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To further improve the thermal efficiency of gas turbines, the recuperator needs to be employed and the printed circuit heat exchanger with airfoil fins meets the recuperator's requirements of high heat transfer capacity, low flow resistance, and high reliability. However, the effect of airfoil fin pitches is not clear and the structure optimization method should be developed. In this study, the heat transfer quantity and pressure drop per length of the flue gas in the airfoil channels are numerically investigated under different Reynolds numbers and airfoil fin pitches. The results show that the effect of the airfoil transverse pitch has a great effect on the performance of the flue gas and the heat transfer quantity is increased by 82.39 %–96.08 % when the transverse pitch is decreased from 6.0 mm to 1.2 mm. At the same time, the pressure drop per length is increased to 189.39–842.47 Pa/m. The heat transfer performance is varied not obviously when the airfoil longitudinal pitch is varied from 4 mm to 15 mm. Based on the numerical data, the multiple-objective genetic algorithm combined with the backpropagation neural network is proposed for the performance predictions and optimizations. The corresponding Pareto front is obtained and the technique for order preference by similarity to the ideal solution method is employed to obtain the optimal point. Under the current conditions, the heat transfer quantity of the optimal point is 521.25 kW/m2, which is decreased by 34.5 % compared to the highest value, and the pressure drop per length of the optimal point is 108.45 Pa/m, which is decreased by 85.2 % compared to the highest value.

The article analyses the thermal insulation characteristics of the recuperator heat transfer unit of the ventilation system of the public building. The results of the thermographic study showed the temperature distribution on the surface of the system elements. Heat losses are calculated by comparing the temperature of the "hottest" places with the temperature of the "coldest" places in the environment. The research was carried out in late autumn when the outdoor temperature fluctuated between +4 and −2 degrees. It is likely that the heat loss would be significantly higher during the coldest five-day period of winter.

Local heat transfer and flow characteristics, which is crucial to the overall performance of supercritical CO2 recuperators, is rarely examined in details in reported studies. In this paper, the local heat transfer and flow characteristics of supercritical CO2 in sinusoidal channel printed circuit heat exchangers are numerically investigated under the working conditions of recuperators. Based on the simplified physical model constituted by 10 pitches, the variations of Re, heat flux, Nu, secondary flow and other relevant parameters along the flow direction are analyzed firstly. Comparison is further made between the high and low temperature recuperators (HTR and LTR). It's observed that the local heat transfer and flow characteristics vary greatly from the inlet to the outlet, especially in the LTR. Differences of 127.5% and 61.7% can be observed on the cold side of the LTR for Re and heat transfer coefficient h, respectively. Results indicate that the temperature difference and heat transfer coefficient h should not be regarded as constant and the distribution of h should be carefully considered in the design of the LTR. The complicated interactions among the varying thermophysical properties, buoyancy and the periodically changed centrifugal force are believed to be the key that shapes the flow fields. Furthermore, the changes of the wavy angle θ are found to have greater influence than the changes of mass flow rate in reshaping the flow field when θ>25°. Though gravity direction strongly affects the local heat transfer and flow characteristics, it's also found that the effects on the overall thermal-hydraulic performance are relatively minor. Yet the installation direction that yields αy=g should better be avoided for the sinusoidal channel printed circuit heat exchanger. [ABSTRACT FROM AUTHOR]

Transient response of the pinch point is crucial to the evaluations of the recuperator efficiency. A reheat and recompression cycle dynamic simulation system for supercritical CO2 is built, and a transient segmented model is developed to explore the dynamic characteristics of the recuperators. The operating conditions including inlet mass flowrate, temperature and pressure of the low temperature recuperator (LTR) change dramatically with the withdraw-mass variation, which causes different response characteristics of the pinch point. The pinch point gradually transfers from the cold end to the hot end of the LTR as the mass flowrate decreases. The higher pinch-point temperature difference leads to lower heat exchanger effectiveness, and the internal pinch point greatly weakens the recuperator performance. A new prediction model is proposed to quickly determine the pinch point location and analyze the operating conditions prone to cause internal pinch point. The range of split ratio in which the internal pinch point exists in the LTR is obtained. The lower-limit of split ratio variation is sensitive to the high- and low-pressures, the isentropic efficiency of the compressor, and the outlet temperature of the precooler, while the upper-limit of split ratio is only related to the pressures of the recuperator. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nowadays, substantial research efforts are being devoted to technologies which could potentially increase propulsion efficiency and reduce emissions of aircrafts. For this purpose, a waste heat recovery (WHR) combined system based on recuperator and organic Rankine cycle (ORC) is proposed in this paper for rotorcraft powerplant application. The concept is systematically analyzed within an integrated multidisciplinary simulation framework targeting the implicit coupling between rotorcraft-engine system and WHR module under designated flight conditions, also taking the additional weight penalty into consideration. Obtained results through quantification of the potential benefits suggest a considerable improvement in engine fuel economy with the adoption of highly effective recuperator, and ORC can significantly increase the power output, representing more than 24% of the engine power with benzene as working fluid. Reducing the power-to-weight ratio of ORC from 4 to 0.5 kW/kg, the added weight of WHR unit grows exponentially from 80 to 450 kg, which heavily penalizes the valuable carrying capability of the rotorcraft and consequently results in an increase of approximately 3.35%–4.2% in fuel consumption for the designated cruise mode of the generic mission scenario. The overall methodology can be effectively deployed to assess the implementation of WHR technologies for rotorcraft powerplant applications under realistic flight operations.

Introduction. One of the most common ways to save heat energy and money is the use of recuperator units in mechanical ventilation systems. In this article, we will talk about the modernized air recuperator. In the process the design feature, layout and operation algorithm of this heat exchanger device will be demonstrated. In order to increase the choice of type and designs of air heat exchangers, designers will be offered and described the variant of designed combined recuperator with an exhaust air intake device from the room, which in the process will be one of the versions of the device increasing the efficiency factor in mechanical ventilation systems. The recuperator is an indispensable element for modern unique buildings and structures.Materials and methods. The recuperator is proposed as an analogue of existing ones and belongs to the field of energy saving in mechanical ventilation systems.Results. The efficiency increase in comparison with analogues is carried out due to: the use of the recuperator as a combined exhaust air intake unit from the room, an increase in the area of contact of heat carriers, a special internal structure capable of more uniform heat transfer, an atypical arrangement of the recuperator installation to avoid freezing and "defrosting" of condensate at the heat transfer surface. The heating flow of the supply air through the combined recuperator with the exhaust air intake device from the room in the mechanical ventilation system is regulated by automation to maintain a more comfortable supply temperature in the room.Conclusions. The new design acquires an increased efficiency compared to its analogues.

Copyright of International Journal of Advances in Engineering & Pure Sciences is the property of Marmara University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The energy efficiency of ventilation systems is very important. The city of Kryvyi Rih in the Dnipropetrovs’k region of Ukraine has a humid continental climate with an average daily temperature of –6.3°C during its coldest month. Consequently, it is necessary to find methods to improve the energy efficiency of ventilation systems. One of the most effective ways to reduce energy consumption in ventilation systems is to use energy-saving technologies to maintain the microclimate of buildings, including the use of recuperators and devices based on renewable energy sources.

World energy consumption is rapidly increasing, and global rising patterns show a higher consumption increase in residential and commercial buildings. Combined heat and power (CHP) systems have been developed and commercialised to distribute and decentralise electricity generation for domestic applications to reduce energy consumption and gas emissions. The use of a micro gas turbine (MGT) shows a number of advantages over other CHP systems including smaller size, ease of operation, and competitive maintenance cost. The low efficiency of the current MGT units in the market combined with the urgent requirement for highly efficient and low-emission energy conversion systems are the motivations for the development of new MGTs using additive manufacturing (AM) techniques. In this study, the current metal-AM systems are reviewed, the development of the MGT combustor and heat exchanger is presented, and the challenges and opportunities toward manufacturing more efficient MGT for domestic applications are discussed. The integration of the combustor and recuperator of the hot section of a MGT is proposed to achieve up to 5% improvement in efficiency with a significant reduction in the weight and size of the system. [ABSTRACT FROM AUTHOR]

The article deals with the problem of increasing the efficiency and competitiveness of the underground coal gasification technology at the expense of utilizing the thermal energy of the underground gas generator, which is lost in the bowels. The authors have been analyzing the suggested by them system "variable phase turbine (VPT) - well recuperator". It could be included into the thermal circuit of the underground coal gasification and be capable of utilizing up to 30% of thermal energy losses of the gas generator, providing high efficiency of electricity generation from a low-grade heat carrier. The idea of using a powerful VPT (up to 100 kW) and corresponding recuperators for a downhole gas generator and the formation of a coal gasification zone along a single well has been a technical innovation which is to be substantiated. To realize this task the authors have developed a certain algorithm for the thermal calculation of convective heat transfer from the "well-gas generator" to the recuperator with a water heat carrier Thus the quantitative assessment of the thermal efficiency which could be obtained from a single heat removal well, has been carried out. The technical parameters of a high power VPT within the thermal circuit of underground coal gasification have been substantiated and could have been realized. Alongside, it become possible to do the calculations for the flow characteristics, the traction jet force, the consumed heat power during the turbine operation and at last for the efficiency and carnotization factor. Such calculations have been successfully carried out. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) is used here to reduce pressure loss and improve heat exchange efficiency in the recuperator associated with a gas turbine. First, numerical simulations of the high-temperature and lowtemperature channels are performed and, the calculated results are compared with experimental data (to verify the reliability of the numerical method). Second, the flow field structure of the low-temperature side channel is critically analyzed, leading to the conclusion that the flow velocity distribution in the low-temperature side channel is uneven, and its resistance is significantly higher than that in the high-temperature side. Therefore, five alternate structural schemes are proposed for the optimization of the low-temperature side. In particular, to reduce the flow velocity in the upper channel, the rib length of each channel at the inlet of the low-temperature side region is adjusted. The performances of the 5 schemes are compared, leading to the identification of the configuration able to guarantee a uniform flow rate and minimize the pressure drop. Finally, the heat transfer performance of the optimized recuperator structure is evaluated, and it is shown that the effectiveness of the recuperator is increased by 1.5%. [ABSTRACT FROM AUTHOR]

A recuperated solar-dish Brayton cycle using an off-the-shelf turbocharger as a micro-turbine and a rectangular cavity receiver with integrated thermal storage is considered in this study. Due to the high temperatures that these solar receivers operate at, a considerable amount of heat is lost to the environment through the aperture, decreasing the solar-to-mechanical efficiency of the cycle. In this work, the heat losses from the solar receiver were reduced by utilising a novel glass channel on the inside of the cavity receiver, running parallel to the receiver walls and cooled by the working fluid (air) flowing from the compressor. The objective of this conceptual study was to investigate the impact of the novel air-cooled window on the performance of the cycle at steady state. An entropy generation minimisation technique combined with a SolTrace analysis was used. Results showed that the maximum solar-to-mechanical efficiencies were on average between 41% and 45% lower than for the cycle without the window. However, it was found that the exhaust temperature of the cycle with the window was higher. Therefore, a higher energy utilisation factor of between 9% and 11% was found when cogeneration was included. [ABSTRACT FROM AUTHOR]

Efficiency is a crucial factor for power cycles. Generally, in the same temperature range, the cycle efficiency for a basic organic Rankine cycle (ORC) is higher than a similar trilateral flash cycle (TFC) for almost all working fluids and heat source/heat sink temperature pairs. According to some recent results, by using super dry working fluids, the thermal efficiency of TFC can outperform its ORC counterpart at high temperatures. This study performed the thermodynamics analysis using three dry working fluids with subcritical basic ORC and TFC with zero to partial recuperated heat ratio. The results showed that using recuperative heat exchange effectively contributes to increasing the efficiency of ORC and TFC. However, the rate of efficiency increase in ORC is higher than the TFC, which can be clearly seen, especially at high maximal cycle temperatures. Using super dry working fluids, the recuperator‐free TFC has favorable cycle efficiency at high heat source temperatures. In contrast, by adding heat recovery for both systems, the ORC can outperform the TFC at 0.4, 0.2, and 0.1 recuperated heat effectiveness for Dodecane, Decane, and Nonane, respectively. [ABSTRACT FROM AUTHOR]

The transcritical CO2 (T-CO2) power cycle using low temperature waste heat is a promising technique for energy saving and environmental protection. However, according to the literature, there is no commercialized unit in service yet. This study provides developers a reference to shorten the design phase of the T-CO2 cycle commercialization process. A sensitivity analysis of the system performance, i.e., thermal efficiency and net power output, regarding the isentropic efficiencies of pump ( η p ) and expander ( η e ) and the heat source temperature ( T h , i n ) has been carried out using MATLAB and NIST REFPROP database. Simple and recuperative configurations are investigated based on their own optimal working pressures. The results show that the enhancement of η e has a greater influence on improving the system performance, but the improvement will diminish as η p , η e , and T h , i n increase. Although better system performance can be achieved with higher η p , η e , and T h , i n , the cost of the system equipment will also increase due to the higher optimal working pressure. In addition, increasing η p and η e will negatively affect the effectiveness of the recuperator. Therefore, the turbomachinery efficiencies and the heat source temperature should be considered simultaneously for the most cost-effective system design. [ABSTRACT FROM AUTHOR]

A performance assessment of advanced sCO2 Brayton cycles integrated with a concentrated solar power and waste heat recovery systems was conducted. Five advanced sCO2 Brayton cycles are examined for the bottoming cycle: dual heater, dual expansion, cascade, partial recuperation, and Kimzey cycles. This study reveals that the dual heater and dual expansion cycles have the best performance among the advanced sCO2 Brayton cycles considered. The findings reveal that the highest cycle efficiency is for the dual heater and dual expansion cycles (29.18%) followed by the Kimzey cycle (27.73%), then the cascade cycle (26.29%). Consequently, the least cycle efficiency is for the partial recuperation cycle (25%). Furthermore, the highest net power takes place in the dual heater and dual expansion cycles. Finally, the findings demonstrate that increasing the pressure ratio of advanced sCO2 Brayton cycles, within the range considered, results in a reduction of the cycle efficiency. [ABSTRACT FROM AUTHOR]

It is well-known that the −70 °C ultra-low temperature freezers have been widely concerned for vaccine and biomedical products storage due to the outbreak of COVID-19. This paper carries out the experimental investigation on performance characteristics of a −70 °C ultra-low temperature medical freezer with single-stage Joule-Thomson refrigeration system by using binary hydrocarbon mixture R601a/R1150 and ternary mixture R601a/R290/R1150. The aim is to explore and verify hydrocarbon refrigerants that can achieve lower energy consumption, thereby providing a scientific basis for the optimization of ultra-low temperature medical freezers. The experimental results show that both R601a/R1150 and R601a/R290/R1150 with a charge of 250 g could achieve the refrigeration temperature below −70 °C in a 568 L large volume vertical freezer. Comparing binary with ternary refrigerants, it is found that the addition of medium-boiling component R290 is beneficial to reduce the daily energy consumption. When the mass fraction of R601a/R1150 is 0.70/0.30, the lowest daily energy consumption for −70 °C is 9.06 kW h·24 h−1. When the mass fraction of the R601a/R290/R1150 is 0.70/0.10/0.20, the daily energy consumption is 8.42 kW h·24 h−1, which is 7.06 % lower than that when using the R601a/R1150. This indicates that careful selection of refrigerant components and composition optimization can lead to substantial energy savings. Furthermore, it is also observed that among these three components, the low-boiling component R1150 has the most significant influence on the system pressures and operating power, followed by R601a and R290. • R601a/R1150 and R601a/R290/R1150 for J-T system could reach temperature below −70 °C. • The addition of R290 is beneficial to reduce system energy consumption. • The appropriate mass fraction range for R290 is 0.10–0.15. • Low-boiling component R1150 has the greatest impact on system pressure and power. [ABSTRACT FROM AUTHOR]

Gas-fired power generation, characterized by high efficiency, low carbon emissions, and flexibility, contributes significantly to the global energy transition. In the present work, a novel dual-stage intercooled and recuperative gas turbine system integrated with transcritical organic Rankine cycle (dICR-GT-tORC) was proposed. System modeling was carried out based on Thermoflex software for different configurations to evaluate the energetic and exergetic performances. It was found that the dICR-GT-tORC exhibited improved thermodynamic performance compared to the gas turbine simple cycle and dICR-GT system, with the system net energy efficiency/exergy efficiency/specific work increasing from 43.88%/41.80%/567 kJ·kg air −1 and 57.21%/54.49%/684 kJ·kg air −1 to 62.48%/59.52%/745 kJ·kg air −1, respectively. An energy utilization diagram analysis revealed that the energy cascade utilization was achieved by coupling a bottoming tORC to fully utilize the waste heat from intercoolers and the exhaust gas. Furthermore, the dICR-GT-tORC demonstrated enhanced environmental performance, reducing the CO 2 emission rate by a maximum value of 29.8%. Additionally, the impacts of key parameters, including the organic working fluid selection, the minimum temperature difference at the pinch point of recuperators and the terminal exhaust gas temperature on the system performance were investigated. It was indicated that the proposed system could be applicable in various practical scenarios from thermodynamic and environmental perspectives. • Dual-stage intercooled and recuperative gas turbine system integrated with transcritical ORC was proposed. • System modeling was conducted for energetic and exergetic performances evaluation. • The energy efficiency of the proposed gas-fired power system reached up to 62.48%. • Influence of key parameters on the system performance was analyzed quantitatively. [ABSTRACT FROM AUTHOR]

This paper discusses a mathematical model for airflow through a cross-flow plate heat exchanger. The exhaust air is used to heat the supply air. Three kinds of plates are considered: made of aluminium, copper, and steel. The purpose of this research was to verify which material used to build the plate heat exchangers uses the exhaust air heat more efficiently. The method of the Trefftz function was used to determine approximate solutions to the analysed problem. The results obtained for 1.2 mm-thick plates and for external winter, summer, and spring–autumn temperatures are discussed. The results indicate that if the efficiency and price of the metals are considered, then steel is the best material for the plate heat exchanger. Thanks to the use of thin steel plates and the reduction in air exchange time to a few minutes, a cheap and efficient cross-flow heat exchanger can be obtained. [ABSTRACT FROM AUTHOR]

The propulsion demands of high-speed naval vessels often rely on gas turbines, producing significant amount of power achieving thus high performance requirements. Gas turbines can be used either to provide purely mechanical propulsion, or alternatively to generate electricity, which is subsequently used by electric drives to propel the ship. However, the thermal efficiencies of gas turbines are lower than those of Diesel engines of similar power. In the context of improving the performance of existing marine gas turbines, it is proposed to enhance engine's performance by integrating a pressure wave supercharger (or wave rotor), while keeping the basic components of the baseline engine unchanged. This article is an application of a method developed by the author for marine gas turbines with and without recuperator, [Fatsis 2019]. It is found that important benefits are obtained for the topped engines in comparison to the self-standing baseline engines. The wave rotor integration is more appropriate for engines with low compression ratios and high turbine inlet temperatures. Application of wave rotor technology to recuperated marine gas turbines shows efficiency gain exceeding 19% for all the compression ratio and turbine inlet temperatures examined. Abbreviations: COGAS, Combined gas turbine and steam turbine; COGES, Combined gas turbine electric and steam; GTE, Gas turbine engines [ABSTRACT FROM AUTHOR]

In this paper, design and development of an energy-efficient oil-fired tilting furnace with an innovative recuperator are reported. During the melting of metals, it is reported that around 50% of the total energy is lost in flue gases. Therefore, there is always a need to improve upon the efficiency of the furnaces. The design of the recuperator is based upon the application of all the three basic modes of heat transfer to preheat the incoming air. Financial and environmental aspects were also evaluated after upgradation with the recuperator. The internal hollow pipe of the proposed recuperator is so designed that at its exterior cylindrical surface, multiple turns of a guide way are welded in a spiral fashion. This increases the heat transfer between the flue gas and ambient air to the burner. The study shows that the efficiency of the oil-fired tilting furnace got enhanced by 50% after implementing the proposed recuperator. Specific fuel consumption without the recuperator was 0.166 kg/kWh, which was reduced to 0.138 kg /kWh with the recuperator. The principle of increasing thermal efficiency and limiting fuel consumption was based on heat recovery from the combustion products to preheat the cold incoming fuel mixture. Therefore, this study focuses on the relations between combustion and heat exchanges on a large scale. The exergy evaluation technique was used constructively to estimate the furnace's efficiency since the exergy efficiency is an additional sustainable appraisal in real situations. A channel for flue gases is provided in the developed furnace, which helps to divert hazardous gases away from the working environment. [ABSTRACT FROM AUTHOR]

A thermodynamic model of basic and recuperative transcritical organic Rankine cycles (TRCs) associated with using five pure and six mixed fluids as working fluids has been developed. This model can be employed to investigate the effects of recuperators at inlet expander temperatures (Texp,in) of 150–200°C and inlet expander pressures (Pexp,in) of 3.7–6.9 MPa. The ratio of change (ROC) of the first‐ and second‐law efficiencies (ηI and ηII) was positively correlated with the heat transfer rate of the recuperator and exhibited an opposite trend for a specific volume ratio. ROC was substantially affected by operating parameters and working fluid. However, the recuperator heat transfer rate was negligibly affected by the mixture temperature glide (Tglide). A universal empirical equation of ηI,II was proposed for both TRC configurations. The equation, a function of the specific volume ratio, can predict the system efficiencies for pure and mixed fluids, even if a mixture has an arbitrary mole fraction. As Tglide of R600a‐base mixture and R245fa/R134a was lower than 16 K, they had low error rates and low standard deviations. Finally, the equation was highly accurate in ηII prediction, particularly at a Texp,in of 160°C and 170°C and a Pexp,in of 4.9–5.8 MPa. [ABSTRACT FROM AUTHOR]

To further improve the thermal efficiency of diesel engines, a waste heat recovery system model utilizing organic Rankine cycle (ORC) is constructed and verified through system bench test and heat exchanger bench test. To recover waste heat from diesel engine exhaust, ethanol, cyclopentane, cyclohexane, R1233zd (E), and R245fa were selected for comparison. The quality of heat source, the quality of evaporator, the system output, and the system complicity were taken as variables for comparison. Analysis shows that for ORC systems without recuperator, ethanol system has the best system output of the five in a wide operation temper range, with the highest exergy efficiency of 24.1%, yet the exergy efficiency increase after the application of recuperator, 9.0%, is limited. For low temperature exhaust, cyclopentane system has the best performance with or without recuperator, and the cyclopentane system with recuperator has the best performance in terms of exergy efficiency, 27.6%, though complex heat exchangers are also required for high power output. The system output of the R1233zd system is better than the R245fa system, yet the advantage of low evaporate temperature can be better utilized for low quality waste heat recovery.

In the paper, a feasible ecological effect of modernization of a conventional metallurgical furnace intended for charge material preheating before plastic working processes is described. The modernization activities involved replacement of the previous recuperator, the negative pressure control system of the furnace and a proposal for application of modern low emission burners. The suggested design of a recuperator with a higher energy recovery level due to a decreased flue gas temperature will contribute to reduced consumption of electrical energy that is necessary for the extraction ventilator drive. The modernization activities led to decreased total process-induced CO2 emissions resulting from lower consumption of gas and electrical energy (nearly 11 % in relation to the state before the modernization).

Supercritical CO 2 power cycles might be capable of providing the cost reductions and efficiency improvements necessary to reach concentrating solar power (CSP) cost targets, but require large, highly effective recuperators. Fixed-bed regenerators are a periodic heat exchanger that could be an effective yet low-cost alternative to these recuperators. This study presents a techno-economic comparison of regenerators and recuperators for a 100 MWe supercritical CO 2 power cycle for CSP applications. We quantify the levelized cost of energy (LCOE) for the power plant with both types of heat exchangers, and explore sensitivity of LCOE to parameters such as CSP-specific capital costs, power cycle component capital costs, and regenerator valve replacements costs. Results indicate that the incumbent printed circuit heat exchangers achieve the lowest LCOE, unless the upper extreme of PCHE capital cost and lower extremes of regenerator and valve capital and O&M costs are realized. Sensitivity analysis also illustrates that the primary heat exchanger cost is the most influential of power cycle components, and that CSP component capital cost is more influential than power cycle capital costs. This illustrates the importance of reducing the cost of heliostats, receivers, and thermal energy storage for achieving CSP LCOE targets. • Techno-economic analysis uses vendor-data derived cost correlations from literature. • Comparison of PCHEs and regenerators for recuperation. • PCHEs enable lower LCOE than regenerators under most circumstances. • CSP-specific components influence cost much more than power cycle components. • Economic optimization recommends lower recompression fraction than prior studies. [ABSTRACT FROM AUTHOR]

Carbon dioxide power systems (СО2-PS) are thermal power facilities in which carbon dioxide (СО2) is used as a working fluid. Given a fairly high initial temperature upstream of the turbine, their efficiency may be higher than that of steam turbine analogs. In all developed countries, intense studies aimed at development of СО2-PSs for various purposes are carried out, as a rule, with active participation of the state sector, including the development of state programs and addressed budgetary financial support, with the majority of R&D works carried out in the capacity of national laboratories and research institutes, with planning the works and monitoring their progress. Special attention is paid to solving the problem of decreasing the metal intensity and cost of heat-transfer equipment. It is shown—taking as an example a feasibility study of modifying the domestically developed 1200 MW sodium-cooled fast nuclear power facility by replacing the steam power plant by a СО2-PS—that such modification for large capacity power plants with moderate initial temperature levels results in degraded economic efficiency as a consequence of much higher metal intensity, larger overall dimensions, and cost of the heat-transfer equipment. Better economic efficiency in comparison with similar steam turbine plants can be achieved by increasing the initial temperature and decreasing the capacity of a single power unit. At the initial design stages, it is advisable to place the focus on developing a small capacity power part equipment of one standard size (with a standardized main compressor) intended for being used in СО2-PS at solar, nuclear, and thermal power facilities. The development of an experimental demonstration (ED) small-capacity СО2-PS intended for carrying out tests and experimentally perfecting the equipment and technology of its operation is a mandatory stage in the development of СО2-PSs for different capacities and purposes. For decreasing the cost of ED СО2-PS recuperators, it is necessary to construct a bench for testing the heat-transfer modules (HTMs) of which the СО2-PS recuperators will be assembled. A basic thermal cycle circuit of the bench facility that will accurately replicate the operation conditions of HTMs as part of the ED СО2-PS recuperators is developed. The tasks that have to be solved based on the experimental study results are described, and examples of the schematic diagrams of microchannel heat exchangers using which the HTMs can be made more compact are given. Detailed design documents for HTM equipment shall be developed in coordination with the development of technological documentation and plans for improving the technological preparation of manufacture at the industrial partner enterprise that will undertake the task of producing the ED СО2-PS heat-transfer equipment. [ABSTRACT FROM AUTHOR]

The main aim of present study is to optimize a high-temperature recuperator equipped with corrugated helical heat exchanger numerically. This heat exchanger has inner corrugations and/or outer blades. Different geometrical parameters are analyzed according to thermal-hydraulic performance (THP) of the studied helical heat exchanger. The model with the maximum THP evaluation criteria index is introduced as the optimum model. Moreover, the effects of ash fouling characteristics on THP of recuperator are presented. The ash particles material is chosen K2SO4 with the density of 2665 kg/m3. As it is realized in this paper, in case of simulating the problem in steady-state condition, employing the two-phase model achieves to higher average Nusselt number (Nu) values versus all considered mass flow rates. However, it should be noted that in these two approaches the ash fouling characteristics are not determined. By transient solving, the ash fouling characteristics are applied on the outer wall of helical heat exchanger and therefore the convectional heat transfer coefficient is reduced. Hence, in case of employing two phase approach (with ash fouling characteristics) model, lower average Nu values are achieved and it is clear that these values are more validated than attained values from two other approaches. Usage of inner and/or outer corrugations has a substantial influence on THP of recuperator and increases the PEC index values versus all considered mass flow rates sharply. The recuperator equipped with finned helical heat exchanger with a = 3 mm, b = 7 mm, H = 8 mm, g = 2 mm and f = 3 mm is introduced as the optimum model in present work.

Depending on their applications, heat losses from the shells of rotary kilns account for 3-25% of the total heat input. Over the hottest zone of the kiln shell, an annular duct with a variable diameter is formed. Two air streams entering the annulus at both ends flow to a common extraction point to receive the thermal power equal to the ambient heat loss of the bare kiln. The design does not require airtightness, utilizes the entire heat loss, and by the variation of the air-flow can be used over the kilns with variable operating parameters (±20% heat loss), which show similar surface temperature patterns. The main disadvantage of the design is the approaching of the surfaces of the kiln and the recuperator at the outlet of preheated air. This means that for a given heat loss and a surface temperature pattern, the rotational eccentricity of the kiln shell is the most influencing parameter that defines the air preheating temperature and the efficiency of the recuperator. To solve the problem, four redesigns with: double annuluses, the usage of radiation fins, air addition, and a combination of two basic designs are analyzed by the use of analytical and CFD models. From the listed redesigns: first could be used only to prevent overheating, second has a modest positive effect, third should be applied in combination with fourth. [ABSTRACT FROM AUTHOR]

Copyright of Electronics & Control Systems is the property of National Aviation University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The transcritical CO2 (T-CO2) power cycle using low temperature waste heat is a promising technique for energy saving and environmental protection. However, according to the literature, there is no commercialized unit in service yet. This study provides developers a reference to shorten the design phase of the T-CO2 cycle commercialization process. A sensitivity analysis of the system performance, i.e., thermal efficiency and net power output, regarding the isentropic efficiencies of pump (ηp) and expander (ηe) and the heat source temperature (Th,in) has been carried out using MATLAB and NIST REFPROP database. Simple and recuperative configurations are investigated based on their own optimal working pressures. The results show that the enhancement of ηe has a greater influence on improving the system performance, but the improvement will diminish as ηp, ηe, and Th,in increase. Although better system performance can be achieved with higher ηp, ηe, and Th,in, the cost of the system equipment will also increase due to the higher optimal working pressure. In addition, increasing ηp and ηe will negatively affect the effectiveness of the recuperator. Therefore, the turbomachinery efficiencies and the heat source temperature should be considered simultaneously for the most cost-effective system design.

This paper discusses a mathematical model for airflow through a cross-flow plate heat exchanger. The exhaust air is used to heat the supply air. Three kinds of plates are considered: made of aluminium, copper, and steel. The purpose of this research was to verify which material used to build the plate heat exchangers uses the exhaust air heat more efficiently. The method of the Trefftz function was used to determine approximate solutions to the analysed problem. The results obtained for 1.2 mm-thick plates and for external winter, summer, and spring–autumn temperatures are discussed. The results indicate that if the efficiency and price of the metals are considered, then steel is the best material for the plate heat exchanger. Thanks to the use of thin steel plates and the reduction in air exchange time to a few minutes, a cheap and efficient cross-flow heat exchanger can be obtained.

Summary: Improving energy utilization efficiency and exploiting renewable energy source have become more crucial with the growing concern on energy crisis and environmental problem. Organic Rankine cycle, a clean, low‐cost, and efficient energy utilization technology, is eliciting increasing attention. In this study, the recent research studies on organic Rankine cycle configuration modifications integrated with pure organic fluid are summarized from the perspectives of nomenclature, configuration modifications, theoretical and numerical methods, and experimental development. Results reveal that the nomenclature on the common organic Rankine cycle configurations is confusing; the research studies on organic Rankine cycle configurations are mainly focused on numerical research studies, and theoretical and experimental research studies are relatively limited. The experimental and numerical studies are mostly related to organic Rankine cycle with a recuperator due to its higher thermal and exergy efficiencies. Most experimental research studies are contributed by Chinese scholars, which indicate that China has paid much attention to improving the global environment. More theoretical and experimental research studies on other organic Rankine cycle configurations are urgently needed. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ballistics / Dandao Xuebao is the property of Journal of Ballistics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Stack-based thermal resistance network model developed for micro channel heat exchangers. • Correlations developed with straight, sinusoidal and zigzag channels for sCO 2 recuperator. • Hybrid model demonstrates that 20 rows are sufficient to attain the correct stack performance. • Several combinations of stack dimensions generated for different channel configurations. • Sinusoidal channel offered least pressure drop and stack volume compared to straight and zigzag channels. In this work, a full-scale Thermal Resistance Network (TRN) coupled with a unit-cell-based CFD model identified as the hybrid model is developed and implemented in designing a Mini Channel Heat Exchanger (MCHE) as a recuperator used in sCO 2 Brayton power block. The TRN framework converts the MCHE domains into a thermal circuit using resistances and advection currents that can be used to model the entire stack with varying thermo-physical properties of working fluids. The results from the TRN model with CFD-based heat transfer and pressure drop correlations developed for different channel lengths, are compared with the original CFD data to ascertain the lowest possible channel length for precise correlation development. An appropriate channel length is further used for deriving correlations for sinusoidal and zigzag flow paths. The hybrid model helps determine the upper limit of the side width (fin width) of the channels based on equivalent thermal resistance between fluid and walls as the lower limit is constrained by stress criteria. The present model estimates that at least 20 rows/plates need to be modelled for the correct performance estimation of a full-scale MCHE. The minimum rate of heat loss-based stack optimization approach is implemented in estimating the optimum number of rows and stack dimensions. The channel and stack dimensions are obtained and compared for straight, sinusoidal, and zigzag flow paths for Reynolds numbers ranging from 5 × 103 to 20 × 103, ensuring a temperature pinch of 5 °C at the cold inlet. For cold inlet Reynolds number and channel diameter of 1.5 × 104 and 1.5 mm, the stack volumes for straight, zigzag, and sinusoidal channels are 1.8 m3, 1.21 m3, and 1.15 m3, respectively with sinusoidal and zigzag paths resulting in almost similar pressure drop as ∼110 Pa, 27% lower compared to the straight channel. The article presents a guideline for hybrid model implementation in designing mini/micro channel heat exchangers. [ABSTRACT FROM AUTHOR]

The distributed energy supply system provides a good scheme for energy supply. The micro gas turbine with a recuperator is a common power device in distributed energy supply systems. In recent years, several achievements have been made in the development of micro gas turbine recuperators. Plate-fin and primary surface recuperators have been used in mature applications. Moreover, the thermodynamic properties of the heat transfer channel have been studied in detail. Among them, the cross wavy primary surface recuperator developed by Capston Company is one of the important achievements. This paper reviews the technical development of thermodynamic performance of micro gas turbine recuperator in recent years. The micro gas turbine recuperators are divided into plate-fin and primary surface recuperators commonly. In this paper, the correlation formula, heat exchange enhancement, optimum design and the influence of recuperator on the overall machine performance are reviewed. It has been found that the plate-fin recuperators have been sufficiently studied by scholars, and the results are more comprehensive. As for the primary surface recuperators, which have just become popular in recent years, the research results are less comprehensive due to their unique structure. In the future development of micro gas turbine recuperators, this will be the future research and development trend due to the high heat exchange efficiency and the lack of comprehensive research on primary surface recuperators. [ABSTRACT FROM AUTHOR]

Despite the fact that aviation gas turbine engines (GTE) have reached a high degree of sophistication, requirements for the improvement of their efficiency are constantly increasing. Reduction of specific fuel consumption and specific weight of the engine unit makes it possible to improve aircraft performance. One of the effective means of reducing specific fuel consumption and obtaining high thermal efficiency of a gas turbine engine is the use of heat recovery, so the interest in it holds throughout the period of development of gas turbine engines. However, the use of heat recovery in aircraft gas turbine engines is faced with a contradiction: on the one hand, heat recovery allows reducing specific fuel consumption, but, on the other hand, it increases the weight of the power plant due to the presence of a heat exchanger. Moreover, with the increase in the degree of regeneration, specific fuel consumption decreases, whereas the mass of the power plant increases.To obtain the desired effect, it is necessary to optimize simultaneously both the parameters of the engine work process and the degree of regeneration of the heat exchanger according to the criteria of evaluating the engine unit in the aircraft system. For this purpose, it is necessary to have a mathematical model for estimating the weight of a highly efficient aircraft heat exchanger. The article presents a developed mathematical model for calculating the weight of a compact plate heat exchanger used to increase the efficiency of a gas turbine engine due to the heating of compressed air entering the combustion chamber by the hot gas that enters the combustion chamber from behind the turbine. We chose a rational pattern of relative motion of the working media in the heat exchanger, the optimal type of plate-type heat transfer surface in terms of minimizing the weight of the heat exchanger and the hydraulic losses in the air and gas ducts. For the selected surface type, the dependence of the specific weight of the heat exchanger on the degree of regeneration is determined for different nozzle exhaust velocities on the basis of a computational algorithm. To assess the reliability of the obtained model, comparative analysis of the effect of the degree of regeneration on the specific weight of the heat exchanger was carried out, based on the comparison of the results of calculations for the developed model with the data of other authors and with the data for the produced regenerators.

The rising environmental problems due to fossil fuels' consumption have pushed researchers and technologists to develop sustainable power systems. Due to properties such as abundance and nontoxicity of the working fluid, the supercritical carbon ( sCO 2 ) dioxide Brayton cycle is considered one of the most promising technologies among the various sustainable power systems. In the current study, a mathematical model has been developed and coded in Matlab for the recompression of the supercritical carbon dioxide Brayton cycle sCO2-BC. The real gas properties of supercritical carbon dioxide ( sCO 2 ) were incorporated into the program by pairing the NIST's Refporp with Matlab© through a subroutine. The impacts of the various designs of the cycle's individual components have been investigated on the performance of sCO 2 − BC . The impact of various sedative cycle parameters, i.e., compressor's inlet temperature (T 1) , and pressure ( P 1 ), cycle pressure ratio ( P r ), and split mass fraction (x), on the cycle's performance (η c y c ) were studied and highlighted. Moreover, an optimization study using the genetic algorithm was carried out to find the abovementioned cycle's optimized values that maximize the cycle's per-formance under provided design constraints and boundaries. [ABSTRACT FROM AUTHOR]

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).