Showing papers in "Forschung Im Ingenieurwesen-engineering Research in 2006"

A powerful way of cooling computer chip using liquid metal with low melting point as the cooling fluid

Abstract: With the improvement of computational speed, thermal management becomes a serious concern in computer system. CPU chips are squeezing into tighter and tighter spaces with no more room for heat to escape. Total power-dissipation levels now reside about 110 W, and peak power densities are reaching 400–500 W/mm2 and are still steadily climbing. As a result, higher performance and greater reliability are extremely tough to attain. But since the standard conduction and forced-air convection techniques no longer be able to provide adequate cooling for sophisticated electronic systems, new solutions are being looked into liquid cooling, thermoelectric cooling, heat pipes, and vapor chambers. In this paper, we investigated a novel method to significantly lower the chip temperature using liquid metal with low melting point as the cooling fluid. The liquid gallium was particularly adopted to test the feasibility of this cooling approach, due to its low melting point at 29.7 °C, high thermal conductivity and heat capacity. A series of experiments with different flow rates and heat dissipation rates were performed. The cooling capacity and reliability of the liquid metal were compared with that of the water-cooling and very attractive results were obtained. Finally, a general criterion was introduced to evaluate the cooling performance difference between the liquid metal cooling and the water-cooling. The results indicate that the temperature of the computer chip can be significantly reduced with the increasing flow rate of liquid gallium, which suggests that an even higher power dissipation density can be achieved with a large flow of liquid gallium and large area of heat dissipation. The concept discussed in this paper is expected to provide a powerful cooling strategy for the notebook PC, desktop PC and large computer. It can also be extended to more wide area involved with thermal management on high heat generation rate.

Fluid flow identification on base of the pressure difference measured on the secant of a pipe elbow

Abstract: The paper presents a new method for indirect flow rate measurement in elbow flow meters. The idea of the method consists in selecting such a Reynolds number value, assumed as a coefficient in fluid flow equations, which fulfils with set accuracy the condition of equality between the measured and the computed pressure difference at the end points of the secant of the elbow arch. The calculus takes into account also the accurate flow geometry, the values of coefficients which describe the thermo-physical properties of the fluid at the measurement temperature, and proper equations of the turbulence model.

CFD analysis of the dynamic behaviour of a pipe system

Abstract: An unsteady flow of viscous-compressible fluid through a pipe system induced by a transient disturbance at the pipe intake is studied by means of ANSYS-CFX Navier-Stokes code. The disturbance is predefined as a time-dependent boundary condition at the pipe inlet. The flow through the pipe is calculated using a system of RANS equations combined with various turbulence models. Based on data obtained by analysing a single straight, circular pipe, advanced systems of three and seven pipes are modeled and systematically analysed. The pressure responses of complex, periodically excited systems are observed under various boundary conditions. Time-domain results are transformed into the frequency-domain in order to determine the frequency content of the dynamic response for each simulation. Considering relevant criteria, an approach is presented for the determination of crucial parameters to enable the evaluation of system operation. An original diagram of such parameters is proposed, which allows convenient evaluation of the performance of various pipe systems.

A method of vehicle active suspension design

Abstract: This paper contributes to the design of active suspension systems, by the use of spatial vehicle model, without filtered feedback of the control system. A method of “stochastic parameters optimisation” has been utilized for the optimisation of the parameters of active suspension. The optimisation objective was simultaneous minimization of sprung mass vibration and standard deviation of forces in tire-to-ground contact area and vehicle handling.

Analysis and optimization of a fixed-tank vehicle

Abstract: This paper attempts to optimize the critical characteristics of a fixed-tank vehicle, with respect to its vertical dynamics. For the description of the vehicle, a linear half-car model with 6 degrees of freedom is implemented, corresponding to its pitch-bounce motion and the suspension characteristics, as well as the equivalent stiffness and damping coefficients of tank’s supports and vehicle suspensions are optimized under various road excitations, with respect to the vertical performance of the chassis and the tank. The BFGS, BOX and Evolution Strategy are the algorithms which are implemented for the optimization tasks.

Cost minimization of 2D continuum structures under stress constraints by increasing commonality in their skeletal equivalents

Abstract: It is well known that, for real-life engineering problems, minimum weight does not necessarily mean minimum cost, thus it is of practical value to simultaneously achieve both layout optimization and cost minimization of a structure. Towards this direction, the present paper discusses a procedure of four steps concerning 2D continuum structures under stress constraints only. The continuum is first substituted by an equivalent skeletal structure, which is then optimized using the Sequential Quadratic Programming (SQP) technique. In the sequel the optimized structural members of equal or near-equal cross-sections are appropriately grouped and finally all optimized structural members of imposed critical minimum or near-minimum cross-section are eliminated. Both grouping and elimination procedures were based on a simple statistical manipulation. The proposed procedure was applied to four test cases, namely the short and long cantilever, the MBB beam and the L-shape beam. The conclusion of the present work was that, for 2D continuum structures under stress constraints only, the proposed procedure provided the means for both layout optimization and structural cost minimization.

Two-dimensional scattering from an impenetrable cylindrical obstacle in an acoustic quarterspace

Abstract: The problem of sound scattering by an infinitely long hard or soft circular cylindrical obstacle suspended near a rigid corner is investigated The separation of variables technique, the appropriate wave field expansions and the method of images along with the translational addition theorem for cylindrical wave functions are used to derive a closed-form analytical solution in form of infinite series The analytical results are illustrated with a numerical example in which the cylindrical obstacle is positioned near the rigid boundary of a water-filled acoustic quarter-space The backscattering form function amplitude and spatial distribution of the total acoustic pressure are evaluated and discussed for representative values of the parameters characterizing the system The effects of incident wave frequency, angle of incidence and proximity of the cylinder to the rigid boundary are examined Limiting case involving an infinite cylinder in an acoustic halfspace is considered and fair agreement with a well-known solution is established

R-410A and R-404A real gas thermodynamic relations and their application for predicting exergy efficiency in vapor compression heat pumps

Abstract: Enthalpy and entropy equations, as these resulted from the Martin-Hou Equation of State, are presented for the promising mixtures R-404A and R-410A that replace the HCFC-22 in refrigerator and heat pump systems. Based on these equations, a model was developed to simulate the relevant thermodynamic heat pump cycle for vapour compression systems. The variation of exergy efficiency factor, COP and exergy flow is outlined. Moreover focusing on the partial derivatives of pressure, on the real gas heat capacity at constant volume and on real gas heat capacity at constant pressure, useful characteristics such as sound velocity and isentropic exponents are derived and plotted in charts, for a wide area of state conditions.

Finite element analysis of transient free convection flow over vertical plate

Abstract: A finite element method is used to study the heat-transfer response of an incompressible, laminar, transient free convection flow over a semi-infinite vertical plate. The non-dimensional governing equations are solved by the finite element method (FEM). The resulting non-linear integral equations are linearized and solved using the Newton–Raphson iteration. The resulting first-order ordinary differential equations with respect to time are solved using the implicit Euler scheme. Numerical results for the details of the velocity and temperature contours and profiles as well as heat transfer rate in terms of Nusselt number which are shown on graphs have been presented.

Messung der Spraycharakteristik zur Bestimmung des Wärmeübergangskoeffizienten bei der Spraykühlung

Abstract: Um die Abkuhlung von Bauteilen durch ein Wasser-Luft-Spray numerisch zu berechnen, ist die Kenntnis des Warmeuberganges notwendig, z. B. in Form des Warmeubergangskoeffizienten. Puschmann hat zur Bestimmung des Warmeubergangskoeffizienten einen empirischen Ansatz ermittelt [1]. Fur diesen Ansatz muss die Wasserbeaufschlagungsdichte sowie die Tropfengeschwindigkeit und die Tropfengrose des Sprays bekannt sein. Fur die Anwendung des Randschichtvergutens aus der Schmiedewarme wurde die Beaufschlagungsdichte mittels Patternatoruntersuchungen ermittelt und Tropfeneigenschaften eines Wasser-Luft-Sprays mittels Phasen-Doppler-Anemometer gemessen. Es wurden Weberzahlen bestimmt, um das Tropfenverhalten beim Auftreffen auf die Bauteiloberflache zu charakterisieren und Warmeubergangskoeffizienten berechnet.

The study of micro scale effects in continuum flows with an experimental set-up with a continuously decreasing characteristic length

Abstract: In order to find out at which length scale Lc micro effects (scaling effects in the continuum range) occur, we designed an experimental set-up with a slender cone (cone angle 14°) imbedded in a sleeve as the geometrical counter part.

Messung des transienten Massenaustrages und der kurzzeitigen thermofluiddynamischen Vorgänge während der Reaktorentlastung

Abstract: Auf der Grundlage einer Differenzmessung der Anderung der Reaktionskraft am Reaktor in Abhangigkeit von der Entlastungszeit unter Ausklammerung der versuchstechnisch inerten Reaktormasse last sich die integral ausgetragene Masse mit einer Genauigkeit von rund 2% wiedergeben. In Verbindung mit einer parallelen, zeitlich hochauflosbaren Messung der Leitfahigkeit des aufwallenden Gemisches vor dem Austragstutzen im Reaktorkopf konnte ein Zusammenhang zwischen den heftigen Schwingungen der Reaktionskraft und den damit einhergehenden Schwankungen bei dem Massenaustrag sowie dem periodisch sich wiederholenden stosweisen Aufwallen des Gemisches aufgrund von Blasenbildung bzw. Verdampfung hergestellt werden.

Konvektionsexperimente mit flüssigkristallinen Tracerteilchen in einem engen vertikalen Spalt

Abstract: Die thermische Konvektion einer Flussigkeit in einem engen vertikalen Spalt wurde mit Hilfe der Flussigkristall-Tracertechnik experimentell untersucht. Dieses optische Messverfahren erlaubt das zweidimensionale simultane Messen von Stromungsgeschwindigkeits- und Temperaturfeld in einer Flussigkeit. Die Untersuchung soll zum Verstandnis des stromungsmechanischen Verhaltens von Flussigkeiten in engen Spalten beitragen, wie sie zum Beispiel in Bioreaktorsystemen vorkommen. Das Problem ist jedoch auch von grundlegendem Interesse hinsichtlich des Warme- und Stofftransports. Gemessene Temperatur- und Geschwindigkeitsfelder der untersuchten Flussigkeiten werden vorgestellt und diskutiert.

Influence of variable fluid properties during in-tube cooling on performance of CO2 refrigeration cycle

Abstract: This present study aims to investigate the influence of variable fluid properties on CO2 tube cooling process. A transient mathematical model for non thermally equilibrium fluid and solid domains is solved by means of finite difference technique. The effect of constant fluid properties assumption on cycle performance is studied. The validity of such assumption is investigated where it is found that it leads to higher gas cooler outlet temperature. The efficiency of the cooler is also affected and will tend the cycle to operate at a erroneous optimum cooling pressure.

Shape and motion reconstruction of non rigid objects from their 2D projections under uniform expansion conditions

Abstract: This paper deals with the 3D-motion and structure reconstruction of a particular class of nonrigid objects based on a sequence of their 2D orthographic projections (images). The investigation focuses on the case where it is known a-pri-ori that the object deforms continuously in a uniform manner performing either expansion or contraction at a constant but, at the same time, unknown rate. Epipolar equations are properly extended to meet the requirements of this particular problem. It is shown that four point correspondences over four views yield a unique solution to motion and structure reconstruction. The theory is supported by a numerical result.