Melda Ozdinc Carpinlioglu

A Modification on Ergun's Correlation for Use in Cylindrical Packed Beds With Non-spherical Particles

An experimental study was conducted to determine the pressure drop characteristics of cylindrical packed beds through which turbulent pipe flow was passing. This study was planned to clarify the applicability of the well-known Ergun correlation proposed for beds composed with spherical particles on beds with non-spherical particles. The experimental packed beds were constructed by using two different irregular-shaped and one spherical-shaped packing materials for understanding the effects of particle shape or sphericity, particle size, bed porosity, and bed length to diameter ratio on the pressure drop. The beds were constructed by using zeolite, chickpea and glass bead materials to cover the particle sphericity range of 0.55 ≤ Φ ≤ 1.00. Systematic experiments and the data analysis procedure showed that the well-known Ergun correlation can be applied to all of the experimental beds composed with non-spherical and/or spherical particles with a maximum deviation of ±20%. This deviation can, however, be decreased to a negligible level of ±4% if some simple modifications, including the use of particle Reynolds number, Rep, a new form of particle friction factor, f*p, and some adopted empirical constants in the well-known Ergun correlation, are used.

An approach for transition correlation of laminar pulsatile pipe flows via frictional field characteristics

Abstract Transition of laminar pulsatile pipe flow into turbulence is one of the current research topics in flow dynamics. Despite the existence of a considerable number of theoretical and experimental studies, the physical mechanism of transition is not well defined. Furthermore, there is almost no information on the start and the end of the transition in terms of pulsatile flow parameters. In this paper, an approach which consists of attempts to correlate the governing flow parameters is presented to reveal the transition process with particular emphasis on the frictional field. The experimental data collected in slightly compressible, Newtonian, one-dimensional laminar pulsatile pipe flow without a flow reversal were compiled for this purpose. The common oscillation parameters, dimensionless frequency parameter ω′ and velocity amplitude ratio A1 were the main variables of the experimental study covering the ranges of 7≤ ω′ ≤28 and 0.05≤A1≤0.8. The time history of local static pressure gradient and axial velocity field were accumulated and the data were expressed through pulsatile flow, instantaneous λu(t) and time-averaged λ u, ta friction factors using momentum-integral equation. A reference friction factor ratio λR, whose definition was based on the concept of steady flow friction was introduced. The start and the end of transition were predicted through the functional relationships of λR with time-averaged and oscillating Reynolds numbers, Reta and Reos by means of a trial–error procedure. The proposed correlations and determined approximate critical limits of transition are only valid in the corresponding ranges of 2000≤ Re ta ≤60 000 , 620≤ Re os ≤18 800 and the analysis is open to discussion.

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.

Experimental study on an open cycle desiccant cooling system

This paper presents the design and construction of an experimental desiccant cooling system that uses natural zeolite as the desiccant. This is the first use of this desiccant in an actual or experimental system. The primary system components are originally designed and constructed. The paper provides a sufficient detail on the design procedure of the components as well as the methods of measurements. Experiments are conducted to cover a wide range of system and operating parameters. For the investigated cases, the coefficient of performance, the cooling capacity, and the moisture removal capacity take maximum values of 0.95, 16 kW/kg dry air, and 6.5 g/kg dry air, respectively. Exergy analysis is performed for a typical operation of the unit and the exergy destructions and exergy efficiencies are calculated. The greatest exergy destruction occurs in the desiccant wheel and the exergy efficiency of the unit is 3.3 percent.

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.

Discharge Regimes of Polydisperse Powders through Conical Hoppers under Positive Flow Conditions

Discharge characteristics of polydisperse powders through a conical hopper were experimentally investigated by observing the solids discharge regimes under different positive pressure differences (i.e., ΔP > 0) and also measuring the corresponding solids discharge rates. The observations and measurements were systematically conducted at least four diameters of hopper orifice (2.5 mm ≤ Do ≤ 30.0 mm) under five positive ΔP values (0 Pa ≤ ΔP ≤ 1405 Pa) for the test powders: river sand, zeolite, fertilizer, and sawdust. Effects of positive ΔP on both discharge regime and solids discharge rate are first predicted for different orifice diameters and test powders in this study. One of the novel results on the discharge regime is that increase of positive ΔP value up to a critical value conserves or successively stabilizes the discharge regime observed when ΔP = 0 (i.e., for gravity flow condition) through the same hopper. However, the additional increase of positive ΔP over this critical value destabilizes the discharge regime, as in conformity with the effect of increase in negative ΔP cited in the literature.

Effect of spherical roughness elements upon transition of a 3-D boundary layer

The influence of isolated spherical roughness elements upon the transition of a three-dimensional boundary layer on a swept flat plate is discussed in this paper. Perturbations induced by the roughness are found to be more effective on the start of transition rather than the crossflow of the laminar undisturbed boundary layer at the roughness location.