Gökhan Arslan

Heat Transfer Characteristics for Condensation of R134a in a Vertical Smooth Tube

In this study, condensation of pure refrigerant R134a vapor inside a smooth vertical tube was experimentally investigated. The test section was made of a copper tube with inside diameter of 7.52 mm and length of 1 m. Experimental tests were conducted for mass fluxes in the range of 20–175 kg/m2s with saturation pressure ranging between 5.8 and 7 bar. The effects of mass flux, saturation pressure, and temperature difference between the refrigerant and tube inner wall (ΔT) on the heat transfer performance were analyzed through experimental data. Obtained results showed that average condensation heat transfer coefficient decreases with increasing saturation pressure or temperature difference (ΔT). In addition, for the same temperature difference (ΔT), heat can be removed from the refrigerant at a higher rate at relatively low pressure values. Under the same operating conditions, it was shown that average condensation heat transfer coefficient increases as mass flux increases. Finally, the most widely used heat transfer coefficient correlations for condensation inside smooth tubes were analyzed through the experimental data. The best fit was obtained with Akers et al.s (1959) correlation with an absolute mean deviation of 22.6%.

Modeling, simulation, and optimization of a solar water heating system in different climate regions

To design an effective solar water heating system (SWHS), parameters such as the energy consumption rate, total cost, and climatic region characteristics must be analyzed during the time interval (annual or seasonal) of the predicted use. In this paper, the optimum dimensions of a SWHS were determined using the life cycle cost (LCC) analysis constraint by the 40% solar fraction for the different regions of Turkey for annual and seasonal periods. Particle swarm optimization/Hooke and Jeeves hybrid optimization algorithm was applied. The optimum number of solar collectors and the volume of the hot water storage tank of the SWHS were determined. The optimization process showed that LCC could be reduced for all regions in the range of 3.3%–5.8% in the annual simulation period and 1.8%–4.8% in the period of the summer season simulation. The optimization process carried out in the winter season revealed that the optimization results obtained over different time periods can make a difference in the relations between the optimization parameters. Accordingly, the performance of the SWHS could be improved using a design according to the optimum results obtained at the time interval of the usage. The optimization results obtained in the summer season led to a saving in LCC, while the results obtained in the winter season led to an improvement in the systems thermal performance. Finally, the relative influence of possible operating parameters on an optimum SWHS was investigated through sensitivity analysis.To design an effective solar water heating system (SWHS), parameters such as the energy consumption rate, total cost, and climatic region characteristics must be analyzed during the time interval (annual or seasonal) of the predicted use. In this paper, the optimum dimensions of a SWHS were determined using the life cycle cost (LCC) analysis constraint by the 40% solar fraction for the different regions of Turkey for annual and seasonal periods. Particle swarm optimization/Hooke and Jeeves hybrid optimization algorithm was applied. The optimum number of solar collectors and the volume of the hot water storage tank of the SWHS were determined. The optimization process showed that LCC could be reduced for all regions in the range of 3.3%–5.8% in the annual simulation period and 1.8%–4.8% in the period of the summer season simulation. The optimization process carried out in the winter season revealed that the optimization results obtained over different time periods can make a difference in the relations bet...