The paper is dedicated to an issue of the influence of a nonuniform flow of mediums in a cross-flow water-air heat exchanger, the core of which is a bundle of elliptical finned tubes. The main purpose of the work is to determine the impact of non-uniform water inflow for various mass flow rates on the thermal efficiency of the heat exchanger. Multivariate analyses were carried out for various temperatures of water, and for measured nonuniform air distribution at the heat exchanger input. Two variants of water distribution were considered: non-uniform water distribution assumed considering a non-uniform air inflow and water distribution resulting from hydraulic resistances calculated for different locations of water inlet and outlet nozzles. Simulation results were compared with the experimental outcomes obtained in cases of the non-uniform natural inflow of both mediums and to the computation results for a case of the uniform media inflow. The results obtained in this work confirm the significant deterioration of the thermal efficiency of heat exchangers caused by a non-uniform media inflow (by as much as 18.5% compared to the case of a uniform media inflow) which is compliant with other numerous works. The control of the water flow through the individual heat exchanger tubes enables the improvement of thermal efficiency by 4.5% to 18.6% compared to the device with uncontrolled inflow of working fluids, which for some of the analyzed cases is even better than a completely uniform inflow of heat carriers.

In this paper a novel non-linear optimization problem is formulated to maximize the social welfare in restructured environment with generalized unified power flow controller (GUPFC). This paper presents a methodology to optimally allocate the reactive power by minimizing voltage deviation at load buses and total transmission power losses so as to maximize the social welfare. The conventional active power generation cost function is modified by combining costs of reactive power generated by the generators, shunt capacitors and total power losses to it. The formulated objectives are optimized individually and simultaneously as multi-objective optimization problem, while satisfying equality, in-equality, practical and device operational constraints. A new optimization method, based on two stage initialization and random distribution processes is proposed to test the effectiveness of the proposed approach on IEEE-30 bus system, and the detailed analysis is carried out.