Modeling of a Solid/Liquid Thermal Storage System

2003 ◽  
Author(s):  
J. S. Mulvey ◽  
R. F. Boehm
Keyword(s):  
Storage System ◽  
Heat Removal ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Solid Matrix ◽  
Second Law ◽  
Second Law Analysis ◽  
The Finite Difference Method ◽  
Design Options ◽  
Solid Liquid

A computational model utilizing the finite difference method was developed to simulate the behavior of a simple thermal storage system. The system analyzed utilizes the deposition of heat from a fluid to a solid matrix in the initial part of cycle followed by heat removal in the latter part. The storage system was divided into perpendicular slices with respect to the direction of the heat transfer fluid (HTF) flow. To further reduce the area of the slice on which the calculations were performed, the symmetry of the design was then used. Two dimensional conduction and convection calculations were performed within the plane generated by each slice. Interaction between the slices was limited to only the HTF flow rate. It was assumed that the system would experience no losses to the ambient and the HTF contained in each slice would be fully mixed. First and Second Law analysis were incorporated as a means of evaluating different configurations of the storage system design. A technique that allows the designer to choose between design options is discussed.

Second Law Analysis of a Stirling Cryocooler With Optimal Design of the Regenerator and Losses

2001 ◽  
Author(s):  
E. D. Rogdakis ◽  
N. A. Bormpilas
Keyword(s):  
Gas Flow ◽  
Optimization Technique ◽  
Internal Heat ◽  
Thermodynamic Characteristics ◽  
Coefficient Of Performance ◽  
Solid Matrix ◽  
Second Law ◽  
External Temperature ◽  
Technical Requirements ◽  
Second Law Analysis

Abstract The aim of the research in this paper is a second law analysis of a Stirling cryocooler. A one-dimensional model is proposed for the simulation of the gas flow in the expansion space, the regenerator, the warm-end, the compression space and the compressor. Helium gas is selected as the working medium. An algorithm has been developed considering parametrically the most from the main operational tasks of the thermodynamic cycle. Performance indices such as heat input, efficiency, external dimensions of the engine and technical requirements are taken into account as constraints. Engine operating parameters i.e. speed, external temperature, mean pressure are fixed. The regenerator loss has a critical influence on the cryocooler efficiency and the reduction of this kind of internal irreversibilities is extremely difficult due to the generator is subject to rapidly cycling flows accompanied by steep temperature gradients and large pressure variations. The second flow analysis of the regenerator identifies two principal losses, the irreversible internal heat transfer into the solid matrix and the hydraulic resistance. An optimization technique leads to entropy generation charts, extremely useful for a good design of the regenerator. Finally the main thermodynamic characteristics (net refrigeration, power input and the coefficient of performance) of the cryocooler are given both cases with and without external and internal irreversibilities.

Experimental Exploration of a Small Scale Pneumatically Pumped Thermal Storage System

2016 ◽  
Author(s):  
Inri Rodriguez ◽  
Jesus Cerda ◽  
Daniel S. Codd
Keyword(s):  
High Temperature ◽  
Storage Tank ◽  
Pulse Width Modulation ◽  
Low Cost ◽  
Storage System ◽  
Heat Engine ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Small Scale ◽  
Constant Frequency

A prototype water-glycerol two tank storage system was designed to simulate the fluidic properties of a high temperature molten salt system while allowing for room temperature testing of a low cost, small scale pneumatically pumped thermal storage system for use in concentrated solar power (CSP) applications. Pressurized air is metered into a primary heat transfer fluid (HTF) storage tank; the airflow displaces the HTF through a 3D printed prototype thermoplate receiver and into a secondary storage tank to be dispatched in order to drive a heat engine during peak demand times. A microcontroller was programmed to use pulse-width modulation (PWM) to regulate air flow via an air solenoid. At a constant frequency of 10Hz, it was found that the lowest pressure drops and the slowest flowrates across the receiver occurred at low duty cycles of 15% and 20% and low inlet air pressures of 124 and 207 kPa. However, the data also suggested the possibility of slug flow. Replacement equipment and design modifications are suggested for further analysis and high temperature experiments. Nevertheless, testing demonstrated the feasibility of pneumatic pumping for small systems.

Experimental Study of a Novel Thermal Storage System Using Sands With High-Conductive Fluids Occupying the Pores

2014 ◽  
Author(s):  
Jingxiao Han ◽  
Ben Xu ◽  
Peiwen Li ◽  
Anurag Kumar ◽  
Yongping Yang
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Low Cost ◽  
Storage System ◽  
Solid Material ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Large Capacity ◽  
Conductive Fluid ◽  
Media System

Because of the capability of large capacity thermal storage, concentrated solar power (CSP) technology is getting more attentions in the recent years. The energy storage allows power generation using solar energy during the late afternoon and evening time. For a large capacity of thermal energy storage, a dual-media system is typically adopted for reducing the use of the heat transfer fluid (HTF), which is usually expensive. In a dual-media system, the solid material must have large heat capacity and be inexpensive. One type of configuration for a dual-media system is that HTF flowing in pipes which are imbedded into the solid material. The present study considers sands, a major component of concrete, as low-cost solid thermal storage materials. The novel approach is that the sand is saturated with high thermal conductive fluid. Compared to using concrete for thermal storage, this method avoids issues of heat transfer degradation associated with the mismatch of thermal expansion of pipes and concrete. Since only sands are porous materials and the heat transfer performance is low, a high conductive fluid (XCELTHERM® 600 hot oil) was used to saturate sands, which then forms a new thermal storage material that can have better heat transfer. Results of thermal storage process with sands only and with the oil-saturated sands are presented and discussed.

Experimental Study of Thermal Energy Storage Using Natural Porous Media

2017 ◽  
Author(s):  
A. J. Al Edhari ◽  
C. C. Ngo
Keyword(s):  
Experimental Study ◽  
Porous Media ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Storage Unit ◽  
Storage Media

Thermal energy storage has been an area of research interest due to the need to store solar energy or excess energy for later use in many applications including district heating. The focus of a lot of research is on exotic and expensive storage media. This paper presents an experimental study of thermal energy storage using porous media readily available and commonly found in nature such as sand, soil, pebble rocks and gravel. This study also considers a simple and inexpensive thermal storage system which could be constructed easily and examines what could be done to increase the thermal storage performance. The thermal storage system examined in the present study was a thermal energy storage unit with embedded horizontal pipes carrying water as the heat transfer fluid for thermal charging. Different thermal storage configurations were examined by adjusting the thermal charging temperature and using different storage media. The temperature distribution within the storage media was monitored for 10 hours using a data acquisition system with K-type thermocouples. The results indicate that a thermal storage system using sand as storage media is slightly better compared with gravel or pebble rocks as storage media.

Second Law Analysis of an Energy Storage System Consisting of an Electrolysis Plant and the Graz Cycle With Internal H2/O2 Combustion

2019 ◽  
Author(s):  
Simeon Dybe ◽  
Tom Tanneberger ◽  
Panagiotis Stathopoulos
Keyword(s):  
Energy Storage ◽  
Power Plants ◽  
Storage System ◽  
Electric Energy ◽  
Energy Storage System ◽  
Working Fluid ◽  
Energetic Efficiency ◽  
Second Law ◽  
Electric Energy Storage ◽  
Second Law Analysis

Abstract The expansion of renewable energy generation must go hand in hand with measures for reliable energy supply and energy storage. A combination of hydrogen and oxygen as storing media provided from electrolysis at high pressure and zero emission power plants is a very promising option. The Graz cycle is an oxy-fuel combined power cycle that can operate with internal H2/O2 combustion and steam as working fluid. It offers thermal efficiencies up to 68.5% (LHV). This work applies a second law analysis to the Graz cycle and determines its exergetic efficiency. Exergy destruction is broken down to the cycle’s components thus providing insights on the location and magnitude of the cycle’s inefficiencies. A sensitivity analysis identifies the cycle’s exergetic and energetic efficiency as a function of representative parameters, offering an approach for future improvements. The combination of the cycle with an electrolysis plant is subsequently analyzed as an electric energy storage system. The round trip efficiency of the storage and back conversion system is computed by taking into account the additional compression of the reactants. As part of this analysis, the effect of the electrolyzer’s operational pressure is studied by comparing several commercial electrolyzers.

Longer Passage of Airflow in Multiple Packed-Bed Thin Tanks Versus in a Short Big Tank for Improved Thermal Storage Performance

2018 ◽  
Author(s):  
Yan Wang ◽  
Peiwen Li ◽  
Zhifeng Wang ◽  
Bei Yang ◽  
Guofeng Yuan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Storage System ◽  
Thermal Power ◽  
Thermal Storage ◽  
Packed Bed ◽  
Heat Transfer Fluid ◽  
Storage Efficiency ◽  
Storage Material ◽  
Solar Thermal Power ◽  
Storage Performance

A very challenging issue about solar thermal power generation is the use of a high temperature heat transfer fluid (water, oils, or molten salts) for heat transfer and thermal storage material, which may freeze at night or cold weather. When choosing air as the heat transfer fluid, the problem of freezing is eliminated. In order to increase the performance of thermal storage system which uses air as the heat transfer fluid passing through a packed bed (by ceramic spheres of Al2O3), multiple small-diameter tanks are considered to replace a single large-diameter tank with the same packed-bed volume and airflow rate in this paper. Analysis about the thermal storage performance in a short big tank and in cascade thin tanks has been made for comparison. A long passage of airflow and faster flow speed of air in the cascade thin tanks has been found significantly beneficial to thermal storage. Results about the increased thermal storage performance and increased pressure loss will be presented. Longer passage of airflow made it possible to have a longer time of high temperature of outflow air during discharging period. And faster speed of the fluid enhanced the heat transfer between air and thermal storage material. The total effective energy and thermal storage efficiency of cascade thin-tank thermal energy storage (TES) are higher. The thermal storage efficiency in the two types of thermal storage arrangement was compared for optimal design. The obtained results are of great significance to the development of using air as heat transfer fluid and rocks or ceramic spheres as the thermal storage material for thermal storage system in concentrated solar thermal power plants.

Second Law Analysis of Adsorption Cycles With Thermal Regeneration

1996 ◽  
Vol 118 (3) ◽  
pp. 229-236 ◽  
Author(s):  
M. Pons
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Optimal Operation ◽  
Heat Transfer Fluid ◽  
Second Law ◽  
Heat Sources ◽  
Thermal Regeneration ◽  
Environment Friendly ◽  
Second Law Analysis ◽  
Adsorption Processes

Adsorption processes can be used for operating environment-friendly refrigeration cycles. When combined with the thermal regeneration process, these cycles can have quite high performance. The second law analysis of the adsorption cycles with thermal regeneration is fully developed. The different heat transports between heat transfer fluid and adsorbent, between adsorbate and condenser/evaporator heat sources, and between heat transfer fluid and heat sources are analyzed. The entropy balance is then completely established. Consistency between the first law and second law analysis is verified by the numerical values of the entropy productions. The optimal Operation of an adsorber is then described, and the study of those optimal conditions lead to some correlation between the different internal entropy productions.

Dynamic Performance of Solar PCM Thermal Storage System

2012 ◽  
Author(s):  
Taha Aldoss
Keyword(s):  
Dynamic Performance ◽  
Storage System ◽  
Thermal Storage ◽  
Time Dependent ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Time Step ◽  
Discharge Temperature ◽  
Cooling Coils

The dynamic performance of a PCM thermal storage system is investigated. The most affecting parameters on the system performance are the type and properties of PCM material, and the heat transfer fluid (HTF) inlet temperature. The time variant solar collector discharge temperature and that from the heating/cooling coils due to space load variation results in time dependent HTF inlet temperature. This paper is to study the behavior of the PCM thermal storage system under such time dependent HTF inlet temperature operating condition. A simple one dimensional model were used and solved numerically using the finite difference technique. To assure stability of solution the right time step and element size were applied. A MATLAB Program is formulated and used to solve the result system of equations. Results are presented in terms of the storage tank fluid temperature profiles, effectiveness of PCM usage and capacity of the storage system. The above were calculated for the cases of constant and a time-dependent HTF inlet temperature conditions for comparison. The performance of the PCM storage system is found to be substantially different for the above two mode of operation.

scholarly journals High-Temperature Chloride-Carbonate Phase Change Material: Thermal Performances and Modelling of a Packed Bed Storage System for Concentrating Solar Power Plants

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5339
Author(s):  
Giovanni Salvatore Sau ◽  
Valerio Tripi ◽  
Anna Chiara Tizzoni ◽  
Raffaele Liberatore ◽  
Emiliana Mansi ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Phase Change ◽  
Power Plants ◽  
Solar Power ◽  
Storage System ◽  
Ternary Eutectic ◽  
Thermal Storage ◽  
Packed Bed ◽  
Heat Transfer Fluid

Molten salts eutectics are promising candidates as phase change materials (PCMs) for thermal storage applications, especially considering the possibility to store and release heat at high temperatures. Although many compounds have been proposed for this purpose in the scientific literature, very few data are available regarding actual applications. In particular, there is a lack of information concerning thermal storage at temperatures around 600 °C, necessary for the coupling with a highly efficient Rankine cycle powered by concentrated solar power (CSP) plants. In this contest, the present work deals with a thermophysical behavior investigation of a storage heat exchanger containing a cost-effective and safe ternary eutectic, consisting of sodium chloride, potassium chloride, and sodium carbonate. This material was preliminarily and properly selected and characterized to comply with the necessary melting temperature and latent enthalpy. Then, an indirect heat exchanger was considered for the simulation, assuming aluminum capsules to confine the PCM, thus obtaining the maximum possible heat exchange surface and air at 5 bar as heat transfer fluid (HTF). The modelling was carried out setting the inlet and outlet air temperatures at, respectively, 290 °C and 550 °C, obtaining a realistic storage efficiency of around 0.6. Finally, a conservative investment cost was estimated for the storage system, demonstrating a real possible economic benefit in using these types of materials and heat exchange geometries, with the results varying, according to possible manufacturing prices, in a range from 25 to 40 EUR/kWh.

Second-Law Analysis of Vapor Compression Heat Pumps With Solution Circuit

1994 ◽  
Vol 116 (3) ◽  
pp. 453-461
Author(s):  
K. Amrane ◽  
R. Radermacher
Keyword(s):  
Heat Pump ◽  
Heat Pumps ◽  
Single Stage ◽  
Heat Transfer Fluid ◽  
Second Law ◽  
Fluid Temperature ◽  
Ammonia Vapor ◽  
Vapor Compression ◽  
Second Law Analysis ◽  
Work Input

A second-law analysis is conducted on both the single-stage vapor compression heat pump with solution circuit (VCHSC) and its modified version, the cycle with a preheater and additional desorber. The results are compared to a conventional heat pump cycle operating with pure ammonia. The location and magnitude of the irreversibilities of the individual components constituting the cycles are determined. The entropic average temperature is used in computing the irreversibilities. The total work input to the heat pumps is then conveniently decomposed into two parts: the minimum work input or the work of a reversible cycle operating between the desorber and absorber entropic average temperatures, plus an additional input of work caused by the irreversibilities of the different processes of the cycles. The analysis reveals that the compressor is the most inefficient component of the heat pumps with losses accounting for about one fourth of the work input. The irreversibilities in the desorber and absorber are found to be minimum when there is a good match in both the solution and heat transfer fluid temperature glides. By adding a preheater and an additional desorber, the irreversibilities in the single-stage VCHSC are considerably reduced. However, it is shown that it is the preheater and not the additional desorber that has by far the most significant impact on the heat pump’s efficiency improvements. Compared to a conventional ammonia vapor compression cycle, the modified VCHSC, which has twice as many sources of irreversibility, shows nevertheless a maximum improvement of 56.1 percent in second-law efficiency.

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