Availability Of Thermal Energy Research Articles

Experimental and theoretical analysis of a micro-cogenerative solar ORC-based unit equipped with a variable speed sliding rotary vane expander

A promising solution for the Combined Heat and Power (CHP) micro production is certainly represented by Organic Rankine Cycle (ORC)-based power units. In the domestic appliances with electrical power range of the units below 1 kW, the reduced dimensions of the components represent a critical aspect as well as the need to guarantee a high reliability. When the hot source is represented by solar energy, the optimization of the electricity production keeping insured the thermal energy availability represents an aspect which invites to a proper management of the unit. Solar-based ORC-recovery units frequently work in off-design conditions due to the variability of the hot source and to the Domestic Hot Water (DHW) requirements. For this reason, the design and the selection of the components should be carefully performed. The expander is commonly retained the key component of the unit being the one that mainly affects the behaviour. For the mentioned power ranges, the volumetric expander is the best technological option and, among those available, Sliding Rotary Vane Expander (SVRE) are gaining a sensible interest. At off design conditions, according to permeability theory, the expander intake pressure linearly varies with mass flow rate of the Working Fluid (WF) which is the most suitable and easiest parameter to be changed. This modifies the performances of the unit, both from a thermodynamic and technological point of view. In this paper, the speed variation of the expander is considered as control parameter to restore design expander intake pressure. In order to assess a strategy for the speed variation of the expander, in this paper a comprehensive model of the SVRE is presented when it operates in a solar-driven ORC-based unit. The model is physically based and recovers and widens the permeability theory developed by the authors in previous works. An experimental ORC-based unit was fully instrumented and operated, coupled with a reservoir, usually present when flat plate solar collectors are used, which store the thermal energy which fulfils thermal energy requests and feeds the generating unit. The model was widely validated with the experimental data properly conceived for the purpose. In the unit the expander speed was varied and, thanks to the permeability theory, the relationships between WF flowrate variations, inlet expander pressure and expander speed variation were investigated. The potentiality of a control strategy of the expander revolution speed of the expander was fixed as well as a deeper understanding of the SVRE behaviour and relationships between operating variables. In particular, it was observed that varying the speed from 1000 RPM up to 2000 RPM, the expander behaviour was optimized ensuring proper working condition matching with a (30–100 g/s) flowrate range.

Experimental investigation to quantify the influence of single artificial indentations on vapour bubble dynamics and the associated heat transfer rates

Dependence of single vapour bubble dynamics and the associated heat transfer phenomena on the type of artificial indentations created on the heated substrate has been studied. Experiments under nucleate boiling regime have been carried out for conical indentations of varying cone angles (2γ = 30, 60 and 90o) and cylindrical cavity keeping the depth of features constant (hc = 500 μm). Rainbow schlieren deflectometry has been employed for simultaneous mapping of bubble dynamics and thermal field in a completely non-intrusive and real time manner. Direct comparison of the rainbow schlieren images shows a relatively large partition of thermal energy through natural convection for conical indentation of small cone angle and cylindrical cavity. For large-angled conical indentation, increased availability of thermal energy for bubble growth process results in the formation of relatively larger-sized vapour bubble at a relatively slower rate. In addition, due to the relative differences in the amount of vapour entrapped inside the cavities between any two bubbling cycles, the consistency of bubbling features was found to be much higher for larger cone angled cavity. The evidence for increased partition of thermal energy transfer through natural convection has been seen in the form of an increase in the portion of superheat layer in the vicinity of vapour bubble for conical cavity with small cone angles from the whole-field temperature reconstructions. For ΔTsup = 10 K, the heat transfer performance of surfaces with conical cavity with large cone angle (2γ = 90o) is significantly much better than the other conical and cylindrical cavities.

Functional space expansion driven by transitions between energetically advantageous traits in the deep sea.

Climate change is shifting community structure and biodiversity on a global scale, in part due to alterations of chemical and thermal energy availability. These changes may impact ecosystem functioning through their influence on functional diversity. We investigate patterns of functional diversity, functional niches, and functional traits in bivalve communities across the energetic gradient of the deep Atlantic Ocean. We use the functional traits feeding type, tiering, and motility level to define the axes of functional space and the unique combinations of these traits as functional niches. We find that increased energy affords new species, added into functional space through niche expansion rather than niche packing. Underlying this pattern are complex dynamics of gains and losses of individual functional niches, with few adapted to the low- and high-energy extremes, and most occurring at intermediate energy. Adaptive qualities of specific traits are evidenced by those functional niches occurring at energetic extremes. Tradeoffs between these traits within the intermediate energy zone underlie an increased coexistence of functional niches, which in turn drives a unimodal pattern of functional niches and expansion of used functional space. This work suggests that energy-limited communities may be especially vulnerable to continued shifts in food availability through the Anthropocene.

Operation maps in calcium looping thermochemical energy storage for concentrating solar power plants

Calcium Looping (CaL) process used as thermochemical energy storage system in concentrating solar plants has been extensively investigated in the last decade and the first large-scale pilot plants are now under construction. Existing research focuses on improving global efficiencies under steady-state and single modes of operation: energy storage or energy retrieval. However, TCES systems will operate under different operation points to adapt the load of its reactors to the solar availability and the energy demand from the power cycle. A thorough analysis of the operation modes provides an extremely large number of potential situations to operate the system. In this study, operation maps which maximize thermal energy availability and energy storage efficiency are defined. Furthermore, a novel approach for the management of partially carbonated solids is examined to reduce the circulation of inert material in the system based on preliminary experimental results which allows for a partial separation of carbonated solids. Two threshold scenarios are analysed: (i) no solids separation as considered in most CaL TCES studies and (ii) ideal total solids separation. The aims of this work are to set methodological criteria to define the optimal operation map and to assess the effect of partially carbonated solids separation on the energy penalties and equipment size. The inclusion of a solid separation stage leads to a maximum increase of energy storage efficiency of 26 % and a size reduction between 53 and 74 % of those heat exchangers affected by solids streams.

Thermally assisted efficient electrochemical lithium extraction from simulated seawater

Extracting lithium electrochemically from seawater has the potential to resolve any future lithium shortage. However, electrochemical extraction only functions efficiently in high lithium concentration solutions. Herein, we discovered that lithium extraction is temperature and concentration dependent. Lithium extraction capacity (i.e., the mass of lithium extracted from the source solutions) and speed (i.e., the lithium extraction rate) in electrochemical extraction can be increased significantly in heated source solutions, especially at low lithium concentrations (e.g., < 3 mM) and high Na+/Li+ molar ratios (e.g., >1000). Comprehensive material characterization and mechanistic analyses revealed that the improved lithium extraction originates from boosted kinetics rather than thermodynamic equilibrium shifts. A higher temperature (i.e., 60 oC) mitigates the activation polarization of lithium intercalation, decreases charge transfer resistances, and improves lithium diffusion. Based on these understandings, we demonstrated that a thermally assisted electrochemical lithium extraction process could achieve rapid (36.8 mg g-1 day-1) and selective (51.79% purity) lithium extraction from simulated seawater with an ultrahigh Na+/Li+ molar ratio of 20,000. The integrated thermally regenerative electrochemical cycle can harvest thermal energy in heated source solutions, enabling a low electrical energy consumption (11.3–16.0 Wh mol-1 lithium). Furthermore, the coupled thermal-driven membrane process in the system can also produce freshwater (13.2 kg m-2 h-1) as a byproduct. Given abundant low-grade thermal energy availability, the thermally assisted electrochemical lithium extraction process has excellent potential to realize mining lithium from seawater.

Performance analysis of hybrid power configurations: Impact on primary energy intensity, carbon dioxide emissions, and life cycle costs

Utilization of Natural gas and Hydrogen to support current and future building energy needs to offset the total electric demand while improving the grid resiliency and energy efficiency was investigated. Demand side energy management will play an important role in efficiently managing the available energy resources. Performance assessment of different power generation and energy management configurations is presented in this paper. Development of solutions in addressing grid resiliency by providing the ability to design suitable configurations for meeting individual building energy needs is discussed. Primary movers (PM) such as internal combustion engines (ICE) and fuel cells (FC) along with small scale auxiliary renewable energy source such as photovoltaics (PV) were considered. Key attributes of total carbon foot-print, life cycle costs including capital and operational expenditure, electric grid offset or peak shaving capability, thermal energy availability and its further potential to offset total electric demand, and primary energy intensity are analyzed and discussed in detail.

Integration of solar latent heat storage towards optimal small-scale combined heat and power generation by Organic Rankine Cycle

Abstract Thermal energy and distributed electricity demand are continuously increased in areas poorly served by a centralized power grid. In many cases, the deployment of the electricity grid is not economically feasible. Small-scale Organic Rankine Cycle (ORC) appears as a promising technology that can be operated by solar energy, providing combined heat and power (CHP) generation. Additionally, thermal energy storage can ensure stable and continuous operation in case of scarce thermal energy availability. This paper evaluates the potential application of latent heat storage to enhance solar ORC performance at operating temperatures between 80 °C and 140 °C, aiming at improving the efficiency and capacity of ORC for low-cost non-concentrating solar-thermal collectors. Three thermal energy storage scenarios are considered. Scenario 1 and 2 consist of reference cases based on a solar ORC system integrated with a conventional hot water tank and a pressurised water tank. Scenario 3 implements a storage unit based on a phase change material. The simulation was carried out through models developed in TRNSYS for solar energy balance and ASPEN for ORC system performance. The results show that solar latent heat storage tank can provide 54% of useful collector gains with a higher and narrower temperature range in the evaporator, increasing the annual thermal energy capacity by 19%, reducing annual heat losses by 66% and decreasing the investment cost by 50% in comparison with a pressurised water tank. It also allows increasing the efficiency of ORC cycle by approximately 18% (from 8.9% to 10.5%) with a higher net generated power than a conventional water tank integration, scaled up from 498 W to 1628 W. These results highlight the potential benefits that latent heat integration provides to improve the low-cost solar ORC performance for powering electricity and thermal energy supply.

Biomass retrofit for existing solar organic Rankine cycle power plants: Conceptual hybridization strategy and techno-economic assessment

This study aims to investigate techno-economic benefits of biomass retrofit for practical concentrated solar power (CSP) organic Rankine cycle (ORC) power plants. In this regard, technical parameters of an existing CSP-ORC plant currently running in Ottana (Italy) have been adopted for analyses. The plant consists of linear Fresnel collectors solar field, coupled with a two-tank oil-based thermal energy storage (TES) device, feeding a 630 kWe ORC plant. Fixed and modular biomass hybridization approaches were proposed for retrofit. In the fixed approach, biomass furnace constantly supplies thermal energy to ORC such that a pre-determined minimum power production is guaranteed, with or without solar thermal energy availability. In the modular approach, biomass furnace is regulated to supply balance thermal energy needed to continuously operate the ORC at its full capacity. Furthermore, beyond the biomass retrofit case study, a newly integrated design case study was introduced, with modified solar field and TES capacity. By using the meteorological conditions of Ottana, results of techno-economic performance for the retrofit case study showed that annual net electrical efficiency increases by 4–5 percent points, relative to the solar-only ORC plant. Marginal levelized cost of electricity (LCOE) of between 103 €/MWh and 109 €/MWh were obtained. Also, marginal net present value (NPV) ranges from 1.83 M€ to 3.22 M€. For the newly integrated design case study, results showed that design case with modular hybridization approach represents the highest annual net electrical efficiency, at 19.8%. For this approach, economic results showed that LCOE ranges between 130 €/MWh and 146 €/MWh. Beyond current state-of-the-art, the results obtained in this study show that biomass retrofit for existing CSP-ORC plants can lead to higher full-load operation hours and more prospective plant economics. Moreover, the implemented modular approach enables scheduled power profile to be followed, thereby enhancing plant dispatchability.

A review on thermal energy storage systems in solar air heaters

The drying needs of agricultural, industrial process heat requirements and for space heating, solar energy is one of the prime sources which is renewable and pollution free. As the solar energy is inconsistent and nature dependent, more often there is a mismatch between the solar thermal energy availability and requirement. This drawback could be addressed to an extent with the help of thermal energy storage systems combined with solar air heaters. This review article focuses on solar air heaters with integrated and separate thermal energy storage systems as well as greenhouses with thermal storage units. A comprehensive study was carried out in solar thermal storage units consisting of sensible heat storage materials and latent heat storage materials. As the phase change heat storage materials offer many advantages over the sensible heat storage materials, the researchers are more interested in this system. The charging and discharging characteristics of thermal storage materials with various operational parameters have been reported. All the possible solar air heater applications with storage units have also been discussed.

Study of EU DEMO WCLL breeding blanket and primary heat transfer system integration

The Water-Cooled Lithium Lead breeding blanket is a candidate option for the realization of European DEMO power plant. One of the main functions of the breeding blanket is to recover the thermal power from the first wall and the breeding zone and to drive it to the Primary Heat Transfer System. Moreover, due to the DEMO pulsed operation, an Energy Storage System is foreseen in order to ensure thermal energy availability and reduce cycling loading during dwell time. The blanket design must interface with the Primary Heat Transfer System and the Intermediate Heat Transfer System in an integrated solution with the aim of delivering feasible power plant, with high conversion efficiency.A thermal-hydraulic model of the main components of the water cooled Primary Heat Transfer System is developed, using RELAP5 system code, to support the design and sizing. A RELAP5/Mod3.3 extended version has been set-up to implement PbLi and molten salt (HITEC) fluid proprieties, as well as the relevant heat transfer correlations. The results of the preliminary applications provide a comprehensive set of thermo-hydraulic parameters (i.e. coolant inventory, pressure drops), relevant for the assessment of the design integration.

Dependency of production planning on availability of thermal energy in commercial greenhouses – A case study in Germany

Commercial greenhouses are often referred to as the optimum heat dump for very low grade waste heat from a variety of sources. However availability, temperature levels and fluctuations in the availability necessitate a very different approach towards production planning as compared to traditional systems where energy supply is adapted to production demand and not the converse.In this study, a commercial ornamental plant nursery that had switched its heat supply from natural gas to utilizing the waste heat of a commercial CHP system in 2007 was analysed. The differences between production planning and temperature regimes before and after switching to waste heat were compared. Furthermore, the degree of utilization of the waste heat available was evaluated.The study undertaken showed three main results: Firstly, greenhouses present a good opportunity for the use of the low grade waste heat. However production needs to be planned very carefully to facilitate the production of high quality plants, for which traditional cultivation planning is unsuitable. Secondly, when planning on utilizing the heat (7.1 GWhth/a) of a CHP system which is sized based on electricity output (6.7 GWhel/a), to the full capacity, additional users need to be found and ideally heat storage integrated. Currently heat utilization amounts to less than 45% (3.1 GWhth) in total. Especially in summer most of the heat is discarded. Thirdly, several scenarios for utilization optimization were considered. The scenarios described allow for an increase of heat utilization to 62% or 4.4 GWhth using some of the heat to run absorption chillers to provide cooling in summer and storing excess heat in long term heat stores (300 MWhth) to reduce the additional gas demand. The results of the economic evaluation show that the integration of a cold store, supplied by the coolth by using an absorption chiller is financially attractive with a resulting payback period of 2.9 years, whilst consideration of integration of a PCM heat store is far from being viable with a payback period of almost 300 years.

A test of species–energy theory: patch occupancy and colony size in tropical rainforest litter‐nesting ants

Species–energy theory can account for spatial variation in the abundance and community composition of animals, though the mechanisms of species–energy theory are under contention. We evaluated three competing mechanisms at the local spatial scale by conducting an in vivo light manipulation over supplemental ant nests placed in the leaf litter of a Costa Rican tropical rainforest. We found that the light environment did not alter the 10% rate of occupation of the supplemental nests, but light did alter the size of colonies and the genus‐level composition of the community. Light levels in the foraging range were positively associated with colony sizes of all ants, whereas light levels directly on the nest site were predictive of the occurrence of ant genera. Colonies of specialized predators, dacetine ants, were larger in more shaded foraging environments, and the functional group of generalized myrmicines exhibited an opposite pattern, with smaller‐sized colonies in response to shading. Responses of twig‐dwelling ants to the light environment were most consistent with the metabolic cost hypothesis as a mechanism of species–energy theory. We found mixed support for the thermal energy availability hypothesis, and scant support for the chemical energy hypothesis, as the litter depth, a measure of prey density, was not predictive of ant responses. In summary, at the local scale, we found patterns in colony size and life history are governed by light‐dependent mechanisms.

Mooney scorch time and cure index of epoxidized natural rubber in presence of sodium carbonate

AbstractThe effect of sodium carbonate on the Mooney scorch time and cure index of epoxidized natural rubber (ENR 50) was studied with concentrations of 0–2 phr and 100–160°C temperatures. A conventional vulcanization system based on an ASTM formulation was used throughout the investigation on the gum and carbon black filled rubber compound. The results indicated that the scorch time and cure index for the gum and filled compounds increased to a maximum value at 0.15 phr of sodium carbonate, and further loading of sodium carbonate caused it to decrease. This observation was attributed to the neutralization of the residual acid in ENR 50 in the initial stage, thus reducing the formation of ether crosslinks via an acid‐catalyzed ring‐opening reaction with the epoxide group in ENR 50. However, as the sodium carbonate was increased beyond 0.15 phr, the excess sodium carbonate enhanced the vulcanization rate as shown by the drop of the scorch time and cure index. The peak maximum was more evident at lower temperature and its peak height decreased with increasing temperature, suggesting that the neutralization effect by sodium carbonate was overshadowed by the faster cure rate resulting from the availability of thermal energy to overcome the activation energy of vulcanization as the temperature was elevated. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 1352–1355, 2001

Choice of thermal energy system for solar absorption cooling

It is essential to operate a solar vapour absorption cooling system only at design conditionsin order to maximize the saving of conventional electrical energy. The paper deals with the analysis of a solar thermal energy system by coupling the collector field, an auxiliary thermal energy source, the thermal energy reservoir and the generator of the absorption chiller in a single closed loop, thus ensuring optimum performance of the chiller at design conditions. This analysis is preceded by a quasi steady-state analysis for the system without the auxiliary source to obtain the temperature history of the reservoir, the hourly thermal energy availability and the resulting cooling effect. The comparative results of the two systems highlight the importance of auxiliary thermal energy source in mximizing the electrical energy saving. The utility of auxiliary energy input is highly attractive because of its high effective COP and higher equivalent electrical conversion efficiency.

熱エネルギの利用に関する熱力学的評価分科会報告(分科会報告No.278)

熱エネルギの利用に関する熱力学的評価分科会報告(分科会報告No.278)

Rolling textures in f.c.c. and b.c.c. metals

Three basic assumptions are made in the present theory of rolling textures. 1. (1) The stress system in rolling is biaxial, a more realistic approximation than separate tensile and compressive stresses. 2. (2) Deformation in f.c.c. metals occurs by slip on octahedral planes. Cross slip is considered to be important, and its extent depends on the material, being a function of the stacking fault energy, on the internal stresses governed by the amount of reduction and on the availability of thermal energy, (3) Textures are developed as a consequence of deformation on two main slip systems. It is envisaged that accommodating deformation will occur in the regions of grain boundaries, but will not contribute significantly to texture development. Under conditions in which extensive cross slip does not occur, the predicted rolling texture is of the “alloy” type, {110}〈112〉, whereas when extensive cross slip occurs, rotations are towards the irrational “pure metal” texture and finally towards the orientation {112}〈111〉. Experimental evidence in the form of quantitative {111} pole figures illustrates the development with increasing reductions of rolling textures in aluminium and silver, and observations are made of slip traces in rolled metals. The observations are all consistent with theory, which can be extended to account for the rolling textures in b.c.c. metals.