Carrier Temperatures Research Articles

Tl2XY (X, Y = S, Se) monolayers with low lattice thermal conductivity and high thermoelectric performance by full-band approach with four scattering mechanisms

Abstract The low lattice thermal conductivity and high thermoelectric performance of the Janus Tl2SSe monolayer in the temperature region of 300–700 K are identified based on the thermoelectric properties of the Tl2S2, Tl2SSe, and Tl2Se2 monolayers. The transport coefficients for carrier concentrations and temperatures are obtained by solving the linearized Boltzmann transport equation in a full-band electronic structure. Four scattering mechanisms of acoustic deformation potential, optical deformation potential, polar optical phonon, and ionized impurity scatterings are considered. The ionized impurity scattering is recognized as the most important. The lattice thermal conductivity of the Janus Tl2SSe monolayer is substantially smaller than those of the Tl2S2, Tl2Se2 monolayers with higher symmetry. Moreover, we find that the Janus structures of the Tl2SSe monolayer increase the dielectronic constants and enhance the polar optical phonon scattering, then reduce the power factor to some extent. Therefore, the lattice thermal conductivity actually couples with the transport coefficient and cannot be individually regulated as is usually assumed. However, the ZT value of the Tl2SSe monolayer can still reach 1.77 at 700 K even if the intrinsic concentration and the bipolar effect are included. Therefore, the Tl2SSe monolayer is expected to be a promising candidate for thermoelectric materials.

First‐Principles Study of Structural and Elastic, Electronic, and Thermoelectric Properties of PdSe2

The thermoelectric material in orthorhombic (Pbca) phase is studied with the help of density functional theory implemented in WIEN2k. The main properties of investigated are elastic, electronic, and thermoelectric properties. The anisotropy factors obtained with the elastic constants indicate that is strongly anisotropic. The Tran and Blaha‐modified Becke–Johnson exchange potential is used for bandgap calculations. The BoltzTraP code is used to find out the thermoelectric properties of . At 300 K, the maximum value of the Seebeck coefficient is 200 μV K−1 for the hole carrier concentration of 2.5 × 1019 cm−3 and is 241 μV K−1 for the electron carrier concentration of 1.2 × 1019 cm−3. The power factor (PF) and figure of merit (ZT) are calculated for different carrier concentrations and temperatures. The optimum value of ZT for bulk PdSe2 as calculated in this work is ≈0.6 for hole carrier concentration (p = 2.6 × 1020 cm−3) at 800 K, which suggests as a potential material in thermoelectric applications at higher temperatures.

Design and Performance Analysis of a Small-Scale Prototype Water Condensing System for Biomass Combustion Flue Gas Abatement

This article outlines the design and performance of a flue gas condensation system integrated with a biomass combustion plant. The system comprises a biomass plant fuelled by wood chips, generating flue gases. These gases are condensed via a double heat exchanger set-up, extracting water and heat to reduce concentrations of CO, CO2, and NOx while releasing gases at a temperature close to ambient temperature. The 100 kW biomass plant operates steadily, consuming 50 kg of wood chips per hour with fuel energy of 18.98 MJ/kg. Post combustion, the gases exit at 430 °C and undergo two-stage cooling. In the first stage, gases are cooled in a high-temperature tube heat exchanger, transferring heat to air. They then enter the second stage, a flue gas/water heat exchanger, recovering sensible and latent thermal energy, which leads to water condensation. Flue gas is discharged at approximately 33 °C. Throughout, parameters like the flue gas temperatures, mass flow, fuel consumption, heat carrier temperatures, and water condensation rates were monitored. The test results show that the system can condense water from flue gas at 75 g/min at 22 °C while reducing pollutant emissions by approximately 20% for CO2, 19% for CO, 30% for NO, and 26% for NOx.

Cheese whey for production of breast milk‐derived bifidobacteria: Influence of fermentation conditions on the survival to spray drying and storage

Common factors influencing the survival of microbes to spray drying include microbial intrinsic resistance, properties of the carrier, inlet and outlet temperatures, and rate of feeding. In this work, cheese whey was used as both a growth medium and a carrier for spray drying of Bifidobacterium animalis subsp. lactis INL1. The growth of the strain was favoured by acid conditions, reaching higher counts when pH was not controlled during fermentation and when pH was controlled at a constant value of 5.5, compared with 6.5. Powders containing ca. 9 log order (cfu/g) of B. lactis INL1 were obtained by direct spray drying of the culture coming out of the fermenter. No differences in survival to spray drying were observed in terms of fermentation conditions. However, fermentation conditions are considered to have influenced the strain's survival along the storage. Spray drying in acid conditions was detrimental to the survival along storage.

Electronic, Mechanical, and thermoelectric properties of Ge/Zn co-doped SnSe: first-principles calculations

Materials based on tin selenide have attracted significant attention due to their unique properties, particularly their high ZT value. This study investigates the impact of co-doping Germanium and Zinc on the electronic, mechanical, and thermoelectric properties of SnSe crystal using first-principles calculations. The doped structure demonstrated a p-type semiconducting behavior with a triclinic stable structure, which was predicted by the calculated elastic constants. Thermoelectric properties were studied for both doped and undoped systems across a wide range of carrier concentrations and temperatures. Results showed that co-doping SnSe with Ge/Zn reduced electronic thermal conductivity at room temperature while simultaneously doubling the Seebeck coefficient. This promising combination of features suggests high thermoelectric performance for the material.

NOx emissions during oxygen-enriched combustion of sewage sludge and corresponding hydrochar

This study proposed an oxygen-enriched combustion technology for the resource utilization of hydrochar prepared from sewage sludge (SS) through hydrothermal carbonization (HTC). However, its application potential relies heavily on NOx emissions. To investigate NOx emissions during oxygen-enriched combustion of hydrochars prepared at different temperatures (200 °C, 240 °C, and 280 °C), real-time NOx concentrations were recorded under varying conditions, including different carrier gases (N2 and CO2), temperatures (600 °C, 800 °C, and 1000 °C), and oxygen concentrations (20 %, 30 %, and 40 %). In comparison to air combustion processes, the NOx emissions during the devolatilization stage were considerably depressed in oxygen-enriched combustion. A high concentration of CO2 inhibited NH3 production and HCN oxidation, and generated increased amounts of CO to facilitate NOx reduction. Elevated temperatures also reduced the NOx release during the oxygen-enriched combustion of SS and hydrochar, as the accelerated oxygen consumption weakened the oxidation reactions of HCN and NH3; the enhanced reduction reaction rate and increased CO production also promoted NOx reduction. Elevated oxygen concentrations, however, promoted NOx release owing to the increased NH3 and HCN oxidation by an increased number of oxidizing groups. Additionally, the reduction of reducing gases and rapid char combustion hindered NOx reduction. The NOx-N conversion of the hydrochars was much lower than that of SS under different conditions. HTC effectively reduced the nitrogen content of SS, with nitrogen in HC-280 existing as stable heterocyclic -N. HC-280 showed significantly less nitrogen conversion at low temperatures (9.03 % reduction at 600 °C) and high oxygen concentrations (2.01 % reduction at 40 % O2) compared to SS, highlighting the potential of combining HTC and oxygen-enriched combustion.

Studies on the Extraction of the Guaranteed Fuel Reserve in the Tanks of the Expended Stage

The hard landing of the spent stage of promising launch vehicles (LV) in the designated areas of the fall leads to the collapse of the structure, the spillage of the remnants of the guaranteed fuel reserve, the outbreak of fires, and, as a result, require large expenditures for the complete elimination of man-made consequences. Residues of the guaranteed fuel are additional stocks of propellant components in the rocket blocks of the stage of LV, designed to compensate for the disturbing factors acting in flight on the LV. They are characterized by carcinogenic and mutagenic effects on the environment. The article considers the issue of extraction of unprocessed residues of guaranteed fuel. An experimental stand and a program for conducting experiments have been developed to study the extraction process. The purpose of the study is to conduct a comparative analysis of the results of mathematical modeling and physical modeling. Based on the results of the physical experiment, a mathematical model, and the results of a comparative study of two types of models are presented: The calculated heat carrier (HC) temperatures at the experimental model setup (EMS) inlet (according to the first law of thermodynamics and the Navier-Stokes equations) and the measured HC temperature at the EMS inlet during experiments were compared.

Electron-phonon coupling, bipolar effects, and thermoelectric performance of the CuSbS2 monolayer.

The thermoelectric performance of the CuSbS2 monolayer is determined using the relaxation times obtained from electron-phonon coupling calculations and the transport properties of phonons and electrons. Based on the fully relaxed structure, the lattice thermal conductivity and the electronic transport coefficients are evaluated by solving the Boltzmann transport equation for phonons and electrons under relaxation time approximation, respectively. The tendencies of the transport coefficients depending on the carrier concentrations and temperatures are studied to understand the thermoelectric performance. Based on the bipolar effect, the transport coefficients and intrinsic carrier concentrations, we determined the dimensionless figure of merit ZT in the 300-800 K range. The results demonstrate that the CuSbS2 monolayer should be an p-type semiconductor, and the maximum ZT of 1.36 is obtained, indicating that the monolayer is a good candidate for high-temperature thermoelectric devices. Substantial bipolar effects are observed, and the ones in the x-direction are stronger in comparison to those in the y-direction, which is responsible for the smaller ZT in the x-direction.

RESEARCH OF TECHNOLOGICAL POSSIBILITIES OF HEAT PUMPS’ APPLICATION IN DISTRICT HEATING OF RESIDENTIAL BUILDINGS

The main users of district heating (DH) systems are multi-apartment buildings – 53% of these buildings in Lithuania are supplied with heat from DH systems. Heating systems in buildings are the largest final consumer of energy, accounting for almost half of total energy consumption in many European countries. One of the measures planned for the Lithuanian energy policy in the heat sector of renewable energy sources (RES) until 2030 is the installation of heat pumps (HP) in the DH networks. The purpose of the study is to evaluate the technological possibilities of integrating HP into existing buildings to evaluate the low temperature heat supply. To evaluate the potential temperature lowering of the building heating system, a graph of the lowest possible building heating system temperatures is set, according to which the heat pump for the heating substation is selected, which would raise the temperature of the heat carrier supplied from DH networks to the required temperature for the heating and hot water systems of the building. Applying thermodynamic analysis, a mathematical model is developed that evaluates the ability of the HP to raise the temperature of the supplied heat carrier at the heat substation and determines the energy efficiency of such a solution. During the simulation, two alternatives of constant (regardless of outdoor air temperature) heat carrier temperatures supplied from DH networks were considered: 60 °C (alternative A) and 55 °C (alternative B). To adapt the most appropriate option for the integration of HP, it would be appropriate to combine both alternatives, i. y. to supply 60 °C from the DH network in the cold period of the year and 55 °C in the warm period of the year.

Theory of non-equilibrium ‘hot’ carriers in direct band-gap semiconductors under continuous illumination

The interplay between the illuminated excitation of carriers and subsequent thermalization and recombination leads to the formation of non-equilibrium distributions for the ‘hot’ carriers and to heating of both electrons, holes and phonons. In spite of the fundamental and practical importance of these processes, there is no theoretical framework which encompasses all of them and provides a clear prediction for the non-equilibrium carrier distributions. Here, a self-consistent theory accounting for the interplay between excitation, thermalization, and recombination in continuously-illuminated semiconductors is presented, enabling the calculation of non-equilibrium carrier distributions. We show that counter-intuitively, distributions deviate more from equilibrium under weak illumination than at high intensities. We mimic two experimental procedures to extract the carrier temperatures and show that they yield different dependence on illumination. Finally, we provide an accurate way to evaluate photoluminescence efficiency, which, unlike conventional models, predicts correctly the experimental results. These results provide a starting point towards examining how non-equilibrium features will affect properties hot-carrier based application.

CASE ANALYSIS OF HEAT PUMP INTEGRATION IN DISTRICT HEATING SYSTEM

The installation of heat pumps in district heating (DH) systems is one of the most promising technologies to increase the efficiency of heat supply by using renewable energy sources and reducing heat carrier temperatures in the networks. The possibilities of installing heat pumps in DH systems are very wide, but most often the main purpose of their application is to increase the temperature of the supplied heat carrier at the heat substations of individual consumers or their groups. This paper describes a study that analyzed the possibilities of integrating an individual heat pump at a heat substation in a building to reduce the temperature of the heat carrier in the return line. The results of the study revealed the dependences of the reduction of the heat demand of the building from the DH network, the power of the heat pump, the coefficient of performance (COP), and the reduction of the return temperature.

Optimizing Large-Scale Solar Field Efficiency: Latvia Case Study

Solar energy transformation technologies are increasingly being used worldwide in the district heating sector. In the Baltic states, only one district heating company has implemented a large-scale solar collector field into its thermal energy production system, which is analyzed within this research. In this study, we analyzed the first year operation of the solar field, solar collector efficiency, and several influencing factors, i.e., ambient air temperature, heat carrier flow, and the temperature difference between the supply and return heat carrier temperatures. The study includes collecting and compilation of the data, analyzing influencing factors, and data analysis using the statistical analysis method. In addition, the research presents a simplified multi-regression model based on the actual performance of a large-scale solar field, which allows for forecasting the efficiency of solar collectors by taking into account the main operational parameters of the DH system. The results show that solar energy covers around 90% of the summer heat load of a particular district heating system. However, they also show room for improvements in producing all the necessary heat in the summer using solar energy. The regression analyses show that the most significant correlation between all parameters examined was obtained in May, reaching R2 = 0.9346 in solar field efficiency evaluation. This is due to several suitable conditions for solar energy production, i.e., placing solar collectors at an angle for them to be the most productive, having enough space in the storage tank, and the demand for thermal energy being still higher than in the summer months.

Theoretical analysis of injection driven thermal light emitters based on graphene encapsulated by hexagonal boron nitride

We develop the device model for the proposed injection (electrically) driven thermal light emitters (IDLEs) based on the vertical hexagonal boron nitride layer/graphene layer/ hexagonal boron nitride layer (hBNL/GL/hBNL) heterostructures and analyze their dynamic response. The operation of the IDLEs is associated with the light emission of the hot two-dimensional electron-hole plasma (2DEHP) generated in the GL by both the lateral injection from the side contacts and the vertical injection through the hBNL (combined injection) heating the 2DEHP. The temporal variation of the injection current results in the variation of the carrier effective temperature and their density in the GL leading to the modulation of the output light. We determine the mechanisms limiting the IDLE efficiency and the maximum light modulation frequency. A large difference between the carrier and lattice temperatures of the IDLEs with an effective heat removal enables a fairly large modulation depth at the modulation frequencies about dozen of GHz in contrast to the standard incandescent lamps. We compare the IDLEs with the combined injection under consideration and IDLEs using the carrier Joule heating by lateral current. The obtained results can be used for the IDLE optimization.

A new physical insight into the zero-temperature coefficient with self-heating in silicon-on-insulator fin field-effect transistors

The conflicting impacts of temperature on the threshold voltage and mobility, and consequently on the transfer characteristics of a MOSFET, result in a zero-temperature coefficient (ZTC) point. This point is very important for ensuring the stability of the circuit against temperature variations, as the drain current is temperature independent at this bias voltage. In this work, for the first time, we analyze ZTC bias-point instability caused by the self-heating effect (SHE). For this, we discuss the impact of lattice and carrier temperatures, influenced by the SHE, on the ZTC point, which is important in fin field-effect transistors. We report that the SHE causes the ZTC gate bias voltage to be lowered significantly, by about 16% of the overdrive voltage. We also explain the physics of this phenomenon and present a model to explain this change in the ZTC bias caused by the SHE. We discuss the relation between the change in ZTC due to changes in the threshold voltage, saturation velocity, and their temperature derivatives. Our results also show that the drift of the ZTC (i.e. ) is more critical at higher drain-to-source voltages (V DS). It is important, from an analog-circuit point of view, to predict the ZTC bias point drift caused by the SHE. Furthermore, a common-source amplifier biased at the ZTC predicted by our model-based method is simulated to validate the stability of the circuit against temperature variations. To improve the device design, the device dimensions are optimized to minimize the drift of the ZTC.

Characterization of the photothermal interaction on a viscothermoelastic semiconducting solid cylinder due to rotation under Lord-Shulman model

This paper deals with the photothermal interaction of an isotropic, homogenous, semiconducting, viscothermoelastic solid cylinder in the context of Lord-Shulman's of generalized thermoelasticity theory. The cylinder rotates around its axis with constant angular velocity. The bounding surface of the cylinder has been thermally shocked. The governing equations have been constructed in the Laplace transform domain and numerically calculated inversions of Laplace using the Tzou method. The numerical results for the carrier density increment, temperatures increment, strain, stress, and stress-strain energy have been represented graphically with various values mechanical relaxation time, angular velocity parameter, and lifetime parameter of a photogenerated carrier. The mechanical relaxation time and angular velocity of the rotation parameter have minimal effects on the carrier density function and temperature increment, while its effects on the strain, stress, and stress-strain energy are significant. The photogenerated carrier's lifespan parameter has essential implications on all functions studied.

Characterization of the photothermal interaction due to ramp-type heat on a semiconducting two-dimensional solid cylinder based on the Lord–Shulman model by using double Laplace transform

This article deals with a new model of photothermoelastic and semiconducting two-dimensional solid cylinder in the context of Lord–Shulman's theory of thermoelasticity. The surface of the cylinder has been loaded by ramp-type heat. The double Laplace transform has been applied, and its inversions have been calculated by using the Tzou method. The numerical results for the carrier density increment, temperatures increment, strain, stress, and stress–strain energy have been represented graphically. The ramp-time heat parameter, relaxation time parameter, and cylindrical axis length significantly affect all the studied functions. The ramp-time heat parameter controls the energy generated through the semiconducting materials.

Effect of recombination process in femtosecond laser-induced modification on Ge crystal* *Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11804227).

The dynamics of produced excited carriers under the irradiation of Ge crystal is investigated theoretically by using femtosecond laser pulse. A two-temperature model combined with the Drude model is also used to study the nonequilibrium carrier density, carrier and lattice temperatures, and optical properties of the crystal. The properties of the surface plasmon wave when excited are also studied. The influences of non-radiation and radiative recombination process on the photoexcitation of the semiconductor during pulse and the relaxation after the pulse are described in detail. The results show that the effects of Auger recombination on the nonequilibrium carrier density and optical properties of the crystal and the properties of the surface plasmon polariton are great, whereas the effect of radiative recombination is extremely small.

Characterization of the photothermal interaction on a viscoelastic semiconducting solid cylinder due to ramp-type heating based on green-naghdi theories

This paper is dealing with the photothermal interaction of a homogenous, isotropic, semiconducting, viscothermoelastic solid cylinder in the context of Green-Naghdi theories of generalized thermoelasticity (type-I, -II, and -III). The ramp-type heating has thermally loaded the bounding surface of the cylinder. The governing equations have been constructed in the Laplace transform domain, and the Laplace inversions have been calculated numerically by using the Tzou method. The numerical results for the carrier density increment, temperatures increment, strain, stress, and stress-strain energy have been represented in figures with various values of mechanical relaxation time and ramp-time heat parameter. The mechanical relaxation time has minimal effects on the carrier density function and temperature increment, while its effects on the strain, stresses, and stress-strain energy are significant. The ramp-time heat parameter has significant effects on all the studied functions.

Some physical properties and adsorption isotherms of vacuum-dried honey powder with different carrier materials

This study was aimed at determining effects of different carrier materials and temperatures on water adsorption properties and net isosteric heat of vacuum-dried honey powders. The particle size and Carr index of samples were between 100.04 and 169.29 μm and 23.03–26.59%, respectively. The adsorption isotherms of samples were type II and the Caurie and Peleg models were found to be best for evaluating the adsorption properties of samples. The mean X0 values and adsorption surface areas of samples with maltodextrin, gum Arabic and whey protein isolate were 4.43, 4.76 and 4.22 g/100 g dry matter and 74.89, 65.51 and 68.76 m2/g, respectively. Increasing the temperature decreased the number of adsorbed layers and adsorption surface area of samples. Additionally, the net isosteric heat of samples decreased from 10.09 to −0.78, 20.02 to −0.53 and 7.30 to 0.04 kJ/mol when the moisture content increased by 3–50 g/100 g dry matter in samples with maltodextrin, gum Arabic and whey protein isolate, respectively.

Slow carrier cooling in methylammonium lead bromide quantum dots: Evidence of hot phonon bottleneck

Photoinduced charge carrier dynamics studies in lead halide perovskites helps in explaining key processes like carrier trapping, diffusion and multiexciton dynamics etc. which are of importance to understand the fate of excitons. In the present study, we investigate the dynamics in methylammonium lead bromide perovskite nanocrystals under low and high pump intensity to study hot carrier cooling mechanisms. The single exciton studies conducted under low pump fluences (<N> = 0.3) revealed slow carrier decay with a significant fraction of >1 ns decay times as expected due to long radiative carrier recombination times. This also indicated that fast carrier trapping does not occur as evidenced by absence of any fast decay components. The hot carrier (HC) cooling mechanisms were verified by studying carrier density dependence of carrier temperature decays as extracted from the higher energy part of exciton bleach. These studies revealed a very fast cooling of ∼150 fs under low carrier density 1.5 × 1017/ cm3. However additional experiments under higher carrier densities of ∼1018-1019/cm3 showed a very slow carrier temperature decay with decay time ∼100 ps for the highest intensity investigated. The analysis of hot carrier lifetimes revealed Auger heating and acoustic phonon up-conversion as reason for hot carrier relaxations at higher intensities. Additionally, we carried out experiments under hole quencher, we found lower initial carrier temperatures and faster decay indicating highly efficient hole transfer to the quencher in a time scale faster than cooling of carrier at higher intensities. These results hint at possibility of molecular design for enabling efficient hot carrier extraction from these Quantum Dots (QDs).