Flux Calculations Research Articles

The importance of the soluble and colloidal pools for trace metal cycling in deep-sea pore waters

Physical and chemical trace metal speciation are important for our understanding of metal cycling and potential toxicity to marine life. Trace metals can behave differently in diffusion processes or particle-solution interactions and have different bioavailabilities depending on their physical and chemical forms, which often depend on redox conditions. Here we investigated dissolved (< 0.2 µm) and soluble (< 0.02 µm) concentrations of Mn, Co, Ni, Fe, Cu, V, Mo, U, Cd, and As in oxic and suboxic deep-sea sediments of the central equatorial Pacific Ocean. Vanadium, Mo, U, As, and Cd showed no significant concentration differences between their dissolved and soluble forms, suggesting that they are present as inorganic ionic species or organic complexes in the truly dissolved or small colloidal fraction. In contrast, the colloidal fraction (> 0.02 µm < 0.2 µm) of Mn, Co, Ni, and Cu increased with depth in oxic pore waters and Fe had the largest but variable colloidal pool. Soluble Mn, Co, and Ni were released in the uppermost 2-4 cm in the sediment because of reductive dissolution. The increasing colloidal fraction with depth suggests a decrease in the concentration of small organic ligands with depth, that are abundant in the surface sediment pore waters, and instead an increasing importance of larger (> 0.02 µm) inorganic nanoparticles and colloids such as Mn and Fe (oxyhydr)oxides that control Mn, Fe, and Co cycling at depths > 10 cm. The distribution of Ni and Cu cannot be exclusively explained by inorganic nanoparticles and a shift from low to larger high molecular weight organic ligands might occur. These findings provide new insights into trace metal distributions in the dissolved phase, highlighting the diversity of metal complexes and the need to incorporate these in future calculations of benthic metal fluxes and ecotoxicity assessments, especially in oxic pore waters.

Development and preliminary verification of a 1D–3D coupled flow and heat transfer model of OTSG

Introduction: A simulation model was developed by coupling a one-dimensional (1D) system code and 3D CFD software, to analyze the three-dimensional (3D) flow and heat transfer characteristics of the once-through steam generator (OTSG).Methods: The shell side of the OTSG was simulated by FLUENT, and the tube side was simulated by the system code LOCUST. Through spatial mapping, the 1D and 3D simulations were coupled along the outer wall of the OTSG's helically coiled tubes.Results and Discussion: This coupling method enabled the acquisition of high-resolution flow and heat transfer characteristics of the OTSG, and the error of heat flux calculation result by the coupled model is within 15%. Through coupling simulation analysis of the prototype OTSG, it was found that the inlet and outlet temperature difference reached as high as 150°C. The unevenness of the radial temperature distribution increased along the flow direction, and the wake swing effect caused by the sweeping flow of the tube bundle at the exit position was evident. The results of this study provide reference and a coupled simulation method for the engineering design and thermal-hydraulic characteristics analysis of OTSG.

The GeoCarb greenhouse gas retrieval algorithm: simulations and sensitivity to sources of uncertainty

Abstract. The Geostationary Carbon Cycle Observatory (GeoCarb) was selected as NASA's second Earth Venture Mission (EVM-2). The scientific objectives of GeoCarb were to advance our knowledge of the carbon cycle, in particular, land–atmosphere fluxes of the greenhouse gases carbon dioxide (CO2) and methane (CH4) and the effects of these fluxes on the Earth's radiation budget. GeoCarb would retrieve column-integrated dry-air mole fractions of CO2 (XCO2), CH4 (XCH4) and CO (XCO), important for understanding tropospheric chemistry), in addition to solar-induced fluorescence (SIF), from hyperspectral resolution measurements in the O2 A-band at 0.76 µm, the weak CO2 band at 1.6 µm, the strong CO2 band at 2.06 µm, and a CH4/CO band at 2.32 µm. Unlike its predecessors (OCO-2/3, GOSAT-1/2, TROPOMI), GeoCarb would be in a geostationary orbit with a sub-satellite point centered over the Americas. This orbital configuration combined with its high-spatial-resolution imaging capabilities would provide an unprecedented view of these quantities on spatial and temporal scales accurate enough to resolve sources and sinks to improve land–atmosphere CO2 and CH4 flux calculations and reduce the uncertainty of these fluxes. This paper will present a description of the GeoCarb instrument and the L2 retrieval algorithms which will be followed by simulation experiments to determine an error budget for each target gas. Several sources of uncertainty will be explored, including that from the instrument calibration parameters for radiometric gain, the instrument line shape (ILS), the polarization, and the geolocation pointing, in addition to forward model parameters including meteorology and spectroscopy, although there are some other instrument-related sources of uncertainty that are left out for this study, including that from “smile”, the keystone effect, stray light, detector persistence, and scene inhomogeneity. The results indicate that the errors (1σ) are less than the instrument's multi-sounding precision requirements of 1.2 ppm, 10 ppb, and 12 ppb (10 %), for XCO2, XCH4, and XCO, respectively. In particular, when considering the sources of uncertainty separately and in combination (all sources included), we find overall RMSEs of 1.06 ppm for XCO2, 8.2 ppb for XCH4, and 2.5 ppb for XCO, respectively. Additionally, we find that, as expected, errors in XCO2 and XCH4 are dominated by forward model and other systematic errors, while errors in XCO are dominated by measurement noise. It is important to note that the GeoCarb mission was canceled by NASA; however, the instrument is still in development and will be delivered to NASA, in full, with the hope that it will eventually be adopted in a future mission proposal.

Development of solver with user interface for surface radiative exchange based on OpenFOAM platform

Surface radiative exchange is widely used in the fields related to industrial and environment. Accurate and rapid calculation of the surface radiant heat flux can predict and prevent accidents. In this study, a solver for surface radiative exchange based on the OpenFOAM platform is developed. The solver’s accuracy can be verified by calculating the net heat rate of the cubic cavity and the triangular-prism geometries. The solarLoad radiation model is used to study the variation of heat flux with respect to the solar incidence angle for a satellite in orbit and a human standing in a room with a window. Finally, a Graphical User Interface (GUI) based on the PyQt5 for this solver is developed to simplify the operation process and make the solver user-friendly.

Numerical Model of Simultaneous Multi-Regime Boiling Quenching of Metals

This work presents a heat transfer and boiling model that computes the evolution of the temperature field in a representative steel workpiece quenched from 850 or 930 °C by immersion in water flowing at average velocities of 0.2 or 0.6 m/s, respectively. Under these conditions, all three boiling regimes were present during cooling: stable vapor film, nucleate boiling, and single-phase convection. The model was based on the numerical solution of the heat conduction equation coupled to the solution of the energy and momentum equations for water. The mixture phase approach was adopted using the Lee model to compute the rates of water evaporation–condensation. Heat flux at the wall was calculated for all regimes using a single semi-mechanistic model. Therefore, the evolution of boiling regimes at every position on the wall surface was automatically determined. Predictions were validated using laboratory results, namely: (a) videorecording the upward motion of the wetting front along the workpiece wall surface; and (b) cooling curves obtained with embedded thermocouples in the steel probe. Wall heat flux calculations were used to determine the importance of the simultaneous presence of all three boiling regimes on the heat flux distribution. It was found that this simultaneous presence leads to high heat flux variations that should be avoided in production lines. In addition, it was determined that the corresponding inverse heat conduction problem to estimate the active heat transfer boundary condition must be set-up for 2D heat flow.

PEANUTS: a software for the automatic computation of solar neutrino flux and its propagation within Earth

We present PEANUTS (Propagation and Evolution of Active NeUTrinoS), an open-source Python package for the automatic computation of solar neutrino spectra and active neutrino propagation through Earth. PEANUTS is designed to be fast, by employing analytic formulae for the neutrino propagation through varying matter density, and flexible, by allowing the user to input arbitrary solar models, custom Earth density profiles and general detector locations. It provides functionalities for a fully automated simulation of solar neutrino fluxes at a detector, as well as access to individual routines to perform more specialised computations. The software has been extensively tested against the results of the SNO experiment, providing excellent agreement with their results. In addition, the present text contains a pedagogical derivation of the relations needed to compute the oscillated solar neutrino spectra, neutrino propagation through Earth and nadir exposure of an experiment.

Analysis of Radon Near-Surface Measurements, Using Co-Located Ozone Data, Radio-Sounding Vertical Profiles, Sensible Heat Flux and Back-Trajectory Calculation

Simultaneous and co-located observations of near-surface Radon-222, ozone and meteorological parameters in a central Italy observation site operated by the University of L’Aquila (Italy), are used to study the physical drivers of the radon abundance during night-time hours. The knowledge of the potential temperature vertical gradient in the surface layer of nocturnal thermal inversion is made possible using co-located radio-sounding vertical profiles of pressure and temperature, thus making possible to indirectly infer the local surface flux of atmospheric radon (16 ± 6 mBq m−2 s−1). The dynamical removal due to turbulent convective motions is found to be the dominant controlling process, determining large differences in the near-surface radon abundance between stable and unstable conditions of the nocturnal Planetary Boundary Layer (PBL). Usual unstable PBL conditions during daytime hours induce an effective dynamical vertical dilution of surface radon, which rapidly reaches a quasi-steady-state abundance during mid-day and afternoon hours, with very low concentration values (5.1 ± 2.0 Bq m−3). Using back-trajectory reanalyses, estimates of local radon fluxes and vertical mixing efficiencies inside the PBL along the air mass latitudinal-longitudinal path and finally the irreversible radon loss due to radioactive decay, we have explored the fraction of daytime radon attributable to long-range advection in the continental near-mountain measurement site of L’Aquila (44 ± 18%).

Typical X-Ray Outburst Light Curves of Aql X-1

We show that the typical X-ray outburst light curve of Aql X-1 can be reproduced by accretion onto a neutron star in the frame of the disk instability model without invoking partial accretion or the propeller effect. The knee and the subsequent sharp decay in the X-ray light curve can be generated naturally by taking into account the weak dependence of the disk aspect ratio, h/r, on the disk mass-flow rate, Ṁin , in the X-ray irradiation flux calculation. This Ṁin dependence of h/r only slightly modifies the irradiation temperature profile along the hot disk in comparison to that obtained with a constant h/r. Nevertheless, this small difference has a significant cumulative effect on the hot disk radius, leading to a much faster decrease in the size of the hot disk and thereby to a sharper decay in the X-ray outburst light curve. The same model also produces the long-term evolution of Aql X-1, consistent with its observed outburst recurrence time and typical light curve. Our results imply that the source accretes matter from the disk in the quiescent state as well. We also estimate that the dipole moment of the source μ ≲ 4 × 1026 G cm3 (B ≲ 4 × 108 G at the surface).

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

SPATIAL VARIABILITY OF METHANE EMISSIONS FROM SOILS OF WET FORESTS: A BRIEF REVIEW

Comparative the effect of distribution transformer coil shape on electromagnetic forces and their distribution using the FEM

Abstract During the normal life of the transformers, they are subjected to different electromagnetic stresses. One of these stresses is the electromagnetic forces resulting from the passage of short-circuit current in the transformer coils due to internal or external faults and may lead to the failure of the transformer when this electromagnetic force exceeds the threshold level. This work deals with the computation and analysis of leakage magnetic flux and electromagnetic forces when the worst-case fault (symmetrical short-circuit current) occurs in distribution transformer (DT) coils using the finite element method (FEM). The three types of DTs that were adopted in this work are similar in capacity and voltage transformation ratio (250 kVA and 11,000/416 V), but they are different in the shape of coils (oval, cylindrical, and rectangular coils). ANSYS software was used to build two-dimensional models of the three transformers, which were different in coil shapes and in the type of iron core. The objective of this work is to compare the effect of coil shape on the distribution of electromagnetic forces and their value, in order to find out which coil shape is the best to withstand electromagnetic forces when short-circuit current is passed in the coils. The results of the simulation of the finite element models were approximately equivalent to the results of the design calculations that depend on the classical method (the analytical method), but the FEM is more accurate, due to the accuracy of calculating the magnetic flux and its distribution, which cannot be calculated using the classical method. One of the most important contributions of this research is the analysis and calculation of electromagnetic forces for three types of DTs with different coils by applying the same design parameters to all the transformers. The research also contributed to determining the best coil shape by comparing simulation results, and it was found that transformers with cylindrical coils are the best to withstand electromagnetic forces due to the homogeneity of the cylindrical coil structure from all sides.

Measurement and calculation of magnetic flux density generated by the second cooling zone electromagnetic stirring (S-EMS) of a slab continuous casting strand

In the current study, a measurement of the magnetic flux density in the second cooling zone was performed for a 1250 mm width and 200 mm thickness slab continuous casting strand generated by the electromagnetic stirring with varied current intensity and frequency. From the narrow face to the width center of the slab, the magnetic flux density showed a increased, decreased, increased to a peak, and finally decreased trend. The magnetic flux density was decreased from the wide side to the thickness center of the slab, while an increase occurred from the model top to the stirrer center along the casting direction. To broaden the measurement range of the electromagnetic stirring parameters, the electromagnetic field in the strand and stirrer was calculated based on the finite element method, and the current input was achieved using the node loading approach. The effect of the mesh density on the calculation accuracy was investigated, and it was found that the 20 mm cell size in the strand region and the 10 mm cell size in the coil conductor and the iron core were enough to achieve a good agreement between the calculation and measurement. The empirical equations, Bx = 0.165.f 0.63.I −0.57.(–6870.x4–9700.x3–4260.x2–495.x + 90), By = 0.167.f −0.5.I 0.45. (4272.y2 + 0.2733.y + 101.4), and Bz = 0.1724.f −0.5.I 0.45.(0.0191.exp(24.16.z − 16.12.z2) + 2.3) were derived to estimate the local magnetic flux density based on measured values across the width of the slab and calculated values along the casting direction under diverse operational conditions. These equations hold practical significance in elucidating the spatial distribution of magnetic flux density within the strand region in the second cooling zone.

Research on the distribution of heat fluxes during infrared drying of grain material

Purpose. To develop mathematical models of unsteady heat and mass transfer during the infrared (IR) drying process, and to create an algorithm for calculating the variable power of IR energy input to ensure quality drying of thermolabile material. Methods. The methods of mathematical modeling used to describe the unsteady drying process of thermolabile material in a dryer are based on the formalized description in the form of nonlinear inhomogeneous differential equations, taking into account the change in the power of IR energy input during the drying process. Results. A dependency for calculating the perceivable power of the IR source by the grain, based on the given process mode parameters, has been obtained. The drying kinetics of the grain, derived from formula (10), more accurately characterizes the process from a physical point of view than the drying equation (8) with a constant coefficient kck. It was established that three characteristic periods of the drying process can be traced in the graphical dependencies: I – heating; II – constant drying rate; III – falling drying rate. The calculation of heat fluxes for downward cross-ventilation of the grain layer, where air washes over IR heaters and reflectors and heats up to 35 °C, is presented. It was found that in the implementation of the process with a downward airflow, it is necessary to supply 20–25 % less radiant energy to the material at the same drying exposures according to the graphical dependencies. Conclusions. A mathematical description of the unsteady drying process of thermolabile material in a dryer, considering the change in the power of IR energy input during drying, has been formulated. An algorithm for calculating parameters that can be used for process identification and optimization of the operating parameters of existing grain dryers has been developed. Keywords: drying, grain material, mathematical model, diffusive transfer, moisture content, temperature, speed.

Numerical viscosity control in Godunov-like smoothed particle hydrodynamics for realistic flows modeling

In this study, we introduce a way to control the viscosity of the numerical approximation in the Godunov-like smoothed particle hydrodynamics (SPH) methods. This group of SPH methods includes momentum and energy fluxes in the right-hand sides of the equations, which are calculated by the solution of the Riemann problem between each pair of neighboring particles within the support radius of the smoothing kernel, which is similar to the procedure for the calculation of fluxes across cell boundaries in Godunov schemes. Such SPH methods do not require the use of artificial viscosity since the significant numerical viscosity is already introduced by a Riemann problem solution. We demonstrate that such a numerical viscosity may be measured and obtain the explicit expression for it depending on smoothed particle properties. In particular, we have found that Godunov-like SPH method with interparticle contact algorithms produces numerical viscosity several orders of magnitude higher than physical viscosity in materials. Modern approaches, such as SPH with monotonic upstream-centered scheme for conservation laws or weighted essentially non-oscillatory reconstruction techniques, have not only lower numerical viscosity but also too large for modeling real-world viscous flows. By constructing a correcting viscous stress tensor based on the analytical solution for discontinuous viscous flow, it is possible to reduce the viscous stresses of numerical origin. The use of such a correction makes it possible to improve the agreement with experiments in the simulation of viscous flows without using schemes of higher order reconstruction.

A volume of fluid based method for consistent flux computation in large-density ratio two-phase flows and its application in investigating droplet bag breakup behavior

This article introduces a novel method for computing consistent fluxes, which enables highly robust simulations of two-phase flow problems characterized by large-density ratios. The approach is based on the geometric reconstruction volume of fluid method and utilizes a staggered grid implementation. This allows for accurate and robust simulation of phenomena like droplet bag breakup in flows with intense velocity shear and significant density differences. Through numerical experiments, it has been demonstrated that this method can reliably simulate two-phase flows with large-density ratios while preserving excellent energy conservation properties. Expanding on these findings, the researchers have developed a solver that leverages block-structured adaptive mesh to perform high-fidelity simulations of droplet bag breakup scenarios. Remarkably, this solver accurately reproduces three distinct breakup patterns: bag mode, stamen mode, and sheet-stripping mode. A comprehensive analysis has also been conducted by comparing the dimensionless maximum cross-stream radius with experimental test results. Furthermore, the study investigates the kinetic energy spectrum of fully developed two-phase turbulence under different droplet generation mechanisms and examines the distribution of droplet sizes. The numerical results validate the efficacy and reliability of this method in accurately simulating two-phase flows characterized by significant density disparities and interface momentum exchange.

2019–2021年黄土高原典型粮草复合生态系统日通量数据集

As a typical ecosystem type on the Loess Plateau, the grain and grass complex ecosystem plays a vital role in maintaining regional food production and animal husbandry development. Understanding the characteristics of carbon water flux and energy partitioning in the grain and grass complex ecosystem on the Loess Plateau is of great significance for understanding the regional climate, carbon water cycle and its coupling process on the Loess Plateau. The dataset contains the carbon and water flux data accumulated by the National Field Scientific Observation and Research Station of Qingyang Grassland Agricultural Ecosystem, Lanzhou University, from January 2019 to December 2021. The data indexes include net ecosystem exchannge (NEE) of CO2, total ecosystem productivity (GEP), ecosystem respiration (RE), evapotranspiration (ET), latent heat flux (H), net radiation (Rn), and rainfall (P). The studied ecosystem is a grain and grass complex ecosystem, which belongs to the typical agricultural production type of the Loess Plateau and has strong regional representation. The dataset was prepared in strict accordance with international flux observation technical standards from field observation, data warehousing, and quality control to flux calculation. The comprehensive and high-quality data in this dataset can provide a foundation for research on crop production, efficient use of water resources, carbon source and sink management, and response to global climate change in the Loess Plateau.

A finite volume scheme with an adaptive heat flux calculation for fast temperature prediction for wire arc additive manufacturing

Thermal simulations are an essential tool for optimizing the wire arc additive manufacturing process. However, their adoption in the process optimization workflow is still challenged by the long computational time required for the numerical solution of the thermal models. In this article, a Finite Volume scheme is proposed for predicting the temperature field evolution during wire arc additive manufacturing. A novel adaptive calculation of the heat flux is used for the acceleration of the numerical solution of heat conduction problems with a moving heat source. Numerical tests and experimental data are utilized to assess the performance of the proposed method in comparison to an explicit Finite Element scheme and a standard explicit Finite Volume scheme. Compared to the reference schemes, the accuracy loss is demonstrated to be negligible for the application to process planning. Depending on the simulated case, more than twice the computational efficiency of the reference schemes is achieved. The results demonstrate the suitability of the method for the simulation of heat conduction problems with a moving heat source and particularly for fast temperature predictions for wire arc additive manufacturing.

К РАСЧЕТАМ АНТРОПОГЕННЫХ ВЫБРОСОВ ИЗ ИСТОЧНИКОВ И АБСОРБЦИЙ ПОГЛОТИТЕТЯМИ ПАРНИКОВЫХ ГАЗОВ В ЛЕСНОМ И СЕЛЬСКОМ ХОЗЯЙСТВЕ ДЛЯ ЕЖЕГОДНОГО НАЦИОНАЛЬНОГО ДОКЛАДА РЕСПУБЛИКИ КАЗАХСТА

The results presented in the article were obtained in the process of preparing the National Report on the inventory of anthropogenic emissions from sources and absorption of greenhouse gases not regulated by the Montreal Protocol, in terms of land use. The report is submitted annually by the Republic of Kazakhstan, as a party to the United Nations Framework Convention on Climate Change (UNFCCC). Preliminary calculations of the dynamics of carbon dioxide (CO2) associated with land use in the Republic of Kazakhstan for 1991...2020 showed that its absorption from the atmosphere by natural ecosystems could range from 3 to 50...60 million tons per year, and emissions into the atmosphere – from 10 to 45 million tons/year. In the process of research, a detailed analysis of the country's existing system of ground-based monitoring of land use and land resources was carried out with calculations of anthropogenic CO2 flows at various territorial levels. The results obtained confirm the possibility of calculating greenhouse gases at the zonal and regional levels. This confirms the possibility of additional control of calculations of greenhouse gas fluxes associated with land use and assessment of the potential for a possible increase in absorption volumes for natural ecosystems (Forests and Pastures) and reductions in emissions for the Croplands agroecosystem.

CALCULATION OF POWER TRANSFORMER INDUCTANCE MATRIX

Practical calculations of electric equipment and electric networks are performed using equivalent circuits. Without taking into account saturation phenomena, electromagnetic processes in a power transformer are described by a system of linear equations, which can be represented in matrix form. The transformer inductance matrix contains self and mutual winding inductances, whose values for one phase are determined directly from the passport data containing the results of no-load and short circuit experiments. Mutual inductances between phases depending on the type and size of the magnetic core are not usually given in the transformer documentation. It does not allow to simulate the operating modes that differ from the steady state with uniform phase load.
 
 The purpose of the work is to develop an algorithm for calculating elements of the power transformer inductance matrix according to its passport data and magnetic circuit parameters.
 
 The scientific novelty lies in use of information about magnetic circuit type and size to determine elements of the inductance matrix.
 
 Materials and methods. Methods of linear electric and magnetic circuit theory are used in the work.
 
 Results. The proposed algorithm for calculation of power transformer inductance matrix includes three stages: calculation of self and mutual inductances for one phase; construction of an equivalent circuit for a magnetic circuit and calculation of magnetic fluxes in order to take into account the mutual influence of windings on various phases; assembly of the inductance matrix of three-phase transformer. A method is proposed for constructing the transformer inductance matrix with an arbitrary type of magnetic circuit, phases and windings quantity. The method involves preliminary calculation of the coefficient matrix that characterizes the magnetic circuit and depends mainly on its type and, to a less, on the ratio of geometric dimensions in rods and yokes. The coefficient matrix can be calculated in advance and used to determine the inductance matrix of a wide range of transformers.
 
 Conclusions. 1. The passport data of the transformer do not allow to model transformer operation at unbalanced load validly. 2. An algorithm for determining the inductance matrix of transformers has been developed. 3. A method for compilation of a transformer inductance matrix with an arbitrary type of magnetic circuit, the number of phases and windings is introduced. The practical significance of the algorithm is determined by the simplicity of algorithmizing, as well as by the possibility of using it in computer simulation of electrical circuits with transformers, for example, using the modified nodal analysis method.

Some features of thermohaline processes in the coastal zone of Arctic seas

The thermohaline processes in the Arctic coastal zone of seas in Russia are analyzed on the example of some parts of the Barents and Kara Seas: specifically, the Medynsko-Varandey site and the near-mouth coast of the Ob and Yenisey. For comparison with the thermohaline characteristics of international waters, the authors used observation data obtained by Admiral Vladimirsky oceanographic research ship in the summer — autumn of 2014 and Professor Multanovsky in the summer — autumn of 2019 (“Transarctica 2019”). The study aims to obtain typical and extreme distributions of hydrological characteristics in order to estimate heat and salt fluxes in the bottom layers. The characteristic substance fluxes can be used in the calculations of fluxes in bottom sediments, which have a significant effect on permafrost thawing. Such sedimentary rocks constitute a new source of minerals in the Arctic zone. In order to calculate heat and salt fluxes, it is necessary to obtain high spatial resolution data. The available data may be insufficient, thus requiring integrated oceanological observations in the coastal zone.

Calculation of Thermalized Component of Neutron Spectra in a D-D Neutron Generator

The results of the thermalized flux calculation that incorporate radiative capture reactions in the presence and absence of polyethylene blocks that form an enclosure for a deuteron-deuteron (D-D) neutron generator are presented. This method can be used to measure the moderated neutron flux component in a mixture of moderated and primary neutron spectra. Using 20-cm-thick polyethylene blocks to surround a D-D neutron generator, the moderation of primary neutrons was investigated using nine indium foils. In this paper, the relationship between the moderated neutron flux and the radiative capture rates in the presence and absence of polyethylene blocks is derived. This is compared to a MCNP simulation and a calculation of modulated flux that ignore the primary neutron components.