A dual-intake-port technology as a design option for a Sliding Vane Rotary Expander of small-scale ORC-based power units

Fatigati, Fabio; Bartolomeo, Marco Di; Battista, Davide Di; Cipollone, Roberto

doi:10.1016/j.enconman.2020.112646

Cited by 25 publications

(16 citation statements)

References 29 publications

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“…The high accuracy of these models is witnessed by several contributions in the literature [40,41]. Of course, also the indicated diagram is well represented and the effects produced by some unconventional solutions, like for instance, a double port intake technology [43,44]. Weakest points of the SVREs are the low values of the volumetric and mechanical efficiencies, which risk vanishing the superior characteristics of these machines when compared with the dynamic or volumetric reciprocating machines (low revolution speed, absence of vibrations, wide off design capabilities, management of mixtures of liquid and vapor at saturation, flexible shaping, etc.).…”

Section: Mathematical Model Of Svrementioning

confidence: 96%

Experimental Validation of a New Modeling for the Design Optimization of a Sliding Vane Rotary Expander Operating in an ORC-Based Power Unit

et al. 2020

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Sliding Rotary Vane Expanders (SVRE) are often employed in Organic Rankine Cycle (ORC)-based power units for Waste Heat Recovery (WHR) in Internal Combustion Engine (ICE) due to their operating flexibility, robustness, and low manufacturing cost. In spite of the interest toward these promising machines, in literature, there is a lack of knowledge referable to the design and the optimization of SVRE: these machines are often rearranged reversing the operational behavior when they operate as compressors, resulting in low efficiencies and difficulty to manage off-design conditions, which are typical in ORC-based power units for WHR in ICE. In this paper, the authors presented a new model of the machine, which, thanks to some specific simplifications, can be used recursively to optimize the design. The model was characterized by a good level of physical representation and also by an acceptable computational time. Despite its simplicity, the model integrated a good capability to reproduce volumetric and mechanical efficiencies. The validation of the model was done using a wide experimental campaign conducted on a 1.5 kW SVRE operated on an ORC-based power unit fed by the exhaust gases of a 3 L supercharged diesel engine. Once validated, a design optimization was run, allowing to find the best solution between two “extreme” designs: a “disk-shaped”—increasing the external diameter of the machine and reducing axial length—and by a “finger-shaped” machine. The predictions of this new model were finally compared with a more complex numerical model, showing good agreement and opening the way to its use as a model-based control tool.

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Section: Mathematical Model Of Svrementioning

confidence: 96%

Experimental Validation of a New Modeling for the Design Optimization of a Sliding Vane Rotary Expander Operating in an ORC-Based Power Unit

et al. 2020

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“…Consequently, the residual margin for plant enhancement should be exploited through the definition of a control strategy, able to properly cope with (i) the need for plant downsizing (e.g., reduced heat exchange surfaces, reduced mass flowrates of working fluid), (ii) the limitations on the applicable fluid type [25][26][27] and (iii) the constraints on admissible operating temperatures and pressures [28][29][30]. Both the low characteristic mass flowrates of working fluid and the variability of the thermal energy at the evaporator call for dedicated design of rotary equipment [31][32][33].…”

Section: Introductionmentioning

confidence: 99%

“…More specifically, the expander design has to account for the possibility of a two-phase expansion, with a variable superheating degree and proper operation in a wide RPM range. In addition, the need for mass flowrate modulation via proper selection of the pump speed, calls for a pump designed for reduced energy absorption within the whole operating RPM range [33]. As a matter of fact, mass flowrate, cycle pressures (namely, the pressure at expander inlet) and expander speed are inter-related, particularly in volumetric machines, where the processing of a variable mass flowrate is associated with speed modulation: to keep the cycle operating pressures (namely, the pressure at expander inlet) unaffected in presence of an increased mass flowrate, a higher expander RPM is needed, to allow a quicker process of vane fillingemptying.…”

Section: Introductionmentioning

confidence: 99%

“…As a matter of fact, mass flowrate, cycle pressures (namely, the pressure at expander inlet) and expander speed are inter-related, particularly in volumetric machines, where the processing of a variable mass flowrate is associated with speed modulation: to keep the cycle operating pressures (namely, the pressure at expander inlet) unaffected in presence of an increased mass flowrate, a higher expander RPM is needed, to allow a quicker process of vane fillingemptying. Nonetheless, this ends up affecting lubrication and friction losses and eventually the plant energy output [33].…”

Section: Introductionmentioning

confidence: 99%

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Experimental Assessment of a Multi-Variable Control Strategy of a Micro-Cogeneration Solar-ORC Plant for Domestic Application

et al. 2021

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Suitability to off-design operation, applicability to combined thermal and electrical generation in a wide range of low temperatures and pressures and compliance with safety and environmental limitations qualify small-scale Organic Rankine Cycle plants as a viable option for combined heat and power generation in the residential sector. As the plants scale down, the electric and thermal output maximization has to account for issues, spanning from high pump power absorption, compared to the electric output of the plant, to intrinsically low plant permeability induced by the expander, to the intermittent availability of thermal power, affected by the heat demand for domestic hot water (DHW) production. The present paper accounts for a flat-plate solar thermal collector array, bottomed by an ORC unit featuring a sliding vane expander and pump and flat-plate heat exchangers. A high-temperature buffer vessel stores artificially heated water – electric heaters, simulating the solar collector - and feeds either the hot water line for domestic use or the ORC evaporator, depending on the instantaneous demand (i.e., domestic hot water or electric power), the temperature conditions inside the tank and the stored mass availability. A low-temperature receiver acts like the heat sink of the ORC unit and harvests the residual thermal power, downstream the expander: a dedicated control, modelled to properly modulate the mass addition/subtraction to this storage unit allows to restore the operating points of the cycle and to limit the incidence of off-design operation, via real-time adjustment of the cycle operating parameters. Indeed, the possibility of continuous ORC generation depends on (i) the nature of the demand and (ii) the amount of hot water withdrawn from the high-temperature buffer vessel. The time-to-temperature for the mass stored inside the buffer affects the amount of ORC unit activations and eventually the maximum attainable generation of electric energy. The plant energy performance is experimentally assessed, and various characteristic operating points are mapped, based on test runs carried out on a real-scale ORC pilot unit.

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“…Consequently, only little leverage on the performance enhancement is available from the optimum selection of fluid type, operating temperatures and pressures. A number of attempts can be retrieved in the scientific literature, ranging from the mainstream approaches -relying on the selection of highly performing fluids [28][29][30] and proper rotary equipment [31][32][33] -to more pioneering techniques, such as the enhancement of the heat exchanging sections, particularly in low-temperature small-scale plants with only few kW electricity production [34][35][36]: a common feature is the high additional cost required by those improvements and the fact that most of the time it is hardly offset by the gain on the power generation it assures.…”

Section: Introductionmentioning

confidence: 99%

Multi-Variable Control and Optimization Strategy for Domestic Solar-ORC Combined Heat and Power Generation System

et al. 2020

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The feasibility of a solar-ORC system for domestic combined heat and power generation (CHP) is deeply affected by both the time-varying ambient conditions (e.g. solar irradiance, temperature, wind speed) and the thermal and electrical load profiles variability of the final application. The definition of a proper control strategy is proven to be a major design-challenge for successful operation of solar-ORC systems, with the main goal of assuring that the thermal power demand for space heating and Domestic Hot Water (DHW) production and the electricity needs are simultaneously satisfied. The rising demand for energy-autonomous systems also calls for the inclusion of a storage system within the base-layout, that could assure the electricity demand is properly matched after sunset or in very-low irradiance conditions, such as cloudy days. A comprehensive model accounts for the dynamic of the plant-integrated unit, featuring an ORC-based plant that bottoms a flat plate solar thermal collector: a parametric study is presented, and an off-design analysis is performed to properly assess the energy performance of the system. The heat availability to the ORC heat exchanger is evaluated, based on solar availability, thermal losses in the pipes and plant requirements, in terms of operating temperature and pressures and organic fluid mass flowrate. R245fa is selected as working fluid in the ORC-section. Sliding vanes machines expander and pump – are considered as rotary equipment. Flat plate heat exchangers complete the base layout, the analysis accounts for. Due to the need for DHW production, a storage unit for hot water is present, upstream the recovery branch: dependently on the ability the fluid at the collector outlet has to meet the ORC requirements for proper operation (about 110°C), the ORC evaporator is fed and the recovery section enabled. Both continuous and unsteady operation underwent an in-depth analysis, as well as the benefits associated with different discharge times for the storage unit. A dedicated control strategy is defined, dependently on whether the electrical output or the thermal one need to be maximized, and accounts for either a flash or a progressive tank discharge. A virtual platform allowed the setting-up of a pilot plant, for direct performance assessment, in presence of different amounts of tank discharges per day and different lower temperatures at the storage tank.

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A dual-intake-port technology as a design option for a Sliding Vane Rotary Expander of small-scale ORC-based power units

Cited by 25 publications

References 29 publications

Experimental Validation of a New Modeling for the Design Optimization of a Sliding Vane Rotary Expander Operating in an ORC-Based Power Unit

Experimental Validation of a New Modeling for the Design Optimization of a Sliding Vane Rotary Expander Operating in an ORC-Based Power Unit

Experimental Assessment of a Multi-Variable Control Strategy of a Micro-Cogeneration Solar-ORC Plant for Domestic Application

Multi-Variable Control and Optimization Strategy for Domestic Solar-ORC Combined Heat and Power Generation System

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