Vedat Oruç

A test rig for the investigation of airflow through collapsible tubes

Abstract In this paper, an experimental set-up for investigating airflow through collapsible tubes has been described in detail. The test rig is basically composed of an airtight chamber socalled ‘Starling resistor’, which includes a length of collapsible tube attached to rigid tubes at its ends, a compressor supplying steady airflow, and measuring devices. The self-excited oscillations that develop due to strong fluid-pipe interaction cause the flow to be time dependent. A data acquisition system is utilized to obtain the measurements. Therefore, it is possible to measure simultaneously the time-dependent parameters, which are upstream and downstream pressures, velocity downstream of the collapsible tube. It has been verified by referring to the experimental results that the calibration of the whole system is satisfied and the measuring instruments give sensible output in combination with the data acquisition system. The presented test rig should be useful in point of view for testing possibility of airflow in soft elastic tubes.

Thermodynamic Analysis of a Refrigeration System Operating with R1234yf Refrigerant

After restriction of European Union on using high-GWP refrigerants, the investigations have been directed to utilize low-GWP refrigerants in available systems to determine the suitability of their operating conditions. In this study, energy and exergy parameters were investigated as a result of using R1234yf in a refrigeration system originally constructed to operate with R134a. The experimental work was conducted at two different ambient temperatures of 20 and 40 °C, while the evaporation temperature was 0 °C. The temperature, pressure, electrical power consumption, and mass flow measurements in the system revealed cooling capacity, COP, and exergetic efficiency for both R134a and R1234yf refrigerants.

Theoretical approximations to analyse the onset of self-excited oscillations in flow through collapsible tubes

Abstract In this study, flow through collapsible tubes is analysed theoretically for the case of the onset of collapse which induces self-excited oscillations. The basic tools in the theoretical calculations are the linear stability theory and the tube law. The experimental data in the form of measured oscillation frequency at the onset of collapse of an elastic tube is supplied as a base input parameter for the theoretical approximations. The calculations offer a possibility for estimating the unmeasured parameters such as critical oscillation speed, speed index, and tube cross-sectional area at the onset of collapse. It was seen by referring to the obtained results that theoretical predictions agreed with the experimental measurements.

A Correlation Study for the Positional Dependence of Friction Factor in Dilute Phase Flows

Results of a comprehensive study on the flow friction factor data collected on suspensions of solid granular particles of semolina, fly ash, and alumina having a size range of 75.5 µm ≤ dp ≤ 275 µm in air are presented. The experimental study was composed of 250 separate test cases in which airflow Reynolds number Re = UD/ν and loading ratio Mp/Ma were varied systematically covering the ranges of 50,000 ≤ Re ≤ 100,000 and 5% ≤ Mp/Ma ≤ 25%. An upward flow field with variable inclinations α of 10°, 20°, and 30° with the horizontal plane and a horizontal flow field, i.e, 0° inclination, were used to determine the influence of gravitational forces. Local static pressure gradients measured along the flow field with distance x were used to determine local air-particle friction factor fp + a, which was observed to be under the influence of particle type, Mp/Ma, Re, and flow line inclination, α. The proposed correlation for the variation of fp + a with x/D was evaluated to reach a generalized form exhibiting interactive influence of Re, Mp/Ma , α, and particle type.