Latent heat

About: Latent heat is a research topic. Over the lifetime, 13503 publications have been published within this topic receiving 302811 citations.

Energy balance closure at ChinaFLUX sites

Abstract: Network of eddy covariance observation is measuring long-term carbon and water fluxes in contrasting ecosystems and climates. As one important reference of independently evaluating scalar flux estimates from eddy covariance, energy balance closure is used widely in study of carbon and water fluxes. Energy balance closure in ChinaFLUX was evaluated by statistical regression of turbulent energy fluxes (sensible and latent heat) against available energy (net radiation, soil heat flux, canopy heat storage) and the energy balance ratio (EBR) and the frequency distribution of relative errors of energy balance (δ). The trends of diurnal and seasonal variation of energy balance in ChinaFLUX were analyzed. The results indicated that the imbal-ance was prevalent in all observation sites, but there were little differences among sites because of the properties variation of sites. The imbalance was greater during nocturnal periods than daytime and closure was improved with friction velocity intensifying. Generally the results sug-gested that estimates of the scalar turbulent fluxes of sensible and latent heat were underesti-mated and/or that available energy was overestimated. Finally, we discussed certain factors that are contributed to the imbalance of energy, such as systematic errors associated with the sam-pling mismatch, systematic instrument bias, neglected energy sinks, low and high frequency loss of turbulent fluxes and advection of heat and water vapor.

SSiB and its sensitivity to soil properties-A case study using HAPEX-Mobilhy data

Abstract: LSIE Global and Planetary Change 13 (1996) 183-194 GLEIBAL AND PLANETARY CHANGE SSiB and its sensitivity to soil properties-—a case study using HAPEX-Mobilhy data Yonglcang Xue 3’, Fanrong J. Zeng 3, C. Adam Schlosser '3 E Center firtr 0c*ean—Lond—Annrr.tphere .S:nrJies', 40-=H Powder Mitt Road, Suite 302, Coloerton. MD 2t'J?U5, USA q' Geophy.stt'df Fluid Dynomt'c.s Laboratory. Frfnc'eton, .vr oases. use Received 5 May 1995: accepted 23 Au gust 1995 Abstract In this paper, SSiB’s development and some of its major parameterizations in the model are briefly reviewed. The soil moisture parameterizations, which are a key element in the model, are comprehensively described. The sensitivity study shows that hydraulic conductivity at saturation, B parameter, and wilting point have a profound impact on the simulation of soil moisture, but with different features. Both hydraulic conductivity at saturation and B parameter influence the soil moisture simulation by changing the soil hydraulic conductivity and the field capacity. The changes in equilibrium soil water content in this study are consistent with the changes in field capacity. The wilting point affects the soil moisture through vegetation transpiration. Through these sensitivity studies, improvements in modeling the soil moisture content of HAPEX—Mobilhy data are made. The soil moisture simulations at six Russian sites are also re-examined. After applying the results from the sensitivity studies of the HAPEX—Mobilhy data, the soil moisture simulation of the Russian data is significantly improved. 1. Introduction The SSiB biosphere model (Xue et al., 1991) used in this study is a simplified version of the Simple Biosphere Model (SiB) (Sellers et al., 1986). The vegetation—soil layer affects the radiative transfer at the surface, the partitioning of surface energy into sensible heat flux and latent heat flux. SSiB is intended to realistically simulate the biophysical ex- change processes. The biophysical controls on these exchange processes are mutually consistent by mod- eling the vegetation explicitly. The biosphere model is linked to a general circulation model (GCM) of the atmosphere through fluxes of radiation, sensible and latent heat, and momentum. A coupled biosphere model—GCM has been shown to be an improvement over the “bucket” model for simulations of the hydrologic cycle and the surface energy partition (Sato et al., 1989). To apply the coupled biosphere model—GCM for extended-range prediction and climate studies, we reduced vegetation and soil parameters from SiB. The values of many of the parameters are scarce for different biornes in different parts of the world. Large number of parameters with only approxi— mately known values would matte the sensitivity testing and model validation difficult. Our studies found some vegetation and soil parameters have little effects in the long term GCM simulations. We also used one canopy layer in the SSiB. The multilayer model is more realistic and might be easier to com- pare with the observations over a single site, but it U921-Slfll/96/$l5.DU @ 1996 Elsevier Science a.v. All rights reserved SSDI U921-S] 3l{95}DU{}45-3

Melting of PCM in a thermal energy storage unit: Numerical investigation and effect of nanoparticle enhancement

Abstract: SUMMARY The present paper describes the analysis of the melting process in a single vertical shell-and-tube latent heat thermal energy storage (LHTES), unit and it is directed at understanding the thermal performance of the system. The study is realized using a computational fluid-dynamic (CFD) model that takes into account of the phase-change phenomenon by means of the enthalpy method. Fluid flow is fully resolved in the liquid phase-change material (PCM) in order to elucidate the role of natural convection. The unsteady evolution of the melting front and the velocity and temperature fields is detailed. Temperature profiles are analyzed and compared with experimental data available in the literature. Other relevant quantities are also monitored, including energy stored and heat flux exchanged between PCM and HTF. The results demonstrate that natural convection within PCM and inlet HTF temperature significantly affects the phase-change process. Thermal enhancement through the dispersion of highly conductive nanoparticles in the base PCM is considered in the second part of the paper. Thermal behavior of the LHTES unit charged with nano-enhanced PCM is numerically analyzed and compared with the original system configuration. Due to increase of thermal conductivity, augmented thermal performance is observed: melting time is reduced of 15% when nano-enhanced PCM with particle volume fraction of 4% is adopted. Similar improvements of the heat transfer rate are also detected. Copyright © 2012 John Wiley & Sons, Ltd.