Sajad Alimohammadi

• PhD
• Lecturer at Technological University Dublin

A wall-bounded dual jet is formed through combining a wall jet, flowing directly adjacent to a solid wall, with a parallel, co-flowing offset jet. The combination of a wall and offset jet in this manner is commonly encountered across many industrial applications, such as electronics cooling, wastewater evacuation, and noise suppression technologies...

A wall bounded dual jet is the combination of a wall jet, flowing adjacent to a solid boundary, and a second parallel flowing jet offset from the boundary by some distance. The dual jet flow is distinctly different to that of either wall or offset jet, particularly in the region near the jet exit plane. This study represents just the 2nd experiment...

The demand for rapid, high-quality, and controlled mixing at the microscale has led to the development of various types of micromixers. Micromixers are commonly categorised as active, or passive based on whether they utilise external energy to enhance mixing. Passive micromixers utilise a complex geometry to enhance the diffusion coefficient at low...

This numerical study investigates the impact of a pair of adjacent micro synthetic jets on fluid dynamics inside a microchannel. Both the presence and absence of cross flow are considered. The oscillatory movement of a membrane, causing fluid ejection and ingestion through orifices, leads to generating a zero net mass flux jet. This synthetic jet c...

A dual jet system, comprising a wall jet flowing tangential to a solid wall and a parallel offset jet, possesses a unique flow field that has proven advantageous in many industrial applications. Despite this, investigations of dual jets are severely underrepresented in the published literature, meaning their flow and heat transfer characteristics a...

The miniaturization of electronic packages and their associated high-power density circuits requires more innovative cooling solutions. Single phase pulsating flows offer a promising solution due to their disruption of the thermal boundary layer. This study aims to bridge the knowledge gap by using experimental and computational methods to investig...

A dual jet flow comprises a wall jet, discharged immediately parallel to a solid boundary, flowing alongside a parallel jet whose exit is offset from the solid boundary by some distance. Despite the widespread industrial application of dual jet flows, experimental analysis of their flow and heat transfer characteristics is severely underrepresented...

The miniaturization of electronic devices and the rapid increase in heat flux from faster and more powerful processors have raised concerns regarding adequate cooling and thermal management solutions. The present experimental work investigates the thermophysical characterization of a sessile evaporating droplet using thin-foil thermography. This st...

The development of current and next generation high performance electronic devices has led to miniaturization in more densely packed spaces. The increasing power levels has resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Implementation of single-phase cooling systems u...

Dual jet flow is a topical area of research due to their wide range of current and potential uses in industry. Despite this, there is still a lack of published studies which focus on the characterization of dual jet flow, particularly regarding their heat transfer capabilities. The objective of this investigation is to therefore build upon the avai...

The development of current and next generation high performance electronic devices has led to smaller components in more densely packed spaces. The increasing power levels have resulted in ever-increasing heat flux densities which necessitates the evolution of new liquid-based heat exchange technologies. Pulsating flow in single-phase cooling syste...

The use of dual jets in industry is widespread, yet the characterisation of dual jet flow remains relatively underrepresented in the published literature. As such, the flow mechanisms and heat transfer capabilities of dual jets is not fully understood, meaning it is not possible to accurately control or optimise their behaviour towards specific app...

While numerous applied studies have successfully demonstrated the feasibility of unsteady cooling solutions, a consensus has yet to be reached on the local instantaneous conditions that result in heat transfer enhancement. The current work aims to experimentally validate a recent analytical solution (on a local time-dependent basis) for the common...

This research is part of a comprehensive study to determine reformative actions for cooling regimes within the Irish data centre market. To achieve this goal, preliminary Exergy, Entropy change and operational cost analyses were used. It is determined that there is no clear advantage for using one cooling method over another without knowing the dat...

The ever rising heat fluxes encountered in electronic devices present a challenging thermal engineering problem. Not only is heat transfer enhancement a goal but more recently control of the enhancement is desired, especially in large scale data facilities where the heated outlet coolant fluid may be of use. Flow pulsation is one of the most common...

Genetic algorithms (GAs) are considered to be one of the main types of evolutionary algorithms (EAs) and are being increasingly used in various engineering design applications. To a large extent, plate-fin heatsinks are used in the thermal management of compact electronic equipment and data centers. The shape optimization of the heatsinks is not ri...

The rapid global increase in energy consumption by data centres requires new improved cooling solutions and techniques to be developed and implemented. In a typical data centre, approximately a third of the total power consumption is needed for the cooling infrastructure, resulting in high power usage effectiveness (PUE) values. The main culprits o...

The authors wish to make the following corrections to this paper [...]

Synthetic jet actuators (SJA) are emerging in various engineering applications, from flow separation and noise control in aviation to thermal management of electronics. A SJA oscillates a flexible membrane inside a cavity connected to a nozzle producing vortices. A complex interaction between the cavity pressure field and the driving electronics ca...

Pulsating flow has potential for enhanced cooling of future electronics and photonics systems. To better understand the mechanisms underlying any heat transfer enhancement, it is necessary to decouple the mechanical and thermal problems. The current work performs a parametric analysis of the flow hydrodynamics using particle image velocimetry (PIV)...

Traditional plate-fin heatsinks are used in abundance in data centres and telecommunication systems for electronic integrated circuit and component cooling, without much regard for geometric shape optimisation. Any improvements in the effectiveness of the heatsinks impacts the energy consumed by the information communication and technology (ICT) ce...

Air-based convective cooling of electronic components is facing a dual challenge: (i) an increasing cooling demand and (ii) a drive towards weight reduction. For many electronic components, plate-fin heat sinks are chosen to dissipate the generated heat. The first objective (i) can be approached using shape optimisation, however, the weight-saving...

Plate-fin heat sinks are used as a passive cooling technique to dissipate the heat generated by high power electronic components such as power amplifiers in wireless telecommunication hardware. There has been an increasing demand for cooling performance enhancement, and this could be achieved using numerical shape optimisation. Here, computational...

Flow vectoring by a pair of synthetic jets is suitable for modification of the global flow characteristics with practical applications in active flow control and adaptive heat convection. The interaction of a pair of synthetic jets, with a separation distance s = 3.3D, stroke length L0 = 29D, and Reynolds number Re = 300, are investigated numerical...

This paper presents a comprehensive numerical–experimental study performed on unsteady impinging jets with flow pulsation and builds on an experimentally validated numerical Reynolds-averaged Navier Stokes (RANS) CFD model for fluid flow and heat transfer simulations of steady impinging jets. The model accounts for intermittent pulsation with a squ...

Synthetic jets have become an interesting method of electronic cooling recently, resulting in continued research activities in this field. A pair of adjacent synthetic jets is investigated numerically using computational fluid dynamics and experimentally using particle image velocimetry. The investigation covers the free adjacent synthetic jets (ca...

Impinging jet flows are used in various cooling, heating, drying and flow control applications, from electronic equipment cooling to active flow control over airfoils and bluff bodies. Unsteady impinging jet flows, such as pulsating and synthetic jets, can yield an additional enhancement in heat transfer rate compared to steady flow, however accur...

Pulsating flows can yield an additional enhancement in heat transfer rate compared to steady flows; however numerical modeling of pulsating jet impingement remains challenging. There is no clear consensus in the literature on (i) the most reliable computational methodology for this case, and (ii) the magnitude and dependencies of the heat transfer...

The existing methods of heat removal from compact electronic devises are known to be deficient as the evolving technology demands more power density and accordingly better cooling techniques. Impinging jets can be used as a satisfactory method for thermal management of electronic devices with limited space and volume. Pulsating flows can produce an...

This paper presents a computational fluid dynamics (CFD) methodology to accurately predict the heat transfer characteristics of an unconfined steady impinging air jet in the transitional flow regime, impinging on a planar constant-temperature surface. The CFD methodology is validated using detailed experimental measurements of the local surface hea...

The aim of this paper is to develop the technical knowledge, especially the optimum geometries, for the design and manufacturing of a supersonic gas–gas ejector for a waste-heat driven vehicle cooling system. Although several studies have been performed to investigate the effects of geometrical configurations of gas–gas ejectors, a progressive desi...

The idea of replacing vapor jet refrigeration system instead of conventional vehicle cooling system is the main goal of a comprehensive study. First part of this study is reported in this paper. The ejector is the heart of these systems, and its optimum design is critically important to the coefficient of performance (COP) of the whole system. Firs...

In order to make the engine operate in a high performance and more environmentally friendly process, other fuels can be used instead of gasoline. In this paper, a comparison among six prevalent fuels, Methanol, Ethanol, Gasoline, Methane, Ethan, and Propane, in a spark ignition internal combustion engine is studied. A computational code is prepared...