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14:20   Session 2B: Small Scale Systems (1) Chair: Piero Colonna 14:20 20 mins Experimental investigation of a transcritical Organic Rankine Cycle with scroll expander for low temperature waste heat recovery Arnaud Landelle, Nicolas Tauveron, Remi Revellin, Philippe Haberschill, Stephane Colasson Abstract: During the last decades, organic Rankine cycle (ORC) became a popular way to recover low-grade waste heat. Ways of improvement for ORC have been investigated trough thermodynamics analysis. The use of transcritical cycle could theoretically improve the cycle efficiency and recover more heat from waste sources but there have been few experimental test benches to confirm the interest of transcritical cycles and investigate operational behaviours. In this study, an experimental investigation of a transcritical organic Rankine cycle is presented. The test bench is composed of a diaphragm pump, two plate heat exchangers (PHE) for heating, a 10kWe scale hermetic scroll compressor modified to run as an expander, a PHE condenser and a PHE regenerator. The regenerator can be isolated to compare standard and regenerative configurations. The working fluid used is R134a refrigerant with a critical pressure and temperature of 40.5bar and 101.2°C. The heat source has a maximum power of 200kWth at 150°C and uses pressurized water as heat transfer fluid. The prototype is tested at different conditions, both steady state and heat/cold sources dynamics are investigated. In order to evaluate the performance of the system, temperatures, pressures, mass flows are measured as well as expander and pump shaft speeds and electric powers. Heat source temperature ranges from 90°C to 120°C with a maximum power of 145kWth. The scroll expander runs with an inlet pressure up to 43bars and a pressure ratio around 2, producing a maximum power of 6kWe with a 68% expander efficiency at 1600rpm. An energetic and exergetic analysis of the cycle and the components is performed. Due to high pump consumption, the maximum net power is 2kWe resulting in a maximum energetic and exergetic efficiency of 2% and 8% respectively. Subcritical and transcritical operations are compared, expander has higher output power and efficiency at transcritical condition but the ORC performs equally just below and above the critical pressure mainly because of pump consumption increases. 14:40 20 mins Possibilities of Water-Lithium Bromide absorption power cycles for low temperature, low power and combined power and cooling systems Vaclav Novotny, Vaclav Vodicka, Jakub Mascuch, Michal Kolovratnik Abstract: Absorption power cycles (APC) provide an alternative to the ORC as an interesting thermodynamic cycle for waste heat recovery. Particular advantage of the APC is in a multicomponent working fluid that allows for a temperature glide along boiling and condensation (desorption and absorption). This phenomenon provides a good temperature match of hot and cold streams in the heat exchangers during the phase change. Thus it is possible to achieve higher exergy efficiency of the heat addition when sensible heat is used as a heat source. Similarly good temperature match and lower cooling fluid flow through absorber-condenser for heat rejection lowers the parasitic load of fans or cooling tower pumps. As a result, higher net efficiency can be achieved in comparison to a single component working fluid. In the past, the only considered APC has been Kalina cycle operating with water-ammonia mixture as a working fluid, while other fluid combinations were only rarely considered. Recently there came into an attention an aqueous solution of Lithium Bromide (LiBr), typically known from absorption cooling. Compared to ammonia-water mixture the pressure levels in the cycle are very low, typically both high and low pressure in vacuum. This results in high volumetric flow, bulky device, but when turbine is used it can achieve high efficiency and increased material cost are for small units is only of a marginal importance. In this study after the introduction of theoretical advantages in efficiency and of design features and constraints, we present results of several case studies for potential application. These are waste heat recovery from hot air stream, low temperature geothermal application, coupling with vacuum solar collectors, bottoming cycle for ORC and a combined cooling and power cycle as an alternative to the cooling-only absorption cycle. 15:00 20 mins Towards development of 1-10 kW PILOT ORC units operating with Hexamethyldisiloxane and using rotary vane expander Jakub Mascuch, Vaclav Novotny, Vaclav Vodicka, Zbynek Zeleny Abstract: Micro-cogeneration and small scale waste heat recovery has its place in the concept of sustainable future and distributed electricity generation as it should provide environmental, economical and social advantages. ORC belongs among perspective technologies to achieve a successful commercialization. Domain of power output below 10 kW is particularly interesting because it brings a possibility of energy production to a wide range of potential customers. Widespread of solid fuels fired heating systems and desire for renewable energy suggest combination of biomass and cogeneration systems. There is an eight-year history of an ORC development at the Czech Technical University aiming at applications for cogeneration and waste heat recovery with power output between 1 and 10 kW. This work shows the overall development over four different ORC units. Development of different concepts, configurations or choice of technologies is presented in this work together with the obtained performance parameters. Common feature of all presented units are use of rotary vane expander (of which three different generations have been designed and tested). 15:20 20 mins Experimental investigation of four volumetric expanders Olivier Dumont, Rémi Dickes, Vincent Lemort Abstract: The aim of this paper is to facilitate the selection of the expander for a small scale organic Rankine cycle based on an experimental comparison of a piston, a screw and two scroll expanders. First, based on a literature review, a comparison between these three technologies of volumetric expansion machines - namely piston, screw and scroll expanders – is performed. Following that, four displacement expanders (~2kWe) are tested in a small-scale ORC using R245fa as working fluid: a variable speed swatch-plate piston prototype, an oil-free twin-screw, a modified lubricated hermetic scroll compressor operating at a constant speed, and finally a variable-speed modified scroll compressor. The machines performance are compared in terms of isentropic efficiency and filling factor. The maximum isentropic efficiencies achieved are 53% for the piston expander and the screw expander, 76% for the variable speed scroll and 81 % for the constant speed scroll machine. However, these performances are not representative because of the limitations of the test-rig in terms of mass flow rate and pressure drop. The utilization of semi-empirical models calibrated with the measurements allows to predict the isentropic efficiency in optimal conditions without the limitations of the test-rig. When selecting an expander, other considerations than efficiency have to be taken into account such as the flexibility, the working conditions and the compactness of the expansion device. Based on the experimental results and these practical considerations, some guidelines are drawn to help the reader selecting a volumetric expander. 15:40 20 mins Numerical CFD simulations on a small-scale ORC expander using a customized grid generation methodology Giuseppe Bianchi, Sham Rane, Ahmed Kovacevic, Roberto Cipollone, Stefano Murgia, Giulio Contaldi Abstract: Positive displacement machines are the most suitable devices for small-scale waste heat to power conversion units based on an Organic Rankine Cycle (ORC) due to their capabilities of handling small mass flow rates and high pressure ratios. Among the available technologies, sliding vane machines provide unique features such as low operating revolution speed, geometrical flexibility and uncomplicated manufacturing. Nonetheless, research and product development in this field have been constrained by the lack of interfaces between deforming and moving fluid domains that characterize sliding vane devices and the design tools at the state of the art. This research work tackles this challenge and presents the development of an analytical grid generation for sliding vane machines that is based on user defined nodal displacement. Through this approach, the numerical methodology discretizes the fluid domains enclosed between the cells and ensures conservation of intrinsic quantities by maintaining the cell connectivity and structure. Transient 3D single phase simulations on a small scale ORC expander were further set up in the ANSYS CFX solver and provided insights on the main flow field as well as in the leakage paths between rotor blade tips and casing. The numerical results were eventually validated with reference to an experimental dataset related to a waste heat to power conversion application in compressed air systems where the sliding vane ORC expander worked with R236fa, at a pressure ratio of 2.65 and at 1551 RPM.