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Purpose This study aims to investigate heat and mass transfer in a one-row heat exchanger. The required equations are obtained based on two-dimensional model analysis in a cell of the heat exchanger. By using finite difference approach, the obtained equations are solved to determine distribution of temperature and the efficiency of the heat exchanger in the case of partially wet surface. In this research, Lewis Number as unity and water vapor saturation as parabolic are assumed. Obtained results show that increase in thermal conductivity fin leads to decreasing thermal resistance; therefore, temperature changes in radial from center to out of fin are reduced and efficiency of fin increases. Design/methodology/approach In this regard, fin material plays a significant role in fin efficiency. Changes in airflow also result in an efficiency increase by temperature and relative humidity, and efficiency is decreased by airflow velocity increase, and these changes are almost linear. Moreover, the fins with more wet surface are more sensitive to changes in fin dimensions and air flow characteristics, and it is a result of conjugate heat transfer mechanism, in which latent heat transfer in the fins with more wet surface has a significant role. Findings Thermal property and geometry of the fin under wet conditions play a more important role than the fin under dry conditions. Changes in airflow result in an efficiency increase by temperature and relative humidity, and efficiency is decreased by airflow velocity increase, and these changes are almost linear. Fins with more wet surface are more sensitive to changes in fin dimensions and air flow characteristics. Originality/value Effects of the temperature of water supply and mass flow rate were considered in the study. The results had good agreement with actual data.

Level of utilization of clean energy has grown dramatically in recent years due to increased pollution and environmental issues. For instance, the extra potential energy in water supply system is usually wasted, due to its low capacity. Design of a proper turbine has recently been given more attention by researchers to apply this clean energy. In the present paper, a modified Savonius turbine, suitable for use in a 4-inch pipe, is designed. Turbine with two blades is tested in a laboratory rig and also simulated with the FLUENT software. By matching numerical and laboratory results, simulations are expanded and the blades number effect on turbine performance is studied under determined hydraulic conditions. The flow field around the modified Savonius turbine is interpreted by the 3D streamlines and pressure contours. The obtained results indicate that increasing the turbine blade numbers up to 5 and more causes the turbine efficiency first to rise and then to fall, respectively.

Due to limitation of energy resources, a large body of research activities has been turned to investigate potential alternative avenues to supply energy. In this regard, the renewable sources, which can provide the sustainable and cleaner energy production, have increasingly become attractive. Hydropower has the highest proportion of the renewable energy sources. Availability and high efficiency are the undeniable advantages of the hydro potentials. In this paper, hydro-energy extraction from pipelines by a new designed vertical axis turbine is studied experimentally and numerically. The turbine scheme is inspired by the Savonius rotor turbine, which includes two semicircular blades that is built by the 3D printer and installed vertically in a 100 mm transparent pipe. A sloped block is used just before the turbine blades to concentrate the flow and enhance the efficiency. In experiments, flow rate ranges from 2.7 × 10−3 m3/s to 7.3 × 10−3 m3/s and pressure drop that occurs through the turbine is less than 10.5 kPa. Numerical results show an acceptable agreement with experiments and assure that numerical method is reliable. Following successful validation, numerical studies are expanded, in order to study more details on the new turbine performance. According to the numerical results, the characteristic curves of the new turbine are depicted and described. In numerical simulation, for different turbine rotational speeds, the flow rate and the pressure difference examined are up to 12 × 10−3 m3/s and 30 kPa, respectively. Using the obtained results, investigations and studies are performed to describe turbine behavior under the effects of changing the clearance and flow field conditions. Finally, cyclic variations of turbine flow rate, torque and minimum pressure on the turbine blade are described by velocities streamlines. This approach might preform design improving for such a turbine.

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