Off-Design of a Pumped Thermal Energy Storage Based On Closed Brayton Cycles

Abstract The growth of renewable energy source requires reliable, durable and cheap storage technologies. In this field, the Pumped Thermal Energy Storage (PTES), is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e. the inventory control, is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase.

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Optimization of a Packed Bed Thermal Energy Storage Unit

Journal of Solar Energy Engineering ◽

10.1115/1.3268201 ◽

1987 ◽

Vol 109 (3) ◽

pp. 170-175 ◽

Cited By ~ 17

Author(s):

H. Torab ◽

D. E. Beasley

Keyword(s):

Energy Storage ◽

Cross Section ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Relative Size ◽

Packed Bed ◽

Operating Conditions ◽

Fluid Temperature ◽

Storage Unit ◽

Energy Storage Unit

The optimization of the design of a packed-bed thermal energy storage unit is presented. A one-dimensional, transient, two-phase model is chosen for the packed bed which assumes uniformity at each cross section within the packing. The governing equations for the time dependent temperature distributions in both the solid and fluid phases are solved using a fully implicit formulation. The accuracy of the numerical method is demonstrated by comparison with experimental measurements of temperature distribution in a randomly packed bed of uniform spheres. The goal of the optimization is to achieve maximum utilization of the thermal energy storage and recovery capabilities of the storage medium for a given set of operating conditions. The optimum combination of bed length, size of the packing particles, and relative size of the bed cross section to the particle diameter is determined, subject to constraints on the maximum allowable pressure drop across the packing, the maximum outlet fluid temperature, and the total amount of supplied energy. The thermodynamic availability is examined as the measure of storage utilization. The monotinicity method is utilized for the optimization process. This method identifies a global optimum without any special computations, and prevents acceptance of false optimum solutions, as could be generated by numerical techniques. The results of the study provide guidelines for choosing the size of the packing and the packing particle subject to the constraints for a practical operating system.

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Heat Transfer in a High-Temperature Packed Bed Thermal Energy Storage System—Roles of Radiation and Intraparticle Conduction

Journal of Energy Resources Technology ◽

10.1115/1.2792693 ◽

1996 ◽

Vol 118 (1) ◽

pp. 50-57 ◽

Cited By ~ 22

Author(s):

A. A. Jalalzadeh-Azar ◽

W. G. Steele ◽

G. A. Adebiyi

Keyword(s):

Heat Transfer ◽

High Temperature ◽

Energy Storage ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Storage System ◽

Packed Bed ◽

Energy Storage System ◽

Operating Conditions ◽

Thermal Energy Storage System

A model is developed and experimentally verified to study the heat transfer in a high-temperature packed bed thermal energy storage system utilizing zirconium oxide pellets. The packed bed receives flue gas at elevated temperatures varying with time during the storage process and utilizes air for the recovery process. Both convection and radiation are included in the model of the total heat transfer between the gas and the pellets. It is found that thermal radiation and intraparticle conduction do not play a major role in the overall heat transfer in the packed bed under the specified operating conditions. An uncertainty analysis is performed to investigate the propagation of the uncertainties in the variables to the overall uncertainty in the model predictions and the experimental results.

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Thermal Energy Storage Through Melting of a Commercial Phase Change Material in an Annulus with Radially Divergent Longitudinal Fins

International Journal of Thermofluid Science and Technology ◽

10.36963/ijtst.20070102 ◽

2020 ◽

Vol 7 (1) ◽

Author(s):

Tonny Tabassum Mainul Hasan ◽

Latifa Begum

Keyword(s):

Energy Storage ◽

Phase Change ◽

Phase Change Material ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Storage System ◽

Operating Conditions ◽

Melting Time ◽

Bottom Part ◽

Change Material

This study reports on the unsteady two-dimensional numerical investigations of melting of a paraffin wax (phase change material, PCM) which melts over a temperature range of 8.7oC. The PCM is placed inside a circular concentric horizontal-finned annulus for the storage of thermal energy. The inner tube is fitted with three radially diverging longitudinal fins strategically placed near the bottom part of the annulus to accelerate the melting process there. The developed CFD code used in Tabassum et al., 2018 is extended to incorporate the presence of fins. The numerical results show that the average Nusselt number over the inner tube surface, the total melt fraction, the total stored energy all increased at every time instant in the finned annulus compared to the annulus without fins. This is due to the fact that in the finned annulus, the fins at the lower part of the annulus promotes buoyancy-driven convection as opposed to the slow conduction melting that prevails at the bottom part of the plain annulus. Fins with two different heights have been considered. It is found that by extending the height of the fin to 50% of the annular gap about 33.05% more energy could be stored compared to the bare annulus at the melting time of 82.37 min for the identical operating conditions. The effects of fins with different heights on the temperature and streamfunction distributions are found to be different. The present study can provide some useful guidelines for achieving a better thermal energy storage system.

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