Thermostatic System Research Articles

Phase Transitions in PbZr1-xTixO3 Ceramics Prepared by Different Techniques

In this work, we present our study of the phase transitions and the temperature dependence of the optical properties of the PbZr0.235Ti0.765O3 films prepared by multi-target reactive sputtering and sol-gel methods. Optical measurements were performed with the J. A. Woollam spectral ellipsometer operating in rotating analyzer mode. The main ellipsometric angles Ψ and Δ were measured in the spectral range from 300 to 1200 nm. High-temperature measurements were performed in a specially designed thermostat system. The samples were heated to 500°C to reach the paraelectric phase. The temperature dependences of the refractive index and the absorption coefficient at fixed wavelengths, and the optical gap Eg obtained from isoabsorption curves at a=1000 cm-1 were obtained from ellipsometric experiment.

Effect of Microwave Radiation on the Acetate-Catalyzed Hydrolysis of Phenyl Acetate at 25 °C

In this paper we present the experimental results obtained from phenyl acetate hydrolysis in a microwave-irradiated environment and in water solutions containing catalytic acetate ions. The kinetics of the reaction were studied in an irradiated environment where radiation, at a frequency of 2.45 GHz, was given to the reacting system at a power of 0.500±0.025 W. The energy absorbed by the reacting system was measured using a directional coupler, which can separate the radiation directed to the reactor from any reflected one. The system was irradiated with a power greater than that required to run the reaction; however, any energy in excess of that absorbed by the reaction was quite easily taken up by a thermostatic system. In this way the reaction system could run without any thermal effect due to radiation. The temperature was set at 25°C and was kept constant during the reaction by using carbon tetrachloride as the thermostating fluid. The results obtained show that the kinetics of the reaction studied were greatly enhanced with respect to those of the reaction running in a nonirradiated environment. The kinetic constant at zero concentration of the catalytic species rises from 0.000192 h -1 in a nonirradiated environment to the value 0.002758 h -1 found in this paper. The observed kinetic constant retains the same value for all of the studied catalytic acetate ion concentrations. This fact suggests that microwave radiation produces something like a catalytic effect which can replace that given by acetate ions in nonirradiated environments.

Geometric approach to response theory in non-Hamiltonian systems

The theory of differential forms and time-dependent vector fields on manifolds is applied to formulate response theory for non-Hamiltonian systems. This approach is manifestly coordinate-free, and provides a transparent derivation of the response of a thermostatted system to a time-dependent perturbation.

Converting from Steam to Gas

This article reviews how some factory managers are reducing energy and maintenance costs by replacing their aging steam systems with natural-gas-fired heating units. The benefits of lower energy bills and greater energy efficiency are obvious, but switching from steam to gas heating can also increase worker comfort, boosting morale and productivity. Such bonuses have been gained recently at a CF&I Steel L.P. works in Pueblo, Colo., and a Chrysler Corp. engine facility in Kenosha, Wisconsin. The process of switching to gas can reduce maintenance costs, because gas systems have an inherently less troublesome design than steam-distributed piping systems. A major advantage of infrared h eating systems is that they can provide the same degree of comfort at lower energy costs than conventional forced-air systems and boiler systems such as CF&I’s. Each group of five heaters in the CF&I machine shop was placed in a single thermostat system with a 24-hour timer as an additional measure to ensure efficiency.

Geometric structure of the non-equilibrium thermodynamics of homogeneous systems

A geometric model for non-equilibrium thermodynamics is constructed as a codimension one submanifold of a contact space in which the action of the contact form represents the second law of thermodynamics. This model generalizes that of the thermostatic system as a Legendre submanifold of a contact space. A thermodynamic system in the contact manifold is locally the graph of a generalized energy function defined on the symplectic manifold of all 2 n conjugate variables. Non-equilibrium processes are paths on this graph. The Gibbs contact form acting on admissible non-equilibrium paths reproduces the Clausius-Duhem inequality and measures dissipation. A gradient relaxation process is defined, in which the dissipation is maximal for fixed control variables. The Kelvin-Voigt model and Newton's law of cooling are shown to be such gradient relaxation processes. Affinities are defined in terms of the generalized energy function, and the classical non-equilibrium linear Onsager relations are generalized for gradient relaxation processes.

Aggregation of a quenched Lennard-Jones system under shear.

The thermodynamic decomposition of an unstable thermostatted system of Lennard-Jones disks is investigated by nonequilibrium molecular dynamics. The system, first unsheared and then subjected to planar Couette flow, is studied after temperature quenches into the unstable vapor-liquid and the vapor-solid coexistence regions of the phase diagram. An interconnected morphology, characteristic of spinodal decomposition, forms after quenching. The cluster growth is found to be temporally self-similar, and the structure factor S(q,t) obeys the dynamic scaling relation S(q,t)\ensuremath{\sim}${\mathit{q}}_{\mathit{m}}^{\mathrm{\ensuremath{-}}{\mathit{d}}_{\mathit{f}}}$(t)S\ifmmode \tilde{}\else \~{}\fi{}[q/${\mathit{q}}_{\mathit{m}}$(t)]. Here, q is the scattered wave vector magnitude, ${\mathit{q}}_{\mathit{m}}$(t) is the location of the low angle peak in S(q,t), S\ifmmode \tilde{}\else \~{}\fi{}(x) is a time-independent structure function which has a maximum at x=1, and ${\mathit{d}}_{\mathit{f}}$ is a fractal dimension. ${\mathit{d}}_{\mathit{f}}$ is relatively insensitive to the postquench state point, but may depend on the shear rate. The primary influence of shear is to accelerate the aggregation---an effect that has also been observed experimentally in dense gelling silica suspensions. The similarities between these simulations and experiment suggest that a characteristic fractal dimension of a dense gel may be determined from measurements of S(q,t). \textcopyright{} 1996 The American Physical Society.

Compensation of temperature variations disturbing performance of an amperometric biosensor for continuous monitoring

A method for compensating the temperature variations disturbing the response of a biosensor is proposed. Using a miniature thermistor probe, the temperature of the sensing system is measured simultaneously with the current of the biosensor and a normalized signal is calculated which does not depend on temperature. In this way, a thermostat system is not necessary. This approach is tested using a cholinesterase-based amperometric enzyme electrode for the determination of inhibiting substances. It is demonstrated that detection of an inhibitor (0.5 μM paraoxon) using the normalized signal is possible even with a simultaneous temperature change of 15 °C in 5 min.

5356815 Apparatus for microbiological analysis of biological samples in liquid suspension by light-scattering technique

An apparatus for microbiological analysis of biological samples in liquid suspension by light-scattering technique, which employs test-tube containers (11) made of a material transparent to electromagnetic radiations of a determined wave length. Each container (11) cooperating with a thermostat system (17) and at least momentarily with a stirring assembly (31) and relative keeper stirring means (18). The container (11) cooperating with a focussing and collimation system (22) and with a monitoring device (24), is illuminated by electromagnetic radiation of a determined wave length (74) emitted with its own axis (29) of emission and transmitted through the container (11) by the focussing and collimation system (22). The radiation is scattered by any microorganisms present in the sample with an intensity related to their number and morphology. This scattered radiation is picked-up in succession with desired timing by the monitoring device (24) according to determined angles, from 0° to 180°, in relation to the emission axis (29). A computer collects the resulting data and constructs a curve representing intensity of scattered radiation versus time. The curve parameters are compared with reference values contained in a data bank of the computer (13) for determination of the typical parameters of the analysis i.e., the counting, the replication rate and the morphology of microorganisms present in the sample.

Reproducibility of sample separation using liquid or forced air convection thermostatted high performance capillary electrophoresis systems

AbstractRun‐to‐run sample separation reproducibility has been compared on two commercial high performance capillary electrophoresis units which differ in the mode by which the capillary temperature is thermostatted. Three standard analytes, differing dramatically in molecular character and size, were used for the analysis: benzoic acid, a 14 amino acid peptide from human chorionic gonadotropin, and ribonuclease A represent, respectively, small stable organic molecules, small peptides with little or no secondary structure, and proteins with secondary structure. These standards were evaluated with regard to reproducibility of migration time, peak area, and peak height. The analyses, performed in buffers of optimum pH for the separations, demonstrated that the liquid and forced air convection thermostatted systems both performed extremely well. The reproducibility, as judged by the percent coefficient of variance (% CV) of replicate analyses, was generally found to be less than 1 % (migration time); the reproducibility decreased in the order migration time > peak height > peak area. Whereas the absolute % CV values for MTrel (migration relative to a standard) observed with the liquid thermostatted system were 2‐ to 4‐fold lower than those observed with the forced air convection thermostatted system, there was little statistically significant difference between the two. As expected, the data indicated a reduction in reproducibility as the complexity of the analyte increased, perhaps as the result of an increased potential for wall interactions. Comparing separations in which low (≈︁1 watt/meter [W/m] of capillary) and high (>5 W/m) Joule heat was generated by altering the sodium chloride content of the buffer revealed few statistically significant differences in the reproducibility obtained from the two systems. With these particular standard analytes and their respective buffer systems, there appears to be little difference between forced air convection and liquid thermostatting of the capillary.

A dilatometer for low-expansion materials

Materials with low coefficients of linear expansion are of considerable interest. The following are the basic specifications for dilatometers to be used with them: stability in the displacement sensor and small contributions from the components to the measured thermal expansion. Only interference dilatometers meet those requirements strictly, but new dilatometers have been described [i] based on the measurement of electrical quantities whose sensitivity is greater than that of an interference dilatometer, while not completely meeting those requirements. Here we describe a capacitance dilatometer for the range 300-5 K, which combines high stability in the displacement sensor with almost complete absence of thermal expansion in the body. The means of excluding the thermal expansion in the body is derived from [2], but we used a radio-frequency oscillator because of the lack of good Soviet capacitance bridges. Also, to improve specimen installation for routine measurements, the temperature monitoring system was mounted in a special unit, which was in thermal contact with the specimen. The dilatometer cell (Fig. I) is novel. The capacitance change is determined from the frequency of the oscillator present in the cryostat along with the cell. The cryostat is not subject to any particular specifications, as it can be a circulation one or have a system of vessels containing coolants linked to the cell by a cold finger. The cell and oscillator are linked by a common copper body; copper provides good thermostatic control (!3 x 10 .4 K), and thus stability in size during the measurement in spite of the high temperature coefficient of expansion for copper. The specimen 1 is heated independently of the body 2, which is provided by the support 3 with specimen resting on the insulators 4. The measurement thermometer 5 and control thermometer 6 work with the heater 7 to provide a given temperature in the support. Thermal contact between the support and the specimen occurs over a fairly large area, and in addition, the specimen is enclosed in the foil 9, which also has thermal contact with the support. We used cylinders i00  0.i mm long and 15-25 mm in diameter with ground flat ends. The large diameter was chosen to give better temperature equalization for materials with low thermal conductivity. A difference from [2] was that the support enabled one to mount the specimen on the thermal insulators together with the heating and thermostatic control system and simplified the specimen mounting. The support should not participate in the thermal expansion, which was a task handled as in [3]. The support consisted of two mating copper parts held by the bolts 8. The plane of contact between the upper disk is the plane of support containing the insulators, while the plane of contact for the lower part is the plane of contact with the specimen. When the temperature varies, the position of the plane of contact in space does not alter, so the expansion of the substrate does not influence the measured expansion of the specimen.

Thermodynamics of Nitinol

A self-consistent macroscopic thermodynamics is developed for the calculation of work, heat, and dissipation for thermodynamic paths of the shape memory alloy, Nitinol. The thermodynamic system analyzed is a Nitinol helix for which extensive force–length–temperature (FLT) equation of state measurements have been made. The Nitinol system exhibits significant hysteresis and is determined to be a nonequilibrium thermostatic system. A set of equations of state are provided which correlate all reversible and irreversible Nitinol thermodynamic paths to both the set of helix (FLT) thermodynamic state variables and to new ‘‘history’’ state variables. It is shown that these equations predict observed cyclic behaviors not previously interpreted. In the absence of calorimetric measurements for the Nitinol helix system, a physical assumption is made that reversible paths are of constant phase. This assumption is used to estimate the reversible path thermal and mechanical heat capacities for the Nitinol system. With the state equations and the estimated reversible path heat capacities, the nonequilibrium thermostatic formalism is employed to derive expressions for the heat flow for any Nitinol thermodynamic path. It is shown that predicted calorimetric quantities are in good qualitative agreement with measurements. It is also shown that the calorimetric quantities are sensitive to state equation coefficients, which in turn are sensitive to cold-working or ‘‘conditioning’’ of the material. The large heat of transformation, ∼2.4 cal/g, an estimated isentropic temperature change of 22 °C and the large dimensional changes associated with the shape memory effect, imply that Nitinol may be useful for many applications, including use as a working medium for low-grade thermal-energy conversion (i.e., heat engines).

Investigation of available toggle switches for thermostatic control systems

A useful approach to the investigation of toggle switches has been devised which gives new insight into their electrical performance. A high-speed camera is used to generate the nonlinear contact velocity characteristics and two digital transient recorders record voltage and current transients across the contacts. The information gained is combined to produce arc energy data which give an indication of long-term switch performance under AC operating conditions. Results are presented for commercially available toggle switches, but the method appears to be suitable for most switches, including medium-capacity circuit breakers.

A thermostatic control system for nonlinear optical experiments at low temperatures

A cryostat specifically designed for maintaining nonlinear optical crystals at temperatures between room temperature and -175°C is described. The sample is held in a vacuum environment, and its temperature is kept within 0.1°C of the desired value by applying regulated power to a sample holder which is connected to a liquid-nitrogen-cooled heat sink through a thermal resistance. The system is easily constructed and can be evacuated with a mechanical pump. It can operate longer than 6 h on a single filling of liquid nitrogen with the pump disconnected.

A thermostatic system for biomedical applications.

A thermostatic system for biomedical applications.

Comfort Control for Central Electric Heating Systems

Central electric heating systems typically consist of a number of low-mass heating elements. Due to this low mass, fast rates of temperature rise and fall will occur in the furnace. The end result can be large and uncomfortable temperature swings in the living space. In order to provide good comfort, the control system used must take into account the characteristics of an electric furnace. An analog computer study was conducted to determine the best method of controlling an electric central heating system. The analog computer optimized the thermostat design parameters to provide the required end result of homeowner comfort and long heat equipment life. Since mechanical thermostats have practical limitations on minimum switching differentials and only solid-state electronics could overcome this difficulty, the computer optimized controller was built using integrated circuit electronics. A field test compared the performance of a conventional ON-OFF mechanical thermostat system with the new solid-state controller. The conventional system produced excessive room temperature swings of 3°F, while the new controller produced small swings of less than 1°F.

Critical factors in three roll mills

Modern three roll mills are fitted with automatic temperature control equipment, each roll with its own thermostat system. In addition to uniform and reproducible working temperatures, this ensures savings in water consumption of up to 30%. With mechanical and hydrostatic roll adjustment systems any variation in the roll gap produces a corresponding variation in the contact pressure. With hydrodynamic pressure systems, the roll gap can be altered with a constant contact pressure.

Study of the Ultrasensitive Pyroelectric Thermometer

A major microcalorimetric problem, the development of a very sensitive thermometer, is considered. The theory of a pyroelectric thermometer is reviewed and verified calorimetrically. A thermostatic system utilizing both a layer of low thermal diffusivity material and a large heat sink was used to strongly attenuate external temperature fluctuations. A pyroelectric thermometer, used in the thermostat, measured temperature changes as large as 2.52×10−3 °C and as small as 6×10−6 °C. The sensitivity of the thermometer was limited by the temperature stability of the thermostat. Technically simple modifications of the calorimeter could make the detection of temperature changes as small as 5×10−7 °C possible. Detection of temperature changes smaller than 10−7 °C may be achieved by changes in size, shape, and material of the pyroelectric sensing element.

A Novel Thermostat

IT is often necessary to maintain an apparatus at a constant temperature. This may be done by immersing it in a circulating liquid maintained at a constant temperature by a thermostat, or by jacketing it with alternate shells of thermally conducting and insulating materials heated to the selected temperature by means of an internal electric heater. These methods have the disadvantages that the thermostatic system makes the apparatus less accessible, the control of the temperature to within a narrow range requires some complication in the whole system, and it is difficult to prevent ‘hunting’.