Simulation of Compression Heat Pump Cycles Using NH3/H2O Mixtures to Estimate Their Working Domains

A computer-aided process design methodology is used to determine the limits of NH3/H2O mixtures in different heat pump cycles from 20 °C to 150 °C. The evaluation is based on a defined parameter set consisting of the coefficient of performance, total heat transfer area and volumetric heat capacity. Simple cycles with two heat flows were chosen to meet good process integration capabilities. The results are shown in a sink outlet/temperature lift matrix considering current technical limits. R1366mzz(Z) in a standard compression cycle with internal heat exchanger serves as a benchmark. To provide temperatures up to 150 °C the lift of the heat pump has to increase to about 80 K of which only the wet compressions cycle with NH3/H2O is capable of. The working domains of NH3/H2O and R1366mzz(Z) are similar, when a two-stage compression for NH3/H2O is applied

Time-dependent condensation of bosonic potassium

We calculate the time-dependent formation of Bose--Einstein condensates (BECs) in potassium vapours based on a previously derived exactly solvable nonlinear boson diffusion equation (NBDE). Thermalization following a sudden energy quench from an initial temperature $T_\mathrm{i}$ to a final temperature $T_\mathrm{f}$ below the critical value and BEC formation are accounted for using closed-form analytical solutions of the NBDE. The time-dependent condensate fraction is compared with available $^{39}$K data for various scattering lengths.Comment: 8 pages, 3 figure

Experimental investigation of additively manufactured high-temperature heat exchangers

This article examines various additively manufactured heat exchangers for high-temperature applications. The heat exchangers differ in terms of their internal fin structure as well as optimizations in terms of manufacturing quality. Starting from a reference fin type, optimizations with focus on low pressure drop and high heat transfer are performed. The heat exchangers are investigated experimentally, focusing on the laminar flow regime between 60<Re<600. By means of a presented evaluation algorithm, the Nusselt numbers for the different fin types and designs are determined. The investigations show that even the smallest manufacturing deviations result in up to 70–120% higher f-factors and up to 30% higher Nu numbers. Taking these manufacturing deviations into account in the design process leads to very good agreement with the numerically determined values and the influence of surface roughness is comparatively small. Furthermore, the influence of internal heat radiation is of minor importance for the heat exchangers considered here

Local heat transfer coefficients during the evaporation of 1,1,1,2-tetrafluoroethane (R-134a) in a plate heat exchanger

The evaporation heat transfer coefficient of the refrigerant R-134a in a vertical plate heat exchanger was investigated experimentally. The area of the plate was divided into several segments along the vertical axis. For each of the segments, the local value of the heat transfer coefficient was calculated and presented as a function of the mean vapor quality in the segment. Owing to the thermocouples installed along the plate surface, it was possible to determine the temperature distribution and vapor quality profile inside the plate. The influences of the mass flux, heat flux, pressure of system and the flow configuration on the heat transfer coefficient were also taken into account and a comparison with literature data was performed

Multi-Person Motion Tracking via RF Body Reflections

Recently, we have witnessed the emergence of technologies that can localize a user and track her gestures based purely on radio reflections off the person's body. These technologies work even if the user is behind a wall or obstruction. However, for these technologies to be fully practical, they need to address major challenges such as scaling to multiple people, accurately localizing them and tracking their gestures, and localizing static users as opposed to requiring the user to move to be detectable. This paper presents WiZ, the first multi-person centimeter-scale motion tracking system that pinpoints people's locations based purely on RF reflections off their bodies. WiZ can also locate static users by sensing minute changes in their RF reflections due to breathing. Further, it can track concurrent gestures made by different individuals, even when they carry no wireless device on them. We implement a prototype of WiZ and show that it can localize up to five users each with a median accuracy of 8-18 cm and 7-11 cm in the x and y dimensions respectively. WiZ can also detect 3D pointing gestures of multiple users with a median orientation error of 8 -16 degrees for each of them. Finally, WiZ can track breathing motion and output the breath count of multiple people with high accuracy

A characteristic map as an approach for rapid estimating the thermal conductivity of high-temperature oxide ceramics demonstrated on 10Sc1CeSZ

This work presents an easy applicable method for estimating thermal conductivity of oxide ceramic samples in a high-temperature SOFC/SOEC system. An experimental investigation establishes a thermal conductivity map for various oxide ceramics in the temperature range of 700 - 900 °C. Material specific properties are determined using laser flash analysis, displacement measurement for density and differential scanning calorimetry for heat capacity. The total thermal conductivity, incorporating conduction and radiation, is assumed based on a linear relationship with temperature gradient. Deviations in measurements are attributed to increasing radiation effects. The method provides a rough estimation of thermal conductivity, with 8YSZ exhibiting good agreement with literature values and 10Sc1CeSZ showing a range of 2.3 (+0.32/-0.48) - 2.8 (+0.96/-1) W/mK

Impact of Carbon Dioxide on the Non-Catalytic Thermal Decomposition of Methane

Economically and ecologically, the thermal decomposition of methane is a promising process for large scale hydrogen production. In this experimental study, the non-catalytic decomposition of methane in the presence of small amounts of carbon dioxide was analyzed. At large scales, natural gas or biomethane are possible feedstocks for the thermal decomposition and can obtain up to 5% carbon dioxide. Gas recycling can increase the amount of secondary components even further. Experiments were conducted in a packed flow reactor at temperatures from 1250 to 1350 K. The residence time and the amounts of carbon dioxide and hydrogen in the feed were varied. A methane conversion of up to 55.4% and a carbon dioxide conversion of up to 44.1% were observed. At 1300 K the hydrogen yield was 95% for a feed of methane diluted in nitrogen. If carbon dioxide was added to the feed at up to a tenth with regard to the amount of supplied methane, the hydrogen yield was reduced to 85%. Hydrogen in the feed decreases the reaction rate of the methane decomposition and increases the carbon dioxide conversion

Experimental Investigation of Coupled Transport Mechanisms in a PEM Based Thermoelectric Energy Converter

Thermoelectric energy converters based on galvanic cells (TGC) offer the possibility of direct conversion of low-temperature waste heat into electrical energy and could therefore be a promising approach for an increase in the overall efficiency of energy conversion. Due to an externally applied heat source, a temperature gradient across the electrolyte is induced, leading to a gradient in the chemical potential of the species and an electrical potential difference between the electrodes. The aim of approaching an internal equilibrium state leads to various coupled molecular transport mechanisms taking place in the electrolyte, impacting the open circuit voltage (OCV) and the performance of the TGC. By applying the theory of non-equilibrium thermodynamics (NET) to describe these coupled processes, the interactions that occur can be characterized in more detail. In this work, a polymer electrolyte membrane (PEM)-based TGC with two H2/H2O electrodes of different temperatures and gas compositions is experimentally investigated. By controlling the gradients in temperature and concentration, different impacts on the resulting OCV can be identified. In addition, we present the measured coupling coefficient, representing the singular relation between the transport of the hydrogen ions inside the membrane and the electrical potential difference between the electrodes for a wide variety of working conditions

Coupled Transport Effects in Solid Oxide Fuel Cell Modeling

With its outstanding performance characteristics, the SOFC represents a promising technology for integration into the current energy supply system. For cell development and optimization, a reliable quantitative description of the transport mechanisms and the resulting losses are relevant. The local transport processes are calculated by a 1D model based on the non-equilibrium thermodynamics (NET). The focus of this study is the mass transport in the gas diffusion layers (GDL), which was described as simplified by Fick’s law in a previously developed model. This is first replaced by the Dusty-Gas model (DGM) and then by the thermal diffusion (Soret effect) approach. The validation of the model was performed by measuring U, j-characteristics resulting in a maximum deviation of experimental to simulated cell voltage to up to 0.93%. It is shown that, under the prevailing temperature, gradients the Soret effect can be neglected, but the extension to the DGM has to be considered. The temperature and heat flow curves illustrate the relevance of the Peltier effects. At T = 1123.15 K and j = 8000 A/m2, 64.44% of the total losses occur in the electrolyte. The exergetic efficiency for this operating point is 0.42. Since lower entropy production rates can be assumed in the GDL, the primary need is to investigate alternative electrolyte materials. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Thermal performance measurement of additive manufactured high-temperature compact heat exchangers

Due to increased distribution of high-temperature processes in energy and process plants, more efficient and compact high-temperature heat exchangers are being developed. The additive manufacturing allows the construction of compact sizes and application-specific requirements. To evaluate the thermal performance of these heat exchangers, experimental investigations are evident. This study presents a test rig for testing compact high-temperature heat exchangers as well as a first set of thermal performance data of an additively manufactured plate-fin heat exchanger. The test rig can provide a maximum fluid temperature of 900°C and a maximum mass flow rate of 0.8 kg/min. A steam unit can add steam to the fluid stream to evaluate the influence of gas radiation on the thermal performance. The capabilities of this test rig are being tested with the plate-fin heat exchanger, varying the mass flow rate between 0.2 - 0.52 kg/min at a hot and cold inlet temperature of 750°C and 250°C. The overall effectiveness of the heat exchanger is approx. 0.9