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This study presents a dynamic analysis of compact heat exchangers (CHEs) integrated within an aircraft Environmental Control System (ECS), with emphasis on their transient thermal behaviour under varying operating conditions. A dynamic model is developed using the ECS library in a 1-D system simulation platform. Characteristic maps of heat exchanger effectiveness as functions of hot and cold fluid mass flow rates are generated in MATLAB for the primary heat exchanger (PHE), secondary heat exchanger (SHE), reheater (RHX), and condenser (CND), and subsequently imported into the ECS library framework. The model employs pressure–temperature sources at the inlets and temperature–mass flow sinks at the outlets on both hot and cold sides. Dynamic performance is evaluated in terms of hot- and cold-side outlet temperatures, hot-side heat flow rate, and system response time. Parametric analysis reveals that the fluid channel volume has a dominant influence on transient response compared to heat exchanger effectiveness. For an isolated heat exchanger, the dynamic response time increases from approximately 10 s to 25 s as the fluid channel volume increases from 0.5 m³ to 1.5 m³. Stabilised hot-side outlet temperatures of about 86 °C, 162 °C, 369 °C, and 453 °C are obtained for effectiveness values of 0.98 (SHE), 0.84 (PHE), 0.43 (RHX), and 0.25 (CND), respectively, corresponding to hot-side heat flow rates of 339.40 kW, 288.17 kW, 146.84 kW, and 88.37 kW. Furthermore, an integrated ECS configuration combining the PHE and SHE is modelled, demonstrating longer response times for the SHE (≈ 20–40 s) compared to the PHE (≈ 10–25 s) over the same range of fluid channel volumes. The results clearly demonstrate the significance of transient analysis in the design and optimisation of compact heat exchangers for aerospace ECS applications.

Understanding the influence of angular orientation on mixed convection heat transfer and pressure drop in circular tubes with swirl generators is crucial for optimizing thermal performance in various engineering applications, including heat exchangers and energy systems. This study aims to investigate the impact of angular orientation on heat transfer enhancement and pressure drop characteristics in a uniformly heated circular tube equipped with a twisted-tape longitudinal swirl generator. An experimental approach was employed, varying key parameters such as Reynolds number (435–10,130), heat flux (2, 3, and 4 kW/m²), twist ratio (P/D = 3, 4, and 5), and angular orientation (15° and 30°). The setup was validated against established correlations for Nusselt number and friction factor, demonstrating strong agreement. The results reveal that angular orientation significantly affects heat transfer and pressure drop at Reynolds numbers up to ~ 1000, where mixed convection plays a dominant role. Beyond this, forced convection prevails. In a plain channel, the transition from laminar to transitional flow occurs at Reynolds numbers of 2924–4088 for a 15° angle of inclination (AoI) and 3001–4274 for a 30° AoI, with the transition occurring slightly earlier at the lower angle. The Richardson number varied from 2.5 in the low laminar regime to 0.0087 in the turbulent regime, with additional variations observed when turbulators were introduced.

The special features of silver-capped iron nanoparticles, like their excellent ability to conduct heat, adjustable magnetism, and resistance to rust, make them highly sought after for industrial heat transfer uses. The medical and industrial fields are rapidly adopting a new technology that shows promise in areas such as electronics cooling, biomedical heating, solar thermal, and nanofluids. The flow of silver-capped iron nanoparticles through a Forchheimer medium with the CC effect is the subject of this work because of these applications. Additionally, thermal radiation and exponential heat sources are considered. The mixed convective situation improves the boundary. The governing equations of flow are reduced by employing similarity transformations from a PDE to an ODE. Utilizing a set of similar variables, the modeled problem will be converted into a set of ODEs. With RKF-45, the resulting set of ODEs will be solved. Through the graphs, the behaviours of many significant parameters will be examined and discussed in cases when these factors are and , Velocity of the fluid is more controllebele in hybrid nanoparticles case then that of nanoparticles case. Rate of heat transfer is more influence by silver capped iron oxide nanoparticle when compared to silver nanoparticles. The temperature profile increases when improves. There is an improvement in the thermal boundary layer as well. Convective cooling diminishes with decreasing velocity, and thermal energy tends to build up, increasing the fluid’s temperature. Reduced flow further thickens the thermal boundary layer, which raises the temperature profile even more. For both silver and silver oxide nanoparticles Nusselt number increases when and values grow. However, when values rise, the reverse effect is seen. Silver nanoparticles and silver oxide nanoparticles, skin friction decreases as the and parameters increase.

The research involves an experimental investigation into the performance of a flow assisting air heat exchanger under varying angular orientation and uniform external heat fluxes without and with spring turbulators. The investigation was performed for Reynolds numbers ranging from 511 to 9676 and inclination angle 15° and 30°. Three heat fluxes (2, 3, and 4 kW/m 2 ) were applied to the test section to investigate the effect of external surface heating on the range of transition flow regime and thermohydraulic performance. Transition from laminar to turbulent flow for plain channel at different heat fluxes and inclinations occurs within specific Reynolds number ranges: 2436–4446 for 15° inclination at 4 kW/m 2 , 2574–4289 at 3 kW/m 2 , and 2850–4152 at 2 kW/m 2 ; for 30° inclination, the ranges are 2518–4151, 2712–4361, and 2992–4346 at the respective heat fluxes. When it comes to the effect of inclination on Nusselt number, the transition occurs sooner at lower angles, but is delayed as the angle increases. Additionally, the Nusselt number decreases as the angle of inclination increases. When comparing the Nusselt numbers of plain tubes to those with spring turbulators, the latter shows a significantly greater enhancement. In laminar flow, a maximum 100% deviation exists between highest and lowest friction factors, decreasing to 75% with increasing Reynolds number; all insert configurations exhibit highest friction factor at 15° due to stronger buoyancy forces.

The rapid advancement of high-density electronic devices and data centres has heightened the demand for effective thermal management solutions capable of handling elevated heat fluxes within compact domains. Conventional cooling techniques often fail to meet these requirements efficiently. This study presents a numerical investigation of heat transfer enhancement in a mini-channel heat sink through the combined use of passive vortex generators (ribs) and externally applied magnetic fields. A two-dimensional simulation was conducted for a 40 mm × 4 mm mini-channel employing a 2% Fe 3 O 4 –water nanofluid, with magnets positioned at X = 15 mm and X = 25 mm to generate non-uniform magnetic fields ranging from 800 to 2000 G. Three rib configurations parallel, staggered, and ribbed were evaluated across a Reynolds number range of 50, 75, 100, 150, 180, and 210. Results indicate that the ribbed configuration provides the highest heat transfer improvement, achieving up to a 65% increase relative to the baseline, while the parallel arrangement attained the highest absolute Nusselt number. The friction factor increased with stronger magnetic fields but decreased with higher Reynolds numbers. The thermal enhancement factor remained consistently above unity, with peak values of 2.06 for ribbed, 1.77 for parallel, and 1.52 for staggered layouts. Overall, this study demonstrates that integrating rib-induced vortex generation with magnetic field effects offers a promising strategy for enhancing the thermal performance of mini-channel heat sinks, addressing the cooling demands of next-generation electronic and data centre applications.

Dynamic analysis of the Environmental Control System (ECS) is essential for enhancing system performance and control. This study presents the dynamic modeling and analysis of a two-wheel bleed air ECS for aircraft, developed using the ECS library in Dymola, a commercial 1-D dynamic simulation software based on the Modelica language. The model represents a high-pressure water separator two-wheel bleed air ECS and focuses on the transient behavior of its key components. The analysis captures the dynamic response in terms of hot-side heat flow rate for the compact heat exchangers, outlet temperatures on the hot and cold sides of the heat exchangers, and the outlet temperature of the cold air unit (CAU). Additionally, corrected flow and corrected speed of the CAU, along with shaft power, torque, and angular speed, were investigated. To ensure reliability, a separate steady-state analysis was conducted using MATLAB, as dynamic studies of such systems are limited in the literature. The simulation results show strong agreement with the steady-state MATLAB analysis, validating the accuracy of the developed model. System-level responses were obtained at approximately 26 s, 52 s, and 78 s for shaft mass moments of inertia of 0.01 kg m 2 , 0.02 kg m 2 , and 0.03 kg m 2 , respectively. These results demonstrate the influence of shaft inertia on dynamic performance. The developed dynamic model provides a valuable tool for system-level analysis during the early design phase, particularly when experimental data are not available.

The influence of non-uniform heat transfer on a circular tube with a twisted tape insert using nanofluid (NF) is examined. The circular tube had an inner diameter 20 mm, with 0.5 mm thickness and 2 m of length. Wall heat flux conditions were examined for Reynolds number ranging from 5 000 to 25 000. Heat flux distribution included partial heating at different circumferential positions. Water was used as a base fluid, while single and multi-nano particles are used for simple and hybrid nanofluids (HNF). The goal of this study is to augment the thermal performance by incorporating non-uniform heating, using a twisted tape insert and by using nanoparticle of different volume fraction. NF act as a fluid additive and twisted tape act as a turbulence promoter and they enhance the heat transfer rate. However, major disadvantage in this investigation is the pressure drop incurred due to the twisted tape and NFs. Hence, a series of simulation are carried out to find out the optimum configuration of the set-up for which heat transfer will be enhanced with minimum pressure drop.

Present study reports a computational investigation on heat transfer and pressure drop characteristics for flow through a heat exchanger tube fitted with novel hybrid ribs by using magnetic nanofluid (Fe 3 O 4 ). Effects of different rib geometry on heat transfer and pressure drop characteristics have been investigated for Reynolds number ranging from 3 000 to 22 000. Until now, there is little information available in the literature on the method of quantifying the effect of forced convection on the heat transfer and pressure drop of hybrid rib (HR) inserts by using magnetic nanofluid (MNF). The transition SST models along with governing equations (continuity, momentum, and energy equations) are numerically solved with ANSYS Fluent 19.2. The simulation results are validated with established correlations and excellent agreement was found. Heat transfer coefficient is more in combined arrangement (HR and MNF) compared to acting alone arrangement (only MNF).

This study delves into the computational exploration of the impact of magnetic intensity, magnetic nanofluid, flow rates and heat transfer coefficient in the form of Nusselt number on inclined ribbed channels with both parallel and staggered configurations for the cooling of sodium-ion and lithium-ion batteries in electric vehicles. Employing Fe 3 O 4  + H 2 O as the working fluid, within a minichannel with multiple magnets at different locations, namely 15 mm, 25 mm and 15 mm and 25 mm, the parallel and staggered inclined ribbed channel Nusselt number (Nu) increased with magnetic field intensity, reaching maximum of 152.81% for staggered ribbed minichannel configuration at 2000 Gauss (G). Similarly, the skin friction experienced an increment with magnetic field intensity for staggered ribbed minichannel configuration and for parallel ribbed minichannel when both the magnets were placed at the location of 15 mm and 25 mm from the inlet but decreased with increasing Reynolds number. Notably, the thermal enhancement factor (TEF) consistently surpassed greater than unity for all investigated cases. These findings carry significant implications, particularly in EV cooling, offering valuable insights for developing more efficient and tailored cooling solutions for advanced EV battery thermal management.

The objective of this article is to study the work carried out in heat transfer augmentation using active and passive techniques. A comprehensive summary of the work is highlighted to showcase the strength of these techniques in terms of enhancement in heat transfer. In this work, research studies done in the area of electrohydrodynamic, magnetic field, corona wind, vortex generators, tape and coil inserts, roughness, and modified duct were reviewed and an attempt has been made to make a common platform on which the performance enhancement has been compared and presented. It was found out that passive methods are comparatively more investigated than active methods due to their safe and sound operation along with no additional requirement of power. Result shows that duct modification is an effective and efficient way for heat transfer enhancement (HTE). Based on the literature studied, more emphasis must be focussed on the usage of HTE methods in combination to get the advantages of both the methods and they should complement each other in the best possible way. On comparing the active and passive way of THE, results with active methods are more appreciable. However, passive techniques gain more momentum due to ease of operation and low cost of equipment. Use of passive augmentation techniques, i.e. vortex generators, artificial roughness, etc., changes flow pattern significantly that helps in the heat transfer augmentation. Although understanding of fluid flow behaviour is very essential and helps in the cause of the heat transfer augmentation that will further help in using compound techniques, altering the duct’s surface using ribs, dimples, roughness, etc., shows the thermal performance enhancement of more than 200% when the results were compared with the plain channel. The modified duct may be combined with any other passive augmentation technique which will further lead to performance enhancement.