Solar Dynamic Organic Rankine Cycle Heat Rejection System Simulation

<div class="htmlview paragraph">The increasing need for higher electrical power levels for military and scientific space purposes has spurred development of energy conversion systems with higher efficiencies than the traditional solar array. Numerous nuclear options are currently under development. These fuels eliminate the need for large deployable solar arrays or concentrators, allow unrestricted pointing and maneuvering, and are inherently less susceptible to natural and threat environments; they are the only viable energy source for outer planetary exploration. Fission reactors are the most desirable nuclear source for electric power levels above 10 kW. Radioisotope sources have been used in conjunction with thermoelectrics up to 1 kWe for planetary exploration. However, for radioisotope systems in the 1 to 10 kWe range, a much higher conversion efficiency is required. For over 15 years, NASA and the Department of Energy (DOE) have been developing closed cycle turbo-alternator (dynamic) power conversion systems for space use. The Air Force and DOE are jointly developing such a system under the Dynamic Isotope Power System (DIPS) program.</div> <div class="htmlview paragraph">Two closed dynamic cycles are being evaluated for use as part of the DIPS system. They are the Closed Brayton Cycle (CBC) which uses an inert (single phase) gas as the working fluid. The other system is the Organic Rankine Cycle (ORC) which utilizes the phase change properties of the working fluid. Each has a significantly different effect on the design of a radiative heat rejection system, primarily because of the temperature variation of the CBC single phase heat rejection versus the nearly constant temperature two-phase (condensing) ORC heat rejection. The heat rejection system plays an important role, since the power conversion efficiency is strongly dependent on the heat rejection temperature. The lower the rejection temperature, the higher the efficiency. However, the radiator area requirement increases as the rejection temperature is reduced. On a weight optimization basis both systems are comparable, however, the ORC system requires more radiator area for the same cycle efficiency. With the design requirement that the radiator be mounted around the circumference of the vehicle, available area is limited. Therefore, the heat rejection system design may not be a clear-cut weight optimization but rather a matter of area reduction at minimum penalty to efficiency and weight.</div> <div class="htmlview paragraph">The paper presents the results of an optimization study performed on the heat rejection system for a space based ORC power system using an isotope heat source. The radiator sizing depends on the heat rejection temperature, radiator configuration, and radiator properties such as the fin effectiveness, emissivity, and absorptivity. The optimization analysis to evaluate the effect of each of these parameters on the system weight and area is presented.</div>

Review of organic Rankine cycle for small-scale applications

The study aims to investigate the application of the organic Rankine cycle (ORC) in the bioenergy with carbon capture and storage (BECCS) using gasification of sewage sludge. The tool used in the investigation is the aspen plus software with refprop property methods for calculating fluid properties. The reason for this study is that a detailed analysis of the proposed BECCS process flow diagram indicates that a certain amount of waste heat is available in the exhaust gas from the high-to-intermediate pressure gas turbine. Some of this energy can be used by applying expansion in a low-pressure turbine, optionally by applying regenerative water heating, which is then redirected to the combustion chamber, or finally by incorporating the ORC into the main cycle. For the ORC cycle, different configurations are studied, with regeneration and using different working fluids. For the highest efficiency of the cycle, the regenerative heating of high-pressure water is applied and a suitable ORC working fluid with optimal saturation parameters and mass flow is selected. Such modified proposed BECCS power plant hybrid systems with ORC are compared to the reference case with lower pressure expansion. A study of the heat duty and temperature distribution in heat exchangers is carried out. Five ORC fluids were investigated, namely ethanol, refrigerants R236ea, R245fa, R1233zd(E), and water, which gave a net efficiency of the whole power plant of 39.71%, 40.02%, 40.26%, 40.34%, and 39.35% respectively, while the proposed BECCS reference case gave 38.89%.

By employing the SAFT-VR Mie equation of state, molecular-based models are developed from which the thermodynamic properties of pure (i.e., single-component) organic fluids and their mixtures are calculated. This approach can enable the selection of optimal working fluids in organic Rankine cycle (ORC) applications, even in cases for which experimental data relating to mixture properties are not available. After developing models for perfluoroalkane (n-C4F10+n-C10F22) mixtures, and validating these against available experimental data, SAFT-VR Mie is shown to predict accurately both the single-phase and saturation properties of these fluids. In particular, second-derivative properties (e.g., specific heat capacities), which are less reliably calculated by cubic equations of state (EoS), are accurately described using SAFT-VR Mie, thereby enabling an accurate prediction of important working-fluid properties such as the specific entropy. The property data are then used in thermodynamic cycle analyses for the evaluation of ORC performance and cost. The approach is applied to a specific case study in which a sub-critical, non-regenerative ORC system recovers and converts waste heat from a refinery flue-gas stream with fixed, predefined conditions. Results are compared with those obtained when employing analogue alkane mixtures (n-C4H10+n-C10H22) for which sufficient thermodynamic property data exist. When unlimited quantities of cooling water are utilized, pure perfluorobutane (and pure butane) cycles exhibit higher power outputs and higher thermal efficiencies compared to mixtures with perfluorodecane (or decane), respectively. The effect of the composition of a working-fluid mixture in the aforementioned performance indicators is non-trivial. Only at low evaporator pressures (<10bar) do the investigated mixtures perform better than the pure fluids. A basic cost analysis reveals that systems with pure perfluorobutane (and butane) fluids are associated with relatively high total costs, but are nevertheless more cost effective per unit power output than the fluid mixtures (due to the higher generated power). When the quantity of cooling water is constrained by the application, overall performance deteriorates, and mixtures emerge as the optimal working fluids.

Plate heat exchangers (PHEs) are used extensively in industrial applications and, owing to their compactness, and higher thermal efficiency, they are keys component of organic Rankine cycle (ORC) application. This study presents the experimental heat transfer characteristics during flow boiling of R245fa refrigerant with a commercial working fluid used in ORCs; inside brazed plate heat exchanger with chevron angle of 65 degree. The flow boiling heat transfer characteristics were measured with varying saturation temperatures, mass flux and heat flux, which range from 55.5 °C-61.8 °C, 15.5-17.4 kg m−2 s−1, and 6400-10120 W m−2, respectively. The experimental results showed that flow boiling heat transfer coefficient is dependent upon the heat flux and mass flux. The results showed that the heat transfer coefficient increases with the increase of heat flux, and then starts to decrease due to local dry out. However, at low mass flux, locally triggering dry out was more prominent than that high mass flux. The heat transfer coefficient showed to be sensitive to the change in the saturation temperature. Moreover, flow boiling heat transfer coefficient showed a linear relationship with mass flux of the refrigerant.

An alternative pathway from hot dry rock to green hydrogen by organic Rankine cycle applications

Experimental evaluation of nucleate pool boiling heat transfer correlations for R245fa and R1233zd(E) in ORC applications

Cycle analysis and environmental assessments of cascade organic rankine cycle on diesel engine ships

Expansion devices for organic Rankine cycle (ORC) using in low temperature heat recovery: A review

The Organic Rankine Cycle (ORC) power cycle is a well-established solution for harnessing heat sources to generate energy. Presently, ORC systems predominantly employ hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) as working fluids. However, these substances possess significant greenhouse gas effects and are slated for future bans. To address this, it is imperative to establish rational selection criteria and corresponding techniques for evaluating working fluids suitable for industrial ORC applications. This chapter presents the working fluid selection criteria and screening methods for environmentally friendly working fluids. The chapter is organized as follows: (1) The fundamentals of working fluids section provide a broad introduction to the core principles of working fluids; (2) the working fluid section outlines reasonable selection criteria for identifying potential alternatives; (3) the screening of ORC working fluids section discusses possible working fluid candidates, simulation approach, and thermodynamic models in detail, which is very important to access the thermodynamic performance of ORC cycle; and (4) an example of the simulation of an ORC for working fluid selection section demonstrates the strategy for the selection of a working fluid considering a defined ORC architecture.

Techno-economic assessment for the integration into a multi-product plant based on cascade utilization of geothermal energy

Nowadays, the use of Organic Rankine Cycle (ORC) in decentralised applications is linked with the fact that this process allows to use low temperature heat sources and offers an advantageous efficiency in small-scale applications. Many state of the art applications like geothermal and biomass fired power plants as well as new applications like solar desalination with reverse osmosis, waste heat recovery from biogas digestion plants or micro-Combined Heat and Power (micro-CHP) systems can successfully use the ORC process. The investigation of supercritical parameters in ORC applications seems to bring promising results in decentralised energy production. This paper presents the results from the simulation of the ORC process in normal and supercritical fluid parameters and discusses the efficiency variation in various applications.

A new indicator for minimizing size of an ORC power plant based on heat exchanger and turbine design parameters

Indonesia has high potential biomass energy sources from palm oil mill industry activities. The growing interest on Organic Rankine Cycle (ORC) application to produce electricity by utilizing biomass energy sources are increasingly due to its successfully used for generating electricity from rejected waste heat to the environment in industrial processes. In this study, the potential of the palm oil empty fruit bunch, and wood chip have been used as fuel for biomass to generate electricity based ORC with combustion processes. The heat from combustion burner was transfer by thermal oil heater to evaporate ORC working fluid in the evaporator unit. The Syltherm-XLT thermal oil was used as the heat carrier from combustion burner, while R245fa was used as the working fluid for ORC unit. Appropriate designs integration from biomass combustion unit to ORC unit have been analyzed and proposed to generate expander shaft-work. Moreover, the effect of recuperator on the total system efficiency has also been investigated. It was observed that the fuel consumption was increased when the ORC unit equipped recuperator operated until certain pressure and decreased when operated at high pressure.

Modelling and parametric analysis of small-scale axial and radial-outflow turbines for Organic Rankine Cycle applications