Showing papers on "Latent heat published in 2016"
TL;DR: In this article, a review of thermal energy storage using phase change materials (PCMs), mainly using liquid-solid transition to store latent heat, allows a more compact, efficient and therefore economical system to operate.
563 citations
TL;DR: In this article, the authors performed a cross-validation experiment for predicting carbon dioxide, latent heat, sensible heat and net radiation fluxes across different ecosystem types with 11 machine learning (ML) methods from four different classes (kernel methods, neural networks, tree methods, and regression splines).
Abstract: . Spatio-temporal fields of land–atmosphere fluxes derived from data-driven models can complement simulations by process-based land surface models. While a number of strategies for empirical models with eddy-covariance flux data have been applied, a systematic intercomparison of these methods has been missing so far. In this study, we performed a cross-validation experiment for predicting carbon dioxide, latent heat, sensible heat and net radiation fluxes across different ecosystem types with 11 machine learning (ML) methods from four different classes (kernel methods, neural networks, tree methods, and regression splines). We applied two complementary setups: (1) 8-day average fluxes based on remotely sensed data and (2) daily mean fluxes based on meteorological data and a mean seasonal cycle of remotely sensed variables. The patterns of predictions from different ML and experimental setups were highly consistent. There were systematic differences in performance among the fluxes, with the following ascending order: net ecosystem exchange (R2 0.6), gross primary production (R2> 0.7), latent heat (R2 > 0.7), sensible heat (R2 > 0.7), and net radiation (R2 > 0.8). The ML methods predicted the across-site variability and the mean seasonal cycle of the observed fluxes very well (R2 > 0.7), while the 8-day deviations from the mean seasonal cycle were not well predicted (R2
473 citations
TL;DR: In this paper, the authors used integrated hydrologic simulations that couple vegetation and land-energy processes with surface and subsurface hydrology to study transpiration partitioning at the continental scale.
Abstract: Understanding freshwater fluxes at continental scales will help us better predict hydrologic response and manage our terrestrial water resources. The partitioning of evapotranspiration into bare soil evaporation and plant transpiration remains a key uncertainty in the terrestrial water balance. We used integrated hydrologic simulations that couple vegetation and land-energy processes with surface and subsurface hydrology to study transpiration partitioning at the continental scale. Both latent heat flux and partitioning are connected to water table depth, and including lateral groundwater flow in the model increases transpiration partitioning from 47 ± 13 to 62 ± 12%. This suggests that lateral groundwater flow, which is generally simplified or excluded in Earth system models, may provide a missing link for reconciling observations and global models of terrestrial water fluxes.
322 citations
TL;DR: In this article, the phase change diagram of salt-water systems, melting temperatures, heat of fusion, specific heat, density, thermal conductivity, and thermal diffusivity in solid and liquid states and viscosity in the liquid state for 18 salt hydrates.
252 citations
TL;DR: In this article, a survey of chloride-based thermal energy storage for concentrating solar power (CSP) plants is presented, including phase equilibria data and estimates of latent heat of fusion for some eutectics.
186 citations
TL;DR: In this paper, a shell-and-tube latent heat thermal storage unit was designed to investigate the dynamic thermal behavior of a PCM, and the thermal properties, including that of melting temperature and latent heat, were detected by Differential Scanning Calorimetry.
159 citations
TL;DR: In this paper, the melting characteristics of phase change materials (PCMs) in an annular with different installation angle of fins (θ) via a numerical simulation method, which is based on an enthalpy-porous medium model.
143 citations
TL;DR: In this paper, the use of ceramic containers comprising a cap and a cup for macro-encapsulation of metallic PCMs, and a sealing method of the containers to endure the thermal stress from volume expansion during the phase change was proposed.
137 citations
TL;DR: In this article, a review of the significant processes taking place during phase transition, the recent advantages and the appropriate PCMs in the range of buildings operation conditions is presented, while the critical mechanisms in heat transfer augmentation are examined while the recent state of the art methods are reported.
124 citations
TL;DR: In this paper, a review of the previous experimental and theoretical research studies on using paraffin wax as phase change material with different performance enhancement techniques is presented, with respect to synthesis, characterization and thermophysical properties of the nanoenhanced phase change materials.
Abstract: Increasing energy demand calls for the implementation of proper thermal energy storage which is one of the most important components of solar energy conversion systems. Phase change material based latent heat energy storage systems have emerged as a promising option to effectively store thermal energy. Generally, paraffin wax is used as the most common phase change material for low to medium temperature storage applications because it has a large latent heat and low cost besides being stable, nontoxic and non-corrosive. The performance of paraffin wax based latent heat energy storage systems (LHESS) is limited by its poor thermal conductivity. In this paper, the previous experimental and theoretical research studies on LHESS using paraffin wax as phase change material with different performance enhancement techniques are reviewed. Further, research works related to dispersing different kind of nanoparticles in paraffin wax for the enhancement of its thermal conductivity are comprehensively reviewed with respect to synthesis, characterization and thermophysical properties of the nanoenhanced phase change material.
119 citations
TL;DR: In this paper, a two-dimensional finite volume based numerical model along with enthalpy-porosity technique is employed to simulate the phase change of storage media during the discharging mode.
TL;DR: In this paper, the latent heat, L m, sensible heat Q sens, and ability of the prepared PCMs to store and release thermal energy were investigated using specific home-made equipment based on the transient guarded hot plane method (TGHPT).
TL;DR: In this article, a semi-analytical model was developed to characterize capillary-limited thin-film evaporation from silicon micropillar wicks in the absence of nucleate boiling, and the insights gained from experiments were used to model the capillary pressure, permeability, and thermal resistance.
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TL;DR: In this paper, the main components of the energy balance are net radiation, latent heat flux, sensible heat flux (H), and soil heat flux(G), and the relative importance of the components depends mainly on the availability of water for evaporation, and the extreme cases will be the humid environment (LE approaches Rn) and the desert environment (Rn is partitioned between H and G).
Abstract: The main components of the energy balance are net radiation, latent heat flux (LE), sensible heat flux (H) and soil heat flux (G). These can be manipulated through changes in net radiation, LE, H or G. The relative importance of the components depends mainly on the availability of water for evaporation. The extreme cases will be the humid environment (LE approaches Rn) and the desert environment (Rn is partitioned between H and G). The energy balance of farming (energy produced per unit energy consumed in all farming operations) may be also analyzed in terms of inputs and outputs which can be estimated by assessing the energy embodied in the amount of materials employed (fertilizers, water, seeds) and in the operations performed.
TL;DR: In this article, a numerical study with parallel simulations using the fully coupled meteorology-chemistry model WRF-Chem with a high-resolution emission inventory for agricultural fires was conducted to explore the underlying processes that link air pollution to weather modification.
Abstract: . Biomass burning is a main source for primary carbonaceous particles in the atmosphere and acts as a crucial factor that alters Earth's energy budget and balance. It is also an important factor influencing air quality, regional climate and sustainability in the domain of Pan-Eurasian Experiment (PEEX). During the exceptionally intense agricultural fire season in mid-June 2012, accompanied by rapidly deteriorating air quality, a series of meteorological anomalies was observed, including a large decline in near-surface air temperature, spatial shifts and changes in precipitation in Jiangsu province of East China. To explore the underlying processes that link air pollution to weather modification, we conducted a numerical study with parallel simulations using the fully coupled meteorology–chemistry model WRF-Chem with a high-resolution emission inventory for agricultural fires. Evaluation of the modeling results with available ground-based measurements and satellite retrievals showed that this model was able to reproduce the magnitude and spatial variations of fire-induced air pollution. During the biomass-burning event in mid-June 2012, intensive emission of absorbing aerosols trapped a considerable part of solar radiation in the atmosphere and reduced incident radiation reaching the surface on a regional scale, followed by lowered surface sensible and latent heat fluxes. The perturbed energy balance and re-allocation gave rise to substantial adjustments in vertical temperature stratification, namely surface cooling and upper-air heating. Furthermore, an intimate link between temperature profile and small-scale processes like turbulent mixing and entrainment led to distinct changes in precipitation. On the one hand, by stabilizing the atmosphere below and reducing the surface flux, black carbon-laden plumes tended to dissipate daytime cloud and suppress the convective precipitation over Nanjing. On the other hand, heating aloft increased upper-level convective activity and then favored convergence carrying in moist air, thereby enhancing the nocturnal precipitation in the downwind areas of the biomass-burning plumes.
TL;DR: In this article, a conceptual energy storage system design that utilizes ultra high temperature phase change materials is presented, where the energy is stored in the form of latent heat and converted to electricity upon demand by TPV (thermophotovoltaic) cells.
TL;DR: In this article, the authors demonstrate a simple method to nanoencapsulate magnesium nitrate hexahydrate, employing in situ miniemulsion polymerization with ethyl-2-cyanoacrylate as the monomer.
Abstract: Thermal energy storage has many important applications and is most efficiently achieved by latent heat storage using phase change materials (PCMs). Salt hydrates have advantages such as high energy storage density, high latent heat and incombustibility. However, they suffer from drawbacks such as incongruent melting and corrosion of metallic container materials. By encapsulating them in a polymer shell, problems can be eliminated. Here we demonstrate a simple method to nanoencapsulate magnesium nitrate hexahydrate, employing in situ miniemulsion polymerisation with ethyl-2-cyanoacrylate as the monomer. Using sonication to prepare miniemulsions improved the synthesis by reducing the amount of surfactant required as the stabiliser. The thermal properties were analysed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Fourier transform infrared spectroscopy (FTIR) was employed to prove the presence of salt hydrate within the nanocapsules. The results show that the capsules are 100–200 nm in size, have salt hydrate located in the core and are stable over at least 100 thermal cycles with only a 3% reduction in latent heat. Supercooling is also drastically reduced. To the best of our knowledge, this is the first time that an encapsulated salt hydrate PCM has been proven to have a lifetime of 100+ heat uptake/release cycles.
TL;DR: In this article, the heat transfer rate enhancement caused by natural convection of solid-liquid phase change materials undergoing melting is quantified based on experimental observations and a heat transfer enhancement factor and an effective heat transfer coefficient were developed.
TL;DR: In this paper, a shell-and-tube latent heat thermal energy storage (LHTES) system is built using the eutectic molten salt as the phase change material (PCM) to make an efficient use of solar energy at medium-temperature of around 200.0°C.
TL;DR: In this article, the transient response of packed bed latent heat thermal energy storage system in removing fluctuations in the heat transfer fluid (HTF) temperature during the charging and discharging period is presented.
TL;DR: In this paper, the authors investigated the contribution of synoptic-scale waves and their attendant atmospheric rivers to the tropically excited Arctic warming (TEAM) mechanism and showed that localized tropical convection over the Maritime Continent precedes the peak of the planetary-scale wave life cycle by ~10-14 days.
Abstract: Heretofore, the tropically excited Arctic warming (TEAM) mechanism put forward that localized tropical convection amplifies planetary-scale waves, which transport sensible and latent heat into the Arctic, leading to an enhancement of downward infrared radiation and Arctic surface warming. In this study, an investigation is made into the previously unexplored contribution of the synoptic-scale waves and their attendant atmospheric rivers to the TEAM mechanism. Reanalysis data are used to conduct a suite of observational analyses, trajectory calculations, and idealized model simulations. It is shown that localized tropical convection over the Maritime Continent precedes the peak of the planetary-scale wave life cycle by ~10–14 days. The Rossby wave source induced by the tropical convection excites a Rossby wave train over the North Pacific that amplifies the climatological December–March stationary waves. These amplified planetary-scale waves are baroclinic and transport sensible and latent heat pol...
TL;DR: In this paper, a comprehensive analysis of SA relevant properties for TES has been carried out in order to select the most appropriate single SA for mixtures analysis, and four eutectic mixtures with potential for long-term TES at temperature around 80°C have been identified.
TL;DR: In this article, a simple shell and tube heat exchanger provides a straightforward design for near-term integration of latent heat thermal energy storage (LHTES) systems in concentrated solar thermal-tower (CST-tower) plants, but currently there is no literature available for this configuration in the 286-565°C temperature range.
TL;DR: In this paper, a lattice Boltzmann method (LBM) was used to simulate conjugate convective heat transfer with phase change in the solid walls, fins and PCM region.
TL;DR: In this article, the design of elastocaloric cooling system driven by hydraulic actuators is presented, where Ni-Ti tubes under axial compressive loading mode are used in the system to provide cooling and heating.
Abstract: This article presents the design of elastocaloric cooling system driven by hydraulic actuators. Ni-Ti tubes under axial compressive loading mode are used in the system to provide cooling and heating. Those Ni-Ti tubes are enclosed in four identical beds, which are driven by two one-way hydraulic cylinders. Operated under the single-stage reverse Brayton cycle, the system achieves heat transfer and heat recovery by using a sophisticated heat transfer fluid network controlled by solenoid valves. Two novel designs to improve the system's performance based on the lessons learned from the previous studies are applied to this prototype. Preliminary test results of the material's latent heat at a specific fluid flow rate and temperature difference agree well with the results reported in the literature. System coefficient of performance of 11.0 and temperature lift of 24.6 K are estimated based on a dynamic model developed in the previous study.
TL;DR: In this article, three different types of paraffin are tested as phase change material (PCM) and water is used as heat transfer fluid (HTF), and the effects of inlet temperature of HTF, flow rate of water and the type of PCM used on the time for charging and discharging heat are discussed.
Abstract: The thermal energy storage is very important because it provides the solution to problems related between the provided and the required energies. This work presents the experimental study of a PCM storage unit for storing latent heat thermal energy. Three different types of paraffin are tested as phase change material (PCM) and water is used as heat transfer fluid (HTF). The temperatures of PCM and HTF, solid fraction and thermal effectiveness are analyzed. The effects of inlet temperature of HTF, flow rate of HTF and the type of PCM used on the time for charging and discharging heat are discussed. The following conclusion can be drawn: (1) HTF flow rate does not have a great effect on the discharging phase compared to the charging phase. (2) Inlet temperature has a great effect on the exchanger performance. It can accelerate charging phase 54.5% and delay the discharging phase by 48.5%. (3) Adding the oil engine to the paraffin can improve the speed of the charging and discharging heat process by 42.4 and 66%, respectively. However, the latent heat of the PCM is considerably reduced.
TL;DR: In this paper, a coupled model is proposed to identify the effects of in-pore transport of liquid water and water vapor as well as phase changes on the hygrothermal behavior of earthen buildings.
TL;DR: In this article, the authors quantified its magnitude, decadal change, and its contribution to the water balance changes in Lake Nam Co, one of the largest lakes on the Tibetan Plateau (with an area of approximately 2000 km2 and a mean depth of approximately 40 m).
Abstract: Most lakes in the interior Tibetan Plateau have expanded rapidly since the late 1990s. Because of a lack of observations, lake water balances and their changes are far from well understood. Evaporation is a component of the lake water balance, and this study quantifies its magnitude, decadal change, and its contribution to the water balance changes in Lake Nam Co, one of the largest lakes on the Tibetan Plateau (with an area of approximately 2000 km2 and a mean depth of approximately 40 m). The lake temperature and the evaporation are simulated by the Flake model. The simulation results are validated against observed lake temperature profile from 2013 and Moderate Resolution Imaging Spectroradiometer lake surface temperature data from 2000 to 2014. The simulated latent heat flux and sensible heat flux are validated against Bowen ratio-derived estimates for 2013. Based on the validated simulation results, the long-term mean annual evaporation is approximately 832 ± 69 mm, and this value is much less than the potential evaporation estimated using the Penman-Monteith equation. The annual evaporation from 1980 to 2014 displays a complex decadal oscillation, mainly due to the changes in energy-related terms (air temperature and radiation). The mean lake evaporation since the late 1990s is greater than previous periods; thus, this change in evaporation has suppressed the recent expansion of Nam Co.
TL;DR: In this paper, the authors systematically screened all polymers available on a large-scale, selected promising ones based on their theoretical properties and experimentally tested more than 50 candidates and found that polyethylene, polyoxymethylene and polyamides are promising even as recycled material.
TL;DR: In this paper, the side and bottom walls of five parallel microchannels were structured with nanowires in a silicon chip to promote thin film evaporation and nucleate boiling, and the wall temperatures were measured from adiabatic condition to critical heat flux (CHF) conditions.