Mortaza Yari

Performance analysis of the different Organic Rankine Cycles (ORCs) using dry fluids

This paper presents the first and second laws of thermodynamics analysis for organic Rankine cycles (ORCs), using dry organic fluids as the working fluids. The dry organic fluids for this study were R227ea, RC318, R236fa, Isobutane, R600a, R245fa, HFE7000, R123 and R113. Effects of the operating parameters such as turbine inlet temperature and pressure on the thermal efficiency, exergy destruction rate and second-law efficiency were evaluated. The ORCs studied in this paper were regenerative ORC with IHE, regenerative ORC, ORC with IHE and basic ORC.

Exergetic analysis of the vapour compression refrigeration cycle using ejector as an expander

A computer simulation of the ejector-compression cycle is carried out using a one-dimensional ejector model. In order to identify the amounts and locations of irreversibility within the components of the cycle, exergy analysis is employed. The effects of evaporating temperature and condensing temperature on the COP, second law efficiency and exergy destruction are investigated. It is concluded that the COP and second law efficiency of the ejector-compression is about 16% higher than that for the vapour compression cycle, under the operating conditions of evaporator temperature, 5°C and condenser temperature, 40°C. Also the total exergy destruction of the vapour compression cycle is about 24% higher than that for the ejector-compression cycle at the given conditions.

A novel cogeneration cycle based on a recompression supercritical carbon dioxide cycle for waste heat recovery in nuclear power plants

In this study, a novel cogeneration cycle based on the recompression S–CO2 Brayton cycle is proposed, analysed and optimised thermodynamically to utilise the waste heat from a nuclear power plant. The cycle was constructed theoretically on the basis of a transcritical CO2 power cycle and a LiBr/H2O Absorption Heat Transformer (AHT) to enhance the overall performance of the cycle. It was found that both the energy and exergy efficiencies of the new S–CO2 cycle are about 5.526% higher than that of the simple S–CO2 cycle. A maximum pure water flow rate of 3.317 kg/s was obtained under the analysed condition for the new S–CO2 cycle.

Evaluation and Optimization of Single Stage Absorption Chiller Using (LiCl + H2O) as the Working Pair

The thermodynamic performance of the absorption chiller using (H2O + LiCl) as the working pair was simulated and compared with the absorption chiller using (H2O + LiBr). The effects of evaporation temperature on the performance coefficient, COP, generation temperature, concentration of strong solution, and flow rate ratio were also analyzed. At the same condensing and absorbing temperature, the simulating results indicated that the performance coefficient for (H2O + LiCl) is approximately equal to (H2O + LiBr) and the generation temperature was lower than that for (H2O + LiBr). On the other hand, the exergetic efficiency, ECOP, which is based on the second law of thermodynamics, for the absorption chiller using (H2O + LiCl), was more than the system using (H2O + LiBr) under the same operating conditions. The absorption chiller cycle was then optimized based on the coefficient of performance. The results show that the coefficient of performance of the absorption chiller, using (H2O + LiBr) at the optimum conditions, was around 1.5–2% higher than that of (H2O + LiCl).

A Novel Recompression S-CO2 Brayton Cycle with Pre-Cooler Exergy Utilization

This study examines the performance of a novel recompression supercritical CO2 (S-CO2) Brayton cycle of nuclear power plant with pre-cooler exergy utilization, which uses a transcritical CO2 cycle to enhance the performance of this new cycle. More attention was paid to irreversibilities generated in the combined cycle. Individual models were developed for each component through the application of the first and second laws of thermodynamics. The effects of the turbine inlet temperature, compressor pressure ratio, maximum cycle pressure, main compressor inlet temperature, and also environment temperature on the first- and second-law efficiencies and also on the exergy destruction of the S-CO2 and the presented new S-CO2 recompression cycles were studied. Finally, the recompression S-CO2 cycles were thermodynamically optimized using the Engineering Equation Solver software. Based on identical operating conditions, a comparison between the new S-CO2 and a simple S-CO2 cycle was also performed. It was found that both the first- and second-law efficiencies of the new S-CO2 cycle are about 5.5 per cent to 26 per cent higher than that of the simple S-CO2 cycle. The exergy destruction of the new S-CO2 cycle is also about 6.7 per cent to 28.8 per cent lower than that of the simple S-CO2 cycle.

Thermodynamic analysis of a modified oxy-fuel cycle, high steam content Graz cycle with a dual-pressure heat recovery steam generator

Energy and exergy analyses are reported for a modified oxy-fuel cycle, which includes the Graz cycle with an atmospheric condensation and a dual-pressure heat recovery steam generator (HRSG). Oxy-fuel cycles are proposed to capture all the produced CO2. Due to limited fossil fuel resources, it is necessary to optimise the use of energy in the power plant cycles as much as possible. The presented configuration improves the energy and exergy efficiency of the cycle with usage of dual-pressure HRSG instead of single pressure. In this study, thermodynamic analysis for the performance of modified Graz cycle has been done which shows the effect of different parameters on the performance of cycle. Results show that the thermal and exergy efficiencies increase up to 54.5% and 47.8%, respectively, by adding of dual-pressure heat recovery steam generator unit.

Waste Heat Recovery From Closed Brayton Cycle Using Organic Rankine Cycle: Thermodynamic Analysis

This study examines the performance of a gas-cooled nuclear power plant with closed Brayton cycle (CBC) combined with an organic Rankine cycle (ORC) plant, as well as the irreversibility within the system. Individual models have been developed for each component, through applications of the first and second laws of thermodynamics. The overall system performance is then analyzed by employing individual models and further application of thermodynamic laws for the entire cycle, to evaluate the thermal efficiency and entropy production of the plant. The effects of the turbine inlet temperature, compressor pressure ratio, evaporator temperature, and temperature difference in the evaporator on the combined cycle first-law, second-law efficiency and exergy destruction rate are studied. Finally optimization of the combined cycle in a systematic way has been developed and discussed. It was found that the combined cycle first-law efficiency is about 9.5–10.1% higher than the simple CBC cycle. Also, the exergy destruction rate for the GT-MHR/ORC combined cycle, is about 6.5–8.3% lower than that of the GT-MHR cycle.Copyright

Entropy generation analysis for Couette?Poiseuille flow through parallel-plates microchannel

This paper presents the first and second laws of thermodynamics analysis for laminar forced convective heat transfer of a Newtonian fluid in a microchannel between parallel plates. Hydrodynamically and thermally fully developed flow with constant properties is examined. Two different forms of the thermal boundary-conditions are considered. The velocity and temperature profiles are analytically determined as a function of the Brinkman and the Knudsen number. The present results are in an excellent agreement with those available in the literature. Entropy generation is shown to decrease with an increase in Kn while increasing Br and Br/Ω results in increasing entropy generation.

Performance characteristics of a novel ejector-expansion transcritical CO2 refrigeration cycle with gas cooler exergy utilisation

In this paper, a novel configuration of ejector-expansion transcritical CO2 (TRCC) refrigeration cycle was presented. A gas cooler exergy was utilised by a supercritical CO2 power cycle to enhance the performance of the presented cycle. Theoretical analysis on the performance characteristics was carried out for the cycle on the basis of the first and second laws of thermodynamics. A parametric study was also conducted to optimise the performance of plant, under various operating conditions. It was found that the coefficient of performance and second-law efficiency of the presented cycle are on average 7.5-28 % higher than those of the conventional ejector-expansion TRCC refrigeration cycle. It was concluded that this cycle could be recognised as a promising refrigeration cycle from the thermodynamic and technical point of views.

Exergoeconomic and exergoenvironmental analysis and optimisation of the three configurations of CO2 transcritical cogeneration cycle using genetic algorithm

In this paper, exergoeconomic and exergoenvironmental analysis and optimisation are performed for three configurations of cogeneration cycles, which differ in their energy sources. The energy sources are solar, biomass and combination of solar and biomass. Three systems are solar-CO2 transcritical cogeneration system (SCTCS), biomass-CO2 transcritical cogeneration system (BCTCS) and solar-biomass-CO2 transcritical cogeneration system (SBCTCS). Hydrogen production rate optimal design (HPROD), refrigeration power optimal design (RPOD) and cost optimal design (COD) are considered for analysis and optimisation. As a result, cogeneration using biomass is the most economic effective system among the three alternative processes. In BCTCS, the cost of products decreased 9% when hydrogen production rate and refrigeration power are decreased from 1.817 l/s to 1.754 l/s and 6.425 kW to 6.103 kW, respectively. The results indicate that the total exergy destruction rate in the PROD case is higher than any other cases; however, the investment cost rate in the HPROD is higher than the two other cases.