The determination of the thermal conductivity of insulation materials depending on which parameters in the application as well as the production is very important. In this direction, the parameters affecting thermal conductivity should be determined to improve the efficiency of the insulation materials. It is also a fact that expanded polystyrene blocks have different thermal conductivities at the same density value depending on the production process. In this study, it was determined, experimentally and numerically, that the thermal conductivity of expanded polystyrene material at different densities is dependent on which parameters and changes in temperature. Expanded polystyrene materials consist of blocks of 30×30 cm with density of 16, 21, and 25 kg/m3 and a thickness of 20 mm. Thermal conductivity measurements were performed in FOX 314 (Laser Comp., USA) operating in accordance with ISO 8301 and EN 12667 standards. The measurements were made for expanded polystyrene blocks at the average temperatures of 10°C, 20°C, 30°C, and 40°C. The numerical study has three stages as the acquisition of electron microscope images (SEM) of expanded polystyrene blocks, modeling of internal structure geometry with CAD program, and realization of solutions with a finite element-based ANSYS program. Findings from experimental and numerical studies and the parameters affecting thermal conductivity were determined. Finally, it is thought that numerical methods can be used to obtain a preliminary idea for EPS material in determining thermal conductivity by comparing the findings of experimental and numerical studies.

Bu makaleye şu şekilde atıfta bulunabilirsiniz(To cite to this article): Doğan B. ve Tan H.," Sialon-Si3N4 esaslı seramik kesici uçların ısıl iletkenliğinin incelenmesi", Politeknik Dergisi, 21(1): 7-12, (2018).Erişim linki (To link to this article): http://dergipark.gov.tr/politeknik/archive

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In this study, a cascade refrigeration system comprising gas and vapor compression cycles operating at ultra-low temperature was designed. In the thermodynamic analyses, R744, R404A, and R410A refrigerants in the high temperature cycle (HTC), and R1150, R170, and R23 in the low temperature cycle (LTC) were used. Thermodynamic analyses were carried out using the Engineering Equation Solver package program. Outputs considered were: system performance(COP), compression ratio, mass flow ratio and HTC cascade outlet temperature. Results show that, at different LTC condenser temperature values, R404A/R23 has the highest COP value, in the LTC, R23 has the highest compression ratio, while R1150 has the lowest one, in the HTC, R404A has the highest compression ratio, while R744 has the lowest one, the performance of the system increased with the decrease of the mass flow ratio.