Sinusoidal Temperature Oscillation Research Articles

Thermo-diffusional radon waves in soils

A new theoretical framework for diurnal and seasonal oscillations of the concentration of radon in soil and open air is proposed. The theory is based on the existing temperature waves in soils and thermo-diffusional gas flux in porous media. As soil is a non-isothermal porous medium, usually possessing a large fraction of microscopic pores belonging to Knudsen's free molecular field, a thermo-diffusional gas flow in soil has to arise. The radon mass transfer equation in soil for sinusoidal temperature oscillations at the soil–atmosphere boundary is solved, which reveals that radon concentration behaves as a damped harmonic wave. The amplitude of radon concentration oscillations and phase shift between radon concentration oscillations and soil temperature depend on the radon diffusion coefficient in soil, rate of radon production, soil thermal conductivity, average soil temperature, decay constant, and heat of radon transfer. Primarily numerical calculations are presented and comparisons with experimental data are shown.

Natural Convection Flow on a Vertical Cylinder with Sinusoidal Temperature Oscillation Under The Effect of Magneto Hydrodynamic

The present work investigates the effect of magneto hydrodynamic (MHD) laminar natural convection flow on a vertical cylinder subjected to sinusoidal temperature oscillation. The governing equations which used are continuity, momentum and energy equations. These equations are transformed to dimensionless equations using vortices-stream function method and the resulting nonlinear system of partial differential equations are then solved numerically using finite difference approximation. A computer program was built to calculate the rate of heat transfer in terms of average Nussle number, velocity distribution as well as temperature distribution for a selection of magneto hydrodynamic parameter range , dimensionless amplitude and dimensionless time τ΄ (0.2 – 0.8). Numerical solution have been considered for a fluid Prenatal 542 number fixed at (Pr=0.7), Rayleigh number . Generally, the results show that Nu increase as Ra, M and a increase and decrease with τ΄. The effect of Ra and M on the rate of heat transfer is concluded by a correlation. The results are found to be in good agreement compared with the results of [Adams, 1954] for the case of no MHD.

Determination of seepage velocity in streambed using temperature record of Russian River, USA

The vertical seepage velocity is an important parameter in the groundwater-surface water (GW-SW) exchange process. It is reported that the periodical fluctuated temperature record of the streambed can be used to determine the seepage velocity. Based on a 1-D flow and heat transport model with a sinusoidal temperature oscillation at the upstream boundary, a new analytical model is built. This analytical model can be used to determine the seepage velocity from the amplitude ratio of the deep and shallow test points. The process of calculation is discussed. The field data are superimposed by multi-periods, so the spectrum analysis and the data filtering are desirable. For the typical seepage medium, the analytical model is effective to compute the seepage velocity between −2 m/d and 6 m/d by using the record of the daily period fluctuation. The temperature time-series analytical model is used to determine the upwards seepage under the condition that the spacing of test points is small (less than 0.2 m). Lastly, a case study for the Russian River shows that this model is very convenient to determine the temporal changes of the GW-SW exchange.

사인 주기의 온도 변화가 가해지는 피부 조직의 생체열 방정식에 대한 해석

본 연구에서는 표면에 사인주기의 온도변화를 주었을 때 인체피부 조직의 온도변화에 대해 연구 하였다. 표피, 진피 및 피하조직으로 이루어진 피부 각 층의 서로 다른 물성치의 영향을 Pennes 열전달 방정식을 이용한 수치해석방법으로 풀이하여 조사하였다. 각 조직의 서로 다른 물성치가 온도분포에 미치는 영향에 대해 조사하였다. 또 물성치 변화의 영향을 많이 받는 진피부분에 대해서 관류율의 영향을 조사하였다. 해석 결과 동일한 물성치를 사용한 경우와 달리 서로 다른 물성치를 사용하였을 때, 피부 깊이에 따른 온도분포가 불연속적으로 나타났다.

Analysis of non-Fourier heat conduction using smoothed particle hydrodynamics

Abstract A gridless discretization technique namely smoothed particle hydrodynamics (SPH) is used to analyze non-Fourier heat conduction. First, the technique has been employed to compute the temperature evolution in a slab subjected to an initial non-uniform temperature distribution with both the ends insulated. In case of parabolic heat conduction the temperature distribution achieves the steady state value through a monotonic change. Non-Fourier heat conduction is characterized by a significant temperature oscillation. The present numerical computation closely matches the analytical solution of the problem. Next, a slab with convective boundary condition at one end and the other end subjected to a sinusoidal temperature oscillation has been considered. Typical temperature oscillation at the convective end has been observed. This is significantly different from temperature variation calculated for parabolic heat conduction.

Temperature response in biological tissue by alternating heating and cooling modalities with sinusoidal temperature oscillation on the skin

This study investigates the transient temperature response in biological tissue immersed in warm and cold water alternately with a sinusoidal temperature oscillation on the skin surface to simulate the contrast therapy which uses alternatively heat and cold modalities in subacute and chronic conditions. In addition, this type of analysis is also applied to assessing the blood perfusion rate in the skin through noninvasive technology by imposing a periodic temperature load onto the skin surface and then measuring the phase shift of the resulting surface heat flux. Based on the Pennes bio-heat transfer equation, the Laplace transform is used to derive an exact solution to the temperature variation in the tissue from the initial oscillation to the final steady periodic oscillation. Furthermore, the solutions to special cases under no perfusion rate, constant temperature, and the combination of these two assumptions are demonstrated in this study. The results show that both a larger perfusion rate and a greater tissue depth decrease the amplitude of the sinusoidal temperature response. Meanwhile, a larger perfusion rate can reduce the phase angle related to the sinusoidal surface temperature oscillation and surface heat flux.

Model-free method for evaluation of activation energies in modulated thermogravimetry and analysis of cellulose decomposition

In modulated thermogravimetry the classical linear temperature–time relationship is perturbed by sinusoidal temperature oscillations of small amplitude. Mass loss and its hypothetical unperturbed derivative are connected by an integral equation with the kernel expressed as the ratio of Arrhenius exponentials with the perturbed and unperturbed temperature in the numerator and denominator, respectively. The solution of this equation by the least-squares method gives activation energy, E. The method is model-free, since E is determined on the basis of the experiment without any theoretical functions. Such a method has been applied to study the decomposition of cotton in air. The plot of activation energy versus the degree of conversion, α , shows that the decomposition is characterized at least by three successive processes. The first one ( ≅ 5 % of mass loss) with E ≅ 90 – 167 kJ mol - 1 can be attributed to the formation of the ether bond between hydroxymethyl groups and hydroxyls in adjacent chains of cellulose an/or to oxidation of chain ends and products of cellulose decomposition. The second process with E ≅ 195.9 kJ mol - 1 over the range 0.2 < α < 0.62 is the first rate-limiting step attributed to depolymerization of cellulose by transglycosylation. The third process with E = 153.1 kJ mol - 1 over the range 0.7 < α < 1 is again the rate-limiting step. It corresponds to the oxidation of the carbon matrix of partly (or completely) carbonized cellulose. Plateaus in E ( α ) can be used to predict the mass loss and provide valuable information about chemistry of decomposition.

Design of an experimental setup to achieve sinusoidal temperature oscillation in ultrahigh vacuum

We designed an experimental setup to produce a temperature oscillation at the surface of a sample, in ultrahigh vacuum. The heating device, a tungsten wire, uses infrared radiation to heat the sample. A regular sine wave cannot produce a harmonic power oscillation, due to the nonlinear character of the Stefan–Boltzmann law of radiation. To achieve it we generate a complex wave form to take into account the thermal behavior of the heating filament as well as its electronic transport properties. An example of temperature oscillation is shown in the case of a tantalum sample, at a 0.12 Hz frequency. It exhibits harmonic behavior with an oscillation amplitude of about 1 K. This method opens the field to new experiments in surface science, to study reversible surface phase transitions.

Possibilities of compositional engineering in zeolite based novel precursors for electronic ceramics

Modulated differential scanning calorimetry (MDSC) was used to study the glass-transition relaxation behavior in blends of poly(butylene terephthalate) (PBT), a semicrystalline polymer, with polycarbonate (PC), an amorphous polymer. Using a temperature-modulated differential scanning calorimeter (TM-DSC), a sinusoidal temperature oscillation was superimposed upon the underlying linear temperature ramp. The reversing, total, and non-reversing heat flow curves were then analyzed. We examined the efficacy of modulated differential scanning calorimeter (MDSC) to extract glass transitions (Tg) when these were covered over by rapid cold crystallization occurring in the same temperature range.Blends were available in PBT/PC compositions of 8020 and 4060, and with high and low molecular weight, Mw, designated ‘H’ or ‘L’, respectively. Samples of very low initial crystallinity were prepared by rapid quenching from the melt. These samples crystallized immediately during the MDSC scan producing complex exothermic peaks when the scanning temperature increased over Tg. All blends exhibited a lower glass transition assigned to the PBT-rich phase. The upper glass transition, assigned to the PC-rich phase, was never observed in 80H20L, 80L20L, or 40L60L. This suggests that PC-L has better miscibility with amorphous PBT, while producing a very broad, indistinct glass transition in the PC-rich phase. The Fox equation was used to determine the mass fraction composition of the two phases, and confirms that better miscibility is achieved when low molecular weight components are blended.Higher crystalline blends were prepared by melt crystallization. The size of the glass-transition step was greatly reduced in the melt crystallized blends compared to the quenched blends. Nonetheless, MDSC was used successfully to observe dual glass transitions at intermediate temperatures between the Tgs of the homopolymers for all melt crystallized blends, except 80L20L. Analysis of the lower Tg indicates better amorphous phase miscibility in blends with PBT-L and PC-L; analysis of the upper Tg indicates better amorphous phase miscibility in blends with PBT-L.

Modulated differential scanning calorimetry study of blends of poly(butylene terephthalate) with polycarbonate

Modulated differential scanning calorimetry (MDSC) was used to study the glass-transition relaxation behavior in blends of poly(butylene terephthalate) (PBT), a semicrystalline polymer, with polycarbonate (PC), an amorphous polymer. Using a temperature-modulated differential scanning calorimeter (TM-DSC), a sinusoidal temperature oscillation was superimposed upon the underlying linear temperature ramp. The reversing, total, and non-reversing heat flow curves were then analyzed. We examined the efficacy of modulated differential scanning calorimeter (MDSC) to extract glass transitions ( T g) when these were covered over by rapid cold crystallization occurring in the same temperature range. Blends were available in PBT/PC compositions of 80 20 and 40 60 , and with high and low molecular weight, M w, designated ‘H’ or ‘L’, respectively. Samples of very low initial crystallinity were prepared by rapid quenching from the melt. These samples crystallized immediately during the MDSC scan producing complex exothermic peaks when the scanning temperature increased over T g. All blends exhibited a lower glass transition assigned to the PBT-rich phase. The upper glass transition, assigned to the PC-rich phase, was never observed in 80 H 20 L , 80 L 20 L , or 40 L 60 L . This suggests that PC-L has better miscibility with amorphous PBT, while producing a very broad, indistinct glass transition in the PC-rich phase. The Fox equation was used to determine the mass fraction composition of the two phases, and confirms that better miscibility is achieved when low molecular weight components are blended. Higher crystalline blends were prepared by melt crystallization. The size of the glass-transition step was greatly reduced in the melt crystallized blends compared to the quenched blends. Nonetheless, MDSC was used successfully to observe dual glass transitions at intermediate temperatures between the T gs of the homopolymers for all melt crystallized blends, except 80 L 20 L . Analysis of the lower T g indicates better amorphous phase miscibility in blends with PBT-L and PC-L; analysis of the upper T g indicates better amorphous phase miscibility in blends with PBT-L.

Temperature oscillation calorimetry in stirred tank reactors with variable heat transfer

AbstractA new method for applying reaction calorimetry to stirred tank reactors with variable heat transfer is presented. Sinusoidal temperature oscillations are induced by an electrical heater placed either in the reactor or in the jacket in order to decouple the chemical heat production from the variable heat transfer during reaction. Multiplication of the reactor heat balance by periodic functions and integration yields the overall heat transfer. Temperature oscillation calorimetry was successfully applied to the free radical polymerization of methyl methacrylate in ethyl acetate which shows a strong decrease in heat transfer.

Origins of convective temperature oscillations in crystal growth melts

Sinusoidal temperature oscillations of large amplitude and with periods ranging from a few seconds to a few minutes have been reported for many different crystal growth melt materials and configurations. In this paper, several models of the origins of these temperature oscillations are described which successfully explain the results reported for various materials. At low values of the Rayleigh number, the instability of the convection roll itself in the form of transverse waves is the primary source of temperature oscillations. At higher values of the Rayleigh number, periodic boundary layer instabilities develop in thermal layers for high Prandtl number fluids (such as molten oxides) and momentum layers for low Prandtl number fluids (such as molten metals and semiconductors).

Sinusoidal Temperature Wave Generating System

A method of generating and measuring sinusoidal temperature oscillations of variable amplitude is described, and typical applications are presented.