Cold heat storage utilizing night-time electricity is one of the relevant technologies for the electric load leveling. Latent heat storage system with a large number of small paraffin particles is one of the promising technologies for the cold heat storage system. Small paraffin particles are generated by nozzle injection of liquid paraffin into cold water. Direct heat transfer between the ascending particles and surrounding cold water enhances the storage of latent heat in a short time. Transportation of solid paraffin particles suspended in water should be the best way to transport cold heat, because the density of cold heat stored in water/paraffin-particle mixture is very high. The present paper aims at investigating flow patterns and pressure loss of water/nonadecane-particle mixture flowing in horizontal and vertical pipes. The inner diameter and the average diameter of the nonadecane particle were 20mm and 3.7mm, respectively. Reynolds number, Froude number and volumetric concentration of nonadecane particles were varied in the ranges of 5000 ≤ Re ≤ 80000, 1 ≤ Fr ≤ 260 and 0.02 ≤ Cv ≤ 0.25. We found the following main results: (1) Four flow patterns were observed in the horizontal flow, (a) flow with a stationary particle bed, (b) flow with a sliding particle layer (c) heterogeneous suspension flow and (d) homogeneous suspension flow. The flow pattern shifted from (a) to (d) with increasing Reynolds number. (2) Homogeneous suspension flow was observed in the vertical up-flow. (3) Homogeneous and heterogeneous suspension flow was observed in the vertical down-flow. (4) The pressure loss coefficients λ of the horizontal flow were correlated by a function of λ and Re (λ = 0.479 Re−0.311) for the heterogeneous and homogeneous suspension flows (Re ≥ about 25000) and by a function of the excess pressure loss coefficient Φ, Fr and Cv (φ/Cv0.58 = 72.4Fr−1.25) for the flow with a sliding particle layer (Re ≤ about 20000). (5) The pressure loss coefficients of the vertical up-flow were correlated by a function of λ and Re (λ = 4.45 Re−0.501) in a large Reynolds number range of Re ≥ about 40000 and by a function of Φ, Fr and Cv (φ/Cv0.47 = 282Fr−1.47) in a small Reynolds number range of Re ≤ about 40000. (6) The pressure loss coefficients of the vertical down-flow were correlated by a function of Φ and Fr (φ = 73.0Fr−0.765).

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