Transfer Phenomena in Fluid and Heat Flows

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Authors: Ivan Kopal, Pavel Koštial, Zora Jančíková, Jan Valíček, Marta Harničárová
Abstract: This paper aims to study the cooling of a solid body. An analytical analysis of a solid body cooling in different regimes is presented, such as a simple first order exponential model, a modified exponential model, a generalized exponential model and the so-called regular temperature regime. The analysis also includes the influence of the dynamically changing relaxation time and we also present the solution of the nonlinear heat equation.
Authors: D. Ramasamy, K. Kadirgama, M.M. Noor, M.M. Rahman
Abstract: Current engines are readily available for CNG bi-fuel conversions because it requires only minor engine modifications. However, CNG flame speed is lower than gasoline, therefore reducing the power and range of the vehicle when operating on CNG. This situation can be improved by increasing the flame speed via higher turbulence generated by swirl motion. A computational fluid dynamics (CFD) model was used to analyse the swirl generated by dissimilar valve lift (DVL) profiles on the intake valve. A 3D engine simulation shows differences in swirl motion and turbulence between the original symmetric valve lift profile and the DVL. The swirl before combustion was found to increase almost 25%. The higher swirl number can increase the turbulence kinetic energy (TKE) level which improves better fuel mixing. The 1 mm DVL proved to be the better choice from CFD analysis and later was tested on a K3-VE engine. Pressure analysis shows peak pressure increased by 5.6% and burn rate shows CNG had a slower burning speed on the small engine
Authors: Sheng Yung Tseng, Shang Wen Hsu, Cheng Hsiung Kuo
Abstract: The time-averaged flow characteristics in the regions upstream and downstream of the side-by-side cylinders of diameter ratio two, arranged at different longitudinal alignments and two gap ratios, are studied via particle image velocimetry (PIV). It is found that the locations of forward stagnation point of the large and the small cylinders do change with the longitudinal alignments. Upstream of the large cylinder, the streamwise variations of U* are nearly independent of the longitudinal alignment for both T*=1.5 and 1.0. However, upstream of the small cylinder, the streamwise variations of U* indeed depend on T*. Upstream of the small cylinder, the streamwise variations of V* are strongly affected by T* and, the largest magnitude of V* occurs at CLA for both T*=1.5 and T*=1.0. Also, the locations of the largest magnitude of V* move closer to the small cylinder as the T* reduces. For different T* and L*, the flow rate (or the averaged velocity through the gap) and the gap orientation will be changed at the same Reynolds number (Re=1000). The effect of pressure difference across the gap may be overwhelmed or be counterbalanced by that of the gap orientation leading to quite different flow structures in the downstream region of the cylinder couples. The effects of longitudinal alignment are to (1) change the forward stagnation points of the large and the small cylinders; (2) modify the region of mutual interaction between two wakes. (3) As S* reduces, the gap orientation takes the dominance over the pressure difference across the gap to switch the gap flow so that the wide-wake is formed behind the small cylinder especially for T*=1.0 and TEA.
Authors: Kwon Se Kim, Doo Seuk Choi
Abstract: Using an analytical model, a clear investigation was performed into the phenomenon of decreasing overall pressure and velocity of a plunger when its stroke within a natural gas injector changes. The results indicated the following mesh sizes from the mesh matrix: 0.0005 mm minimum, 12.7 mm maximum, 1,107,420 nodes, and 5,856,567 elements. Consequently, the pressure was affected by the stroke height from the designed plunger shape, and although the height of the plunger stroke changes over 0.150 mm, the absence of the phenomenon of pressure drop was noticeable.
Authors: Takeji Arai
Abstract: A laser beam with a fixed diameter emitted from an oscillator acts as a heat-spot (or hot-spot by the heat source) on the surface of the material that irradiates. The shape of the heat-spot on the material has been treated as constant for a long time, regardless of the speed of the material to be processed. In fact, on the surface of the material the light and the material mutually act on each other, so the shape of the heat-spot which appears on the surface many vary depending on the processing speed. In order to confirm this, an experiment was performed using infrared sensors sheet, and using a galvanized steel sheet. The experiment confirmed that the shape of the heat-spot on the material surface depends on the processing speed. The decreasing ratio of deformation with respect to the speed was determined, and it was applied to high-speed cutting processing with a fiber laser. We also studied the rate of change of the preheating-area and the removal-area in the heat-spot which is an important domain when performing high-speed cutting.
Authors: Milena Kušnerová, Ivan Kopal, Vojtěch Václavík, Lukáš Gola, Tomáš Dvorský, Jan Valíček, Marta Harničárová, Vojtěch Šimíček
Abstract: This article presents the results of an experimental research dealing with the measurement of the thermal characteristics of concretes based on natural and artificial aggregates (steel slag). The samples of concrete composites were prepared on the basis of natural aggregate fractions 0/4, 4/8 and 8/16 mm and on the basis of steel slag fr. 4/8 mm. The volume ratio of the individual aggregate fractions in all experimental mixtures used for the production of concrete composites was 40:30:30 (fr. 0/4: 4/8: 8/16). The prepared samples of concrete composites based on natural aggregate and natural aggregate combined with steel slag were subjected to the tests of strength characteristics, water-tightness, thermal characteristics using a commercial device ISOMET 2104 (measurement of the coefficient of thermal conductivity λ, specific heat capacity c, and the coefficient of thermal diffusivity a), and heating in a prototype calorimetric computer-controlled chamber. The main attention was focused on the testing of the value changes of the coefficients of thermal conductivity λ depending on the changes of temperatures within the range of -5 °C to + 40 °C. The measurements of these thermal characteristics have very high informative value, especially because these material parameters are not tabulated for the newly designed building materials, and that is why they are not examined at extreme temperatures. This is a reason why they cannot be used as important data during the thermal calculations of a non-insulated concrete structure (e.g. using polystyrene and / or glass wool).
Authors: Marta Harničárová, Zuzana Mitaľová, Milena Kušnerová, Jan Valíček, Dušan Mitaľ, Ivan Kopal, Vojtěch Václavík
Abstract: Wood plastic composite (WPC) materials represent modern materials that are attracting interest worldwide. WPC are composite materials and they have properties of both components – plastic and wood. WPC materials are formed by combining two substances – discontinuous reinforcements (wood particles or cellulose microfibers) and a continuous binder (plastic matrix), in a certain proportion. The authors describe WPC machined surfaces after turning. On the basis of a set of experimental data collected by surface and mechanical tests obtained from the WPC materials, the mechanical deformation work was evaluated, the value of which presents specific information about the material as a specific material coefficient.
Authors: Juan Alejandro Flores-Campos, J.A. Perrusquía Guzmán, Juan Alfonso Beltrán-Fernández, Luis Héctor Hernández-Gómez
Abstract: In this paper the problem of guiding a parabolic trough solar concentrator through a system based on a water displacement mechanism is addressed. The actuator mechanism consists of a set of four on/off electrovalves in ”H-bridge” configuration, a small water pump, a sun sensor and two containers half-filled with water, installed on the side ends of the concentrator. To guide and balance the concentrator, a sliding mode controller (SMC) to enable / disable the opening and closing of the valves that control the direction and flow of water between the two containers is proposed. The validity of the implementation of the proposed law of control applied to the actuator mechanism is verified with stability analysis and simulation results.
Authors: Bin Xian Shen, Wei Qiang Liu
Abstract: Platelet mixer is a type of high-efficient equipment which can mix fluids through platelet micro-channels by cross-bedded injection. It overcomes disadvantages that the fluid is centralized around the inlet and it improves the diffusion. In this work, the platelet mixer is used for pre-mixer in a rocket engine, and the diffusion of oxygen and air in pre-mixer is analyzed. The high speed jet leads to a strong shear force near the inlet which produces counter-rotating stream-wise vortices around the jet. The angle between the direction of jet and radial direction influences both the stream-wise vortices and diffusion. The vortices intensity increases as the angle increase from 0o to 20o.

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