Reference Environment Temperature Research Articles

Assessment of a cogeneration system for ceramic industry by using various exergy based economic approaches

This study presents various exergy based economic analyses of a gas turbine cogeneration system (COGEN) for a ceramic tile plant for five different reference environment temperatures. Specific Exergy Costing (SPECO) method, which uses fuel-product exergy approach and flow costs, and Exergy-Cost-Energy-Mass (EXCEM) method, which considers exergy loss and destruction with cost association, are used. It has been found that the irreversibilities due to chemical combustion reactions, occurring in the combustion chamber (CC) of the gas turbine unit, wall tile (WD) dryer and ground tile dryer (GD), have negative effects for the destructed exergy cost rate of themselves and overall system. In addition, depending on the destructed exergy cost ratio, the exergy based economic factor rates of these components are found to be lower than others. While the increase of the COGEN's and all of its components' destructed exergy cost rates are direct proportionally to the increase in the environment temperature, they are inversely proportional to the exergy based economic factor. As a result of the SPECO method, in the EXCEM method, the exergy cost parameters of the CC are much higher than the other components at all reference environment temperatures because of the high destructed exergy value of the CC. The system needs to be optimized in terms of eliminating the irreversibilities encountered intensively in the components such as CC, WD, GD. Consequently, these results show that the focus should be on the CC first, then on the WD and GD.

Assessment of a Geothermal Combined System with an Organic Rankine Cycle and Multi-effect Distillation Desalination

An analysis is reported of a geothermal-based electricity-freshwater system in which an organic Rankine cycle is integrated with a multi-effect distillation desalination unit. The system is driven by geothermal hot water extracted from the production well. Mass, energy, entropy, and exergy rate balances are written for all system components, as are energy and exergy efficiency expressions for each subsystem. The exergy destruction rate associated with the temperature and chemical disequilibrium of the freshwater and brine with the reference environment are taken into account to reveal accurate results for irreversibility sources within the desalination process. The developed thermodynamic model is simulated using thermodynamic properties of the working fluids (i.e., ammonia, seawater, distillate, and brine) at each state point. A sustainability analysis is performed that connects exergy and environmental impact concepts. That assessment expresses the extent of the contribution of the system to sustainable development and reduced environmental impact, using exergy methods. Results of the sustainability analysis indicate that, with an increase in the reference environment temperature from 20 to 35 ^circ{rm C}, the exergy destruction rate decreases for the multi-effect distillation and organic Rankine cycle systems respectively from 6474 to 4217 kW and from 16,270 to 13,459 kW. Also, the corresponding sustainability index for the multi-effect distillation and organic Rankine cycle systems increases from 1.16 to 1.2 and 1.5–1.6, respectively, for the same increase in reference environment temperature.

Thermodynamic performance assessment of boron based thermochemical water splitting cycle for renewable hydrogen production

The present study is related with the thermodynamic performance assessment of renewable hydrogen production through Boron thermochemical water splitting cycle. Therefore, all step efficiencies and overall cycle efficiency are calculated based on complete reaction. Additionally, a parametric study is conducted to determine the effect of the reference environment temperature on the overall cycle efficiency. In this regard, exergy efficiencies, exergy destruction rates and also inlet and outlet exergy rates of the cycle are calculated and presented for various reference temperatures. The exergy efficiency of the cycle is calculated as 0.4393 based on complete reaction and occurs at 298 K. This study has shown that Boron thermochemical water splitting cycle has a great potential due to cycle performance. As a result, Boron based thermochemical water splitting cycle can help achieve better environment and sustainability due to high exergetic efficiency. By the way, economic and technical issues of the storage and transportation of the hydrogen can find a proper solution if the hydrogen production reaction of the Boron thermochemical water splitting cycle takes place on-board of a vehicle.

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.

Energy and exergy assessments of dehydrogenation of propane for propene production

ABSTRACTThe energy and exergy assessments of the dehydrogenation of propane for propene production process were performed. The results show that when the reaction temperature rises from 400°C to 1000°C, the range of inlet and outlet exergy is 2268∼2376 and 2265∼2341 kJ/mol C3H6, respectively, and the range of exergy destruction is 6.31∼33.24, 9.93∼35.15 and 3.59∼31.99 kJ/mol C3H6 at 5, 25 and 45°C reference environment temperature, respectively. The range of exergy efficiency at discussed reference environment and reaction temperature is 98.52∼99.84%, and decreases with the increasing of reaction temperature and increases with the decreasing of reference environment.

Performance characterization of zero carbon emission microgrid in subtropical climate based on experimental energy and exergy analyses

Energy and exergy analyses are effective tools to characterize the microgrid performance in different operating conditions and to identify the scope of making system more efficient. Exergy analysis provides details information regarding maximum possible work, losses, types of losses and its locations. In present study an attempt has been made to characterize the performance of photovoltaic (PV) and fuel cell (FC) based AC microgrid using the energy and exergy analyses. A microgrid comprising of PV (5 kWp) and FC (1 kW) as primary and auxiliary generators respectively is developed at Centre for Energy Studies (CES), Indian Institute of Technology (IIT) Delhi. Excess PV electricity is used to generate the hydrogen using electrolyzer that is stored in metal hydride (MH) tank. Experimental energy and exergy analyses are carried out for different operating conditions that give energy efficiencies of PV system, FC system, MH and electrolyzer as 12.6%, 59.1%, 83.4% and 49.4% respectively. Maximum exergy efficiencies of PV, FC, MH and electrolyzer are estimated as 13.5%, 59.4%, 82.8% and 49.6% respectively. The exergy values are calculated at various environment reference temperatures (0 °C, 8 °C, 16 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C and 45 °C) to estimate the seasonal effects on the exergy performance of system. The exergy efficiency of entire hydrogen generation and utilization cycle increases with increase in reference environment temperature. The overall energy and exergy analyses of entire AC microgrid in different operating modes are also performed. According to the obtained experimental results maximum overall energy and exergy efficiencies of AC microgrid are 12.57% and 13.47% respectively.

Thermodynamic performance assessment of solar based Sulfur-Iodine thermochemical cycle for hydrogen generation

Recent studies show that thermochemical cycles has a great potential for green hydrogen generation. In this study, the thermodynamic performance assessment of a solar based Sulfur-Iodine (S-I) thermochemical cycle for hydrogen generation is performed focusing on the energy and exergy methods. Moreover, we investigated that various reference environment and reaction temperatures effects on energy and exergy efficiencies of S-I cycle steps. The results of thermodynamic analyses indicated that energy and exergy efficiency of S-I cycle are found to be 43.85% and 62.39%, respectively. In addition, the overall energy and exergy efficiencies of cycle are computed as, 32.76% and 34.56%, respectively. It was concluded that the S-I thermochemical cycle offers a feasible and a diverse option for hydrogen generation and seems to be a promising cycle.

Analysis and evaluation of a new renewable energy based integrated system for residential applications

In this study, a solar based Rankine cycle and geothermal based system for multigeneration is designed and developed. It consists of a Rankine cycle with reheating for power generation, an absorption chiller cycle for cooling, a drying process to dry wet products, useful heat from the condenser of the Rankine cycle, and other useful heat out from heat exchangers. The overall energy and exergy efficiencies of the single generation and multigeneration systems are studied, and it is observed that the energy efficiency of the multigeneration system is higher than the single generation system. The energy efficiency of the single and multigeneration systems are 7% and 37%, respectively. Similarly, the overall exergy efficiencies for the single generation and multigeneration systems are also studied and presented in this paper. In addition to this, parametric studies are performed to observe the effects of different substantial parameters, namely inlet pressure and temperature of the turbine, and reference environment temperature in order to investigate the variations in the system performance in terms of the energy and exergy efficiencies.

The exergy efficiency assessment of heat recovery exchanger for air handling units, using a state property – Coenthalpy

Exergy analysis is relevant to HVAC systems since both work and heat are present in the energy transformation processes. In this paper, an algorithm for the exergy analysis of a ventilation heat recovery exchanger (HRE) is proposed. It involves calculating exergy flows using coenthalpy as the state property. In exergy analysis, Borel considers coenthalpy k as direct potential of the exergy flow. As a result, universal and functional exergy efficiencies of a HRE are calculated. In any case, the solutions for exergy efficiency lie in the interval 0–1. The functional exergy efficiency proposed in the paper serves as the basis for determining the universal algorithm for the exergy analysis of a HRE at a varying reference environment temperature (RET). The values of these exergy efficiencies are discussed by numerical examples derived from the application of the developed algorithm. Functional exergy efficiency broadens the possibilities of increasing the exergy efficiency of processes taking place in HRE as well as allowing the application of exergy-optimal design and control of energy transformation processes in HVAC systems, the popularity of which is ever more increasing.

Energy and exergy analyses of hydrogen production step in boron based thermochemical cycle for hydrogen production

This study deals with a thermodynamic assessment of hydrogen production step of the boron based thermochemical cycle. In addition, this step is assessed for its merits and demerits in terms of energetic and exergetic performances for various reference environment temperatures. In this regard, the energy and exergy efficiencies of this step are calculated as 11.00% and 20.34% and also the hydrogen production step of the cycle inlet, outlet exergy rates and exergy destruction are calculated as 1653.32 kJ/mol, 336.31 kJ/mol and 317.02 kJ/mol while the reference environment temperature is kept constant at 298 K, respectively. The technical and economic problems of the hydrogen storage and transportation find a possible solution provided that the hydrogen production step of this cycle is performed on-board of a vehicle.

Comparative assessment of various chlorine family thermochemical cycles for hydrogen production

This study deals with a comparative assessment of various chlorine family cycles, namely copper–chlorine (CuCl), magnesium–chlorine (MgCl), iron–chlorine (Fe–Cl) and vanadium–chlorine (V–Cl) cycles, which are driven by heat and/or electricity. Hydrogen production through thermochemical and/or hybrid cycles can play a significant role in reducing greenhouse gas emissions and hence offering opportunities for better environment and sustainability. In this paper, we conduct energy and exergy analyses of the VCl cycle and examine both energy and exergy efficiencies of the cycle. We also undertake a parametric study to investigate how the overall cycle performance is affected by changing the reference environment temperature and cycle operating conditions. The performance of VCl cycle are evaluated and compared with CuCl, MgCl and FeCl cycles. Furthermore, these cycles are discussed and compared with each other through their advantages and challenges. As a result, VCl cycle offers a good potential due to its high efficiency over 40% based on a complete reaction. In this regard, VCl cycle appears to be one of the most promising low temperature cycles. It may, therefore, compete with other low temperature cycles such as copper–chlorine.

Thermodynamic Analysis of Hydraulic Braking Energy Recovery Systems for a Vehicle

In this study, a thermodynamic analysis of a hydraulic braking energy recovery system used in vehicles is performed for newly developed systems. The present system is related to the field of energy efficiency in vehicles. The energy recovery system comprises a first pump, a hydraulic accumulator, and a hydraulic motor. The first pump is a variable displacement hydraulic pump (VDP). The hydraulic accumulator is connected to the first pump which operates to store hydraulic fluid under pressure. The hydraulic motor is hydraulically connected to the accumulator to receive hydraulic fluid. The motor is adapted to drive a second hydraulic pump, which is hydraulically connected to the auxiliary system, using hydraulic energy stored in the accumulator. The overall charging and discharging efficiencies, and the overall system efficiency is calculated and presented in this paper. For the purpose of the analysis, EES (engineering equation solver) is used. In addition, parametric studies are performed to observe the effects of different substantial parameters, namely, the inlet pressure and temperature of the accumulator, and the reference environment temperature, in order to investigate the variations in the system performance in terms of the efficiencies. Two systems are developed and it is found that the charging and discharging efficiencies for one system are 83.81% and 87.73%, while for the other system the charging and discharging efficiencies are 81.84% and 85.67%, respectively.

Performance assessment of a direct formic acid fuel cell system through exergy analysis

In this study, performance assessment of a direct formic acid fuel cell system is conducted, including evaluation of a broad set of operating parameters. The fuel cell system is modeled and simulated by using sub-routine developed by Matlab. The system components, such as compressor, humidifier and heat exchangers, are also taken into consideration. Effects of varying operating temperature, pressure, membrane thickness, current density, anode–cathode stoichiometry and reference properties on the system are evaluated to predict the performance as close to real-cases as possible. It is found that increasing the temperature greatly favors the performance of the direct formic acid fuel cell system, low pressure and high reference environment temperature values have the same effect on the cell performance. The maximum exergetic efficiency by broad parametric investigation is estimated as 24%, where the power production is 10 kW.

Energy and exergy analyses of a solar-biomass integrated cycle for multigeneration

A biomass and solar integrated system for multigeneration of useful outputs, in which two renewable energy sources are combined to produce multiple outputs (e.g., power, cooling, hot water, heated air), is developed and presented. Energy and exergy analyses are used to assess the performance of the cycle, and the effects of various system parameters on energy and exergy efficiencies of the overall system and its subsystems are examined. The overall energy and exergy efficiencies of the system are found to be 66.5% and 39.7% respectively. Furthermore, the effect is also investigated of reference-environment temperature on energy and exergy efficiencies for the system, when operated only on biomass and solar energy.

Exergy analysis of a solar pond integrated with solar collector

In this paper we present the energetic and exergetic performance of a solar pond integrated with four flat plate solar collectors. The integrated solar pond system was built and tested at Cukurova University in Adana, Turkey. The solar pond consists of salty water zones to prevent convection heat losses from the heat storage zone (HSZ) of the solar pond. The temperature distributions of the solar pond and the inlet–outlet of the heat exchanger were measured by using thermocouples and a data acquisition device. An energy and exergy models were developed to study the energetic and exergetic performance of the integrated solar pond. The energy and exergy performances were compared for the each zone of the solar pond. The reference environment temperature in the exergy analysis was specified as the average representative temperature of each month of the year. The energetic and exergetic performances of the integrated solar pond for the heat storage zone were found to be maximum 32.55% and 28.69% in August, and to be minimum 9.48% and 5.51% in January, respectively.

Performance Assessment of a Potato Crisp Frying Process

Frying is a common and popular cooking method, which has been widely used in food manufacturing, though it is a very energy-intensive process. Energy analysis has been commonly used to assess the performance of fryers. In this study, we attempted to exergetically assess the performance of a potato crisp frying system, which consists of three main components, a combustor, a heat exchanger, and a fryer. In the analysis, we utilized the actual operational data obtained from the literature. We determined exergy destruction in each system component and the whole system. We calculated universal and functional exergy efficiency values for the system components and compared them with each other. We also undertook a parametric study to investigate how the overall cycle performance was affected by changing the reference environment temperature and some operating conditions. We illustrated the exergy results through the Grassmann (exergy loss and flow) diagram. We calculated the universal exergetic efficiency values of 58, 82, and 77% for the combustor, heat exchanger, and fryer, respectively, with a universal exergetic efficiency value of 4% for the whole frying system. We found that the fryer had the highest functional exergetic efficiency value of 74%, followed by the heat exchanger with 47% and the combustor with 0.08%.

Development and analysis of a new renewable energy-based multi-generation system

A renewable energy-based multi-generation system is developed and studied energetically and exergetically. Two renewable sources of energy, biomass and geothermal, are combined to deliver five useful outputs for residential applications. The energy products from biomass sources are used to drive an organic Rankine cycle and a vapour absorption chiller, and further used to dry the wet material in an industrial dryer. A double flash system is used in the geothermal power cycle, which includes a multistage steam turbine. Outlet water flows from the separators and the steam turbine are used to heat water used in households. Liquefied gas is produced through the Linde Hampson liquefaction cycle, in which the compressor is directly coupled to organic Rankine cycle turbine. The energy efficiency of the system is found to be 56.5% and the exergy efficiency 20.3%. The largest exergy destructions are found to occur in both combustion chamber and boiler. The variations in exergy efficiencies and exergy destructions for the system components are determined with respect to changes in the reference-environment temperature and other major system parameters.

Development of an integrated renewable energy system for multigeneration

In this paper, we propose a new integrated, solar and geothermal energy based system for multigeneration applications, which comprises two ORC (organic Rankine cycles) for power generation, an absorption chiller cycle for cooling production and a drying system to dry wet products. In addition, some useful heat is recovered from the condensers of the ORC for heating applications. In order to determine the irreversibilities, almost all the system components are examined energetically and exergetically. The overall energy and exergy efficiencies of the system are found to be 54.7% and 76.4%, respectively. Moreover, to analyze the system efficiently, parametric studies are also performed to observe the effects of different substantial parameters namely inlet pressure and temperature of the ORC turbine, and reference environment temperature in order to investigate the variations in the system performance in terms of the energy and exergy efficiencies.

Performance assessment of solar-driven integrated Mg–Cl cycle for hydrogen production

The present study develops a new solar energy system integrated with a Mg–Cl thermochemical cycle for hydrogen production and analyzes it both energetically and exergetically for efficiency assessment. The solar based integrated Mg–Cl cycle system considered here consists of five subsystems, such as: (i) heliostat field subsystem, (ii) central receiver subsystem, (iii) steam generation subsystem, (iv) conventional power cycle subsystem and (v) Mg–Cl subsystem. Also, the inlet and outlet energy and exergy rates of all of subsystems are calculated and illustrated accordingly. We also undertake a parametric study to investigate how the overall system performance is affected by the reference environment temperature and operating conditions. As a result, the overall energy and exergy efficiencies of the considered system are found to be 18.18% and 19.15%, respectively. The results show that the Mg–Cl cycle has good potential and attractive overall cycle efficiencies over 50%.

Experimental investigation of energy and exergy performance of square and circular solar ponds

Solar energy is a free, clean and widely available renewable energy. Various kinds of solar systems provide scope for several studies on energy and exergy analysis. Solar ponds are one of applications for collecting and storing solar energy simultaneously and are usable in regions with readily available land, much sunlight, and access to low-priced salt.In the present work, an experimental investigation of the energetic and exergetic performance of two prototype solar ponds with square and circular cross sections has been carried out. The solar ponds were built at Bafgh city, a city near Yazd in the central part of Iran. The cross sectional area and depth of both prototype solar ponds are 3m2 and 1.5m, respectively. During 11months of energy storage operation, a data acquisition system was used to measure the temperature variations along the height of the solar ponds and to capture the development of thermal stratification. Data collection is done with 10min intervals.Thermal analysis of an experimental solar pond is usually a complicated task due to variations of many involved factors such as solar radiation, thermophysical properties of operating fluid, climatic changes etc. The energy performances of the solar ponds under investigation are carried out by modeling the solar incident radiation on the ponds surface, calculating energy exchange within each zone and thermal energy losses to the environment. Although the data are collected for almost one year of operation, however, the energy analysis is performed for some warmer months of the year during which the ponds are in the charging or energy storing period.An exergy balance model is also developed to investigate the exergetic performance of solar ponds. Monthly averaged exergy efficiencies are obtained for different regions of the ponds and compared with the corresponding energy efficiencies. The monthly average temperature of ambient is considered as the reference environment temperature for the exergy analysis. It was demonstrated that the circular solar pond has superior thermal performance than the square one. Stored water in the storage zone of the circular solar pond reaches to a higher temperature in comparison with the square one. It is attributed to the different shading effect in the two solar ponds. The maximum energy efficiencies for NCZ and HSZ of circular solar pond are found to be 17.25% and 25.8%, respectively while the corresponding values for the square solar pond are 17.39% and 23.65%. Maximum exergy efficiency for NCZ and HSZ are 0.86% and 2.44% for circular solar pond and 0.71% and 1.91% for the square solar pond.