Nowadays, the Mechanical Circulatory Support (MCS) within the Ventricular Assist Devices (VAD) appears to be a reliable and effective solution for patients with advanced heart failure (HF). After many years of work, extracorporeal pulsatile VADs have been replaced by new generations of implantable continuous flow (CF) pumps. Clinical experience has shown that present-day pump constructions still need to be improved to minimize the risk of complications during heart assistance. One of the complications is the pump inflow obstruction caused by the ingrowth of tissue into the blood inflow path and pump thrombosis. The main goal is to develop a coating for the external surface of the inflow cannula to provide controlled tissue ingrowth. The smooth surface of the cannula external wall results in the tissue overgrowth into the pump inflow orifice, and may be a source of emboli. The paper presents external surface modifications of the inflow cannula performed by different VAD manufacturers within the topography characterization. The inflow cannulas used in CF VADs are mainly made of titanium alloy due to its mechanical properties and high biocompatibility. In general, the discussed surface coatings were characterized by the roughness of about ≈ Ra = 15 μm, high porosity and good wettability Φ ≈ 60°. The surface was covered with titanium microspheres or titanium mesh. The developed surfaces and clinical experience confirm the ability to control the tissue ingrowth along the external surfaces of the inflow cannula at the tissue-implant interface.
Sorbents are substances binding other substances on their surface. Effective sorbents have a porous surface. The adsorption activity of the surface is closely related to the local radius of curvature of surface irregularities. Suitable sorbents are natural and synthetic solids of amorphous or microcrystalline structure (Kyncl et al. 2008). Globally, the following adsorbents are the most used: activated carbon, zeolites, silica gel, activated alumina (Bakalár et al. 2005). A characteristic of effective adsorbents is large surface area of hundreds of square meters multiply by gram to the power of minus one [m 2 ∙g −1 ]. Other important features of adsorbents include specific volume, porosity, average pore diameter, pore distribution, etc. Some natural materials or industrial waste with high adsorption capacity, which naturally reduces the overall cost of their disposal, can be used for adsorption of heavy metal cations. Some of low-cost sorbents are: lignin, chitin, seaweed/ algae, zeolites, clays, fly-ash, peat, sand grains coated with iron oxide, modified cotton and wool (Pavolová et al 2006). In experiments of Cu and Zn removal from wastewater the following adsorbents were used (Bakalár et al. 2005): - Lewatit S100, which is strongly acidic, gel-like cationic ion exchange resin with particles of equal size based on styrene-divinylbenzene copolymers. Monodisperse beads are chemically and osmotically highly stable. - Chitosan, which is prepared from chitin, naturally occurring in the shells of crustaceans, by deacetylation using strongly alkaline solution. Chitin is a homopolymer composed of β-(1-4)- -N-acetyl-D-glucosamine. The ability of crustaceans shells to bind metal ions is assigned to the presence of exoskeleton in the molecule of chitin and chitosan. - Synthetic zeolite, which is included in the group of aluminosilicates, was prepared by zeolitization of fly-ash from energy industry. - Bentonite, which is included in the group of hydrated aluminosilicates, the main ingredient is mineral montmorillonite. - Slovakit, which is an inorganic composite sorbent made from pure natural ingredients. Its composition is a subject of patent protection. The aspect of time, i.e. the time the specific sorbent reaches the maximum adsorption capacity for the heavy metal removed, is also important in removal of Cu 2+, Zn 2+ and Pb 2+ cations. The experimental measurements of cations adsorption using the above mentioned sorbents are made at the initial concentration of 10 mg∙L −1 of heavy metal. The time to reach the equilibrium for all sorbent during separation of Cu 2+ cations from model solutions of wastewater was about 60 seconds except for chitosan for which it was almost 2 minutes. This is relatively very good result. The equilibrium of Zn 2+ cations adsorption at the experimental measurements for all the selected sorbents was reached in about 80 seconds except for chitosan for which this time was 2 minutes 5 seconds. This time was on average around 20 minutes longer compared to the adsorption of Cu 2+ ions. The adsorption of Pb 2+ cations was carried out at the experimental measurements in about 83 seconds for all the selected sorbents, except for synthetic zeolite for which the time was 1 min 15 seconds. The adsorption of Pb 2+ cations compared to the cations of Cu 2+ was 23 seconds faster and compared to the cations of Zn 2+ was 3 seconds longer. The most appropriate for the removal of Cu 2+, Zn 2+, and Pb 2+ is Lewatit S100 among the used sorbents; the equilibrium was reached in approximately 35 seconds, 45 seconds, and 83 seconds for Zn 2+, Cu 2+, and Pb 2+, respectively. According to the experimental measurements the longest adsorption time was for chitosan – about 2 minutes for Cu 2+ and Zn 2+, and about 1.5 minutes for Pb 2+.
Niniejszy artykuł dotyczy przeglądu badań intensyfikacji wymiany ciepła podczas wrzenia pęcherzykowego. Badania te związane są z różnego rodzaju powierzchniami i czynnikami wrzącymi, stosowanymi w celu poszukiwania coraz sprawniejszych, a zarazem coraz mniejszych wymienników ciepła. Temat intensyfikacji wymiany ciepła jest zagadnieniem często poruszanym ze względu na postęp techniki w dziedzinie chłodzenia maszyn i urządzeń, zarówno mechanicznych jak i elektronicznych, a także ze względu na rozwój techniki rakietowej, kosmicznej i energetyki. Nowe dielektryczne czynniki wrzące badane są na różnego rodzaju powierzchniach strukturalnych odprowadzających ciepło. Dąży się do uzyskania możliwie dużych gęstości strumienia ciepła dla niewielkich powierzchni odprowadzających ciepło, przy jednoczesnym jak najmniejszym ich przegrzaniu. Do rozwoju badań nad intensyfikacją wymiany ciepła podczas wrzenia pęcherzykowego przyczyniło się wytwarzanie powierzchni wykorzystujących kilka metod intensyfikacji wymiany ciepła, przez co możliwe jest znaczne zwiększenie współczynnika przejmowania ciepła w stosunku do powierzchni gładkich. Zaproponowane własne powierzchnie z układem porów i miniżeber umożliwiają wytworzenie dużej liczby ośrodków nukleacji, co prowadzi do znacznego wzrostu współczynnika przejmowania ciepła.
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The article describes the review of studies on pool boiling heat transfer enhancement. The research relates to various surfaces and boiling fluids which are used in the search of more effective and progressively smaller heat exchangers. The subject of pool boiling heat transfer enhancement is a common issue to be discussed in terms of the advancement of the cooling machines and devices, both mechanical and electronic ones, and also due to the progress of rocketry, aerospace and energy. Newer and newer refrigerants to be tested on a variety of surfaces emitting heat are produced. It results in achieving maximal heat fluxes for small surfaces and simultaneous attempts to reduce their superheat. The construction increasingly modified structures contributed to the development of research on the pool boiling heat transfer enhancement. Due to this, it is possible to significantly increase the heat transfer coefficient in relation to smooth surfaces. Own surfaces with the proposed arrangement of pores and minifins make it possible to provide a large number of nucleation sites. This leads to a substantial intensification of the heat flux transferred from the investigated surfaces.
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MHD nonlinear steady flow and heat transfer over a porous surface stretching with a power-law velocity and of constant heat flux is investigated. The governing nonlinear partial differential equations are reduced to nonlinear ordinary differential equations by using similarity transformation. As the presented solution method requires the magnetic field to vary in space in a specific manner, a special form for the variable magnetic field is chosen. Resulting equations are numerically solved by Runge–Kutta shooting method. Values of skin-friction and rate of heat transfer are obtained. The effect of magnetic field, stretching parameter, magnetic interaction parameter, suction parameter and Prandtl number over a flow field and other physical quantities have been discussed in detail.
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