Exergy Transfer Analysis Research Articles

Study on optimal operation conditions in the heating process of a crude oil single-disk floating roof tank: Insights from exergy transfer analysis method

Due to China’s high demand for foreign crude oil, reducing oil storage energy consumption has become the focus of national attention. In this paper, the mathematical model of the heating process of a single-disk floating roof tank is established. The variation law of the external exergy loss, internal exergy dissipation, exergy flow density and exergy transfer coefficient at different positions of the tank in the heating process are calculated and analysed. The obtained results show that the total exergy flow density is positively correlated with the coil temperature, the number of coil pipes and the diameter of the coil pipes. It is positively correlated with the tank level at the initial stage of heating. The exergy effective utilization rate is proposed to evaluate the energy consumption of the coil in the heating process of the storage tank. The obtained results show that the exergy effective utilization rate is negatively correlated with the liquid level and the temperature of the coil and positively correlated with the number and diameter of the coil, When the heating temperature is 100 °C, the maximum exergy effective utilization rate is 38.73 %.

Exergy Transfer Analysis of Biomass and Microwave Based on Experimental Heating Process

Exergy transfer and microwave heating performances of wheat straw particles as affected by microwave power (250, 300, and 350 W), feeding load (10, 30, and 50 g), and particle size (0.058, 0.106, and 0.270 mm) were investigated and detailed in this study. The results show that when the microwave power increased from 250 to 350 W, the average heating rate increased in the range of 23.41–56.18 °C/min with the exergy transfer efficiency increased in the range of 1.10–1.89%. When the particle size increased from 0.058 to 0.270 mm, the average heating rate decreased in the range of 20.59–56.18 °C/min with the exergy transfer efficiency decreased in the range of 0.70–1.89%. When the feeding load increased from 10 to 50 g, the average heating rate increased first and then decreased in the range of 5.96–56.18 °C/min with the exergy transfer efficiency increased first and then decreased in the range of 0.07–1.89%. The highest exergy transfer efficiency was obtained at a microwave power of 300 W, feeding load of 30 g, and particle size of 0.058 mm.

Comprehensive exergy transfer analysis of a cyclonic furnace integrated recirculating mixed flow grain dryer

Investigation of exergy transfer is an important aspect for all grain drying industry. Exergy transfer of rice husk fired cyclonic furnace assisted recirculating mixed flow dryer (MFD) equipped with a heat exchanger, was sought in this study. A cyclonic furnace (CF) having capacity 0.5 MW and recirculating MFD were designed and developed to investigate exergy transfer during grain drying. Efficiency of furnace was determined to quantify performance of CF for industrial grain drying system. Exergetic efficiency was also thoroughfare performed for the developed CF, air mixing chamber (heat exchanger) and MFD. Thermal efficiency of the CF varied from 68.96 to 87.01% during drying of high moisture maize grain. Exergy efficiency of the CF, heat exchanger and drying chamber marked between 58.8 and 63.5%, 74.6–93.29%, and 3.03–21.9%, respectively. Exploration of exergy inflow persist between 53.32 and 60.51 kJ/s and 7.58 to 9.81 kJ/s while exergy outflow ranged between 7.58 and 9.81 kJ/s and 1.52 to 3.10 kJ/s, respectively for heat exchanger and drying chamber. Results based on exergy losses indicates that 44.01–51.54 kJ/s and 5.87–7.50 kJ/s of exergy is just loss through heat exchanger and drying chamber, respectively. Exergy improvement potential and sustainability index varied between 1.02 and 1.80 kJ/s and 1.17–1.40 kJ/s, respectively. Quality of final product is in acceptable range as color difference of dehydrated maize kernel varied from 9.19 ± 0.46 to 17.05 ± 0.13. Exergy results indicate that CF can aptly be applied for grain drying industry in commercial scale.

Exergy transfer principles of microwavable materials under electromagnetic effects

Microwave technology is gaining an essential relevance for heating processes at an industrial level due to its improvements in energy savings and product quality. Nevertheless, the microwave system design and material selection during the applications are key points that play an essential role in the successful performance of the process, its implementation, and its operation. The proper function of the microwave highly depends on the design and a good selection of the materials. There are different kinds of materials for microwave applications such as transparent (not able to be heated), semi-transparent (low absorption of microwaves), and susceptor (materials with high capacity to absorb microwaves and transform them into thermal energy). This investigation shows the way each of these materials converts microwaves into heat. Both heat transfer and exergy transfer analyses are presented, focused on those materials with high interactions with microwaves (susceptors). The heat transfer studies demonstrated the way microwaves are transformed into heat, and the exergy analysis shows the quality of those transformations. Exergy transfer analysis of microwave heating systems sheds light on the efficiency of the energy transformation taking place during microwave processing. Consequently, by combining studies of microwavable materials with exergy transfer analysis, conclusions for new microwave designs can be reached, improving this promising technology's final performance. In this sense, this work provides an easy method to determine different materials' behavior under microwave effects.

Performance and Exergy Transfer Analysis of Heat Exchangers with Graphene Nanofluids in Seawater Source Marine Heat Pump System

A marine seawater source heat pump is based on the relatively stable temperature of seawater, and uses it as the system’s cold and heat source to provide the ship with the necessary cold and heat energy. This technology is one of the important solutions to reduce ship energy consumption. Therefore, in this paper, the heat exchanger in the CO2 heat pump system with graphene nano-fluid refrigerant is experimentally studied, and the influence of related factors on its heat transfer enhancement performance is analyzed. First, the paper describes the transformation of the heat pump system experimental bench, the preparation of six different mass concentrations (0~1 wt.%) of graphene nanofluid and its thermophysical properties. Secondly, this paper defines graphene nanofluids as beneficiary fluids, the heat exchanger gains cold fluid heat exergy increase, and the consumption of hot fluid heat is heat exergy decrease. Based on the heat transfer efficiency and exergy efficiency of the heat exchanger, an exergy transfer model was established for a seawater source of tube heat exchanger. Finally, the article carried out a test of enhanced heat transfer of heat exchangers with different concentrations of graphene nanofluid refrigerants under simulated seawater constant temperature conditions and analyzed the test results using energy and an exergy transfer model. The results show that the enhanced heat transfer effect brought by the low concentration (0~0.1 wt.%) of graphene nanofluid is greater than the effect of its viscosity on the performance and has a good exergy transfer effectiveness. When the concentration of graphene nanofluid is too high, the resistance caused by the increase in viscosity will exceed the enhanced heat transfer gain brought by the nanofluid, which results in a significant decrease in the exergy transfer effectiveness.

Energy-matrices, exergy, economic, environmental, exergoeconomic, enviroeconomic, and heat transfer (6E/HT) analysis of two passive/active solar still water desalination nearly 4000m: Altitude concept

In spite of numerous valuable researches for evaluating the effect of different parameters for analyzing exergy/environmental/economic/energy-matrices/heat transfer of solar stills; the effect of high altitude (highlands) on these parameters and comparing two active/passive systems was not performed. This paper conducted a meticulous analysis of two active and passive solar stills at different altitudes (Tochal: 3964 m and Tehran: 1171 m) during seven consecutive days between 24.07.2018 and 30.07.2018. The geometry of solar stills in both experiments is similar and for active type, the system utilized with thermoelectric (Peltier) modules and powered by a photovoltaic panel. Results revealed that altitude has a direct effect on the exergy of solar stills where the summit-located solar stills (passive and active) have higher exergy efficiency. Furthermore, higher evaporative exergy is obtained by both active solar stills at the Peak of Tochal Mountain and the center of Tehran. Likewise, heat transfer analysis showed that the highest and lowest heat transfer coefficients are obtained by active solar still at the Peak of Tochal Mountain and passive solar still in Tehran respectively. However, due to the higher glass temperature, the highest radiative heat transfer coefficients are obtained by Tehran-located systems. Economic results showed that the highest and lowest cost of water with 0.0079 and 0.0372 $/L are assessed by passive solar still in Tehran and active solar still at the Peak of Tochal Mountain respectively. Energy-matrices indicated that the lowest and highest energy payback time based on energy and exergy with 1.57 and 52.75 years attained by passive solar still in Tehran. Also, Environmental analysis showed that higher CO2 mitigation obtained by active solar stills rather than passive types in both locations. Also, enviroeconomic as well as exergoeconomic (based on energy) parameters showed that both passive and active SSs at the city of Tehran have higher values rather than that of solar stills at the summit because of higher days of operation during the year.

Exergy transfer characteristics analysis of turbulent heat transfer enhancement in surfactant solution

This paper presents an exergy transfer analysis for turbulent drag reducing surfactant solution flow with and without heat transfer enhancement devices which employ static or dynamic mixers. Heat transfer and pressure drop measurements were performed at an inlet temperature of 297.7–298.2 K in pipe flow with a concentric tube heat exchanger. The environmental temperature in the analysis was set to be 288.2 K in assumption of a cooling system. The experimental range of the Reynolds number was 1.0×104 to 4.2×104. Adding surfactant to a water flow decreases the exergy transfer Nusselt number, Nue, owing to the heat transfer reduction and increases the exergy transfer efficiency, ηeff, by a maximum of 9.3% at high Reynolds numbers at moderate fluid transport distance owing to the drag reduction. Also the secondary flow caused by the enhancement devices increases Nue. The proposed flow performance curve which provides ηeff for an arbitrary Nue shows that ηeff in viscoelastic fluid flow compared to Newtonian fluid flow is small independently of the fluid transport distance, and that the installation of heat transfer enhancement devices has a positive effect on energy-saving in certain ranges of Reynolds numbers and fluid transport distances.

Numerical study of cullet glass subjected to microwave heating and SiC susceptor effects. Part II: Exergy transfer analysis

The mathematical model of exergy transfer in cullet glass heated by microwave inside of a cubical cavity with the aid of a susceptor is presented. Part I of this paper presented a numerical combined electromagnetic and heat transfer model by applying both transient Maxwell’s equations and heat transfer equations. Then, the electromagnetic and temperature fields were used to obtain the exergy transfer analysis in the oven. Exergy transfer analysis informs us about the efficiency of energy transformations taking place during the heating process, since it explains how the quality of the energy behaves along the heating process. The rate of internal exergy, exergy flowing and destroyed exergy were obtained and presented for this transient process. Part I showed that the susceptor location could change the temperature fields of cullet glass. So, an exergy analysis is important to understand the irreversibilities produced by a susceptor during preheating (microwaves activation) and heating process of the cullet glass, and how they could be minimized. Exergy transfer analysis shows how both, electromagnetic and heat transfer, are responsible of the irreversibilities generated in the heating process.

Local exergy cost analysis of microwave heating systems

The purpose of this work is to collect and interrelate the fundamental concepts about exergy transfer analysis and local exergy cost applied to the analysis of microwave heating systems. First, thermoeconomics and exergoeconomics are reviewed. Local exergy analysis is presented next, including local efficiency, and local cost associated. Emphasis is put on local cost that an electromagnetic field can generate and its association with microwave heating exergy. Unsteady-state of exergy cost transfer and exergy costing are difficult to perform during microwave heating due to the complex combination of electromagnetic fields and heat transfer analysis, while the electromagnetic field distribution occurs at a time scale of nanoseconds, heat and exergy cost transfer occurs at time scale of seconds. For this reason, simulations reported to date deal only with cases of First and Second Law of Thermodynamics with no mention of local efficiency or local cost, leaving an open promising field of research. By and large, results are presented for two heating methods, conventional and microwave.

Exergy transfer analysis of an aluminum holding furnace

This study presents the unsteady exergy transfer analysis of an aluminum holding furnace with new heating resistance scheme. This holding system consists of four multilayer refractory walls and one resistance heating system which is responsible of maintaining the appropriate aluminum temperature and composition for further casting. The purpose of this analysis is to understand and identify heat losses and irreversibilities of the holding process of an aluminum furnace by means of the First and Second Law of Thermodynamics. In this study, bi-dimensional temperature and exergy fields during heat and exergy transfer processes are presented. The exergy balance is completely computed for this system, obtaining: exergy transfer, exergy variation rate, and destroyed exergy rate.

Exergy transfer analysis of microwave heating systems

Exergy transfer analysis is proposed as a complementary method for analyzing and better understanding of the efficiency of microwave heating systems, which play a key role in medicine, chemical engineering, food industry and material processing. Since this method is able to detect and quantify in detail where irreversibilities occur, it can be a useful first step in the improvement of microwave systems. First, the different approaches for modeling microwave systems and interactions wave-thermal system are reviewed. Then, relation between Poynting vector, energy and exergy in microwaves is analyzed in depth. Afterwards, a 2-D model of energy and exergy transfer for a microwave heating system is presented. The model is based on Lambert's Law and is applied for the analysis of a potato heating. A comparison with a conventional heating is also presented, where the irreversibility evolution of both process, microwave and conventional, is analyzed with the presented methodology, presenting advantages and disadvantages for each process. This simple example proposed for illustration demonstrates how the analysis of exergy transfer results allows one not only to characterize the global exergy efficiency of the system but also analyze in depth the time and space distribution of exergy flows, exergy variation and irreversibility.

Exergy Transfer Analysis of Forced Convection in External Flow over a Flat Plate

On the basis of linear non-equilibrium thermodynamic theory, exergy transfer analyses of laminar and turbulent forced convection are conducted in terms of external flows over a flat plate. Two kinds of non-dimensional concepts involving the definition of the local and mean exergy transfer Nusselt number and non-dimensional exergy flux are incorporated into exergy transfer analysis. The new analytical expressions for the local and mean exergy transfer Nusselt number and non-dimensional exergy flux are adopted to describe the exergy transfer characteristics over a flat plate. By taking air as working fluid, the influences of flat plate geometry, Reynolds number, and other operating parameters on the exergy transfer Nusselt number and non-dimensional exergy flux are examined. It is shown how the flow geometric parameters and Reynolds number, etc., may be selected in order to maximize the exergy utilization associated with a specific external convection process. In addition, the results obtained from exergy transfer analysis are compared with those obtained from traditional heat transfer analysis.

Exergy transfer analysis of a pin fin in external flow

Based on the non-equilibrium thermodynamic theory, a general exergy transfer model is developed to describe the exergy transfer characteristics of external convection by using Black Body Approach. This model is applied to the study of fin efficiency for exergy transfer, which is defined as the ratio of the actual exergy transfer rate to the ideal exergy transfer rate. Both the analytical expressions and numerical analysis are conducted to determine the fin efficiency for exergy transfer by using pin fin as object and air as working fluid. The resulting fin efficiency for exergy transfer is compared with that for energy transfer.

Exergy transfer analysis of convection heat transfer

AbstractIn this paper, based on the fundamentals of thermodynamics and heat transfer, an analysis is made of the exergy transfer of convection heat transfer. Some exergy transfer differential equations are derived under constant thermophysical property and uncompressible laminar flow in the convection heat transfer process. Taking one‐ and two‐dimensional convection heat transfer as examples, respectively, the exergy functions are solved and calculated. Their results agree well with those results from thermodynamic analysis. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(2): 66–73, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/htj.20146

EXERGY TRANSFER ANALYSIS FOR CENTRIFUGAL COMPRESSED HIGH POWER HEAT PUMP DEVICE

According to exergy transfer theory, establishment of the exergy transfer mode of unit and device for an online high power centrifugal compressed heat pump is focused on. Some criterions to analyze and evaluate the devices and equipments such as exergy exchange rate, exergy power degressive rate, exergy fluid density degressive rate, and exergy resistance coefficient are raised and defined. The calculation formulas for each criterion are presented also. Using these model and criterions, through an exergy transfer analysis on the energy quality activities during the process of the energy exchange and transfer in the heat pump, the results show that exergy power degressive rate is the highest in throttle and compressor because the flow speed and flow state have the instant drastic changes in the process of flow throttle, which cause the significant loss of exergy, and some deficiencies exist for the compressor mechanism performance and thermophysical properties of refrigerants performance. The exergy resistance coefficient is the highest in evaporator, which reflects that the structure design has the distinct limitation. Exergy power degressive rate and exergy fluid density degressive rate have the same value in the throttle which indicate that the structure factors of the equipment and the time conditions have the same impacts on the throttle. The results of exergy transfer analysis reveal the influence degree of structure design and thermodynamics property of the main equipment, and thermophysical properties of refrigerants impact the process of energy usage in the devices, and indicate the structure design of compressor can be improved further. The method by flow throttling and intensity of pressure decreasing is not appropriate in terms of the significant impacts on the rational energy usage of the devices; the primary problem of the evaporator is caused by the refrigerant factor but not its structure design. From the calculation of the energy analysis and exergy analysis on the devices, it is indicated that energy analysis only reflects the quantitative energy utilizing, and exergy analysis is only the static analysis of energy activities. However, in terms of the dynamic analysis, exergy transfer analysis provides the new information including not only the design parameters for the heat pump device and principle equipments, but also the impacts on the performance of energy usage under the situation with the random running of the equipment system. Therefore, it can provide the detailed suggestions to improve on the heat pump unit designs and direct the device operation.