For modern thermal applications, open cell porous metals provide interesting opportunities to increase performance. Several types of cellular metals show an anisotropic morphology. Thus, using different orientations of the structure can boost or destroy the performance in thermal applications. Examples of such cellular anisotropic structures are lotus-type structures, expanded sheet metal, and metal fiber structures. Lotus-type structures are made by casting and show unidirectional pores, whereas expanded sheet metal structures and metal fiber structures are made from loose semi-finished products that are joined by sintering and form a fully open porous structure. Depending on the type of structure and the manufacturing process, the value of the direction-dependent heat conductivity may differ by a factor of 2 to 25. The influence of the measurement direction is less pronounced for the pressure drop; here, the difference varies between a factor of 1.5 to 2.8, depending on the type of material and the flow velocity. Literature data as well as own measurement methods and results of these properties are presented and the reasons for this strongly anisotropic behavior are discussed. Examples of advantageous applications, for example a latent heat storage device and a heat exchanger, where the preferential orientations are exploited in order to gain the full capacity of the structure’s performance, are introduced.

No abstract

Wetterdaten sind die Grundlage der Auslegung und Berechnung von heiz- und raumlufttechnischen Anlagen. Die DIN 4710:2003–01 fasst statistische Mittelwerte zu Lufttemperatur und -feuchte, Sonnenschein- und Winddaten sowie Bodentemperaturen zusammen. Diese finden bei der Auslegung von Anlagen oberflächennaher Erdwärmenutzung Anwendung. Im bereits erschienenen ersten Teil dieses aus zwei Teilen bestehenden Beitrags wurde ein Überblick über die vorhandenen Daten gegeben und in deren Strukturierung eingeführt. Anhand der Daten der Wetterstation Potsdam wurde die Berechnung der Monatsmittelwerte für Tiefen bis –100 cm erläutert.

In this study different types of multi-walled carbon nanotubes (MWCNT) were produced by the fixed bed and aerosol chemical vapor deposition (CVD) method. Nanocomposite materials were prepared by incorporation of different MWCNTs in copper matrix using powder metallurgy methods. By using hot pressing in combination with hot extrusion, the orientation of the carbon reinforcement was tuned from 3D to 1D alignment. After a selective etching process the carbon reinforcement is partially free-standing at the composite surface, but still embedded in the metal matrix. The engineered surface acts almost like a black body. The spectral evaluation of the surface functionalization will be shown for wavelengths from 200 nm to 20 µm. These results are compared to bulk copper. The free-standing MWCNT also behave like fins/pins in heat exchanger structures or surface enhancement in pool boiling. The experimental setup will be explained and the measurement described for pure copper. The theoretical heat transfer coefficient of the engineered surface is calculated depending on diameter and length of the free-standing MWCNTs. The results are compared to bulk copper.

Um die in den Planungsphasen aufgestellten Bilanzen möglichst einheitlich und verständlich vorlegen zu können sind Vorzeichenkonventionen notwendig. Diese werden für die Energieströme an der Erdoberfläche in Anlehnung an VDI 3789 vorgelegt.