Condensation in ducts

Phase changing flows are being considered for thermal management in space platforms. The resulting flow patterns are very complicated and extremely sensitive to gravity action. Concerning fluid flow in ducts, the available evidence indicates that although the pressure loss does not depend too much on the fluid flow pattern,the heat transfer (and resulting phase change) does. A simple exercise to illustrate this point is presented in this paper. It deals with condensing flow in straight circular cross-sectional ducts. Two extreme configurations are considered here, one corresponds to a stratified flow and the other to an annular flow. Both types of flow patterns have been extensively considered in the past and from this point of view almost nothing is new in the paper, but past results look conflictive and this could be due to the limitations and computational intricacies of the models used. Thus the problem has been reformulated from the onset and the results are presented as the evolution of the vapor quality (vapor to total mass flow rate) along the duct, in typical cases. The results presented here indicate that within the validity of the present models and the assumed ranges of mass flow rate, duct diameter, thermal conditions and fluid characteristics,the length of the ducts required to achieve complete condensation under zero gravity are an order of magnitude larger than in horizontal tubes under normal terrestrial conditions.

An elicitor isolated from smut teliospores (Sporisorium scitamineum) enhances lignin deposition on the cell wall on both sclerenchyma and xylem in sugarcane leaves

Sugarcane leaf shows the classical arrangement of cells which defines a C4 species. Vascular bundles consist of xylem, phloem and fibres, surrounded by an outer layer of sclereids and an inner ring of stone cells associated with the phloem. Some sclereids located below and above the vascular bundles act as docking cells and connect the vascular bundle to the internal surfaces of upper and lower layers of the epidermis. A compact mass of sclereids occupies the total internal volume of the leaf edge. Neither docking cells nor the internal mass of sclereids in the edge were markedly coloured by acriflavin or phloroglucinol, indicating the absence of lignin in their cell walls. However, such staining indicated that fibres of the vascular bundle and the external layer of sclereids were strongly lignified. Incubation of leaf discs with an elicitor produced by the pathogen Sporisorium scitamineum increased the thickness of the lignified cell walls of sclereids as well as the mid and small xylem vessels, as a possible mechanical defense response to the potential entry of the pathogen.