Grid-Independent Air Conditioning Using Underground Thermal Energy Storage (UTES) and Reversible Thermosiphon Technology: Experimental Results

2011 ◽  
Author(s):  
Bidzina Kekelia ◽  
Kent S. Udell
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Air Conditioning ◽  
High Heat ◽  
Low Energy ◽  
Working Fluid ◽  
High Heat Flux ◽  
High Heat Transfer

Thermal energy storage in subsurface soils can produce both inexpensive capacity and storage timescales of the order of a year. In concept, storing excess ambient or solar heat in summer for future winter use and winter “cold” for summer air conditioning can provide essentially zero-carbon space heating and cooling. An innovative ground coupling using a reversible (pump-assisted) thermosiphon with its high heat flux characteristics, intrinsic to two-phase heat pipes, as an inground heat exchanger is proposed and its performance is evaluated in a series of lab-scale experiments. Extraction and injection of heat from/into the water-saturated sand with a single thermosiphon unit representing a cell in an array of thermosiphons is modeled. These results demonstrate that near freezing point of water, due to weak or no natural convection, heat transfer is mainly due to conduction. Also, due to low energy input requirement for pumping working fluid and high heat transfer potential of the reversible thermosiphon, seasonal thermal energy or “cold” storage can be provided for low energy air conditioning applications.

Temperature-Staged Thermal Energy Storage Enabling Low Thermal Exergy Loss Reflux Boiling in Full Spectrum Solar Systems

2016 ◽  
Author(s):  
Terry J. Hendricks ◽  
Bill J. Nesmith ◽  
Jonathan Grandidier
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Storage ◽  
Phase Change ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
High Heat ◽  
High Heat Flux ◽  
Full Spectrum ◽  
Solar Systems

Hybrid full spectrum solar systems (FSSS) designed to capture and convert the full solar wavelength spectrum use hybrid solar photovoltaic/thermodynamic cycles that require low thermal exergy loss systems capable of transferring high thermal energy rates and fluxes with very low temperature differentials and losses. One approach to achieving this capability are high-heat-flux reflux boiling systems that take advantage of high heat transfer boiling and condensation mechanisms. Advanced solar systems are also intermittent by their nature and their electrical generation is often out-of-phase with electric utility power demand, and their required power system cycling reduces efficiency, performance (dispatchability), lifetime, and reliability. High temperature thermal energy storage (TES) at 300–600°C enables these reflux boiling systems to simultaneously store thermal energy internally to increase the energy dispatchability of the associated solar system, as this can increase the power generation profile by several hours (up to 6–10 hours) per day. Many TES phase change materials (PCM’s) exist including KNO3, NaNO3, LiBr/KBr, MgCl2/NaCl/KCl, Zn/Mg, and CuCl/NaCl, which have various operating melting points and different latent heats of fusion. Common, cost effective TES PCM’s are FeCl2/NaCl/KCl mixtures, whose phase change temperature can be varied and controlled by simple composition adjustments. This paper presents and discusses unique “temperature-staged” thermal energy storage configurations using these TES materials and analysis of such systems integrated into high-heat-flux reflux boiling systems. In this specific application, the TES materials are designed to operate at staged temperatures surrounding an operating design point near 350°C, while providing 18 kW of source heat transfer to operate a thermoacoustic power system during off-sun conditions (e.g., temporary cloud conditions, after sun-down). This work discusses relevant configurations, and critical thermal and entropy models of the TES configurations, which show the inherent minimization of thermal exergy during critical heat transfers within the configurations and systems envisioned.

scholarly journals Effect of thermal energy storage in energy consumption required for air conditioning system in office building under the African Mediterranean climate

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 201-212 ◽  
Author(s):  
Mohamed Abdulgalil ◽  
Franc Kosi ◽  
Mohamed Musbah ◽  
Mirko Komatina
Keyword(s):  
Heat Transfer ◽  
Energy Consumption ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Air Conditioning ◽  
Office Building ◽  
Weather Data ◽  
Time Shift ◽  
Partial Load

In the African Mediterranean countries, cooling demand constitutes a large proportion of total electrical demand for office buildings during peak hours. The thermal energy storage systems can be an alternative method to be utilized to reduce and time shift the electrical load of air conditioning from on-peak to off-peak hours. In this study, the Hourly Analysis Program has been used to estimate the cooling load profile for an office building based in Tripoli weather data conditions. Preliminary study was performed in order to define the most suitable operating strategies of ice thermal storage, including partial (load leveling and demand limiting), full storage and conventional A/C system. Then, the mathematical model of heat transfer for external ice storage would be based on the operating strategy which achieves the lowest energy consumption. Results indicate that the largest rate of energy consumption occurs when the conventional system is applied to the building, while the lowest rate of energy consumption is obtained when the partial storage (demand limiting 60%) is applied. Analysis of results shows that the new layer of ice formed on the surface of the existing ice lead to an increase of thermal resistance of heat transfer, which in return decreased cooling capacity.

Two-Phase Spray Cooling With Water/2-Propanol Binary Mixture: Investigation of Mass Diffusion Resistance

2016 ◽  
Author(s):  
Sai Sujith Obuladinne ◽  
Huseyin Bostanci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Spray Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
High Heat Transfer

Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients (HTCs) and critical heat flux (CHF) levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. The two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermophysical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used working fluids today, including refrigerants and dielectric liquids, have relatively poor properties and heat transfer performance. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach. This study aimed to conduct an initial investigation on the spray cooling characteristics of practically important binary mixtures and demonstrate their capability for challenging high heat flux applications. The working fluid, water/2-propanol binary mixture at various concentration levels, specifically at x1 (liquid mass fraction of 2-proponal in water) of 0.0 (pure water), 0.25, 0.50, 0.879 (azeotropic mixture) and 1.0, represented both non-azeotropic and azeotropic cases. Tests were performed on a closed loop spray cooling system using a pressure atomized spray nozzle with a constant liquid flow rate at corresponding 20°C subcooling conditions and 1 Atm pressure. A copper test section measuring 10 mm × 10 mm × 2 mm with a plain, smooth surface simulated high heat flux source. Experimental procedure involved controlling the heat flux in increasing steps, and recording the steady-state temperatures to obtain cooling curves in the form of surface superheat vs heat flux. The obtained results showed that pure water (x1 = 0.0) and 2-propanol (x1 = 1.0) provide the highest and lowest heat transfer performance, respectively. At a given heat flux level, the HTC values indicated strong dependence on x1, where the HTCs depress proportional to the concentration difference between the liquid and vapor phases. The CHF values sharply decreased at x1≥ 0.25.

Comparison of Thermal Performance of 3D Printed Shell and Tube Heat Exchanger With Commercial Plate Heat Exchanger for Thermal Energy Storage (TES) by Incorporating Phase Change Materials (PCM)

2020 ◽  
Author(s):  
Ashok Thyagarajan ◽  
Nandan Shettigar ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Heat Exchanger ◽  
Phase Change ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Working Fluid ◽  
Temperature Differential ◽  
Shell And Tube ◽  
Dry Cooling

Abstract Wet cooling is predominantly used in thermoelectric power plants for condensing steam from the turbine owing to their low system cost and for their ability to render lower turbine back pressure (in comparison to dry cooling). However, the implementation of wet cooling in arid regions is costly while implementation of dry cooling in arid regions can degrade operational reliability (while also increasing both capital costs and operational costs). As a result, alternate technologies are needed to wean power plants from using fresh water resources while also enhancing the operational reliability of dry cooling. Air cooled heat exchangers installed in arid climates are inoperable on certain days during summer as the ambient air temperature can exceed the temperature of the steam at the turbine exhaust and may lead to power plant shutdown, in-turn, causing instability in the electric supply grid infrastructure (thus compromising reliability). In order to combat these shortcomings, supplemental cooling options may be needed. Thermal Energy Storage (TES) platforms can provide an attractive option for supplemental cooling. Phase Change Materials (PCM) are often used as viable options for Latent Heat Thermal Energy Storage Systems (LHTESS) as they have small footprint owing to the high latent heat values of PCM. The objective of this study is to analyze the performance of various LHTESS platforms by utilizing different configurations of the Heat Exchangers (HX) that are filled with PCM. The scope of this study is limited to using an organic Phase Change Material (PCM) and two different HX configurations are explored in this study: (a) a Shell and Tube Heat Exchanger that was fabricated using Advanced Manufacturing (AM) technique (i.e., “3D Printing”); and (b) a conventional Chevron Plate Heat Exchanger (PHX) that was procured commercially from a vendor. The thermal response and performance characteristics (e.g., power rating and HX effectiveness) of the two HX configurations are measured experimentally in order to ascertain their efficacy for melting and solidification of the PCM for different flow rates and inlet temperature values of the working fluid. The working fluid is called the Heat Transfer Fluid (HTF). The HTF used in this study is tap water. The PCM used in this study is PureTemp 29 (commercially procured from Pure Temp Inc., Minneapolis, MN). The propagation of the melt and the freeze fronts were monitored and tracked based on the nature of the transient temperature profiles recorded by an array of thermocouples. The array of thermocouples were strategically mounted at different locations within the HX containing the PCM. For the 3D-Printed HX (Shell and Tube HX), the thermocouples were located at different radial and axial locations within the shell containing the PCM. For the PHX, the thermocouples were located at different heights (for different plates containing the PCM). The transient values of the power and capacity ratings for the HX were estimated based on the time-history of the transient values of the temperature differential for the bulk temperature of the HTF flowing between inlet and outlet ports of the HX (and this was correlated with the transient profile and location as well as the propagation of the solid-liquid interface within the HX). The performance characteristics of both HX, analyzed from the experimental data, show that the average power rating for the melting-cycle is consistently higher than that of the solidification-cycle due to the dominance of free convection during melting (resulting in higher values of the effective heat transfer coefficients for the same temperature differential values); while the solidification process is dominated by transient conduction (resulting in lower values of the effective heat transfer coefficients for the same temperature differential values).

scholarly journals Molten Nitrate Salt Development for Thermal Energy Storage in Parabolic Trough Solar Power Systems

2008 ◽  
Author(s):  
Robert W. Bradshaw ◽  
Nathan P. Siegel
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Power Plants ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Parabolic Trough ◽  
Heat Transfer Fluids

Thermal energy storage can enhance the utility of parabolic trough solar power plants by providing the ability to match electrical output to peak demand periods. An important component of thermal energy storage system optimization is selecting the working fluid used as the storage media and/or heat transfer fluid. Large quantities of the working fluid are required for power plants at the scale of 100-MW, so maximizing heat transfer fluid performance while minimizing material cost is important. This paper reports recent developments of multi-component molten salt formulations consisting of common alkali nitrate and alkaline earth nitrate salts that have advantageous properties for applications as heat transfer fluids in parabolic trough systems. A primary disadvantage of molten salt heat transfer fluids is relatively high freeze-onset temperature compared to organic heat transfer oil. Experimental results are reported for formulations of inorganic molten salt mixtures that display freeze-onset temperatures below 100°C. In addition to phase-change behavior, several properties of these molten salts that significantly affect their suitability as thermal energy storage fluids were evaluated, including chemical stability and viscosity. These alternative molten salts have demonstrated chemical stability in the presence of air up to approximately 500°C in laboratory testing and display chemical equilibrium behavior similar to Solar Salt. The capability to operate at temperatures up to 500°C may allow an increase in maximum temperature operating capability vs. organic fluids in existing trough systems and will enable increased power cycle efficiency. Experimental measurements of viscosity were performed from near the freeze-onset temperature to about 200°C. Viscosities can exceed 100 cP at the lowest temperature but are less than 10 cP in the primary temperature range at which the mixtures would be used in a thermal energy storage system. Quantitative cost figures of constituent salts and blends are not currently available, although, these molten salt mixtures are expected to be inexpensive compared to synthetic organic heat transfer fluids. Experiments are in progress to confirm that the corrosion behavior of readily available alloys is satisfactory for long-term use.

scholarly journals Latent Heat Phase Change Heat Transfer of a Nanoliquid with Nano–Encapsulated Phase Change Materials in a Wavy-Wall Enclosure with an Active Rotating Cylinder

2021 ◽  
Vol 13 (5) ◽  
pp. 2590
Author(s):  
S. A. M. Mehryan ◽  
Kaamran Raahemifar ◽  
Leila Sasani Gargari ◽  
Ahmad Hajjar ◽  
Mohamad El Kadri ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Phase Change ◽  
Latent Heat ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Wavy Wall ◽  
Governing Equations ◽  
Stefan Number ◽  
Change Material

A Nano-Encapsulated Phase-Change Material (NEPCM) suspension is made of nanoparticles containing a Phase Change Material in their core and dispersed in a fluid. These particles can contribute to thermal energy storage and heat transfer by their latent heat of phase change as moving with the host fluid. Thus, such novel nanoliquids are promising for applications in waste heat recovery and thermal energy storage systems. In the present research, the mixed convection of NEPCM suspensions was addressed in a wavy wall cavity containing a rotating solid cylinder. As the nanoparticles move with the liquid, they undergo a phase change and transfer the latent heat. The phase change of nanoparticles was considered as temperature-dependent heat capacity. The governing equations of mass, momentum, and energy conservation were presented as partial differential equations. Then, the governing equations were converted to a non-dimensional form to generalize the solution, and solved by the finite element method. The influence of control parameters such as volume concentration of nanoparticles, fusion temperature of nanoparticles, Stefan number, wall undulations number, and as well as the cylinder size, angular rotation, and thermal conductivities was addressed on the heat transfer in the enclosure. The wall undulation number induces a remarkable change in the Nusselt number. There are optimum fusion temperatures for nanoparticles, which could maximize the heat transfer rate. The increase of the latent heat of nanoparticles (a decline of Stefan number) boosts the heat transfer advantage of employing the phase change particles.

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