Longitudinal Temperature Profiles Research Articles

MHD FREE CONVECTION FLOW OF A NANOFLUID PAST A VERTICAL PLATE IN THE PRESENCE OF HEAT GENERATION OR ABSORPTION EFFECTS

This work is focused on the numerical solution of steady natural convection boundary-layer flow of a nanofluid consisting of a pure fluid with nanoparticles along a permeable vertical plate in the presence of magnetic field, heat generation or absorption, and suction or injection effects. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary-layer equations of the problem are formulated and transformed into a non-similar form. The obtained equations are then solved numerically by an efficient, iterative, tri-diagonal, implicit finite-difference method. Comparisons with previously published work are performed and are found to be in excellent agreement. Representative results for the longitudinal velocity, temperature, and nanoparticle volume fraction profiles as well as the local heat transfer rates for various values of the physical parameters are displayed in both graphical and tabular forms.

Thermal inactivation of airborne viable Bacillus subtilis spores by short-term exposure in axially heated air flow

In this investigation, an experimental facility was developed for quantifying the inactivation of viable bioaerosol particles in a controlled axially heated air flow. The tests were conducted with Bacillus subtilis var. niger endospores. The thermal inactivation of aerosolized spores was measured based on the loss of their culturability that resulted from a short-term exposure to air temperatures ranging from ∼150 to >1000 °C. The cross-sectional and longitudinal temperature profiles in the test chamber were determined for different heating and flow conditions. The characteristic exposure temperature ( T e ) was defined using a conservative approach to assessing the spore inactivation. Experimentally determined inactivation factors ( IF) were corrected to account for the temperature profiles in the axially heated air flow. The reported IF-values serve as the lower approximation of the actual inactivation. Two data sets obtained at different flow rates, Q=18 and 36 L min −1, represent different exposure conditions. In both cases, the thermal exposure of aerosolized spores produced no effect or only a moderate inactivation when the T e remained below ∼200 °C for 18 L min −1 and ∼250 oC for 36 L min −1. The IF-values increased exponentially by about four orders of magnitude as the temperature rose by 150 °C. Depending on the flow rate, IF exceeded ∼10 4 at T e >320 °C ( Q=18 L min −1) or >360 °C ( Q=36 L min −1). At T e ≈375–400 °C, the spore inactivation obtained at both flow rates reached the limit of quantification established in this study protocol, which translates to approximately 99.999% viability loss. The findings were attributed primarily to the heat-induced damage of DNA and denaturation of essential proteins. Up to a certain level of the thermal exposure, these damages are repairable; however, the self-repair capability diminishes as the heat rises and then the damage becomes totally irreversible. The data generated in this study provide an important reference point for thermal inactivation of stress-resistant spores in various biodefense/counterterrorism and air quality control applications.

Observations of plasma heating by fast electron transport at the back side of solid targets

Fast adiabatic plasma heating of a thin solid target irradiated by a high intensity laser has been observed by optical fast interferometry diagnostic. It is driven by the hot electron current induced by the laser plasma interaction at the front side of the target. Radial and longitudinal temperature profiles are calculated to reproduce the observed rear side plasma expansion. The main parameters of the suprathermal electrons have been calculated from these observations.

X-ray spectroscopy of buried layer foils irradiated at laser intensities in excess of 1020 W/cm2

Observations of a rapid decrease in thermal temperature as a function of depth of solid targets irradiated with a short pulse, ultrahigh-intensity laser are reported. This phenomenon is investigated using the Titan short pulse laser with intensities greater than 1020 W/cm2 interacting with buried layer targets. The longitudinal temperature profile is determined by measuring K-shell spectra from a 0.4 μm copper tracer layer placed at various depths (i.e., 0–1.5 μm) within the 2.4 μm thick target. It is observed that the line ratios (He-like K-shell lines) as a function of temperature require a consideration of at least three parameters to analyze the K-shell spectra: hot electron population, time-dependent plasma conditions, and opacity. Here, the study of the effect of these three parameters on measured spectra in the short pulse high intensity laser-matter interactions using the atomic model FLYCHK [H.-K. Chung et al., High Energy Density Phys. 1, 3 (2005)] is presented.

Use of Thermal Infrared Imagery to Complement Monitoring and Modeling of Spatial Stream Temperatures

Thermal infrared (TIR) surveys are effective methods to map surface spatial temperature patterns along a river. We used two data sets of TIR-derived longitudinal temperature profiles to analyze reach-scale spatial patterns of thermal heterogeneity of the Wenatchee River, in the Pacific Northwest region of the United States as part of a temperature total daily maximum load investigation. The TIR data indicate that the river has a general downstream heating trend; the magnitudes, reach variability, and longitudinal gradients are influenced by the headwater conditions, channel morphology, tributary locations, flow rates, and weather. Detailed TIR images facilitate identifying regions with high local thermal heterogeneity where we recommend a weighted average approach to estimate local spatial average temperature using temperatures from pixels of the thermally distinctive areas rather than using the temperature extracted from pixels sampled along the central part of the channel. TIR-derived daily maximum temp...

Experimental Study and Modeling of an Adiabatic Fixed-bed Reactor for Methanol Dehydration to Dimethyl Ether

One-dimensional heterogeneous plug flow model was employed to model an adiabatic fixed-bed reactor for the catalytic dehydration of methanol to dimethyl ether. Longitudinal temperature and conversion profiles predicted by this model were compared to those experimentally measured in a bench scale reactor. The reactor was packed with 1.5 mm γ-Al 2O 3 pellets as dehydration catalyst and operated in a temperature range of 543-603 K at an atmospheric pressure. Also, the effects of weight hourly space velocity (WHSV) and temperature on methanol conversion were investigated. According to the results, the maximum conversion is obtained at 603.15 K with WHSV of 72.87 h −1.

Stabilized premixed combustion within atmospheric gas porous inert medium (PIM) burner

In this study, a modified technique based on the quenching region concept is proposed to enhance the flame stability within porous inert media (PIM). The new technique eliminates disadvantageous features inherent with this category of PIM combustion, such as the high-pressure drop and the continuous degradation of the quenching region. To demonstrate the validity of the proposed technique, the premixed combustion of liquefied petroleum gas and air in the fuel-lean range in PIM burner under atmospheric pressure was examined experimentally. Improved relevant longitudinal temperature profiles and low levels of NO x and CO emissions could be obtained throughout the entire range of operating conditions with no traces of flashback formation. The results also revealed an extension of the fuel-lean burning limit beyond what was typically ex-perienced in free-flame combustion systems. Eventually, the stronger and more robust proposed configuration permits the utilization of PIM combustion technology to cover a new and wider spectrum of practical applications.

Cold Mass Cooling Design Studies for an LHC Inner Triplet Upgrade

A luminosity upgrade of the CERN Large Hadron Collider (LHC) is planned to coincide with the expected end of life of the existing inner triplet quadrupole magnets. The upgraded inner triplet will have much larger heat loads to be removed from the magnets by the cryogenics system. As part of the LHC Accelerator Research Program (LARP), a design study has been completed to investigate the required characteristics of the cold mass cooling system within the framework of a design temperature profile. These characteristics are the beam pipe annulus, collar radial cooling channels, yoke radial cooling channels, yoke longitudinal cooling channels, and heat exchanger connecting pipe. Using these parameters in conjunction with energy deposition calculations, longitudinal and radial temperature profiles for an entire inner triplet are calculated and presented.

Fast electron transport and induced heating in solid targets from rear-side interferometry imaging

Fast adiabatic plasma heating of a thin solid target irradiated by a high intensity laser has been observed by an optical fast interferometry diagnostic. It is driven by the hot electron current induced by the laser plasma interaction at the front side of the target. Radial and longitudinal temperature profiles are calculated to reproduce the observed rear-side plasma expansion. The main parameters of the suprathermal electrons (number, temperature, and divergence) have been deduced from these observations.

Effects of warm water inflows on the dispersion of pollutants in small reservoirs

The effects of the warm water discharged by a nuclear power plant (NPP) into a small reservoir are studied. A case study is presented (José Cabrera NPP—Zorita Hidráulica Reservoir) with experimental data of the reservoir stratification and predicted data of the dispersion of radioactive pollutants from operative or accidental releases. The vertical and longitudinal temperature profiles, electrical conductivity and transparency of the reservoir water were measured for an annual cycle. The results indicate that the continuous warm water discharge from the NPP causes permanent and artificial reservoir stratification. The stratification is significant within 1500 m upstream and 1000 m downstream from the warm water outfall. The pollutant dispersion has been predicted by using a flow model based on N T perfect-mixing compartments in series with feedback. The model parameter, N T , is calculated from the longitudinal diffusion coefficient. The prediction of pollutant dispersion by means of this model shows that the stratification slows down the vertical mixing in the whole water body, and reduces the reservoir volume that is effective for the dilution and dispersion of pollutants. This means that, in the case of a radioactive pollutant release, the reservoir radioactivity level could increase significantly.

Longitudinal profiles of plasma parameters in a laser-ignited capillary discharge and implications for laser wakefield accelerator applications

The evolution of longitudinal electron density and temperature profiles in plasma channel produced by a low-current Plexiglas capillary discharge with laser ignition was investigated by spectroscopic methods. The plasma was produced by an electric discharge using a 0.5mm diameter, 15mm long Plexiglas capillary. The electron density measured in near-outlet region was found to be lower by 30%. Simulations show that this variation of the plasma density near the entrance of the capillary can pose substantial difficulties for external injection of electrons for laser wakefield accelerator applications.

HEAT EXTRACTION PROPERTIES OF A SEWER HEAT EXCHANGE PIPE

Sewage thermal energy is a kind of untapped one that we can easily obtain in a big city. To apply sewage heat to road heating in winter, a heat extraction test was carried out using a heat exchange pipe sank in fluid in a mimic sewer pipe. A longitudinal temperature profile of heat carrier fluid was measured along the heat exchange pipe. The extracted heat increased as the flow rate of sewage or of heat carrier fluid (heat exchange fluid) became high. A quasi-Nusselt number, Nuq was proposed to predict the overall heat transfer coefficient of the heat exchange pipe. The value of Nuq was normalized by the overall heat transfer coefficient, and the heat conductivity and diameter of the heat exchange pipe. As a result, the following relation, Nuq=2.483×103Reh0.34Res0.2Pr0.4 was obtained, where Reh and Res are the Reynolds number of heat exchange pipe and sewage and Pr is the Prandtl number.

Modeling of the Pyrolysis of Large Samples of Polyethylene Including the Melting Process

An experimental and theoretical study has been carried out on the thermal degradation of large samples of high density polyethylene in an inert atmosphere. The experimental results show the existence of significant longitudinal temperature profiles inside the solid, which are basically due to its low thermal conductivity and the melting process. The polyethylene undergoes important volume variations during the experiments: expansion during the melting process and contraction due to pyrolysis. The mathematical model developed takes into account the volume variation and the melting process using the enthalpy method. The temperature profiles and the solid conversion are predicted, and good agreement with the experimental temperature results is obtained. Some discrepancies are observed in the case of solid conversion, probably due to the resistance to mass transfer of product gases in the solid.

Analyses of Acoustic Characteristics of Pulse Combustors under Operating Condition.

Acoustic characteristics of a two dimensional valveless pulse combustion systems having various geometrical constructions are first measured and numerically analyzed under the cold and stagnant conditions, and effects of each acoustic element on the overall resonant properties of the pulse combustion systems are clearly estimated and explained. Comparison of the acoustic resonant behavior numerically analyzed with that experimentally measured yields a suitable set of the acoustic parameters for each system construction, such as the damping factor and reflection coefficient. Frequency characteristics of the resonant pressure fluctuation in the combustion chamber are then numerically estimated under a typical pulse combustion condition, by introducing not only the acoustic parameters obtained but also the longitudinal temperature profile measured. It is found that the resonant pressure exhibits a sinusoidal character and retards in phase by about 35 degree after the original pressure oscillation applied, being in good agreement with those measured in the proposed pulse combustor. It is also confirmed that, by applying it to another type of the pulse combustor, the proposed numerical method can clearly predict the variation in the profile of pressure fluctuation with the tailpipe length.

MULTISCALE THERMAL REFUGIA AND STREAM HABITAT ASSOCIATIONS OF CHINOOK SALMON IN NORTHEASTERN OREGON

We quantified distribution and behavior of adult spring chinook salmon (Oncorhynchus tshawytscha) related to patterns of stream temperature and physical habitat at channel-unit, reach-, and section-level spatial scales in a wilderness stream and a disturbed stream in the John Day River basin in northeastern Oregon. We investigated the effectiveness of thermal remote sensing for analyzing spatial patterns of stream temperature and assessed habitat selection by spring chinook salmon, evaluating whether thermal refugia might be responsible for the persistence of these stocks in rivers where water temperatures frequently exceed their upper tolerance levels (25°C) during spawning migration. By presenting stream temperature and the ecology of chinook salmon in a historical context, we could evaluate how changes in riverine habitat and thermal spatial structure, which can be caused by land-use practices, may influence distributional patterns of chinook salmon. Thermal remote sensing provided spatially continuous maps of stream temperature for reaches used by chinook salmon in the upper subbasins of the Middle Fork and North Fork John Day River. Electivity analysis and logistic regression were used to test for associations between the longitudinal distribution of salmon and cool-water areas and stream habitat characteristics. Chinook salmon were distributed nonuniformly in reaches throughout each stream. Salmon distribution and cool water temperature patterns were most strongly related at reach-level spatial scales in the warm stream, the Middle Fork (maximum likelihood ratio: P < 0.01), and most weakly related in the cold stream, the North Fork (P > 0.30). Pools were preferred by adult chinook salmon in both subbasins (Bonferroni confidence interval: P ≤ 0.05); however, riffles were used proportionately more frequently in the North Fork than in the Middle Fork. Our observations of thermal refugia and their use by chinook salmon at multiple spatial scales reveal that, although heterogeneity in the longitudinal stream temperature profile may be viewed as an ecological warning sign, thermal patchiness in streams also should be recognized for its biological potential to provide habitat for species existing at the margin of their environmental tolerances.

Free convection analysis of a window cavity and its longitudinal temperature profile

Window condensation in dwellings and offices can be very troublesome. It not only obstructs the view through the windows, but also runs off, accelerating the deterioration of paintwork, frames and furniture. In the present article, measurements and modelling techniques have been used to study the longitudinal temperature variation of double-glazed windows. It has been shown, herein, that the above temperature variation is primarily due to the buoyancy driven flow of gas within the sealed enclosure. This flow of gas alternates between the heated inward and cooled outward panes. The present work provides a physical model which can be used to calculate, with precision, the temperatures along the height of double-glazed windows. This method may be a prerequisite for the quantification of condensation, so commonly encountered in the European and North American climates.

Oscillating flow of a heat-conducting fluid in a narrow tube

Thermoacoustic refrigeration occurs in periodic flow in a duct with heat transfer within the fluid and to the tube. This study considers the periodic limit cycle with large pressure oscillations that is obtained in a tube when prescribed, phase-shifted, periodic velocities at the tube ends, at frequencies lower than acoustic eigenmodes, sweep a length comparable to the tube length. The temperature differences between the two ends are of arbitrary magnitude, heat transfer in the transverse direction within the fluid is assumed to be very effective and the thermal mass of the wall is large. The geometry is two-dimensional, axisymmetric, and conduction is accounted for, not only in the fluid, but also with and within the tube wall. A perturbation solution valid in a local near-isothermal limit determines the equilibrium longitudinal temperature profile that is reached at the periodic regime, the pressure field including longitudinal gradients, and the longitudinal enthalpy flux. Results are presented for tubes open at both ends and also with one end closed. In the latter case, a singularity occurs in the temperature at the closed end, with behaviour identical to Rott's result for acoustic flow with small pressure amplitude. Other new results obtained for tubes open at both ends show that when velocities at both ends are in opposite phase, internal singularities in the temperature profiles may occur.

A single-sweep, nanosecond time resolution laser temperature-jump apparatus

We describe a fast temperature-jump (T-jump) apparatus capable of acquiring kinetic relaxation transients via real-time fluorescence detection over a time interval from nanoseconds to milliseconds in a single sweep. The method is suitable for aqueous solutions, relying upon the direct absorption of laser light by the bulk water. This obviates the need for additives (serving as optical or conductive heaters) that may interact with the sample under investigation. The longitudinal temperature profile is made uniform by counterpropagating heating pulses. Dead time is limited to one period of the probe laser (16 ns). The apparatus response is tested with aqueous tryptophan and the diffusion-controlled dimerization of proflavine.

Modelling of temperature distribution in a solid polymer electrolyte fuel cell stack

The production of electricity in a fuel cell system is associated with the production of an equivalent amount of thermal energy, both for large size power plants and for transportation applications. The heat released by the cells must be removed by a cooling system, characterized by its small size and weight, which must be able to assure uniform work conditions and reduce performance losses. Based upon realistic assumptions, a mathematical model has been developed to determine the temperature and current density distribution in a solid polymer electrolyte fuel cell (SPEFC) stack as a function of operating conditions and stack geometry. The model represents a useful tool to identify operating conditions, such as to have an optimal longitudinal and axial temperature profile, so allowing the design of cooling system and bipolar plates. In this paper, the model has been applied to determine the temperature profile of an experimental SPEFC stack. The model is validated by comparing model results with experimental measurements; simulated and experimental results agree satisfactorily.

The effect of bonding wires on longitudinal temperature profiles of laser diodes

The thermal effect of bonding wires in laser diodes is analyzed using the analytical temperature solution for a five-layer structure and an iteration technique. Finite element method is used to confirm the results. Due to the bonding wire, the longitudinal temperature profile of laser diodes exhibits significant reduction at the foot of the wire even with uniform longitudinal heat distribution. For lasers designed with uniform longitudinal current density, heat increases toward the laser facets because of nonradiative recombination of carriers through surface quantum states on the facets. This leads to local temperature concentration on and near the facets. The conduction of heat through the bonding wire at the top center of laser chips further enhances this temperature concentration. In use, the stripe electrode of laser diodes is at uniform voltage. Under this operation condition, the current density would increase in the higher temperature regions due to bandgap decrease, causing higher heat flux. And consequently even higher temperature. Accordingly, the location of bonding wire and the shape of stripe electrode require careful consideration in the design phase to achieve uniform longitudinal temperature profile.