Showing papers on "Latent heat published in 2019"

The FLUXCOM ensemble of global land-atmosphere energy fluxes

Abstract: Although a key driver of Earth’s climate system, global land-atmosphere energy fluxes are poorly constrained. Here we use machine learning to merge energy flux measurements from FLUXNET eddy covariance towers with remote sensing and meteorological data to estimate global gridded net radiation, latent and sensible heat and their uncertainties. The resulting FLUXCOM database comprises 147 products in two setups: (1) 0.0833° resolution using MODIS remote sensing data (RS) and (2) 0.5° resolution using remote sensing and meteorological data (RS + METEO). Within each setup we use a full factorial design across machine learning methods, forcing datasets and energy balance closure corrections. For RS and RS + METEO setups respectively, we estimate 2001–2013 global (±1 s.d.) net radiation as 75.49 ± 1.39 W m−2 and 77.52 ± 2.43 W m−2, sensible heat as 32.39 ± 4.17 W m−2 and 35.58 ± 4.75 W m−2, and latent heat flux as 39.14 ± 6.60 W m−2 and 39.49 ± 4.51 W m−2 (as evapotranspiration, 75.6 ± 9.8 × 103 km3 yr−1 and 76 ± 6.8 × 103 km3 yr−1). FLUXCOM products are suitable to quantify global land-atmosphere interactions and benchmark land surface model simulations. Machine-accessible metadata file describing the reported data (ISA-Tab format)

Augmenting the productivity of solar still using multiple PCMs as heat energy storage

Abstract: In recent years, several research studies were conducted to enhance the productivity of solar stills. One of the approaches was the integration of latent heat energy storage mediums (phase change materials (PCM)) in the conventional solar stills to extend the water yield ability after the sunshine hours. Though several studies were conducted in this research area, none of the studies analyzed and reported the time of day at which the PCM start to release the stored latent heat, especially in the case of use of multiple PCMs. The present study is an experimental investigation that compare the thermal performance of three same-sized passive solar stills, i.e., conventional solar still (Still 1), still with single phase change material (Still II), still with two phase change materials (Solar III). The two PCMs used in still III are chosen in such a way that both the PCMs have almost same latent heat storage capacity, but different phase change temperature range. PCM1 and PCM2 used in solar still III have the phase change temperature (PCT) range of 58.03 °C–64.5 °C and 53.05 °C–62 °C, respectively. The experiments were conducted for the climatic conditions of Chennai, India during the month of February to May. The major inference from the experiments conducted is that, when multiple PCMs are employed in a still, selection of PCM with appropriate PCT range is very important. PCM1 should start discharging the stored latent heat energy stored once the solar radiation gets diminishing and PCM2 should start to release the heat when PCM1 has almost discharged the entire stored energy. By this way, the time of yield can be prolonged. In the results, the thermal performance of Still I, II and III was analyzed in terms of hourly yield per day and exergy efficiency. The yield of Still I was 3.680 L/m2/day while the yield of Still II and III were 4.020 L/m2/day and 4.400 L/m2/day, respectively. The exergy efficiency of still I, II and III were found to be 3.92%, 3.23% and 3.52%, respectively.

Air-Sea Fluxes With a Focus on Heat and Momentum

Abstract: Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m-2 and a bias of less than 5 W m-2. At present this accuracy target is met only at OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500 - 1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1 - 3 measurement platforms in each nominal 10° by 10° boxes. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean’s influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.

Magnetically-accelerated large-capacity solar-thermal energy storage within high-temperature phase-change materials

Abstract: Solar-thermal energy storage within phase change materials (PCMs) can overcome solar radiation intermittency to enable continuous operation of many important heating-related processes. The energy harvesting performance of current storage systems, however, is limited by the low thermal conductivity of PCMs, and the thermal conductivity enhancement of high-temperature molten salt-based PCMs is challenging and often leads to reduced energy storage capacity. Here, we demonstrate that magnetically moving mesh-structured solar absorbers within a molten salt along the solar illumination path significantly accelerates solar-thermal energy storage rates while maintaining 100% storage capacity. Such a magnetically-accelerated movable charging strategy increases the latent heat solar-thermal energy harvesting rate by 107%, and also supports large-area charging and batch-to-batch solar-thermal storage. The movable charging system can be readily integrated with heat exchanging systems to serve as energy sources for water and space heating by using abundant clean solar-thermal energy.

Enhancement of solidification rate of latent heat thermal energy storage using corrugated fins

Abstract: Latent heat thermal energy storage (LHTES) is considered one of the most promising thermal energy storage technologies. The main disadvantage of LHTES is the low thermal conductivity of the phase change material (PCM). Finned tubes are commonly used to improve heat transfer in LHTES. This study aims to gain a better understanding of how curving or branching the fins affects the fins’ performance and effectiveness. This paper investigates the use of longitudinal corrugated fins in enhancing the solidification rate of the PCM located in the annular area between two concentric tubes. The impact of both the number of corrugations per fin and the corrugation height was investigated using numerical modeling. The results showed that the novel corrugated fin configurations reduced the solidification time compared to straight fins due to the increase of the fins length. However, the effectiveness of the corrugated fins was generally lower than that of straight fins.

Analytical Modeling of In-Process Temperature in Powder Bed Additive Manufacturing Considering Laser Power Absorption, Latent Heat, Scanning Strategy, and Powder Packing.

Abstract: Temperature distribution gradient in metal powder bed additive manufacturing (MPBAM) directly controls the mechanical properties and dimensional accuracy of the build part. Experimental approach and numerical modeling approach for temperature in MPBAM are limited by the restricted accessibility and high computational cost, respectively. Analytical models were reported with high computational efficiency, but the developed models employed a moving coordinate and semi-infinite medium assumption, which neglected the part dimensions, and thus reduced their usefulness in real applications. This paper investigates the in-process temperature in MPBAM through analytical modeling using a stationary coordinate with an origin at the part boundary (absolute coordinate). Analytical solutions are developed for temperature prediction of single-track scan and multi-track scans considering scanning strategy. Inconel 625 is chosen to test the proposed model. Laser power absorption is inversely identified with the prediction of molten pool dimensions. Latent heat is considered using the heat integration method. The molten pool evolution is investigated with respect to scanning time. The stabilized temperatures in the single-track scan and bidirectional scans are predicted under various process conditions. Close agreements are observed upon validation to the experimental values in the literature. Furthermore, a positive relationship between molten pool dimensions and powder packing porosity was observed through sensitivity analysis. With benefits of the absolute coordinate, and high computational efficiency, the presented model can predict the temperature for a dimensional part during MPBAM, which can be used to further investigate residual stress and distortion in real applications.