Joule-Brayton Cycle Research Articles

Thermo-ecological performance analysis of a Joule-Brayton cycle (JBC) turbine with considerations of heat transfer losses and temperature-dependent specific heats

This study presents a new performance analysis criterion called Effective Ecological Power Density (EFECPOD) and its application to a Joule-Brayton cycle (JBC) turbine. Effective efficiency (EE), effective power (EP), cycle temperature ratio and turbine volume are considered together and the performance is stated a unique value by the developed criterion. emissions formation and turbine dimensions are considered by the cycle temperature ratio and turbine volume, respectively. The turbine volume is also related to production cost of the heat engine. Therefore, the proposed criterion is essential for multipurpose optimization. Furthermore, this criterion can be developed and applied to the other gas cycles and heat engines. Also, a performance investigation for the JBC gas turbine in terms of EE, EP and effective power density (EPD) has been carried out using a new finite-time thermodynamics modeling (FTTM). The influences of engine design parameters such as cycle temperature ratio, cycle pressure ratio, turbine speed, intake temperature, intake pressure and equivalence ratio on the EE, EP, EPD and EFECPOD have been examined. The results presented can be an essential tool for JBC turbine designers.

Optimization of Heliostat Field in a Thermal Solar Power Plant with an Unfired Closed Joule-Brayton Cycle

In the last decades, concentrating solar power (CSP) has been gaining increasing attention as a sustainable technology for producing electricity. Nowadays, in the world, 483.6 MWs are produced by CSP plants of which 457 MW are already in commercial stage, whereas the other 430 MWs are under construction. In this paper, a solar tower with an unfired closed Joule-Brayton cycle of 10 MW peak power, located in Seville, is analyzed. The cycle, that employs only atmospheric air, without fuel consumption, relies on the possibility to vary the mean density of the air flowing in the plant. By using an auxiliary compressor and a bleed valve, a variable mass flow rate can be obtained so to keep the temperature at turbine inlet constant. On the other hand, in the concentrated solar plant, the number of installed heliostats can reflect towards the receiver the nominal thermal power, even with reduced values of the DNI. With the increase of the radiation, when the thermal energy flux achieves the limit tolerable by the receiver, a part of heliostats is defocused. On the contrary, in the presence of transients, due, for example, to clouds or in case of low solar radiation, the mirrors will be all, or in part, oriented towards the receiver face, so to keep constant the receiver outlet air temperature at the design value. Both the above mentioned control systems, without any fuel addition, act with the common goal of maintaining constant the air temperature at turbine inlet. However, they intervene at different times: at rated power, heliostats work, while the air flow rate is kept constant at the maximum value; when the nominal conditions are no longer achievable (the DNI values are insufficient), the adjustment is performed through the modulation of the pressure base control system, focusing the entire surface of the mirrors on the receiver. The analysis shows how the interaction between these systems influences the number and size of heliostats to be installed in the solar field. The study of the state of art has demonstrated that, in tower systems currently in operation, without storage, a solar multiple of 1.3 is generally used; our contribution shows how, with the air density control system, this value may be reduced, with consequent benefit on the heliostats cost. The numerical tests have been carried out by using the WINDELSOL software to optimize the heliostat field configuration and the THERMOFLOW, for the thermodynamic analysis.

Analysis of a Concentrating Solar Power Tower Operating with a Closed Joule Brayton Cycle and Thermal Storage

Analysis of a Concentrating Solar Power Tower Operating with a Closed Joule Brayton Cycle and Thermal Storage

Thermo-ecological performance analyses and optimizations of irreversible gas cycle engines

This paper reports ecological performance analyses and optimization of irreversible gas cycle engines such as Joule–Brayton cycle (JB), Atkinson cycle (AC), Otto cycle (OC), Diesel cycle (DC), Miller cycle (MC), Dual-Atkinson cycle (DAC), Dual-Diesel cycle (DDC), Dual-Miller cycle (DMC) engines based on the ecological coefficient of performance (ECOP) criterion which covers internal irreversibility, heat leak and finite-rate of heat transfer. Comprehensive computational analyses have been conducted to investigate the global and optimal performances of the gas cycle engines. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been acquired introducing the compression ratio, cut-off ratio, pressure ratio, air recharging ratio, source temperature ratio and internal irreversibility parameter. The changes of cycle performances with respect to these parameters are examined and demonstrated with figures.

Thermal efficiency of direct, inverse and sCO2 gas turbine cycles intended for small power plants

The aim of this paper is to study whether the efficiency loss that takes place at low Reynolds numbers (Re) can be a problem for small power gas turbines and, if this is the case, to assess whether the use of alternative power cycles such as supercritical sCO2 or inverse Joule–Brayton cycles might solve this problem.First, two different methods for the estimation of the Reynolds efficiency loss are explained and compared. Then, the design parameters of a number of existing commercial gas turbines are used in order to show that this efficiency loss begins to be significant when the shaft power is lower than about 1.5 MW. Efficiency and Re calculations are carried out subsequently for inverse and sCO2 1 MW cycles intended for medium range temperatures. For such small powers, the supercritical sCO2 closed loop Brayton cycle seems to be a promising alternative, as the Reynolds number experiences an increase due to the high fluid density. Also, sCO2 cycles achieve good efficiencies due to the compressor work reduction obtained near the critical point. The inverse cycle is a less interesting option because its efficiency is low and there is no significant improvement in the Reynolds number.

A Case of Study of a Concentrating Solar Power Plant with Unfired Joule-Brayton Cycle

A solar closed air Brayton cycle, with rated power of 50 MW, was considered. The system is composed of a concentrating solar tower with volumetric receiver, an intercooling and regenerating gas turbine and an evaporative tower cooling system. The characteristic feature of the system is a control strategy able to adjust the plant in a large range of load, maintaining net electric conversion efficiency almost constant. The concentrating solar power (CSP) plant operates without adding fuel and can heat air up to a maximum temperature of 850°C, at the solar tower outlet. The numerical analysis was performed by SAM for the solar tower and by Thermoflex © for the assessment of the performance of the whole system. The thermal energy input was calculated on the basis of the DNI of the TMY from Seville. Results show an electricity production greater than 75GWh per year, with a significant sparing fossil fuel consumption and avoided CO2 emissions.

Optimal operation of a large-scale liquid hydrogen plant utilizing mixed fluid refrigeration system

This work proposes a new modified liquid hydrogen plant that uses a multi-component refrigerant (MR) refrigeration system. A plant capable of producing 100 tons of liquid hydrogen per day is simulated and optimized. Based on a previously published work, this paper represents an improvement for more realistic large-scale plant cycles. Importantly, this work contains a preliminary study of the variables and constraints together with methods for adjustment to achieve optimal steady-state operation. The optimization problem contains 23 variables and 26 constraints. Similar to the MR system, this system can be used to cool the normal feed hydrogen gas from 25 °C to the equilibrium temperature of −193 °C, and a simplified five-component mixture of refrigerant suggested for the plant is described. However, the novelty of this work relative to the previous work lies in the transition of the equilibrium ortho–para hydrogen gas from −193 °C to −253 °C via a new proposed configuration, which recommends a four H2 Joule–Brayton cycle refrigeration system with optimization. Additionally, the plant optimization was conducted using two additional pinch temperatures (1 °C and 3 °C). The overall power savings is increased with a pinch temperature of 1 °C compared with that of 3 °C. The simulated overall power consumption of the proposed plant is 5.91kWh/kgLH2, which represents a 50% reduction compared with the current plant in Ingolstadt with an energy consumption of 13.58kWh/kgLH2. Pressure drops are also employed in the heat exchangers in the study simulation, but the results show that they do not have a significant impact on the overall plant total power consumption.

Thermodynamic cycles optimised for medium enthalpy units of concentrating solar power

Concentrated solar power presents the drawback of decreasing radiation capture efficiency as the temperature of the receiver increases, because thermal losses increase as well. Low temperature at the receiver is an advantage for radiation concentrators, as they present high capture efficiency, but this fact changes into a drawback because of the low efficiency of the thermodynamic cycles working with a low temperature heat source.An analysis is presented on the performance of real fluids working with such a type of heat sources that can be generated in simple solar thermal units. Both Joule–Brayton cycles and dry-turbine Rankine cycles are considered, using regenerative heat exchangers for heat recovering. The driving force of this research is to look for working fluids with actual thermodynamic characteristics which fit well with temperatures of the heat source and sink. Some unconventional substances, as refrigerant R-125 or SF6, show good performance. They may be suitable at certain regimes of Rankine and Brayton cycles and could work in fast-reacting systems. Of course, differences in the performance of Brayton and Rankine cycles convey differences in the complexity and cost of the components, but they offer a wide field for coherently choosing the working fluid and thermal conditions.

Restrictions on linear heat capacities from Joule-Brayton maximum-work cycle efficiency.

This paper discusses the possibility of using the Joule-Brayton cycle to determine the accessible value range for the coefficients a and b of the heat capacity at constant pressure C(p), expressed as C(p) = a + bT (with T the absolute temperature) by using the Carnot theorem. This is made for several gases which operate as the working fluids. Moreover, the landmark role of the Curzon-Ahlborn efficiency for this type of cycle is established.

Simulation of Solarized Combined Cycles: Comparison Between Hybrid Gas Turbine and ISCC Plants

The present paper investigates two different solarized combined cycle layout configurations. In the first scheme, a solarized gas turbine is coupled to a solar tower. Pressurized air at the compressor exit is sent to the solar tower receiver before entering the gas turbine (GT) combustor. Here, temperature is increased up to the nominal turbine inlet value through natural gas combustion. In the second combined cycle (CC) layout, solar energy is collected by line focusing parabolic trough collectors and used to produce superheated steam in addition to the one generated in the heat recovery boiler. The goal of the paper is to compare the thermodynamic performance of these concentrating solar power (CSP) technologies when working under realistic operating conditions. Commercial software and in-house computer codes were combined together to predict CSP plant performance both on design and off-design conditions. Plant simulations have shown the beneficial effect of introducing solar energy at high temperature in the Joule–Brayton cycle and the drawback in terms of GT performance penalization due to solarization. Results of yearly simulations on a 1 h basis for the two considered plant configurations are presented and discussed. The main thermodynamic parameters such as temperatures, pressure levels, and air and steam flow rates are reported for two representative days.

Variations on the Zilch Cycle

Thermo dynamic cycles in introductory physics courses are usually made up from a small number of permutations of isothermal, adiabatic, and constant-pressure and volume quasistatic strokes, with the working fluid usually being an ideal gas. Among them we find the Carnot, Stirling, Otto, Diesel, and Joule-Brayton cycles; in more advanced courses, steam cycles and refrigerators based on real working fluids are often introduced. Any additional cycles made up from the same simple strokes, and any extended analysis of known cycles, are welcome additions to the teaching repertory, as they provide more opportunities for practice and discussion.1–7 Our purpose in this note is to extend the analysis of the zilch cycle, introduced in Ref. 1, by presenting its TS diagram and by proposing several variations that do not contain adiabatic strokes, thus allowing a simpler mathematical treatment. As a bonus, we also provide results that make it possible to represent practically any elementary ideal-gas cycle in a TS diagram.

An improved model to evaluate thermodynamic solar plants with cylindrical parabolic collectors and air turbine engines in open Joule–Brayton cycle

An improved model to analyze the performance of solar plants operating with cylindrical parabolic collectors and atmospheric air as heat transfer fluid in an open Joule–Brayton cycle is presented. In the new model, the effect of the incident angle modifier is included, to take into account the variation of the optical efficiency with the incidence angle of the irradiance, and the effect of the reheating of the fluid also has been studied.The analysis was made for two operating modes of the plants: with variable air flow rate and constant inlet temperature to the turbine and with constant flow rate and variable inlet temperature to the turbine, with and without reheating of the fluid in the solar field. When reheating is used, the efficiency of the plant is increased.The obtained results show a good performance of this type of solar plant, in spite of its simplicity; it is able to compete well with other more complex plants operating with different heat transfer fluids.

An evaluation of thermodynamic solar plants with cylindrical parabolic collectors and air turbine engines with open Joule–Brayton cycle

A performance analysis of innovative solar plants operating with cylindrical parabolic collectors and atmospheric air as heat transfer fluid in an open Joule–Brayton cycle, with and without intercooling and regeneration, is presented.The analysis was made for two operating modes of the plants: with variable air flow rate and constant inlet temperature to the turbine and with constant flow rate and variable inlet temperature to the turbine.The obtained results show a good performance of this type of solar plant, in spite of its simplicity; it seems able to compete well with other more complex plants operating with different heat transfer fluids.

Unsteady Conjugate Heat Transfer Analysis of an Immersed Particle Innovative Heat Exchanger

The improvement of both heat recovery Joule-Brayton cycles and closed cycle (externally fired) gas turbine plants is strongly limited by the availability of high efficiency heat exchangers. In such a scenario, a nonconventional heat exchanger was recently proposed; this device employs falling solid particles to perform heat transfer between two separate gas flows and was designed with a 1D model neglecting conduction within the particles. Although the experimental reliability of this assumption was already obtained for one particle size, there is no proof available of the quantitative effect introduced by the above mentioned simplification and, more importantly, no indication of when this assumption becomes unacceptable. In this work, direct numerical simulation (DNS) of a solid particle immersed in a gas flow has been performed in order to further validate the hypothesis of negligible conduction and to enhance the design of the proposed heat exchanger. Unsteady conjugate heat transfer has been used to predict the final temperature of the solid sphere for Reynolds numbers ranging from 30 to nearly 300, the computational grid being generated with the immersed boundary (IB) technique. A validation of the study is presented, together with grid independence and boundary independence assessment. The results fully confirmed the worthiness of the initial assumption, with a 1.4% maximum error for high Reynolds conditions (large diameter particles) with respect to the 1D model. Additionally, the code has been employed to explore the influence of the wake in the case of aligned particles, namely, the worst possible situation in terms of efficiency of the heat transfer mechanism. Finally, the discrepancy between the results obtained with an axisymmetric domain and a 3D domain, in terms of final temperature of the particle, have been investigated for the highest Reynolds number, when the flow is supposed to lose its axial symmetry.

An Immersed Particle Heat Exchanger for Externally Fired and Heat Recovery Gas Turbines

Designing and manufacturing high-efficiency heat exchangers is usually considered a limiting factor in the development of gas turbines employing either heat recovery Joule–Brayton cycles or external combustion. In this work, an innovative heat exchanger is proposed, modeled, and partially tested to validate the developed numerical model employed for its design. The heat exchanger is based on an intermediate medium (aluminum oxide Al2O3) flowing in countercurrent through an hot stream of gas. In this process, heat can be absorbed from the hot gas, temporarily stored, and then similarly released in a second pipe, where a cold stream is warmed up. A flow of alumina particles with very small diameter (of the order of hundreds of microns) can be employed to enhance the heat transfer. Experimental tests demonstrate that simple one-dimensional steady equations, also neglecting conduction in the particles, can be effectively employed to simulate the flow in the vertical part of the pipe, namely, to compute the pipe length required to achieve a prescribed heat exchange. On the other side, full three-dimensional computational fluid dynamics simulations have been performed to demonstrate that a more thorough gas flow and particle displacement analysis is needed to avoid a bad distribution of alumina particles and, thus, to achieve high thermal efficiency.

Thermodynamic analysis of the reverse Joule–Brayton cycle heat pump for domestic heating

The paper presents an analysis of the effects of irreversibility on the performance of a reverse Joule–Brayton cycle heat pump for domestic heating applications. Both the simple and recuperated (regenerative) cycle are considered at a variety of operating conditions corresponding to traditional (radiator) heating systems and low-temperature underfloor heating. For conditions representative of typical central heating in the UK, the simple cycle has a low work ratio and so very high compression and expansion efficiencies and low pressure losses are required to obtain a worthwhile COP. An approximate analysis suggests that these low loss levels would not necessarily be impossible to achieve, but further investigation is required, particularly regarding irreversible heat transfer to and from cylinder walls. In principle, recuperation improves the cycle work ratio, thereby making it less susceptible to losses, but in practice this advantage is compromised when realistic values of recuperator effectiveness are considered.

ANALYSES OF THE THERMAL EFFICIENCY AND THE OUTPUT POWER IN A JOULE-BRAYTON CYCLE

The analyses on Joule-Brayton cycle, which could be used for a high efficiency power generation system, using the temperature and the pressure of compressor have been carried out. As a result, when the ratio of maximum temperature to the minimum temperature in the cycle increased, the thermal efficiency increased. By analyzing the efficiency and the output power, it is understood that the ratio of compressor outlet pressure to the compressor inlet pressure, as well as the pressure ratio across the compressor for maximum thermal efficiency and maximum output power are different. The maximum thermal efficiency could be an important technical parameter; however, the maximum output power is significant in the cost and the size of system. For that reason, depending on the required system for maximum efficiency or for maximum power, the ratio of temperature and pressure are designed

Proposal of an innovative, high-efficiency, large-scale hydrogen liquefier

An innovative, efficient and large hydrogen liquefier is described. Innovations lie in the fact that (i) the feed, 10kgs−1, is refrigerated in heat exchangers catalytically promoting the ortho–para conversion (ii) down to the low temperature of 20.5K and at the high pressure of 60bar at which it is available and (iii) lastly expanded to the storage conditions of 1.5bar and 20K through a liquid-phase turbomachine; (iv) refrigeration is via four helium recuperative Joule–Brayton cycles arranged so that the refrigerant follows the cooling curve of hydrogen and the volume flow rates in compression and expansion processes are typical of axial-flow high-efficiency turbomachines; (v) compression is accomplished in 15 intercooled 8-stage devices derived from gas turbine technology. Heat exchangers require specific surfaces comparable to current state-of-the-art liquefiers. Nevertheless, the predicted work of approximately 18MJkg−1 is half as much as the requirement of those liquefiers and corresponds to a second-law efficiency of almost 48%.

Brayton refrigeration cycle for gas turbine inlet air cooling

In this paper, a new approach to enhance the performance of gas turbines operating in hot climates is investigated. Cooling the intake air at the compressor bell mouth is achieved by an air Brayton refrigerator (reverse Joule Brayton cycle) driven by the gas turbine and uses air as the working fluid. Fraction of the air is extracted from the compressor at an intermediate pressure, cooled and then expands to obtain a cold air stream, which mixes with the ambient intake. Mass and energy balance analysis of the gas turbine and the coupled Brayton refrigerator are performed. Relationships are derived for a simple open gas turbine coupled to Brayton refrigeration cycle, the heat rejected from the cooling cycle can be utilized by an industrial process such as a desalination plant. The performance improvement in terms of power gain ratio (PGR) and thermal efficiency change (TEC) factor is calculated. The results show that for fixed pressure ratio and ambient conditions, power and efficiency improvements are functions of the extraction pressure ratio and the fraction of mass extracted from the air compressor. The performance improvement is calculated for ambient temperature of 45°C and 43.4% relative humidity. The results indicated that the intake temperature could be lowered below the ISO standard with power increase up to 19.58% and appreciable decrease in the thermal efficiency (5.76% of the site value). Additionally, the present approach improved both power gain and thermal efficiency factors if air is extracted at 2 bar which is unlike all other mechanical chilling methods. Copyright © 2007 John Wiley & Sons, Ltd.

Performance optimization of a Joule-Brayton engine based on the efficient power criterion

The proper optimization criteria to be chosen for the optimum design of heat engines may differ depending on their purposes and working conditions. If the heat engine design was done not to obtain maximum work or power, but to have maximum benefit from energy, then the design objective is to get maximum efficiency. In this study, a new performance analysis is applied to a reversible Joule-Brayton cycle based on a new criterion which is proposed for all kind of heat engines. The proposed criterion, called efficient power, is defined as the multiplication of power by efficiency. Therefore, this criterion considers not only the power output but also the cycle efficiency. Maximizing the efficient power function gives a compromise between power and efficiency. The results showed that the design parameters at maximum efficient power (mep) conditions lead to more efficient engines than that at the maximum power conditions and that the mep criterion may have a significant power advantage compared to the maximum power density criterion.