Initial Temperature Difference Research Articles

A practical heat transfer model for geothermal piles

Idealized heat source models, which assume constant heat flux along the entire length of heat sources, cannot be used for accurate quantification of ground temperature response during thermal operation of geothermal piles. This paper presents an annular cylinder heat source model that can realistically simulate heat transport by the fluid circulating through the tubes embedded in heat exchanger piles. A finite difference code is developed for simultaneous solution of partial differential equations, which describe both transient and steady-state heat transfer from a geothermal pile to the surrounding soil. Results show that the use of a constant heat flux along the entire length of a heat exchanger pile may significantly misinterpret thermal response over time after the start of heat exchange operation. The impact of different model parameters on the performance of a geothermal pile is investigated through a sensitivity study. Based on the results from sensitivity study, initial temperature difference between ground and circulation fluid, thermal conductivity of soil, and radius of circulation tube are identified to be the most important parameters that affect thermal efficiency of a geothermal pile.

Zeolites in Mafic Pyroclastic Rocks from the Sandikli-Afyonkarahisar Region, Turkey

AbstractGeologic mapping and crystal-chemical analysis of Middle-Upper Miocene volcanics in the Sandıklı-Afyonkarahisar region of Turkey, coupled with published zeolite analyses has revealed that western Turkey hosts unique zeolitic mineral assemblages with distinct paragenetic sequences. The present investigation focused on pyroclastic deposits, including low to intermediate potassic trachytic/trachyandesitic tuffs (LPT) and high potassic tephriphonolitic, tephritic, and trachybasaltic tuffs (HPT), each of which contains various styles of zeolites. Optical petrography, X-ray powder diffraction, and chemical analyses have revealed varying degrees of lithification, probably related to differences in initial emplacement temperature, depositional mechanism and thickness, chilling rate, and extent of mafic composition. Zeolitization was further influenced by meteoric flushing in a hydrologically open system. Chabazite in the LPT from the Selçik area occurs extensively as coatings and infillings of pores. Phillipsite in the HPT found in the Ballık, Küfeke, and Ömerkuyu areas dominates the assemblage and is accompanied by chabazite and minor amounts of analcime. Analcime was probably generated by alteration of leucite which is found as a pyrogene mineral. Alkali zeolites or Ca-bearing zeolites formed as a consequence of the addition of Ca and/or the removal of Na (i.e. dissolution of analcime). The paragenetic sequence may be described as: analcime/phillipsite → chabazite → calcite. The characterization of these assemblages may lead to better exploitation strategies for natural zeolitic resources in the region.

Scanning tunneling microscope-quartz crystal microbalance study of temperature gradients at an asperity contact

Investigations of atomic-scale friction frequently involve setups where a tip and substrate are initially at different temperatures. The temperature of the sliding interface upon contact has thus become a topic of interest. A method for detecting initial tip-sample temperature differences at an asperity contact is described, which consists of a scanning tunneling microscope (STM) tip in contact with the surface electrode of a quartz crystal microbalance (QCM). The technique makes use of the fact that a QCM is extremely sensitive to abrupt changes in temperature. In order to demonstrate the technique's capabilities, QCM frequency shifts were recorded for varying initial tip-substrate temperature differences as an STM tip was brought into and out of contact. The results are interpreted within the context of a recent model for thermal heat conduction at an asperity contact, and it is concluded that the transient frequency response is attributable to small changes in temperature close to the region of contact rather than a change in the overall temperature of the QCM itself. For the assumed model parameters, the results moreover reveal substantial temperature discontinuities at the boundary between the tip and the sample, for example, on the order of 10-15 °C for initial temperature differences of 20 °C.

Study on the solidification kinetics of high-density polyethylene during thin-walled injection molding process

Abstract In this work, the effect of the initial and secondary temperature differences on the solidification behaviors of high-density polyethylene (HDPE) during the thin-walled injection molding (TWIM) was intensively investigated. Simulated temperature profiles using the enthalpy transformation methodology were compared with an in situ temperature measurement, and reasonable agreement was achieved between calculations and measurements. Two-dimensional wide-angle X-ray diffraction characterization shows that the formation of oriented crystal structures was considerably affected by the thermal gradient within the injection-molded article. The present study can be practically significant to the optimization of the cooling parameters during the TWIM of crystalline polymers as well as to the further study on the relationship among “processing-structure-property” of polymeric materials.

Duration of off-loading and recurrence rate in Charcot osteo-arthropathy treated with less restrictive regimen with removable walker

ObjectiveRecent literature on acute diabetic Charcot osteoarthropathy (CA) reports unusually long periods of off-loading. Data suggest that this might increase the re-currence rate. Subsequently we evaluated the influence of duration of off-loading on the risk of required re-casting. Research Design and MethodsIn this retrospective consecutive series from 2000 to 2005, 56 people with diabetes and an acute Charcot foot were included. The inclusion criteria were an initial persistent temperature difference more than 2°C between the two feet, oedema, and typical hot spots on a bone scintigram, radiology, and a typical clinical course. Treatment was off-loading in a removable cast and 2 crutches. In-door walking was allowed. Gradually augmented weight bearing was prescribed when the skin temperature difference had decreased to a level less than 2°C and edema had subsided. Re-casting was required for immediate exacerbation during re-load as well as for recurrence — defined as new swelling and skin temperature difference of more than 2°C in the same foot occurring after a stable interval of at least one month after full weight bearing. ResultsThe duration of off-loading for all patients was 141±21days (mean±SD). Three patients (5%) were re-casted immediately for exacerbation after re-load and 7 patients (12 %) after recurrence of the CA. Duration of re-casting was 79±44days. The primary period of off-loading was not statistically significantly different for those not requiring versus those requiring re-casting: 142±24days compared to 134±41days. Neither were the differences in demographic data, metabolic regulation, BMI or localization of CA. ConclusionsPatients with risk of exacerbation or recurrence of CA could not be identified in the present study and there was no relation to the duration of off-loading. Nevertheless off-loading periods with immobilisation should be kept as short as possible, due to other side effects. This can be obtained by early gradual augmented re-loading.

The Optimization of ITD in Direct Air-Cooled System

In order to improve the technical economy of direct air-cooled system, based on the thermodynamic model of the air-cooled system, taking the annual total cost as the objective function, the face velocity of air and the ITD (initial temperature difference) value as parameters, this article has researched the optimal ITD of direct air-cooled system in theory, and given the uncertainty analysis in the end to reflect the influence of economic parameters. The results shows that the technical economy of direct air-cooled system can achieve optimal under the condition of economic parameters change. Thus, the results of studying will provide helpful guidance for the optimization of direct air-cooled system.

The Optimization of ITD in Direct Air-Cooled System

In order to improve the technical economy of direct air-cooled system, based on the thermodynamic model of the air-cooled system, taking the annual total cost as the objective function, the face velocity of air and the ITD (initial temperature difference) value as parameters, this article has researched the optimal ITD of direct air-cooled system in theory, and given the uncertainty analysis in the end to reflect the influence of economic parameters. The results shows that the technical economy of direct air-cooled system can achieve optimal under the condition of economic parameters change. Thus, the results of studying will provide helpful guidance for the optimization of direct air-cooled system.

Thermal stability and degradation kinetic study of white and colored cotton fibers by thermogravimetric analysis

Abstract Thermal degradation behavior using thermogravimetry (TG), chemical composition and crystallinity by X-ray diffraction of white and naturally colored cotton fibers (ruby, beige, brown and green) were studied. Flynn-Wall-Ozawa method was used to investigate the thermal decomposition kinetics of the different fibers. The white cotton fiber has higher thermal stability and higher apparent activation energy (E a) value compared to the colored fibers. There are no significant differences in initial temperature of degradation in air or in nitrogen atmosphere for the same type of fiber. Chemical composition and crystallinity influenced the thermal degradation behavior of the fibers studied.

Explicit equations for transient heat conduction in finite solids for Bi > 2

A set of correlations is developed for transient heat conduction in finite solids (plates, cylinders and spheres) exposed to high Biot number convection boundary conditions. For Bi ≥ 3, the error of the approximate solutions is well below 1% of the initial temperature difference driving the transient.

Thermal-Boundary-Layer Response to Convected Far-Field Fluid Temperature Changes

Fluid flows of varying temperature occur in heat exchangers, nuclear reactors, nonsteady-flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method was developed with the capability to predict the transient laminar thermal-boundary-layer response for similar or nonsimilar flow and thermal behaviors. The method was tested for the step change in the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes in the magnitude and sign of the fluid-wall temperature difference were considered, including flow with no initial temperature difference and built-up thermal boundary layer. The equations for momentum and energy were solved based on the Keller-box finite-difference method. The accuracy of the method was verified by comparing with related transient solutions, the steady-state solution, and by grid independence tests. The existence of a similarity solution is shown for a step change in the far-field temperature and is verified by the computed general solution. Transient heat transfer correlations are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from predictions by quasisteady models commonly used. The deviation is greater and lasts longer for large Prandtl number fluids.

TU‐D‐AUD C‐05: Development of a Novel Absorbed Dose to Water Calorimeter‐Based Standard for HDR Ir‐192 Brachytherapy

Purpose: To study parameters affecting the design of a new standard for absorbed dose to water for high dose rate iridium‐192 brachytherapy sources based on 4 °C stagnant water calorimetry. Method and Materials: The absorbed dose rate of a Nucleotron microSelectron‐HDR brachytherapy source was measured for sources with nominal air kerma strength Sk,air 21000 and 38000 U at several source‐detector separations dsrc‐det ranging between 25–30 mm. The irradiation time was adjusted to ensure a minimum dose of 1 Gy delivered to the measurement point. The heat‐loss correction was calculated using COMSOL MULTIPHYSICS™ and is defined as the ratio of the temperature in the calorimeter under ideal conditions to realistic conditions. Results: The heat‐loss corrected dose rate measurements had a standard deviation of 1.5%, while the agreement between our measurements and the calculated dose rate results obtained using the TG‐43 formalism was within 6.5%. The effects of convection were calculated to be negligible as the glass vessel serves as a convective barrier significantly decoupling the water velocity in the interior and exterior of the vessel (differences in velocity reaching one to two orders of magnitude). It was found that small uncertainties on dsrc‐det significantly affects the shape of the drift curve, while varying the exact value of SK,air, irradiation time, and differences in initial source temperature at the time of insertion into calorimeter have minimal effects. Differences between the shape of experimental and calculated drift curves can be used to optimize the calculation parameters. Conclusion: Feasibility of water calorimetry for absolute dosimetry for HDR brachytherapy sources has been shown both numerically and experimentally. We believe absolute absorbed dose rate measurements with uncertainties significantly better than 5% are possible. Revisions to experimental designs are underway to improve the robustness of setup and improve the repeatability and uncertainty on measurements.

Stability diagram and effect of initial density stratification for a two-layer system in a supercritical fluid

A numerical study of the stability in a two-layer system filled with a single pure supercritical fluid subjected to an initial temperature difference is performed. The very large compressibility and the very low heat diffusivity of near-critical fluids lead to a Rayleigh-Taylor-like gravitational instability of the heat diffusion layer. This instability is similar to the one of two miscible fluids where molecular species diffusion coefficient is replaced by the heat diffusion coefficient. Our numerical results are consistent with respect to the dispersion relation derived by Duff et al. [Phys. Fluids 5, 417 (1962)] for a system of two incompressible miscible fluids (argon-bromine mixture falling into helium or air). It has also been shown that when the thickness of the lower layer becomes smaller than the heat diffusion length based on the maximum growth rate, the system is stable [Phys. Fluids 17, 054102 (2005)]. A linear stability diagram has been established as a function of three parameters: the thickness of the lower layer, the density difference between the two layers and the distance to the critical point. When the critical point is approached, the high initial stratification (due to the high compressibility) of this Rayleigh-Taylor-like configuration has seen the effect of stabilizing the system.

Sensitivity studies on vortex development over a polynya

The development of a cyclonic vortex over a polynya is investigated with the primitive equation mesoscale model METRAS. The impact of different atmospheric processes on vortex development is determined by calculating the terms of the vorticity tendency equation. Sensitivity studies are performed for different large-scale situations (geostrophic winds 1 ms−1, 3 ms−1, 20 ms−1, initial ice-water temperature difference of 35 K or 17.5 K) and for different polynya sizes and shapes. In general, the vortex develops within a few hours. It is intensified by buoyancy, mainly resulting from latent heat release. Advective and diffusive processes hinder the vortex development. The intensification depends on the actual situation and is faster over small polynyas and heterogeneous ice cover. These situations result in intensification periods of only 12 to 18 hours for the vortex, but create very strong vortices. Halved horizontal temperature gradients also about halve the vortex intensity. The lifetime and intensification of a vortex increases with the time the air mass spends over the water. Thus, weak winds show a slower development of the vortex but the vortex intensifies for more than 24 hours. Over big polynyas several vortices develop, a long polynya results in a longer and narrower vortex which intensifies over a longer period.

Scalar perturbations in two-temperature cosmological plasmas

We study the properties of density perturbations of a two-component plasma with a temperature difference on a homogeneous and isotropic background. For this purpose, we extend the general relativistic gauge-invariant and covariant (GIC) perturbation theory to include a multifluid with a particular equation of state (ideal gas) and imperfect fluid terms due to the relative energy flux between the two species. We derive closed sets of GIC vector and subsequently scalar evolution equations. We then investigate solutions in different regimes of interest. In particular, we study long-wavelength and arbitrary-wavelength Langmuir and ion-acoustic perturbations. The harmonic oscillations are superposed on a Jeans-type instability. We find a generalized Jeans criterion for collapse in a two-temperature plasma, which states that the species with the largest sound velocity determines the Jeans wavelength. Furthermore, we find that within the limit for gravitational collapse, initial perturbations in either the total density or charge density lead to a growth in the initial temperature difference. These results are relevant for the basic understanding of the evolution of inhomogeneities in cosmological models.

Simulating the Relaxation Dynamics of Microwave-Driven Zeolites

We have performed equilibrium and nonequilibrium molecular dynamics simulations to study how microwave (MW)-heated zeolite systems relax to thermal equilibrium. We have simulated the relaxation of both ionic and dipolar phases in FAU-type zeolites, finding biexponential relaxation in all cases studied. Fast-decay times were uniformly below 1 ps, while slow-decay times were found to be as long as 14 ps. Fast-decay times increase with an increase in the initial temperature difference between MW-heated ions/dipoles and the equilibrium system. Slow-decay times were found to be relatively insensitive to the details of the MW-heated nonequilibrium state. Velocity, force, and orientational correlation functions, calculated at equilibrium to explore the natural dynamics of energy transfer, decay well before 1 ps and show little evidence of biexponential decay. In contrast, kinetic energy correlation functions show strong biexponential behavior with slow-decay times as long as 14 ps. We suggest a two-step mechanism involving initial, efficient energy transfer mediated by strongly anharmonic zeolite-guest forces, followed by a slower process mediated by weakly anharmonic couplings among normal modes of the zeolite framework. In addition to elucidating relaxation from MW-heated states, we expect that these studies will shed light on energy transfer in other contexts, such as adsorption and reaction in zeolites, which often involve significant heat release.

240 Delayed Cord Clamping in Very Low Birthweight Infants Reduces the Incidence of Intraventricular Hemorrhage and Late Onset Sepsis

Background: The current prevailing obstetrical practice at birth in the USA is that the umbilical cord of the very low birth weight (VLBW) infant is immediately clamped. The aim of this study was to compare the effects of immediate (ICC) and delayed (DCC) cord clamping on infants born between 24 and 31.6 weeks on two primary outcome variables: bronchopulmonary dysplasia (BPD) and suspected necrotizing enterocolitis (NEC). Secondary outcome variables were blood pressure, hematocrit, late onset sepsis (LOS), and intraventricular hemorrhage (IVH). The hypothesis was that DCC would result in less BPD and suspected NEC.Methods: This was an unmasked randomized controlled trial in which women in labor with infants between 24 and 31 weeks were randomized to ICC (cord clamped at 5 to 10 seconds) or DCC (30 to 45 seconds) groups. DCC infants were held 20–30 cm. below the introitus as possible. The exact time of cord clamping was measured. All neonatal care was at the discretion of the attending physicians.Results: Intention-to-treat analyses revealed no differences in maternal variables, birth weights, gestational age, Apgar scores, initial temperature, and peak serum bilirubin levels. There were no signficant differences in the incidence of BPD (25% vs 22%, p = .78) or suspected NEC (55% vs. 39%, p = .16). Significant differences in IVH (13 vs. 5, p = .03, OR 2.6, 955 CI, 1,6.5) and LOS (8 vs. 1, p = .01) were found between the ICC and DCC groups. In the ICC group, 12 had a grade I-2 IVH compared to 5 in the DCC group. One ICC infant had a grade 4 IVH.Conclusions: Delayed cord clamping appears to protect very low birth weight infants from IVH and sepsis. DCC is an easy to implement intervention.

The growth and structure of double-diffusive cells adjacent to a cooled sidewall in a salt-stratified environment

Observations and measurements are reported on the patterns and rates of growth in time of the double-diffusive cells that form adjacent to a cooled sidewall in a salt-stratified environment. Fluid near the wall is cooled and sinks a distance h where its density, increased by cooling, matches that of the salt-stratified ambient. The fluid separates from the wall, moving outwards as a cool, fresher layer beneath a warmer, more saline region. This leads to growing double-diffusive cells that advance outward at a rate, found by dimensional reasoning, to initially be proportional to N(0)h, where N-0 is the initial buoyancy frequency in the ambient and h is the intrusion's vertical thickness. Near the wall at the top of each cell, the sinking colder fluid is continually replaced by selective withdrawal from the ambient 'far field'. The fluid being withdrawn from the ambient is always the least dense in the cell, and as the experiment proceeds, the straining of the fluid in the ambient region reduces the stratification. The vertical density gradient inside the cell relaxes by continuous hydrostatic adjustment (CHA) to match the ambient and the speed of advance reduces. Measurements of the rate of advance of the cell nose were made in tanks of different lengths L with a range of initial salinity gradients and temperature differences. A simple two-dimensional model is developed to describe the rate of extension of the cells and the internal density gradient as functions of time in which the tank length appears as an important variable. This effect does not seem to have been recognized previously. The rates of evolution in each run involve the time scale tau = L/(C(H)hN(0)), where C-H approximate to 10(-2) is a heat transfer coefficient. The mean length of the cells (l) over bar (t) and the internal buoyancy frequency as functions of time are given by(l) over bar (t)/L = t/tau - (t/2tau)(2), N = N-0(1 - t/2tau).Inversion of the first of these expressions results in t/tau = 2 - 2{1 - ((l) over bar (t)/L)}(1/2) from which a time scale tau(-1) can be estimated. The measurements from individual runs when plotted in this way generally produce accurate straight lines as the model predicts, from which C-H is found. This should be approximately the same for each run; the mean over all runs was found to be 9.3 x 10(-3) with standard deviation 2.4 x 10(-3). The velocity scale of the intrusions at the beginning of an experiment is of order 10(-2) cm s(-1), for typical parameters of water at temperature 20 degreesC, cooled wall temperature of 0 degreesC and mean salinity of 5%.

Higher IL-10 levels are associated with less effective clearance of Plasmodium falciparum parasites.

The implications of high levels of the immune regulatory cytokine IL-10 in Plasmodium falciparum malaria are unclear. IL-10 may down-regulate pro-inflammatory responses and also exacerbate disease by inhibiting anti-parasitic immune functions. To study possible inhibiting effects on parasite clearance, IL-10 plasma levels were determined in 104 Tanzanian children, 1 to 4 years old, with acute uncomplicated P. falciparum malaria, and analysed for association with parasite densities during 3 days of anti-malarial treatment. Higher baseline IL-10 plasma levels were associated with statistically significantly higher parasite densities after 24, 48 and 72 h of treatment. These associations could not be explained by differences in initial parasitaemia, temperature, age, sex or type of treatment. Induction of high IL-10 production might be a direct or indirect mechanism whereby the parasite evades the immune response.

Thermal investigations of some bird nests

This paper presents results from cooling investigations on bird eggs run in nests of several songbird species with contact and contact-less infrared thermometry and with a false colour thermography demonstration of temperature fields on egg surfaces and of the protecting nests. All experiments were performed on single or on up to four (clutch situation) fresh quail eggs. Results indicate that typical cooling curves show a two-phase exponential behaviour consisting of an initial part of warming the still air and the inside surface of the nest and a second part of egg cooling itself. Single eggs lying open to environment may experience a reduction of the cooling rate to 32% when placed in an open nest and even down to 14% in a covered nest. This corresponds to a prolongation of the time to cool down to half of the initial temperature difference from 11 to 35 and 80 min, respectively. IR photos demonstrate the strong thermal gradients of about 10 K of clutch eggs from the inner contact zone to their blunt ends.

Heat Storage Characteristics of Phase Change Material Microcapsule Slurry in a Rectangular Cavity with a Heating Vertical Wall.

This paper has dealt with the Heat storage characteristics of the microcapsule slurry composed of phase change material (PCM) as a latent heat storage material and water. A rectangular cavity with a heating vertical wall, which was filled with the microcapsule slurry, was selected as the present research model. The heating wall temperature, the width of the cavity and the PCM concentration were set as parameters. It was clarified that the transportation of latent heat evolved by melting of the PCM in the slurry exerted on a remarkable influence on the natural convection heat transfer. In addition, it was found that the heat transfer coefficient reached a local maximum value with an increase in initial temperature difference between heating wall and PCM. The heat storage completion time also have a local maximum value with an increase in heating wall temperature due to the latent heat by melting the PCM in the slurry.