Internal Entropy Generation Limits for Direct Sensible Thermal Storage

2003 ◽  
Vol 125 (2) ◽  
pp. 85-93 ◽  
Author(s):  
K. O. Homan
Keyword(s):  
Entropy Generation ◽  
Analytical Models ◽  
Liquid Volume ◽  
Liquid Stream ◽  
Storage Devices ◽  
Thermal Mixing ◽  
Energy Store ◽  
Charging And Discharging Processes ◽  
Temperature Liquid ◽  
High Or Low Temperature

This paper presents results for the entropy generated internally during the charging and discharging processes of a direct, sensible thermal energy store. The two processes correspond to the inflow of either a low or high temperature liquid stream into an enclosure initially filled with a uniformly high or low temperature liquid, respectively. The level of internal entropy generation due to thermal mixing between the inflow and the initial liquid volume corresponds to losses in the usable fraction of the stored volume and therefore decreased efficiency. Empirically, the observed behavior of direct sensible storage devices spans the range of nearly mixed to highly stratified. In the present work, analytical models for the fully-mixed and ideally-stratified limits are used to bound these behaviors and to analytically determine the corresponding entropy generation levels. The ratio of total entropy generation for the ideally-stratified limit relative to that of the fully-mixed limit is shown to vary as 8/πPe. The limiting behaviors therefore define a continuum of entropy generation levels separated by up to several orders of magnitude for typical Peclet numbers. A published numerical model which accounts for aspects of the observed thermal mixing is then examined in relation to these limits. The model predicts entropy generation levels midway between the limiting behaviors which suggests significant potential for improvements in the efficiency of direct sensible storage devices.

Second Law Aspects of Simplified Models for Sensible Thermal Storage

2000 ◽  
Author(s):  
K. O. Homan
Keyword(s):  
Numerical Model ◽  
Entropy Generation ◽  
Thermal Storage ◽  
Heat Fluxes ◽  
Analytical Models ◽  
Storage Devices ◽  
Thermal Mixing ◽  
Thermal Layer ◽  
Temperature Liquid ◽  
The One

Abstract This paper presents results for entropy generation during the inflow of a low temperature stream into a sensible thermal storage vessel initially filled with a uniformly high temperature liquid. The level of internal entropy generation due to thermal mixing between the cold and hot liquid corresponds to losses in the usable fraction of the stored volume and therefore decreased efficiency. Empirically, the observed behavior of sensible storage devices spans the range of nearly mixed to well stratified. In this investigation, analytical models for these two limits, the fully mixed and ideally stratified conditions, are used to bound the entropy generation levels of the observed behaviors. A numerical model for stratified storage systems based on the one-dimensional convective energy equation which accounts for aspects of the observed thermal mixing is then examined in relation to the afore-mentioned limits. The results show that even at moderate throughflow rates, the fully mixed and ideally stratified limits are separated by orders of magnitude in terms of entropy generated. The empirically-based numerical model exhibits mixing levels midway between these two limits and thereby underscores the potential for significant improvements in efficiency. Examination of the numerical model shows the crucial importance of resolving the evolution of the interior thermal layer and the boundary heat fluxes in computing the entropy generation.

scholarly journals Thermodynamic Performance of Molten Salt Heat Storage System Used for Regulating Load and Supplying High Temperature Steam in Coal-Fired Cogeneration Power Plants

2020 ◽  
Vol 194 ◽  
pp. 01034
Author(s):  
Haihua Luo ◽  
Qiang Shen ◽  
Yunfei Chen ◽  
Shien Sun ◽  
Junguang Lin ◽  
...  
Keyword(s):  
High Temperature ◽  
Molten Salt ◽  
Entropy Generation ◽  
Power Plants ◽  
Heat Storage ◽  
Storage System ◽  
Analytical Models ◽  
Electricity Production ◽  
Second Law ◽  
High Temperature Steam

In order to accept more electricity from renewable energy, cogeneration power plants are considering to reduce electricity production, which affects the heat supply. Here we present a molten salt heat storage system for coal-fired cogeneration power plants, which can supply high temperature steam to users and decouple the heat and electricity production. The first and second law-based analytical models for the cycle and a real device are built. Two water input methods are taken into account. The results show that the high and low temperatures in the two molten salt tanks influence the design of the components and the entropy generation distribution significantly. The pinch temperature difference in the discharge duration limits the lowest molten salt temperature. The device with real heat exchangers produces higher entropy generation and lower second law efficiency. Environmental water input requires more heat and entropy generation for the same steam supply. Recommendations are provided for practical designs.

Maintaining Redundancy in Peer-to-Peer Storage Systems

2010 ◽  
pp. 616-634
Author(s):  
Anwitaman Datta ◽  
Di Wu ◽  
Liu Xin ◽  
Adam Wierzbicki
Keyword(s):  
Quality Of Service ◽  
Storage Systems ◽  
End Users ◽  
Peer To Peer ◽  
Analytical Models ◽  
Storage Space ◽  
Storage Devices ◽  
Empirical Results ◽  
P2p Storage

Peer-to-Peer (P2P) storage systems leverage the combined storage capacity of a network of storage devices (peers) contributed typically by autonomous end-users as a common pool of storage space to store and share content. A major challenge in such a system comprising of autonomous participants is to guarantee quality of service in terms of persistence and availability of the stored content. This chapter focuses on the different possible design choices for maintaining redundancy in P2P storage systems, including algorithm details of maintenance mechanisms, analytical models to understand system’s dynamics, empirical results from simulation experiments as well as experiences from prototype deployments.

On Simplified Models for the Rate- and Time-Dependent Performance of Stratified Thermal Storage

2007 ◽  
Vol 129 (3) ◽  
pp. 214-222 ◽  
Author(s):  
Ying Ji ◽  
K. O. Homan
Keyword(s):  
Entropy Generation ◽  
Peclet Number ◽  
Volume Fraction ◽  
Thermal Storage ◽  
Time Dependent ◽  
Simplified Models ◽  
Péclet Number ◽  
Thermal Mixing ◽  
Discharge Volume ◽  
Cumulative Entropy

In direct sensible thermal storage systems, both the energy discharging and charging processes are inherently time-dependent as well as rate-dependent. Simplified models which depict the characteristics of this transient process are therefore crucial to the sizing and rating of the storage devices. In this paper, existing models which represent three distinct classes of models for thermal storage behavior are recast into a common formulation and used to predict the variations of discharge volume fraction, thermal mixing factor, and entropy generation. For each of the models considered, the parametric dependence of key performance measures is shown to be expressible in terms of a Peclet number and a Froude number or temperature difference ratio. The thermal mixing factor for each of the models is reasonably well described by a power law fit with Fr2Pe for the convection-dominated portion of the operating range. For the uniform and nonuniform diffusivity models examined, there is shown to be a Peclet number which maximizes the discharge volume fraction. In addition, the cumulative entropy generation from the simplified models is compared with the ideally-stratified and the fully-mixed limits. Of the models considered, only the nonuniform diffusivity model exhibits an optimal Peclet number at which the cumulative entropy generation is minimized. For each of the other models examined, the cumulative entropy generation varies monotonically with Peclet number.

Room-temperature liquid metal and alloy systems for energy storage applications

2019 ◽  
Vol 12 (9) ◽  
pp. 2605-2619 ◽  
Author(s):  
Xuelin Guo ◽  
Leyuan Zhang ◽  
Yu Ding ◽  
John B. Goodenough ◽  
Guihua Yu
Keyword(s):  
Energy Storage ◽  
Liquid Metals ◽  
Electronic Conductivity ◽  
Energy Storage Devices ◽  
Storage Devices ◽  
High Electronic Conductivity ◽  
Temperature Liquid ◽  
Further Development ◽  
Superior Electrochemical Properties ◽  
Alloy Systems

Liquid metals and alloy systems that feature inherent deformability, high electronic conductivity, and superior electrochemical properties have enabled further development of next-generation energy storage devices.

Second Law Analysis Optimal Design of a Mixer for Sanitary Water

2014 ◽  
Author(s):  
Adriano Sciacovelli ◽  
Vittorio Verda ◽  
Stefano Mauro
Keyword(s):  
Optimal Design ◽  
Entropy Generation ◽  
Cold Water ◽  
Hot Water ◽  
Pressure Losses ◽  
Thermal Mixing ◽  
Average Temperature ◽  
Design Variables ◽  
Commercial Code ◽  
Energy Equations

In this work, entropy generation analysis is used in the search for the optimal design of a mixer for sanitary water. An innovative design of the device is considered: hot water and cold water enter a manifold from five orifices, which opening is controlled by actuators, depending on the requested mass flow rate and average temperature. The design variables are the position of the various orifices, which are modified in order to minimize the mixing length and response time of the device, as well as the global pressure losses. Analysis is conducted using a thermofluid dynamic model which includes continuity, momentum and energy equations, that are solved using a commercial code. Results are then used to calculate the entropy generation distribution, in order to properly consider the various sources of irreversibilities, some of which are necessary (thermal mixing) and some undesired (pressure losses).

scholarly journals Simulation of Photovoltaic Array in DC Microgrid with MPPT using Perturb & Observe Method

2021 ◽  
Vol 9 (VI) ◽  
pp. 2854-2865
Author(s):  
Bhukya Yuktha Mukhi
Keyword(s):  
Energy Storage ◽  
Power Sharing ◽  
Duty Ratio ◽  
Energy Storage Devices ◽  
Dc Microgrid ◽  
Storage Devices ◽  
Photovoltaic Array ◽  
Point Of Common Coupling ◽  
Charging And Discharging Processes ◽  
The Stability

If The stand-alone dc microgrid system with a PVA i.e solar renewable energy source is operated without any supportive energy storage sources like battery and supercapacitor, then it will lead to an unstable operation of a DC microgrid, so it necessitates the usage of energy storage devices for maintaining stability in the system and also to improve the efficiency of PVA we have used an MPPT controller with P&O algorithm which provides a required duty ratio for DC-DC boost converter and this converter sees that the maximum power can be transmitted from PVA to loads. In this paper, we present how we performed a simulation study by integrating Simulink models like PVA, MPPT, battery, and Supercapacitor at Point of common coupling with DC loads and observed the stability of the system with different conditions like the change of irradiances during charging and discharging processes of storage devices and observed how is the power-sharing from PVA, Battery, and supercapacitor concerning change in load.

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