Variation Of Exergy Efficiency Research Articles

Comparative study on the organic rankine cycle off-design performance under different zeotropic mixture flow boiling correlations

Zeotropic mixture utilization enhances the performance of the Organic Rankine cycle (ORC) significantly. For geothermal ORC power plants, the zeotropic mixture flow boiling correlation plays a vital role in both evaporator design and system performance evaluation. Based on the screened zeotropic mixture R1224yd(Z)/R1234ze(E) (0.452/0.548), a comparative analysis of 4 flow boiling correlations is performed to assess their impact on both evaporator design and system performance under off-design conditions. The results underscore a substantial impact of these correlations on determining the plate length, with the largest relative difference being 53.8%, consequently resulting in uncertainties of 31.7% and 23.4% for the evaporator exergy loss and cost, respectively. Under off-design working conditions, the relative difference in net power output varies from 16.43% to 7.67%. The exergy efficiency variation is up to 11.82% and the electricity production cost (EPC) uncertainty is up to 11.2% at the working condition with the maximum difference in net output work. This study provides valuable insights for selecting the appropriate zeotropic mixture flow boiling correlation in practical evaporator design and evaluating the off-design performance of ORC systems.

Energy and exergy-based threshold setting for the auxiliary heating source of a hybrid solar/IR drying system

In special case of spirulina drying, the energy and exergy investigations were performed for a pure solar dryer and a hybrid solar/infrared (IR) drying system. For three drying temperatures 40, 50 and 60 °C, the specific energy consumption (SEC) and energy utility ratio (EUR) were evaluated and it was found that the maximum contribution of IR to the drying process was at 40 °C, in which SEC was reduced by 12.18 % and EUR was increases by 14.4 %. But at higher temperatures, negligible contribution of auxiliary heat source was found and less fraction of supplied power was used for removing the water content of the samples. The variation of exergy efficiency was also evaluated at different temperatures, and it was noted that the hybrid dryer had the best performance at 40 °C, while the conventional solar dryer showed better exergy efficiencies at 50 °C and 60 °C. As a result, a convenient criterion was established for optimum use of IR source in a hybrid system. Uncertainty analysis was performed.

Multi-Objective Optimization of the Basic and Regenerative ORC Integrated with Working Fluid Selection.

A multi-objective optimization based on the non-dominated sorting genetic algorithm (NSGA-II) is carried out in the present work for the basic organic Rankine cycle (BORC) and regenerative ORC (RORC) systems. The selection of working fluids is integrated into multi-objective optimization by parameterizing the pure working fluids into a two-dimensional array. Two sets of decision indicators, exergy efficiency vs. thermal efficiency and exergy efficiency vs. levelized energy cost (LEC), are adopted and examined. Five decision variables including the turbine inlet temperature, vapor superheat degree, the evaporator and condenser pinch temperature differences, and the mass fraction of the mixture are optimized. It is found that the turbine inlet temperature is the most effective factor for both the BORC and RORC systems. Compared to the reverse variation of exergy efficiency and thermal efficiency, only a weak conflict exists between the exergy efficiency and LEC which tends to make the binary objective optimization be a single objective optimization. The RORC provides higher thermal efficiency than BORC at the same exergy efficiency while the LEC of RORC also becomes higher because the bare module cost of buying one more heat exchange is higher than the cost reduction due to the reduced heat transfer area. Under the heat source temperature of 423.15 K, the final obtained exergy and thermal efficiencies are 45.6% and 16.6% for BORC, and 38.6% and 20.7% for RORC, respectively.

Exergoeconomic optimization and working fluid comparison of low-temperature Carnot battery systems for energy storage

The increasing share of renewable energy in energy constituent requires the development of large-scale energy storage technologies to tackle with the grid connection problem, Carnot Battery is a possible candidate. In this study, the theoretical models of two Carnot Battery systems with four different working fluid pairs were established, analyzed and compared. Genetic algorithm was introduced in the optimization. The results show that working fluid pairs R245fa-HFO-1336mzz(Z) (the former for ORC, the latter for heat pump) presents the best economic performance, reaching the lowest levelized cost of storage (LCOS) of 0.2631 $·kWh−1 when the thermal storage temperature is 130 °C. The power-to-power efficiency (P2P) competes with LCOS, with the increase of P2P the LCOS decreases. The working fluid pairs R245fa-HFO-1336mzz(Z) and HFO-1336mzz(Z)-HFO-1336mzz(Z) show better exergoeconomic performance, the obtained optimum value of P2P is 42.63%. The variation of exergy efficiency (ηex) with thermal storage temperature is non-monotonic. The working fluid pairs with the highest ηex is HFO-1336mzz(Z)-R245fa, and the maximum value is 19.88%. In each configuration, the most costing components are turbine and compressor. In addition, the throttling valve, compressor and heat exchanger takes large proportions in the total exergy destruction.

Energy, exergy, economic (3E) analysis, optimization and comparison of different Carnot battery systems for energy storage

Energy storage is the key to solve the grid connection problem of renewable energy. Carnot Battery is one of the promising energy storage technologies nowadays. In this work, four Carnot Battery systems were constructed using organic Rankine cycle and vapor compression heat pump. Energy, exergy and economic (3E) models of the aforementioned systems were built. Using genetic algorithm as the optimization method, the levelized cost of storage was employed as the objective function. The systems were investigated, analyzed and compared according to the optimization results. The results show that regenerative systems that consist of a regenerative vapor compression heat pump present better thermo-economic performance. With thermal storage temperature increasing from 90 °C to 130 °C, the value of levelized cost of storage gradually decreases from 0.42 $/kWh to 0.29 $/kWh. The power-to-power efficiency decreases continuously with the increase of thermal storage temperature, however, the variation of exergy efficiency with thermal storage temperature is non-monotonic. The maximum value of 19.12% is achieved in system BORC-RVCHP when the thermal storage temperature is 100 °C. Also, it can be found that the value of the levelized cost of storage increases gradually with the lift of power-to-power efficiency. The cost and exergy destruction of each component are also calculated and compared. Two components that take the largest proportion in total investment cost are turbine and compressor for all the considered system configurations in this work.

Energy and Exergy Analysis of the Air Source Transcritical CO2 Heat Pump Water Heater Using CO2-Based Mixture as Working Fluid

Given the large demand nowadays for domestic hot water, and its impact on modern building energy consumption, air source transcritical CO2 heat pumps have been extensively adopted for hot water production. Since their system efficiency is limited by significant irreversibility, a CO2-based mixture could offer a promising drop-in technology to overcome this deficiency without increasing system complexity. Although many CO2 blends have been studied in previously published literature, little has been presented about the CO2/R32 mixture. Therefore, a proposed mixture for use in transcritical CO2 heat pumps was analyzed using energy and exergy analysis. Results showed that the coefficient of performance and exergy efficiency variation displayed an “M” shape trend, and the optimal CO2/R32 mixture concentration was determined as 0.9/0.1 with regard to flammability and efficiency. The irreversibility of the throttling valve was reduced from 0.031 to 0.009 kW⋅kW−1 and the total irreversibility reduction was more notable with ambient temperature variation. A case study was also conducted to examine domestic hot water demand during the year. Pure CO2 and the proposed CO2 blend were compared with regard to annual performance factor and annual exergy efficiency, and the findings could provide guidance for practical applications in the future.

Indirect mechanical heat pump assisted humidification‐dehumidification desalination systems

In this study, four new indirect heat pump assisted mechanical vapor compression humidification-dehumidification (HDH) systems are proposed and their superiorities over the reference system are demonstrated from thermodynamics and thermoeconomics viewpoints. The proposed models are configured based on an HDH unit and a simple cascade heat pump, an HDH unit and a heat pump with an ejector, an HDH unit and a cascade heat pump with an ejector, and an HDH unit and a vapor injection heat pump. Although employing a heat pump with cascade and ejector configurations improved gain-output-ratio (GOR) and specific power consumption (SPC) values in comparison with the base system, the performance metrics of such layouts are still inferior to those of the HDH unit coupled with the vapor injection heat pump. It is found that the desalination unit with vapor injection mechanism has the highest GOR and the lowest SPC values of 9.22 and 71.29 kWh/m3, respectively, under constant electrical power of 31.26 kW. Overall, proposal of the cascade heat pump, heat pump with an ejector, cascade heat pump with an ejector, and a vapor injection heat pump instead of the conventional heat pump improved GOR by 4.83%, 10.03%, 11.52%, and 14.25%, respectively. Meantime, the SPC of the HDH unit coupled with a simple heat pump decreased by 4.6%, 9.1%, 10.26%, and 12.46% when a cascade heat pump, a heat pump with an ejector, a cascade heat pump with an ejector, and a vapor injection heat pump were used instead of the conventional heat pump, respectively. Also, it is found that a maximum improvement of 14.13% can be achieved in exergy efficiency with a cost penalty of only 1.59 $/m3. Also, it was found that with the use of a simple cascade heat pump instead of the simple heat pump, the exergy efficiency can be enhanced by 4.9%, while the unit cost of the distilled water (UCDW) was degraded by 51.32%. Likewise, the HDH unit coupled with the cascade heat pump with an ejector was resulted in high UCDW compared to the base system, while its exergy efficiency was not enhanced so significantly. Variation of exergy efficiency versus the intermediate temperature had a maximum value of 1.93% (for the HDH unit coupled with a simple cascade heat pump) and 2.05% (for the HDH unit coupled with a cascade heat pump with an ejector) at Tint = 315 K. Moreover, it was found that the UCDW can be decreased with the rise of the intermediate temperature and cascade heat exchanger temperature difference as the fresh water cost rate decreases as a result, while the exergy efficiency can be increased with the rise of the cascade heat exchanger temperature difference.

Exergy Optimization of a Solar Collector in Flat Plate Shape Equipped with Elliptical Pipes Filled with Turbulent Nanofluid Flow: A Study for Thermal Management

In this paper, forced convection of a multiwalled carbon nanotube (MWCNT)–water nanofluid (NF) in a new flat plate solar collector (FPSC) equipped with elliptical pipes instead of circular ones is investigated. The three-dimensional conservation equations were solved in the domain with the finite volume method (FVM) based on the semi-implicit method for pressure linked equations (SIMPLE) algorithm. The laminar-turbulent range of the Reynolds number (Re) and the volume fraction of the NF (ϕ) were 50–12,000 and 0–0.1, respectively. The optimization process was accomplished through the comparison of diverse parameters to attain the optimal case with the highest exergy efficiency. In this study, it was concluded that, in the case of using elliptical pipes instead of circular tubes, the time that the fluid was inside the FPSC increased, which led to an increase in the outlet temperature, while the exergy efficiency of the FPSC increased. Additionally, it was observed that using elliptical pipes enhanced the outlet fluid temperature, energy efficiency, and exergy efficiency. Generally, while the trend of exergy efficiency variation with effective parameters was rising, applying elliptical pipes caused the efficiency to increase. In addition, the exergy efficiency variation decreased when these parameters were changed. The highest value of exergy efficiency was 7.1%. On the other hand, for each specific FPSC, there was a unique mass flow rate at which the exergy efficiency reached its maximum value, and for higher mass flow rates, the efficiency was slightly diminished and then remained unchanged. Finally, the highest exergy efficiency was achieved for ϕ = 0.10%.

Evaluation of an existing helium liquefier in refrigerator and mixed-mode operation through exergy analysis

Present day, all small scale helium liquefiers operate in Claude cycle with two turbines in series arrangement. In this paper, an effort has been made to investigate the exergy characteristics of a small scale liquefier and its components at design and various off-design refrigeration and mixed mode operation under steady state condition. The variation of exergy efficiency, exergy destruction, exergy output-destruction interrelations, refrigeration- liquefaction capacity correlation, etc. have been evaluated by increasing refrigeration load in steps starting at pure liquefaction till pure refrigeration mode in the experiment. As the experimental data were not sufficient for complete analysis, Aspen Hysys software has been used to determine the remaining process parameters required to understand the thermodynamic cycle. The significance of the variation of exergy parameters at different modes of operation have been reported to establish the importance of the present study. Though the results are specific for the existing helium liquefier (model HELIAL 50 of Air Liquide DTA, France) with some associated constraints, the results may be useful to the designers of helium systems where flexibility of operation is a desirable feature.

From Entropy Generation to Exergy Efficiency at Varying Reference Environment Temperature: Case Study of an Air Handling Unit

The continuous energy transformation processes in heating, ventilation, and air conditioning systems of buildings are responsible for 36% of global final energy consumption. Tighter thermal insulation requirements for buildings have significantly reduced heat transfer losses. Unfortunately, this has little effect on energy demand for ventilation. On the basis of the First and the Second Law of Thermodynamics, the concepts of entropy and exergy are applied to the analysis of ventilation air handling unit (AHU) with a heat pump, in this paper. This study aims to develop a consistent approach for this purpose, taking into account the variations of reference temperature and temperatures of working fluids. An analytical investigation on entropy generation and exergy analysis are used, when exergy is determined by calculating coenthalpies and evaluating exergy flows and their directions. The results show that each component of the AHU has its individual character of generated entropy, destroyed exergy, and exergy efficiency variation. However, the evaporator of the heat pump and fans have unabated quantities of exergy destruction. The exergy efficiency of AHU decreases from 45–55% to 12–15% when outdoor air temperature is within the range of −30 to +10 °C, respectively. This helps to determine the conditions and components of improving the exergy efficiency of the AHU at variable real-world local climate conditions. The presented methodological approach could be used in the dynamic modelling software and contribute to a wider application of the Second Law of Thermodynamics in practice.

Exergy performance assessment of a linear parabolic trough photovoltaic thermal collector

This paper presents the exergy performance assessment of a linear parabolic trough photovoltaic thermal collector. The governing equations of a concentrating photovoltaic thermal collector (CPVT) are obtained through an energy balance for the various components of the system. The electrical analysis of PV cells is carried out by a four-parameter model of current-voltage. By introducing the various exergy components in the system, the system exergy efficiency is obtained. The simulation results of present study are in good agreement with previous studies data. The results show that the exergy efficiency variation with respect to the fluid velocity and channel diameter is negligible. Increasing fluid velocity from 0.08 to 0.43 m/s increases the electrical efficiency and thermal efficiency 1.05% and 2.2%, respectively. An increase of receiver width from 0.06 to 0.2 m increases the exergy efficiency and thermal efficiency by 1.47%, and 9.4%, respectively. Increasing channel diameter from 0.017 to 0.06 m increases the thermal efficiency and electrical efficiency 2.75% and 3.9%, respectively. By increasing the collector length from 3 to 90 m initially the thermal efficiency increases to 62.5% and then decreases to 60%. The exergy efficiency has a slight change with increasing collector length. An increase of fluid inlet temperature from 20 to 90 °C increases the exergy efficiency by 8.2%. Meanwhile, the thermal and electrical efficiencies reduce by 6.5% and 3.35%, respectively. An increase of the incident beam radiation from 50 to 1000 W/m2 enhances the electrical efficiency by 6.6% and increases the exergy efficiency by 15.7%, while the thermal efficiency has an ascending/descending trend. The increase of ambient temperature increases the exergy efficiency and thermal efficiency by 7.6% and 5.1%, respectively. The impact of receiver width and ambient temperature on electrical efficiency is negligible.

Exergy analysis of a hybrid solar‐fossil fuel power plant

AbstractIn this study, exergy analysis, energy analysis, and mathematical modeling are performed in a 35 MW solar‐fossil fuel power plant. The losses of exergy and energy in different components and also changes of the efficiency of exergy and energy are analyzed at a specific day, 20th June. The assumed power plant in this study is Solar Electric Generating Station VI (SEGS VI), located in California's Mojave Desert. A parametric study, under different working conditions, including different working pressures, temperatures, collector output temperature, steam flow rate, and heat transfer fluid (HTF) flow rate is studied and the effect of variation of parameters on the performance of the plant is investigated. Authors found that, the maximum exergy loss happens in the collector and the maximum energy loss occurs in the condenser. Energy analysis shows that 47% of the total loss energy in the cycle happens in the condenser, as the main component that wastes energy. From exergy analysis, the collector and then boiler are the main components wasting exergy where 68.32% of total exergy loss occurs in these two components in hybrid mode (solar‐fossil fuel). Exergy and Energy efficiency variations throughout the day show that minimum exergy efficiency (32.7%) and maximum energy efficiency (23%) occurs at 12 am. Exergy efficiency variation versus turbine inlet pressure shows that the maximum exergy efficiency (26%) accure at 95 bar. The changes of the absorbed heat and solar irradiation of the 20th of June shows a good agreement with the measured data in validated reference.

Experimental investigation of first and second laws in a direct absorption solar collector using hybrid Fe3O4/SiO2 nanofluid

In this study, energy and entropy analysis of a residential-type direct absorption solar collector using hybrid Fe3O4/SiO2 nanofluid is evaluated experimentally. The hybrid nanofluid samples are prepared in the different volume ratios of Fe3O4/SiO2 (25:75, 50:50 and 75:25) and different volume fractions (500 ppm, 1000 ppm and 2000 ppm). The appropriate nanofluid samples for using as the working fluid of the collector are chosen based on the results of stability and optical properties of nanofluid. Then, outdoor thermal performance of collector is investigated using the experimental setup based on EN12975-2. Measurement of nanofluid optical properties using the spectrophotometry method shows that the extinction coefficient of 2000 ppm hybrid Fe3O4/SiO2 nanofluid is on average 10 cm−1 higher than that of the base fluid. Results of energy analysis display that the collector efficiency is increased by mass flow rate and volume fraction of nanofluid asymptotically. The asymptotic value is about 83% for 2000 ppm hybrid Fe3O4/SiO2 nanofluid. The findings indicate that the variation of exergy efficiency of a direct absorption solar collector with the volume fraction and mass flow rate is similar to energy efficiency. The enhancement of exergy efficiency is 66.4% for mass flow rates of 0.0225 kg s−1 by increasing the volume fraction from 0 to 2000 ppm. It is also observed that dimensionless entropy generation number is decreased by nanofluid volume fraction and by mass flow rate. The lowest entropy generation number is obtained in the mass flow rate of 0.0225 kg s−1 and the volume fraction of 2000 ppm. The variation of Bejan number by volume fraction shows that the contribution of pressure drop in entropy generation is insignificant.

Exergy analysis of a weir‐type cascade solar still connected to PV/T collectors

In this study, the exergy analysis of a weir-type cascade solar still connected to photovoltaic thermal (PV/T) collectors is provided. By formulating the energy balance for different components of solar still system, the governing equations were obtained as a set of non-linear ordinary differential equations. A perfect exergy analysis is used to obtain irreversibility rates, exergy fractions and exergy efficiency. To find various temperatures and freshwater productivity, the governing equations are solved numerically. Moreover, through experimental data of previous studies, the numerical results were validated. In this study, the effect of the mass flow rate of brackish water and the number of PV/T collectors on the hourly variation of exergy efficiency, irreversibility rates and exergy fractions were investigated. Results showed that by connecting two PV/T collectors to the cascade solar still, the exergy efficiency can be improved twice. Moreover, the connection of two PV/T collectors and use of their output electrical power for heating brackish water can increment the fresh water production rate by 56.8%. The absorber plate and PV/T collectors include maximum 55.8 and 36.8% of system total irreversibility, respectively. The maximum exergy fraction is obtained in evaporating with a value of 0.85.

Energy and exergy analysis of a new direct-expansion solar assisted vapor injection heat pump cycle with subcooler for water heater

A new direct-expansion solar assisted vapor injection heat pump cycle with subcooler for water heater is proposed in this paper which aims to improve the performance of traditional subcooler vapor injection heat pump cycle by utilizing the solar energy. The new cycle has two working modes (SVIC mode and DX-SVIC mode) to be switched according to the solar radiation intensity. The performance enhancement potential of the new cycle is investigated by comparing with the traditional cycle through theoretical method. Under the considered conditions, the new cycle yields an average of 14.6% and 42.9% improvement in the heating coefficient of performance and heating capacity aspects compared with the traditional cycle, respectively. Both the new cycle and the traditional cycle have optimum injection pressures to obtain the maximum heating coefficient of performance. The simulation results indicate that the DX-SVIC mode outperforms the SVIC mode on most solar radiation condition, while the latter one is suitable for the extremely low and no solar radiation condition. The energy performance and heat exergy of the new cycle are improved with enhancing the solar radiation, while the variation of exergy efficiency shows contrary tendency. As increasing the injection pressure, the exergy input decreases more rapidly than the heat exergy, and thus the exergy efficiency is improved. The increase of the solar collector area always leads to the energy performance improvement of the new cycle.

Energy and Exergy Analysis and Optimization of a Heat Sink Collector Equipped with Rotational Obstacles

In this paper, the forced convection flow in a heat sink collector equipped with stationary and rotational obstacles is studied numerically. Three-dimensional governing equations are solved by control volume approach based on the SIMPLE algorithm and k.. turbulence model. Reynolds numbers are considered in the laminar-turbulent range of 50 < Re < 12,000. The optimization was carried out by variation of related parameters. It is concluded that using heat sink, instead of a customary instrument, increases the outlet temperature from the collector and exergy efficiency due to longer installing of the fluid inside the collector. Also, it is realized that using the stationary and rotational obstacles enhance the outlet fluid temperature (about 2.5°C), energy efficiency and exergy efficiency. Nevertheless, using the rotational obstacles is more effective than the stationary obstacles. While the trend of exergy efficiency variation with effective parameters is increasing, applying the obstacles precipitates the efficiency increment (from 4% to 5.3%). In addition, for the case that the trend of exergy efficiency variation by changing these parameters is decreasing, the decreasing trend gets slow. There is a unique mass flow rate (0.005 kg/s) that the exergy efficiency gets a maximum value and for the higher mass flow rates, the efficiency decreases slightly and then remains unchanged.

Energy and Exergy Analysis of Multi-Temperature PCMs Employed in a Latent Heat Storage System and Parabolic Trough Collector

AbstractThis study represents the exergy analysis of the evacuated tube parabolic trough collector and the cascaded latent heat storage system using multi-temperature phase change material (PCMs) during the charging process. The objective of the work is to control the losses and increase the efficiency of the system. The exergy analysis has been conducted on the basis of the first and second laws of thermodynamics in a parabolic trough collector with various mass flow rates of the heat transfer fluid (HTF). The overall variation of exergy efficiency of the collector with varying mass flow rate of the HTF is 5.9 %. The thermodynamic analysis of the cascaded latent heat storage system has been done during the charging process in which the PCM absorbs energy from the HTF and undergoes a phase transformation from the solid to the liquid state. The exergy analysis is conducted by varying the mass flow rate of the HTF in the storage system for both insulated and non-insulated systems. It is noticed that the variation of exergy stored for 5 and 10 liters per minute is 24.609 kW and 40.48 kW, respectively. It is concluded that the high range of energy and exergy stored in the system is achieved by the high flow rate of the HTF.

Comparative thermodynamic analysis of a hybrid refrigeration system for promotion of cleaner technologies

This article presents a comparative thermodynamic analysis based on numerical methods for a hybrid refrigeration system suitable to operate as vapour absorption system (VA), vapour compression–absorption system (VCA) and vapour compression system (VC). The working fluid employed for the first two systems is ammonia–water and it is pure ammonia in case of the third system. The system is being powered by waste energy and conventional energy depending on the mode of operation. The effect on performance parameters like COP and exergy efficiency during all modes of operation has been evaluated by keeping the uniform parametric conditions like condenser temperature (40 °C) and evaporator temperature (5 °C) for all the modes of operation. The effect of ambient temperature on the exergy loss in each component of the different modes of operation have also been evaluated and discussed. The results obtained indicate that COP and exergy efficiency for VCA mode initially increases and then decreases whereas for VA and VC mode the COP and exergy efficiency decreases with condenser temperature. The analysis also reveals that with the variation in evaporator temperature the COP and exergy efficiency for VC mode increases whilst for VA and VCA mode the COP shows a slight increase whereas exergy efficiency decreases. The variation of exergy efficiency and exergy loss in different components with condenser and evaporator temperature shows that exergy efficiency is found to be the highest in VC mode whereas the lowest in VCA mode for both the temperature variations. The variation of compressor work and exergy loss in compressors with evaporator and condenser temperature shows that compressor work and exergy loss is lesser for VCA mode when compared to VC mode.

Efficiency assessment of key psychometric processes

The study focuses on defining energy and exergy efficiencies based on three different types of approaches. For each of five key psychometric processes, such as heating or cooling, heating with humidification, cooling with dehumidification, evaporative cooling, and adiabatic mixing, parametric studies are carried out. Two efficiencies are newly proposed here in this study, and the third efficiency is taken from the literature for comparison purposes. The results show that for heating process exergy efficiency varies from 0.012 to 0.48 with rise in ambient temperature. Increasing ambient temperature results in variation of exergy efficiency from 0.014 to 0.29 for heating with humidification process. For cooling with dehumidification process exergy efficiency varies from 0.002 to 0.73 with rise in ambient temperature. The exergetic efficiency of evaporative cooling process varies from 0.64 to 0.03 with an increase in ambient temperature. For adiabatic mixing process, exergy efficiency varies from 0.65 to 0.94 with rise in ambient temperature.

Thermo-economic analysis of heat pipe heat exchanger for waste heat recovery in thermal systems

Thermo–economic analysis of Heat Pipe Heat Exchanger (HPHE) for waste heat recovery in thermal systems using the P1–P2 and NTU methods is presented. The optimum effectiveness of a HPHE is given as a polynomial equation, whereas the net savings and payback period are given in closed form to enable the HPHE designer to determine the optimised values directly. In addition to this, exergy analysis of HPHE for waste heat recovery in thermal systems is formulated. The variation of exergy efficiency with respect to change in inlet temperature is also presented.