A Numerical Case Study: Effect of Heat Leakage on Thermodynamic Efficiency of Cylinders in Cross-Flow

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Mustafa Erguvan ◽  
David W. MacPhee
Keyword(s):  
Energy Efficiency ◽  
Reynolds Number ◽  
Cross Flow ◽  
Exergy Efficiency ◽  
Thermodynamic Efficiency ◽  
Inlet Temperature ◽  
Heat Leakage ◽  
Lower Reynolds Number ◽  
Energy And Exergy ◽  
Artificial Heat

Numerical and thermodynamic analyses have been undertaken in this study to examine energy and exergy efficiencies of in-line tube banks for unsteady cross-flow. Pitch ratio (PR) and the number of in-line tubes are varied for Reynolds numbers of 500 and 10,000, and artificial heat leakages are modeled as a source term. Numerical results are compared with published values, and good agreements are obtained regarding Nusselt number and pressure drop. Whereas the energy efficiency varied between 72% and 99%, the exergy efficiency ranged from 40% to 70%. It was found that while viscous dissipation has a low effect on energy and exergy efficiencies for the lower Reynolds number, it has a significant effect for the higher Reynolds number. On the other hand, heat leakage had a greater effect on exergy efficiency compared to energy efficiency, especially for the lower Reynolds number case. Overall, this study verified how heat leakage could play a vital role on efficiency for low-inlet temperature heat recovery systems.

scholarly journals Energy and Exergy Analyses of Tube Banks in Waste Heat Recovery Applications

Energies ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 2094 ◽  
Author(s):  
Mustafa Erguvan ◽  
David MacPhee
Keyword(s):  
Energy Efficiency ◽  
Reynolds Number ◽  
Heat Recovery ◽  
Waste Heat ◽  
Cross Flow ◽  
Exergy Efficiency ◽  
Circular Cylinders ◽  
Published Data ◽  
Energy And Exergy ◽  
Exergy Analyses

In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature applications.

scholarly journals Energy and Exergy Efficiency Analysis of Fluid Flow and Heat Transfer in Sinter Vertical Cooler

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4522
Author(s):  
Zude Cheng ◽  
Haitao Wang ◽  
Junsheng Feng ◽  
Yongfang Xia ◽  
Hui Dong
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Fluid Flow ◽  
Waste Heat ◽  
Exergy Efficiency ◽  
Inlet Temperature ◽  
Operational Parameters ◽  
Flow And Heat Transfer ◽  
Maximum Value ◽  
Energy And Exergy

In order to fully understand the energy and exergy transfer processes in sinter vertical coolers, a simulation model of the fluid flow and heat transfer in a vertical cooler was established, and energy and exergy efficiency analyses of the gas–solid heat transfer in a vertical cooler were conducted in detail. Based on the calculation method of the whole working condition, the suitable operational parameters of the vertical cooler were obtained by setting the net exergy efficiency in the vertical cooler as the indicator function. The results show that both the quantity of sinter waste heat recovery (SWHR) and energy efficiency increased as the air flow rate (AFR) increased, and they decreased as the air inlet temperature (AIT) increased. The increase in the sinter inlet temperature (SIT) resulted in an increase in the quantity of SWHR and a decrease in energy efficiency. The air net exergy had the maximum value as the AFR increased, and it only increased monotonically as the SIT and AIT increased. The net exergy efficiency reached the maximum value as the AFR and AIT increased, and the increase in the SIT only resulted in a decrease in the net exergy efficiency. When the sinter annual production of a 360 m2 sintering machine was taken as the processing capacity of the vertical cooler, the suitable operational parameters of the vertical cooler were 190 kg/s for the AFR, and 353 K for the AIT.

Energy and Exergy Performance Comparative Analysis of Solar Driven Organic Rankine Cycle Using Different Organic Fluids

2021 ◽  
pp. 1-38
Author(s):  
Md. Tareq Chowdhury ◽  
Esmail M. A. Mokheimer
Keyword(s):  
Energy Efficiency ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Exergy Efficiency ◽  
Optimum Operating ◽  
Inlet Temperature ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet ◽  
Energy And Exergy ◽  
Organic Fluids

Abstract In this study, the performance of Parabolic Trough Collector (PTC) integrated with Organic Rankine Cycle (ORC) is investigated to find the optimum operating scenarios and to assess the exergy destruction at different components of the system. Commercial PTC LS-2 model with Therminol VP-1 as heat transfer fluid was integrated with an organic Rankine cycle that was examined for its thermal and exergetic performance using different organic fluids. It was found that every fluid has an optimum pressure and temperature level at which it works better than other fluids. R134a (Tetrafluoroethane, CH2FCF3) showed the best performance for the turbine inlet temperature range from 340 K — 440 K regarding the achieved energy and exergy efficiencies. At a temperature of 362.8 K and a pressure of 2750 kPa, R134a showed the highest energy efficiency of 8.55% and exergy efficiency of 21.84% with the lowest mass flow rate required in ORC. Energy efficiency of other fluids namely, R245fa (Pentafluoropropane, CF3CH2CHF2), n-pentane and Toluene were less than 5%. On the other hand, Toluene exhibited thermal efficiency of 23.5 % at turbine inlet temperature of 550 K and pressure of 2500 kPa, while the exergy efficiency was 62.89 % at solar irradiation of 1 kW/m2.

Energy and Exergy Analysis of an Organic Rankine Cycle used for Ylang-Ylang Essential Oil Distillery Waste Heat Recovery for Power Production in Anjouan Island

2021 ◽  
Vol 1 (1) ◽  
pp. 15-24
Author(s):  
Malik El’Houyoun Ahamadi ◽  
Hery T. Rakotondramiarana
Keyword(s):  
Energy Efficiency ◽  
Essential Oil ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Power Production ◽  
Exergy Efficiency ◽  
Inlet Pressure ◽  
Working Fluid ◽  
Energy And Exergy ◽  
Residual Heat

In the ylang-ylang essential oil distillers in Anjouan Island, the used energy is 100% firewood biomass. A large amount of this energy is dissipated in the environment just in the combustion chamber itself. As it turns out, the flue gases in this process take away the most part of it. Thus, in a process of energy efficiency of stills, the present work aims at assessing the possibility to convert the residual heat from the process into electricity. For that purpose, energy and exergy modeling of an organic Rankine cycle was implemented. It was found that a large amount of exergy is destroyed in the evaporator. Similarly, it emerges that the exergy efficiency of the cycle depends on the inlet temperatures of the exhaust gases in the evaporator and on the inlet pressure of the working fluid in the turbine, and that it is much better for low exhaust gas temperatures. At these low values of gas temperatures, it appears that the improvement in exergy efficiency and energy efficiency are linked to the increase in the inlet pressure of the working fluid in the turbine. It follows from the obtained results that the discharged hot water and the residual heat of gases having temperatures ranging from 180°C to 300 °C, could be used for power production which can reach electrical powers between 1.4kW and 4.5kW  

scholarly journals Energy, Exergy and Environmental Compatibility Analyses of LPG and Household Kerosene Utilisations as Domestic Fuels in Nigeria: 1980 – 2019

2021 ◽  
pp. 46-56
Author(s):  
I. Badmus ◽  
A. J. Bakri
Keyword(s):  
Energy Efficiency ◽  
Urban Areas ◽  
Exergy Efficiency ◽  
Liquefied Petroleum Gas ◽  
Environmental Compatibility ◽  
Energy And Exergy ◽  
Process Energy

Household kerosene and Liquefied Petroleum Gas form the bulk of domestic fuels, especially in Nigerian urban areas. Data on both fuels, from 1980 to 2019, were collected, mainly from Nigerian National Petroleum Corporation sources. Energy, exergy and environmental compatibility analyses were carried out on the utilisation of LPG for cooking, and household kerosene for both cooking and lighting. Kerosene lighting, with 0.05% energy efficiency and 0.045% exergy efficiency, was extremely poor. Cooking, with different mixes of both fuels, yielded energy efficiencies ranging from 35.04% to 44.54%. Corresponding exergy efficiencies were from 7.75% to 9.98%. Associated environmental compatibility factors were from 0.71749 to 0.73945. Overall process energy efficiencies, involving both cooking and lighting, were from 4.05% to 34.19%. Corresponding exergy efficiencies were from 0.93% to 7.61%. Overall environmental compatibility factors ranged from 0.71746 to 0.73259. Energy and exergy efficiencies, as well as environmental compatibility factors, increased directly with increase in LPG utilisation in the fuel-mix. 

Turbulent Convective Heat Transfer in a Transversely Grooved Tube with Natural Convection Effect

2015 ◽  
Vol 741 ◽  
pp. 458-461
Author(s):  
Xiang Yang Shen ◽  
Jing Ding ◽  
Jian Feng Lu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Average Nusselt Number ◽  
Inlet Temperature ◽  
Lower Reynolds Number ◽  
Grooved Tube ◽  
The Heat Transfer Coefficient

The turbulent convective heat transfer in a transversely grooved tube of molten salt with natural convection effect has been numerically investigated. In general, the average Nusselt number with and without considering natural convection in transversely grooved tube was almost equal. According to the simulated results, the heat transfer coefficient of transversely grooved tube in upside region was lower than that of downside region. The effect of natural convection on unilateral heat transfer in transversely grooved tube was more obvious with lower Reynolds number and higher inlet temperature, and the effect of natural convection on unilateral heat transfer was lower with bigger groove deep.

scholarly journals An energy and exergy analysis of photovoltaic system in Bantul Regency, Indonesia

2018 ◽  
Vol 9 (1) ◽  
pp. 1
Author(s):  
Arif Rahman Hakim ◽  
Wahyu Tri Handoyo ◽  
Putri Wullandari
Keyword(s):  
Energy Efficiency ◽  
Exergy Analysis ◽  
Environmental Temperature ◽  
Exergy Efficiency ◽  
Photovoltaic System ◽  
Pv System ◽  
High Solar Radiation ◽  
Energy And Exergy ◽  
Energy And Exergy Analysis ◽  
Special Region

Energy and exergy analysis has been conducted on photovoltaic (PV) system in Bantul Regency, a special region of Yogyakarta, Indonesia. The PV exergy analysis was used to determine the performance of the PV system by considering environmental factors other than solar irradiance. This research aims to obtain values of exergy and energy efficiencies in the PV system. The experiment results show that the energy efficiency value produced by the PV system was 8.62–74.18%, meanwhile its exergy efficiency was 0.29%-9.40%, respectively. The value of exergy efficiency is lower than the value of energy efficiency. This result confirmed that the environmental factor greatly affects the output of the PV system. It can be concluded that high solar radiation does not always increase the production of exergy, since it is also influenced by the environmental temperature and the PV cells' temperature.

scholarly journals Energy and exergy efficiency of heat pipe evacuated tube solar collectors

2016 ◽  
Vol 20 (1) ◽  
pp. 327-335 ◽  
Author(s):  
Farzad Jafarkazemi ◽  
Emad Ahmadifard ◽  
Hossein Abdi
Keyword(s):  
Heat Pipe ◽  
Solar Collector ◽  
Theoretical Method ◽  
Exergy Efficiency ◽  
Inlet Temperature ◽  
Solar Collectors ◽  
Evacuated Tube Solar Collector ◽  
Energy And Exergy ◽  
Water Mass Flow Rate ◽  
Evacuated Tube

In this paper, a heat pipe evacuated tube solar collector has been investigated both theoretically and experimentally. A detailed theoretical method for energy and exergy analysis of the collector is provided. The method is also evaluated by experiments. The results showed a good agreement between the experiment and theory. Using the theoretical model, the effect of different parameters on the collector?s energy and exergy efficiency has been investigated. It is concluded that inlet water temperature, inlet water mass flow rate, the transmittance of tubes and absorptance of the absorber surface have a direct effect on the energy and exergy efficiency of the heat pipe evacuated tube solar collector. Increasing water inlet temperature in heat pipe evacuated solar collectors leads to a decrease in heat transfer rate between the heat pipe?s condenser and water.

scholarly journals Evolution of Energy and Exergy Efficiency in the European Road Freight Industry, 1978–2018

2021 ◽  
Vol 9 ◽  
Author(s):  
Alessandro Martulli ◽  
Ray Galvin ◽  
Franco Ruzzenenti
Keyword(s):  
Energy Efficiency ◽  
Rebound Effect ◽  
Exergy Efficiency ◽  
Transport Sector ◽  
Commercial Vehicles ◽  
Rebound Effects ◽  
Energy And Exergy ◽  
Road Freight ◽  
Remarkable Progress ◽  
Engine Power

In the last four decades the European truck industry has made remarkable progress in energy efficiency, but this higher efficiency has failed to materialize in lower consumption per unit of load and distance (Tkm). One possible explanation is rebound effects due to average traveling speed and power enhancements. An original set of data covering forty years of truck tests of 526 commercial vehicles and 28 different European brands shows that energy efficiency (fuel economy) of heavy-duty trucks improved by 43% and (engine) power by 44%. We propose exergy as a metric to capture both dimensions and estimate that exergy efficiency increased by 73% over the same period, with an estimated speed rebound effect generally positive among the trucks tested on road conditions. Rebound effects caused by increased speed add to other sources of rebound like load, distance and frequency of journeys to potentially undermine gains delivered by higher energy efficiency. Our results provide evidence of the existence in the transport sector of a trade-off between power and efficiency as theoretically described by finite-time thermodynamics.

Exergy and Energy Analysis of Coal Gasification in Supercritical Water with External Recycle System

2019 ◽  
Vol 17 (11) ◽  
Author(s):  
Cui Wang ◽  
Hui Jin ◽  
Chao Fan ◽  
Kui Luo ◽  
Shenghui Guo
Keyword(s):  
Energy Efficiency ◽  
Supercritical Water ◽  
Coal Gasification ◽  
Exergy Efficiency ◽  
Flow Ratio ◽  
Slurry Concentration ◽  
Energy And Exergy ◽  
Exergy Balance ◽  
Experimental Researches ◽  
Gasification Temperature

Abstract Supercritical water gasification (SCWG) is a novel and clean technology for lignite translating into hydrogen-rich gas. Previous experimental researches show that the use of external recycle system of liquid residual can improve the energy efficiency, but there is not a theoretical model to figure out the component of which exergy lost most and to provide guidance for further optimization of the existing system. In this paper, the thermodynamic model of liquid residual external recycle system was established, based on which energy and exergy balance of the system was evaluated and the exergy efficiency of the main equipment was calculated. Moreover, the influence of recycle flow ratio (0–37.5 %), gasification temperature (550 °C–650 °C), gasification pressure (23–25 MPa) and slurry concentration (2.73–4.15 %) on the exergy and energy efficiency were analyzed. The results showed that the exergy destruction rate of reactor was the highest, which reached 5.52 kW. Both energy and exergy efficiency increased as recycle flow ratio, gasification temperature and pressure increased. The energy and exergy efficiency of the system reached 70.26 % and 56.86 % respectively at the condition of recycle flow ratio of 30 %, gasification temperature of 650 °C, pressure of 25 MPa and slurry concentration of about 2.93 %.

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