[en] Highlights: • Gas accumulation in an inverse U-bend due to sudden pressure drop and temperature rise was investigated. • Accumulated gas volume and interface were analyzed for various liquid velocity and temperature. • The onset conditions of gas accumulation varied depending on the liquid temperature and the orifice size. • The higher the liquid temperature and velocity, the faster the gas accumulation. The gas accumulation occurring in an inverse U-bend due to sudden pressure drop and temperature rise was characterized. The initial conditions of gas accumulation, the changes in accumulated gas volume, and the interface limits were investigated for various liquid velocities, liquid temperatures, and orifice sizes; the liquid temperature was increased from 20 °C in the liquid velocity range from 0.162 to 0.315 m/s. The rise in the liquid velocity corresponded to higher temperature at OGA and rate of gas accumulation. When the liquid velocity exceeded about 0.32 m/s, there was no longer gas accumulation. Under the liquid temperature of 40 ℃, the cavitation and gas accumulation were triggered by sudden pressure drop. The onset conditions of gas accumulation varied depending on the liquid temperature and the orifice size; the higher the liquid temperature and velocity, the faster the gas accumulation.

[en] The fittings such as diffusers and reducers are essential flow elements in a piping system, which play a role to connect the different sized pipes or to branch a part of main stream to other piping. However, their central role is to convert the dynamic energy (velocity) of a flow into the static energy (pressure), or vice versa. When designing a piping system, the pressure drop calculation is very important due to the estimation of power consumption for maintaining a required flowrate. For this reason, many coefficient values of the standard sized fitting products are usually provided by manufacturers or by engineering handbooks. In this study, some analytical calculations were performed to find the optimum angles of non-standard reducers and diffusers based on a dimensionless aspect ratio (length/diameter). The results showed that the optimum angles decreased exponentially as the aspect ratio increased and vice versa. Especially, the optimum angle of a diffuser converged to about 5° when the aspect ratio is over 10. Furthermore, these results were verified through the CFD calculations and the previous reported data.

[en] Metallic continuous heat exchangers are discussed. They are classified according to the field of application. Heat transfer modes are reviewed (radiation, conduction, convection); the convective modes more frequent in continuous exchangers are emphasized (natural or forced convection with or without phase changes in the fluids involved). Some indications relating to pressure drop calculation in these apparatus are given before the calculation itself. The thermal and hydraulic aspects are stressed and rudiments are given in view of a mechanical study

[en] The actual results of steady state pressure drop measurements in liquid phase for the LOBI-installation are presented and relevant data from the pressure drop investigations at LOBI are summarized

[en] The pressure drops through contractions in horizontal single and two-phase flow were investigated. A total of 167 measurements were made for four different entrance shapes to study the effects of the entrance shape on the pressure drop through a contraction in horizontal single and two-phase flow. From this data, pressure drops were calculated and compared with the pressure drops predicted by analytical models for single and two-phase flow. For single phase flow the agreement between the data and predictions is within ±25%, whereas for two-phase flow Hoopes model, which gives a better agreement than the homogeneous model, underpredicts the data as much as 45%. In addition, the effects of void fraction and liquid phase mass velocity on the pressure drop through the sudden flow channel constraction were investigated for two-phase flow. (Author)

[en] The Korea Nuclear Fuel Co. requested the high frequency flow-induced vibration and pressure drop tests of top, mid, IFM, bottom grid candidates of HIPER and protective grid candidates of a commercial fuel. The following results were obtained for each test. 1) High frequency flow-induced vibration of HIPER spacer grids Measured maximum vibration amplitude of the HIPER mid grid was under 21 mm/s at lower region of the grid's center spring. The peak vibration amplitudes of the upper, IFM, and bottom grids were 5∼10 times less than that of the mid grid. Peak frequency associated with the peak amplitude have gradually increased with the flow velocity. This suggested that a high frequency vibration of grid was originated from the vortex shedding due to the thickness edge of grid strap. 2) Hydraulic vibration test of protective grids for a commercial fuel Peak vibration amplitudes of 16x16 type fuel protective grids were above 200 mm/s at the frontal direction of HyGrid 4. There might be a strong resonance near at the measurement point of the grid. Peak vibration amplitude of 17x17 type fuel were measured by 46.6 mm/s, 376.5 mm/s for the ACE7 and RFA protective grids in order. Peak frequency also had increasing trend with the bundle flow velocity. Measured pressure drops of 16x16 type fuel protective grids were comparatively higher than those of the reference fuel protective grids

[en] Highlights: • A new transshipment type model for inter-plant heat exchanger network is proposed. • New constraints are used to identify three inter-plant heat integration schemes. • A model with linear constraints is developed, allowing non-isothermal mixing. • Better results with lower total annual cost can be obtained by the proposed model.

[en] Equations for calculating the loss coefficient in combining flows in tee functions are obtained by an integral linear momentum balance. It is a practice, when solving this type of problem, to neglect the pressure difference in the upstream location as well as the wall-fluid interaction in the lateral branch of the junction. In this work it is demonstrated the influence of the above parameters on the loss coefficient based on experimental values and by apropriate algebraic manipulation of the loss coefficient values published by previous investigators. (Author)

[en] The results of an experimental investigation in divided-flow fittings head loss are presented. The main purposes are to verify the minimum value of the coefficient and to see it as a Carnot-Borda head-loss. The Reynolds number influence on head loss coefficients were qualitatively identified. The 90 degrees cross section fittings used in this experiment had a unitary area ratio. (Author)

[en] Single phase natural circulation is of interest in various energy systems, including solar heaters, nuclear reactors, geothermal power production, engine and computer cooling. The present paper deals with an experimental study on the influence of pressure drops on the behavior of a single-phase natural circulation loop. In a simple rectangular loop (MTT-1) located at DITEC, three series of tests have been carried out, with localized pressure drops (orifices of 6 mm, 10 mm and 14 mm diameter in the vertical legs) and different power levels. The experimental data are analyzed and compared with previous results obtained with smooth pipes, demonstrating the stabilizing effect of the pressure drops on the overall behavior of the loop