Characterization of a short microchannel device for surface cooling

The development of microchannel devices is expanded widely due to the demand for small scale electronic devices. In order to increase the capability of the electronic devices, high heat transfer performance with low energy consumption cooler is required. This study is focusing on the characterization of new short microchannel for surface cooling purposes with the channel dimension of 800 µm wide, 200 µm length, 100 µm depth and total area of one cm2. Deionized water is used as the transport medium. A map of microchannel characteristics is plotted in term of average thermal resistance, pumping power, power supplied and mass flow rate of the fluid. From this mapping, it is shown that the thermal resistance decreased as the pumping power decreased. The results also show that the heat flux has not affected the value of pumping power. The different for each heat flux value is ranged between 3 to 4 %. The mapping presented in this study provides potential characteristics information and conditions to apply this particular microchannel for surface cooling

Flame propagation and burning rates of methane-air in a closed combustion vessel

The propagation and burning rates of methane-air mixtures were investigated at initial atmospheric pressure with temperature range of 298-302K and equivalence ratio range of 0.8 to 1.3. Experiments were performed in a cylindrical constant volume combustion chamber where the mixture is ignited by centrally located electrodes. The images of spherically expanding flame were observed and recorded using schlieren photography technique with high speed camera system. Analysis of the flame area yield flame radii and further burning rates in term of outwardly flame speed propagation can be calculated. Results shows that smooth spherical flames were observed throughout the flame propagation for all equivalence ratios. The fastest flame propagation was recorded at equivalence ratio 1.0 and 1.2. In addition, flame speed of each equivalence ratio exhibits small fluctuation probably arising from acoustic disturbance. This disturbance becomes more apparent at higher equivalence ratio

Numerical investigation of rectangular twisted hole on film cooling for gas turbine blades

This paper investigates a new method of film cooling using swirling coolant flow through a rectangular twisted film cooling holes with spirally corrugated tube. Two different air flows with different in temperatures were used in this study. Throughout the investigation, blowing ratio was varied from 0.5 to 2.0 with several configuration of rectangular twisted angle of 0°, 90°, 180°, 270° and 360°. The results of cooling effectiveness obtained were compared against a standard untwisted tube. Results show that the overall thermal effectiveness improved significantly when the temperature difference between the air flows is at 25 degrees. Such improvement is supported by heat transfer enhancement that obtained from 19% to 57%. Based on the findings, the study concludes that using a simple geometry of film cooling hole with specific twisted configuration may result to improve the convective heat transfer coefficient

Design and development of auxiliary components for a new two-stroke, stratified-charge, lean-burn gasoline engine

A unique stepped-piston engine was developed by a group of research engineers at Universiti Teknologi Malaysia (UTM), from 2003 to 2005. The development work undertaken by them engulfs design, prototyping and evaluation over a predetermined period of time which was iterative and challenging in nature. The main objective of the program is to demonstrate local R&D capabilities on small engine work that is able to produce mobile powerhouse of comparable output, having low-fuel consumption and acceptable emission than its crankcase counterpart of similar displacement. A two-stroke engine work was selected as it posses a number of technological challenges, increase in its thermal efficiency, which upon successful undertakings will be useful in assisting the group in future powertrain undertakings in UTM. In its carbureted version, the single-cylinder aircooled engine incorporates a three-port transfer system and a dedicated crankcase breather. These features will enable the prototype to have high induction efficiency and to behave very much a two-stroke engine but equipped with a four-stroke crankcase lubrication system. After a series of analytical work the engine was subjected to a series of laboratory trials. It was also tested on a small watercraft platform with promising indication of its flexibility of use as a prime mover in mobile platform. In an effort to further enhance its technology features, the researchers have also embarked on the development of an add-on auxiliary system. The system comprises of an engine control unit (ECU), a directinjector unit, a dedicated lubricant dispenser unit and an embedded common rail fuel unit. This support system was incorporated onto the engine to demonstrate the finer points of environmental-friendly and fuel economy features. The outcome of this complete package is described in the report, covering the methodology and the final characteristics of the mobile power plant

Flameless combustion of propane-air mixture in a laboratory scale burner

In this work, the operational and emission of the laboratory scale burner under the flameless combustion regime using propane is examined. The combustor is equipped with parallel jet burner systems with controlled gas fuel and oxidizer. The combustor consists of several ports that are used to measure temperature variation and analyze gas emission. The atmospheric air was heated by flowing it inside the chamber until the air temperature increased to approximately the auto ignition temperature of the fuel. The furnace under investigation has successfully produced temperature uniformity ratios that are one order of magnitude less than such of the visible flame mode. It is observed that, flameless combustion can be achieved by using propane as a fuel. The value of NOX emission during flameless combustion was reduced of about 70% in average compared to the conventional flame at certain range of equivalence ratio

Fundamental studies of combustion of droplet and vapour mixtures

There are few experimental data of a fundamental nature that clearly demonstrate the similarities and differences in burning rates between single phase and two phase combustion, either in laminar or turbulent conditions. Such data are essential towards a better understanding of the spray combustion phenomena as well as a whole system. In the present study, experimental investigations of combustion of droplet and vapour air mixtures under quiescent and turbulence conditions have been conducted in a fan stirred combustion vessel. Aerosols were generated by expansion of gaseous pre-mixture to produce a homogeneously distributed suspension of fuel droplets. Spherically expanding flames following central ignition were employed to quantify the flame structure and propagation rate. The effect of droplets on flame propagation was investigated by comparing the burning rate of gaseous mixtures at initial pressure and temperature close to those of aerosol mixtures. In quiescent conditions, aerosols of two different fuels, isooctane and ethanol, were investigated at near atmospheric conditions. The effect of fuel droplets, up to 31 J.1m diameter, on laminar flame propagation was examined at a wide range of equivalence ratios. In the early stages of flame development, inertia of fuel droplets leads to local enrichment in equivalence ratio which increases the initial burning rate of lean aerosols but decreases that of rich ones. For the later stages of flame propagation, the presence of liquid droplets causes earlier onset of instabilities and cellularity than for gaseous flames, particularly at rich conditions. This leads to an enhanced burning rate and is probably due to heat loss from the flame and local disturbances due to droplet evaporation and subsequent diffusion processes. In turbulent studies, the effect of isooctane droplets up to 14 J.1m in diameter on flame propagation was examined at various values of root mean square turbulence velocities between zero and 4.0 mls. It is suggested that during early flame development, the turbulence was found to induce droplet motion before flame initiation which dominated over those resulting from the flame, negating the effect of droplet inertia. In the later stages, the presence of droplets in a low turbulent flame resulted in a significant burning rate enhancement. However, this enhancement became progressively less important as turbulent wrinkling became dominant. Between low and high turbulence, there was a transition regime between instability dominated and turbulence dominated regimes. As a consequence, the burning rate enhancement due to droplets under this transition range was rather complex

Pressure rise generation by the combustion of methane-air in a closed vessel

Experimental investigations were made to measure the variation of pressure development in a confined space at different equivalence ratio of methane-air combustion. A cylindrical vessel combustor that correspond to spherically expanding flame is used in this experiment. The experiment is subjected for only premixed methane-air mixture from five different equivalence ratio,Φ which are lean (0.7, 0.8), stoichiometric (1.0) and rich (1.2, 1.4). The instantaneous and maximum pressure were recorded using dynamic pressure transducer. The result of pressure profile at stoichiometry condition was compared with the previous work by other researcher. Based on the experimental investigation, the trend line of the buildup pressure profile at various equivalence ratio in this experiment is similar as obtain in previous work done in whichshows increment as the equivalence ratio moves from lean to slightly rich mixture. However it will eventually decrease when the mixture is too rich. The knowledge of maximum pressure can further be used to interpret the burning velocity of flame propagation

Characterisation of aerosol combustible mixtures generated using condensation process

An accidental release of a liquid flammable substance might be formed as an aerosol (droplet and vapour mixture). This phenomenon might be due to high pressure sprays, pressurised liquid leaks and through condensation when hot vapour is rapidly cooled. Such phenomena require a fundamental investigation of mixture characterisation prior to any subsequent process such as evaporation and combustion. This paper describes characterisation study of droplet and vapour mixtures generated in a fan stirred vessel using condensation technique. Aerosol of isooctane mixtures were generated by expansion from initially a premixed gaseous fuel-air mixture. The distribution of droplets within the mixture was characterised using laser diagnostics. Nearly monosized droplet clouds were generated and the droplet diameter was defined as a function of expansion time. The effect of changes in pressure, temperature, fuel-air fraction and expansion ratio on droplet diameter was evaluated. It is shown that aerosol generation by expansion was influenced by the initial pressure and temperature, equivalence ratio and expansion rates. All these parameters affected the onset of condensation which in turn affected the variation in droplet diameter

Effect of diluted and preheated oxidizer on the emission of methane flameless combustion

In combustion process, reduction of emissions often accompanies with output efficiency reduction. It means, by using current combustion technique it is difficult to obtainlow pollution and high level of efficiency in the same time. In new combustion system, low NOxengines and burners are studied particularly. Recently flameless or Moderate and Intensive Low oxygen Dilution (MILD) combustion has received special attention in terms of low harmful emissions and low energy consumption. Behavior of combustion with highly preheated air was analyzed to study the change of combustion regime and the reason for the compatibility of high performance and low NOx production. Sustainability of combustion under low oxygen concentration was examined when; the combustion air temperature was above the self-ignition temperature of the fuel. This paper purposes to analyze the NOx emission quantity in conventional combustion and flameless combustion by Chemical Equilibrium with Applications (CEA) software

Early flame development in the combustion of droplet and vapour mixtures

Experimental investigations of combustion of droplet and vapour mixtures under quiescent condition have been conducted in a closed combustion vessel. Droplet and vapour mixtures or aerosol mixtures were generated by expansion of iso-octane gaseous pre-mixture to produce a homogeneously distributed suspension of fuel droplets. The aerosol mixtures were ignited centrally in the combustion vessel and the flame development was recorded by schlieren photography. The effect of fuel droplets in the early stage of flame propagation was investigated by comparing the flame structure and flame speed of gaseous mixtures at identical conditions. Comparison between gaseous and aerosol flame have shown quantitatively that the presence of fuel droplets causes earlier onset of instabilities and cellularity than for gaseous flames, particularly at rich conditions. This difference was shown to be a function of droplet size and overall equivalence ratio. It is suggested that these factors lead to vary the local equivalence ratio which increases the initial burning rate of lean aerosols, but decreases that of rich ones