Thermodynamic Speed of Sound Data for Liquid and Supercritical Alcohols

Because of their caloric and thermal nature, speed of sound data are vital for the development of fundamental Helmholtz energy equations of state for fluids. The present work reports such data for methanol, 1-propanol, 2-propanol, and 1-butanol along seven isotherms in the temperature range from 220 to 500 K and a pressure of up to 125 MPa. The overall expanded uncertainty varies between 0.07% and 0.11% with a confidence level of 95%. The employed experiment is based on a double path length pulse-echo method with a single piezoelectric quartz crystal of 8 MHz, which is placed between two reflectors at different path lengths. Measured speed of sound data for the four alcohols are fitted with double polynomial equations and compared with literature sources

Thermodynamic speed of sound of xenon

Thermodynamic speed of sound data are an important basis for the development of Helmholtz energy equations of state because of their thermal and caloric nature. Moreover, they can be measured rapidly and with a high accuracy. Xenon is sampled with the pulse-echo technique to provide speed of sound data covering a temperature range from 217 K to 500 K with a pressure of up to 100 MPa. The measurement cell’s path length is calibrated with water and validated with the reference equation of state by Wagner and Pruß (2002). At a confidence level of 95% (k=2), the data have an overall expanded uncertainty of up to 0.17% near the critical point and less than 0.1% in the liquid and supercritical regions. The results are in good agreement with the Helmholtz energy equation of state by Lemmon and Span (2006) with a maximum deviation of up to 1.1%. The present data are also used to optimize the parameters of the Lennard-Jones potential and its truncated and shifted form for xenon. This parameterization leads to a convincingly better performance for the speed of sound calculation, but the representation of other properties, like the vapor-liquid two phase region, is significantly deteriorated

Henry’s Law Constant of Noble Gases in Water, Methanol, Ethanol, and Isopropanol by Experiment and Molecular Simulation

Henry’s law constant data for the noble gases helium, neon, argon, krypton, xenon, and radon in the pure solvents water, methanol, ethanol, and propan-2-ol are predicted over a wide temperature range by molecular simulation. Furthermore, gas solubility measurements are carried out for neon, krypton, and xenon in propan-2-ol, yielding experimental Henry’s law constant values that are employed, together with data from the literature, to evaluate present simulation results. Suitable molecular force field models are identified for each binary system, and new models for helium and neon are presented. By examining the entire set of binary systems, a characteristic trend of the solubility behavior concerning the molecular size of the solutes and solvents is identified. The present work contributes consistent Henry’s law constant data for 24 binary solute–solvent pairs over the entire relevant temperature range and improves the database considerably

Messverfahren für die akustischen Absorption zur Bestimmung der Volumenviskosität reiner Fluide

A realistic description of fluid mechanical and acoustic processes requires the volume viscosity of the medium to be known. This work describes how the volume viscosity of pure fluids can be determined by measuring acoustic absorption with the pulse-echo method. The challenge in realizing such a measurement method lies in the separation of the different dissipative effects that superimpose on absorption. Diffraction effects ultimately cause a dissipation of acoustic energy and acoustic reflector surfaces have a small, but finite transmission coefficient. Further, influences of the transducer (in particular its frequency response), as well as the system’s electrical components have to be taken into account. In contrast to the classical approach relying on the amplitude ratio, the absorption is determined by the moments of the amplitude spectrum. The measurement system applied is originally designed for precision measurements of the sound velocity by means of the propagation time difference of two acoustic signals.Eine realitätsnahe Beschreibung strömungsmechanischer wie akustischer Vorgänge setzt voraus, dass die Volumenviskosität des Mediums bekannt ist. In diesem Beitrag wird gezeigt, wie sich die Volumenviskosität reiner Fluide über eine Messung der akustischen Absorption durch Puls-Echo-Messungen ermitteln lässt. Die Herausforderung bei der Realisierung eines derartigen Messverfahrens liegt in der Trennung der unterschiedlichen dissipativen Effekte, welche der Absorption im Fluid überlagert werden. Beugungseffekte endlich großer Schallwandler bedingen zum Beispiel eine Dissipation der akustischen Energie im Raum. Im Gegensatz zur klassischen Methode über das Amplitudenverhältnis, wird die Absorption über die Momente des Amplitudenspektrums bestimmt. Als Messsystem dient dabei ein Aufbau, welcher zur präzisen Messung der Schallgeschwindigkeit über die Laufzeitdifferenz zweier akustischer Signale ausgelegt ist

Determining the heat flow through the cabinet walls of household refrigerating appliances

The increase of the thermal conductivity of PUR foam in the insulation of the cabinet is an important cause for aging processes of household refrigerating appliances. To determine the influence of the PUR foam aging on energy consumption, the development of a new measurement method is necessary because current methods influence the aging behavior of household refrigerators and are therefore not applicable in general. Based on a latent heat sink, constructed as an ice water bucket, a new measurement method is developed to determine the k · A value over time. With this method, the k · A value of four household refrigerating appliances was determined over an interval of 14 months. The k · A value increased between 3.6 % and 11.5 % during this period.BMWi, 03ET1544A, Verbundvorhaben ALGE: Alterungsmechanismen von Haushaltskältegeräte

Experimental study of two cascaded organic Rankine cycles with varying working fluids

Organic Rankine cycles convert low-temperature heat from different sources, like solar, geothermal or biomass, into electricity and may thus help to meet the energy demand in an environmentally friendly way. While single ORC systems have been studied extensively, there are only very few experimental works on systems consisting of two cascaded organic Rankine cycles (two-ORC). In this work, an experimental study is carried out on the performance of a two-ORC system that consists of a high temperature (HT) cycle and a low temperature (LT) cycle. Each cycle is composed of the four significant components, i.e. expander, evaporator, condenser and pump, while the LT cycle is equipped with a throttle as expansion device. The HT cycle utilized heat from electrical heaters, while the LT cycle was driven by the waste heat from the HT cycle. The test rig utilizes Therminol 66 as a source that is heated up by electrical heaters with a power of 158 kW. Propane, butane, pentane and cyclopentane are chosen as working fluids for the present experiments. Parameter variations are carried out to study the thermodynamic characteristics of each cycle. The aim is to investigate the HT cycle performance considering turbine power output, thermal efficiency and exergy efficiency. The effect of the HT cycle on the LT cycle is examined by studying the heat transfer rate between the two cycles, characteristics of heat exchangers and pinch point temperature difference. A further goal is to explore the system performance under different conditions to maximize the exergetic utilization of the heat source. The results confirm that turbine power output and thermal efficiency increase with heat source temperature and turbine inlet pressure in the HT cycle. The maximum achieved thermal and exergy efficiencies are 5.5% and 20.2%, respectively, while the maximum turbine power output is 4.92 kW. Heat transfer measurements show that the maximum transferred heat flow from the HT cycle to the LT cycle is 23 kW when pentane is used as a working fluid. Temperature profiles and the pinch point temperature difference in the heat exchangers of both cycles are assessed under conditions where the highest turbine power is obtained. The experimental tests are promising and show that the two-ORC system is suitable to utilize heat sources in various temperature ranges

Amélioration des performances des équipements frigorifiques domestiques par l'intégration de matériaux à changement de phase dans le cadre de la nouvelle norme mondiale IEC 62552:2015 relative aux réfrigérateurs

The influence of latent heat storage elements on the cooling performance and the temperature rise time of household refrigerating appliances is studied experimentally in the context of the “new global refrigerator standard” IEC 62552:2015. In addition to the daily energy consumption, this international standardization introduced performance tests for cooling capacity and temperature rise time. While the cooling capacity has long been anchored in various test procedures of consumer organizations, the temperature rise time, which has only been tested on freezers so far, will be a decisive factor in the future. Moreover, the need for so-called "smart appliances" that may balance power consumption is increasing since such devices may compensate the volatility of renewable energies and thus stabilize the power grid. Against this background, eight commercial household refrigerators and refrigerator-freezers are equipped with polymer-bound phase change materials (PCM) and their performance is determined under the new standard test conditions. The results show that the introduction of PCM increases the cooling capacity by up to 33 % and also increases the temperature rise time by up to 145 %, without affecting power consumption, as compared to the unmodified refrigeration appliances

Measurement procedure for acoustic absorption and bulk viscosity of liquids

A measurement procedure using a modified two-chamber pulse-echo experimental setup is presented, enabling acoustic absorption and bulk viscosity (volume viscosity) measurements in liquids up to high temperature and pressure. Acoustic absorption measurements are particularly challenging, since other dissipative effects, such as diffraction at the acoustic source and at acoustic reflectors, are typically superimposed to the measurement effect. Acoustic field simulations are performed, allowing to investigate acoustic wave propagation qualitatively. The absorption coefficient is determined by evaluating the signal spectrum’s raw moments and applying a method to identify and correct systematic measurement deviations. Measurement uncertainties are estimated by a Monte Carlo method. In order to validate the present measurement procedure, the acoustic absorption in liquid methanol, n-hexane, n-octane, and n-decane is determined experimentally and compared to literature data. The measurement results for methanol are additionally validated by comparison to bulk viscosity data sampled with molecular dynamics simulation