Terms Of Energy Flux Research Articles

Energy efficient surfaces on building sandwich panels—A dynamic simulation model

The choice of building envelope is critical for the energy performance of buildings. The major part of the energy used by a building during its lifetime is used for maintaining a suitable interior thermal climate under varying exterior conditions. Although exterior heat radiation properties (i.e. total solar reflectivity and long wave thermal emissivity) have been well accepted to have a large impact on the need for active cooling in warmer climate, the effect of a reduced thermal emissivity on interior surfaces on the building thermal energy flux is rarely studied. This paper addresses the sensitivity of the thermal energy flux through a sandwich panel, by systematically varying the surface thermal emissivity (both interior and exterior) and total solar reflectance of exterior surface, for three geographical locations: southern, middle and northern Europe. A model is introduced for calculating the effect of both interior and exterior optical properties of a horizontal roof panel in terms of net energy flux per unit area. The results indicate potential energy saving by the smart choice of optical properties of interior and exterior surfaces.

OBSERVATIONAL LIMITS ON THE SPIN-DOWN TORQUE OF ACCRETION POWERED STELLAR WINDS

The rotation period of classical T Tauri stars (CTTS) represents a longstanding puzzle. While young low-mass stars show a wide range of rotation periods, many CTTS are slow rotators, spinning at a small fraction of break-up, and their rotation period does not seem to shorten, despite the fact that they are actively accreting and contracting. Matt & Pudritz (2005) proposed that the spin-down torque of a stellar wind powered by a fraction of the accretion energy would be strong enough to balance the spin-up torque due to accretion. Since this model establishes a direct relation between accretion and ejection, the observable stellar parameters (mass, radius, rotation period, magnetic field) and the accretion diagnostics (accretion shock luminosity), can be used to constraint the wind characteristics. In particular, since the accretion energy powers both the stellar wind and the shock emission, we show in this letter how the accretion shock luminosity L_UV can provide upper limits to the spin-down efficiency of the stellar wind. It is found that luminous sources with L_UV > 0.1 L_Sun and typical dipolar field components < 1 kG do not allow spin equilibrium solutions. Lower luminosity stars (L_UV < 0.1 L_Sun) are compatible with a zero-torque condition, but the corresponding stellar winds are still very demanding in terms of mass and energy flux. We therefore conclude that accretion powered stellar winds are unlikely to be the sole mechanism to provide an efficient spin-down torque for accreting classical T Tauri stars.

Eddy damped quasinormal Markovian simulations of superfluid turbulence in helium II

A two fluid (the normal fluid and the superfluid) spectral model based on the HVBK equations is used to compute the energy spectra of developed turbulence in superfluid helium (helium II) at different temperatures and different values of mutual friction coefficients, looking for both asymptotic and realistic helium II solutions. An original computational model is proposed, based on the model suggested by L’vov, Nazarenko, and Skrbek [JLTP 145, 125 (2006)] for mutual friction term and an eddy damped quasinormal Markovian closure for the energy flux term. On the one hand, the four asymptotic solutions predicted by theoretical analysis are confirmed. On the other hand, we present results for normal and superfluid energy spectra in realistic cases using experimental values of the mutual friction coefficients corresponding to helium II. Good qualitative agreement in the small scale range is found with the direct numerical simulation results obtained by Roche, Barenghi, and Leveque [Europhys. Lett. 87, 54006 (2009)].

An open system framework for integrating critical zone structure and function

The ''critical zone'' includes the coupled earth surface systems of vegetation, regolith and groundwater that are essential to sustaining life on the planet. The function of this zone is the result of complex interactions among physical, chemical and biological processes and understanding these interac- tions remains a major challenge to earth system sciences. Here we develop an integrated framework based on thermodynamic theory to characterize the critical zone as a system open to energy and mass fluxes that are forced by radiant, geochemical, and elevational gradients. We derive a statement that demonstrates the relative importance of solar radia- tion, water, carbon, and physical/chemical denudation mass fluxes to the critical zone energy balance. Within this framework we use rates of effective energy and mass transfer (EEMT; W m -2 ) to quantify the relevant flux-gradient relations. Synthesis of existing data demonstrates that variation in energetics associ- ated with primary production and effective precipita- tion explains substantial variance in critical zone structure and function. Furthermore, we observe threshold behavior in systems that transition to primary production predominance of the energy flux term. The proposed framework provides a first order approximation of non-linearity in critical zone pro- cesses that may be coupled with physical and numerical models to constrain landscape evolution.

Free surface, current profile and buoyancy effects upon internal wave energy flux profiles in sill regions

A non-hydrostatic ocean circulation model is used to determine the distribution of the horizontal energy flux terms due to internal waves in sill regions. Calculations show that although the linear energy flux term is significant, the contribution from the non-linear terms is appreciable. In addition, unlike as is often assumed in deep ocean situations, the free surface contribution to the energy flux distribution often dominates. The magnitude and relative importance of the energy flux terms are influenced by how the fluctuating velocity due to internal waves is computed. In addition changes in vertical stratification affects the relative contribution of the energy flux terms although the free surface term still dominates.

SWarm: A simple regression model to estimate near-surface snowpack warming for back-country avalanche forecasting

Daytime warming in near-surface snowpack layers occurs as a result of short wave radiation penetrating the top portion of the snowpack. While there is some understanding of diurnal temperature fluctuations and their effects on snowpack stability, quantified estimates of their magnitude are not readily available to avalanche forecasters in western Canada. During the winters of 2005 and 2006, near-surface temperatures were measured on a knoll located in the Columbia Mountains of British Columbia. The field dataset was used to develop a near-surface warming model, based on linear regression analysis of predictor variables derived from surface energy flux terms. To facilitate use in large forecast areas where representative meteorological data are typically scarce, consideration was given to the availability of input data. In this dataset, a variable based on daily maximum incoming short wave radiation proved to be the only significant predictor of near-surface daytime warming. Based on slope, aspect, expected cloud cover and number of days since snowfall, the model predicts the magnitude of daytime warming, in a below freezing snowpack, 10 cm below the snow surface with an estimated root mean square error of 1.6 °C.

A control volume derivation of the energy equation for LII modeling

This paper considers the unsteady energy equation for a particle undergoing processes relevant to laser-induced incandescence. The energy equation is derived using both an integral control volume formalism and a differential approach. Confusion in the previous literature over the form of the energy equation is traced to the evaluation of the energy flux terms to and from the particle surface. Terms such as the heat of sublimation or heat of combustion are shown to arise naturally in both the control volume and differential derivations. Problems associated with the confusion regarding the flux terms resulting in incorrect energy equations are also identified.

A new framework for isolating individual feedback processes in coupled general circulation climate models. Part I: formulation

This paper proposes a coupled atmosphere–surface climate feedback–response analysis method (CFRAM) as a new framework for estimating climate feedbacks in coupled general circulation models with a full set of physical parameterization packages. The formulation of the CFRAM is based on the energy balance in an atmosphere–surface column. In the CFRAM, the isolation of partial temperature changes due to an external forcing or an individual feedback is achieved by solving the linearized infrared radiation transfer model subject to individual energy flux perturbations (external or due to feedbacks). The partial temperature changes are addable and their sum is equal to the (total) temperature change (in the linear sense). The decomposition of feedbacks is based on the thermodynamic and dynamical processes that directly affect individual energy flux terms. Therefore, not only those feedbacks that directly affect the TOA radiative fluxes, such as water vapor, clouds, and ice-albedo feedbacks, but also those feedbacks that do not directly affect the TOA radiation, such as evaporation, convections, and convergence of horizontal sensible and latent heat fluxes, are explicitly included in the CFRAM. In the CFRAM, the feedback gain matrices measure the strength of individual feedbacks. The feedback gain matrices can be estimated from the energy flux perturbations inferred from individual parameterization packages and dynamical modules. The inter-model spread of a feedback gain matrix would help us to detect the origins of the uncertainty of future climate projections in climate model simulations.

Energy and pseudoenergy flux in the internal wave field generated by tidal flow over topography

The mechanical energy and pseudoenergy budgets in the internal wave field generated by tidal flow over topography is considered using a nonlinear, two-dimensional numerical model. The Boussinesq and rigid lid approximations are made, viscosity and diffusion are ignored and the flow is treated as incompressible. Both ridge and bank edge topographies are considered. The nonlinear energy equation and an equation for pseudoenergy (kinetic energy plus available potential energy) are satisfied to within less than 1%. For a uniform stratification (constant buoyancy frequency N) the available potential energy density is identical to the linear potential energy density 1 2 ( g 2 / N 2 ) ρ ˜ d 2 where ρ ˜ d is the density perturbation. For weak tidal flow over a ridge in the deep ocean, using a uniform stratification, the generated waves are small, approximately 2% of the water depth, and the traditional expression for the energy flux, 〈 u ˜ p ˜ d 〉 accurately gives the pseudoenergy flux. For a case with strong tidal flow across a bank edge, using a non-uniform stratification, large internal solitary waves are generated. In this case, the linear form of the potential energy is very different from the available potential energy and the traditional energy flux term 〈 u ˜ p ˜ d 〉 accounts for only half of the pseudoenergy flux. Fluxes of kinetic and available potential energy are comparable to the traditional energy flux term and hence must be included when estimating energy fluxes in the internal wave field.

Influences of biomass heat and biochemical energy storages on the land surface fluxes and radiative temperature

The interest of this study was to develop an initial assessment on the potential importance of biomass heat and biochemical energy storages for land‐atmosphere interactions, an issue that has been largely neglected so far. We conducted flux tower observations and model simulations at a temperate deciduous forest site in central Missouri in the summer of 2004. The model used was the comprehensive terrestrial ecosystem Fluxes and Pools Integrated Simulator (FAPIS). We first examined FAPIS performance by testing its predictions with and without the representation of biomass energy storages against measurements of surface energy and CO2 fluxes. We then evaluated the magnitudes and temporal patterns of the biomass energy storages calculated by FAPIS. Finally, the effects of biomass energy storages on land‐atmosphere exchanges of sensible and latent heat fluxes and variations of land surface radiative temperature were investigated by contrasting FAPIS simulations with and without these storage terms. We found that with the representation of the two biomass energy storage terms, FAPIS predictions agreed with flux tower measurements fairly well; without the representation, however, FAPIS performance deteriorated for all predicted surface energy flux terms although the effect on the predicted CO2 flux was minimal. In addition, we found that the biomass heat storage and biochemical energy storage had clear diurnal patterns with typical ranges from −50 to 50 and −3 to 20 W m−2, respectively; these typical ranges were exceeded substantially when there were sudden changes in atmospheric conditions. Furthermore, FAPIS simulations without the energy storages produced larger sensible and latent heat fluxes during the day but smaller fluxes (more negative values) at night as compared with simulations with the energy storages. Similarly, without‐storage simulations had higher surface radiative temperature during the day but lower radiative temperature at night, indicating that the biomass energy storages act to dampen the diurnal temperature range. From these simulation results, we concluded that biomass heat and biochemical energy storages are an integral and substantial part of the surface energy budget and play a role in modulating land surface temperatures and must be considered in studies of land‐atmosphere interactions and climate modeling.

GENERALIZATIONS OF THE ENERGY-FLUX PARABOLIC EQUATION

Parabolic equations written in terms of energy flux are inherently immune to the problem of energy conservation at vertical interfaces. Mikhin [J. Comp. Acoust. 9 (2001) 183–203] achieved exact reciprocity and energy conservation in a finite-difference PE model following this approach. However, his model used the implicit Crank–Nicolson scheme in range that requires a small range step for accurate solution. The present paper generalizes the exponential propagator of Collins [J. Acoust. Soc. Am. 93 (1993) 1736–1742] to solve the energy-flux PE. The obtained solution remains strictly reciprocal and energy conserving, while allowing large range steps. The numerical efficiency is improved by one or two orders of magnitude. A technique is proposed to calculate the acoustic pressure within the large steps, so the solution combines fast advance in range with dense range sampling. Numerical examples are provided.

Relationships among canopy scale energy fluxes and isoprene flux derived from long-term, seasonal eddy covariance measurements over a hardwood forest

The flux of isoprene, one of the more reactive biogenic volatile organic compounds, was measured using eddy covariance techniques on a continuous basis during the 2000–2002 growing seasons at a mixed hardwood forest in northern lower MI. Daytime fluxes of isoprene and both sensible ( H) and latent heat flux (LE) were linearly correlated with a positive slope on a daily basis, but the slopes of these relationships varied from one day to the next. Under drought conditions and longer time periods, LE fluxes were suppressed yet isoprene emissions were enhanced; thus, the slope of the isoprene to LE relationship was increased. For example, seasonally averaged LE fluxes were reduced in 2000 as a result of reduced rainfall, and average isoprene fluxes were 1.5 times greater in 2000 compared to years 2001 and 2002. The strong daily correlation between isoprene fluxes and associated energy fluxes is an important relationship that should be accurately reflected in canopy models used for estimating biogenic emissions. In addition, in cases where land surface model output includes latent heat fluxes, the latent heat fluxes may be used as a surrogate for above canopy light and temperature to provide a simple estimate of isoprene emissions. Observed isoprene fluxes are compared to the Biogenic Emission Inventory System (BEIS3) biogenic emission model and to a canopy scale biogenic emission model (WSU-BEIS) that includes a leaf energy budget and accounts for vertical changes in light and temperature through the canopy. Comparison of the emission models with observations showed that the fractional gross errors in isoprene flux estimates were approximately 37% for both models in 2001 and 2002, but increased to approximately 62% in 2000 when less rain occurred and LE fluxes were reduced. The BEIS3 model does not treat sensible or latent heat flux, but the simple scaling and leaf energy budget used in WSU-BEIS yields estimates of LE within approximately 50% of observations. Estimates of sensible heat flux with WSU-BEIS were larger than observed and indicate that the simple scaling approach may not be capable of treating all of the dynamics of canopy energy transfer accurately. Nonetheless, the strong relationships observed between isoprene flux and the energy flux terms provide a basis for testing these and other canopy models used for estimates of biogenic emissions.

Nonhydrostatic and nonlinear contributions to the energy flux budget in nonlinear internal waves

We use high‐resolution two‐dimensional simulations to model the generation and evolution of nonlinear internal waves formed as a result of the interaction of a first‐mode internal wave field with idealized slopes. The derivation of the energy equation and the energy flux terms are presented. By employing an analysis of the distribution of the energy flux across the shelf break, we quantify the contributions to the energy flux budget from nonhydrostatic as well as nonlinear effects in comparison to the contribution from the baroclinic pressure anomaly term used widely for linear internal waves. Our results show that the contributions to the total energy flux from these additional terms are significant in these large nonlinear internal waves, consistent with recent field observations.

Decomposition of the spatially filtered and ensemble averaged kinetic energy, the associated fluxes and scaling trends in a rotor wake

Particle image velocimetry data obtained in the rotor wake of a turbomachine are used for examining elements of the ensemble averaged and spatially filtered kinetic energy. These two distinct averaging processes decompose the kinetic energy into four parts, consisting of the mean-flow resolved, mean-flow subgrid, fluctuating resolved, and fluctuating subgrid parts. Their evolution equations include energy flux terms among these parts. The results elucidate the fundamental difference between the filtered turbulence (Reynolds) production and the ensemble averaged subgrid scale (SGS) dissipation rates. Each of these terms consist of three energy fluxes, but only one of them is common to both, the flux from the mean-flow resolved to the fluctuating subgrid kinetic energy parts. The other two elements of the SGS dissipation are the fluxes from the mean-flow resolved to the mean-flow subgrid parts and the fluctuating resolved to the fluctuating subgrid parts. Likewise, the other two contributions to the turbulence production are the fluxes from the mean-flow resolved to the fluctuating resolved parts and the mean-flow subgrid to the fluctuating subgrid parts. In order to examine the decay rates of the kinetic energy parts throughout the rotor wake, a new method for determining the scaling parameters is introduced. The mean-flow resolved and subgrid parts scale with the modified velocity defect squared, but the decay rates of the turbulence parts are slower.

Polarized high-brilliance and high-resolution soft x-ray source at ELETTRA: The performance of beamline BACH

BACH, a soft x-ray beamline for polarization-dependent experiments at the Italian synchrotron radiation facility ELETTRA, was recently completed and characterized. Its performance, in terms of energy resolution, flux and polarization, is presented. Based on two APPLE II undulators, BACH covers the energy range between 35 and 1600 eV with the control of the light polarization. The monochromator is equipped with four gratings and allows one to work either in a high resolution or in a high flux mode. After the monochromator, the beamline is split into two branches with different refocusing properties. One is optimized to exploit the performance of the soft x-ray spectrometer (ComIXS) available at the beamline. Resolving powers between 12000 at 90 eV photon energy and 6600 near 867 eV were achieved using the high-resolution gratings and the smallest available slit width (10 μm). For the high-brilliance grating, which works between 290 and 1600 eV, resolving powers between 7000 at 400 eV and 2200 at 867 eV were obtained. The flux in the experimental chamber, measured with the high-resolution gratings for linearly polarized light at the best achievable resolution, ranges between 4×1011 photons/s at 125 eV and 2×1010 photons/s between 900 and 1250 eV. In circularly polarized mode the flux is two times larger for energies up to 380 eV. A gain of nearly one order of magnitude is obtained for the high-brilliance grating, in accordance with theoretical predictions. Flux beyond 1.3×1011 photons/s was measured up to 1300 eV, and thus over nearly the complete energy range covered by this high-brilliance grating, with a maximum of 1.6×1011 photons/s between 800 and 1100 eV. First results from polarization measurements confirm a polarization above 99.7% for both linearly and circularly polarized modes at low energies. Circular dichroism experiments indicate a circular polarization beyond 90% at the Fe L2/L3 edge near 720 eV.

A STUDY OF THE STRUCTURE, ENERGY FLUXES AND EMERGING TRENDS IN TRADITIONAL CENTRAL HIMALAYAN AGROFORESTRY SYSTEMS

SUMMARY Agroforestry has been practised throughout the central Himalayan region for a very long time. However, the structure of this traditional agroforestry system is more than a simple combination of woody and herbaceous components on the same unit of land. This subsistence strategy has evolved under the constraints and opportunities peculiar to the region, and has permitted the rural folk to thrive in an environment of inherently low productivity. It features interactions among five components: • crop fields • a private land support system (trees in and around crop field) • a forest support system (natural forest around the village, village community forests, etc.) • livestock and • man in the uniquely specific socio-economic-cultural setting of the region. The present study indicates that the private land support system in central Himalaya has become very weak with the passage of time due to the ever increasing human and livestock populations and their associated demands. Although the import of energy into the system amounts to only 6.0% of the total utilized energy, this independence of outside energy sources has been achieved at the cost of envirionmental degradation of species rich forests, soil erosion and silting of reservoirs at about thrice the rate of their designed capacity. The cropping patterns, fodder, firewood and manure fluxes of Siloti and Chanoti villages have been used to exemplify and amplify other data, and describe the agroforestry system in terms of energy fluxes among its different components. The livestock component plays a vital role in linking the other components and maintaining the health of the cropland. Arable crop production is largely at the cost of energy derived from adjacent forests because the private land support component is diminishing. However, as a consequence of the unsustainable drain on the forest component, the survival of the present form of traditional agroforestry system is endangered. To make the system ecologically sound and sustainable, it is essential to revive and increase the tree component in the private land support system even at the expense of agricultural production.

Energy-Conserving and Reciprocal Solutions for Higher-Order Parabolic Equations

The energy conservation law and the flow reversal theorem are valid for underwater acoustic fields. In media at rest the theorem transforms into well-known reciprocity principle. The presented parabolic equation (PE) model strictly preserves these important physical properties in the numerical solution. The new PE is obtained from the one-way wave equation by Godin12 via Pade approximation of the square root operator and generalized to the case of moving media. The PE is range-dependent and explicitly includes range derivatives of the medium parameters. Implicit finite difference scheme solves the PE written in terms of energy flux. Such formalism inherently provides simple and exact energy-conserving boundary condition at vertical interfaces. The finite-difference operators, the discreet boundary conditions, and the self-starter are derived by discretization of the differential PE. Discreet energy conservation and flow reversal theorem are rigorously proved as mathematical properties of the finite-difference scheme and confirmed by numerical modeling. Numerical solution is shown to be reciprocal with accuracy of 10–12 decimal digits, which is the accuracy of round-off errors. Energy conservation and wide-angle capabilities of the model are illustrated by comparison with two-way normal mode solutions including the ASA benchmark wedge.

ENERGY-CONSERVING AND RECIPROCAL SOLUTIONS FOR HIGHER-ORDER PARABOLIC EQUATIONS

The energy conservation law and the flow reversal theorem are valid for underwater acoustic fields. In media at rest the theorem transforms into well-known reciprocity principle. The presented parabolic equation (PE) model strictly preserves these important physical properties in the numerical solution. The new PE is obtained from the one-way wave equation by Godin12 via Padé approximation of the square root operator and generalized to the case of moving media. The PE is range-dependent and explicitly includes range derivatives of the medium parameters. Implicit finite difference scheme solves the PE written in terms of energy flux. Such formalism inherently provides simple and exact energy-conserving boundary condition at vertical interfaces. The finite-difference operators, the discreet boundary conditions, and the self-starter are derived by discretization of the differential PE. Discreet energy conservation and flow reversal theorem are rigorously proved as mathematical properties of the finite-difference scheme and confirmed by numerical modeling. Numerical solution is shown to be reciprocal with accuracy of 10–12 decimal digits, which is the accuracy of round-off errors. Energy conservation and wide-angle capabilities of the model are illustrated by comparison with two-way normal mode solutions including the ASA benchmark wedge.

Mapped discretization strategies for curvilinear adaptively redistributed grids in semiconductor device modeling

We develop numerical solution schemes for semiconductor device models based on mapped discretization strategies and curvilinear, nonuniform grids. Such grids typically arise in adaptive redistribution schemes, and they offer several advantages when gridding irregular domain shapes or resolving complex solution profiles. We consider the hydrodynamic class of equations as a representative model for carrier transport. A mathematical transformation of variables is used to map the device equations from the physical coordinate system to a reference system in which the numerical discretization is performed. We develop a Scharfetter–Gummel type of discretization, formulated in the mapped reference domain, for the current density and energy flux terms in the transport model. The solution of the mapped discrete system is carried out in a fully-coupled, implicit form, and nonsymmetric gradient-type iterative strategies are used for solving the algebraic systems. Numerical results demonstrating the performance of the scheme with and without mesh adaptation are presented for test problems.

Effects of body size on suspension feeding and energy budgets of the pearl oysters Pinctada margaritifera and P. maxima

This study compared suspension feeding, assimilation efficiency, respiration and excretion, and energy budgets (= scope for growth, SFG) in relation to body size in 2 pearl oysters, Pinctada margaritifera and P. maxima, at a low food concentration (ca 5000 cells m1⁻¹ Tahitian Isochrysis galbana). Clearance rate (CR), respiration rate (R) and ammonia excretion rate (E) were strongly correlated with body size (p < 0.001) in both species, with exponents of 0.60 and 0.61 (CR), 0.44 and 0.56 (R), and 0.64 and 0.78 (E), respectively, for P. margaritifera and P. maxima. CR did not differ significantly between the species, but absorption efficiency, which was unrelated to size, was significantly greater in P. maxima (57.5 vs 51%, p < 0.05). There was, however, no significant difference in absorbed energy (AE) between the species. Respired energy (RE) and excreted energy (EE) as proportions of AE were significantly lower (p < 0.01) in P. maxima of 0.1 g dry soft tissue wt (ca 36 mm shell height, SH). The former was 0.36 compared to 0.58 in P. margaritifera of the same size. Thus, P. maxima of 0.1 g dry soft tissue wt exceeded P. margaritifera of the same size in SFG, which accords with the former species' more rapid early growth. Both species of pearl oysters have a high ability to acquire energy under low phytoplankton conditions. Both species are exceptional bivalves in terms of energy fluxes, with clearance rates of 50 to 100 l h⁻¹ in large oysters of 150+ mm SH. They show among the highest CR, R, E and SFG values recorded for bivalves (using 1 g dry soft tissue wt as a standard size). The largest giant clam, Tridacna gigas, is one tropical bivalve with comparable SFG. It, however, is dependent on energy from autotrophy as well as heterotrophy to achieve its high SFG.