Relative Temperature Difference Research Articles

H2 production by the thermoelectric microconverter coupled with microbial electrolysis cell

Microbial electrolysis cell (MEC) is a kind of environmental methods to produce H2. However, extra voltages are always supplied to overcome the energy barrier. In this study, the thermoelectric microconverter-MEC coupled system for H2 production from acetate was first investigated. The results showed that the thermoelectric microconverter could directly convert waste heat energy to electricity, even at relative low temperature difference as 5 °C. In the elevated hot side temperatures, the hydrogen yield and coulombic efficiency were gradually increased from 1.05 to 2.7 mol/mol acetate and from 27 to 83%, respectively. Meanwhile, the hydrogen production rate and current density were also increased with hot side of the thermoelectric microconverter ranging from 35 to 55 °C. A relatively high cathodic hydrogen recovery (RH2) (81–95%) was obtained during the whole experimental period. The community analysis revealed that Geobacter accounted for over 29% of total genus in the anode biofilm, which matched the MEC performance well. Therefore, waste heat is a great potential power source and it could effectively help MEC produce hydrogen via using the thermoelectric microconverter.

Two energy balance closure approaches: applications and comparisons over an oasis-desert ecotone

Studies of energy balance that rely on eddy covariance (EC) are always challenged by energy balance closure, which is mainly caused by the underestimations of latent heat flux (LE) and sensible heat flux (Hs). The Bowen ratio (BR) and energy balance residual (ER) approaches are two widely-used methods to correct the LE. A comprehensive comparison of those two approaches in different land-use types is essential to accurately correcting the LE and thus improving the EC experiments. In this study, two energy balance approaches (i.e., BR and ER) were compared to correct the LE measured at six EC sites (i.e., three vegetated, one mixed and two non-vegetated sites) in an oasis-desert ecotone of the Heihe River Basin, China. The influences of meteorological factors on those two approaches were also quantitatively assessed. Our results demonstrated that the average energy closure ratio ((LE+Hs)/(Rn–Gs); where Rn is the surface net radiation and Gs is the surface soil heat flux) was approximately close to 1.0 at wetland, maize and village sites, but far from 1.0 at orchard, Gobi and desert sites, indicating a significant energy imbalance at those three latter sites. After the corrections of BR and ER approaches that took into account of soil heat storage, the corrected LE was considerably larger than the EC-measured LE at five of six EC sites with an exception at Gobi site. The BR and ER approaches yielded approximately similar corrected LE at vegetated and mixed sites, but they generated dissimilar results at non-vegetated sites, especially at non-vegetated sites with low relative humidity, strong wind, and large surface-air temperature difference. Our findings provide insight into the applicability of BR and ER approaches to correcting EC-based LE measurements in different land-use types. We recommend that the BR-corrected and ER-corrected LE could be seriously reconsidered as validation references in dry and windy areas.

Transpiration and Thermophoresis Effects on Non-Darcy Convective Flow Past a Rotating Cone with Thermal Radiation

In this article, mathematical model is developed for transport phenomena in an incompressible viscous fluid regime adjacent to a rotating vertical cone with thermal radiation and transpiration effects. The governing equations for the pertinent geometry are non-dimensionalized by employing specified transformations. A set of resultant equations are solved by numerical method. The solutions of this model are carried out under physical realistic boundary conditions to compute velocities, temperature and concentration functions distributions. The results are compared with previously available existing results. The excellent agreement has been found. The effect of thermal radiation, transpiration (surface injection/suction) and Forchheimer parameters, thermophoretic coefficient and relative temperature difference parameter on flow characteristics is illustrated graphically. It is observed that substantial influence has been exerted on flow characteristics, heat transfer rate (Nusselt number) and mass transfer rate (Sherwood number) for various values of transpiration parameter. The wall thermophoretic velocity changes according to the variation of physical parameters.

Compressibility effect on natural convection flow along a vertical plate with isotherm and streamwise sinusoidal surface temperature

In the present investigation compressibility effect on two-dimensional steady natural convection boundary layer flow of a viscous fluid past a vertical plate has been studied. The governing equations are transformed into a non-dimensional form and the solutions are obtained by four different methods, namely, a perturbation method for the small values of local compressibility variable, ξ, asymptotic solutions for large ξ, the direct finite difference method and the implicit finite difference method with Keller-box scheme for all ξ. In order to examine the results obtained from the four methods, calculations have been carried out for a wide range of parameters. The results obtained by the above mentioned four methods are compared and found in excellent agreement. Moreover, the effects of various practical values of the relative temperature difference, α, and the surface temperature wave amplitude a on the local skin friction, the rate of heat transfer and the isotherms are shown graphically.

Heat pump without particle transport or external work on the medium achieved by differential thermostatting of the phase space.

We propose a mechanism that enables heat flow from a colder region to a hotter region without necessitating either particle transport or external work on the conductor, thereby bypassing the compressor part of a classical heat pump cycle. Our mechanism relies on thermostatting the kinetic and configurational temperatures of the same particle differently. We keep the two ends of a conductor, which in the present study is a single dimensional ϕ(4) chain, at the same kinetic temperature T(0), but at different configurational temperatures--one end hotter and the other end colder than T(0). While external energy is needed within the thermostatted regions to achieve this differential thermostatting, no external work is performed on the system itself. We show that the mechanism satisfies the statistical form of the second law of thermodynamics (the fluctuation theorem). The proposed mechanism reveals two interesting findings: (i) contrary to traditional thermodynamics where only the kinetic temperature is thought to govern heat conduction, configurational temperature can also play an important role, and (ii) the relative temperature difference between the kinetic and configurational variables governs the direction of heat flow. The challenge, however, is in developing experimental techniques to thermostat the kinetic and configurational variables of the same particle at different values.

Impact of cabin environment on thermal protection system of crew hypersonic vehicle

Hypersonic crew vehicles need reliable thermal protection systems (TPS) to ensure their safety. Since there exists relative large temperature difference between cabin airflow and TPS structure, the TPS shield that covers the cabin is always subjected to a non-adiabatic inner boundary condition, which may influence the heat transfer characteristic of the TPS. However, previous literatures always neglected the influence of the inner boundary by assuming that it was perfectly adiabatic. The present work focuses on studying the impact of cabin environment on the thermal performance. A modified TPS model is created with a mixed thermal boundary condition to connect the cabin environment with the TPS. This helps make the simulation closer to the real situation. The results stress that cabin environment greatly influences the temperature profile inside the TPS, which should not be neglected in practice. Moreover, the TPS size can be optimized during the design procedure if taking the effect of cabin environment into account.

Radiation Effects in Flow through Porous Medium over a Rotating Disk with Variable Fluid Properties

The present study investigates the radiation effects in flow through porous medium over a permeable rotating disk with velocity slip and temperature jump. Fluid properties density(ρ), viscosity(μ), and thermal conductivity(κ)are taken to be dependent on temperature. Particular case considering these fluid properties’ constant is also discussed. The governing partial differential equations are converted into nonlinear normal differential equation using similarity alterations. Transformed system of equations is solved numerically by using Runge-Kutta method with shooting technique. Effects of various parameters such as porosity parameterK, suction parameterWs, rotational Reynolds number Re, Knudsen number Kn, Prandtl number Pr, radiation parameterN, and relative temperature difference parameterεon velocity profiles along radial, tangential, and axial direction and temperature distribution are investigated for both variable fluid properties and constant fluid properties. Results obtained are analyzed and depicted through graphs and table.

Idealized Numerical Experiments on Cyclone Development in the Tropical, Subtropical, and Extratropical Environments

Abstract The development of cyclones, particularly in the Southern Hemisphere summer, is active in the tropics and extratropics but is inactive in the subtropics. To elucidate the influence of environmental fields on the cyclone development in the tropics, subtropics, and extratropics, idealized numerical experiments are conducted using a nonhydrostatic channel model. The experiments examine the development of a weak initial vortex within a zonally uniform environmental field that consists of five factors: the Coriolis parameter, zonal wind, potential temperature, relative humidity, and surface temperature difference between the ocean and atmosphere. The idealized experiments successfully reproduce the significant cyclone development in the tropical and extratropical environment as well as no cyclone development in the subtropical environment. This result confirms the dominant role of the environmental field in controlling the cyclone development. To clarify which environmental factor is responsible for the suppression of cyclone development in the subtropics, a series of sensitivity experiments is performed. A tropical cyclone cannot develop in the subtropics because of low temperature, strong stratification, and strong vertical shear compared to the tropics. On the other hand, an extratropical cyclone cannot develop in the subtropics because of the small Coriolis parameter and weak vertical shear compared to the extratropics. The relative humidity and surface temperature difference play only secondary roles. These results provide useful insights into the climatological distribution of various types of synoptic-scale cyclones.

Spin state transition and partitioning of iron: Effects on mantle dynamics

Experimental studies at pressure and temperature conditions of the Earth's lower mantle have shown that iron in ferropericlase (Fp) and in Mg-silicate perovskite (Pv) undergoes a spin state transition. This electronic transition changes elastic and transport properties of lower mantle minerals and can play an important role in mantle convection. Here we focus on the geodynamic effect of the spin-induced density modifications caused by the volume collapse of Fp and by the variation of Fe partitioning (KPv–Fp) between Fp and Pv. Since KPv–Fp behavior strongly depends on alumina content, we explore two end-member compositions, one Al-bearing (with 4.7 wt% Al2O3 in Pv) and the other Al-free. We use the theoretical model by Sturhahn et al. (2005) to calculate the spin configuration of Fp over a range of pressure–temperature conditions, and use experimental results to model Fe partitioning. We then apply the Mie–Grüneisen–Debye equation of state to obtain the density of the mineral assemblages. The calculated amplitude of the density change across the spin state transition is less than 1%, consistent with experiments by Mao et al. (2011); our density profiles differ from PREM by less than 1.5%. The spin-induced density variations are included in a three dimensional convection code (Stag3D) for a compressible mantle. We find small temperature differences between models with and without spin state transitions, since over billions of years the relative temperature difference is less than 50 K. However the relative RMS vertical velocity difference is up to 15% for an Al-free system, but only less than 6% for an Al-bearing system.

Theoretical and Experimental Study of Spectral Selectivity Surface for Both Solar Heating and Radiative Cooling

A spectral selectivity surface for both solar heating and radiative cooling was proposed. It has a high spectral absorptivity (emissivity) in the solar radiation band and atmospheric window band (i.e., 0.2~3 μm and 8~13 μm), as well as a low absorptivity (emissivity) in other bands aside from the solar radiation and atmospheric window wavelengths (i.e., 3~8 μm or above 13 μm). A type of composite surface sample was trial-manufactured combining titanium-based solar selective absorbing coating with polyethylene terephthalate (TPET). Sample tests showed that the TPET composite surface has clear spectral selectivity in the spectra of solar heating and radiation cooling wavelengths. The equilibrium temperatures of the TPET surface under different sky conditions or different inclination angles of surface were tested at both day and night. Numerical analysis and comparisons among the TPET composite surface and three other typical surfaces were also performed. These comparisons indicated that the TPET composite surface had a relative heat efficiency of 76.8% of that of the conventional solar heating surface and a relative temperature difference of 75.0% of that of the conventional radiative cooling surface, with little difference in cooling power.

Thermal load in a medium-sized European city using the example of Aachen, Germany

In this paper we focus on air temperature and its distribution within a medium-sized European city (Aachen) to identify those areas where high levels of thermal load are likely to be observed. The temperatures for the whole city area are examined by means of a GIS-based model. This approach based on mobile measurements demonstrates the distribution of air temperature differences in relation to a reference station and allows for a detailed analysis of the influencing factors of urban structure and land use. Despite the fact that air temperature distribution in Aachen is largely determined by terrain, the influences of land use and urban structures are apparent in the model results. The evaluation of afternoon and evening air temperature data for the summer half-year (April–September) show that the importance of factors contributing to thermal load varies in the course of the day. During daytime the highest air temperature arises in industrial areas with a high degree of surface sealing. However, during the evening inner-city residential quarters with a dense building structure show the highest thermal load. Forest and green spaces also determine the specific air temperature patterns but their impact varies in the course of the day and with the size of neighborhood used for correlation statistics. The spatial structure of the modeled temperature distribution is in accordance with the spatial structure of the surface radiant temperatures from a thermal image over wide areas of Aachen. Deviations are obvious for buildings whose roof materials cause surface temperatures that differ significantly from air temperatures modeled for the 2 m level. Furthermore, the comparison makes obvious the limits of the model: the effects of cold air drainage flows and wind directions cannot be assessed. However, this is not considerably detrimental to the results.

대규모 도시 재개발에 따른 기상환경변화

Urbanization affects the local thermal environment due to the large scale land use changes. To investigate the weather environment change of large scale urban redevelopment, 9 surface temperature and humidity observations were accomplished at Eunpyeong new town area. The observation period is from March 2007 to February 2010. In the center of development area, the air temperature has increased and relative humidity has decreased, by the changes of the land cover and building construction. In the area where the green zone is maintained, air temperature and relative humidity were not changed significantly. The air temperature and relative humidity for the other development observation stations is decreased and increased, respectively. The relative temperature difference between study area and a neighboring rural location was increased during observation periods. The difference is the highest during winter. The urban-rural minimum temperature difference was increased at development area, which means that urbanization affects increasing of minimum temperature in study area.

Quantitative modeling of blistering zones by active thermography for deterioration evaluation of stone monuments

Abstract Infrared thermography for stone monuments to date has primarily focused on qualitative analysis to judge the location of defect zones using relative temperature differences, but there are difficulties in mapping a blistering zone and quantitatively calculating its area. Therefore, this study used quantitative modeling to map blistering zones with graduated heating thermography. To achieve this goal, the following steps were performed: acquisition of thermographic images by passive and active methods, construction of a temperature distribution curve, establishment of the critical temperature and transitional zone, classification of the relative deterioration grades of the blistering zone, monochrome processing, vectorization, and deterioration evaluation of the blistering zone. After evaluating the blistering degree of the specimen through modeling, the total areas and rates were calculated as 359.3 cm 2 and 80.1%, respectively. This study was very useful for identifying the location, area, and relative degree of deterioration of blistering zones that were not easily detectable with the naked eye. In the future, if quantitative modeling of blistering zones is actively applied to deterioration maps, the reliability of deterioration evaluation for stone monuments will be improved, and additional deterioration, such as scaling, may be prevented.

Investigation of entropy generation in MHD and slip flow over a rotating porous disk with variable properties

In the present study the effects of magnetic interaction number, slip factor and relative temperature difference on velocity and temperature profiles as well as entropy generation in magnetohydrodynamic (MHD) flow of a fluid with variable properties over a rotating disk are investigated using numerical methods. The nonlinear governing equations of flow and thermal fields are reduced to ordinary differential equations by the Von Karman approach and are then solved numerically under the related boundary conditions. The results are compared with previous studies. The profiles for radial, tangential and axial velocities and temperature profiles, average entropy generation rate and average Bejan number are sketched for different values of magnetic interaction number, slip factor, relative temperature difference, suction/injection parameter and the effects of these parameters are discussed.

The effect of BRDF surface on radiative heat transfer within a one-dimensional graded index medium

The traditional diffuse or specular surface assumption, which is simple but provides limited information, is insufficient to fully characterize a real surface. The BRDF (Bidirectional Reflectance Distribution Function) surface, which is closer to the real surface, is introduced into the radiative heat transfer problem for the first time. A Minnaert model for the BRDF surface is applied and the genetic algorithm is used to obtain the parameters of the proposed model. The DRESOR (Distribution of Ratios of Energy Scattered by medium Or Reflected by surface) method and the RMC (Reverse Monte Carlo) method are extended to solve the radiative heat transfer within a 1-D absorbing, emitting and scattering graded index medium with BRDF surfaces. The temperature and radiative flux distributions under radiative equilibrium are analyzed under different kinds of graded indexes, optical thicknesses and scattering albedos. The results obtained by the DRESOR method and the RMC method coincide well with each other, which indicates the accuracy of the calculation. Compared with the corresponding diffuse surface, though the relative temperature difference of the BRDF surface is slightly within ±2%, the radiative flux increases significantly by 3.5–12%. And this influence is enhanced by the shortening of the optical thickness while varies little with the changes of graded index and scattering albedo.

Effects of breaking vibrational energy equipartition on measurements of temperature in macroscopic oscillators subject to heat flux

When the energy content of a resonant mode of a crystalline solid in thermodynamic equilibrium is directly measured, assuming that quantum effects can be neglected it coincides with temperature except for a proportionality factor. This is due to the principle of energy equipartition and the equilibrium hypothesis. However, most natural systems found in nature are not in thermodynamic equilibrium and thus the principle cannot be taken for granted. We measured the extent to which the low-frequency modes of vibration of a solid defy energy equipartition, in the presence of a steady state heat flux, even close to equilibrium. We found, experimentally and numerically, that the energy separately associated with low-frequency normal modes depends strongly on the heat flux, and decouples noticeably from temperature. A relative temperature difference of 4% across the object around room temperature suffices to excite two modes of a macroscopic oscillator, as if they were at equilibrium, separately, at temperatures about 20% and a factor of 3.5 higher. We interpret the result in terms of new flux-mediated correlations between modes in the nonequilibrium state which are absent at equilibrium.

Universality of energy conversion efficiency for optimal tight-coupling heat engines and refrigerators

A unified χ-criterion for heat devices (including heat engines and refrigerators), which is defined as the product of the energy conversion efficiency and the heat absorbed per unit time by the working substance (de Tomás et al 2012 Phys. Rev. E 85 010104), is optimized for tight-coupling heat engines and refrigerators operating between two heat baths at temperatures Tc and Th( > Tc). By taking a new convention on the thermodynamic flux related to the heat transfer between two baths, we find that for a refrigerator tightly and symmetrically coupled with two heat baths, the coefficient of performance (i.e., the energy conversion efficiency of refrigerators) at maximum χ asymptotically approaches when the relative temperature difference between two heat baths is sufficiently small. Correspondingly, the efficiency at maximum χ (equivalent to maximum power) for a heat engine tightly and symmetrically coupled with two heat baths is proved to be up to the second order term of ηC ≡ (Th − Tc)/Th, which reverts to the universal efficiency at maximum power for tight-coupling heat engines operating between two heat baths at small temperature difference in the presence of left–right symmetry (Esposito et al 2009 Phys. Rev. Lett. 102 130602).

Application of Infrared Imaging Technology in Fault Diagnosis of Electrical Equipment

Most of electrical equipment failure are associated with overheating and have the characteristics of regional in power systems, temperature and grey value has the nonlinear mapping relationship in infrared image. In this paper, in order to extract image edge features, the infrared image would be preprocessed, then we can achieve identification mark of higher image gray value and automatic achieve the positioning of electrical equipments high temperature area by the topology matrix correction, and then using relative temperature difference method to judge electrical equipment failure. Experimental results show that this method can quickly and effectively locating and identify suspected overheat fault of electrical equipment.

The Infrared Diagnostic Technology of Power Transmission Devices and Experimental Study

Study on a monitoring method of the faults of high voltage device. Research the measurement theory of infrared thermal imager about the faults of high voltage device. And design a judging method which bases on the relative temperature difference of high voltage device. Then design software which recognizes the faults of high voltage device with the infrared technology. This software scan unusual point of the infrared picture on all sides, and then indent the faults of these device and feed back the faults information, according to the judging method. Last, do the simulation test about the faults of devices, and then identify the faults of current mutual inductor and voltage mutual inductor. The results state that this technology realizes the analysis ability autumnally of the devices faults, and improve the work efficiency to monitor these devices. It helps to guarantee power grid moving safely.

An experimental study on geysering phenomena induced by buoyancy in a heating system

The geysering phenomenon caused by the interaction of buoyancy of vapor and resistance of piping, include initial heat up process, intermittent vapor venting, periodically significant fluctuation of flow parameters and alternative flow patterns, influenced by the factors, including different height of upper plenum, diameter of vertical column, initial subcooling, coolant inventory and heating power, which is experimentally investigated by using a small scale experiment facility. The experimental results show that the geometry of the rising pipe and heating power are the key influence factors based on quantitative statistical analysis of the experimental data, and the geysering phenomenon is more obvious under greater ratio of height to diameter of vertical pipe and larger heating power. A dimensionless number GEY defined by the normalized pressure difference to relative temperature difference ratio of the vertical column is proposed to identify the venting and reflux in the geysering and to determine the period of geysering, and the reciprocal GEY crest factor can be the indicator of geysering. Based on the mechanism analysis, the system internal heat models are developed to obtain the heat transfer capacity of the system, and the results of which agree with the experimental data.