Cornel Suciu

Capillary layer structure effect upon heat transfer in flat heat pipes

The research presented in this paper aimed to determine the maximum heat transfer a heat pipe can achieve. To that purpose the structure of the capillary layer which can be deposited on the walls of the heat pipe was investigated. For the analysis of different materials that can produce capillarity, the present study takes into account the optimal thickness needed for this layer so that the accumulated fluid volume determines a maximum heat transfer. Two materials that could be used to create a capillary layer for the heat pipes, were investigated, one formed by sintered copper granules (the same material by which the heat pipe is formed) and a synthetic material (cellulose sponge) which has high absorbing proprieties. In order to experimentally measure and visualize the surface characteristics for the considered capillary layers, laser profilometry was employed.

Atomization of liquid droplets in multipoint injection

The present paper aims to investigate the atomization process of a liquid that turns into very small drops due to high pressures. Liquid drops in motion encounter a coaxial gas flow of different speed and temperature. It is of interest to study the way the liquid jet first breaks into droplets in the vicinity of the nozzle, and then how the droplet atomization process occurs. The evolution of droplet size and velocity throughout the flow must be determined. It is necessary to make a connection between the mechanisms which start the atomization process and the corresponding environmental conditions. The influences of average droplet diameter, gas velocity and liquid surface tensions in the atomization process are analyzed. It was hypothesized that Rayleigh-Taylor instability occurs as the dominant mechanism for the formation of primary droplets. The present work seeks to eliminate the empirical correlations adopted for the atomization, and to determine droplet size by analytical calculation, based on the working environment parameters.

Modeling of heat transfer in microchannels of a CPU-heat sink cooling system

Electronic equipment cooling processes require development of more and more complex systems. In order to achieve adequate cooling, phenomena like Joule Thomson, Peltier or the thermal tube principle are now employed. Correct Central processing unit (CPU) functioning imposes use of efficient heat exchangers. Experimental investigations showed a different behavior for heat radiators, depending on the flow channels configuration and chosen route for the air circulated by the system fan. For the present study, the adopted mathematical model takes into consideration several aspects, such as flow regime, air viscosity, microchannel physical parameters and characteristics of CPU-cooler interface material. Temperature variations in CPU area were analytically calculated starting from a Holman model, completed by resolution of Fourier equations for a stationary unidirectional regime, with parallel flat walls, and internal heat sources. The CPU was assumed to generate all the heat. A CPU cooling system behavior was investigated using a heat transfer model, created in ANSYS, for the above-mentioned conditions.

Optical investigation of electromagnetic fuel atomizers

The devices that ensure atomization of fluids (injectors and atomizers) are largely employed in contemporary technology. Injectors play a very important part in the functioning of various systems based on combustion of liquid fuels, such as internal combustion engines and turbines, jet engines, furnaces etc. During operation, these devices are subjected to important pressures and need to work within very strict parameters. It is therefore important to have very precise active surfaces. The present work aimed to investigate such devices after certain degrees of usage in order to verify the evolution of surface micro-characteristics and their influence upon operating parameters. In order to achieve the abovementioned purpose, an optical evaluation of the surface was conducted using laser profilometry. Surface measurements were conducted on several injectors, after various degrees of usage, by aid of a laser profilometer equipped with a confocal sensor that has a vertical working range of 13mm and a resolution of 1μm1. After the surface micro-topography was measured, 3D and 2D representations, as well as individual profiles of the active surfaces, were analyzed and the significant parameters were determined. Surface wear and presence of combustion residues was analyzed in terms of its influence upon operating conditions.

A new mechatronic set-up and technique for investigation of firearms

Since ancient times, mankind has manifested interest in the development and improvement of weapons, either for military or hunting purposes. Today, in competition with these legal practices, the number of those who commit crimes by non-compliance with the regime of weapons and ammunition has increased exponentially. This is why the technology and methods employed in the area of judicial ballistics, requires constant research and continuous learning. The present paper advances a new experimental set-up and its corresponding methodology, meant to measure the force deployed by the firing pin. The new experimental set-up and procedure consists of a mechatronic structure, based on a piezoelectric force transducer, which allows to measure, in-situ, the force produced by the firing pin when it is deployed. The obtained information can further be used to establish a correspondence between this force and the imprint left on the firing cap. This correspondence furthers the possibility of elaborating a model that would permit ballistic experts to correctly identify a smoothbore weapon.

Investigations upon the effects of an auxiliary brake system on the working parameters of diesel engines

Classical systems have the main disadvantage of being unable to ensure that high load diesel engine vehicles are slowed in good conditions, for the entire range of combinations of inclinations and lengths of sloped public roads. On such roads, where brakes are used repeatedly and for long periods, friction components that enter classical braking systems will overheat and lead to failure. The present paper aims to investigate, the efficiency of a braking system based on compression release, called a Jake Brake. In such a system, the exhaust valve is actuated at a certain predetermined angle of the crankshaft. The presented research was conducted on an experimental rig based on a four-stroke mono-cylinder diesel engine model Lombardini 6 LD400. Pressure and temperature evolutions were monitored before and during the use of the Jake Brake system. As the generated phonic pollution is the main disadvantage of such systems, noise generated in the vicinity of the engine was monitored as well. The monitored parameters were then plotted in diagrams that allowed evaluating the performances of the system.

Measurement strategy and analytic model to determine firing pin force

As illustrated in literature, ballistics is a branch of theoretical mechanics, which studies the construction and working principles of firearms and ammunition, their effects, as well as the motions of projectiles and bullets1. Criminalistics identification, as part of judiciary identification represents an activity aimed at finding common traits of different objects, objectives, phenomena and beings, but more importantly, traits that differentiate each of them from similar ones2-4. In judicial ballistics, in the case of rifled firearms it is relatively simple for experts to identify the used weapon from traces left on the projectile, as the rifling of the barrel leaves imprints on the bullet, which remain approximately identical even after the respective weapon is fired 100 times with the same barrel. However, in the case of smoothbore firearms, their identification becomes much more complicated. As the firing cap suffers alterations from being hit by the firing pin, determination of the force generated during impact creates the premises for determining the type of firearm used to shoot the respective cartridge. The present paper proposes a simple impact model that can be used to evaluate the force generated by the firing pin during its impact with the firing cap. The present research clearly showed that each rifle, by the combination of the three investigated parameters (impact force maximum value, its variation diagram, and impact time) leave a unique trace. Application of such a method in ballistics can create the perspectives for formulating clear conclusions that eliminate possible judicial errors in this field.

Friction coefficient influence upon fluid jet atomization

The work presented herein illustrates the differences between aerodynamic friction coefficients of liquid droplets of different shapes and dimensions that come into contact with air. Aerodynamic friction forces on a drop can be calculated if the aerodynamic coefficient of friction and cross-sectional area normal to the flow are known. The crosssectional area can be calculated on the basis of the maximum diameter of the droplet, dc, if it is assumed that the deformed droplets have the form of a flattened spheroid. According to Clift et al[6], when a drop of liquid has weak internal tensions or high surface tension due to viscosity, external flow may differ from the surrounding liquid drop at the same Reynolds number. Internal tensions that exist in most systems of practical importance are negligible compared to surface tension. Given the fact that the ratio of the viscosity of the liquid and the gas jet spray is significant, we can assume that internal circulation is an important parameter.

Roughness effect upon the flow of R134a refrigerant through rectangular microchannels

The present paper investigates the impact of rectangular micro-channel surface quality upon the flow of R134 refrigerating agent over a rectilinear stretch. For the present investigations, heat exchangers were built from copper plates in which rectangular micro-channels were manufactured. The surface of each region containing micro-channels was accurately mapped by aid of laser profilometry and surface quality parameters were determined, including surface roughness. As micro-channel dimensions are a few tens of micrometers and surface roughness can in some cases of refrigerant flow, reach significantly close values, it is interesting to evaluate roughness influence upon flow speed. The flow regime has an important influence upon mass flow and heat transfer. It is important to study roughness influence upon the non-continuum effect, as pressure rises in the micro-channel (reaching maximum values up to 17·105 Pa).

Applications of magneto-rheologic fluids in semi-active suspension systems

The present paper aims to investigate the impact of using magneto-rheologic fluids in semi-active suspension systems. For that purpose, the suspension system behavior will be analyzed in the case of dynamic control. It is verified whether a semi-active suspension system that uses magneto-rheologic fluids offers significant advantages by report to passive suspension systems. Two approaches were considered. The first one consisted of simulating both passive and semiactive suspension systems using Matlab Simulink. The conducted simulations yielded results for motion, speed, and accelerations of sprung and un-sprung masses. The second approach consisted of building an experimental set-up that uses a damper that is constructively contains a magneto-rheologic fluid, to which an adjustable variable magnetic field can be applied by means of a coil, in its turn controlled in current by a driver. The driver receives its excitation signals from sensors put in contact to the road surface model. The experimental set-up was conceived so that the un-sprung mass follows the road bumps. Simulation results were then compared to experimental ones.