215 research outputs found
Een experimentele en numerieke analyse van een (in)stationaire stroming in een 2-dimensionaal model van de halsslagadervertakking
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Effect of kinetics on the thermal performance of a sorption heat storage reactor
Full text linkTo reach high solar fractions for solar thermal energy in the built environment, long-term heat storage is required to overcome the seasonal mismatch. A promising method for long term heat storage is to use thermochemical materials, TCMs. In this research, a lab-scale test thermochemical heat storage system is tested experimentally and modeled numerically. Water-zeolite 13X is used as the working pair in an open packed bed reactor. The purpose of this study is to understand the effects of the kinetic parameters for the adsorption of water vapor on zeolite 13X (2 mm spherical beads), on the thermal performance of a sorption heat storage packed bed reactor. A mathematical model is developed incorporating the kinetics model and the isotherm curves and including the heat losses from the side wall of the reactor, and is validated by comparing the calculated temperature profiles with experimental ones from a lab-scale test setup. The numerical and experimental results are used to calculate the heat fluxes in the reactor and are compared to evaluate the thermal performance of the reactor. With the validated model, a parameter study is carried out into the effect of the reaction kinetics and the gas flow rate on thermal performance of a thermochemical heat storage reactor under full scale normal operating conditions. From this work, predictions of the thermal dynamics of an adsorption bed on reactor scale can be achieved, which can and will be used for further studies on the design and optimization of a thermochemical heat storage system
The wake behaviour behind a heated horizontal cylinder
No full textThe behaviour of vortex structures shed from a heated cylinder is experimentally investigated by means of 2-D particle tracking velocimetry. Within this investigation the ReD number was chosen to be 73. The RiD number, the dimensionless number which presents the relative importance of the induced heat, varies between 0 and 1. The experiments were carried out in a large towing tank where the disturbances caused by boundary layers could be minimised. The results show that for small RiD numbers the induced heat results in a deflection of the vortex street in negative y-direction. Within the vortex street a linking of two subsequently shed vortices occurs where the vortex shed from the lower half of the cylinder rotates around the vortex shed from the upper half. These phenomena are assumed to be caused by a strength difference between the vortices shed from the upper half of the cylinder and the lower half. For RiD=1 the effect of the induced heat and buoyancy becomes even more pronounced resulting in a more upwards directed vortex street
Numerical analysis of an optical method to determine temperature profiles in hot glass melts
No full textIn the present study a technique is developed to determine temperature profiles in hot glass melts, using intensity measurements performed at various wavelengths in the infrared spectrum. To that end an analytical model is developed which describes the internal energy transfer in a glass layer and the spectral intensity emerging from the glass layer. The spectral intensity so calculated is confronted with a measured spectral intensity to reconstruct the temperature profile in the glass layer. Because the temperature reconstruction from the measured spectral intensity is an ill posed inverse problem, Tikhonov regularization and the L-curve method are used to determine a meaningful temperature distribution in the glass layer. In order to gain insight into the accuracy of the temperature measurement method a sensitivity analysis is made using numerical simulations. The influence of random noise on the measurement signal and systematic errors in the properties is investigated. Furthermore, the temperature reconstruction of linear, logarithmic and parabolic temperature distributions is analysed
An experimental analysis of the flow field in a three-dimensional model of the human carotid artery bifurcation
No full textSteady flow measurements were carried out in a rigid three-dimensional model of the human carotid artery bifurcation at a Reynolds number of 640 and a flow division ratio of . Both axial and secondary velocities were measured with a laser-Doppler anemometer. In the bulb opposite to the flow divider a zone with negative axial velocities was found with a maximal diameter of about 60% of the local diameter of the branch and a cross-sectional extent of about 25% of the local cross-sectional area. In the bulb the maximum axial velocity shifted towards the divider wall and at the end of the bulb an axial velocity plateau arose near the non-divider wall. Halfway through the bulb, secondary flow showed a vortex through which fluid flowed towards the divider wall near the bifurcation plane and back towards the non-divider wall near the upper walls
The influence of heat on the 3D-transition of the von Karman vortex street
No full textThe wake behind a horizontally mounted heated cylinder with circular cross-section is visualised using an electrochemical tin precipitation method. In the experiments ReD and RiD, both based on main stream properties, were set to 117 and varied between 0 and 1.5, respectively. The wake becomes 3D from RiD˜0.3. For small Richardson values (RiD1), the upward buoyancy force seems to prevent the formation of the coherent vortex structures and the plumes are already formed close behind the cylinder. The spanwise positions at which the plumes originate, are determined by the occurrence of 3D flow structures at the rear end of the cylinder. The distance between these structures is typically 1.8D and independent of the Richardson number
Mixed convective heat transfer in a horizontal bend
No full textThe effect of a developing secondary flow, induced by both centrifugal and buoyancy forces, on heat transfer inside a horizontal curved pipe is studied. The governing equations are solved in a finite element formulation using triquadratic elements for the velocity as well as for the temp. field. The results show that secondary flow considerably increases heat transfe
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