Thermal Attenuation Research Articles

Effect of replacing B2O3 with CuO on the structural, optical absorption, thermal, mechanical, and gamma-ray shielding properties of B2O3–Bi2O3–K2O glass

This paper delves into the effect of replacing B2O3 with CuO on the structural, optical absorption, thermal, mechanical, and gamma(γ)-ray shielding properties of four CKB glasses formulated as (65-y)B2O3–15Bi2O3–20K2O-yCuO (where y = 0, 0.3, 0.6, and 1.2 mol%). The glasses were created using the melt-quenching technique, and their non-crystalline structure was verified by X-ray diffraction (XRD) analysis. Fourier-transform infrared (FTIR) spectroscopy identified several structural groups, predominantly consisting of BO3, BO4 units, and B–O–B linkages. Thermal properties, assessed via Differential Scanning Calorimetry (DSC), indicated that the glass transition temperature was highest for the 0.3 mol% CuO sample (CKB0.3), demonstrating enhanced thermal stability in comparison to other compositions. Density measurements correlated positively with CuO concentration, peaking at 1.2 mol%, while molar volume, boron molar volume, oxygen packing density, and boron-boron separation distances showed a decreasing trend with increased CuO concentration. UV–Vis absorption spectroscopy indicated a decline in the optical energy gap and an increase in Urbach energy, attributed to the conversion of BO3 into BO4 units in the glass matrix. Mechanical properties, evaluated using the Makishima-Mackenzie model, demonstrated enhancements in elastic moduli and micro-hardness with rising CuO concentration. The γ-ray shielding properties (γ-RPs) were examined at energies of 0.662, 1.173, and 1.333 MeV, revealing that both the linear attenuation coefficient and effective atomic number reached their maximum values at 1.2 mol% CuO (CKB1.2). While CKB1.2 exhibited excellent mechanical and γ-ray shielding performance, CKB0.3 excelled in thermal stability and demonstrated γ-ray shielding efficiency comparable to CKB1.2. This suggests that CKB0.3 is a promising candidate for radiation shielding applications requiring a balanced combination of thermal stability and effective γ-ray attenuation properties, particularly at 0.662 MeV.

Photothermal measurement of material properties for translucent thermal barrier coatings

In this study, a photothermal nondestructive method was proposed to measure the material parameters of semi-transparent or translucent thermal barrier coatings (TBCs). We derived a theoretical model for the photothermal signal from a two-layer semi-infinite material system with a translucent first layer after a pulse laser excitation. Its solution was verified by numerical solution. A data regression algorithm based on a least-squares fitting was used for the determination of the material parameters in the translucent first layer material. To verify this new method, an experimental system was set up with a pulse laser for thermal excitation and an infrared camera for image acquisition of the thermal emission transient from several translucent EBPVD TBC samples. The predicted coating thickness is consistent with the measured value by an optical microscope. The predicted thermal conductivity and optical attenuation coefficients in the absorption and emission band are found to be in good agreement with reference values.

Thermal Relaxation in Janus Transition Metal Dichalcogenide Bilayers.

In this work, we employ molecular dynamics simulations with semi-empirical interatomic potentials to explore heat dissipation in Janus transition metal dichalcogenides (JTMDs). The middle atomic layer is composed of either molybdenum (Mo) or tungsten (W) atoms, and the top and bottom atomic layers consist of sulfur (S) and selenium (Se) atoms, respectively. Various nanomaterials have been investigated, including both pristine JTMDs and nanostructures incorporating inner triangular regions with a composition distinct from the outer bulk material. At the beginning of our simulations, a temperature gradient across the system is imposed by heating the central region to a high temperature while the surrounding area remains at room temperature. Once a steady state is reached, characterized by a constant energy flux, the temperature control in the central region is switched off. The heat attenuation is investigated by monitoring the characteristic relaxation time (τav) of the local temperature at the central region toward thermal equilibrium. We find that SMoSe JTMDs exhibit thermal attenuation similar to conventional TMDs (τav~10-15 ps). On the contrary, SWSe JTMDs feature relaxation times up to two times as high (τav~14-28 ps). Forming triangular lateral heterostructures in their surfaces leads to a significant slowdown in heat attenuation by up to about an order of magnitude (τav~100 ps).

Enhancing the radiation shielding performance of polyepoxide composites based on cement bypass dust

In this study, radiation shielding composite materials were created by combining epoxy with cement bypass dust (CBPD) at different weight percentages (0%, 10%, 20%, and 30%). The solution casting technique was employed to construct these materials. The FTIR spectra confirmed the formation of the composites and the production of complexes. The morphology and elemental content of the produced composite samples were illustrated using SEM pictures and EDX spectra. In addition, the research findings demonstrated that the composites exhibited improved resistance to changes in temperature as the loading of CBPD increased. The gamma-ray attenuation coefficients of composites consisting of Epoxy + x% CBPD exhibited an increase, along with an increase in the neutron removal cross-section. However, there was a gradual increase in both the mean free path (MFP) as well as the half value layer (HVL) with increasing energy. Additionally, the experimental and theoretical data for attenuation parameters were compared using the Phy-X/PSD software. The relationship between the effective atomic and electron numbers of the Epoxy + x% CBPD composites has been studied. The values of fast and thermal neutron attenuation were analyzed using the NGCal software. In general, these composites are appropriate for use in radiation shielding applications.

4D-STEM and Eels Analysis of Complex C-Based Sensor Architectures

Transforming high-carbon precursors into open-porous carbon foams and coatings via thermal processes is gaining attention as a sustainable method for various applications, including catalysis, energy utilization, and sensing [1]. In this research, we adopt a one-step laser patterning approach to selectively pyrolyze doctor-bladed ink coatings on flexible PET substrates, thereby producing highly porous, intricately designed CO2 sensor structures with a thickness of about 50 µm. Our ink formulation includes glucose as a pore-forming agent and adenine as a nitrogen source to enhance sensing capabilities. Laser processing in an oxygen-rich setting results in flexible, highly porous sensor heterostructures characterized by distinct areas enriched with nitrogen and oxygen functionalities. The laser intensity’s attenuation with depth leads to the development of a distinctly porous graphitic surface layer (serving as the electrical transducer layer) and a denser nitrogen-enriched lower sensor layer, linked by a narrow transitional region [2]. To understand the formation and functionality of these sensors, we conducted an in-depth TEM analysis of cross-sections of the complete device, prepared through ultramicrotomy cross-sectioning. STEM-EELS elemental distribution maps distinctly show the chemical composition differences between the upper and lower layers of the sensor. Principal component analysis was utilized to separate the complex sensor structures into their constituent crystalline and amorphous carbon and nitrogen-containing phases. 4D-STEM analysis exposed the arrangement of the crystalline graphitic phase and the orientation of graphite basal planes adjacent to the pores of the open-porous sensor. Analyzing these structural parameters is essential for understanding the electrical performance of the sensor, as depicted in Figure 1 [3]. Figure 1: A (top)) SEM micrograph of sensor embedded in epoxy, (bottom) depth-dependent thermal laser intensity attenuation; B (left)) HA ADF-STEM micrograph showing different sensor layers, (middle) STEM-EELS nitrogen distribution map, (right) PCA bond analysis, C) HRTEM images of sensor from transducer (top) and sensor (bottom) layers with SAED image of respective ROIs (inset); D) 4D-STEM analysis depicting misalignment angle between graphitic carbon basal plane normal relative to the pore surface normalReferences[1] M. Hepp, et al. npj Flexible Electronics 6, 1-9 (2022)[2] H. Wang, et al. Advanced Functional Materials 32, 2207406 (2022)[3] C. Ophus, et al. Microscopy and Microanalysis 28, 390-403 (2022) Acknowledgements: We acknowledge use of the DFG-funded Micro-and Nanoanalytics Facility (MNaF) at the University of Siegen (INST 221/131-1). Figure 1

Evaluation of Some Heavyweight Minerals as Sustainable Neutron and Gamma-Ray Attenuating Materials: Comprehensive Theoretical and Simulation Investigations

AbstractThis study comprehensively evaluates the radiation attenuation efficiencies of hematite and barite, commonly used materials in radiation shielding, using theoretical and simulation investigations. The MCNP-5 code was used to obtain the linear attenuation coefficient (LAC) within the energy range of 0.015–15 MeV, with validation by the XCOM program. Based on these LAC values, various gamma-ray shielding parameters were determined: mass attenuation coefficient, half-value layer, radiation protection capacity, mean free path, transmission factor, and equivalent thickness to lead (ETPb). Additionally, effective atomic number (Zeff) and electron density (Neff) were calculated, including both single-energy and energy-dependent forms for photon absorption and interaction. Furthermore, MCNP-5 simulations and NGCal program calculations were used to assess thermal neutron attenuation, while the NXcom program determined fast neutron behavior. This analysis revealed superior γ-ray shielding for barite compared to hematite. Similarly, the NXcom program indicated better fast neutron shielding for barite. However, interestingly, simulations validated a 210% higher effectiveness in thermal neutron attenuation for hematite. Finally, comparing the studied materials with other shielding materials demonstrated promising potential as environmentally friendly alternatives for effective shielding against various radiation types.

Frequency-domain analysis of two controllable attenuators for control processes and perturbations in a constant temperature chilled-water system

Constant temperature and humidity rooms (CTHRs) that require ultra-high precision (≤±0.1 °C) are widely used in semiconductors and other high-end manufacturing. To achieve this, the air handling unit’s chilled water system should be able to handle temperature fluctuations in all frequencies. However, traditional methods use attenuators for internal perturbations (usually at high frequency) and electric heating with PID control for external ones (usually at low frequency) separately and can’t differentiate frequencies and their sources, which can lead to ineffective control and energy waste. Therefore, this study proposed two chilled water systems based on two controllable attenuators, i.e., a plate heat exchanger (PHE) and a water mixing pump (WMP), that can simultaneously achieve full frequency range control at an ultra-high precision without reheating. An experimental setup was used to validate and obtain the attenuation performance of the two schemes. The fast Fourier transform was conducted to decouple the system’s internal and external perturbations in the frequency domain. The frequency-domain response features of the thermal control and attenuation processes for low-frequency and high-frequency fluctuations under the two schemes were analyzed. The results showed that, first, both schemes can achieve ultra-high precisions. Second, the PHE scheme had a more robust attenuation performance, while the WMP scheme exhibited a broader effective control frequency range. Third, the pumps in both schemes were the primary source of perturbations that constitute the temperature fluctuation, and the flow rate stability was closely related to the degree of pump perturbation. Finally, 10-3 Hz can be considered the delineation frequency between the low- and high-frequency of the system’s fluctuations, which can be simultaneously attenuated by the proposed controllable attenuators.

Multiphase Symbiotic Engineered Elastic Ceramic-Carbon Aerogels with Advanced Thermal Protection in Extreme Oxidative Environments.

Elastic aerogels can dissipate aerodynamic forces and thermal stresses by reversible slipping or deforming to avoid sudden failure caused by stress concentration, making them the most promising candidates for thermal protection in aerospace applications. However, existing elastic aerogels face difficulties achieving reliable protection above 1500°C in aerobic environments due to their poor thermomechanical stability and significantly increased thermal conductivity at elevated temperatures. Here, a multiphase sequence and multiscale structural engineering strategy is proposed to synthesize mullite-carbon hybrid nanofibrous aerogels. The heterogeneous symbiotic effect between components simultaneously inhibits ceramic crystalline coarsening and carbon thermal etching, thus ensuring the thermal stability of the nanofiber building blocks. Efficient load transfer and high interfacial thermal resistance at crystalline-amorphous phase boundaries on the microscopic scale, coupled with mesoscale lamellar cellular and locally closed-pore structures, achieve rapid stress dissipation and thermal energy attenuation in aerogels. This robust thermal protection material system is compatible with ultralight density (30mg cm-3), reversible compression strain of 60%, extraordinary thermomechanical stability (up to 1600°C in oxidative environments), and ultralow thermal conductivity (50.58mW m-1 K-1 at 300 °C), offering new options and possibilities to cope with the harsh operating environments faced by space exploration.

Multi-dimensional investigation of ceiling jet temperature characteristics beneath curved ceiling produced by fire in the utility tunnel

To study the temperature profile beneath the curved ceiling from a multi-dimensional perspective, an experimental investigation was conducted in utility tunnels with two different sizes, and a series of models were established to predict a two-dimensional longitudinal temperature profile and transverse temperature attenuation in this study. The prediction models for the two-dimensional longitudinal temperature profile were developed by modeling the vertical temperature distribution, thermal boundary layer thickness, Gaussian thermal layer thickness and maximum longitudinal temperature attenuation. Through the experimental validation on two sizes, it is found that the proposed prediction model can express the longitudinal temperature profile from a two-dimensional view within the relative error range of 20%. Besides, the prediction model for transverse temperature attenuation was established by the definition of characteristic tilt angle, and the three detailed expressions of this model were proposed according to different types of ceiling jets after impingement. The proposed prediction model for transverse temperature attenuation was also validated, and the verification results showed that the relative error of the transverse temperature attenuation prediction model can be controlled within a 25%. The developed prediction models in this study can be applied in the fire protection engineering of utility tunnels.

A re-activation model for 169Yb intensity modulated brachytherapy sources accounting for spatiotemporal isotopic composition.

Intensity modulated brachytherapy based on partially shielded intracavitary and interstitial applicators is possible with a cost-effective 169Yb production method. 169Yb is a traditionally expensive isotope suitable for this purpose, with an average γ-ray energy of 93keV. Re-activating a single 169Yb source multiple times in a nuclear reactor between clinical uses was shown to theoretically reduce cost by approximately 75% relative to conventional single-activation sources. With re-activation, substantial spatiotemporal variation in isotopic source composition is expected between activations via 168Yb burnup and 169Yb decay, resulting in time dependent neutron transmission, precursor usage, and reactor time needed per re-activation. To introduce a generalized model of radioactive source production that accounts for spatiotemporal variation in isotopic source composition to improve the efficiency estimate of the 169Yb production process, with and without re-activation. A time-dependent thermal neutron transport, isotope transmutation, and decay model was developed. Thermal neutron flux within partitioned sub-volumes of a cylindrical active source was calculated by raytracing through the spatiotemporal dependent isotopic composition throughout the source, accounting for thermal neutron attenuation along each ray. The model was benchmarked, generalized, and applied to a variety of active source dimensions with radii ranging from 0.4 to 1.0mm, lengths from 2.5 to 10.5mm, and volumes from 0.31 to 7.85 mm3, at thermal neutron fluxes from 1×1014to1×1015 n cm-2 s-1. The 168Yb-Yb2O3 density was 8.5g cm-3 with 82% 168Yb-enrichment. As an example, a reference re-activatable 169Yb active source (RRS) constructed of 82%-enriched 168Yb-Yb2O3 precursor was modeled, with 0.6mm diameter, 10.5mm length, 3 mm3 volume, 8.5g cm-3 density, and a thermal neutron activation flux of 4 × 1014 neutronscm-2s-1. The average clinical 169Yb activity for a 0.99 versus 0.31 mm3 source dropped from 20.1 to 7.5Ci for a 4×1014ncm-2s-1 activation flux and from 20.9 to 8.7Ci for a 1×1015ncm-2s-1 activation flux. For thermal neutron fluxes ≥2×1014ncm-2s-1, total precursor and reactor time per clinic-year were maximized at a source volume of 0.99 mm3 and reached a near minimum at 3mm3. When the spatiotemporal isotopic composition effect was accounted for, average thermal neutron transmission increased over RRS lifetime from 23.6% to 55.9%. A 28% reduction (42.5 days to 30.6 days) in the reactor time needed per clinic-year for the RRS is predicted relative to a model that does not account for spatiotemporal isotopic composition effects. Accounting for spatiotemporal isotopic composition effects within the RRS results in a 28% reduction in the reactor time per clinic-year relative to the case in which such changes are not accounted for. Smaller volume sources had a disadvantage in that average clinical 169Yb activity decreased substantially below 20Ci for source volumes under 1mm3. Increasing source volume above 3 mm3 adds little value in precursor and reactor time savings and has a geometric disadvantage.

Design and Study of Novel Composites Based on EPDM Rubber Containing Bismuth (III) Oxide and Graphene Nanoplatelets for Gamma Radiation Shielding.

The mechanical, thermal and gamma radiation attenuation properties of ethylene-propylene-diene monomer (EPDM)-based composites containing graphene nanoplatelets (GNs) and bismuth (III) oxide nanoparticles (B) were investigated. The use of polyethylene glycol (PEG) as a compatibilizer to improve the dispersion of the fillers was also investigated. The results showed that the combined use of these fillers resulted in a drastic increase in mechanical properties, reaching 123% and 83% of tensile strength and elongation at break, respectively, compared to those of EPDM. In contrast, the addition of PEG to composites containing EPDM GNs and B resulted in composites with lower values of mechanical properties compared to the EPDM/B/GN-based composite. However, the presence of PEG leads to obtaining a composite (EPDM/B/GNP) with a mass attenuation coefficient to gamma radiation (137Cs, 662 keV) superior to that composite without PEG. In addition, the composite EPDM, B and PEG exhibited an elongation at break 153% superior to unfilled EPDM. Moreover, the binary filler system consisting of 100 phr of bismuth (III) oxide and 10 phr of GN leads to reaching 61% of the linear damping coefficient of the EPDM composite compared to that value of the unfilled EPDM. The study of the morphology and the state of filler dispersion in the polymer matrix, obtained using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively, provides a useful background for understanding the factors affecting the gamma radiation attenuation properties. Finally, the results also indicated that by adjusting the formulation, it is possible to tune the mechanical and thermal properties of EPDM composites reinforced with bismuth oxide and graphene nanoplatelets.

Structural, mechanical, thermal, optical, and gamma rays attenuation properties of a developed sodium aluminum zinc lead borate glass

A host glass matrix of sodium aluminum zinc borate reinforced by 15, 30, and 45 mol% of PbO to serve as a shield against gamma rays. The penetration of PbO within the proposed host glass transforms the BO3 units into BO4 ones and fills the interstitial spaces, which in turn had been reflected on the mechanical, thermal, and optical properties. The harness and elastic moduli of the considered glasses improved with the augmentation of Pb2+ ions. The considered glass possessed high thermal stability and its glass transition temperature increased with the increase of PbO concentrations. Optically, the transparency of the produced glasses exceeds 75% with the inclusion of Pb2+ ions and increasing the Pb2+ ions enhancing its electrical insulating nature. Increasing PbO concentrations enhanced the glasses' ability to attenuate gamma rays of energies 661.64, 1173.23, and 1332.51 keV. A reduction in the required half-value layer by 59.697, 54.867%, and 53.460% at 45 mol% of PbO was observed. Hence, based on the suitable mechanical properties, high thermal stability and transparency, and effective ability to attenuate gamma rays, the glass containing 45 mol% PbO was nominated for use as a protective shield in various nuclear applications.

Synthesis and Characterization of La2O3–BaO–Na2O–SiO2–Bi2O3 Glass as a Potent Shield Against Ionizing Radiation

In recent years, the scientific community has spent significant effort exploring radiation-shielding glass materials. The present work was conducted by synthesizing a glass series of 20La2O–10BaO –15Na2O–(55−x)SiO2–xBi2O3, x: 0, 5, 15, and 25 wt%. After producing the samples, in-depth studies were performed on the physical, optical, thermal, and radiation attenuation properties of the fabricated glass series. A radical color change from nearly neutral to dark-brown color occurred as Bi2O3 entered the glass network. The density values equaled 2.8324, 2.9511, 3.0992, and 3.3657 g cm−3 for LBSS1 to LBSS4 samples, respectively. According to XRD patterns, neither sharp nor moderate peaks developed; a hump-like formation between 20 and 35 degrees was visible in all glass samples. FTIR measurement revealed transmission as a function of varying wavenumber from 4000 to 400 cm−1 for the prepared glass specimens, and different bond types were noted. The UV–Vis technique removes it displayed that increasing Bi2O3 content blocked light transmission throughout the glass medium. The radiation-shielding parameters of linear attenuation coefficient (LAC), mass attenuation coefficient, transmission factor, and half value layer were calculated with experimental and MC simulation methods for all glass samples at six different energies between 356 and 1332 keV. The results were compared with the Phy-X database, and good agreement was obtained. The highest LACs were obtained at the lowest energy (356 keV) with values of 0.3108, 0.3455, 0.4471, and 0.5486 cm−1 for LBSS1, LBSS2, LBSS3, and LBSS4 glasses, respectively. The photon attenuation ability of the LBSS glasses increased by increasing the Bi2O3 ratio, especially at low energies. Therefore, the authors can conclude that future applications, such as observation window in CT rooms, may efficiently exploit LBBS4 glass system.

Novel composite based on silicone rubber and a nano mixture of SnO2, Bi2O3, and CdO for gamma radiation protection

Recently, there has been a surge of interest in the application of radiation-shielding materials. One promising research avenue involves using free-lead metal oxides/polymer composites, which have been studied for their radiation shielding and characterization properties. This study reinforced the dimethylpolysiloxane (silicone rubber) composites with micro- and nano-sized particles of tin oxide, cadmium oxide, and bismuth oxide as additive materials. The composites were tested with 20 and 50 weight fractions, and their attenuation coefficients were measured using a NaI(TI) detector at gamma-ray energies ranging from 59.54 to 1408.01 keV. Also, the thermal and mechanical properties of the composites were observed and compared with those of free silicone rubber. The results showed that the 50% nano metal oxide/SR composites exhibited better thermal stability and attenuation properties than the other composites, also possessing unique attributes such as lightweight composition and exceptional flexibility. Consequently, this composite material holds immense potential for safeguarding vital organs, including the eyes and gonads, during radiological diagnosis or treatment procedures. Its exceptional ability to absorb a significant portion of incident rays makes it an invaluable asset in the field of radiation protection.

Evaluation of neutron shielding performance of cementless binder manufactured with desalination reject brine

This study investigated the feasibility of desalination reject brine as a new water resource for the nuclear construction industry by evaluating the thermal neutron shielding properties of Ca(OH)2–Na2CO3-activated fly ash (FA-NC) binder manufactured with reject brine since the high chloride concentration is believed to promote neutron shielding performance. High Cl− concentration encouraged rapid and greater early-age strength development of FA-NC binder mixed with reject brine, which is the main mechanism of the accelerator. A series of chemical and microstructural analyzes were conducted, namely, XRD, TG, and MIP tests, to investigate the influence of the reject brine. The use of reject brine remarkably improved the thermal neutron attenuation performance of the FA-NC binder and achieved 98.76 % of thermal neutron shielding efficiency. Furthermore, the reject brine provided an increased efficacy in fast neutron attenuation. To further analyze the practical application potential, a 190 × 90 × 57 mm sized brick sample was made using rejected brine mixed FA-NC binder and tested with the followings: water absorption and TCLP.

Optical, thermal and gamma ray attenuation characteristics of tungsten oxide modified: B2O3–SrCO3–TeO2–ZnO glass series

The glass series modified by tungsten oxide was created using the compounds (75-x) B2O3– 10SrCO3– 8TeO2– 7ZnO - xWO3, where x = 0, 1, 5, 10, 22, 27, 34, and 40% mole percentage. A UV–visible spectrophotometer and thermogravimetric-differential thermal analysis (TG-DTA) methods were employed to characterize the specimen's optical and phase transition attributes, respectively. The mass-attenuation coefficient (AC) of all created glasses from BSTZW0 to BSTZ7 was estimated using Geant4 code from 0.05 to 3 MeV and compared to the XCOM software results, with a relative difference of less than 2% between the two results. The increase of WO3 percentage lead to an increase in the Linear-AC at each studied energy, and this is mainly due to the fact that the higher the percentage of WO3 in the glass increases its density which causes an increase in the Linear-AC, so an energy of 0.06 MeV, as an example, the values of the Linear-AC was 4.009, 4.509, 5.442, 6812, 8.564, 9.856, 10.999 and 11.628 cm−1 form BSTZW0 too BSTZW7, respectively. The Half-VL (value layer), Mean-FP (free path), Tenth-VL, and Radiation attenuation performance (RAP) were also calculated for the current BSTZW-glass samples and revealed that BSTZW7 had the best gamma ray attenuation performance at all discussed energies when compared to other studied glass samples.

Research on the long-term operation performance of deep borehole heat exchangers array: Thermal attenuation and maximum heat extraction capacity

The long-term operation performance and thermal attenuation of deep borehole heat exchangers (DBHEs) array are important for their stable and safe operation. This paper proposed a semi-analytical method to quantitatively evaluate the 100-years operation performance of DBHEs array. Numerical simulation was utilized to determine the heat flux per depth of DBHE, while the finite line heat source model was modified to calculate the ground temperature variation. This allowed to obtain the ground borehole wall temperature, serving as a boundary condition for calculating the water temperature distribution in DBHE using an analytical solution. The results revealed that the line space of DBHEs array directly affected the allowed maximum accumulated heat extraction per DBHE per heating season (Qa,max). With line space decreasing from 100 m to 10 m, the Qa,max decreased from 0.3% to 19.1% compared to the single DBHE. Therefore, a line space larger than 30 m was recommended. Considering practical project with limited space, the inclined DBHEs were recommended in depth direction. For DBHEs array with a line space of 10 m at the surface ground and 100 m at a depth of 2500 m, Qa,max was only 3.2% smaller compared to the single DBHE, which showed an improvement over DBHEs array with a line space of 50 m. The proposed semi-analytical method could be applied in system design, to ensure the long-term safety and stability of DBHEs array.

Energy conversion through deep borehole heat exchanger systems: Heat storage analysis and assessment of threshold inlet temperature

The heating capacity of deep borehole heat exchanger (DBHE) systems gradually attenuates due to the cold accumulation of rock and soil during long-term operation. Therefore, heat storage in rock and soil is crucial to alleviate thermal attenuation and ensure stable operation. However, the mechanism and design methods for heat storage are unclear. In this paper, heat extraction and storage models for DBHE systems are established, the effects of heat storage on system operation are revealed, and a design method for the threshold inlet water temperature of heat storage is proposed. The results show that the fluid in the DBHE should inflow from the inner pipe to release more heat into the rock and soil when adopting heat storage. The heat storage power under fluid inflow from the inner pipe is 10.81 kW higher than that from the annular space under the same operating conditions. Increasing the inlet water temperature is more beneficial than increasing the flow rate to enhance the heat storage power. After 2880 h of operation, the heating power of the DBHE is increased by 3.44% for the next heating season when the storage flow rate is increased from 8 m3/h to 38 m3/h. Thus, a high heat storage inlet temperature with a low flow rate should be adopted during the heat storage period. Furthermore, the threshold inlet water temperature of heat storage is highly dependent on the depth of the DBHE and the geothermal gradient, with percentage contributions of 57.14% and 39.26%, respectively. The multiple linear regression model (R2 = 0.972) has shown high predictive accuracy in the assessment of threshold inlet water temperatures, with a maximum relative error of −5.60%. The findings of this paper provide technical support for designing heat storage using DBHE systems.

Modeling and experimental analysis of high-efficiency fluid temperature fluctuation attenuator based on phase regulator

Temperature fluctuation attenuators are important passive components for disturbance rejection in precise temperature control system, but previous attenuator researches mainly focused on increasing effective heat capacity to achieve better attenuation. In this paper, the temperature phase regulator (TPR) model is proposed as a superior method to reduce fluid temperature disturbances with less capacity. It achieves output temperature fluctuation attenuation by shifting the phase of the delay side temperature signal and mixing it with the normal side. Similar to the principle that notch filters can highly attenuate signals in specific frequency bands, we constructed TPR theoretical models under equal flow ratios and non-equal flow ratios. Different bandwidths, attenuation depths and target center frequencies can be achieved by changing the two parameters of equivalent heat capacity and flow ratio, and the mechanism of parameters affecting the TPR amplitude-frequency characteristics was analyzed. In terms of effect evaluation, we verified the correlation between the frequency domain and the time domain data, and compared the TPR with the thermal capacity attenuator and other popular attenuators in terms of MSE, MAE and Max-min of temperature data. In a typical temperature attenuation test, TPR can achieve 40% and 35% of MAE and Max-min value attenuation rates, which are exceeding the ideal upper limit of other attenuators and far superior to typical attenuators. The experimental data confirmed the feasibility of the heat capacity of the pipe to support the TPR delay side as a pure delay. The experimental results of non-equal flow ratios verified the model reference-ability of changing flow ratio. In the equal flow ratio test, the fit of the actual data curve and the theoretical curve showed the accuracy of the theoretical model, and the MAE attenuation ratio better than 70% reflected the excellent attenuation performance.

Nonlinear Interaction of Modes in a Planar Flow of a Gas with Viscous and Thermal Attenuation

The nonlinear interaction of wave and non-wave modes in a gas planar flow are considered. Attention is mainly paid to the case when one sound mode is dominant and excites the counter-propagating sound mode and the entropy mode. The modes are determined by links between perturbations of pressure, density, and fluid velocity. This definition follows from the linear conservation equations in the differential form and thermodynamic equations of state. The leading order system of coupling equations for interacting modes is derived. It consists of diffusion inhomogeneous equations. The main aim of this study is to identify the principle features of the interaction and to establish individual contributions of attenuation (mechanical and thermal attenuation) in the solution to the system.