Nature Of Temperature Variation Research Articles

Snap-through buckling of fly ash cenosphere/epoxy syntactic foams under thermal environment

Experimental investigation on deflection behaviour of fly ash cenosphere/epoxy syntactic foam at room temperature and under thermal environment (three different heating conditions) is investigated. Influence of fly ash cenosphere volume fraction and nature of temperature variation on deflection behaviour of syntactic foam beam is discussed elaborately. Results reveal that the syntactic foam beam experience snap-through buckling under thermal environment and is reflected by two bifurcation points in temperature-deflection plot. It is observed that the time duration for which the foam beam stays in the first buckled position increases with increase in cenosphere content. Thermal environment induces compressive stresses in the samples causing such snap-through buckling. However, such phenomenon is not observed when mechanical compressive loads are applied under room temperature conditions. Temperature variation across the beam strongly influences snap-through buckling in syntactic foams in addition to volume fraction of filler content.

Bending, buckling and free vibration characteristics of FG-CNT-reinforced polymer composite beam under non-uniform thermal load

Bending, buckling and free vibration behaviors of functionally graded (FG) carbon nanotube (CNT)-reinforced polymer composite beam under different non-uniform thermal loads have been analyzed using finite element method. Extended rule of mixture is used to obtain effective material property of the composite. Four different types of FG beam exposed to four different assumed one-dimensional temperature distributions along the length of the beam are analyzed. Parameters studies are carried out to investigate influences of the volume fraction of the carbon nanotube, functional grading and the nature of temperature variation on bending, buckling and free vibration characteristics. It is found that bending deflection reduces with increase in volume fraction of the CNT except for unsymmetrical functional graded beam. The static bending deflection and deformed shape of the beams are significantly influenced by the nature of temperature field. The critical buckling temperature of the beam with symmetric CNT distribution (where CNTs concentration is far from the neutral axis) is greater than other beams under different temperature fields and its value is less when the beams are exposed to uniform temperature rise above ambient temperature compared to other non-uniform temperature variations. However, the critical buckling temperature is not increasing significantly with increase in volume fraction of the CNT. The fundamental buckling mode shape is not sensitive to the nature of temperature variation but bending amplitude of the buckling mode shape is significantly influenced by functional grading of CNT and volume fraction of the CNT. The natural frequency of the beams reduces significantly with increase in temperature and the free vibration mode shapes are not influenced by temperature rise, nature of temperature variation and volume fraction of the CNT.

On the nature of temperature variations in borehole kun-1 (Kunashir Island)

The study presents the result of continuous temperature monitoring in a 300 m deep borehole located on the Pacific coast of the Kunashir Island. Temperature variations at of 20–240 m depths with periods from a few tens of minutes to a few tens of days and amplitudes in the order of thousandths to tenths of degree are found to result from three main causes: tidal variations of groundwater level in the borehole, natural convection in the borehole, and nonperiodic and spatially heterogeneous changes of the pore pressure resulting in the appearance of an anomalous subsurface fluid regime and generating crossflow between the different aquifers through the annular space. Joint analysis of temperature and seismic data revealed that shallow-focus (up to 30 km) earthquakes with M > 5 occurred southeast of the seismic station created more expressed temperature response at 240 m depth. This response has the form of a 0.05–0.3 K temperature drop, which precedes a seismic event within a period of a few hours to a few days. Tidal analysis of borehole temperature measurements can be used to calculate the strain sensitivity and the method of borehole temperature monitoring can be used to investigate the tectonic regime of the Earth’s crust.

Thermal Conductivity of 2223 BSCCO Superconductor–Polyethylene Glycol Composites Between 20 and 300 K

Thermal conductivity measurements have been taken between 20 and 300 K on composites prepared from polyethylene glycol (PEG) containing various amounts of superconducting (Bi,Pb)2223 powder. The nature of temperature variation of thermal conductivity (λC) of the composites and its magnitude depend strongly on the volume concentration of the high-temperature superconductor (HTSC) filler present in the material. The results have been discussed in the light of models known for polymer–metal powder composites. It is shown that for composites with 2223 powder content <44 vol. %, the measured data can be accounted well with Hamilton–Crosser model, taking the sphericity factor into consideration. Failure of Hamilton–Crosser expression for composites with higher filler concentration is thought to be associated with direct contact between the superconducting grains, which shortcircuits the acoustic mismatch resistance in the composites.

Thermal Diffusion Factors of Inert Gas Mixtures of Natural Isotopic Abundances in Terms of Column Calibration Factor

The column calibration factors F s as a quadratic function of the mean temperatures \bar T are worked out from the estimated values of the logarithmic maximum separation factors ln q max of inert gas isotopic mixtures and their available TD factors α T s' in three columns of comparatively larger geometrical lengths and of varying sizes. The ln q max are determined from the pressure dependence of ln q e in those columns measured by W. M. Rutherford et al. and W. J. Roos et al. The nature of temperature variation of F s , which depends entirely on the column geometry, allows us to estimate the temperature dependence of α T s' for a wide temperature range. Our α T s' through the use of F s are shown to have almost the same order of magnitudes and the same trends as the theoretical ones, while there are larger discrepancies when α T s' are estimated by other methods. This signifies the usefulness of F s in column measurements.

Transfer functions of heat exchangers

AbstractIn the course of research the authors have collected a number of transfer functions for various types of heat exchangers. For the convenience of analysis the heat exchangers may be classified into several basic types described in subsequent pages. In each case certain assumptions are made when one writes down the differential equations of the heat exchanger, which constitute the so‐called mathematical model of the exchanger. If a particular heat exchanger is being classified, it is important to know the nature of temperature variation and the relative directions of flow of the exchanging fluid streams. If the heat exchanger in question matches one of the types described, then the transfer functions listed may be used to obtain its theoretical frequency and transient responses.