Sendogan Karagoz

R134a and various mixtures of R22/R134a as an alternative to R22 in vapour compression heat pumps

Abstract The performance of an air to water vapor compression heat pump has been investigated experimentally. The main purpose of this study was to investigate the possibilities of using R134a as a working fluid to replace R22 for vapor compression heat pumps. Pure R22, pure R134a and some binary mixtures of R22/R134a were considered as working fluids. The performance of the system was characterized by mixture ratio, COP and evaporator air inlet temperature. Comparisons are made between the pure refrigerants and refrigerant mixtures on the basis of the COP. Experimental results show that the mixture ratio affects the COP significantly, and the COP could be improved by using pure R134a or an appropriate mixture of R134a/R22 instead of pure R22. The maximum COP occurred at a mixture ratio of around 50/50% R134a/R22. For a mass percentage of 50% of R134a, the COP was enhanced by about average 25%.

Sustainable Energy Development in Turkey

Abstract Turkeys demand for energy and electricity is increasing rapidly. Turkey is heavily dependent on expensive imported energy resources that place a big burden on the economy, and air pollution is becoming a great environmental concern in the country. As would be expected, the rapid expansion of energy production and consumption has brought with it a wide range of environmental issues at the local, regional, and global levels. With respect to global environmental issues, Turkeys carbon dioxide (CO2) emissions have grown along with its energy consumption. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases. In this regard, renewable energy resources appear to be one of the most efficient and effective solutions for clean and sustainable energy development in Turkey. Turkeys geographical location has several advantages for extensive use of most of these renewable energy sources. This article presents a review of the sustainable energy policies and utilization of the renewable energy sources in Turkey.

Variable-Base Degree-Day Analysis for Provinces of the Eastern Anatolia in Turkey

There is a gap in the information needed by building designers and engineers for simplified energy calculations of buildings in Eastern Anatolia, Turkey. This study was conducted to determine and analyse heating and cooling degree-days for the provinces of the Eastern Anatolia, using hourly dry bulb temperature records. The heating degree-days were calculated for base temperatures from 12 to 22°C and the cooling degree-days for base temperatures from 18 to 28°C, using a temperature step of 2°C. The results are presented in tabular and graphical form and serve the estimation of the energy requirements and fuel consumption of heating and air conditioning systems for either monthly or seasonal operation.

Experimental research of dynamic instabilities in the presence of coiled wire inserts on two-phase flow.

The aim of this study is to experimentally investigate the effect of the coiled wire insertions on dynamic instabilities and to compare the results with the smooth tube for forced convection boiling. The experiments were conducted in a circular tube, and water was used as the working fluid. Two different pitch ratios (H/D = 2.77 and 5.55) of coiled wire with circular cross-sections were utilised. The constant heat flux boundary condition was applied to the outer side of the test tube, and the constant exit restriction was used at the tube outlet. The mass flow rate changed from 110 to 20 g/s in order to obtain a detailed idea about the density wave and pressure drop oscillations, and the range of the inlet temperature was 15–35°C. The changes in pressure drop, inlet temperature, amplitude, and the period with mass flow rate are presented. For each configuration, it is seen that density wave and pressure drop oscillations occur at all inlet temperatures. Analyses show that the decrease in the mass flow rate and inlet temperature causes the amplitude and the period of the density wave and the pressure drop oscillations to decrease separately.

Thermal conductivity of different colored compomers

Background Compomers are mostly used in primary dentition. The thermal conductivity properties of traditional or colored compomers have not been investigated in detail so far. The aim of this in vitro study was to assess and compare the thermal conductivities of traditional and colored compomers. Method Two sets of compomers – namely, Twinky Star (available in berry, lemon, green, silver, blue, pink, gold and orange shades) and Dyract Extra (available in B1, A3 and A2 shades) –were included in this study. All of the traditional and colored compomers were applied to standard molds and polymerized according to the manufacturers’ instructions. Three samples were prepared from each compomer. Measurements were conducted using a heat conduction test setup, and the coefficient of heat conductivity was calculated for each material. The heat conductivity coefficients were statistically analyzed using Kruskal-Wallis and Duncan tests. Uncertainty analysis was also performed on the calculated coefficients of heat conductivity. Results Statistically significant differences were found (p<0.05) between the thermal conductivity properties of the traditional and colored compomers examined. Among all of the tested compomers, the silver shade compomer exhibited the highest coefficient of heat conductivity (p<0.05), while the berry shade exhibited the lowest coefficient (p<0.05). Uncertainty analyses revealed that 6 out of 11 samples showed significant differences. Conclusions The silver shade compomer should be avoided in deep cavities. The material properties could be improved for colored compomers.