Experimental characterization of single screw expander performance under different testing conditions and working fluids

During the last years, one of the most popular ways to recover low-grade waste heat is the organic Rankine cycle (ORC). This technology is widely studied and continuously optimized and, as a result, there are many efficient installations available on the market utilizing heat with stable parameters such as from geothermal sources or from the biomass combustion process. However, if a variable hot source in terms of either temperature or flow rate is introduced, the expansion devices have to work at non-optimal conditions, which decrease the global efficiency of ORC installations, e.g. in the case of waste heat recovery. In order to characterize the performance of a positive displacement expander close enough to the optimum, the influence of pressure ratios, filling factor, and working fluid properties on power output is studied. In this paper, experimental results obtained on a small-scale ORC test setup based on an 11 kWe single-screw expander are presented. Two working fluids are used during the tests, i.e. R245fa and SES36 (Solkatherm). These working fluids are common for ORC installations exploiting low-temperature waste heat. The waste heat source is simulated by an electrically heated thermal oil loop with adjustable temperature and flow rate. Various waste heat inlet flow rates are considered in order to find an optimal evaporation pressure and to maximize the power output with different heat source profiles. Based on the experimental data, the expander model is developed. For each working fluid, optimal working conditions are determined. In most cases, there is under-expansion due to a relatively small built-in volume ratio, causing certain losses. By means of the model, the ideal expansion process is simulated and compared with the real one obtained experimentally to quantify these losses and conclusions can be drawn whether significant benefits can be offered by using an optimized expander instead of an ”off-the-shelf” reversed compressor

Solar heat driven water circulation and aeration system for aquaculture

The proposed design concept of water aeration and updraft circulation in aquaculture is based on the Organic Rankine Cycle (ORC) technology and uses a solar energy absorbed by a floating collector. The pressure required for the aerator is created by evaporating a working fluid and optimized for an average depth of a pond. The working pressure is defined by the maximum achievable temperature of the working fluid. The condensing heat is rejected at a certain depth with the lowest temperature and drives the convective circulation. A prototype is designed by using common materials and off-the-shelf components to ensure maintenance-free and proper capacity to fulfil the needs of an average or a small aquaculture farm: the working fluid in the working chamber evaporates increasing in volume and pumping air out of the vessel as well as the expanded working fluid in the second working chamber. The working fluid is cooled down in the condenser which is submerged into the pond and it is condensed while decreasing in volume. The new design can perform multiple cycles per day increasing the volume of pumped air. In order to make the operation of this unit possible during the night, a heat buffer with a phase changing material (PCM) is used. A parametric study of suitable working fluids and PCMs has been performed in order to select the most appropriate combination for the target applications

Dynamic models for a heat-led organic rankine cycle

Drawn by the benefits of de-centralised and renewable power supply, over 150 Organic Rankine Cycles (ORC), in a range from 400kWel to 2MWel, have been installed in Central Europe. The majority of modules are biomass fired and heat-led by district heating networks. With rising fuel prices however, the economic situation has become critical for many of these facilities and improvements in efficiency are indispensable. The research reported here, provides turbine models to simulate units of that type and suggests recommendations to achieve a higher cycle efficiency. An operating power plant with a design power of 1MWel serves as validation

Thermodynamic analysis of the partially evaporating trilateral cycle

The potential of Organic Rankine Cycles (ORC) to recover low grade waste heat is well known. The high heat recovery potential is partially attributed to a good match of the temperature profiles between working fluid and waste heat stream in the evaporator. This preferable characteristic is mainly induced by the selection of an appropriate working fluid. However, because of the constant temperature evaporation of the working fluid, the heat recovery potential is restricted. In order to overcome this limitation the trilateral cycle (TLC) has been investigated. A Trilateral cycle (also called Triangular cycle) is a modified Rankine cycle. The main difference is that the working fluid is not evaporated but only heated to the saturation temperature. Compared to the ORC, the heat carrier stream can be cooled further and the thermal efficiency is lower. In this study the effect of partial evaporation of the working fluid is investigated

Performance potential of ORC architectures for waste heat recovery taking into account design and environmental constraints

The subcritical ORC (SCORC), sometimes with addition of a recuperator, is the de facto state of the art technology in the current market. However architectural changes and operational modifications have the potential to improve the base system. The ORC architectures investigated in this work are: the transcritical ORC (TCORC), the triangular cycle (TLC) and the partial evaporation ORC (PEORC). Assessing the potential of these cycles is a challenging topic and is brought down to two steps. First, the expected thermodynamic improvement is quantified by optimizing the second law efficiency. Secondly, the influences of technical constraints concerning volumetric expanders are investigated. In the first step, simple regression models are formulated based on an extensive set of boundary conditions. In addition a subset of environmentally friendly working fluids is separately analysed. In the second step, two cases are investigated with the help of a multi-objective optimization technique. The results of this optimization are compared with the first step. As such the effect of each design decision is quantified and analysed, making the results of this work especially interesting for manufacturers of ORC systems

Fluid stability in large scale ORCs using siloxanes: long-term experiences and fluid recycling

The results in this work show the influence of long-term operation on the decomposition of working fluids in eight different power plants (both heat-led and electricity-led) in a range of 900 kWel to 2 MWel. All case study plants are using Octamethyltrisiloxane (MDM) as a working fluid. The case study plants are between six to 12 years old. On one system detailed analyses, including the fluid distribution throughout the cycle, have been conducted. All fluid samples have been analysed via Head Space Gas Chromatography Mass Spectrometry (HS-GC-MS). Besides the siloxane composition, the influence of contaminants such as mineral oil based lubricants (and its components) has been examined. In most cases the original main working fluid has degraded to fractions of siloxanes with a lower boiling point (low-boilers) and fractions with a higher boiling point (high-boilers). As a consequence of the analyses, a new fluid management system has been designed and tested in one case study plant (case study number 8). The measures include fluid separation, cleansing and recycling. Pre-post comparisons of fluid samples have proved the effectiveness of the methods. The results show that the recovery of used working fluid offers an alternative to the purchase of fresh fluid, since operating costs can be significantly reduced. For large facilities the prices for new fluid range from e15 per litre (in 2006) to e22 per litre (in 2013), which is a large reinvestment, especially in the light of filling volumes of 4000 litres to 7000 litres per cycle. With the above mentioned method a price of e8 per litre of recovered MDM can be achieved

Physiological signals: The next generation authentication and identification methods!?

Throughout the last 40 years, the security breach caused by human error is often disregarded. To relief the latter problem, this article introduces a new class of biometrics that is founded on processing physiological personal features, as opposed to physical and behavioral features. After an introduction on authentication, physiological signals are discussed, including their advantages, disadvantages, and initial directives for obtaining them. This new class of authentication methods can increase biometrics’ robustness and enables cross validation. I close this article with a brief discussion in which a recap of the article is provided, law, privacy, and ethical issues are discussed, some suggestions for the processing pipeline of this new class of authentication methods are done, and conclusions are drawn

Case studies of thermally driven heat pump assisted drying

In general, most heat losses in industrial dryers arise due to the discharge of humid air. By using heat pump drying (HPD) systems, heat from the exhaust humid air can be recovered, thus improving the energy efficiency substantially. In this study, the performance of thermally driven HP integration in an animal food and a blood dryer were examined. Computer simulation models of the original high temperature dryers and the proposed system with HP integration and auxiliary heating were developed. It is found that, when using a gas engine, the maximum energy cost saving is limited by the temperature of the coolant fluid. The maximum energy cost saving when using a gas turbine is a bit higher, however at a much higher operating temperature