Pressure Drop Reduction Phenomenon of Slush Nitrogen Flow in a Horizontal Pipe

Abstract

Synopsis:Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase single-component fluids containing solid particles in a liquid. Their density and refrigerant capacity are greater than those of liquid-state fluid alone.Owing to these advantages, there are high expectations for use of slush fluids in various applications such as a clean-energy fuel, fuel for space-planes to improve the efficiency of transportation and storage, and as a refrigerant for high-temperature superconducting power machines. Experimental tests were performed with slush nitrogen to obtain the frictional pressure drop flowing in a horizontal pipe with an internal diameter of 15 mm and a length of 400 mm. The primary objective of the study was to investigate the pressure drop reduction phenomenon according to changes in velocity and the solid fraction. The pressure drop correlation between the friction factor and the Reynolds number was obtained and an empirical correlation between them was derived. The flow pattern for slush nitrogen inside a pipe and the behavior of solid particles were observed using a high-speed video camera and the PIV method. From the experimental results, the pressure drop reduction phenomenon emerged clearly when the flow velocity was higher than 3.6 m/s and the flow pattern of solid particles inside the pipe was pseudo-homogeneous.Keywords: slush hydrogen, slush nitrogen, pressure drop reduction, two-phase flow, hydrogen energy

Pressure drop and flow pattern of slush nitrogen in a horizontal pipe

“…When solid nitrogen particles are generated, the particles are observed from the side observation windows. The particle size is determined to be about 1.0 mm by comparing with the thickness of the blades and the densimeter, and the value of 1.0 mm is very close to the result reported previously . When the solid volume fraction of slush nitrogen reaches the prescribed value, the production is stopped and the production dewar is pressurized with helium gas that is precooled by liquid nitrogen in the heat exchanger to improve the stability of the pressure in the production dewar and also to reduce the heat carried into the dewar by the helium gas.…”

“…But the influence of the solid volume fraction vanished at the mean velocity of about 3.5 m/s, and it is considered that solid particles are capable of suppressing the turbulence of the flow, so that the effective viscosity of slurry may decrease under certain conditions. And the pressure drop reduction at higher velocity has been reported, because the turbulence generation near the pipe wall is suppressed due to the migration of solid particles toward the pipe center, and the pseudo‐homogeneous flow pattern is considered to occur. Except in the pressure drop reduction region, the pressure drop of slush nitrogen increases with the increase of the mean velocity when the solid volume fraction is 4–40% and the mean velocity is 0.2–5.9 m/s, which is very different from the typical slurry flow.…”

“…And the pressure drop reduction at higher velocity has been reported, because the turbulence generation near the pipe wall is suppressed due to the migration of solid particles toward the pipe center, and the pseudo‐homogeneous flow pattern is considered to occur. Except in the pressure drop reduction region, the pressure drop of slush nitrogen increases with the increase of the mean velocity when the solid volume fraction is 4–40% and the mean velocity is 0.2–5.9 m/s, which is very different from the typical slurry flow. In general, slurry flows in a horizontal pipe are more complicated, because the motion of the solid particles is affected by several forces.…”

Investigation of Taylor bubble wake structure in liquid nitrogen by PIV technique

“…As a non-invasive flow sensing methods, particle image velocimetry (PIV) was widely adopted to investigate the flow field around Taylor bubble in ordinary liquid [3,22,29,27,15,16,25,26]. PIV technique has already been used for investigating the flow field of cryogenic fluid [17,18,13,14,31,8]. For example, Xu and Van Sciver [31] developed an experimental approach for applying the PIV technique to the measurements in He II forced flow.…”

Numerical Study of Flow and Heat-transfer Characteristics of Cryogenic Slush Fluid in a Horizontal Circular Pipe (SLUSH-3D)

“…に示す23,24) 。入口流速を U in = 1.5、2.0、3.0、4.0、 5.0 m/s、初期体積固相率をα s = 0.05、0.13、0.20、0.25 と して、流速、固相率が変化する場合の流動・伝熱構造を解 析した。著者がフリーズ・ソー法にて製造したスラッシュ 窒素の固体粒子径(絶対最大値)の平均値は 1.36 mm4,6) …”