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).
numerical analysis of welding processes [ 5 , 8 , 9 , 15 , 16 ]. However, latentheat generated during phase transformations in heat treatment of steel influences temperature distribution and has a significant effect on numerically predicted
Authors:Greg Albright, Mohammed Farid, and Said Al-Hallaj
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.
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.
Authors:V. Torra, C. Auguet, A. Isalgue, F. Lovey, A. Sepulveda, and H. Soul
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.