Experimental Investigations of Adsorption Chiller Cycle Using Stratified Thermal Storage for Heat Recovery

The thesis is aimed at the experimental investigations of a silica gel-water adsorption module used for a commercial adsorption chiller based on a novel heat recovery system (stratisorp) by the use of a stratified thermal storage tank. A stratification system is constructed which is aimed at introducing the water in the tank with minimal mixing in a rotationally symmetric fashion. The qualitative assessment of the stratification system is carried out using Background Oriented Schlieren method

Multiscale Simulation of Thermocline Energy Storage for Concentrating Solar Power

Concentrating solar power (CSP) is a renewable and demonstrated technology for large-scale power generation but requires multiple engineering advancements to achieve grid parity with conventional fossil fuels. Part of this advancement includes novel and inexpensive thermal energy systems to decouple daily power production from intermittent solar collection. Dual-media thermocline tanks, composed of molten salt and solid rock filler, offer low-cost storage capability but the concept has experienced limited deployment in CSP plants due to unresolved concerns about long-term thermal and structural stability. The main objective of the present work is to advance the understanding of thermocline storage design and operation necessary for future commercial implementations. A multiscale numerical approach is conducted to investigate tank behavior at both a device level for comprehensive short-term analysis and at a system-level for reduced-order long-term analysis. A computational fluid dynamics (CFD) model is first developed to simulate molten-salt thermocline tanks in response to cyclic charge and discharge modes of operation. The model builds upon previous work in the literature with an expanded study of the internal solid filler size as well as added consideration for practical limits on tank height. Reducing the internal filler size improves thermal stratification inside the tank but decreases the bed permeability, resulting in a design tradeoff between storage performance and required pumping power. An effective rock diameter of 1 cm is found to be the most practical selection among the sizes considered. Also of interest is the structural stability of the thermocline tank wall in response to large temperature fluctuations associated with repeated charging and discharging. If sufficient hoop stress is generated from storage cycles, the tank becomes susceptible to failure via thermal ratcheting. The thermocline tank model is therefore extended to predict wall stress associated with operation and determine if ratcheting is expected to occur. Analysis is first performed with a multilayer structure to identify stable tank wall designs. Inclusion of internal thermal insulation between the porous bed and the steel wall is found to best prevent thermal ratcheting by decoupling the thermal response of the wall from the interior salt behavior. The structural modeling approach is then validated with a simulation of the 182 MWht thermocline tank installed at the historic Solar One power tower plant. The hoop stress predictions are found to show reasonable agreement with reported strain gage data along the tank wall and verify that the tank was not susceptible to ratcheting. The preceding use of commercial CFD software for thermocline tank simulation provides comprehensive solutions but the ease of application of this approach with respect to different operating scenarios is constrained by high computing costs. A new reduced-order model of energy transport inside a thermocline tank is therefore developed to provide thermal solutions at much lower computational cost. The storage model is first validated with past experimental data and then integrated into a system model of a 100 MWe molten-salt power tower plant, such that the thermocline tank is subjected to realistic solar collection and power production processes. Results from the system-level approach verify that a thermocline tank remains an effective and viable energy storage system over long-term operation within a CSP plant. The system-level analysis is then extended with an economic assessment of thermocline storage in a power tower plant. A parametric study of the plant solar multiple and thermocline tank size highlights suitable plant designs to minimize the levelized cost of electricity. Among the cases considered, a minimum levelized cost of 12.2 cent/kWhe is achieved, indicating that cost reductions outside of thermal energy storage remain necessary to obtain grid parity. As a sensible heat storage method, dual-media thermocline tanks remains subject to low energy densities and require large tank volumes. A possible design modification to reduce tank size is a substitution of the internal rock filler with an encapsulated phase-change material (PCM), which adds a high density latent heat storage mechanism to the tank assembly. The reduced-order thermocline tank model is first updated to include capsules of a hypothetical PCM and then reintegrated into the power tower plant system model. Implementation of a single PCM inside the tank does not yield significant energy storage gains because of an inherent tradeoff between the thermodynamic quality (i.e., melting temperature and heat of fusion) of the added latent heat and its utilization in storage operations. This problem may be circumvented with a cascaded filler structure composed of multiple PCMs with their melting temperatures tuned along the tank height. However, the benefit of a cascade structure is highly sensitive to appropriate selection of the PCM melting points relative to the thermocline tank operating temperatures

Detection of Potential Fishing Zones of Bigeye Tuna (Thunnus Obesus) at Profundity of 155 m in the Eastern Indian Ocean

Remotely sensed data and habitat model approach were employed to evaluate the present of oceanographic aspect in the Bigeye tuna's potential fishing zone (PFZ) at a profundity of 155 m. Vessel monitoring system was employed to acquire the angling vessels for Bigeye tuna from January through December, 2015-2016. Daily data of sub-surface temperature (Sub_ST), sub-surface chlorophyll-a (Sub_SC), and sub-surface salinity (Sub_SS) were downloaded from INDESO Project website. Vessel monitoring system and environmental data were employed for maximum entropy (maxent) model development. The model predictive achievement was then estimated applying the area under the curve (AUC) value. Maxent model results (AUC>0.745) exhibited its probable to understand the Bigeye tuna's spatial dispersion on the specific sub-surface. In addition, the results also showed Sub_ST (43,1%) was the most affective aspect in the Bigeye tuna dispersion, pursued by Sub_SC (35,2%) and Sub_SS (21,6%)

Kinematics and energetics of the mesoscale mid-ocean circulation : MODE

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 1976The temporal and spatial variability of low frequency moored temperature and velocity observations, obtained as part of the Mid-Ocean Dynamics Experiment (MODE), are analyzed to study the kinematics and energetics of mesoscale eddies in the ocean. The temporal variability of the low frequency motions is characterized by three regimes: very low frequencies with periods greater than 200 days, an eddy energy containing band of 80 to 120 day periods, and high frequencies wìth periods less than 30 days. At very low frequencies, the zonal kinetic energy exceeds the meridional at all depths. In the thermocline, the very low frequency zonal flow dominates the total kinetic energy. The greatest contribution to the kinetic and potential energy in the MODE region, except for the thermocline zonal flow, is from an eddy energy containing band of 80 to 120 day periods. Eddy scale kinetic energy spatial variations are confined to this band. At high frequencies, the kinetic and potential energy scale with frequency as ω-2.5 and with depth in the WKB sense. Energy at high frequencies is partitioned evenly between zonal kinetic, meridional kinetic and potential energy and is homogeneous over 100 km. Using the technique of empirical orthogonal expansion, the vertical structure of the energetically dominant eddies is described by a few modes. The displacement is dominated by a mode with a thermocline maximum and in phase displacements with depth, while the kinetic energy is dominated by an equivalent barotropic mode. A smaller portion of the kinetic and potential energy is associated with out of phase thermocline and deep water currents and displacements. The dynamics of the mesoscale eddies are very nonlinear. Using the vertical veering of the current at MODE Center, the estimated horizontal advection of heat contributes significantly to the low frequency thermal balance. The observed very low frequency anisotropic flow is consistent with the nonlinear eddy spindown models, dominated by cascades of vorticity and energy. At high frequencies, the spectral similarity is consistent with advected geostrophic turbulence.The National Science Foundation supported the work through grants GX29034 and IDO-75-03998 and a graduate fellowship

Performance response of packed-bed thermal storage to cycle duration perturbations

Packed-bed thermal stores are integral components in numerous bulk electricity storage systems and may also be integrated into renewable generation and process heat systems. In such applications, the store may undergo charging and discharging periods of irregular durations. Previous work has typically concentrated on the initial charging cycles, or on steady-state cyclic operation. Understanding the impact of unpredictable charging periods on the storage behavior is necessary to improve design and operation. In this article, the influence of the cycle duration (or ‘partial-charge’ cycles) on the performance of such thermal stores is investigated. The response to perturbations is explained and provides a framework for understanding the response to realistic load cycles. The packed beds considered here have a rock filler material and air as the heat transfer fluid. The thermodynamic model is based on a modified form of the Schumann equations. Major sources of exergy loss are described, and the various irreversibility generating mechanisms are quantified. It is known that repeated charge-discharge cycles lead to steady-state behavior, which exhibits a trade-off between round-trip efficiency and stored exergy, and the underlying reasons for this are described. The steady state is then perturbed by cycles with a different duration. Short duration perturbations lead to a transient decrease in exergy losses, while longer perturbations increase it. The magnitude of the change in losses is related to the perturbation size and initial cycle period, but changes of 1–10 % are typical. The perturbations also affect the time to return to a steady-state, which may take up to 50 cycles. Segmenting the packed bed into layers reduces the effect of the perturbations, particularly short durations. Operational guidelines are developed, and it is found that packed beds are more resilient to changes in available energy if the store is not suddenly over-charged (i.e. longer perturbations), and if the steady-state cycle duration is relatively long. Furthermore, using the gas exit temperature to control cycle duration reduces the impact of perturbations on the performance, and reduces the time to return to steady-state operation

A Physics-Informed Auto-Learning Framework for Developing Stochastic Conceptual Models for ENSO Diversity

Understanding ENSO dynamics has tremendously improved over the past decades. However, one aspect still poorly understood or represented in conceptual models is the ENSO diversity in spatial pattern, peak intensity, and temporal evolution. In this paper, a physics-informed auto-learning framework is developed to derive ENSO stochastic conceptual models with varying degrees of freedom. The framework is computationally efficient and easy to apply. Once the state vector of the target model is set, causal inference is exploited to build the right-hand side of the equations based on a mathematical function library. Fundamentally different from standard nonlinear regression, the auto-learning framework provides a parsimonious model by retaining only terms that improve the dynamical consistency with observations. It can also identify crucial latent variables and provide physical explanations. Exploiting a realistic six-dimensional reference recharge oscillator-based ENSO model, a hierarchy of three- to six-dimensional models is derived using the auto-learning framework and is systematically validated by a unified set of validation criteria assessing the dynamical and statistical features of the ENSO diversity. It is shown that the minimum model characterizing ENSO diversity is four-dimensional, with three interannual variables describing the western Pacific thermocline depth, the eastern and central Pacific sea surface temperatures (SSTs), and one intraseasonal variable for westerly wind events. Without the intraseasonal variable, the resulting three-dimensional model underestimates extreme events and is too regular. The limited number of weak nonlinearities in the model are essential in reproducing the observed extreme El Ni\~nos and nonlinear relationship between the eastern and western Pacific SSTs

Experimental study and analysis of a novel layered packed-bed for thermal energy storage applications: A proof of concept

This paper presents a study carried out as part of commissioning and testing of world’s first grid-scale 150 kWe Pumped Heat Energy Storage (PHES) demonstration system. The system employs two novel layered packed-bed thermal stores. The present study experimentally investigates one of the stores designated as “hot thermal store”, which has an energy storage density of 1072 MJ/m3 and stores heat at 500 °C and 12 bar. The layered store is an enhancement of a normal packed-bed store and offers a higher degree of thermal stratification. Experiments show that layering results in about 64 % reduction in pressure loss along with yielding considerably narrower thermocline. Round-trip efficiency, storage capacity and utilisation were calculated based on 1st Law analysis considering both simple and layered mode operation at nominal design conditions. Two cycle control scenarios were considered: time-based and temperature-based. In the time-based scenario, the store shows nearly similar performance in both modes. However, in temperature-based scenario, layered mode outperforms. During cyclic operation, layered mode outperforms as it reaches steady-state in merely 3rd cycle, without any loss in efficiency, capacity and utilisation; simple mode yields competitive efficiency but capacity and utilisation deteriorate after each successive cycle and steady-state is achieved in 20th cycle. 2nd Law analysis was additionally performed to gain insight into various losses and their impact on the performance