Analysis of temperature fluctuations caused by mixing of non-isothermal water streams at elevated pressure. (January 2017)

• Record Type: Journal Article
• Authors: Bergagio, Mattia; Thiele, Roman; Anglart, Henryk
• Is Part Of: International journal of heat and mass transfer. Volume 104(2017:Jan.)
• Page Start: 979
• Page End: 992
• Publication Date: 2017-01
• Subjects: Mixing intensity -- Spectral analysis -- Thermal mixing; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2016.08.082
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Parameters assessing mixing intensity are developed. Experimental temperatures are Hilbert–Huang transformed where mixing is strongest. Relevant temperature frequencies from 0.03 to 0.10 Hz where mixing is strongest. Main spectral peaks imputable to intrinsic mode functions reflecting the largest time scales. The relationship between temperature and velocity spectra is analyzed with CFD. Abstract: Temperatures were measured at the inner surface of an annulus between two coaxial tubes, where three water streams mixed. These temperatures were sampled at either 100 Hz or 1000 Hz. The acquisition time was set to 120 s. Two water streams at 549 K, with a Reynolds number between 3.56 × 10 5 and 7.11 × 10 5, descended in the annular gap and mixed with a water stream at 333 K or 423 K, with a Reynolds number ranging from 1.27 × 10 4 to 3.23 × 10 4 . Water pressure was kept at 7.2 MPa. Inner-surface temperatures were collected at eight azimuthal and five axial positions, for each combination of boundary conditions. To better analyze these temperatures and mixing in the vicinity of the wall, scalars estimating the mixing intensity at each measurement position were computed from detrended temperature time series. Fourier and Hilbert–Huang marginal spectra were calculated for the time series giving rise to the highest values of a mixing estimator of choice. The relationship between temperature and velocity was explored by examining the results of an LES simulation using the same boundary conditions as in one of the experimental cases.