This study experimentally investigates the exhaust gas-side heat transfer and flow characteristics of a novel spiral fin-and-tube heat exchanger (SFTHX) designed for automotive exhaust waste heat recovery. The heat exchanger consists of a helically coiled stainless-steel tube fitted with L-footed spiral aluminum fins. Exhaust gas flows over the finned tube, while water flows inside the tube. The effects of exhaust gas frontal velocity, water flow rate, inlet water temperature, and damper position on the heat transfer rate, heat exchanger effectiveness, and pressure drop are examined. The results show that the heat transfer rate and pressure drop increase with increasing exhaust gas velocity, while a higher water flow rate improves the heat exchanger effectiveness. Decreasing the inlet water temperature enhances both the heat transfer rate and effectiveness. Compared with the fully open damper, the fully closed damper increases the heat transfer rate by 40–55%, with a negligible effect on pressure drop. A maximum waste heat recovery rate of approximately 8 kW is obtained with the damper fully closed at a water flow rate of 10 LPM and engine speeds ranging from 2,000 to 3,000 rpm. The use of a helically coiled tube with L-footed spiral fins represents a new configuration for engine exhaust waste heat recovery. The experimental results confirm its potential to improve heat recovery and energy efficiency in automotive applications.
In this research, the study of the magnetohydrodynamic (MHD) Carreau nanofluid flow of the gyrotactic microorganisms is conducted over a melting radially expanding surface in this research. A generalized mathematical model which includes first-order velocity slip, temperature jump, nonlinear thermal radiation, internal heat generation, and Soret-Dufour effects is developed. The nonlinear partial differential equations are very coupled and are converted to ordinary differential equations and solved using a shooting method and 4th order Runge-Kutta (RK4) algorithm. The key novelty is the capture of the two-way coupling between second order momentum rarefied and dynamic phase change at the interface. In the quantitative aspect, when the configuration is changed from the solid rigid wall to the melting boundary with constant magnetic field, the heat transfer rate is reduced by 23.6% and the mass transfer rate by 24.4%. In addition, the application of first order velocity slip results in a significant decrease in the skin friction coefficient from 1.0784 down to 0.5294, and the second order velocity slip brings much needed corrections at the microscale.
Hydrogen addition is a promising way to enhance the SI engine combustion, however the occurrence of combustion limit its practical use, especially at higher hydrogen share. This study focus on combining methanol blending and liquid fuel injection strategy to optimize the hydrogen knock limit. Methanol volume ratios of 20%, 35%, and 50%, along with injection pressures of 80, 110, and 140 bar, are considered. The outcome showed that methanol addition and higher injection pressures reduced the cylinder pressure, heat release rate and combustion temperature because of methanol charge cooling and wall or piston surface impingement at higher injection pressure. These effects mitigated the end-gas autoignition and allowed higher hydrogen flow rate. The hydrogen knock limit increased from 14 LPM at baseline case to 20 LPM for M50 blend at 140 bar injection pressure, corresponding to a 42.8% improvement. Although methanol blending and higher injection pressure lowered BTE and BMEP, hydrogen addition recovered the performance and combustion characteristics. Methanol blending and higher injection pressure reduced the CO2 and NOx emissions and increased the CO emission, while hydrogen showed an opposite emission trend. The findings exhibits that methanol blending and injection pressure variation can be adopted as a calibration parameters to increase hydrogen substitution and mitigate the combustion knock.
Unconventional oils are difficult to process due to their high viscosity, complex chemistry, and tendency to form coke during upgrading. In this study, in-situ Electron Spin Resonance (ESR) spectroscopy was used to monitor the free radical evolution of a medium-heavy crude oil over a wide temperature range (i.e. −180°C to 200°C). ESR revealed three key regimes: a gradual radical increase of about 147% from 3.0 × 10¹⁶ to 7.5 × 1016 spins/g between −180°C and −80°C due to trapped radical release; a sharp 323 % rise to 3.2 × 1017 spins/g between −80°C and 30°C linked to enhanced radical release due to elevated molecular mobility; and a slower increase up to 4.3 × 1017 spins/g from 30°C to 190°C, nearly 35 %. A sharp decline occurred at 200°C, remaining stable over 50 mins, indicating a balance between radical generation and termination. These findings reveal the critical temperature zones where radical activity transitions, offering insight into free radical reactions as well as coke initiation and pathways to optimize low-severity thermal upgrading of heavy oils. For refinery practice, the identified transition zones can inform temperature selection and process monitoring during low-severity upgrading. Changes in the ESR-derived radical population may provide an early indication of feed instability before substantial coke becomes evident. Translation to process equipment will require validation under continuous-flow and pressurized conditions.
This study presents a novel design featuring cylindrical fins of different heights and diameters inserted inside the cooling channels and on the top surface of the heat sink, aimed at reducing thermal-hydraulic resistance in the substrate volume. Micro-fins are oriented vertically and horizontally, with aspect ratios between 1.2 and 3.6, and are spaced 0.2 mm apart. Cooling is accomplished using water and air operating at Reynolds numbers of 300–500 and 6–14, respectively, within a forced convection laminar regime. The investigation utilizes the finite volume method and computational fluid dynamics (CFD) to model the processes. Numerical results indicate that the configuration with three fins in a upper channel under counter-flow conditions achieves the lowest temperature of 313.97 K, while designs with nine fins in the channel record a temperature of 308 K in the fin domain. Overall thermal resistance reductions of 21% and 15% are achieved in the lower and upper channels, respectively, whereas the fin domain exhibits a reduction of approximately 58% across all configurations studied. The lowest and highest pumping powers of 0.0326 W and 0.0329 W are obtained in the lower and upper channels, respectively, while the highest pumping power in the fin domain reaches 0.00,047 W. In addition, programming analysis shows variability and thermal couplings in the system, revealing a near-perfect correlation between upper and lower channels, indicative of strong internal thermal coupling, while the air stream shows a moderate correlation with both channels. The numerical findings are validated with available experimental and numerical data.
