4.2. Effect of intake air velocity
The impact of intake air velocity on the performance of the REC is studied, shown in Fig. 5(a) and Fig. 5(b). Fig. 5(a) shows the cooling capacity and exergy destruction depending on the intake air velocity varying from 0.4 to 4.0 m/s. It can be observed that the cooling capacity and exergy destruction quickly increases with increasing the intake air velocity. Fig. 5(b) presents the dew point effectiveness and exergy efficiency ratio depending on the intake air velocity. The figure shows the dew point effectiveness and exergy efficiency ratio decrease at the same time with intake air velocity rising. That is because the increase of intake air velocity can lead to the increase of intake air mass flow rates in both channels. The increase of intake air velocity is relatively big comparing to the decrease of the product air outlet temperature. In addition, the higher intake air velocity can lead to the higher pressure loss. Thus, the mechanical exergy is bigger in both channels while the thermal exergy of the product air outlet is samller. It is concluded that both energy and exergy analyses should be considered for the optimization of the process to get the best performance. As the intake air velocity rises from 0.4 to 4.0 m/s, the exergy destruction is increased by about 8.5 times from 25.8W to 245.1W, and the exergy efficiency ratio is reduced by about 96.5%, from 123.5 to 4.3. These indicate that the effect of intake air velocity is greater than the working to intake air ratio on the exergy destruction and exergy efficiency ratio.
surfaces, infiltration, details and the components of buildings were examined in this study. They made a comparison between energy and exergy analyses of fossil plant ground and air source heat pump building heating system, which included the simulation program IDA-ICE. The system was examined in terms of energy, exergy and thermal comport level, and people designed a model related to sink. (Torio and Schmidt 2010), Framework for analysis of solar energy systems in the built environment from an exergy perspective, investigated contradictions and physical inconsistencies, which result from including the conversion of solar radiation, and also energy and exergy loses connected with the natural degradation of solar radiation, therefore, in this paper included direct solar systems, indirect uses of solar radiation. Güngör et al. (2008) investigated values of exergyflow through the buildings and components. In addition to this one, this study included heating system energy and exergyanalysis. Low exergy systems were examined (Shukuya 2008), which was about energy, entropy, exergy flows through the selected buildings and LowEx systems in applications. HVAC Systems’ energy and exergyanalysis were investigated in this paper using the LowEx. They selected a building, found energy demand and according to it, they designed different appropriate HVAC applications for the building. They analyzed all the HVAC systems in terms of energy and exergy (Sakulpipatsin et al. 2010).To design a complementary system using a ground source heat pump and a PV panel, Meggers et al analyzed HVAC system of the selected buildings in terms of energy and exergy using the LowEx tool (Meggers et al. 2012).
A new type of heat and mass exchanger (HMX) taking advantage of the Maisotsenko cycle (M- Cycle)  has attracted great attention in recent years for providing the air below the wet bulb temperature of inlet air without moisture content increase. Usually, the heat and mass transfer characteristics and performance of the HMX are investigated through numerical simulations [2-6], experiments [7-8] and analytic methods [9-11]. However, the most of the previous studies made use of the mathematical models that were sourced from the first law of thermodynamics and neglected the existence of the energy quality and irreversibility of the thermodynamic process. Nevertheless, the exergyanalysis, known as the second law method, can characterize the irreversibility of the heat and mass transfer processes within the HMX and fulfill of the incompleteness of the energyanalysis alone. In conjunction with exergyanalysis, the energy applied can be utilized better and HMX design can be oriented towards a possible state of thermodynamic perfection.
The simulation of cooling system performance in the past was largely energy based. Now studies are being published that perform exergy-based analysis to determine maximum efficiency and evaluate the quality of energy conversions (Harutunian, 2003; Liu, 1994; Paulus, 2000; Wang, 2005; Wu, 2004). An exergyanalysis (also called availability analysis) determines the maximum useful work than can result when a system goes through a process between two specific states or the minimum required for cooling between two states. Applying exergy balances to a system allows for a direct comparison of the amount of work potential supplied to the amount of that has been consumed (Kotas, 1995). A measurement of exergy destruction allows one to determine the work potential destroyed by each system or component due to irreversibility.
Kanoglu Mehmet, Ibrahim Dincer, Rosen, Marc A carried out studied on ExergyAnalysis of Psychrometric Processes for HVAC&R Applications. Mass, energy, entropy, and exergy balances and exergy efficiency relations are developed for common air-conditioning processes that include simple heating and cooling, heating with humidification, cooling with dehumidification, evaporative cooling, and adiabatic mixing of airstreams. An illustrative example of a heating process with humidification is considered and the effects of air temperature and relative humidity at the inlet and exit, the temperature of steam used for humidification, and the dead state properties of exergy efficiency and exergy destruction are investigated. The results indicate that processes with low exergy efficiency and high exergy destruction have significant potential for improving performance.
District energy (DE) and thermal energy storage (TES) are two energy technologies that can enhance the efficiency of energy systems. Also, DE and TES can help address global warming and other environmental problems. In this study, a stratified TES is assessed using exergyanalysis, to improve understanding of the thermodynamic performance of the stratified TES, and to identify energy and exergy behavioural trends. The analysis is based on the Friedrichshafen DE system, which incorporates seasonal TES, and which uses solar energy and fossil fuel. The overall energy and exergy efficiencies for the Friedrichshafen TES are found to be 60% and 19% respectively, when accounting for thermal stratification. It is also found that stratification does not improve the performance of the TES notably. Considering the TES as stratified and fully mixed does not significantly affect the overall performance of the Friedrichshafen TES because, for this particular case, temperatures are very close whether the TES is treated as stratified or fully mixed.
Exergy is defined as the maximum amount of work that can be extracted from a stream as it flows toward equilibrium. This follows the second law of thermodynamics, which states that not all heat energy can be converted to useful work. The portion that can be converted to useful work is referred to as exergy, while the remainder is called non-exergy input Exergyanalysis provides a powerful tool for assessing the quality of energy and quantifying the portion of energy that can be practically recovered. Exergyanalysis uses parameters such as temperature or pressure to determine energy quality and calculate potentially recoverable energy. Exergy or energy quality, diminishes each tune energy is used in a process. For example, a large percentage of energy content can be extracted from flowing steam at high temperatures. As the steam temperature drops (e.g., after passing through a heat exchanger), the percentage of energy that can be recovered is reduced. This drop in energy quality is referred to as a loss of exergy or energy degradation. Exergyanalysis is an efficient technique for revealing withers or not and by how much it is possible to design more efficient thermal systems by reducing the inefficiencies of the units in a system. Also for determine which unit of the system are most
applying conservation of mass, conservation of energy and the second law of thermodynamic principle to design and improve a production system . In improvement of system efficiencies, energyanalysis is a good method to evaluate and have a good significant result and it also disclose whether or not and how to design effective production system by reducing system it efficiency of that production system [7, 8]. Exergy is a joining property of a system and its environment because unlike energy, it turns on the state of both the system and the environment. The exergy of a system in balance with the environment is zero. In the exergyanalysis, the exergy is rate with regard to the reference environment. Therefore, the exquisite properties of the reference environment decide the exergy of a system. The outcome of exergyanalysis is consequently relative to the specified source environment, which in most cases are modeled after the affiliate environment . Exergy is neither a thermodynamic plat of matter nor a thermodynamic potential of a system
For a general system at certain conditions it would be helpful to establish the maximum amount of work that can be obtained by bringing it to equilibrium with the environment, or dead state. Second law of thermodynamics asserts that among all the processes that take a system from state A to state B a reversible process with no entropy generation yields the maximum work. Thus, a new property, namely exergy, can be defined as the amount of work obtained by bringing a system from its current state to the dead state through a reversible process. Exergy proves to be a very powerful tool in analyzing performances, not only for devices that produce work, but also for those that require work to accomplish certain tasks. A practical application in which exergyanalysis gives a much better measure of performance than the energy- based efficiency is geothermal power generation. Typically, the temperature difference between the geothermal well and the environment Frontiers in Heat and Mass Transfer
Abstract: In recent years, the International Maritime Organization agreed on aiming to reduce shipping’s greenhouse gas emissions by 50% with respect to 2009 levels. Meanwhile, cruise ship tourism is growing at a fast pace, making the challenge of achieving this goal even harder. The complexity of the energy system of these ships makes them of particular interest from an energy systems perspective. To illustrate this, we analyzed the energy and exergyflow rates of a cruise ship sailing in the Baltic Sea based on measurements from one year of the ship’s operations. The energyanalysis allows identifying propulsion as the main energy user (46% of the total) followed by heat (27%) and electric power (27%) generation; the exergyanalysis allowed instead identifying the main inefficiencies of the system: while exergy is primarily destroyed in all processes involving combustion (76% of the total), the other main causes of exergy destruction are the turbochargers, the heat recovery steam generators, the steam heaters, the preheater in the accommodation heating systems, the sea water coolers, and the electric generators; the main exergy losses take place in the exhaust gas of the engines not equipped with heat recovery devices. The application of clustering of the ship’s operations based on the concept of typical operational days suggests that the use of five typical days provides a good approximation of the yearly ship’s operations and can hence be used for the design and optimization of the energy systems of the ship.
Abstract -- In this work the energy and exergyanalysis of a hybrid gas turbine cycle has been presented. The thermodynamic characteristic of Brayton-diesel cycle is considered in order to establish its importance to future power generation markets. Mathematical modeling of Brayton-diesel cycle has been done at component level. Based on mathematical modeling, a computer code has been developed and the configuration has been subjected to thermodynamic analysis. Results show that, at any turbine inlet temperature (TIT) the plant specific work initially increases with increase of pressure ratio (r p,c ), and but at very high values of r p,c , it
which is very important to industries. As much as energy is highly important for the process industries, minimum amount of energy should be wasted under normal situations. The traditional method of assessing the energy dispo- sition of an operation involves the application of first law of thermodynamic. The advent of exergy method which is based on the second law of thermodynamic exposes the inadequacies of the first law. Exergyanalysis provides information about the irreversibility state of thermodynamic processes. It thus indicates means of assessing the loca- tions, types and magnitudes of wastes and losses and to identify meaningful efficiencies of the system. The wide spread of the use of exergy method by several researcher has brought about steps towards cutting down on energy cost, conservation of scarce energy resources and reduc- tion of environmental damage. Exergyanalysis method- ologies have been applied to many industrial systems such as: sugarcane bagasse gasification , malt drink produc- tion , flavored yogurt , and fruit juice . Although a considerable volume of energy and exergy-related analy- ses of industrial processes exists in literature, limited work has been reported on energy and exergy analyses of vege- table oil from palm kennel oil processing operations. En- ergy and exergyanalysis for production of vegetable oil from soybean oil, sunflower and olive oil has been reported for Turkey. Only the work of Fadare et al.  and Wa- heed et al.  has respectively reported the energy and exergy analyses of malt drink and fruit juice processing operations in Nigeria. To the best of the authors’ knowl- edge, no work has been conducted on the energy and ex- ergy analyses of edible vegetable oil production in Nige- ria. Therefore, the aim of this study is to analyze the en- ergy consumption pattern and exergy inefficiency of palm kennel oil refining operations in Nigeria, in view of im- proving the efficiency of the system, reduce the produc- tion costs and hence, increase the profitability of edible
Forty-two years have passed since the cre ation of the term »exergy« replacing a much more awkward expression »technical work capa bility«. The term was first introduced and ex plained by a renowned Slovenian scientist wor king in the field of thermodynamics, Professor Zoran Rant. In the years 1961 to 1966 exergy was often among the topical subjects discussed at va rious conferences and conventions on thermody namics especially in Germany. During this time a number of papers and discussions were publis hed about exergy. However, scientists did not all share the same opinion about the importance of exergy, therefore work in this area gradually slowed down and even stopped. A revival of the interest in exergy and its fundamental concepts, introduced by Professor Zoran Rant, came with the oil crisis in the mid-seventies.
The purpose of the study is to compare two heating and cooling (H/C) systems regarding individual thermal comfort conditions and rational building energy use. Real test room is firstly equipped with low exergy (LowEx) system (i.e. heating-cooling ceiling radiative panels) and secondly with a conventional system (i.e. electric heaters, cooling split system with indoor unit). Additional case presents a thermally non- insulated room equipped with a conventional system. Individual thermal comfort conditions are analyzed through the simulation of human body exergy balance (hbExB), human body exergy consumption (hbExC) rates and predicted mean votes (PMV) index. Measurements of energy use and control of temperature conditions are performed on an integrated control system (ICsIE) based on fuzzy logic. The results confirm that both systems create comfort conditions if the room is thermally well insulated. In case of non-insulated room there appears cool radiant exergy that often leads to discomfort conditions. More acceptable comfortable conditions (PMV closer to 0) do not always result in a lower hbExC rate. Individual characteristics with experimental conditions have a significant influence on separate parts of hbExB. LowEx system connected with ICsIE enables to set air temperature and mean radiant temperature and creates optimal thermal comfort conditions for individual user. The measured energy use for heating was by 11 to 27% lower for LowEx system than for the conventional system. The energy use for cooling was by 41 to 62% lower for LowEx system. The presented approach of reciprocal consideration of individual thermal comfort conditions and building energy use is important for the future design of H/C systems and for their application in near zero energy buildings.
In comparison to the M-cycle flow arrangement, Fig. 1(b) shows a type of REC HMX with even higher cooling effectiveness (but with higher pressure loss) . This type of exchanger works as follows: The product air enters into the exchanger from the inlet of dry channel and flows along the channels. Through the penetrations at the end of channel, a certain percentage of the product air, as all of the working air, is redirected into the adjacent wet channel. In this thermal process, as represented in the psychrometric chart of Fig. 1(b), product air is cooled along the dry channels without any increase in humidity, while the working air is initially cooled to the minimum with rise in humidity at a certain distance from the entrance due to the effects of water evaporation. After that, the working air temperature begins to go up in the remainder of the wet channel because the sensible heat transfer from product air in dry sides exceeds the effect of evaporation cooling . This unique arrangement allows the working air to be fully cooled before entering the working channel, thus leading to increased temperature difference and heat transfer between working and product air.
Exergyanalysis of the ERGT cycle could be performed by making suitable extensions to the Excel sheet developed for the energyanalysis. Fig. 4 shows the rate of exergy change across each device in the ERGT system. Neglecting the relatively small exergy input in the hot pressurised water injected in the humidifier, the only external exergy input in the cycle is the heat addition in the combustion chamber, which amounts to about 622 kJ. By cooling the compressed air, the humidifier results in a loss of neary 54 kJ, but the heat-transfer in the regenerator provides about 194 kJ. The gas-generator turbine converts about 350 kJ into work to drive the compressor and the power turbine produces about 460 kJ of useful work. Therefore, the second-law efficiency of the plant approaches 71%. Fig. 5 shows the percentage of exergy destruction in the different components of the system. The figure shows that the combustion process causes the most exergy destruction in the system closely followed by the process in the humidifier. Therefore, any efforts to improve the system's performance should focus on these two processes.
In this study, the energy and exergyanalysis of Reliance Ultra Mega Project (3960MW) in Singrauli ,Madhya Pradesh is presented. The primary objectives of this paper are to analyze the system components separately and to identify and quantify the sites having largest energy and exergy losses. In addition, the effect of varying the reference environment state on this analysis will also be presented. The performance of the plant was estimated by a component-wise modeling and a detailed break-up of energy and exergy losses for the considered plant has been presented.
Recently, alternative cooling approaches have been investigated. Farzaneh-Gord and Deymi-Dashtebayaz  proposed improving refinery gas turbines performance using the cooling capacity of refinerys’ natural-gas pres- sure drop stations. Zaki, et al.  suggested a reverse Brayton refrigeration cycle for cooling the air intake; they reported an increase in the output power up to 20%, but a 6% decrease in thermal efficiency. This approach was further extended by Jassim, et al.  to include the exergyanalysis and show that the second law analysis improvement has dropped to 14.66% due to the compo- nents irreversibilities. Khan, et al.  analyzed a system in which the turbine exhaust gases are cooled and fed back to the compressor inlet with water harvested out of the combustion products. Erickson [25,26] suggested using a combination of a waste heat driven absorption air cooling with water injection into the combustion air; the concept is named the “power fogger cycle”.
In this paper, we present an analysis of energy and exergy utilization in the residential sector of Cameroon by considering the sectoral energy and exergy flows for the years of 2001-2010. Exergyanalysis of Cameroon residential sector utilisation indicates a less efficient picture than that ob- tained by the energyanalysis. Cooking stands out as the most inefficient end use in the Cameroon’s residential sector. In 2010, the energy and exergy efficiency are determined and were respectively 58.74% and 22.63%. Energy and exergy flows diagrams for the overall efficiencies of Cameroon residential sector are illustrated and a comparison with the residential sector of other countries is also done. To carry out this study, a survey of 250 households was conducted and the sharing of the end uses of energy was done and data were gathered.