DIPS Organic Rankine Cycle Heat Rejection System

<div class="htmlview paragraph">To support the Space Exploration Initiative, studies were performed to investigate and characterize Dynamic Isotope Power System (DIPS) alternatives for the surface mission elements associated with a lunar base and subsequent manned Mars expedition. A key part of this characterization was to determine how the mission environment affects system design. The impact of shielding to provide astronaut protection from power system radiation was also examined. Impacts of mission environment and shielding were examined for two representative DIPS types (closed Brayton cycle and Stirling cycle converters). Mission environmental factors included: (1) thermal background; (2) dust and atmospheric corrosion; (3) meteoroid damage; and (4) presence of an atmosphere on Mars.</div> <div class="htmlview paragraph">Physical effects of these factors on thermal power systems were identified and their parametric range associated with the mission and mission environment were determined. The quantitative impacts of these factors on DIPS mass and radiator area were then estimated. Results of the study showed that the greatest impacts result from integration with the user.</div>

A SUNTRACKER (illustrated in figure1), is a Concentrating Solar Power (CSP) unit, in the category of solar dish engines. The novel solar dish engine module (shown in figure 2) is designed to provide 10.1kW electric power (measured at the engine output electric power lugs), from a conversion of 21kW solar energy from the solar dish reflective sun light to the high temperature receiver focal point. Total electric power output from the solar dish engine module is attributed to combined cycles, closed brayton cycle (CBC) and a organic rankine cycle (ORC), both of which are hermetically sealed to atmosphere. The CBC engine receives 21kW solar energy from a solar dish, estimated to have 27 square meters (291 square feet) reflective surface area. However, unlike the photovoltaic (PV) units, the SUNTRACKER will provide increased use of available solar energy from sunlight. Concentrated sunlight from the dish will focus on the CBC engine receiver, which in turn heats the working fluid media to as much as 1600F, pending the ratio of solar dish to receiver areas. A specific gas mixture of xenon/helium, with excellent thermodynamic properties is used for the high temperature application. Turbomachinery in the CBC engine has one moving part / assembly (compressor impeller, alternator rotor and turbine rotor), mounted on compliant foil bearings. Reference figure 4 as an example. The engine operates with a compressor impeller stage pressure ratio 1.6, and is recuperated. Electric power, measured at the CBC engine electric power lugs, is 6.4kW. The CBC engine is not new, (a closed Brayton cycle, sealed to atmosphere) [1], [4], [8], [18], [19]. However, the application to extract thermal energy from the sunlight and provide electric power in commercial and residential use is (patented). In addition, to increase the efficiency of solar energy conversion to electric power, waste heat from the CBC engine provides thermal energy to an ORC engine, to generate an additional electrical output of 3.7kW (measured at the output electric power lugs). With use of an ORC system, the size of the radiator (CBC unit) for heat rejection is reduced significantly. Working fluid HFC-RC245fa [10] was selected for the ORC unit, based on the low temperature application. Also, as with the CBC turbomachinery, the ORC rotor assembly has one moving part, comprised of a pump impeller, alternator rotor and turbine rotor. With the two engines combined, total system thermal efficiency is 48% (10.1kW electric power out / 21kW solar energy in). However, power electronics are needed for conversion of high frequency voltage at the engine output electric power leads to 60/50 Hz power, for customer use. Power electronics losses for this machine, debits the power 0.5 kW. Thus total electric power to the customer, as measured at power electronics output terminals, is 9.6kW. With solar energy, from the reflective sunlight solar dish 21kW and measured output power from the power electronics 9.6kW, the conversion of solar energy to useful electric power an efficiency 46% (i.e. 9.6kW / 21kW). In addition, the design does not require external water / liquid for cooling.

This paper presents trade studies that address the use of the thermionic/AMTEC cell — a cascaded, high-efficiency, static power conversion concept that appears well-suited to space power applications. Both the thermionic and AMTEC power conversion approaches have been shown to be promising candidates for space power. Thermionics offers system compactness via modest efficiency at high heat rejection temperatures, and AMTEC offers high efficiency at modest heat rejection temperature. From a thermal viewpoint, the two are ideally suited for cascaded power conversion: thermionic heat rejection and AMTEC heat source temperatures are essentially the same. In addition to realizing conversion efficiencies potentially as high as 35–40%, such a cascade offers the following perceived benefits: • Survivability — capable of operation in the Van Allen belts. • Simplicity — static conversion, no moving parts • Long lifetime — no inherent life-limiting mechanisms identified • Technology Readiness — Large thermionic database; AMTEC efficiencies of 18% current being demonstrated, with more growth potential available • Technology Growth — applicable to both solar thermal and reactor-based nuclear space power systems Mechanical approaches and thermal/electric matching criteria for integrating thermionics and AMTEC into a single conversion device are described. Focusing primarily on solar thermal space power applications, parametric trends are presented to show the performance and cost potential that should be achievable with present-day technology in cascaded thermionic/AMTEC systems.

<div class="section abstract"><div class="htmlview paragraph">Growing global warming and the associated climate change have expedited the need for adoption of carbon-neutral technologies. The transportation sector accounts for ~ 25 % of total carbon emissions. Hydrogen (H2) is widely explored as an alternative for decarbonizing the transport sector. The application of H2 through PEM Fuel Cells is one of the available technologies for the trucking industry, due to their relatively higher efficiency (~50%) and power density. However, at present the cost of an FCEV truck is considerably higher than its diesel equivalent. Hence, new technologies either enabling cost reduction or efficiency improvement for FCEVs are imperative for their widespread adoption.</div><div class="htmlview paragraph">FCEVs have a system efficiency around 40-60% implying that around half of the input energy is lost to the environment as waste heat. However, recapturing this significant amount of waste heat into useful work is a challenge.</div><div class="htmlview paragraph">This paper discusses the feasibility of waste heat recovery (WHR) technology for a long-haul FCEV heavy duty truck with a rated power of 300 kW. Two WHR system are evaluated – widely used Organic Rankine Cycle (ORC). Working fluids considered for the ORC model are R1233zd(E), R245fa and n-Pentane. The 0-D model of the ORC based WHR systems is developed in Matlab-Simulink platform for analysis. The waste heat generated is quantified at different drive-cycles, namely flat, moderate hilly and hilly terrain, using a complete vehicle simulation tool developed in Simulink platform. The waste heat data from complete vehicle simulation tool is provided as an input for the developed 0-D WHR models. The results show a considerable improvement in the overall fuel consumption of FCEV trucks with WHR systems. The findings imply the importance of WHR in FCEV truck to improve the overall system efficiency.</div></div>

The use of a rotary fluid management device (RFMD) and shear flow condenser for two-phase fluid management in microgravity organic Rankine cycle (ORC) applications is examined. A prototype of the proposed Space Station ORC heat rejection system was constructed to evaluate the performance of the inventory control method. The design and operation of the RFMD, shear flow condenser, and inventory control fluid accumulator are described. A schematic diagram of the ORC, RFMD, and condenser, and a functional diagram of the heat rejection system for the ORC are presented.

<div class="htmlview paragraph">Future space stations and platforms will require a centralized thermal utility to provide temperature control of various heat sinks or sources. Its purpose is to transport large amounts of energy over long distances towards a heat rejection system, with very small temperature differences.</div> <div class="htmlview paragraph">The present paper deals with the heat rejection system. A concept of a multi-tubes condenser has been selected and designed, using ammonia as the working fluid. In order to support and confirm the modelization software, an experiment is set up with a one-tube condenser uniformly cooled, involving limited heat power, but representative of thermo-hydraulic conditions.</div> <div class="htmlview paragraph">This paper presents the test programme. Objectives are first to confirm the selected technology, and to assess internal operation from the measurements of the external temperature along the tube, and differential pressure drop. The experiment which is thought out from an industrial viewpoint also has for purpose to enable simplifications in the modelization, without going into the condensation phenomenon. A description of the test apparatus is also given.</div> <div class="htmlview paragraph">A second condenser tube with asymmetrical cooling, more representative of the space concept (Og), will be tested to quantify the influence of the cooling device on the condensation of the fluid, and adapt the modelization to the space case.</div>

Modelling and optimization of a forced convection heat exchanger for Mars waste heat rejection for power cycle and cryocooling applications

<div class="section abstract"><div class="htmlview paragraph">In today’s world, due to fast depletion of fossil fuel and the increasing CO2 emission, the need to switch to alternate energy sources are higher. Stringent norms on exhaust emissions in IC Engine vehicles implies, very complex after treatment systems. Already many OEMs have refined their development strategies towards phasing out of IC Engines and bringing in Fuel Cell vehicles, Battery Electric Vehicles and Hydrogen IC Engine vehicles. Focus is on Hydrogen for Long Haul vehicles. In this paper cooling system design is demonstrated for Fuel Cell, Battery and Power Electronics system in a Heavy Duty Fuel Cell Electric Truck. Radiator and Fans are selected based on the overall heat rejection and Coolant inlet temperature requirements of components. Cooling system circuit and pump is decided to meet the coolant flow rate targets. High temperature cooling system and Low temperature cooling system are explained in detail. Thermal simulation is done using simulation software KULI. Test results signifies good correlation.</div></div>

<div class="htmlview paragraph">The Space Exploration Initiative, (SEI), has renewed interest in examining various technologies for generating electrical power in space as well as on the surface's of the Moon and Mars. One technology that is of interest is the Closed Brayton Cycle, (CBC). Recent work has further enhanced the capability to perform accurate preliminary design and optimization of CBC power conversion systems for space applications. The basic building block of the computer codes used for this work has been the Closed Cycle Engine Performance, (CCEP), code developed by John Klann at NASA Lewis Research Center. This model was originally developed for the preliminary design and performance analysis of the Space Station Freedom dynamic power conversion system.</div> <div class="htmlview paragraph">Improvements to the model have included linking CCEP with the public domain optimization code COPES/ADS. This linkage has greatly enhanced the utility of the program and streamlined the design process. The designer now has the capability of defining design variables, design constraints and optimization functions. This facilitates studies that explore the interrelationship between system mass, cycle efficiency and radiator area. In a recent study the relationship between system mass, radiator area, cycle efficiency and recuperator effectiveness was examined.</div> <div class="htmlview paragraph">In addition to coupling the design codes with the optimizer, additional modifications have been made to enhance the versatility of the model. A subroutine has been added to allow for an isotope heat source. The radiator code has been modified to allow for the preliminary sizing of the radiator using a closed form solution to the governing equations. To take advantage of the Brayton Cycle's ability to produce significantly more power than when operating at design speed and inlet pressure, the alternator sizing algorithms have been modified to allow for off-design sizing of the alternator. This capability allows the designer to specify the fraction of alternator design output that will be required at the turbomachinery design point. Off-design operation can then be examined at significantly higher power levels.</div> <div class="htmlview paragraph">The final modification that will be discussed is the linking of the finite-element pumped-loop radiator design code with the optimization code COPES/ADS. The radiator code is run externally to the main design routines simply due to the execution time required to converge. Output from the optimized radiator designs are used to update the inputs for the radiator specific mass and fin effectiveness used in CCEP.</div>

Heat rejection design for zero liquid discharge Shand coal-fired power station integrated with CO2 capture and storage

Heat rejection with mechanical pumped cooling loop for lunar surface nuclear reactor power system

Heat rejection from power systems will be necessary for human and robotic activity on the lunar surface. Functional operation of such heat rejection systems is at risk of degradation as a consequence of dust accumulation. The Apollo astronauts encountered marked degradation of performance in heat rejection systems for the lunar roving vehicle, science packages, and other components. Although ground testing of dust mitigation concepts in support of the Apollo mission identified mitigation tools, the brush concept adopted by the Apollo astronauts proved essentially ineffective. A better understanding of the issues associated with the impact of lunar dust on the functional performance of heat rejection systems and its removal is needed as planning gets underway for human and robotic missions to the Moon. Renewed emphasis must also be placed on ground testing of pristine and dust-covered heat rejection system surfaces to quantify degradation and address mitigation concepts. This paper presents a review of the degradation in performance of heat rejection systems encountered on the lunar surface to-date, and will discuss current activities underway to evaluate the durability of candidate heat rejection system surfaces and current dust mitigation concepts.

The transition towards a more affordable, reliable, and sustainable energy provision paradigm is one of the main 21st century challenges that humanity must overcome to protect the planet from the harmful effect caused by climate change. The concentration of CO2 in the atmosphere has been dramatically increasing since the pre-industrial era. If the increase of green-house gasses emissions continues unabated, this will bring dramatic consequences for planet Earth, compromising eventually the existence of many species, including the human race. To avoid a climate change catastrophe, the share of primary energy coming from renewable energy resources must increase from around 15% in 2015 to 65% in 2050. This energy transition can not rely solely on few successful technologies (i.e., solar photovoltaic, and wind energy), but it must count on a larger variety of technical solutions that are suitable for a wider range of renewable sources and diversity of circumstances. For instance, renewable thermal energy sources for power generation (i.e., geothermal reservoir, biomass fuel, and concentrated solar radiation), can provide a large portion of the world electricity demand in the future. However, the exploitation of a good portion of these sources strongly depends on the market success of technologies such as the Organic Rankine Cycle (ORC) power system. One of the key aspects to make ORC systems economically competitive, especially at the smaller sizes (⇡ 1 − 50 kW), is the realization of highly efficient turbomachinery components. The fluid-dynamic design of ORC turbomachinery significantly differs from the design of traditional machines (i.e., steam and gas turbines), and this is mainly due to the different thermo-physical properties and gas dynamic behavior of the organic working fluids. This means that design methods devised for standard steam and gas turbomachinery can not be used for turbomachinery operating in the Non-ideal compressible fluid dynamics (NICFD) region. Furthermore, no experimental campaigns have ever been carried out to create a body of empirical knowledge to support the design highly efficient ORC turbomachinery. As a consequence, the entire design process of ORC turbomachinery relies only on the use of advanced CFD software. The current trend is to couple CFD tools with numerical optimization techniques in order to automatically obtain optimal flow passage geometries. In particular, adjoint-based methods have clearly demonstrated to be the only optimization technique capable of tackling the multi-stage turbomachinery design problem, in which thousands of design variable must be concurrently optimized. Therefore, the research documented in this PhD dissertation aimed at extending the adjoint method in order to perform the fully-turbulent fluid-dynamic shape optimization of 3D multi-stage ORC turbomachinery. This document contains an extensive introduction, three main chapters, each documenting a building block towards the accomplishment of the main goal of this PhD project, and a final concluding chapter that summarizes all the research outcomes of this work and proposes future steps for research in this field. The first part of the thesis describes the extension of the RANS equations, the convective numerical schemes, and the viscous numerical schemes to the use of complex thermo-physical laws, so to simulate turbulent flows of components working in the NICFD thermodynamic region. The second part documents the derivation of the adjoint solver in order to resolve shape-optimization design problems for 2D single row of ORC turbomachinery. Finally, the last part reports the extension of the adjoint method to 3D multi-stage turbomachinery design.

<div class="htmlview paragraph">The Orbiting Carbon Observatory (OCO) instrument is scheduled for launch onboard an Orbital Sciences Corporation LEOStar-2 architecture spacecraft in December 2008. The instrument will collect data to identify CO<sub>2</sub> sources and sinks and quantify their seasonal variability. OCO observations will permit the collection of spatially resolved, high resolution spectroscopic observations of CO<sub>2</sub> and O<sub>2</sub> absorption in reflected sunlight over both continents and oceans. OCO has three bore-sighted, high resolution, grating spectrometers which share a common telescope with similar optics and electronics. A 0.765 μm channel will be used for O<sub>2</sub> observations, while the weak and strong CO<sub>2</sub> bands will be observed with 1.61 μm and 2.06 μm channels, respectively. The OCO spacecraft circular polar orbit will be sun-synchronous with an inclination of 98.2 degrees, mean altitude of 705 km and 98.9 minute orbit period. The OCO mission forms part of NASA's A-Train and leads the afternoon constellation ahead of the Aqua spacecraft.</div> <div class="htmlview paragraph">The instrument thermal design provides two cryogenic temperature zones for the detectors at 120 K and 180 K, one near room temperature zone for the spectrometers at 268 K and one for the electronics and cryocooler at 290 K. It contains three focal plane arrays (FPAs) in three separate housings, two of which are cooled to 120 K, and one to 180 K by a single Northrop Grumman Space Technology (NGST) pulse tube cryocooler. The cryocooler with a coldtip at 110 K, provides refrigeration to all three detectors via a high conductance flexible thermal strap. A variable conductance heat pipe (VCHP) based heat rejection system (HRS), with space viewing radiators, provides cooling for the electronics, cryocooler and maintains the spectrometer at -5°C. The VCHPs, with closed-loop temperature control, transport waste heat from the instrument located inside the spacecraft to the outboard radiators and provide tight temperature control. In survival mode, the instrument is off and the VCHPs are shutdown to minimize survival heater power.</div> <div class="htmlview paragraph">The instrument was fully integrated in December 2007 and has undergone EMI/EMC, vibration, and two thermal vacuum (TV) tests. This paper reports on the results from the TV and thermal balance (TB) tests with an emphasis on the VCHP-based HRS and the cryogenic subsystem (CSS). A brief overview of the thermal control design is presented as well as key test results from the instrument-level thermal vacuum/balance test.</div>

<div class="section abstract"><div class="htmlview paragraph">Waste Heat Recovery System (WHRS) is used to extract heat from the exhaust gas from internal combustion (IC) engines to produce additional power with increase in overall efficiency of the engine. Amongst various WHRS, this paper focuses on WHRS using Rankine Cycle (RC) and Organic Rankine Cycle (ORC). A 100 kVA (80 kW engine) diesel generator was used for this research. Water, R245fa, and R134a were used as the working fluids for the cycle. To assess the performance of WHRS, the system was designed for 80 kW, 70 kW and 60 kW loads and then, for each designed load the WHRS was run for other loads and then compared. Assessment provide simulation results of RC and ORC using Engineering Equation Solver (EES) software. It was found that using water as the working fluid around 20% additional power was achieved. But it limited the working range of the system making it unsuitable for lower loads of 10 and 20 kW for this generator. R245fa and R134a on the other hand provided comparatively less efficiency but covered wide load range. R245fa showed power improvement of 11.2%, and R134a showed a power improvement of 7.0% at 80 kW. At lower powers of 10 and 20 kW the additional powers were 0.84 kW, 1.35 kW and 0.2 kW, 0.43 kW, for R245fa and R134a, respectively and water as the working fluid could not produce any additional power at these lower loads.</div></div>