Effective Temperature Difference Research Articles

Fabrication and performance prediction of Ni/Bi0.5Sb1.5Te3 artificially-tilted multilayer devices with transverse thermoelectric effect

Artificially-tilted multilayer transverse thermoelectric devices (ATMTTDs) have a large degree of design freedom, which is convenient for designing devices for different working conditions. However, evaluation and preparation of ATMTTDs has generally been based on trial and error, and coherent performance optimization strategies for different ATMTTDs applications is still lacking. Here, the relationship between performance evaluation indicators, transverse thermoelectric properties, and geometric structure parameters of ATMTTDs has been established via theoretical calculation and experimental verification. The results show that the tilt angle (θ) has a key effect on the transverse thermoelectric properties of ATMTTDs. The optimal transverse thermoelectric figure of merit, power factor, and Seebeck coefficient of Ni/Bi0.5Sb1.5Te3 (BST) ATMTTDs are theoretically predicted at tilt angles of 11°, 21°, and 45°, respectively. Ni/BST ATMTTDs have been fabricated and the experimental results demonstrated that a maximum power generation efficiency of 1.01% and maximum effective refrigeration temperature difference of 0.4 K are reached at θ = 11°, maximum output power density of 411 W/m2 is obtained at θ = 21°, and a maximum response sensitivity of 420 μV/K is achieved at θ = 45°, which is in good agreement with theoretical predictions. This work provides theoretical guidance for manufacturing ATMTTDs for different applications.

The coupling process of steam condensation and falling film evaporation with non-condensable gas

For the steam condensation process inside a horizontal tube under small temperature difference, the operating parameters such as steam flow rate and temperature difference are narrowed in limited variation ranges to guarantee the high heat transfer performance. When the steam is mixed with non-condensable gas, the effective temperature difference shows more complexity compared with pure steam condensation. In this paper, the condensation process of the mixed steam in the tube cooled by the falling film evaporative seawater outside the tube is calculated with the steam mass flow rate of 2–9 kg/(m2·s), the evaporation temperature of the seawater of 50–70 °C, the total temperature difference of 2–4 °C and the inlet non-condensable gas (NCG) mass fraction of 1–4%. The mixed steam condensation heat transfer model combined with distributed parameter model is established and validated to couple the heat transfer on both sides of the tube. The local saturation temperature depression of the mixed steam condensation is divided into two factors, one caused by the flow resistance and the other caused by the non-condensable gas mass fraction. Both types of saturation temperature depression increase with the increase of the inlet non-condensable gas mass fraction. The mass flow rate and the temperature difference are found to have more significant impact on the total temperature depression on the saturation temperature. Besides, the saturation temperature is found to have no significant impact on the condensation heat transfer of the mixed steam. The mass flow rate corresponding to the maximum heat transfer of the heat transfer tube is presented.

Phase-Change Process Inside a Small-Radii Cylinder Subjected to Cyclic Convective Boundary Conditions: A Numerical Study

Abstract We numerically investigate the melting and solidification behavior of phase-change materials (PCMs) encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square-wave). First, we explore the effects of the Stefan and Biot numbers on the nondimensionalized time required for a PCM initially held at Tcold to melt and reach the crossflow temperature Thot (i.e., reference Fourier number T̃ref). The increase in either Stefan or Biot number decreases T̃ref which can be predicted accurately using the correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed. We further study the effect of the cyclic Fourier number T̃ on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates toward the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and the surface temperature oscillates in the vicinity of the melting temperature. This increases the effective temperature difference with the crossflow and leads to a higher overall heat transfer.

Mapping temperature contours for a long-span steel truss arch bridge based on field monitoring data

The temperature-induced response of long-span steel bridges can be more significant than the structural responses associated with operational loads or structural damage. These responses depend on the spatio-temporal temperature variation in bridge members, including the effective temperature and temperature difference within members. Bridges are designed to withstand the extreme temperature variations predicted for a given site. Hence, numerous studies have employed statistical analysis techniques to provide critical information for the design and maintenance of bridges during life cycles. However, the correlation between the effective temperature and temperature difference is usually ignored, which can result in inaccurate assessment of the extreme temperatures in members. In this work, the joint probability distribution for the temperature variation in a long-span steel truss arch bridge is investigated based on field monitoring data. The extreme temperature variations are mapped on contours with relevant return periods; the results show that the probability distribution of the effective temperature can be described using the normal distribution; the weighted sum of two lognormal distributions can describe the distribution of temperature difference. Moreover, extreme values of the effective temperature and temperature difference do not occur concurrently. The effective temperature and temperature difference in the structural member directly exposed to solar radiation vary significantly, while the temperature of the shaded member can be assumed uniform, which is mainly affected by air temperature. The study leads to more accurate estimation of the temperature extremes in long-span steel truss arch bridges, which is of great importance for proper design and maintenance of bridges.

Испытание компоновки коррекционного контура с пластинчатым теплообменником

Pulse enhanced heat transfer technology is introduced, and a plate heat exchanger is designed. A pulsating valve is installed at the outlet of the heat exchanger to pulsate the heat medium. Pulsating and non-pulsating heat transfer tests are carried out on the same heat exchanger. On the basis of experiments, the effective temperature difference, heat flow and convective heat transfer coefficient of the heat exchanger at different pulse frequencies are analyzed by combining the theory of pulse enhanced heat transfer technology, heat transfer capacity, heat flow and convective heat transfer coefficient. Find the relationship between pulsation frequency of heat transfer effect of heat exchanger. The experimental results show that the heat exchanger has high heat transfer efficiency under the experimental conditions when there is pulsation.

Inverse optimization investigation for thermoelectric material from device level

Thermoelectric generators (TEGs) with improved conversion efficiency are in great need for low-grade heat recovery. Existing studies primarily optimize the dimensionless figure of merit (ZT) of thermoelectric (TE) materials to improve TEG efficiency. However, TE material with a high ZT cannot guarantee that associated TEG has an optimal performance in practical conditions. To solve this problem, an experiment-verified model is proposed considering the effective temperature difference, optimal matching resistance and contact effect. Sensitivity analysis has been conducted to inversely identify the optimization direction of TE materials at the device level. The impacts of the key physical properties on TEG performance are systematically studied under typical operating conditions. The study results show that reducing lattice thermal conductivity is of more priority than increasing the power factor for improving TEG performance. For power factor improvements of TE materials, Seebeck coefficient optimization is found to be more important than electrical conductivity increase. Besides, the impacts of operating conditions on optimizing TE materials are also investigated. Finally, an optimization process to improve the generation performance of TE materials is proposed, which opens up a new way to lead the development of TE materials from the device and application level. The study results are helpful to effectively improve the power generation performance of TEG through the proposed optimized method of TE materials.

Modeling of aircraft infrared signature based on comparative tracking

Infrared (IR) aircraft signature has been studied out of many reasons. Someone of them are related to quality monitoring during the technological development, the other one to the possibility of tracking the aircraft in real time, the third to the formation of the appropriate standard target and so forth. Of particular importance are the procedures for tracking the small point aircraft targets at distances up to 20 km from the point of observation, because these targets may have relatively large changes in the effective radiations when compared to the immediate background. This work is related to the methodology for forming standard target aircraft taking into account: the sizes of some parts and the dimensions of the aircraft, simplified geometry which corresponds to the spatial frequency rate of the our model (Johnson’s criteria) for the representative type of the aircraft and the effective temperature difference between the total infrared signature of an aircraft, for a chosen geometry, in relation to the cold background of the clear sky (without cloudiness).

Ion Mobility Shift of Isotopologues in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at Elevated Effective Temperatures.

Ion mobility spectrometers (IMS) separate ions mainly by ion-neutral collision cross section and to a lesser extent by ion mass and effective temperature. When investigating isotopologues, the difference in collision cross section can be assumed negligible. Since the mobility shift of isotopologues is thus mainly caused by their difference in mass and effective temperature, the investigation of isotopologues can provide important insights into the theory of ion mobility. However, in classical IMS operated at ambient pressure, cluster formation with neutral molecules occurs, which significantly influences the mobility shift of isotopologues and thus makes a sound investigation of the effect of ion mass and effective temperature on the ion mobility difficult. In this work, the relative ion mobility of several organic compounds and their 13C-labeled isotopologues is studied in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at high reduced electric fields up to 120 Td, which allows the investigation of nonclustered ion species and thus enables a sound investigation of the mobility shift of isotopologues. The results show that the measured relative ion mobilities of isotopologues having the same effective temperature and, thus, their ion mass dominating the relative ion mobility agree well with theoretical relative ion mobilities predicted by the theory of ion mobility.

Modelling R Coronae Borealis stars: effects of He-burning shell temperature and metallicity

ABSTRACT The R Coronae Borealis (RCB) stars are extremely hydrogen-deficient carbon stars that produce large amounts of dust, causing sudden deep declines in brightness. They are believed to be formed primarily through white dwarf mergers. In this paper, we use mesa to investigate how post-merger objects with a range of initial He-burning shell temperatures from 2.1 to 5.4 × 108 K with solar and subsolar metallicities evolve into RCB stars. The most successful model of these has subsolar metallicity and an initial temperature near 3 × 108 K. We find a strong dependence on initial He-burning shell temperature for surface abundances of elements involved in the CNO cycle, as well as differences in effective temperature and radius of RCBs. Elements involved in nucleosynthesis present around 1 dex diminished surface abundances in the 10 per cent solar metallicity models, with the exception of carbon and lithium that are discussed in detail. Models with subsolar metallicities also exhibit longer lifetimes than their solar counterparts. Additionally, we find that convective mixing of the burned material occurs only in the first few years of post-merger evolution, after which the surface abundances are constant during and after the RCB phase, providing evidence for why these stars show a strong enhancement of partial He-burning products.

Theoretical and numerical investigations of manufacturing bimetal CRA-lined pipes using thermo-hydraulic forming

In this paper, the theoretical formulation corresponding to the thermo-hydraulic forming process was derived, and it was used for calculating the pressure of the hot water fluid, the contact force and hydraulic pressure under various working conditions. The contact force under different effective temperature differences was also obtained by considering the influence of different factors on the hot water pressing process in manufacturing the bimetal corrosion-resistant-alloy-lined pipes. The theoretical results correlated reasonably well with the finite element results indicating the accuracy of the analytical solution. Also, the theoretical results correlated well with the experimental results when the temperature was low. However, by increasing the temperature level, the theoretical results deviated from the experimental results. The numerical, experimental and theoretical results obtained in this study can be used in optimizing the thermo-hydraulic forming process.

Automobile Waste Heat Recovery System Using Thermoelectric Generator

Energy crisis is major problem in this era. Thermoelectric generator is a promising solution for this problem. This research aims to recover waste heat energy from automobile by converting it into electrical energy using thermoelectric generator. Thermoelectric generator is applied at automobile exhaust system to produce electrical energy from heat energy directly with a phenomenon called see-beck effect. This work develops a heat exchanger model with thermoelectric generator for automobile waste heat recovery in which heat source and cold sink are actually modeled. Main emphasis is put on effective temperature difference across the TEGs to get better performance of the exhaust waste heat recovery system. This research shows that the model is able to produce up to 2.67 W energy using 3 Numbers of TEGs in this design.

Experimental Study on a Pulsation-enhanced Heat Transfer Device

The pulsation-enhanced heat transfer technology is introduced, and a volume coil heat exchanger is designed. A pulsation valve is installed at the heat exchanger outlet of the heat exchanger to pulsate the heat medium, and the same heat exchanger is subjected to pulsation and non-pulsation heat transfer tests. Based on the experiments, combined with the theory of pulsation-enhanced heat transfer technology, heat transfer capacity, heat flow, and convective heat transfer coefficient coefficients, the effective temperature difference, heat flow, and convective heat transfer coefficient of the heat exchanger at different pulse frequencies are analyzed. The relationship between the pulsation frequency of the heat transfer effect of the heat exchanger is obtained. The test results show that the heat exchanger has higher heat exchange efficiency when there is pulsation under the test conditions.

Activity-modulated phase transition in a two-dimensional mixture of active and passive colloids.

We study a two-dimensional binary mixture of active and passive colloids as an idealized model of an hybrid aggregate of living cells and inert particles. We perform molecular dynamics simulations of this system using two different thermostats, and we systematically investigate the effect of varying these two effective temperatures on the system behavior, as characterized by its density, structure and thermoelastic properties. Our results indicate that the presence of active colloids shifts the mixture towards the liquid state and renders it more deformable. Such system softening and melting effects due to the addition of active particles are larger than expected from a linear combination of temperatures of the active and passive components. This heightened effect becomes more pronounced as the effective temperature difference between the two components becomes larger. The binary mixture remains homogeneous for moderate colloidal activity, but segregation arises for large effective temperature difference. Our results provide insights to guide future experimental hybrid aggregate studies with promising biomedical applications.

Study of thermal insulation materials influence on the performance of thermoelectric generators by creating a significant effective temperature difference

Thermoelectric generator are attractive heat engines because they can convert heat directly into electricity via Seebeck effect. However, the energy conversion efficiency of today’s thermoelectric generators is significantly lower than that of conventional mechanical engines. Materials and devices are the main direction of its improvement. Although thermoelectric material has been making some progress, actual thermoelectric devices has remained stagnant with rather poor efficiencies. In this paper, a mathematical model containing heat losses ignored by previous studies are developed and used to discuss how to reduce heat losses to improved thermoelectric performance. In order to reduce and eliminate the impact of heat loss and study the effects of heat loss, the segmented thermoelectric modules filling with different insulation fillers are built to verify the accuracy of the model. Self-made experimental instruments are developed to study of the effect of reducing module heat loss on thermoelectric conversion performance. The results show that the filling of insulation materials makes contribution to the improvement of thermoelectric performance, the efficiency of aerogel filled module is 8.225% higher than that of unfilled module, and the efficiency of thermoelectric module can be improved up to 9.12% by adding ideal thermal insulation materials. The results also showed that the performance of TE module depends on the thermal conductivity of filling materials and its’ filling rate. Those results provided some practical guidelines for the design and improvement of practical thermoelectric modules.

FEATURES OF USE OF THERMAL IMAGER ON UNMANNED AERIAL VEHICLES

The article explains the features of the use of thermal imagers for military intelligence is no longer news, and but when applying them to the unmanned aerial vehicle, there are many features, for example, the conditions of location on board, vibration from the motor, lighting, background noise. This article is devoted to the review of spheres of use of drones and recommended designs. The main initial task is to determine the design of the drone, depending on its purpose: type multicopter or glider. The actual problem is improving the output parameters of thermal imaging cameras. Special technologies will enhance the quality of the manufacture of uncooled microbolometers. To improve the physical characteristics of the camera lens, chemical compounds from several materials are used, for example, lenses from Ge-Sb-Se and enlightenment coatings. An overview of analogue devices gives reason to believe that in order to improve the minimum resolution temperature difference, it is necessary to use more light-weight lenses and to coordinate them with microbolometer matrices. The article gives a comparative description of the basic ready-made solutions of thermal imaging modules that can be used on an unmanned aerial vehicle, as well as a method of estimating the image quality by calculating the minimum effective temperature difference. The results show that considered analogs of thermal imaging modules suggest that in addition to matching the parameters of the microbolometric matrix and the lens plays a big role software, namely algorithms for processing the flow of frames to stabilize the image. In conclusion, the author describes the obtained physico-mathematical model of the thermal imager, which is located on an unmanned aerial vehicle, and ways of controlling the most important output parameters of thermal imagers: spatial and temperature resolution, minimum resolution of temperature difference

From multicolor-photometric observations to a guaranteed mass of AL Cas

We utilize the PAdova and TRieste Stellar Evolution Code (PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters. Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the Wilson-Devinney (W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary (f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference ΔT = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe (DCRL method) and depending on calculation of the W-D code (DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period (Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the (O – C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body (M3 sin i′ = 0.279 M⊙) is derived from our two methods.

Experiments and a simplified theoretical model for a water-cooled, stove-powered thermoelectric generator

A water-cooled, stove-powered thermoelectric generator was designed and tested to provide electricity in off-grid areas and under emergency conditions. An Ω-shaped heat collector, which facilitates the compact incorporation of 20 thermoelectric modules and works under the radiation heat transfer mode, was proposed. A power load test was performed and compared with previous studies, thereby indicating that a standardization is required for future studies. Different aspects for evaluating the performance of a stove-powered thermoelectric generator were discussed, and appropriate parameters to qualify a stove-powered thermoelectric generator were suggested. Thermoelectric efficiency was measured and compared with a theoretical prediction. A simplified theoretical model, which was verified with experimental data, was developed to explore the temperature distribution inside the thermoelectric module and the power generation performance of the entire stove-powered thermoelectric generator. Special efforts were exerted to reveal the influences of thermal grease, ceramic substrate, and thermal contact on the effective temperature difference.

A comparative experimental study on the performance of mixing ventilation and stratum ventilation for space heating

In this paper, a comparative experimental study on the performance of mixing ventilation and stratum ventilation for space heating was carried out. Objective and subjective experiments were both conducted to explore the difference of the thermal performance between the two types of ventilation. In the objective experiment, air temperature distribution, air velocity distribution, and ventilation effectiveness of stratum ventilation and mixing ventilation were discussed. Research results found that stratum ventilation can realize to reduce energy consumption by 25% compared with mixing ventilation. Meanwhile, the indoor thermal comfort was also investigated in this study. Overall thermal sensation and comfort (OTS and OTC), effective draft temperature (EDT) and vertical air temperature difference (VTD) were introduced as the evaluation indicators. By employing stratum ventilation for heating, the indoor comfort can be enhanced by 10.0% with the same supply air parameters as mixing ventilation. As a whole, stratum ventilation showed excellent performance not only on energy saving but also the indoor comfort for space heating. The data obtained in this study can also provide a reference for the design and optimization of stratum ventilation used for space heating.

Heat Transfer Correlations for Laminar Free Convection in Vertical Channels with Asymmetrically Heated Isothermal Walls

Laminar free convection in a vertical channel with isothermal walls is a classical heat transfer problem. In general, the channel walls may be at different temperatures, leading to a difference in the rate of heat transfer at the walls. Although numerical and experimental results are often presented in terms of average wall Nusselt numbers, separate correlations for heat transfer at each wall are rarely available. The few existing relations are complex in form due to the extra parameters introduced to facilitate the correlation of results. Moreover, the existing correlations do not reflect the physics of the problem in full. In this work, the three-temperature problem of laminar-free convection of air in a tall vertical channel with isothermal walls is studied in a new theoretical framework, namely the extended Newton formulation. This formulation eliminates the need for an effective temperature difference, hence simplifying the presentation and correlation of the results. The dQdT technique was utilized along with computational fluid dynamics to calculate the average paired Nusselt numbers that characterize the extended Newton formulation of the problem. The dQdT results were then used to derive heat transfer correlations which are both simpler in form and more accurate than the existing correlations. The proposed correlations are applicable to cases of both channel walls hotter or both colder than the ambient air.

Network of thermoelectric nanogenerators for low power energy harvesting

We report the design, elaboration and measurements of an innovative planar thermoelectric (TE) devices made of a large array of small mechanically suspended nanogenerators (nanoTEG). The miniaturized TE generators based on SiN membranes are arranged in series and/or in parallel depending on the expected final resistance adapted to the one of the load. The microstructuration allows, at the same time, a high thermal insulation of the membrane from the silicon frame and high thermal coupling to its environment (surrounding air, radiations). We show a ratio of 45% between the measured effective temperature of the membrane, (and hence of the TE junctions), and the available temperature of the heat source. The temperature difference generated across the TE junction reaches a value as high as 60 K per mm. Energy harvesting with this planar TE module is demonstrated through the collected voltage on the TE junctions when a thermal gradient is applied, showing a harvested power of 0.06 μWatt for a 0.5cm2 chip for an effective temperature difference of 6.8 K. The optimization of nanoTEGs performances will increase the power harvested significantly and permit to send a signal by a regular communication protocol and feed basic functions like temperature measurement or airflow sensing.