Second law optimization of heat exchangers in waste heat recovery

Erguvan, Mustafa; MacPhee, David

doi:10.1002/er.4664

Cited by 16 publications

(9 citation statements)

References 50 publications

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“…First and second law analyses of the given problem were investigated using the equations explained in section 3.3 for three different parameters, namely outer diameter, mass flow rate, and thermal resistance. The authors also investigated the effect of viscous heating on the energy efficiency since it might have a considerable impact on the energy and exergy efficiencies . However, it was found here that viscous heating effect to the overall energy efficiency is less than 0.06% for the worst case; therefore, viscous dissipation effect is neglected for the energy and exergy efficiencies.…”

Section: Resultsmentioning

confidence: 96%

Thermodynamic analysis of an underground sensible energy storage system

2019

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Electricity production from concentrated solar power (CSP) plants has been more commonplace in the last decade since the sun is one of the most abundant, renewable energy sources. The heat transfer fluid temperature in a CSP plant may go up to 1000 C; however, most of the current power plants operate on temperature ranges between 220 C and 565 C due to decomposition of molten salts in high temperatures. Since the sun is not available at nights and cloudy days, an important consideration is how to store the energy received by the sun to use at other times. In this study, a three-dimensional borehole heat exchanger model is developed to store solar energy underground using concrete and molten salt as a storage medium and heat transfer fluid, respectively.While molten salt is circulating through a pipe, which is placed into the concrete, heat is transferred from the molten salt to the concrete or vice versa during the charging and discharging processes. Numerous simulations are conducted using ANSYS Fluent, with varying borehole diameters, mass flow rates, and thermal resistances of the borehole wall. Average concrete temperature, outlet heat transfer fluid temperature, and energy and exergy efficiencies are investigated for each case. It was found here that while concrete temperature increases with increasing mass flow rate, the increasing trend is minimal after the mass flow rate increases beyond 6 kg/s. There exists a negative relation between the borehole diameter and average concrete temperature during the charging process, and vice versa in discharging. Energy and exergy efficiencies varied from 0.2% to 98.1% and 0.1% to 77.9%, respectively. While the most efficient system was found at a borehole diameter of 550 mm for adiabatic cases, it was found to be 750 mm when heat leakage is taken into consideration. Borehole diameters of 2000 mm performed the worst among all cases due to low heat transfer rates. Heat leakage was found to have a significant impact on energy and exergy efficiencies, especially in energy efficiencies for higher borehole diameters and low mass flow rates in the discharging process.

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Section: Resultsmentioning

confidence: 96%

Thermodynamic analysis of an underground sensible energy storage system

2019

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“…In this study, energy and entropy analyses are undertaken to gain a better understanding of the location and severity of system losses. Only viscous dissipation losses are considered herein, though heat leakage can be a factor [25][26][27][28] but this becomes less pronounced as system size increases. Energy and entropy analyses are conducted in a similar format as in [21,29].…”

Section: Thermodynamic Analysismentioning

confidence: 99%

Thermodynamic Analysis of a High-Temperature Latent Heat Thermal Energy Storage System

MacPhee

Erguvan

2020

Energies

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Thermal energy storage (TES) technologies are becoming vitally important due to intermittency of renewable energy sources in solar applications. Since high energy density is an important parameter in TES systems, latent heat thermal energy storage (LHTES) system is a common way to store thermal energy. Though there are a great number of experimental studies in the field of LHTES systems, utilizing computational codes can yield relatively quick analyses with relatively small expense. In this study, a numerical investigation of a LHTES system has been studied using ANSYS FLUENT. Results are validated with experiments, using hydroquinone as a phase-change material (PCM), which is external to Therminol VP-1 as a heat transfer fluid (HTF) contained in pipes. Energy efficiency and entropy generation are investigated for different tube/pipe geometries with a constant PCM volume. HTF inlet temperature and flow rate impacts on the thermodynamic efficiencies are examined including viscous dissipation effects. Highest efficiency and lowest entropy generation cases exist when when flow rates are lowest due to low viscous heating effects. A positive relation is found between energy efficiency and volume ratio while it differs for entropy generation for higher and lower velocities. Both efficiency and entropy generation decreased with decreasing HTF inlet temperature. The novelty of this study is the analysis of the effect of volume ratio on system performance and PCM melting time which ultimately proved to be the most dominant factor among those considered herein. However, as PCM solidification and melting time is of primary importance to system designers, simply minimizing entropy generation by decreasing volume ratio in this case does not lead to a practically optimal system, merely to decrease heat transfer entropy generation. Therefore, caution should be taken when applying entropy analyses to any LHTES storage system as entropy minimization methods may not be appropriate for practicality purposes.

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“…Second law (exergy) analysis has been a common method to investigate energy conversion systems in order to identify locations and magnitude of exergy losses [30,31]. A theoretical study based on the anaerobic digestion of sewage from WWTP has been conducted by Safari and Dincer [32] in order to investigate the thermodynamic efficiencies of a multigeneration system.…”

Section: Introductionmentioning

confidence: 99%

Can a Wastewater Treatment Plant Power Itself? Results from a Novel Biokinetic-Thermodynamic Analysis

Erguvan

MacPhee

2021

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The water–energy nexus (WEN) has become increasingly important due to differences in supply and demand of both commodities. At the center of the WEN is wastewater treatment plants (WWTP), which can consume a significant portion of total electricity usage in many developed countries. In this study, a novel multigeneration energy system has been developed to provide an energetically self-sufficient WWTP. This system consists of four major subsystems: an activated sludge process, an anerobic digester, a gas power (Brayton) cycle, and a steam power (Rankine) cycle. Furthermore, a novel secondary compressor has been attached to the Brayton cycle to power aeration in the activated sludge system in order to increase the efficiency of the overall system. The energy and exergy efficiencies have been investigated by varying several parameters in both WWTP and power cycles. The effect of these parameters (biological oxygen demand, dissolved oxygen level, turbine inlet temperature, compression ratio and preheater temperature) on the self-efficiency has also been investigated. It was found here that up to 109% of the wastewater treatment energy demand can be produced using the proposed system. The turbine inlet temperature of the Brayton cycle has the largest effect on self-sufficiency of the system. Energy and exergy efficiencies of the overall system varied from 35.7% to 46.0% and from 30.6% to 33.55%, respectively.

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Second law optimization of heat exchangers in waste heat recovery

Cited by 16 publications

References 50 publications

Thermodynamic analysis of an underground sensible energy storage system

Thermodynamic analysis of an underground sensible energy storage system

Thermodynamic Analysis of a High-Temperature Latent Heat Thermal Energy Storage System

Can a Wastewater Treatment Plant Power Itself? Results from a Novel Biokinetic-Thermodynamic Analysis

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