surface exposed to the air fluid may experience three stages, namely the fully wet, partly wet, and fully dry stages. At the fully wet stage, the medium surface is fully covered by a water film, with the convective moisture transfer taking place all over the medium surface; at the partly wet stage, the medium surface is partly covered by water film, with the convective moisture transfer occurring only at the wet surface where free water is present. In this research, a theoretical model is presented to simulate the convective drying of a wet porous medium, and experiments on hot-air convective drying of a wet porous sand layer are carried out to investigate the sand-layer temperature and water content variations during the drying, in which the sand layer thickness is 4 mm, the initial water-film thickness is 0.4 mm, and the hot-air temperatures are 45, 60, and 75°C, respectively. Inverse calculations are conducted to get some insight into the water-film coverage function based on the experimental data, which are necessary for quantitatively evaluating the effective moisture transfer surface area when calculating the convective moisture transfer at the partly wet stage. By combining the coverage function with the wet porous medium drying model, a comprehensive model is obtained. Calculations are implemented to simulate the convective drying of the wet porous sand layer, and the effects of the two constants included in that function on the wet sand-layer drying characteristics are discussed. The calculation results are compared with the experimental data; they agree very well, supporting the effectiveness of the current model in simulating the sand-layer convective drying process.

The challenge of improving the efficiency and sustainability and reducing emissions of diesel engines through the use of different fuel blends-such as diesel, biodiesel, and fuel blends mixed with TiO<sub>2</sub> nanoparticles-is addressed by this research. The study investigates how the performance, emissions, and sustainability aspects of a one-cylinder, four-stroke, water-cooled diesel engine are impacted when 50 and 100 ppm of titanium dioxide (TiO<sub>2</sub>) nanoparticles are added to various blends of diesel and biodiesel under varied engine loads ranging from 25% to 100%. The addition of TiO<sub>2</sub> nanoparticles leads to reductions in brake specific fuel consumption (BSFC) of up to 8% with B0 and up to 14.29% with B15, improvements in energy efficiency of up to 2% with B0 and up to 4.02% with B15, and improvements in exergy efficiency of up to 1.88% with B0 and up to 3.77% with B15. With regard to hydrocarbon (HC) emissions, the use of TiO<sub>2</sub> nanoparticles decreased emissions by up to 18.4% at the cost of nitric oxide (NO) emissions, which increased by up to 5.87%. The exergy performance coefficient (<i>Ex<sub>p</sub></i>) and sustainability index (SI) increased by up to 18.99% and 5.63%, respectively. The percentage changes showed enhanced engine performance, lower emissions, and improved energy conversion efficiency with the inclusion of TiO<sub>2</sub> nanoparticles. The results suggest fuel blends' advantages in terms of energy conversion; however, it is also important to look at the economic feasibility and stability of TiO<sub>2</sub> nanoparticles.

This study developed a two-pass diverging microchannel heat exchanger to avoid flow reversal and partial dry out of HFC-245fa flow boiling in the evaporation cooling systems. It is aimed to improve the diverging microchannel heat exchangers designed by previous studies and to effectively accommodate diverging channels on a limited heating base surface. The test results showed that the maximum heat transfer coefficients in a diverging channel heat exchanger were as much as 20% higher than those in straight channel heat exchanger, while the maximum partial dry-out heat flux is 42% higher in diverging channel heat exchanger. There is no significant difference for the pressure drops in two heat exchangers at low heat fluxes before it reached the partial dry-out condition. For higher flux, the pressure drops in straight channels were higher than those in divergent channels while partial dry out. It is concluded that the two-pass diverging channel design provided higher maximum heat transfer coefficients and higher maximum heat fluxes with lower penalties of pressure drops. It could be a good design to replace the conventional straight channel heat exchanger for evaporation cooling systems.

In this paper, single-phase heat transfer characteristics of water inside internal enhanced tubes were investigated. Refrigerants are boiling or condensing outside the tube. The experimental tubes have internal helical rib heights of 0.25-0.36 mm, helix angles of 40-60°, rib base thicknesses of 0.40-0.79 mm, rib tip thicknesses of 0.078-0.283 mm, and N<sub>s</sub> (starts number per circle) of 40-50. It shows that the heat transfer enhanced ratios usually range from 2.3 to 3.64. The friction factors relative to the smooth tube are about 1.8 to 3.3 times higher. Analyzing the effect of rib geometry on flow and heat transfer, it was found that the higher the height of the internal rib, the better the enhancement of convective heat transfer in the tube. Also, the greater the thickness of the rib tip and base, the more detrimental to the friction factor in the tube. There was no noticeable influence on the heat transfer performance as the helix angle increased from 45° to 50°. For the increase of N<sub>s</sub>, it appears that 45 ribs per circle is the best value in the present study when considering the increase in pressure loss. The thermal-hydraulic performance of 11 tubes was also evaluated. It shows that Tube-1 had the best performance in the condensing tubes and Tube-7 had the best performance in the boiling tubes.