Prevention of Electrostatic Charge Generation in Filtration of Low-Conductivity Oils by Surface Modification of Modern Filter Media

The electrostatic charging behavior of filter elements operating in various hydraulic and lubricating fluids has been re-examined from the perspective of fundamental material properties of the two materials participating in the event. In contrast to the previously proposed mechanisms that focused predominantly on fluid and material conductivities, new evidence strongly suggests that the relative placement of the substrates in the triboelectric series must be taken into account. The positions occupied in the triboelectric series account for the donor/acceptor tendencies exhibited by the materials when brought close together in close proximity ( 10 nm). Nevertheless, this behavior is only an outward manifestation of the deeper underlying characteristics that include material surface energies and, looking even deeper, the associated electron work functions of the interacting materials. Herein we provide several examples of the enhanced understanding of the electrostatic charging/discharging (ESC/ESD) phenomena as they occur in the course of filtration of hydraulic and lubricating fluids through modern filter elements constructed of synthetic glass fiber and polymer materials

Theoretical and Numerical Constant Mean Curvature Surface and Liquid Entry Pressure Calculations for a Combined Pillar–Pore Structure

peer reviewedModern microfabrication techniques have led to a growing interest in micropillars and pillar–pore structures. Therefore, in this paper a study of the liquid entry pressure of a hydrophobic pillar–pore structure and the corresponding liquid–gas interface shape for the pressurized liquid is presented. We theoretically analysed the constant mean curvature problem for the rotationally symmetric case and determined an analytical expression for the liquid entry pressure of a hydrophobic pillar–pore structure. Furthermore, the shape of the liquid–gas interface as well as a formula for the location of the minimum were derived. The results are useful for designing geometries with specific properties, such as preventing or facilitating liquid intrusion into rough structures. We compared these results to multiphase lattice Boltzmann simulations where equilibrium contact angles in the range of (Formula presented.) to (Formula presented.) were tested. In our further analysis, we compared theoretical findings from previous works to our lattice Boltzmann simulations. The presented cases can serve as a benchmark for the development and validation of numerical multiphase models

Novel spacer geometries for membrane distillation mixing enhancement

peer reviewedMembrane distillation is an emerging promising desalination method that requires further improvement in order to become industrially viable. Due to the fact that evaporation is the primary process in membrane distillation, one strategy to boost membrane permeate flux is to optimize the energy supply to the water interface by increasing mixing in the hot channel via the use of optimized spacers. Contemporary spacer designs predominantly induce turbulence, resulting in elevated pumping energy requirements. This study introduces novel spacer geometries, inspired by industrial mixer designs, to surmount the limitations of conventional spacer configurations. The mixing efficiency, thermal performance, and pressure drop induced by the two novel geometries are studied and compared to those of commonly utilized spacer designs. It is confirmed, that the first of these novel geometries significantly enhances mixing, whereas the other causes a lower pressure drop and appears to be a viable solution when a spacer is a necessary structural component. In the course of the analysis, it is also shown that the coefficient of variation coupled with the Nusselt number at the membrane can be used to assess spacers' performance

Investigation of sCO2 Cycle Layouts for the Recovery of Low Temperature Heat Sources

editorial reviewedSince the development of supercritical carbon dioxide (sCO2) power cycles, several different power cycle architectures have evolved. Additional components like reheaters, recuperators and intercoolers were added and split flow configurations were introduced. These specific configurations are typically tailor-made for an explicit application, mostly in the medium-temperature field ranging between 240-480 °C. In the waste heat recovery sector, low grade waste heat (< 240 °C) holds the biggest share of the waste heat worldwide. This work focuses on ultra low temperature heat sources as they face big challenges for cycle efficiency because of the low temperature difference of heat source and heat sink. Consequently, the power generation is on low efficiency and subject of improvement. This study therefore investigates different power cycle configurations for a given low temperature air as heat source and ambient air as a heat sink (20 °C). The main objective is to evaluate different cycles with standardized boundary conditions in order to have an equal base for their comparison. Heat source temperature ranges from 60 to 100 °C are considered. Firstly, sCO2 power cycles from literature are evaluated using the commercial solver EBSILON. This step is meant to validate the numerical set up and results by using a documented cycle configuration from literature with its original boundary conditions. In a second step, the specified low temperature heat source is applied. The configurations are evaluated in terms of mass flow, pressure and thermal performance. Finally, the cycles are classified according to their efficiencies in the low temperature regime. From the results, it is observed that a recuperator step is not feasible in very low temperatures because of the minor superheating in the supercritical region. For turbine inlet temperatures higher than 80 °C, a recuperator starts to be beneficial. Intercooled compression is not suitable for ultra-low waste heat temperatures. A basic 4-component configuration and split flow before heating perform best in the low temperature region of 60 °C. With increasing turbine inlet temperature, more complex cycle configurations such as reheated expansion and intercooled compression might be considered in order to enhance the system efficiency. This study provides a dataset of thermal efficiencies of sCO2 power cycle configurations in the low grade waste heat recovery until 100 °C

Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome KERENA BWR Reactor: Part I

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventionsand are solely driven by thermal gradients and gravitational force. This brings up new needs forperformance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modelling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I deals with numerical and experimental methods for modelling of condensation inside the emergency condensers and on the containment cooling condenser while part II deals with boiling and two-phase flow instabilities

Energy performance comparison of ventilation-based heating versus water-based heating systems in an efficient residential building

The application of air-based heating systems as a possible approach to reduce the construction costs in highly efficient residential buildings is becoming popular. Air-based heating systems have been well-known for their usage in passive houses during the past three decades. Available studies on such systems tend mostly to focus only on comparing exhaust air heat pump technology with conventional systems in efficient buildings. Moreover, most of the existing studies ignore the usual presence of the electrical heaters as backup. Besides, a comprehensive study and comparison between different air-based heating system concepts is still missing. In this study, four different air-based heating system concepts separated by the type of heat source of heat pump for heating and domestic hot water are defined. These systems are compared to four conventional heating system, including floor heating and direct electrical system employing dynamic annual simulations. According to simulation results, the systems with floor heating have shown the best system efficiencies and the lowest energy demand in comparison to the other systems. The main reason for this was the lower supply temperatures of the floor heating systems. Between the air heating systems, the system equipped with an outdoor air heat pump showed a better energy performance than an exhaust air system. The main reason for this could be attributed to the power limitation of exhaust air heat pump systems

Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modeling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modeling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities