Sinusoidal Temperature Fluctuation Research Articles

Active phase and amplitude temperature control method for cryostat: A case in the thermodynamic temperature international comparison system

Achieving highly stable temperature control is essential for cryostats. However, the cryocooler used in cryostats, such as the pulse tube cryocooler, produces regular sinusoidal temperature fluctuations due to its inherent working principles. To establish a highly stable temperature environment, an active phase and amplitude control method for suppressing temperature fluctuation is proposed in this paper, by which the optimal phase and amplitude can be predicted in theory. To validate this approach, a thermal response model was developed based on experiments conducted in the thermodynamic temperature international comparison cryostat at approximately 3.7 K. Based on this model, we conducted both single-stage and multi-stage active temperature control experiments. The results demonstrate that the temperature control effect is the best when the active temperature control current is added at the second cold head, the fluctuation of the comparison copper block from 3.3mK to 0.166mK with 94.9 % suppression rate. The multi-stage joint temperature control reduced the temperature fluctuation with an attenuation rate of 95.4 %. These findings offer significant potential for improving temperature stability in future thermodynamic temperature comparison experiments.

A new mesocosm system to study the effects of environmental variability on marine species and communities

AbstractClimate change will shift mean environmental conditions and also increase the frequency and intensity of extreme events, exerting additional stress on ecosystems. While field observations on extremes are emerging, experimental evidence of their biological consequences is rare. Here, we introduce a mesocosm system that was developed to study the effects of environmental variability of multiple drivers (temperature, salinity, pH, light) on single species and communities at various temporal scales (diurnal ‐ seasonal): the Kiel Indoor Benthocosms (KIBs). Both, real‐time offsets from field measurements or various dynamic regimes of environmental scenarios, can be implemented, including sinusoidal curve functions at any chosen amplitude or frequency, stochastic regimes matching in situ dynamics of previous years and modeled extreme events. With temperature as the driver in focus, we highlight the strengths and discuss limitations of the system. In addition, we examined the effects of different sinusoidal temperature fluctuation frequencies on mytilid mussel performance. High‐frequency fluctuations around a warming mean (+2°C warming, ± 2°C fluctuations, wavelength = 1.5 d) increased mussel growth as did a constant warming of 2°C. Fluctuations at a lower frequency (+2 and ± 2°C, wavelength = 4.5 d), however, reduced the mussels’ growth. This shows that environmental fluctuations, and importantly their associated characteristics (such as frequency), can mediate the strength of global change impacts on a key marine species. The here presented mesocosm system can help to overcome a major short‐coming of marine experimental ecology and will provide more robust data for the prediction of shifts in ecosystem structure and services in a changing and fluctuating world.

Analysis of Unsteady Gas Temperature Measurements in the Appendix Gap of a Stirling Engine

This contribution presents the experimental setup and the results of stationary cylinder wall temperature and unsteady gas temperature measurements in the appendix gap of an experimental machine, which can be switched between different regenerative cycles. Direct measurements in the gap are important for the validation and verification of existing analytical modeling approaches for appendix gap losses because these losses may reduce the power of Stirling engines significantly; so far, no direct measurements have been conducted to prove the modeling assumptions. The gas temperatures are measured by newly developed fine-wire thermocouple probes, the design of which is explained in detail. The results show curved axial wall temperature profiles and roughly sinusoidal gas temperature fluctuations, which are dependent on the radial and axial positions. In the axial center of the gap, the assumption of laminar flow conditions is largely fulfilled; whereas at the open end of the gap, intermittent disturbances are observed, presumably due to turbulent eddies entering the gap from the cylinder volume during the inflow period. A comparison to analytically calculated temperatures shows a qualitatively good agreement in the main section of the appendix gap.

Assessment of synthetic entropy waves for indirect combustion noise experiments in gas turbines

The reduction of aero-engine core-noise, i.e. the one generated in the combustor and in the high-pressure turbine, is a crucial objective for the deployment of low noise propulsion systems. Indirect entropy noise, produced by the propagation within the turbine of combustor-induced entropy waves, is believed to contribute significantly to the core-noise, and still demands a proper experimental demonstration in the turbomachinery environment. To fill this gap, dedicated experiments have been recently carried out in the high-speed turbine facility of the Politecnico di Milano, in which synthetic entropy waves are used to simulate the effects of the burners. The present paper discusses the generation and characterization of synthetic entropy waves for entropy noise experiments in turbines.The entropy waves are generated by injecting alternated spots of hot and cold air, by using a two-ways rotary valve and a pneumatic distribution system. These synthetic entropy waves were experimentally characterized in a nozzle test-section as well as in the actual turbine facility used for indirect noise experiments. Time-resolved total temperature and total pressure measurements were performed by means of a fast thermocouple and a pneumatic pressure probe, both of them specifically developed for the present study. A computational model of the entropy wave propagation process was also constructed to investigate the injection process in detail.Results indicate that, by assigning an optimal feeding pressure to the generation device, circular-shaped spots of hot air characterized by a sinusoidal temperature fluctuation and very weak pressure oscillations are injected into the main stream, properly simulating the entropy waves expected in the core of aero-engines. The amplitude of the temperature oscillation reduces during the stream-wise propagation of the wave and increasing the wave frequency. However, by adopting a proper insulation technology and assigning a sufficiently high thermal power to the generation device, temperature perturbations of the order of 30K (i.e., 10% of the mean temperature level) at 90Hz are achieved. These values match the target of entropy noise studies in the turbine test rig.

Assessment of thermal fatigue damage caused by local fluid temperature fluctuation (part II: crack growth under thermal stress)

In order to assess the crack growth due to thermal fatigue caused by a local temperature fluctuation, it is important to consider the stress gradient in the thickness direction. Even if the stress fluctuation on the surface is sufficiently large enough to initiate fatigue cracks, the initiated cracks may stop growing due to the stress gradient in the thickness direction. In this study, not only the stress on the surface but also the stress in the body was investigated in order to evaluate the crack growth behavior. A trapezoidal temperature fluctuation and a sinusoidal temperature fluctuation were analyzed. It was revealed that the stress range on the surface caused by the former fluctuation could be larger than that caused by the latter. Based on the evaluated stress distribution the stress intensity factor (SIF) was derived by the weight function method. It was shown that, in a crack growth analysis under thermal stress fluctuation, the crack could penetrate the wall thickness when the threshold SIF ΔKth for crack arrest was not assumed. If the ΔKth was considered, cracks could stop growing under the sinusoidal temperature fluctuation, although it was still difficult for cracks to stop growing under the trapezoidal temperature fluctuation. The reason for the arrest of crack growth at the mixing tee and the crack penetration at the branched elbow was reasonably explained from the analyzed results.

J032023 流体温度変動による配管熱疲労に関する研究 : き裂発生・成長挙動に及ぼす拘束係数と波形の影響([J032-02]エネルギープラント安全に向けた構造/熱流体/材料の達成問題(2))

In order to assess the thermal fatigue caused by the local temperature fluctuation, it is important to evaluate the stress gradient in the thickness direction in addition to the stress on the surface. In this study, the stress distribution in the depth direction was investigated for various constraint conditions in order to predict the crack initiation and growth behaviors. Not only a sinusoidal but also a trapezoidal fluid temperature fluctuation was analyzed. It was shown that the stress range on the surface caused by the trapezoidal fluid temperature fluctuation could be more than aEΔT/(1-v) for low frequency condition without the membrane constraint, and it could be 2 aEΔT/(1-v) at the maximum. The SIF was derived by the weight function method using the evaluated stress distribution. It was shown that, even under the thermal stress fluctuation, the crack can penetrates the wall thickness without the threshold SIF ΔK_<th> for crack arrest. If the ΔK_<th> was considered, the crack may stop growing under a sinusoidal fluid temperature fluctuation without the membrane constraint. The reason for the arrest of crack growth at the mixing tee and the crack penetration at the branched elbow was reasonably explained from the analyzed results.

Stress Intensity Factors of Various Surface Cracks Inside a Hollow Cylinder Under Steady State Thermal Striping

A thermal stress problem of a long hollow cylinder was considered in this paper. The outer surface of the cylinder was adiabatically insulated, and the inner surface was heated axisymmetrically by a fluid with sinusoidal temperature fluctuations (hereafter called as thermal striping), whose temperature amplitude (ΔT) and angular velocity (ω) were constant. The heat transfer coefficient h was also assumed to be constant. The stress intensity factor (SIF) due to the thermal stress for a given cylinder configuration varies not only with these three parameters ΔT, ω, and h, but also with time. The temperature and, as a result, SIF fluctuation amplitude soon became constant (Meshii, T., and Watanabe, K., 2004, “Stress Intensity Factor of a Circumferential Crack in a Thick-Walled Cylinder Under Thermal Striping,” ASME J. Pressure Vessel Technol., 126(2), pp. 157–162), which hereafter is called as steady state. If one is interested in fatigue crack growth (assuming Paris law) under this thermal stress, because the SIF range soon converges to a constant, it seemed important to know the maximum value of the steady state SIF range for a given cylinder configuration, for all possible combinations of ΔT, ω, and h. This maximum SIF evaluation is time consuming. Thus in this paper, this maximum steady state SIF range for four typical surface cracks’ deepest point, inside a hollow cylinder for all possible combinations of ΔT, ω, and h were presented as a first step. Thin-to thick-walled cylinders in the range of mean radius to wall thickness parameter rm/W=10.5–1 were considered. Crack configurations considered were 360 deg continuous circumferential, radial, semi-elliptical in the circumferential and radial directions. Normalized crack depth for all cases was in the range of a/W=0.1–0.5. In case of semi-elliptical crack, the normalized crack length a/c was all in the range of 0.063–1.

NORMALIZED STRESS INTENSITY FACTOR RANGE SOLUTIONS OF AN INNER-SURFACE CIRCUMFERENTIAL CRACK IN THIN- TO THICK-WALLED CYLINDERUNDER THERMAL STRIPING BYSEMI-ANALYTICAL NUMERICAL METHOD

The normalized stress intensity factor (SIF) range of an inner-surface circumferential crack in a thin to thick-walled finite-length cylinder under thermal striping was considered in this paper. The edges of the cylinder were rotation-restrained and the outer surface was adiabatically insulated. The inner surface of the cylinder was heated by a fluid with sinusoidal temperature fluctuation. An analytical temperature solution for the problem and our semianalytical numerical SIF evaluation method for the crack were combined and, as a result, it was shown that the transient SIF solution can be expressed in a generalized form by dimensionless parameters such as mean-radius-to-wall-thickness ratio, Biot number, normalized striping frequency, and Fourier number. Finally, normalized SIF ranges for the first cycle and steady state were given for these dimensionless parameters in tables for mean-radius-to-wall-thickness ratio of 10, 5, and 1.

512 温度ゆらぎ下円筒環状き裂の応力拡大係数無次元解

In this paper we analyze the stress intensity factor (SIF) of an inner-surface circumferential crack in a finite-length cylinder under thermal striping. The edges of the cylinder were rotation-restrained and the outer surface was adiabatically insulated. Inner surface of the cylinder was heated by a fluid with sinusoidal temperature fluctuation. We combined an analytical temperature solution for the problem and our SIF evaluation method for the crack, and as a result, showed that the transient SIF solution can be expressed in a generalized form by dimensionless parameters such as mean radius to wall thickness ratio Rm/W, Biot number B, normalized striping frequency Ω and Fourier number Fo. Finally, normalized SIF ranges for the 1 st cycle and steady state were given for these dimensionless parameters in tables.

Modelling chemical and biochemical changes under sinusoidal temperature fluctuations: R.V. Nunes and K.R. Swartzel, J. Food Eng. 11, 119–132

Modelling chemical and biochemical changes under sinusoidal temperature fluctuations: R.V. Nunes and K.R. Swartzel, J. Food Eng. 11, 119–132

Modeling chemical and biochemical changes under sinusoidal temperature fluctuations

Chemical and biochemical reactions depend strongly on the time-temperature history; in particular, regular temperature fluctuations are very important in shelf-life studies. For sinusoidal temperature fluctuations, a new model is examined covering a wide range of mean temperature (−25–50 °C), half amplitude (5–40 °C) and activation energy (40–160 kJ/mol). Not only does this new model approach Arrhenius' closely, but it also includes the reaction order. Based upon the integrated Arrhenius equation, this model yields predictions with errors between one to two orders of magnitude smaller than the widely-used Hicks' model. Avoiding numerical integration, accurate shelf-life predictions are possible provided the kinetic constants associated with chemical and biochemical reactions are known.

The simultaneous measurement of pyroelectric and relaxation currents in poly(vinylidene fluoride)

Previous methods of studying the electrical activity of PVdF have been confused by the existence of both reversible (pyroelectric) and irreversible (relaxation) effects. A new technique is described which enables the two individual effects to be measured simultaneously by applying a thermal excitation which consists of a constant heating rate combined with a small sinusoidal temperature fluctuation. Some preliminary measurements of commercially available 25 mu m PVdF films demonstrate the consistency of the results with previous work. In addition to this, further insight into the nature of the electrical activity of PVdF is given. Of particular note is the observation that pyroelectricity can be enhanced by about 10% following heat treatment of the film at 60 degrees C.

The energy costs of temperature regulation in birds: The influence of quick sinusoidal temperature fluctuations on the gaseous metabolism of the japanese quail ( Coturnix coturnix japonica)

1. 1. Quick sinusoidal temperature fluctuations (constant average 10°C) cause an increase in metabolism in comparison to an invariable constant ambient temperature of the same dimension. 2. 2. At the observed mean value of 10°C metabolism is increased by 0.8% per 1 K/hr based on the values of resting metabolic rate (correlation: M = 53.5 + 0.445 T a, M in J/K g hr, T a = ambient temperature change in K/hr) and 0.6% based on the values of activity metabolism ( M = 70.4 + 0.425 T a). 3. 3. The absolute augmentation of metabolism per 1 K/hr is, by comparison, the same for day and night. Its amount is 0.42 and 0.43 J/K g hr respectively. 4. 4. In the response of metabolism to temperature fluctuations no differences could be found with respect to the amplitude and frequency modifications of temperature. 5. 5. The increase of energy consumption is probably caused to a greater extent by “overshoot” of the feedback control system in the course of adjusting metabolism to new levels according to the ambient temperature conditions. 6. 6. Short term ambient temperature changes (i.e. measuring different temperature levels in one night to test basic metabolism vs ambient temperature) cannot produce reasonable values for basic metabolic rate, since these artificially high values reflect the testing procedure.

Striated solute distributions produced by temperature oscillations during crystal growth from the melt

The effect of sinusoidal temperature fluctuations in the melt on the growth of a crystal is investigated by solving the concentration-diffusion and heat-conduction equations for both solid and liquid phases in a linear approximation. The response of the temperature and concentration at the interface is calculated and the mean concentration and root mean square concentration gradient are found. Results are presented which show how these quantities vary with frequency when the material constants are chosen to be appropriate to metals and to semiconductors.

Steady one-dimensional fluid flow in a semi-infinite porous medium with sinusoidal surface temperature

An equation is presented for computing infiltration rates from a study of temperatures observed near the land surface. The boundary conditions of heat and liquid movement assumed are (1) a sinusoidal temperature fluctuation of constant amplitude at the land surface and (2) a constant and uniform percolation rate normal to the land surface in a homogeneous medium. In natural mediums of average heat properties, percolation rates of the order of 2 cm/day or greater can be detected with ease by analyzing the temperature profile resulting from diurnal temperature fluctuations. Percolation rates of the order of 0.1 cm/day can be detected by analyzing the temperature profile resulting from, annual temperature fluctuations at the land surface. With the most favorable conditions of low heat conductivity, large amplitude of temperature at the surface, and careful measurements of temperature, analysis of diurnal temperature fluctuations may yield accurate detection of velocity to a minimum of 0.3 cm/day.

Chemical and Microbial Activity Rates Under Square‐Wave and Sinusoidal Temperature Fluctuations

SUMMARYTemperature amplitudes to 160° and Q10 values from 1 to 30 were integrated to derive coefficients of fluctuation. Multiplication of the coefficient by the reaction rate at the mean temperature permits ready calculation of the average reaction rate when temperature fluctuations assume either a square‐wave or sinusoidal form of cycling. The method is applicable to any temperature scale. Ascorbic acid solutions were less stable when the temperature was cycled from −6 to 30°F than when held steady at 12°F. Aerobacter aerogenes and Staphylococcus aureus cultures incubated under cyclic conditions from 40 to 80°F usually grew quicker than cultures incubated at a constant temperature of 60°F.

Measuring the Thermal Diffusivity of Metals at Elevated Temperatures

Abstract The Angström-bar method has been modified and adapted to the measurement of thermal diffusivity of metals for temperatures ranging from 300 to 1050 F. A small, sinusoidal temperature fluctuation is superimposed on the mean temperature of a thin-wall tubular specimen by means of simultaneous heating and cooling at one end. Thermal diffusivity was calculated from the phase shift and amplitude ratio of the temperature waves determined at two measuring stations. The effect of possible surface heat loss is considered. Measurements were made on AISI 1018, 1045, 3140 steels, and 1.1 per cent carbon tool steel. Results obtained for electrolytic tough-pitch copper and 2S aluminum showed good agreement with a recent theory of Storm concerning the variation of thermal diffusivity of simple metals with temperature.