Peiwen Li - Academia.edu (original) (raw)

Papers by Peiwen Li

This paper presents an experimental study and analysis of the heat transfer of energy charge and ... more This paper presents an experimental study and analysis of the heat transfer of energy charge and discharge in a packed-bed thermocline thermal storage tank for application in concentrated solar thermal power plants. Because the energy storage efficiency is a function of many parameters including fluid and solid properties, tank dimensions, packing dimensions, and time lengths of charge and discharge, this paper aims to provide experimental data and a proper approach of data reduction and presentation. To accomplish this goal, dimensionless governing equations of energy conservation in the heat transfer fluid and solid packed-bed material are derived. The obtained experimental data will provide a basis for validation of mathematical models in the future.

Elsevier eBooks, 2017

Materials needed for thermal storage include heat transfer fluids (HTFs), fluids for sensible ene... more Materials needed for thermal storage include heat transfer fluids (HTFs), fluids for sensible energy storage, solids and solid-fluid mixtures for sensible energy storage, and also materials for latent heat thermal storage. This chapter will first present the requirements for materials used for thermal energy storage including an HTF and solid materials. Because of the trend in which fluids are becoming popularly used for the HTF and the liquid-alone thermal storage material, some currently available HTFs and their properties are provided for engineering application. To support further development for high-temperature HTFs for both heat transfer and thermal storage application, criteria for selection of the fluids based on their thermal and transport properties are discussed. At the end of the chapter, properties of some solid materials for sensible and latent thermal storage applications are also provided.

A thermal storage process typically involves energy collecting, storage, and delivery using a hea... more A thermal storage process typically involves energy collecting, storage, and delivery using a heat transfer fluid (HTF). We can use the HTF alone as a thermal storage medium, or use dual media (with HTF and another material in a packed bed). System operation, configurations/arrangement of all possible packed-bed and fluid flow for the single medium or dual media thermal storage systems are presented and discussed in this chapter.

This chapter presents information on mathematical models for thermal storage, covering the establ... more This chapter presents information on mathematical models for thermal storage, covering the establishing of proper governing equations to mathematically follow the energy conservation principles for “control volumes” in a thermal storage tank when heat is charged or withdrawn; deciding the boundary condition requirements for the governing equations; and discovering the most efficient mathematical method to solve the governing equations with accuracy, so that the temperatures of fluid and solid media can be determined at any location in the tank at any time. The models address several configurations of thermal storage systems, including single fluid thermal storage, dual media (fluid and packed bed) sensible thermal storage, and dual-media PCM-based latent heat thermal storage. In the dual-media sensible thermal storage, both configurations of solid particle packed bed and integrated solid with fluid pipes passing through are considered and discussed. The transient heat transfer in a packed bed is typically assumed uniform in the radial direction in a storage tank and thus one- or two-dimensional governing equations are sufficient to describe the problems. For convenient design analysis, the models described in the following paragraphs start from a one-dimensional model which has been proven to have no sacrifice of accuracy. Models in three dimensions considering nonuniform flow are briefly introduced at the end of the chapter.

Journal of Solar Energy Engineering-transactions of The Asme, Mar 18, 2022

Eutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are pr... more Eutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are promising for being used as high-temperature heat transfer fluid (HTF) and thermal energy storage (TES) materials in a wide range of temperatures from 230 °C to 750 °C in concentrated solar thermal power systems. To conduct measurement of the heat transfer coefficient of the molten salt at high temperatures, a circulation system and instrumentation of flow and heat transfer was constructed. Experimental measurement of the convective heat transfer coefficients of NaCl-KCl-ZnCl2 (molar fraction: 13.8–41.9–44.3%) inside tubes has been accomplished to find the most suitable heat transfer correlations. Experience of salt processing and operation of the high-temperature heat transfer test system was obtained. Two correlations, Dittus-Boelter equation and Gnielinski’s correlation for Nusselt number against Reynolds number and Prandtl number, are evaluated using the test results, and the latter correlation is recommended due to its better agreement of prediction against tested data.

Elsevier eBooks, 2017

The insulation of the storage tank is paramount to ensure the operation of electricity production... more The insulation of the storage tank is paramount to ensure the operation of electricity production during the night or periods of no sun. Heat transfer exists whenever there is a temperature difference and can occur in three different modes, conduction, convection, and radiation. The purpose of the insulation is to reduce the heat loss to a minimum. The temperature of the storage tank is on the order of 600 K while the ambient temperature is around 300 K. This very large temperature difference causes a large heat loss. A combination of multiple thermal insulation layers, with each serving different purposes (withstand high temperature or super insulating), is necessary to address this problem. It is a formidable task to insulate a storage tank properly.

Journal of Solar Energy Engineering-transactions of The Asme, Jul 5, 2012

This paper presents an experimental study of the energy charge and discharge processes in a packe... more This paper presents an experimental study of the energy charge and discharge processes in a packed bed thermocline thermal storage tank for application in concentrated solar power plants. A mathematical analysis was provided for better understanding and planning of the experimental tests. The mathematical analysis indicated that the energy storage effectiveness is related to fluid and solid material properties, tank dimensions, packing schemes of the solid filler material, and the durations of the charge and discharge times. ...

In the search for advanced and more substantial ways to use renewable energy, concentrated solar ... more In the search for advanced and more substantial ways to use renewable energy, concentrated solar power (CSP) is one of the leading research ideas with the ability to have higher thermal efficiencies and capability of storing energy. Among the various CSP systems, the receiver tube in concentrated solar power tower (CSPT) plant is one of the most crucial components subjected to extreme working conditions. For tubular receiver operates with temperatures above 700°C, preliminary simulations shown an egregious temperature gradient greater than from the sunny side to the shadow region for a smooth tube, and the intense heat on the tube surface also causes deformation and buckling, therefore circumferential flow needs to be induced in order to create more flow mixing for a more uniform temperature distribution. In this study, COMSOL Multiphysics was adopted to explore the coupled hydro-thermal-mechanical effects when the receiver tubes have internal fins. The solar receiver tube is a hybrid material made of Inconel 718 and Boron mixture. The simulation showcases both forced and natural convection along with the solar radiation on one half of the tube. Multiple fins designs were simulated and compared in terms of heat transfer enhancement and minimized pressure drop, and the design of 7-head helical fins was chosen. By introducing the internal fins, the circumferential flow was observed in the flow domain, therefore it eventually led to a more uniform temperature profile for both the outer surface and bulk fluid temperatures. With a more uniform, lower surface temperature, the convective heat losses are considerably lower. The thermal efficiency was enhanced from 79.4% to 80.4%, and the structural deformation was reduced by 21.4%. Simulations were conducted to explore the effect of tube surface roughness on the absorbance and reflectivity. Various randomly generated curves with changing roughness heights were considered. The results proved that the increased surface roughness enhances the solar absorption from 0.55 to 0.80 with the hybrid mixture. This study has potential to transform the design and manufacturing of solar receiver tubes for high temperature applications, and it can directly support the current on-going efforts to reach the US Department of Energy (DOE) CSP 2030 goal.

A group of eutectic ternary halide salts were surveyed and studied for the objective of developin... more A group of eutectic ternary halide salts were surveyed and studied for the objective of developing a high temperature heat transfer fluid with a freezing point below 250°C and a low vapor pressure, below 1.0 atm, at temperatures up to 800°C. The studied salts include: 1) NaCl-KCl-ZnCl2 with a mole fractions of 18.6%-21.9%-59.5% and a melting point of tm=213°C; 2) NaCl-KCl-ZnCl2 with a mole fraction of 13.4%-33.7%-52.9% and a melting point of tm=204°C; and 3) NaCl-KCl-ZnCl2 with mole fraction of 13.8%-41.9%-44.3% and a melting point of tm=229 °C. Vapor pressures of these salts at different temperatures were experimentally obtained using an in-house developed test facility. The results show that vapor pressures of all the three eutectic molten salts are below 1.0 atm at a temperature of 800 °C. The salt of ZnCl2-KCl-NaCl in mole faction of 44.3%-41.9%-13.8% has lowest vapor pressure which is only about 1.0 atm even at a temperature of 900 °C. Viscosities of these salts were measured in the temperature range from after melting to 850°C. At low temperatures near their melting points of the salts, the viscosities are about 16 × 10−3Pa s, while at high temperatures above 700°C the viscosities are around 4 × 10−3Pa s, which is satisfactorily low to serve as heat transfer fluid for circulation in a CSP system. Both the vapor pressure and the viscosities of the studied three eutectic salts demonstrated satisfaction to serve as high temperature heat transfer fluids. Other thermal and transport properties of these salts are expected to be reported in the future for screening out a satisfactory high temperature heat transfer fluid.

Small-scale and low-temperature thermal storage systems have fewer concerns with structural desig... more Small-scale and low-temperature thermal storage systems have fewer concerns with structural designs and construction. However, for large-scale and high-temperature thermal storage systems such as those used in concentrated solar power plants, the structural design and stress analysis for the tanks, tank foundations, connections of pumps with motors through the tank wall, and thermal expansion are critical issues that have to be carefully considered. Due to the high temperature and large quantity of high temperature heat transfer fluid in a container, safety and reliability of containers, pipes, pumps, and other facilities is very critical. This chapter briefly discusses solutions to these issues.

Heat Transfer: Volume 1, 2003

Page 1. Copyright @ 2003 by ASME 1 Proceedings of Summer HT2003 ASME Summer Heat Transfer Confere... more Page 1. Copyright @ 2003 by ASME 1 Proceedings of Summer HT2003 ASME Summer Heat Transfer Conference July 21-23, 2003 Las Vegas, Nevada, USA HT2003-47436 INTERDIGITATED HEAT /MASS TRANSFER AND CHEMICAL/ELECTROCHEMICAL ...

Social Science Research Network, 2022

The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal... more The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal energy storage(TES) was investigated. An indirect contact sensible heat TES experiment setup was built. The TES section is a cylindrical tank, which is embedded with 19 stainless tubes arranged like a hexagonal honeycomb. Air was chosen as the heat transfer fluid to flow inside the tubes and carry heat, while the sand in the tank contacts the outside of tubes. Four types of sand: silver sand, medium sand, filter sand and coarse sand, were selected. The results show that voidage is the determining factor for the TES performance rather than density or grain size. Coarse sand is the best among the four types. For materials such as sand whose basic thermal properties only vary a bit, the change of charge temperature can hardly affect the TES performance. When using air as the heat transfer fluid, the TES efficiency is relatively lower. To enhance heat transfer, a lower air velocity or longer tube length is needed. The simplified 2-D simulation results match well with the experimental results and can be used for the prediction of large scale TES tank performance.

This work considers a packed-bed thermocline for use as an energy storage device in solar thermal... more This work considers a packed-bed thermocline for use as an energy storage device in solar thermal power generation. A preliminary sizing procedure of a thermocline system for a 50 MWe plant is demonstrated along with predicted transient performance under various conditions. The inlet fluid temperatures are modeled as constant or time-dependent. The time-varying inlet conditions represent solar insolation variations throughout the day which roughly take a periodic form. Sinusoidal and periodic functions based on recorded data supply this inlet condition. A constant inlet temperature can be produced by circulating the heat transfer fluid in the collection field. Both possibilities are explored and the performance is compared for various charging time allotments. The study uses an efficient, accurate numerical scheme which has been developed to model the transient behavior of a porous thermocline tank. The model can be a useful tool for thermocline heat storage sizing. This can help take guess work out of the early stages of the design process as many simulations can be run efficiently and accurately.Copyright © 2012 by ASME

This chapter presents methods for calculating the volume of the thermal storage containers/tank t... more This chapter presents methods for calculating the volume of the thermal storage containers/tank to meet the demand of thermal storage for various approaches to thermal storage, including: heat transfer fluid (HTF) thermal storage, solid and HTF dual-media sensible thermal storage, phase change material (PCM) and HTF dual-media latent heat thermal storage, as well as sensible and PCM (latent heat) combined media with HTF thermal storage. Whereas the thermal storage using only HTF is a single medium approach that has ideal energy storage efficiency, other approaches of dual-media thermal storage involve heat transfer between the HTF and the other medium and thus have energy storage efficiency less than 100%. Analysis and computation of the heat transfer between the HTF and the other medium are needed in order to size the volume of the thermal storage container.

A study on the characteristics of a buoyancy-driven flow in a rectangular circulation channel in ... more A study on the characteristics of a buoyancy-driven flow in a rectangular circulation channel in a solar-energy-harvesting device is presented in this paper. The solar-energy-harvesting device is projected to convert solar radiation into electrical energy. As a first step of the energy conversion in the device, a flow is generated by an imbalance of buoyancy forces in the heating and cooling sections for a liquid in the circulation channel. Whereas solar energy is collected to provide the heat, free convection of ambient air provides the cooling in the device. The fluid used in the circulation channel is electrically conductive and has high thermal expansion coefficient. The present investigation focuses on the effects of channel dimensions on the buoyancy-driven flow field and uniformities of velocities. Both analytical and numerical approaches are applied in the study. Analytical closed-form solution is obtained by assuming uni-direction flow. Steady-state two-dimensional laminar solutions are obtained by numerical computation using QUICK scheme and SIMPLE algorithm.

One of the important objectives of the investigation into the behavior of a thermal storage syste... more One of the important objectives of the investigation into the behavior of a thermal storage system is to understand the variation of the temperatures of the fluid when discharged from the thermal storage system. It is the discharged fluid temperature that indicates whether the thermal storage system is fully charged or fully discharged in the respective processes. This chapter will discuss the scenarios of the discharged fluid temperature from single medium (HTF alone) and dual-media thermal storage systems under different operating conditions.

Journal of Solar Energy Engineering-transactions of The Asme, Oct 1, 2015

A concentrated solar power (CSP) plant typically has thermal energy storage (TES), which offers a... more A concentrated solar power (CSP) plant typically has thermal energy storage (TES), which offers advantages of extended operation and power dispatch. Using dual-media, TES can be cost-effective because of the reduced use of heat transfer fluid (HTF), usually an expensive material. The focus of this paper is on the effect of a start-up period thermal storage strategy to the cumulative electrical energy output of a CSP plant. Two strategies—starting with a cold storage tank (referred to as “cold start”) and starting with a fully charged storage tank (referred to as “hot start”)—were investigated with regards to their effects on electrical energy production in the same period of operation. An enthalpy-based 1D transient model for energy storage and temperature variation in solid filler material and HTF was applied for both the sensible heat storage system (SHSS) and the latent heat storage system (LHSS). The analysis was conducted for a CSP plant with an electrical power output of 60 MWe. It was found that the cold start is beneficial for both the SHSS and LHSS systems due to the overall larger electrical energy output over the same number of days compared to that of the hot start. The results are expected to be helpful for planning the start-up operation of a CSP plant with a dual-media thermal storage system.

This paper presents an experimental study and analysis of the heat transfer of energy charge and ... more This paper presents an experimental study and analysis of the heat transfer of energy charge and discharge in a packed-bed thermocline thermal storage tank for application in concentrated solar thermal power plants. Because the energy storage efficiency is a function of many parameters including fluid and solid properties, tank dimensions, packing dimensions, and time lengths of charge and discharge, this paper aims to provide experimental data and a proper approach of data reduction and presentation. To accomplish this goal, dimensionless governing equations of energy conservation in the heat transfer fluid and solid packed-bed material are derived. The obtained experimental data will provide a basis for validation of mathematical models in the future.

Elsevier eBooks, 2017

Materials needed for thermal storage include heat transfer fluids (HTFs), fluids for sensible ene... more Materials needed for thermal storage include heat transfer fluids (HTFs), fluids for sensible energy storage, solids and solid-fluid mixtures for sensible energy storage, and also materials for latent heat thermal storage. This chapter will first present the requirements for materials used for thermal energy storage including an HTF and solid materials. Because of the trend in which fluids are becoming popularly used for the HTF and the liquid-alone thermal storage material, some currently available HTFs and their properties are provided for engineering application. To support further development for high-temperature HTFs for both heat transfer and thermal storage application, criteria for selection of the fluids based on their thermal and transport properties are discussed. At the end of the chapter, properties of some solid materials for sensible and latent thermal storage applications are also provided.

A thermal storage process typically involves energy collecting, storage, and delivery using a hea... more A thermal storage process typically involves energy collecting, storage, and delivery using a heat transfer fluid (HTF). We can use the HTF alone as a thermal storage medium, or use dual media (with HTF and another material in a packed bed). System operation, configurations/arrangement of all possible packed-bed and fluid flow for the single medium or dual media thermal storage systems are presented and discussed in this chapter.

This chapter presents information on mathematical models for thermal storage, covering the establ... more This chapter presents information on mathematical models for thermal storage, covering the establishing of proper governing equations to mathematically follow the energy conservation principles for “control volumes” in a thermal storage tank when heat is charged or withdrawn; deciding the boundary condition requirements for the governing equations; and discovering the most efficient mathematical method to solve the governing equations with accuracy, so that the temperatures of fluid and solid media can be determined at any location in the tank at any time. The models address several configurations of thermal storage systems, including single fluid thermal storage, dual media (fluid and packed bed) sensible thermal storage, and dual-media PCM-based latent heat thermal storage. In the dual-media sensible thermal storage, both configurations of solid particle packed bed and integrated solid with fluid pipes passing through are considered and discussed. The transient heat transfer in a packed bed is typically assumed uniform in the radial direction in a storage tank and thus one- or two-dimensional governing equations are sufficient to describe the problems. For convenient design analysis, the models described in the following paragraphs start from a one-dimensional model which has been proven to have no sacrifice of accuracy. Models in three dimensions considering nonuniform flow are briefly introduced at the end of the chapter.

Journal of Solar Energy Engineering-transactions of The Asme, Mar 18, 2022

Eutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are pr... more Eutectic salts NaCl-KCl-ZnCl2 and NaCl-KCl-MgCl2 are two of the chloride salt systems that are promising for being used as high-temperature heat transfer fluid (HTF) and thermal energy storage (TES) materials in a wide range of temperatures from 230 °C to 750 °C in concentrated solar thermal power systems. To conduct measurement of the heat transfer coefficient of the molten salt at high temperatures, a circulation system and instrumentation of flow and heat transfer was constructed. Experimental measurement of the convective heat transfer coefficients of NaCl-KCl-ZnCl2 (molar fraction: 13.8–41.9–44.3%) inside tubes has been accomplished to find the most suitable heat transfer correlations. Experience of salt processing and operation of the high-temperature heat transfer test system was obtained. Two correlations, Dittus-Boelter equation and Gnielinski’s correlation for Nusselt number against Reynolds number and Prandtl number, are evaluated using the test results, and the latter correlation is recommended due to its better agreement of prediction against tested data.

Elsevier eBooks, 2017

The insulation of the storage tank is paramount to ensure the operation of electricity production... more The insulation of the storage tank is paramount to ensure the operation of electricity production during the night or periods of no sun. Heat transfer exists whenever there is a temperature difference and can occur in three different modes, conduction, convection, and radiation. The purpose of the insulation is to reduce the heat loss to a minimum. The temperature of the storage tank is on the order of 600 K while the ambient temperature is around 300 K. This very large temperature difference causes a large heat loss. A combination of multiple thermal insulation layers, with each serving different purposes (withstand high temperature or super insulating), is necessary to address this problem. It is a formidable task to insulate a storage tank properly.

Journal of Solar Energy Engineering-transactions of The Asme, Jul 5, 2012

This paper presents an experimental study of the energy charge and discharge processes in a packe... more This paper presents an experimental study of the energy charge and discharge processes in a packed bed thermocline thermal storage tank for application in concentrated solar power plants. A mathematical analysis was provided for better understanding and planning of the experimental tests. The mathematical analysis indicated that the energy storage effectiveness is related to fluid and solid material properties, tank dimensions, packing schemes of the solid filler material, and the durations of the charge and discharge times. ...

In the search for advanced and more substantial ways to use renewable energy, concentrated solar ... more In the search for advanced and more substantial ways to use renewable energy, concentrated solar power (CSP) is one of the leading research ideas with the ability to have higher thermal efficiencies and capability of storing energy. Among the various CSP systems, the receiver tube in concentrated solar power tower (CSPT) plant is one of the most crucial components subjected to extreme working conditions. For tubular receiver operates with temperatures above 700°C, preliminary simulations shown an egregious temperature gradient greater than from the sunny side to the shadow region for a smooth tube, and the intense heat on the tube surface also causes deformation and buckling, therefore circumferential flow needs to be induced in order to create more flow mixing for a more uniform temperature distribution. In this study, COMSOL Multiphysics was adopted to explore the coupled hydro-thermal-mechanical effects when the receiver tubes have internal fins. The solar receiver tube is a hybrid material made of Inconel 718 and Boron mixture. The simulation showcases both forced and natural convection along with the solar radiation on one half of the tube. Multiple fins designs were simulated and compared in terms of heat transfer enhancement and minimized pressure drop, and the design of 7-head helical fins was chosen. By introducing the internal fins, the circumferential flow was observed in the flow domain, therefore it eventually led to a more uniform temperature profile for both the outer surface and bulk fluid temperatures. With a more uniform, lower surface temperature, the convective heat losses are considerably lower. The thermal efficiency was enhanced from 79.4% to 80.4%, and the structural deformation was reduced by 21.4%. Simulations were conducted to explore the effect of tube surface roughness on the absorbance and reflectivity. Various randomly generated curves with changing roughness heights were considered. The results proved that the increased surface roughness enhances the solar absorption from 0.55 to 0.80 with the hybrid mixture. This study has potential to transform the design and manufacturing of solar receiver tubes for high temperature applications, and it can directly support the current on-going efforts to reach the US Department of Energy (DOE) CSP 2030 goal.

A group of eutectic ternary halide salts were surveyed and studied for the objective of developin... more A group of eutectic ternary halide salts were surveyed and studied for the objective of developing a high temperature heat transfer fluid with a freezing point below 250°C and a low vapor pressure, below 1.0 atm, at temperatures up to 800°C. The studied salts include: 1) NaCl-KCl-ZnCl2 with a mole fractions of 18.6%-21.9%-59.5% and a melting point of tm=213°C; 2) NaCl-KCl-ZnCl2 with a mole fraction of 13.4%-33.7%-52.9% and a melting point of tm=204°C; and 3) NaCl-KCl-ZnCl2 with mole fraction of 13.8%-41.9%-44.3% and a melting point of tm=229 °C. Vapor pressures of these salts at different temperatures were experimentally obtained using an in-house developed test facility. The results show that vapor pressures of all the three eutectic molten salts are below 1.0 atm at a temperature of 800 °C. The salt of ZnCl2-KCl-NaCl in mole faction of 44.3%-41.9%-13.8% has lowest vapor pressure which is only about 1.0 atm even at a temperature of 900 °C. Viscosities of these salts were measured in the temperature range from after melting to 850°C. At low temperatures near their melting points of the salts, the viscosities are about 16 × 10−3Pa s, while at high temperatures above 700°C the viscosities are around 4 × 10−3Pa s, which is satisfactorily low to serve as heat transfer fluid for circulation in a CSP system. Both the vapor pressure and the viscosities of the studied three eutectic salts demonstrated satisfaction to serve as high temperature heat transfer fluids. Other thermal and transport properties of these salts are expected to be reported in the future for screening out a satisfactory high temperature heat transfer fluid.

Small-scale and low-temperature thermal storage systems have fewer concerns with structural desig... more Small-scale and low-temperature thermal storage systems have fewer concerns with structural designs and construction. However, for large-scale and high-temperature thermal storage systems such as those used in concentrated solar power plants, the structural design and stress analysis for the tanks, tank foundations, connections of pumps with motors through the tank wall, and thermal expansion are critical issues that have to be carefully considered. Due to the high temperature and large quantity of high temperature heat transfer fluid in a container, safety and reliability of containers, pipes, pumps, and other facilities is very critical. This chapter briefly discusses solutions to these issues.

Heat Transfer: Volume 1, 2003

Page 1. Copyright @ 2003 by ASME 1 Proceedings of Summer HT2003 ASME Summer Heat Transfer Confere... more Page 1. Copyright @ 2003 by ASME 1 Proceedings of Summer HT2003 ASME Summer Heat Transfer Conference July 21-23, 2003 Las Vegas, Nevada, USA HT2003-47436 INTERDIGITATED HEAT /MASS TRANSFER AND CHEMICAL/ELECTROCHEMICAL ...

Social Science Research Network, 2022

The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal... more The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal energy storage(TES) was investigated. An indirect contact sensible heat TES experiment setup was built. The TES section is a cylindrical tank, which is embedded with 19 stainless tubes arranged like a hexagonal honeycomb. Air was chosen as the heat transfer fluid to flow inside the tubes and carry heat, while the sand in the tank contacts the outside of tubes. Four types of sand: silver sand, medium sand, filter sand and coarse sand, were selected. The results show that voidage is the determining factor for the TES performance rather than density or grain size. Coarse sand is the best among the four types. For materials such as sand whose basic thermal properties only vary a bit, the change of charge temperature can hardly affect the TES performance. When using air as the heat transfer fluid, the TES efficiency is relatively lower. To enhance heat transfer, a lower air velocity or longer tube length is needed. The simplified 2-D simulation results match well with the experimental results and can be used for the prediction of large scale TES tank performance.

This work considers a packed-bed thermocline for use as an energy storage device in solar thermal... more This work considers a packed-bed thermocline for use as an energy storage device in solar thermal power generation. A preliminary sizing procedure of a thermocline system for a 50 MWe plant is demonstrated along with predicted transient performance under various conditions. The inlet fluid temperatures are modeled as constant or time-dependent. The time-varying inlet conditions represent solar insolation variations throughout the day which roughly take a periodic form. Sinusoidal and periodic functions based on recorded data supply this inlet condition. A constant inlet temperature can be produced by circulating the heat transfer fluid in the collection field. Both possibilities are explored and the performance is compared for various charging time allotments. The study uses an efficient, accurate numerical scheme which has been developed to model the transient behavior of a porous thermocline tank. The model can be a useful tool for thermocline heat storage sizing. This can help take guess work out of the early stages of the design process as many simulations can be run efficiently and accurately.Copyright © 2012 by ASME

This chapter presents methods for calculating the volume of the thermal storage containers/tank t... more This chapter presents methods for calculating the volume of the thermal storage containers/tank to meet the demand of thermal storage for various approaches to thermal storage, including: heat transfer fluid (HTF) thermal storage, solid and HTF dual-media sensible thermal storage, phase change material (PCM) and HTF dual-media latent heat thermal storage, as well as sensible and PCM (latent heat) combined media with HTF thermal storage. Whereas the thermal storage using only HTF is a single medium approach that has ideal energy storage efficiency, other approaches of dual-media thermal storage involve heat transfer between the HTF and the other medium and thus have energy storage efficiency less than 100%. Analysis and computation of the heat transfer between the HTF and the other medium are needed in order to size the volume of the thermal storage container.

A study on the characteristics of a buoyancy-driven flow in a rectangular circulation channel in ... more A study on the characteristics of a buoyancy-driven flow in a rectangular circulation channel in a solar-energy-harvesting device is presented in this paper. The solar-energy-harvesting device is projected to convert solar radiation into electrical energy. As a first step of the energy conversion in the device, a flow is generated by an imbalance of buoyancy forces in the heating and cooling sections for a liquid in the circulation channel. Whereas solar energy is collected to provide the heat, free convection of ambient air provides the cooling in the device. The fluid used in the circulation channel is electrically conductive and has high thermal expansion coefficient. The present investigation focuses on the effects of channel dimensions on the buoyancy-driven flow field and uniformities of velocities. Both analytical and numerical approaches are applied in the study. Analytical closed-form solution is obtained by assuming uni-direction flow. Steady-state two-dimensional laminar solutions are obtained by numerical computation using QUICK scheme and SIMPLE algorithm.

One of the important objectives of the investigation into the behavior of a thermal storage syste... more One of the important objectives of the investigation into the behavior of a thermal storage system is to understand the variation of the temperatures of the fluid when discharged from the thermal storage system. It is the discharged fluid temperature that indicates whether the thermal storage system is fully charged or fully discharged in the respective processes. This chapter will discuss the scenarios of the discharged fluid temperature from single medium (HTF alone) and dual-media thermal storage systems under different operating conditions.

Journal of Solar Energy Engineering-transactions of The Asme, Oct 1, 2015

A concentrated solar power (CSP) plant typically has thermal energy storage (TES), which offers a... more A concentrated solar power (CSP) plant typically has thermal energy storage (TES), which offers advantages of extended operation and power dispatch. Using dual-media, TES can be cost-effective because of the reduced use of heat transfer fluid (HTF), usually an expensive material. The focus of this paper is on the effect of a start-up period thermal storage strategy to the cumulative electrical energy output of a CSP plant. Two strategies—starting with a cold storage tank (referred to as “cold start”) and starting with a fully charged storage tank (referred to as “hot start”)—were investigated with regards to their effects on electrical energy production in the same period of operation. An enthalpy-based 1D transient model for energy storage and temperature variation in solid filler material and HTF was applied for both the sensible heat storage system (SHSS) and the latent heat storage system (LHSS). The analysis was conducted for a CSP plant with an electrical power output of 60 MWe. It was found that the cold start is beneficial for both the SHSS and LHSS systems due to the overall larger electrical energy output over the same number of days compared to that of the hot start. The results are expected to be helpful for planning the start-up operation of a CSP plant with a dual-media thermal storage system.