Effect of Natural Convection on Thermal Energy Storage in Supercritical Fluids

2013 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Adrienne S. Lavine ◽  
H. Pirouz Kavehpour ◽  
Gani B. Ganapathi ◽  
Richard E. Wirz
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Energy Storage ◽  
Supercritical Fluid ◽  
Supercritical Fluids ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Thermal Storage

Heat transfer to the storage fluid is a critical subject in thermal energy storage systems. The storage fluids that are proposed for supercritical thermal storage system are organic fluids that have poor thermal conductivity; therefore, pure conduction will not be an efficient heat transfer mechanism for the system. The current study concerns a supercritical thermal energy storage system consisting of horizontal tubes filled with a supercritical fluid. The results of this study show that the heat transfer to the supercritical fluid is highly dominated by natural convection. The buoyancy-driven flow inside the storage tubes dominates the flow field and enhances the heat transfer dramatically. Depending on the diameter of the storage tube, the buoyancy-driven flow may be laminar or turbulent. The natural convection has a significant effect on reducing the charge time compared to pure conduction. It was concluded that although the thermal conductivity of the organic supercritical fluids are relatively low, the effective laminar or turbulent natural convection compensates for this deficiency and enables the supercritical thermal storage to charge effectively.

scholarly journals Enhanced Thermal Characteristics of NG Based Acetamide Composites

2019 ◽  
Vol 8 (10) ◽  
pp. 4227-4231 ◽  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Phase Change Materials ◽  
Storage System ◽  
Thermal Characteristics ◽  
Energy Storage System ◽  
Melting Time

Fatty acids are a distinguished category of phase change materials (PCM). However, their inferior thermal conductivity value restricts their potential for thermal energy storage system. Carbonaceous nanomaterials have emerged as promising thermal conductivity enhancer materials for organic PCMs. The present study focuses on preparing a novel PCM nanocomposite comprising of small amount of nanographite (NG) in molten acetamide, an organic PCM, for elevation of the thermal characteristics and examining the trend of the nanocomposite through the course of charging / discharging process. These PCM-nanocomposites are prepared by dispersing NG in molten acetamide with weight fractions of 0.1, 0.2, 0.3, 0.4 and 0.5 %. The scanning electronic microscopic (SEM) analysis was conducted for the characterization of PCM nanocomposite. The energy storage behaviour of the prepared nanocomposites were analyzed with the help of differential scanning calorimeter instruments, which showed that there is no observable variation in the melting point of the nanocomposite, and a decline in the latent heat values. Furthermore, thermal conductivity trend of the nanocomposites caused by NG addition was investigated, which indicated enhancement of thermal conductivity with increasing NG concentration. Further, nanocomposites with a 0.4 wt. % of NG, displayed appreciable increase in rate of heat transfer, reducing melting time and solidification time by 48 and 47 %, respectively. The prepared PCM nanocomposites displayed superior heat transfer trend, permitting substantial thermal energy storage.

Investigation of Using Dispersed Particle and Branching Heat Exchnager in Medium Temperature Thermal Energy Storage System to Achieve Maximum Utilization of Solar Power

2013 ◽  
Author(s):  
A. M. M. G. Hasib ◽  
Rambod Rayegan ◽  
Yong X. Tao
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Power Generation ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Energy Storage System ◽  
Medium Temperature ◽  
Change Material

Maximum utilization of solar energy is very critical to achieve, because a significant portion of solar energy is lost in the form of heat. In that case Thermal Energy Storage (TES) can play a significant role by capturing the energy in the form of heat and later on can be used as a backup source of energy for utilizing it in critical time. On the other side, from the view point of conservation of energy, energy cannot be created or destroyed, but surprisingly a significant amount of energy cannot be utilized due to the instantaneous nature of conventional power generation. So storing Energy is the most unique idea that can act as a strong backup for the instantaneous nature of power generation as it not only adds up to the power generation capacity but also serves to be the most reliable medium of supplying power when the energy demand is at peak. In the authors’ previous work a phase change material (molten solar salt comprised of 60% NaNO3+40%KNO3) and a system design for thermal energy storage (TES) system integrated with a solar Organic Rankine Cycle (ORC) has been proposed. The associated research problems investigated for phase change material (PCM) are the low thermal conductivity and low rate of heat transfer from heat transfer fluid to PCM. In this study a detailed numerical modeling of the proposed design using MATLAB code and the relevant calculation and results are discussed. The numerical model is based on 1-D finite difference explicit technique using the fixed grid enthalpy method. To overcome the research problem highly conductive nano-particle graphite is used to enhance the effective thermal conductivity of the PCM material in theoretical calculation. In the later part of the study results from the numerical computation have been utilized to demonstrate a comparison between a conventional heating system (with a simple single tube as a heat exchanger) and a branching heat exchanger in PCM thermal energy storage system using NTU-Effectiveness method. The comparison results show a significant amount of improvement using branching network and mixing nano-particle in terms of heat transfer, thermal conductivity enhancement, charging time minimization and pressure drop decrease. The results of this study can convince us that the proposed medium temperature TES system coupled with solar ORC can be a stepping-stone for energy efficient and sustainable future in small-scale power generation as the system proves to be better in terms of enhanced heat transfer, increased thermal conductivity and overall sustainability.

A 5 kWht Lab-Scale Demonstration of a Novel Thermal Energy Storage Concept With Supercritical Fluids

2013 ◽  
Author(s):  
Gani B. Ganapathi ◽  
Daniel Berisford ◽  
Benjamin Furst ◽  
David Bame ◽  
Michael Pauken ◽  
...  
Keyword(s):  
High Temperature ◽  
Energy Storage ◽  
Molten Salt ◽  
Supercritical Fluid ◽  
Supercritical Fluids ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Tank ◽  
Storage System ◽  
Energy Storage System

An alternate to the two-tank molten salt thermal energy storage system using supercritical fluids is presented. This technology can enhance the production of electrical power generation and high temperature technologies for commercial use by lowering the cost of energy storage in comparison to current state-of-the-art molten salt energy storage systems. The volumetric energy density of a single-tank supercritical fluid energy storage system is significantly higher than a two-tank molten salt energy storage system due to the high compressibilities in the supercritical state. As a result, the single-tank energy storage system design can lead to almost a factor of ten decrease in fluid costs. This paper presents results from a test performed on a 5 kWht storage tank with a naphthalene energy storage fluid as part of a small preliminary demonstration of the concept of supercritical thermal energy storage. Thermal energy is stored within naphthalene filled tubes designed to handle the temperature (500 °C) and pressure (6.9 MPa or 1000 psia) of the supercritical fluid state. The tubes are enclosed within an insulated shell heat exchanger which serves as the thermal energy storage tank. The storage tank is thermally charged by flowing air at >500 °C over the storage tube bank. Discharging the tank can provide energy to a Rankine cycle (or any other thermodynamic process) over a temperature range from 480 °C to 290 °C. Tests were performed over three stages, starting with a low temperature (200 °C) shake-out test and progressing to a high temperature single cycle test cycling between room temperature and 480 °C and concluding a two-cycle test cycling between 290 °C and 480 °C. The test results indicate a successful demonstration of high energy storage using supercritical fluids.

Transient Turbulent Natural Convection in Vertical Tubes for Indirect Thermal Energy Storage

2015 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
H. Pirouz Kavehpour ◽  
Richard E. Wirz ◽  
Adrienne S. Lavine
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Convection Heat Transfer ◽  
Energy Storage System ◽  
Turbulent Natural Convection ◽  
Vertical Tubes

In this study, turbulent natural convection heat transfer during the charge cycle of a Thermal Energy Storage system was studied computationally and analytically. The storage fluids were supercritical CO2 and liquid toluene which are stored in vertical and sealed storage tubes. A computational model was developed and validated to study turbulent natural convection during the charge cycle. The results of this study show that the aspect ratio of the storage tube (L/D) has an important effect on the heat transfer characteristics. A conceptual model was developed that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. This model shows that dimensionless mean temperature of the storage fluid and average Nusselt number are functions of a Buoyancy-Fourier number.

Heat Transfer Behavior of Sulfur for Thermal Storage Applications

2016 ◽  
Author(s):  
Karthik Nithyanandam ◽  
Amey Barde ◽  
Louis Tse ◽  
Reza Baghaei Lakeh ◽  
Richard Wirz
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Elemental Sulfur ◽  
Storage System ◽  
Thermal Storage ◽  
Energy Storage System ◽  
Thermal Energy Storage System ◽  
Transfer Behavior

Efficient and cost-effective thermal energy storage system plays an important role in energy conservation. Elemental sulfur, the thirteenth most abundant element on earth, is actively being researched as a potential thermal storage medium due to its high energy storage density and low cost. The present work investigates the heat transfer behavior of elemental sulfur at temperatures between 50 degree Celsius and 250 degree Celsius. A shell and tube heat exchanger configuration with sulfur stored inside the tubes and heat transfer fluid flowing over the tubes through the shell is considered. A detailed computational model solving for the conjugate heat transfer and solid-liquid phase change dynamics of the sulfur based thermal energy storage system is developed to elucidate the complex interplay between the governing heat transfer and fluid flow phenomena during charge and discharge operations. The developed numerical model is compared with experimental results and a systematic parametric analysis of the effects of various design parameters on the performance of the thermal storage system is reported.

Transient Turbulent Natural Convection in Vertical Tubes for Thermal Energy Storage

2014 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
H. Pirouz Kavehpour ◽  
Richard E. Wirz ◽  
Adrienne S. Lavine
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Convection Heat Transfer ◽  
Energy Storage System ◽  
Turbulent Natural Convection ◽  
Vertical Tubes

In this study, turbulent natural convection heat transfer during the charge cycle of a Thermal Energy Storage system was studied computationally and analytically. The storage fluids were supercritical CO2 and liquid toluene which are stored in vertical and sealed storage tubes. A computational model was developed and validated to study turbulent natural convection during the charge cycle. The results of this study show that the aspect ratio of the storage tube (L/D) has an important effect on the heat transfer characteristics. A conceptual model was developed that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. This model shows that dimensionless mean temperature of the storage fluid and average Nusselt number are functions of a Buoyancy-Fourier number.

Assessment of Natural Convection Heat Transfer in an Isochoric Thermal Energy Storage System

2015 ◽  
Author(s):  
Reza Baghaei Lakeh ◽  
Yetlanezi B. Guerrero ◽  
Karthik Nithyanandam ◽  
Richard E. Wirz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Systems ◽  
Storage System ◽  
Energy Storage System ◽  
Energy Storage Systems ◽  
Thermal Energy Storage System

Most of the renewable energy sources, including solar and wind suffer from significant intermittency due to day/night cycles and unpredictable weather patterns. Energy Storage systems are required to enable the renewable energy sources to continuously generate energy for the power grid. Thermal Energy Storage (TES) is one of the most promising forms of energy storage due to simplicity and economic reasons. However, heat transfer is a well-known problem of most TES systems that utilize solid state or phase change. Insufficient heat transfer impairs the functionality of the system by imposing an upper limit on the power generation. Isochoric thermal energy storage system is suggested as a low-cost alternative for salt-based thermal energy storage systems. The isochoric thermal energy storage systems utilize a liquid storage medium and benefit from enhanced heat transfer due to the presence of buoyancy-driven flows. In this study, the effect of buoyancy-driven flows on the heat transfer characteristics of an Isochoric Thermal Energy Storage system is studied computationally. The storage fluid is molten elemental sulfur which has promising cost benefits. For this study, the storage fluid is stored in horizontal storage tubes. A computational model was developed to study the effect of buoyancy-driven flow and natural convection heat transfer on the charge/discharge times. The computational model is developed using an unsteady Finite Volume Method to model the transient heat transfer from the constant-temperature tube wall to the storage fluid. The results of this study show that the heat transfer process in Isochoric thermal energy storage system is dominated by natural convection and the buoyancy-driven flow reduces the charge time of the storage tube by 72–93%.

Computational Modeling of Latent Thermal Energy Storage System With Embedded Heat Pipes

2010 ◽  
Author(s):  
Karthik Nithyanandam ◽  
Ranga Pitchumani
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Heat Pipes ◽  
Energy Storage System ◽  
High Energy ◽  
Thermal Energy Storage System

Due to the intermittent nature of solar energy availability, storing sun’s energy in the form of latent thermal energy of a phase change material (PCM) is an effective technique that is widely used in energy storage and load management applications. In a Latent Thermal Energy Storage System (LTES), a heat transfer fluid (HTF) exchanges energy with a PCM. The advantages of an LTES include its isothermal operation and high energy storage density. However, the low thermal conductivity of PCM poses a significant disadvantage due to reduction in the rate at which the PCM can be melted (charging) or solidified (discharging). This paper explores an approach to reducing the thermal resistance of PCM in a LTES through embedded heat pipes. A heat pipe is a passive heat transfer device that efficiently transfers large amount of energy between the PCM and HTF thus indirectly amplifying the effective thermal conductivity of PCM. A transient computational analysis of a shell and tube LTES embedded with heat pipes is performed for charging to determine the position of melt front and energy stored as a function of time. The influence of the number and orientation of heat pipes and design configuration of the system is analyzed to identify configurations that lead to improved effectiveness.

Numerical Analysis of Latent Thermal Energy Storage System With Embedded Thermosyphons

2012 ◽  
Author(s):  
Karthik Nithyanandam ◽  
Ranga Pitchumani
Keyword(s):  
Thermal Conductivity ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Solar Power ◽  
Storage System ◽  
High Energy ◽  
Concentrating Solar Power ◽  
Discharge Performance ◽  
Low Thermal Conductivity

Latent thermal energy storage (LTES) system offers high energy storage density and nearly isothermal operation for concentrating solar power generation. However, the low thermal conductivity possessed by the phase change material (PCM) used in LTES system limits the heat transfer rates. Utilizing thermosyphons to charge or discharge a LTES system offers a promising engineering solution to compensate for the low thermal conductivity of the PCM. The present work numerically investigates the enhancement in the thermal performance of charging and discharging process of LTES system by embedding thermosyphons. A transient, computational analysis of the LTES system with embedded thermosyphons is performed for both charging and discharging cycles. The influence of the design configuration of the system and the arrangement of the thermosyphons on the charge and discharge performance of the LTES installed in a concentrating solar power plant (CSP) is analyzed to identify configurations that lead to improved effectiveness.

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