Phase-Transition Thermal Charging of a Channel-Shape Thermal Energy Storage Unit: Taguchi Optimization Approach and Copper Foam Inserts

Thermal energy storage is a technique that has the potential to contribute to future energy grids to reduce fluctuations in supply from renewable energy sources. The principle of energy storage is to drive an endothermic phase change when excess energy is available and to allow the phase change to reverse and release heat when energy demand exceeds supply. Unwanted charge leakage and low heat transfer rates can limit the effectiveness of the units, but both of these problems can be mitigated by incorporating a metal foam into the design of the storage unit. This study demonstrates the benefits of adding copper foam into a thermal energy storage unit based on capric acid enhanced by copper nanoparticles. The volume fraction of nanoparticles and the location and porosity of the foam were optimized using the Taguchi approach to minimize the charge leakage expected from simulations. Placing the foam layer at the bottom of the unit with the maximum possible height and minimum porosity led to the lowest charge time. The optimum concentration of nanoparticles was found to be 4 vol.%, while the maximu possible concentration was 6 vol.%. The use of an optimized design of the enclosure and the optimum fraction of nanoparticles led to a predicted charging time for the unit that was approximately 58% shorter than that of the worst design. A sensitivity analysis shows that the height of the foam layer and its porosity are the dominant variables, and the location of the porous layer and volume fraction of nanoparticles are of secondary importance. Therefore, a well-designed location and size of a metal foam layer could be used to improve the charging speed of thermal energy storage units significantly. In such designs, the porosity and the placement-location of the foam should be considered more strongly than other factors.

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Performance Enhancement of Phase Change Thermal Energy Storage Unit Using Fin and Copper Foam

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.260-261.137 ◽

2012 ◽

Vol 260-261 ◽

pp. 137-141 ◽

Cited By ~ 3

Author(s):

Yong Qi Xie ◽

Jun Song ◽

Peng Tao Chi ◽

Jian Zu Yu

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Energy Storage ◽

Phase Change ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Performance Enhancement ◽

Storage Unit ◽

Energy Storage Unit ◽

Copper Foam

An experimental study has been carried out to evaluate how fin and copper foam enhance the heat transfer performance of phase change thermal energy storage unit. The thickness of fins is 0.8mm, the porosity of the copper foam is 96% and the phase change material (PCM) is 99% pure eicosane. The samples with fin, copper foam and paraffin (FCFP) or with single copper foam and paraffin (CFP) were processed and their response to temperature variations were tested for vertical placement and horizontal placement under different heat flux conditions. The experimental results show that the use of fin and copper foam can make the sample melt much faster than single copper foam and the effective thermal conductivity of the FCFP composite is 10.83 W/(m∙K), which is 2.7 times as that of the CFP composite. In addition, horizontal placement is more contributive to the heat transfer than vertical placement for high thermal conductivity composite.

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Thermal Energy Storage and Heat Transfer of Nano-Enhanced Phase Change Material (NePCM) in a Shell and Tube Thermal Energy Storage (TES) Unit with a Partial Layer of Eccentric Copper Foam

Molecules ◽

10.3390/molecules26051491 ◽

2021 ◽

Vol 26 (5) ◽

pp. 1491

Author(s):

Mohammad Ghalambaz ◽

Seyed Abdollah Mansouri Mehryan ◽

Kasra Ayoubi Ayoubloo ◽

Ahmad Hajjar ◽

Mohamad El Kadri ◽

...

Keyword(s):

Heat Transfer ◽

Graphene Oxide ◽

Energy Storage ◽

Response Time ◽

Phase Change ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Metal Foam ◽

Foam Layer ◽

Copper Foam

Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size.

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