Stirling Cycle Research Articles

Development of a cryogenic condenser and computation of its heat transfer efficiency based on liquefaction of nitrogen gas

Abstract The typical cryogenic condenser described here transfers the refrigerating effect from its inner side to its outer side through the wall of the condenser. The separate close refrigeration cycle operates on Reverse Stirling Cycle using hydrogen or helium as working fluid. The nitrogen gas gets liquefied when it comes in contact with the cold outer surface of the condenser. We have successfully developed a cryogenic condenser using copper of electrolytic grade for a liquefaction duty of 10 liters of liquid nitrogen per hour. Condenser effectiveness is evaluated by assembling it in Cryogenerator model, ZIF-1002 and by noting the liquefaction rate. Both the results are satisfactory. Selection of material, fabrication, testing of the condenser developed for a Cryogenerator have been described in the paper to assess its suitability for a Cryogenerator based on Reverse Stirling cycle liquefier.

Mathematical modeling of Stirling engine operating modes as part of an autonomous power complex based on renewable energy sources

The opportunity of application of Stirling engine with non-conventional and renewable sources of energy. The advantage of such use. The resulting expression for the thermal efficiency of the Stirling engine. It is shown that the work per cycle is proportional to the quantity of matter, and hence the pressure of the working fluid, the temperature difference and, to a lesser extent, depends on the expansion coefficient; efficiency of ideal Stirling cycle coincides with the efficiency of an ideal engine working on the Carnot cycle, which distinguishes a Stirling cycle from the cycles of Otto and Diesel underlying engine. It has been established that the four input parameters, the only parameter which can be easily changed during operation, and which effectively affects the operation of the engine is the phase difference. Dependence of work per cycle of the phase difference, called the phase characteristic, visually illustrates mode of operation of Stirling engine. The mathematical model of the cycle of Schmidt and the analysis of operation of Stirling engine in the approach of Schmidt with the aid of numerical analysis. To conduct numerical experiments designed program feature in the language MathLab. The results of numerical experiments are illustrated by graphical charts.

Dynamic performance analysis and optimization of dish solar Stirling engine based on a modified theoretical model

A modified theoretical model of dish solar Stirling engine was developed based on a Stirling cycle operating with finite shaft rotating speed and the energy balance equations at hot and cold ends. The convergence of solar receiver temperature and charged gas heat releasing temperature represent the stabilization of solar receiver and Stirling engine respectively, thus, to guarantee a steady operation of the overall system. Impacts of meteorological condition, operational parameter of Stirling engine on system performance were investigated and analyzed systematically. Results indicate that higher solar flux intensity improves system performance while wind deteriorates the system performance. With the input solar energy specified, optimal charged gas mass in Stirling engine exists corresponding to the maximal power output. More effective heater, regenerator and cooler contribute to better optimal system performance. Meanwhile, the charged gas mass optimized under the daily average solar flux intensity achieves the maximal mechanical work in a day with less computation. The maximal theoretical peak power output of 25 kW and overall efficiency of 44% are obtained as high performance heat exchangers are adopted and charged gas mass is optimized.

Effects of circumsolar radiation on the optimal performance of a Stirling heat engine coupled with a parabolic dish solar collector

This paper investigates the effects of circumsolar radiation on the optimal performance of a coupled parabolic dish and a Stirling heat engine, referred to as the Dish/Stirling system. The presence of circumsolar radiation results in the widening of the solar cone in which the solar beam (direct) radiation is received by the parabolic dish. This beam radiation cone enlargement effectively degrades the collector performance, especially for the very high concentration ratio collectors such as the parabolic dish. The enlarged solar beam radiation cone angular width results in enhanced solar radiation flux spillage at the receiver due to the inability of the parabolic dish reflector surface to focus a significant fraction of incoming beam radiation. This reduces both the energy input as well as the maximum temperature of the Stirling heat engine cycle and causes a reduction in the overall thermal efficiency of the Dish/Stirling system. The present study analyzes this effect by considering various levels of circumsolar radiation, characterized by a parameter known as the circumsolar ratio. The data for the intercept factor of the parabolic dish collector is based on the circumsolar radiation measurements obtained by researchers at the Lawrence Berkeley Laboratory, and the results of analysis reported by researchers at the Solar Energy Research Institute (currently the National Renewable Energy Laboratory). For the present analysis, this intercept factor data is curve-fitted for different circumsolar ratio, mirror optical errors and the concentration ratio using a MATLAB® program. The overall thermal efficiency of the Dish/Stirling system is maximized with respect to the concentration ratio of the parabolic dish and the maximum temperature ratio of the Stirling heat engine using the first law of thermodynamics. This optimization process is performed using a MATLAB® program. Optimal values of concentration ratio for the parabolic dish collector, and the maximum temperature ratio of the Stirling cycle are obtained corresponding to the maximum overall thermal efficiency of the Dish/Stirling system. The study shows that, for a parabolic collector with low mirror optical error and rim angle of 60°, an increase in circumsolar ratio from 0.02 to 0.2 reduces the maximum overall thermal efficiency, optimal concentration ratio and optimal temperature ratio by about 13%, 18% and 7% respectively. In the case of parabolic collectors with high mirror optical error and rim angle of 60°, an increase in circumsolar ratio from 0.02 to 0.2 reduces the maximum overall thermal efficiency, optimal concentration ratio and optimal temperature ratio by about 10%, 11% and 5% respectively. Similar trends are observed for parabolic dish collectors with rim angle of 40°. Results from this study are presented in the form of performance charts that show the effects of varying circumsolar ratios, mirror optical errors, rim angles, non-dimensional radiation flux and non-dimensional convection loss parameters on the maximum overall thermal efficiency of the Dish/Stirling system.

Exergy and energy analysis of a novel power cycle utilizing the cold energy of liquefied natural gas

The liquefied natural gas, LNG, possesses cold energy that can be put to use in the regasification process for various purposes. In this paper the proposed configuration consists of a Rankine cycle, an Organic Rankine cycle, and a Stirling cycle. The LNG cold energy and the enthalpy of the flue gas, which are the product of the combustion chamber, are used as the heat sink and the heat source of the mentioned cycles, respectively. Thermal and exergy analysis are conducted on the novel cycle. A parametric study is also carried out and finally the optimum working condition for the plant is obtained. The results indicate that in an optimum condition the thermal and exergy efficiencies can reach up to 53.51% and 47.43%, respectively. The parametric analysis shows that the pressure ratio of the Rankine cycle’s turbine and the Brayton cycle’s compressor can have a significant effect on the overall performance of the proposed plant. The overall result from the analysis suggests that implementing the three mentioned cycles (Organic Rankine Cycle, Stirling cycle and Rankine cycle) that employ the LNG cold energy, can lead to 43% increase in the output power in comparison with utilizing the Brayton cycle alone.

Концепція спряжених на критичній ізохорі циклів Стірлінга, працюючих на двоокису вуглецю

В роботі пропонується нова концепція реалізації циклу Стірлінга в області не тільки надкритичних, але й, власне, критичних температури і тиску, заснована на виявленій в наших попердніх роботах вираженій гетерогенній структурі надкритичних флюїдів. Існування такої гетерогенної стаціонарної наноструктури решіткового типу в достатньо широких діапазонах надкритичних властивостей, які були названи не-гіббсівською фазою флюїду, було запропановане (Роганковим В.Б та іншими) у рамках моделі ФТ (флуктуаційної термодинамики). Така флюїдна структура в практичному використанні може бути досить перспективною. Вона проявляється в наявності досить регулярного, решіткового типу просторового розподілу густини флюїду і його теплових властивостей в т.зв. мезоскопічних малих об’ємах всередині робочих порожнин стискання і розширення пропонованої схеми спряжених стірлінгів. Саме поняття спряження означає ідею максимально-ефективного використання теплоти, одержаної в циклі від джерела, шляхом поєднання двох підциклів високого (І) і помірного (ІІ) тиску вздовж критичної ізохори. В роботі введене нове поняття ступеня теплофізичної досконалості (доповнюючий прийняте поняття термодинамічної досконалості, для окремих стадій – ізоліній і вузлів – нод спряженого повного циклу типу Стірлінга-Рейліса, яке дозволяє кількісно оцінити позитивний ефект додаткової внутрішньої рекуперації на загальну регенерацію теплоти. Ізольована від навколишнього середовища конструкція обох підціклів (І) і (ІІ) і об`єднуючого стірлінга є його перевагою у порівнянні з циклами внутрішнього згоряння. В якості потенціально-перспективної робочої речовини пропонується двоокис вуглецю. Таким чином, наша мета полягає у використанні виявлених нанодисперсних властивостей флюїду для формулювання концепції створення спряженного, досить ефективного циклу Стірлінга з перспективним робочим тілом - надкритичним двоокисом вуглецю, замість традиційного використання водороду або гелію.

Techno-economic analysis of thermoelectrics for waste heat recovery

ABSTRACTThis article analyses the technical and economic aspects relating to the application of thermoelectric generators in waste heat recovery. It is explained why material cost reductions are unlikely to result in significant reductions in overall device cost. The difficulties associated with manufacturing modules that can withstand high temperatures are shown to result in high cost to power ratios, despite the favorable thermodynamic conditions. This study also compares the performance of thermoelectric generators to Rankine and Stirling cycles and finds that Rankine cycles are able to achieve superior thermal efficiencies at power outputs above 100 kW. Between the ranges of 10 and 100 kW, the thermal efficiency of thermoelectric generators are comparable to that of Rankine cycles. Below 10 kW, thermoelectric generators have greater efficiency than Rankine cycles, but lower efficiency than Stirling cycles. Future expansion of their use in large-scale waste heat recovery will require commercialization of materials with significantly higher thermal efficiency than presently available.

Development and investigation of a regenerator for a reverse Stirling cycle based cryogenerator

The regenerator is considered to be the heart of the Stirling cycle gas liquefier and it is an efficient compact reversing type heat exchanger. Its packing material is first cooled by the cold gas displaced from the expansion space to the compression space and subsequently this matrix material in turn cools the working gas displaced from the compression space to the expansion space. A regenerator is successfully developed by using copper wool matrix having 50 gauges (0.022 mm). The outer and inner casing has been fabricated from fiber glass reinforced plastic. The matrix material is filled in the casing and sealed with a brass ring of 24 gauges (0.51mm). The regenerator is tested successfully by replacing the original regenerator from ZIF-1002 Cryogenerator machine and by liquefying air. The present paper describes the details of the Regenerator development, its testing and evaluation of its relative effectiveness and the result is encouraging.

Experimental and numerical investigations of operational parameters of TRIUMF’s cyclotron cryogenic system

TRIUMF houses the world’s largest cyclotron built in 1972. The cyclotron accelerates H− ions up to 520 MeV. Proton beams are extracted from the cyclotron by using stripping foils converting H− ions to H+ ions. High availability of the 520 MeV proton beams is a vital part of TRIUMF’s scientific program. Vacuum tank of the cyclotron is ≈ 100 m3 chamber operating at 1 × 10−8 Torr pressure during beam production. The vacuum is achieved through the use of turbo pumps, cryopumps and cryopanels. The cryopanels are a form of a distributed cryopump that does the major portion of pumping. The cryogenic system of cryopanels went through an extensive upgrade from B-20 Stirling cycle cryo-refrigerators to Linde-1630 helium liquefier. Open-loop liquid nitrogen circulation was introduced for cryopanels 80 K shield. Operational costs associated with procurement of liquid nitrogen triggered the search for alternative configurations of cryogenic support for cryopanels. This paper presents the results of TRIUMF’s evaluation for possible upgrades of the existing cryogenic system, as well as experimental and numerical investigations of its operational parameters.

Design and development of porous regenerator for Stirling cryocooler using additive manufacturing

The performance of the Stirling cryocoolers essentially depends on the performance of the regenerator. The regenerator used in Stirling cycles has, essentially, having a high surface area and heat capacity leading to large heat transfers. Packed Metal wool, packed wire Mesh screen, randomly packed sphere, porous metal structure are some of the common types of regenerator matrix materials. Wire mesh based regenerators matrix material are common as it provides high heat transfer area with lower entropy generation rate. The paper study in detail the design and structural parameters of mesh type regenerators of Stirling cryocoolers. The work also involves the design, development and attempt to fabricate a prototype porous type Stirling Cryocooler regenerator with a porosity range of 69–71% using Direct Metal Laser Sintering (DMLS) techniques of additive manufacturing, which will enable to use it as a retrofit regenerator to the existing Stirling cycle based liquid nitrogen plants.

Waste Heat Recovery and Conversion into Electricity: Current Solutions and Assessment

The main energy consumption sectors are the residential, industry and transport. In all of them, a part of the energy consumption is not used and generally rejected as heat in the environment. This is named the waste heat. Firstly, the main way is to optimize the process to reduce the fuel consumption. Then, if there is a residual waste heat, a valorization way is to convert this heat into electricity. Some technologies are developed. The main technology is the Organic Rankine Cycle engine. Then, a new concept, named Turbosol, is based on the quasi-isothermal expansion of a water and oil mixture in a nozzle. Some piston engines are also developed, based on Stirling, Ericsson and Joule cycles. All these technologies are named externally heated engines. Some other research studies concern the thermo-electric effect and the thermo-magnetic effect. In this article, a non-exhaustive list, with description and comments on these technologies is proposed. The aim is to assess the potential of them and identify the current limits. To compare the different technologies in first law efficiency terms is not sufficient. Some new criterions are proposed. The first consideration is to assess the heat rate consumption referred to the heat rate available. To assess the quality of waste heat to power conversion, it is pertinent to evaluate the power output divided by the available heat rate. Then, because of the second law, it is pertinent to evaluate the exergy recovery ratio. These new waste heat criterions are compared to the classical first law efficiency in different cases. Then, the main current issue is to produce enough electrical power output to ensure the profitability. Some thermo-economic considerations are proposed, including the impact of a waste heat taxation.

Enhancing Cooling System of a Combustion Engine by Integrating with a Stirling Cycle

For this article, experimental work was conducted to integrate a Stirling cycle unit onto a vehicle radiator for enhancing the cooling system of a car engine. The Stirling cycle was integrated with...

Analyses of entropy generation and entransy for a Stirling cycle system based on generalized heat transfer law

In this paper, a Stirling cycle heated by a finite reservoir is analyzed and optimized with the entropy generation minimization and the entransy theory based on generalized heat transfer law. Taking the output power and the heat-work conversion efficiency as the optimization objectives, we discuss the optimization applicability of the concepts of entransy loss rate, entransy variation rate associated with work, entransy dissipation rate, entransy loss coefficient, entropy generation rate, entropy generation number and revised entropy generation number in detail. Three numerical cases are presented. The results show that both the entransy loss rate and the entransy variation rate associated with work always increase with the increase of output power, and the entransy loss coefficient always increases with the increase of heat-work conversion efficiency. However, larger entransy dissipation rate and smaller entropy generation rate do not always lead to larger output power, while smaller entropy generation number and smaller revised entropy generation number do not always lead to larger heat-work conversion efficiency, either. Therefore, with the three numerical cases discussed in this paper, we can conclude that the concepts of entransy loss rate, entransy variation rate associated with work and entransy loss coefficient are applicable for the optimization analysis, while the other parameters are not always applicable. Based on the results above, the controversy about the entransy theory is also discussed. The main problems in some negative comments of the entransy theory are summerized and analyzed, such as tampering the original text, logical inconsistency, simple repetition of academic views, renaming key concepts and even personal attacks, etc. It should be noticed that these negative comments are not real academic discussions. To some extent, the results in this paper can also be a responce to some negative comments.

Constant chemical potential cycles for capacitive deionization.

The primary energy consuming operations which occur within a Capacitive Deionization (CDI) cell, are the ion removal (electrosorption), ion concentrating (electrodesorption), and solution switching processes. In theory the maximum system performance for a CDI system arises when solution switching occurs while maintaining a fixed number of ions (N), and when electrosorption/desorption occurs while maintaining a fixed chemical potential (μ). These fixed state variable based operations are analogous to the Carnot cycle, where heat transfer occurs at constant temperature and compression and expansion occur while maintaining constant entropy. In reality, maintaining a constant number of ions during switching is not practically feasible, thus here we investigate two alternative cycles where switching instead occurs while maintaining constant charge or voltage. Unlike constant number of ions, maintaining charge and voltage constant is feasible using a potentiostat. These theoretical cycles were chosen as they are analogues or ideal-like (Stirling and Ericsson) cycles, which are also practically feasible. The thermodynamic analysis reveals that these alternative cycles provide an avenue to approach the theoretical limit with low saline feed water; however, they are not capable of approximating ideal operations at elevated feed-water concentrations.

Development of a linear compressor for a stirling cycle based cryocooler

With a view to minimize the power consumption, a method to evaluate the factors influencing the performance of a compressor driving a Stirling cycle based cryocooler has been proposed. An experimental as well as a numerical approach has been employed to analyze the flexure bearing stiffness. Additionally, gas spring stiffness has been found analytically. Consequently, the undamped natural frequency, of the flexure bearing spring system employed in the compressor has also been calculated. Additionally, in contrast to the traditional and often employed method of assuming the gas spring to be constant, an attempt has been made to find out the variation of the gas spring/stiffness during the compression stroke of the compressor. The effect of leakage of the working gas from the clearance between the piston and cylinder has also been considered.

Fundamental Operating Characteristics of an Active-type Regenerator

This paper shows a new regenerator which is called active-type regenerator for practical use. Then also fundamental operating characteristic of a Stirling cycle machine using an Active-type regenerator are presented. Then technical points for these practical uses are arranged. We designed and developed an active type regenerator which is using polyurethane foam matrix and copper matrix as a heat storage material. Then, the availability of that was evaluated by an experiment. The authors have designed and developed an Active-type regenerator for small size Stirling cycle machine. This paper presents some thermodynamic characteristics shown by PV analysis and experiments on a Stirling cycle machine with an active-type regenerator made of copper matrixes and nylon or urethane matrixes. These results demonstrate that the active-type regenerator is one of the promising candidates as a high efficiency regenerator for the Stirling cycle machine.

Stirling cycle for hot and cold drinking water dispenser

Hot and cold drinking water is one of the currently essential domestic demands. The global market of the water dispenser, which uses the vapour-compression refrigeration cycle, is steadily expanding. However, water dispenser consumes a large amount of the annual electricity of the household sector. In this research, a proposed design of a hot and cold drinking water dispenser operating on the reversed Stirling cycle is presented. In this proposed design, the heat energy rejected from the Stirling cycle is recovered to produce the hot water, such that the water dispenser could achieve higher efficiency in comparison to the conventional water dispensers. A mathematical model was formulated to study the performance of the Stirling cycle. Different design parameters controlling the performance of the Stirling cycle refrigerator/heat pump were optimized in order to achieve the desired cold and hot water temperatures at high energy efficiency.

A novel solar-powered liquid piston Stirling refrigerator

The objective of this research project is to develop a solar-powered refrigerator in the lower capacity range of up to 5 kW of cooling power. With the use of liquid pistons and one of the most efficient thermodynamic cycles known, the Stirling cycle, this product has the potential to outperform rival solar cooling technologies while providing inexpensive, reliable, quiet, environmentally-friendly, and efficient solar cooling for residential use, due to its straightforward manufacturing, simple design and inert working gas. Presented in this paper are the newest results of the theoretical and experimental investigation into deducing the key design parameters and system configuration of the so-called Liquid Piston Stirling Cooler (LPSC), which will help lead to optimal performance. Computer models of the complex unconstrained system have been constructed and validated using the modelling software Sage and shown to replicate system behavior with reasonable accuracy in experiments. The models have been used to predict system improvements and identify limitations imposed by the use of liquid pistons. The results to date provide a unique insight into a relatively little studied area in Stirling cycle research.

Fabrication of Stirling Engine and study its characteristics

Gama Stirling engine was designed and manufactured using low cost materials, which operates on Stirling cycle. Air was used as a working fluid, the engine can be heated by any fuel. This Study showed the properties of the engine, the efficiency dependent on temperature and pressure , the maximum rpm of engine is 900 . These engines can be used to generate power in rural areas that have not completed the required energy that is powered by conventional fuels.

The saturated and supercritical Stirling cycle thermodynamic heat engine cycle

On the assumption that experimentally validated tabulated thermodynamic properties of saturated fluids published by the National Institute of Standards and Technology are accurate, a theoretical thermodynamic cycle can be demonstrated that produces a net-negative entropy generation to the universe. The experimental data on the internal energy can also be used to obtain a simple, empirical equation for the change in internal energy of a real fluid undergoing isothermal expansion and compression. This demonstration provides experimental evidence to the theory that temperature-dependent intermolecular attractive forces can be an entropic force that can enhance the thermodynamic efficiency of a real-fluid macroscopic heat engine to exceed that of the Carnot efficiency.