Experimentalin situinvestigations of turbulence under high pressure

Abstract

In tube injection systems applied in high-pressure processing of packed biomaterials and foods, the pressure-transmitting medium is injected into the vessel to increase the pressure up to 1000 MPa, generating a submerged liquid-free jet. The presence of a turbulent-free jet during the pressurization phase and its positive influence on the homogeneity of the product treatment has already been examined by computational fluid dynamics investigations. However, no experimental data have supported the existence and properties of turbulent flow under high-pressure (HP) conditions up to 400 MPa. This contribution presents the development of two experimental setups: HP-laser Doppler anemometry and HP-hot wire anemometry. For the first time the time-averaged velocity profiles of a free jet during pressurization up to 300 MPa at different Reynolds numbers (Re) have been obtained. In this article, the dependence of the velocity profiles on the Re is discussed in detail. Moreover, the relaminarization phenomenon of the turbulent pipe flow most likely caused by the compressibility effects and viscosity changes of the pressure-transmitting medium is examined.

In situinvestigation of the turbulent–laminar transition of temperature fluctuations during pressure building up to 300 MPa

“…The turbulent fluctuations in the temperature field are obviously damped at the Reynolds number of about 3600, which is a typical value for turbulent pipe flow. This phenomenon supports the previous results obtained by the same authors about the re-laminarization of the turbulent velocity fluctuation occurring during fluid pressurization [3,4]. Initially, fully turbulent flow starts to be damped by increasing viscous forces which grow due to the pressure ramp.…”

“…Song et al showed for the first time that a sudden increase in pressure in liquids can completely re-laminarize the turbulent flow. The suppression of the turbulent velocity fluctuations has been observed by means of high-pressure-hotwire anemometry (HWA) [3,4]. This paper focuses on the investigation of the fluctuations in a liquid's temperature field during the pressure build-up phase.…”

“…In order to understand and optimize HPP, thermofluid-dynamic investigations are necessary, given that in any HPP of biomaterials, diffusive and convective transport of mass, momentum and energy occurs and shows interactions. Thus, investigations of fluid flow under high pressures have been developing extensively during recent years [1][2][3][4]. Up-to-date research shows that the thermo-physical properties of pressuretransmitting media and biomaterials such as density, viscosity, heat conductivity and thermal capacity change drastically with increasing pressure [5,6].…”

Toward a Philosophy and Theory of Volumetric Nonthermal Processing

“…The effect of compression heating of pressure transmitting fluids on bacterial inactivation was studied by Balasubramanian and Balasubramaniam (). Sensors have also been reported for in‐situ measurement of viscosity (Först and Delgado ), velocity fields (Pehl and Delgado ), and turbulence, via high‐pressure laser Doppler anemometry and high‐pressure hot‐wire anemometry (Song and others ). Measurement of intracellular pH in‐situ within Lactococcus lactis and Lactobacillus plantarum cells was reported by Molina‐Gutierrez and others (), using a fluorescence‐based method, which was accurate to within 0.5 pH units in the pH range from 5.0 to 8.0, and 1.0 pH units below pH 5.0.…”