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.

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.

Comparison of Energy Storage Methods for Solar Electric Production

2014 ◽  
Author(s):  
Mostafa Shakeri ◽  
Maryam Soltanzadeh ◽  
R. Eric Berson ◽  
M. Keith Sharp
Keyword(s):  
Energy Storage ◽  
Storage System ◽  
Weather Conditions ◽  
Capacity Factor ◽  
Time Dependent ◽  
Heat Transfer Fluid ◽  
Weather Data ◽  
Flow Battery ◽  
Storage Losses ◽  
Reactor Temperature

Energy storage is key to expanding the capacity factor for electric power from solar energy. To accommodate variable weather patterns and electric demand, storage may be needed not just for diurnal cycles, but for variations as long as seasonal. Five solar electric systems with energy storage were simulated and compared, including an ammonia thermochemical energy storage cycle, compressed air energy storage (CAES), pumped hydroelectric energy storage (PHES), vanadium flow battery, and thermal energy storage (TES). To isolate the influence of the storage system, all systems used the same parabolic concentrator and Stirling engine. For CAES, PHES and battery, the engine directly produced electricity, which was then converted and stored. For TES, heat transfer fluid was heated by the dish and stored, and later used to drive the engine to produce electricity. For ammonia, the dish heated an ammonia dissociation reactor to produce nitrogen and hydrogen, which was stored. Heat was recovered to drive the engine by reforming ammonia from the stored gases. Each system was simulated in TRNSYS with weather data for Louisville, KY and Phoenix, AZ with subsystem efficiencies and storage losses estimated from previous experimental results. All systems including the ammonia cycle involved time dependent storage losses. Losses from the receiver included convection and emitted radiation, both of which depend on receiver temperature. Overall (solar-storage-electric) efficiency of the ammonia cycle depended strongly on synthesis reactor temperature, ranging from less than 1% to ∼18% for both Louisville, KY and Phoenix, AZ, at 500 K to 800 K, respectively. In contrast, the effect of dissociation reactor temperature was less. Overall (solar-electric-storage-electric) efficiencies of the CAES, systems in the limit of zero storage time ranged from ∼10% to ∼18% for solar receiver temperature of 500 K to 800 K. The vanadium flow battery and PHES efficiencies ranged from ∼9% to ∼17% for the same conditions. TES initially provided 12 to 23% efficiency over the same range of temperature. When time-dependent storage losses were included, however, efficiencies for all systems declined rapidly except the ammonia cycle in both locations and PHES in Louisville. The ammonia system had the highest efficiency after one month of storage, an advantage that increased with time of storage. The simulations showed that TES was most efficient for diurnal-scale storage and the ammonia cycle for longer storage. Full capacity factor for solar electric production may be most efficiently accomplished with a combination of direct solar-electric production and systems with both diurnal and long-term storage, the proportions of which depending on weather conditions and electric demand profiles.

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.

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.

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.

Evaluation of Key Design Parameters of an Encapsulated Latent Heat Thermal Storage Unit

2016 ◽  
Vol 852 ◽  
pp. 652-658
Author(s):  
N. Lakshmi Narasimhan ◽  
P. Karthik
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Latent Heat ◽  
Thermal Response ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Design Parameters ◽  
Inlet Temperature ◽  
Storage Unit ◽  
Melting Temperatures

The present work numerically investigates for a latent heat thermal storage (LHTS) unit, the effect of key design parameters such as the inlet temperature of the heat transfer fluid (HTF), initial and melting temperatures of the PCM, thermophysical parameters such as specific heat, thermal conductivity etc., on its performance. A numerical model has been developed considering the discharging mode of operation and solved employing finite difference technique. The parametric study reveals that the effect of HTF inlet temperature on the unit's thermal response is more compared to initial temperature of the PCM and the influence of thermal conductivity of the PCM is very strong compared to specific heat capacity of the solid PCM

The Benefit of Using Multiple Thin Tanks Versus a Short Big Tank for Thermal Storage in Ceramic-Sphere Packed Bed With Airflow

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Yan Wang ◽  
Peiwen Li ◽  
Zhifeng Wang ◽  
Bei Yang ◽  
Guofeng Yuan
Keyword(s):  
Heat Transfer ◽  
Storage System ◽  
Large Diameter ◽  
Small Diameter ◽  
Operation Time ◽  
Thermal Storage ◽  
Packed Bed ◽  
Heat Transfer Fluid ◽  
Optimization Methodology ◽  
Energy Storage Efficiency

Abstract To make a better thermal storage system that uses air as the heat transfer fluid flowing through a packed-bed of ceramic spheres (Al2O3) as thermal storage materials, the present work studied cases using multiple small-diameter thin tanks to replace a large-diameter big tank while keeping the same total volume and the same air flow rate. Performance analysis of thermal storage has been conducted for comparison and optimization. The long flow passage and faster flow velocity of air in the small-diameter tanks was found to significantly benefit thermal storage performance compared with that of a short big tank. It resulted in a longer duration of discharge of high-temperature airflow, if the same operation time is applied to the two situations. The faster airflow enhances the heat transfer between air and thermal storage material, although it incurs larger pressure loss. Overall, the energy storage efficiency of using several thin tanks can be significantly better than that of using a big short tank if the height-to-diameter ratio in the multiple thin tanks is properly optimized. The optimization methodology and results are of great significance to the development of thermal storage systems that use air as heat transfer fluid and rocks or ceramic spheres as the packed-bed material for thermal storage.

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