Flow characteristics in flow networks

A flow network is a system of mutually intersecting holes in a plate or an assembly of plates. The flow at each intersection is characterized by a collision of two flow streams, resulting in complex flow patterns through the downstream holes. In the case of multiple intersections, the flow is periodically disrupted at each succeeding intersection, thus preventing the formation of a fully-developed flow through the holes.An experimental study is presented in this paper to determine flow characteristics in flow networks with various geometry. The intersecting pressure loss coefficient which represents the performance of flow networks is defined and its magnitude empirically determined as functions of geometric and flow conditions. A method is developed to measure the ramming loss in an intersection tube. Flow visualization by means of hydrogen bubble method is applied to observe flow patterns and mixing behavior in the flow network. A physical model is developed to predict the intersection pressure loss in flow networks.List of symbols A total section area of the flow network holes - a section are a of one hole in the flow network - a_t throat area of the orifice - b semi-minor axis of the intersection throat ellipse (Fig. 8) - C_d overall flow discharge coefficient with intersection - C_do overall flow discharge coefficient in the absence of intersection - D_h hydraulic diameter of the flow channel - d hole diameter - f flow friction coefficient - FF compressible flow function - H major axis of the intersection ellipse (Fig. 8) - K_b, K₀ pressure loss coefficients for the miter bend, and quadrant-edged orifice, respectively - K_c, K_e, K_x flow contraction, expansion, and intersection coefficients, respectively - L length of the hole in the flow network, i.e. flow length inside holes - L_e equivalent length of a pipe for the miter bend pressure loss - N_h number of holes in the flow network - N_x number of intersections for each hole - p pitch distance between holes - P_a, P_s, P_t total pressure in the plenum, the ambient pressure, and absolute total pressure in the plenum, respectively - _Pb, p₀ pressure losses in the miter bend and through the quadrant-edged orifice, respectively - p_T, p_H pressure drops in the flow network and its half unit, respectively - Q, Q flow rates passing through the test section equivalent to standard condition and in operating conditions, respectively - R univeral gas constant - s test plate thickness - T, T_t air temperature in the plenum and the absolute temperature of air, respectively - V fluid flow velocity - W mass flow rate of air - diameter ratio in the quadrant-edged orifice - dynamic viscosity of fluid - kinematic viscosity of fluid - intersection angle between holes - fluid density