Exergy efficiency design for multi-stream plate-fin heat exchangers based on entropy generation assessment

2021 ◽  
Vol 34 (3) ◽  
pp. 331
Author(s):  
Jianrong Tan ◽  
Shuyou Zhang ◽  
Jinghua Xu ◽  
Mingyu Gao ◽  
Tiantian Wang ◽  
...  
Keyword(s):  
Entropy Generation ◽  
Heat Exchangers ◽  
Exergy Efficiency

Exergy efficiency design for multi-stream plate-fin heat exchangers based on entropy generation assessment

2021 ◽  
Vol 34 (3) ◽  
pp. 331
Author(s):  
Jinghua Xu ◽  
Mingyu Gao ◽  
Tiantian Wang ◽  
Qianyong Chen ◽  
Shuyou Zhang ◽  
...  
Keyword(s):  
Entropy Generation ◽  
Heat Exchangers ◽  
Exergy Efficiency

scholarly journals Double-Layer Micro Porous Media Burner from Lean to Rich Fuel Mixture: Analysis of Entropy Generation and Exergy Efficiency

Entropy ◽  
2021 ◽  
Vol 23 (12) ◽  
pp. 1663
Author(s):  
Nazmi Che Ismail ◽  
Mohd Zulkifly Abdullah ◽  
Khairil Faizi Mustafa ◽  
Nurul Musfirah Mazlan ◽  
Prem Gunnasegaran ◽  
...  
Keyword(s):  
Porous Media ◽  
Double Layer ◽  
Entropy Generation ◽  
Heat Exchangers ◽  
Fuel Mixture ◽  
Exergy Efficiency ◽  
Operating Conditions ◽  
Cylindrical Shape ◽  
Total Entropy ◽  
Porous Media Burner

Porous media burner (PMB) is widely used in a variety of practical systems, including heat exchangers, gas propulsion, reactors, and radiant burner combustion. However, thorough evaluations of the performance of the PMB based on the usefulness of entropy generation, thermal and exergy efficiency aspects are still lacking. In this work, the concept of a double-layer micro PMB with a 23 mm cylindrical shape burner was experimentally demonstrated. The PMB was constructed based on the utilization of premixed butane-air combustion which consists of an alumina and porcelain foam. The tests were designed to cover lean to rich combustion with equivalence ratios ranging from ϕ = 0.6 to ϕ = 1.2. It was found that the maximum thermal and exergy efficiency was obtained at ϕ = 1.2 while the lowest thermal and exergy efficiency was found at ϕ = 0.8. Furthermore, the findings also indicated that the total entropy generation, energy loss, and exergy destroyed yield the lowest values at ϕ = 1.0 with 0.0048 W/K, 98.084 W, and 1.456 W, respectively. These values can be stated to be the suitable operating conditions of the PMB. The findings provided useful information on the design and operation in a double-layer PMB.

Modelling, Analyses and Optimization for Exergy Performance of an Irreversible Intercooled Regenerated Brayton CHP Plant: Part 1 — Thermodynamic Modelling and Parametric Analyses

2017 ◽  
Author(s):  
Lingen Chen ◽  
Bo Yang ◽  
Huijun Feng ◽  
Zemin Ding
Keyword(s):  
Heat Exchangers ◽  
Variable Temperature ◽  
Pressure Ratio ◽  
Exergy Efficiency ◽  
Heat Reservoir ◽  
Output Rate ◽  
Rate Versus ◽  
Optimum Heat ◽  
Set Up ◽  
Parametric Analyses

A variable-temperature heat reservoir irreversible intercooling regenerated Brayton combined heat and power (CHP) plant model is set up in this paper. The model considers the heat transfer losses in all the heat exchangers, the working substance pressure drop loss in the piping, and the expansion and compression losses in turbine and compressor. Exergy output rate and exergy efficiency are considered as the research targets, and their analytical formulae are obtained. The optimal performances are gotten by optimizing the intercooled pressure ratio and total pressure ratio. The influences of some important parameters on the performances are studied in detail. Besides, the relation of exergy output rate versus exergy efficiency is investigated, and the curve is loop-shaped one. The results indicate that optimum heat capacity rate matching between the heat reservoir and working substance, and optimum heat consumer required temperature exist respectively, which generate double-maximal exergy output rate and double-maximal exergy efficiency, respectively. The heat conductance allocation optimization of all the heat exchangers will be carried out in Part 2 of this paper.

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

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 361 ◽  
Author(s):  
Giedrė Streckienė ◽  
Vytautas Martinaitis ◽  
Juozas Bielskus
Keyword(s):  
Heat Pump ◽  
Entropy Generation ◽  
Energy Demand ◽  
Dynamic Modelling ◽  
Second Law Of Thermodynamics ◽  
Exergy Efficiency ◽  
Second Law ◽  
Air Handling Unit ◽  
Individual Character ◽  
Environment Temperature

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.

Suggestion of new correlations for the exergy efficiency and coefficient of exergy performance of annulus section of conically coiled tube-in-tube heat exchangers

2019 ◽  
Vol 152 ◽  
pp. 309-319 ◽  
Author(s):  
Khaled Al-Salem ◽  
Ebrahim Hosseini ◽  
Alireza Nohesara ◽  
Mohsen Mehri ◽  
Mohamed Ali ◽  
...  
Keyword(s):  
Heat Exchangers ◽  
Exergy Efficiency ◽  
Coiled Tube ◽  
Exergy Performance

scholarly journals Numerical Analysis on the Performance of High Concentration Photovoltaic Systems Under the Nonuniform Energy Flow Density

2021 ◽  
Vol 9 ◽  
Author(s):  
Haifei Chen ◽  
Yunjie Wang ◽  
Yuwei Ding ◽  
Baorui Cai ◽  
Jie Yang
Keyword(s):  
Heat Exchangers ◽  
Energy Flow ◽  
Single Channel ◽  
Exergy Efficiency ◽  
Flow Density ◽  
High Concentration ◽  
Cell Temperature ◽  
Single Jet ◽  
Jet Nozzle

Photovoltaic panels can directly convert solar energy into electricity, but temperature will have a certain impact on the efficiency of photovoltaic cells. Especially under the condition of nonuniform energy flow density of high-power concentration, it is of great significance to maintain the temperature uniformity of cells. Therefore, based on the radiation under nonuniform heat flux density, four heat exchangers were proposed: single-channel serpentine flow, multi-channel flat plate, full jet, and single-jet nozzle. Taking into account the uniformity of the cell temperature, the single-jet nozzle and single-channel serpentine flow can better maintain the uniformity of the temperature field compared with other heat exchangers. Especially under high-concentration energy flow density, considering the quality of heat and electricity, the performance of the four-jet nozzles is the best from the perspective of exergy efficiency. Under the condition of four-jet nozzles, the electrical efficiency and thermal efficiency of the cell can be maintained at about 29 and 62.5%, respectively, and the exergy efficiency of the system can reach 31%.

scholarly journals NANO-FLUID EFFECTS ON TOTAL ENTROPY GENERATION THROUGH PLATE HEAT EXCHANGERS

2019 ◽  
Vol 14 (51) ◽  
pp. 513-527
Author(s):  
M Hefny, ◽  
A Hussein, ◽  
A Hamed ◽  
N Mahmoud
Keyword(s):  
Entropy Generation ◽  
Heat Exchangers ◽  
Total Entropy ◽  
Plate Heat ◽  
Nano Fluid

Methodology for Intrinsic Exergy Analysis as Guide for Process Improvement With a Fuel Droplet Combustion Example

2005 ◽  
Author(s):  
Wladimir Sarmiento-Darkin ◽  
Noam Lior
Keyword(s):  
Process Improvement ◽  
Entropy Generation ◽  
Exergy Analysis ◽  
Combustion Process ◽  
Exergy Efficiency ◽  
Exergy Loss ◽  
System Level ◽  
Base Case ◽  
Droplet Combustion ◽  
Exergy Losses

While exergy analysis is by now commonly used on the system level to identify losses and recommend ways for reducing them, its use on the “intrinsic”, field, level where the exergy of a process is calculated as a function of location and time, is still developing. Intrinsic exergy analysis is a most useful method for identifying and understanding the specific reasons for exergy losses in a process, and in devising methods for their reduction. A good example, which is the sample case of this paper, is the analysis of exergy losses in combustion processes, which are known to be responsible for around 30 % of the fuel potential to produce power. In this paper we develop a methodology for intrinsic exergy analysis and for its use for process improvement, using the case of combustion of a n-heptane droplet as example. The time-dependent continuity, energy and species conservation equations together with the reaction kinetics, state equations, and temperature and concentration dependent transport properties, are solved numerically to determine the temperature and concentrations fields. These results are then used to calculate the rates of local entropy generation to determine the spatial and temporal irreversibilities produced during the combustion process, as well as the exergy efficiency. The results obtained indicate, among other things, that after ignition has taken place, the exergy loss (or entropy generation) component most responsible for the overall exergy loss is the chemical entropy, having the same order of magnitude as the rest of the entropy generation terms combined for all the cases evaluated. The computed exergy efficiency for the base case is 68.4%, in agreement with previous droplet combustion exergy studies. To develop guidelines for the process improvement, the sensitivity of the second law efficiency to the initial gas temperature (Tgi), reaction rate (ω), and combustion duration were analyzed. The results generated several promising improvement avenues.

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