Experimental investigation on flash evaporation of water at different water depths with functional analysis method
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ORIGINAL
Experimental investigation on flash evaporation of water at different water depths with functional analysis method Siguang Li 1 & Yanjun Li 1 & Lili Liu 2 & Longbin Yang 1
&
Xiaojin Zhang 3 & Runzhang Xu 4
Received: 9 June 2020 / Accepted: 3 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract It is important to study the temperature stratification phenomenon in flash evaporation to well design the marine accumulator and some related industrial equipment. Therefore, a series of flash evaporation experiments with initial temperature of 65.0 °C ~ 84.4 °C and superheat degree of 5.0 °C ~ 30.0 °C are carried out to study the temperature variations at different water depths. Meanwhile, the functional analysis method is used to obtain the global and local digital characteristic of flash evaporation. Also, the application domain of this method is discussed in detail. Finally, the effects of initial temperature and superheat degree on the variation of non-equilibrium fraction are studied by the functional analysis method. Results show that the temperature of the deeper water drops earlier and faster than that of the shallower water, and the temperature stratification phenomenon is obvious at the beginning 20s of flash evaporation. This phenomenon gradually disappears as the flash evaporation proceeds. Increasing the initial temperature effectively accelerates the drop of water temperature. However, due to the large temperature decline, increasing the degree of superheat only increases the decreasing rate of temperature, but does not significantly reduce the duration time of flash evaporation. Nomenclature H water height [m]. T temperature [°C]. NEF Non-equilibrium fraction. t time [s]. I integration. s sample standard deviation. CV coefficient of variation. x observed values of sample. N sample size.
Subscripts 0 start of flash. e equilibrium. i, j time step. avg average value. n number of experiments.
Greek symbols ΔT superheat degree [°C]. x the average of observed value.
If a liquid is suddenly exposed to an environment below its saturation pressure, it will become superheat and the corresponding heat surplus will be released in the form of latent heat of evaporation. In general, we call this phenomenon as flash evaporation. With a large amount of steam generation and significant temperature drop, flash evaporation has many applications, such as desalination [1], spray cooling [2, 3], food drying [4], heat recovery [5], power plant [6] and so on. It is hard to mention all the work on flash evaporation because of the huge amount of the existing references. To our best knowledge, flash evaporation was firstly studied by Miyatake et al. [7, 8]. They measured the temperature variation of pure water and proposed the non-equilibrium fraction (NEF) that equals to the ratio of local superheat degree on the entire superheat degree, and some parameters derived by NEF, such as the non-equilibrium temperature difference
* Longbin Yang [email protected] 1
College of Power and Energ
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