Key Engineering Materials Vol. 597

Abstract: Natural convection in inclined cubic cavity, discretely heated, is studied numerically using a three-dimensional finite volume formulation. Two heating square portions are placed on the vertical wall of the enclosure, while the rest of the considered wall is adiabatic. These sections, similar to the integrated electronic components, generate a heat flux q". The opposite vertical wall is maintained at a cold uniform temperature Tc and the other walls are adiabatic. The fluid flow and heat transfer in the cavity are studied for different sets of the governing parameters, namely the Rayleigh number Ra (10³ ≤ Ra ≤ 10⁷), the cavity inclination γ (- 45° ≤ γ ≤ 45°) and the position of the heating sections λ (0.3 ≤ λ ≤ 0.7). The dimensions of the heater sections, ε = D / H and the longitudinal aspect ratio of the cavity Ax = H / L are respectively fixed to 0.35 and 1.

Abstract: The paper discusses the concept of single-parameter operational control of turbomachinery, with particular application for hydraulic turbines for power management facilities, subject to varying operating parameters, where load control is additionally facilitated by changing rotational speed.

Abstract: Nanofluids are expected to enhance heat transfer in many thermal systems. Present efforts are concentrated on boiling heat transfer of nanofluids, although single phase convection is of key importance in various appliances such as car radiators or heating systems. This paper presents experimental results of heat transfer during free convection of water-Al₃O₃ nanofluid from horizontal tube covered with metallic porous coating. Contrary to theoretical considerations deterioration of heat transfer was observed.

Abstract: Wetting is the interaction of a liquid with a solid and is found in numerous natural processes as well as being of extreme importance to many industrial and engineering processes, such as absorption, distillation, flotation, gas scrubbing, condensation. Wetting is of key importance in boiling process, because contact angle, that is the measure of the degree of wetting, affects density of active nucleation sites, bubble departure diameter, and finally critical heat flux [. If the liquid will completely spread out on the solid surface and the contact angle will be close to zero degrees, the surface is called superhydrophilic. Less hydrophilic surfaces will have contact angle below 90o. If the surface is hydrophobic, the contact angle will be larger than 90o. Surfaces with contact angle larger than 150o are called superhydrophobic Fig. 1.

Abstract: As part of a cluster project in the Aerospace research cluster at the Hochschule Bremen, the model rotor blade of a wind turbine is to be aerodynamically optimized with a more effective stall barrier. The flow element to be developed should provide very effective interruption of the radial flow on the rotor blade. A combination of this flow element and the "Splitflap" flow element allows the aerodynamic efficiency of the rotor blade to be further improved.

Abstract: In the course of the research aiming on the optimisation of beer fermentation, a large number of fermentations have been performed under various boundary conditions. We carried out different measurements, including temperature and velocity investigations. Due to turbidity, the latter cannot be performed easily by using common techniques like laser Doppler anemometry or particle image velocimetry. Therefore the ultrasound Doppler velocimetry got utilised. It permits measurements in opaque fluids and provides velocity fields for any time during the fermentation.

Abstract: One of the key challenges on the area of energy engineering is the system development for increasing the efficiency of primary energy conversion and use. An effective and important measure suitable for improving efficiencies of existing applications and allowing the extraction of energy from previously unsuitable sources is the Organic Rankine Cycle. Applications based on this cycle allow the use of low temperature energy sources such as waste heat from industrial applications, geothermal sources, biomass, fired power plants and micro combined heat and power systems.Working fluid selection is a major step in designing heat recovery systems based on the Organic Rankine Cycle. Within the framework of the previous original study a special tool has been elaborated in order to compare the influence of different working fluids on performance of an ORC heat recovery power plant installation. A database of a number of organic fluids has been developed. The elaborated tool should create a support by choosing an optimal working fluid for special applications and become a part of a bigger optimization procedure by different frame conditions. The main sorting criterion for the fluids is the system efficiency (resulting from the thermo-physical characteristics) and beyond that the date base contains additional information and criteria, which have to be taken into account, like environmental characteristics for safety and practical considerations.The presented work focuses on the calculation and optimization procedure related to the coupling heat source – ORC cycle. This interface is (or can be) a big source of energy but especially exergy losses. That is why the optimization of the heat transfer between the heat source and the process is (besides the ORC efficiency) of essential importance for the total system efficiency.Within the presented work the general calculation approach and some representative calculation results have been given. This procedure is a part of a complex procedure and program for Working Fluid Selection for Organic Rankine Cycle Applied to Heat Recovery Systems.

Abstract: The knowledge of the behavior of thin liquid layers on solid surfaces is of fundamental interest as far as basic research or applications like technical coating or lubrication processes are concerned. The subject is currently getting more important, particularly due to the increasing requirements of thin liquid layer functionalities. We therefore studied the development of the liquid layer thickness distribution field as well as the liquid layer disturbance propagation on a plane solid surface in the vicinity of a curved solid surface experimentally and numerically using LIF (Laser-induced Fluorescence) and CFD (Computational Fluid Dynamics), respectively. The investigation focusses on the influence of the initial layer thickness and solid surface curvature as well as liquid properties like viscosity and surface tension on the film behavior, especially close to solid edges. Experimental and numerical results are shown pointing out relevant quantities for disturbance propagation and validation.

Abstract: In the paper the experimental analysis of passive heat transfer intensification in the case of modeled plate heat exchanger is conducted. The plate heat exchanger is chosen for the analysis because this kind of heat exchangers could be prospectively applied in the ORC systems, however other areas or application are equally possible. The experimental set-up was assembled at the Department of Energy and Industrial Apparatus of Gdansk University of Technology. The passive intensification was obtained by a modification of the heat transfer surface. The roughness of surface was increased by use of glass shot.During the experiment single-phase convective heat transfer in the single phase system was studied. The experiment was done in two stages. In the first stage the model of commercial plate heat exchanger was investigated, while in the second stage the identical one but with modified heat transfer surface. Model of heat exchanger consisted of three plates. The direct comparison of thermal and flow characteristics between both devices was possible due to assurance of equivalent conditions at the inlet to the system.The thermal and hydraulic characteristics are presented. The thermal analysis shows that in some range of heat flux density the overall heat transfer coefficient was higher for the commercial heat exchanger, while for the other was higher for the heat exchanger with modified surface. The influence of larger roughness on heat transfer cannot unequivocally be evaluated. Therefore as the next step the systematic investigations of model heat exchangers (only with one hot and one cold passage) will be conducted.