Methods of Increasing Net Work Output of Organic Rankine Cycles for Low-Grade Waste-Heat Recovery

An organic Rankine cycle (ORC) is a thermodynamic cycle that is particularly well-suited for waste heat recovery. It is generally employed for waste heat with temperatures in the range of 80 °C – 300 °C. When the application is strictly to convert waste heat into work with no restrictions on heat source exit temperature, thermal efficiency is not as relevant as other aspects of the cycle performance. In such an application, maximization of net power may be the objective rather than maximization of thermal efficiency. An air-cooled ORC for waste-heat conversion is studied in the present work. Two alternative cycle configurations which could increase the net power produced from a heat source with a given temperature and flow rate are proposed and analyzed. These cycle configurations are: • An ORC with two-phase flash expansion • An ORC with a zeotropic working fluid mixture (ZRC) A simplified ORC model is introduced which calculates the pinch point in the heat exchangers based on a specified minimum temperature difference. This model is used to assess the merits of each cycle configuration with respect to a baseline ORC when the finite capacity of the heat source and heat sink fluids is considered. The finite capacity of the heat sink fluid is incorporated into the model in terms of a condenser fan power requirement. Of all working fluids studied for the baseline ORC, R134a and R245fa result in the highest net power. The ORC with two-phase flash expansion offers the most improvement over the baseline cycle provided the expander can handle two-phase flow at the same isentropic efficiency as in the baseline case. Relative improvements are highest at low source temperatures. The maximum increase in net power is 84% over the baseline ORC when water is the working fluid at a source temperature of 80 °C. At low source temperatures, the improvements decrease with increasing condenser fan power requirements. The improvements of the ZRC are also higher for low heat source temperatures. The ZRC shows improvement between 20% and 40% over the baseline as long as the condenser fan power is not negligible. At the highest estimated condenser fan power, the ZRC shows up to 92% improvement at a source temperature of 100 °C, while the ORC with flash expansion is no longer beneficial. This work represents a first step toward identifying a more optimal ORC configuration for waste heat recovery. Other data, including experimental validation, operating experience, and economic analysis particular to an application will be required to support a final recommendation

Development and a Validation of a Charge Sensitive Organic Rankine Cycle (ORC) Simulation Tool

Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution strategies: condenser subcooling and total working fluid charge of the system. The latter allows the subcooling level to be predicted rather than specified as an input. The overall cycle model is composed of independent models for pump, expander, line sets, liquid receiver and heat exchangers. Empirical and semi-empirical models are adopted for the pump and expander, respectively. A generalized steady-state moving boundary method is used to model the heat exchangers. The line sets and liquid receiver are used to better estimate the total charge of the system and pressure drops. Finally, the individual components are connected to form a cycle model in an object-oriented fashion. The solution algorithm includes a preconditioner to guess reasonable values for the evaporating and condensing temperatures and a main cycle solver loop which drives to zero a set of residuals to ensure the convergence of the solution. The model has been developed in the Python programming language. A thorough validation is then carried out against experimental data obtained from two test setups having different nominal size, working fluids and individual components: (i) a regenerative ORC with a 5 kW scroll expander and an oil flooding loop; (ii) a regenerative ORC with a 11 kW single-screw expander. The computer code is made available through open-source dissemination

Role of Germination in Murine Airway CD8+ T-Cell Responses to Aspergillus Conidia

Pulmonary exposure to Aspergillus fumigatus has been associated with morbidity and mortality, particularly in immunocompromised individuals. A. fumigatus conidia produce β-glucan, proteases, and other immunostimulatory factors upon germination. Murine models have shown that the ability of A. fumigatus to germinate at physiological temperature may be an important factor that facilitates invasive disease. We observed a significant increase in IFN-γ-producing CD8+ T cells in bronchoalveolar lavage fluid (BALF) of immunocompetent mice that repeatedly aspirated A. fumigatus conidia in contrast to mice challenged with A. versicolor, a species that is not typically associated with invasive, disseminated disease. Analysis of tissue sections indicated the presence of germinating spores in the lungs of mice challenged with A. fumigatus, but not A. versicolor. Airway IFN-γ+CD8+ T-cells were decreased and lung germination was eliminated in mice that aspirated A. fumigatus conidia that were formaldehyde-fixed or heat-inactivated. Furthermore, A. fumigatus particles exhibited greater persistence in the lungs of recipient mice when compared to non-viable A. fumigatus or A. versicolor, and this correlated with increased maintenance of airway memory-phenotype CD8+ T cells. Therefore, murine airway CD8+ T cell-responses to aspiration of Aspergillus conidia may be mediated in part by the ability of conidia to germinate in the host lung tissue. These results provide further evidence of induction of immune responses to fungi based on their ability to invade host tissue

Performance Benefits for Organic Rankine Cycles with Flooded Expansion

An organic Rankine cycle (ORC) is often used in waste heat recovery applications. These are typically small-scale applications where cycle thermal efficiency is low, and the benefits of traditional cycle enhancements (such as reheat stages or feed-water heaters) do not typically outweigh the costs required to implement them. An ORC with flooded expansion and internal heat regeneration is an alternative enhancement that provides comparable benefits at reduced cost and complexity. The improvement in efficiency for the ORC with flooded expansion and internal regeneration is analyzed for several working fluids and for two flooding media: water and Zerol 60 compressor lubricant. It is shown that internal regeneration alone provides most of the efficiency enhancement for dry working fluids (R600a, n-Pentane, and R245fa). n-Pentane is shown to offer the most efficient cycle even without flooded expansion in most cases. A quantitative comparison is given between the proposed cycle and the reheat and feedwater heater cycles with internal regeneration. In applications where a hydrocarbon may not be appropriate as a working fluid, R245fa and R717 show promise as alternatives. R717, which shows the most benefit from flooded expansion and internal regeneration, requires this enhancement in order to be competitive with the dry working fluids

Experimental Testing of an Organic Rankine Cycle with Scroll-type Expander

An organic Rankine cycle (ORC) is a power cycle employing an organic working fluid. The term ORC is also applied generally to any Rankine cycle with a low-grade heat source (80° – 300°C). Because ORC are often employed in small-scale applications, use of positive displacement equipment is favored over the centrifugal units used in large-scale power plants. A key feature of a positive displacement expander is its built-in volume ratio. An ORC with a scroll-type expander is studied experimentally. Data for steady state tests of the ORC are presented according to a proposed steady state standard. It is shown that the adiabatic efficiency of the expander can be fully characterized by its filling factor and the expansion volume ratio imposed across it. In particular, the peak adiabatic efficiency occurs near a filling factor of unity and an expansion volume ratio near the built-in volume ratio of the expander. The influence of the expander’s performance on cycle efficiency is considered. A procedure is presented which allows prediction of cycle performance based on knowledge of the expander efficiency versus expansion volume ratio, cycle operating conditions, and working fluid. Using this procedure, an optimal expander can be chosen for a set of cycle operating conditions based on its peak efficiency and built-in volume ratio

Development of a general organicRankine cycle simulation tool: ORCSIM

This paper presents a generalized framework for simulating steady-state performance of organic Rankine cycles named ORCSim. A Basic ORC (with or without internal regeneration) and an ORC with liquid-flooded expansion (ORC) are the current cycle configurations implemented. The overall architecture of the simulation code is described and an introduction of the individual component models is also provided. Emphasis is giv-en to the solution algorithm, which is based on the subcooling level or the total fluid charge of the system, and improvements compared to existing models. The thermo-physical properties have been integrated by means of a wrapper, which couples the CoolProp library with flooding medium properties, typically lubricants. Both the simulation code and the graphical user interface (GUI) have been developed in the Python pro-gramming language and it will be released as fully open-source. Finally, an example of the ORCSim capabili-ties is shown by performing two simulations

Automated Contouring and Planning in Radiation Therapy: What Is ‘Clinically Acceptable’?

Developers and users of artificial-intelligence-based tools for automatic contouring and treatment planning in radiotherapy are expected to assess clinical acceptability of these tools. However, what is ‘clinical acceptability’? Quantitative and qualitative approaches have been used to assess this ill-defined concept, all of which have advantages and disadvantages or limitations. The approach chosen may depend on the goal of the study as well as on available resources. In this paper, we discuss various aspects of ‘clinical acceptability’ and how they can move us toward a standard for defining clinical acceptability of new autocontouring and planning tools