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850 71.0 1.3 2.0 Utilizing the latent heat of melting to make power is a possible kind of storage energy manner, especially for

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Abstract  

A method was devised to evaluate latent heats of vaporization from quasi-isothermal isobaric analysis data. The procedure requires the recording of at least two diagrams: one for the investigated liquid, and the other for a standard liquid with a known latent heat of vaporization. Use of the method to determine the heats of vaporization of some alcohols, with water as standard liquid, led to results close to those previously reported in the literature. The main advantage of the procedure consists in the fact that it requires only small amounts of sample (5–10 mg).

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Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)2·8H2O and Sr(OH)2·8H2O are promising latent heat storage materials.

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numerical analysis of welding processes [ 5 , 8 , 9 , 15 , 16 ]. However, latent heat generated during phase transformations in heat treatment of steel influences temperature distribution and has a significant effect on numerically predicted

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Abstract  

The use of phase change materials (PCMs) in thermal storage is not a new concept, but engineers are continually finding new ways to utilize them in a wide range of applications. A PCM takes advantage of high latent heat in the phase change process to store large amounts of heat while undergoing only a small change in temperature. This property makes PCMs suitable for thermal storage purposes in a wide range of engineering applications. Due to the nature of these applications, it is vital to have a precise knowledge of the thermal characteristics of any PCM. Unfortunately, due to the low thermal conductivities and high latent heats found in PCMs, current measuring tools such as differential scanning calorimetry, provide inconsistent results. This paper conjectures that these errors come from the effects of low thermal diffusivity samples as well as improper data analysis methods.

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The thermal behaviour of sodium acetate trihydrate (NaAc · 3H2O) was investigated by DTA, Q-TG and measurements of the solubility properties. The nucleation efficiency of Na4P2O7 · 10H2O for the crystallization of NaAc · 3H2O melts is not stable over long periods. Stratification can be ascribed to the formation of anhydrous sodium acetate in the supercooled melts. Under static heat storage conditions, NaAc · 3H2O and Na4P2O7 · 10H2O do not exhibit stable behaviour.

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Metastable effects on martensitic transformation in SMA

Part VIII. Temperature effects on cycling

Journal of Thermal Analysis and Calorimetry
Authors: V. Torra, C. Auguet, A. Isalgue, F. Lovey, A. Sepulveda, and H. Soul

Abstract  

The use of Shape Memory Alloys (SMA) in technical applications as damping in civil engineering structures requires the characterization of the alloy for each specific application. This involves the evolution of the mechanical properties and damping capacity with the number of cycles, frequency, maximum deformation, applied stresses, and the evolution of the alloy with aging time and temperature. In particular, the temperature effects associated to self-heating need to be evaluated. In continuous cycling the effects of latent heat, the associated dissipation induced by the hysteresis, the heat flow to surroundings and the cycling frequency induce different states of temperature in the specimen, which in turn produces changes in the transformation-retransformation stresses. In this article, the temperature effects associated to cycling are outlined for different cycling frequencies. The results show that, for relatively faster frequency the temperature arrives at an oscillatory state superimposed to an exponential increase. For lower frequencies, some parts of the sample attain temperatures below room temperature. The experimental results are represented with an elementary model (the 1-body model or the Tian equation used in calorimetric representation) of heat transfer. For the higher fracture where life requirements are associated to damping in stayed cables for bridges, the results show (for the NiTi alloy) a reduction of the hysteresis width as the frequency increases for deformations up to 8%. For reduced deformation, under 2% appears an asymptotic behavior where the frictional area is practically independent of the cycling frequency (up to 20 Hz). In addition, it is shown that more than 4 million of working cycles can be attained if the maximum applied stress is kept below a threshold of about 200 MPa. Although under this condition the deformation must remain lower than 2% a reasonable damping capacity can still be obtained.

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 Particle size/μm Expansion ratio/mL g −1 Thermal conductivity/W m −1 K −1 Melting point/°C Latent heat/J g −1

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