Methane adsorption onto silicas with various degree of hydrophobicity

The methane adsorption onto a hydrated surface of hydrophobic silica AM1 alone and impregnated by arginine, and silica gel Si-100 has been studied using low-temperature 1H NMR spectroscopy. It has been shown that the methane adsorption onto the AM1 surface depends on the degree of hydration and pretreatment type. The maximum adsorption (up to 80 mg/g) is observed for a sample hydrated after complete drying. It has been established that the adsorption is determined by a number of clusters of bound water of small radii. Based on a shape of the temperature dependence of the adsorption, it has been assumed that not only physical adsorption occurs, but also the quasi-solid methane hydrates are formed. It has been established that the amount of methane adsorbed onto a surface of a composite system AM1/arginine under isobaric conditions increases by tens of times (from 0.5 to 80 mg/g) in the presence of pre-adsorbed water pre-adsorbed at the surface. Probable mechanisms of the methane adsorption are physical adsorption on a surface, condensation in narrow voids between silica nanoparticles and nano-scaled (1-10 nm) water clusters, and the formation of solid (clathrate) methane hydrates. Water, adsorbed at a surface in a wide range of hydration, forms various clusters. This water is mainly strongly associated and characterized by chemical shifts in the range dH = 4-6 ppm. The hydrate structures with methane/water are quite stable and can exist even in the chloroform medium. However, in this case, a part of water transforms into a weakly associated state and it is observed at dH = 1.5-2 ppm.

In-situ performance evaluation of historic box-type windows with vacuum glazing

Climate protection objectives and energy efficiency targets imply stricter performance expectations from both new and retrofit building projects. Given the related important role of the building envelope, there is a need for a holistic approach to the design, construction, as well as laboratory and field testing of buildings’ window and wall systems. In this context, the present contribution reports on recent efforts regarding the thermal retrofit of box-type windows. In the course of an actual research project, vacuum insulated glass (VIG) elements were integrated with ten existing box-type windows at six locations in Austria. To facilitate empirical testing and evaluation of these windows, a detailed concept for a continuous in-situ performance monitoring concept was designed and implemented together with the required monitoring infrastructure. This infrastructure involves the deployment of regular state-of-the-art IoT (Internet of Things) technology and enables the continuous monitoring of the salient performance indicators (including temperature, relative humidity, and heat flow). The derived values of performance indicators (such as the fRsi-value) can facilitate, among other things, the assessment of water vapor surface condensation risk. Collected data since mid-2020 cover both hot and cold weather periods have been analysed to capture performance differences between alternative vacuum glass settings at the testing locations. The alternative implementations pertain to different positions of the glazing layer (inside versus outside), different opening directions of the casements, and different positions of box-type within the opaque wall. Moreover, for comparison purposes, monitoring equipment was integrated into a comparable regular box-type window (with float glass or insulation glass) at each of the demonstration sites. Occurrences of potential visible or functional defects (including surface condensation) have been documented as well. The paper presents, analyses, and discusses the preliminary findings of this effort in detail.

Efficiency of Different Balcony Slab Modernization Method in Retrofitted Multi-Family Buildings

Many buildings have considerable thermal bridges at the junction of balcony slabs with walls. To achieve the new EU directive targets related to energy efficiency, greater attention should be paid to such design details. This study analyzes the efficiency of traditional balcony slab modernization methods, the use of modern insulation materials and a new alternative system: an added self-supporting light balcony system (LKBD) in retrofitted large-panel buildings. The main objective was to capture cost-effective renovation methods from both the heat loss reduction perspectives and risk of surface condensation. The analyses, carried out in four buildings, have shown that at current costs, the thermal modernization of balconies is not economically efficient (SPBT>98.4 years). However, it is necessary because leaving the balcony slabs without insulation or only insulating them from the bottom carries the risk of surface condensation. The most cost-effective renovation method is to insulate the balcony slabs from below and above with the thickest possible XPS layer (SPBT = 98.4 years; 107.4 years). Replacing XPS with modern material increases SPBT by almost 50%, for the LKBD system, SPBT = 269.2–281.5 years. More favorable energy and economic effects related to the reduction of balcony thermal bridges were achieved in the wall with lower insulation.

Features of the interaction of molecular oxygen with the condensation surface in the plasma of a low-pressure arc discharge

A model has been developed for studying the features of the thermal interaction of molecular oxygen in the near-surface condensation layer in the plasma of a low-pressure arc discharge. It was found that the input power and pressure of the gas mixture exert the main influence on the electron temperature and on the density of positive ions (O_2^+ and O+). It is shown that at a fixed pressure, the ion density increases with an increase in the power of the system, and vice versa.

Hygrothermal Analysis of CLT-Based Retrofit Strategy of Existing Wall Assemblies According to EN 13788 Standard

In the framework of the ongoing EU-funded innovation project called e-SAFE (energy and Seismic Affordable rEnovation solutions), several solutions for the energy and seismic deep renovation of reinforced-concrete (RC) framed buildings in the EU countries are going to be developed and demonstrated. One of these solutions makes use of cross laminated timber (CLT) panels connected to the existing RC frame through specifically designed dampers to increase the seismic and energy performances of the existing envelope. This paper aims to preliminary assess the hygrothermal performance of such CLT panels when applied to various typical wall structures under different climate conditions in Italy through numerical simulations carried out according to the EN 13788 Standard and considering various indoor vapor production classes. Results show that the most problematic existing wall structures are uninsulated concrete walls, for which a risk of surface condensation and mold growth is predicted in all climate zones because of their low thermal resistance (U-value of 3.55 W·m-2·K-1), followed by uninsulated solid brick walls (U-value of 1.81 W·m-2·K-1). The application of CLT panels is found to not only significantly improve the thermal behaviour of the walls, but also to eliminate any surface and interstitial condensation issues in all climate zones.

Grieb M., Brümmer A. Investigation into the effects of surface condensation in steam-driven twin screw expanders / trans. from Engl. M. A. Fedorova

During the operation of twin screw expanders with slightly superheated vapours or even two-phase fluids, surface condensation on machine parts occurs during the filling period and the expansion phase when the working fluid is in contact with cooler inner surfaces. This heat exchange from the working fluid to adjacent machine parts effects the working cycle and the efficiency of these machines. Short time scales and the periodicity of the process indicate the condensation process is best described by models for dropwise condensation. In this paper the effects of surface condensation on the operation of twin screw expanders are initially discussed in a simulation-based investigation. Chamber model simulation coupled with a thermal analysis is used for the thermodynamic simulation, whereby heat transfer coefficients are systematically varied. It is found that during the inlet phase condensate emerges on the inner surfaces of the machine being substantially cooler than the working fluid. This results in a higher mass being trapped within the working chamber and, thus, an increasing mass flow rate of the machine. An increase in power output is, however, not observed. The results obtained from chamber model simulations are finally compared against experimental data of a screw expander prototype