1,721,000 research outputs found
Enhancing the phase distribution in parallel vertical channels with single and double chamber coaxial headers
No full textIn this paper, in order to maximize the degree of flow rate uniformity of the two phase flow distribution into parallel vertical channels, a number of distributor fittings have been tested with respect to a test section characterized by a horizontal header and a series of vertical upward channels. The fluids are air and water and the flow regimes at the header cover the intermittent and annular flow pattern conditions. The ranges of liquid and gas superficial velocities are 0.45–1.2 and 1.5–16.5 m/s, respectively. A header geometry without any inserts, such as the smooth reference header, is taken as a reference case. Data from a number of inserts to enhance the uniformity of distribution are compared to the reference case, such as a series of cylindrical distributors with in-line holes along their length (“flutes”). New data in particular are presented for the “double chamber flute” fitting. As in previous studies by the Authors, extracted mass flow rates of liquid and gas from parallel channels are recast in terms of normalized flow rates and normalized standard deviation of phases. A new overall performance parameter is used for data reduction and for summarizing the comparison between the flute fitting configurations
A simplified approach for predicting the intermittent behaviour of gas-liquid mixtures in pipes
No full textA new approach to the classical slug flow model is here proposed based on an original correlation for the minimum liquid level in the stratified regions of intermittent horizontal flows. This correlation is obtained by fitting experimental data obtained from a statistical analysis of void fraction signals from ring impedance probes. The new procedure improves the original model in terms of computing time reduction and algorithm simplification. In addition, it is demonstrated that the new closure relationship can be derived with more consistent experimental results, with respect to the slug length, which is employed in the original approach. The predictions of the main flow parameters are presented with reference to the classical and new approach, and all the results are critically compared with literature experimental data. It is demonstrated that the simplified procedure is able to predict the pressure drops and average void fraction values in good agreement with experimental measurements, while only the slug frequency and slug length predictions are affected by poor reliabilit
The effect of the flow direction inside the header on two-phase flow distribution in parallel vertical channels
No full textThe experimental investigation presented in this paper is aimed at understanding the main mechanisms which drive the flow distribution inside a two-phase horizontal header in order to design improved distributors and to optimise the flow distribution inside compact heat exchanger.
Experimentation was devoted to establish the influence of the inlet conditions and of the channel/distributor geometry on the phase/mass distribution into parallel vertical channels. The study is carried out with air-water mixtures and it is based on the measurement of component flow rates in individual channels and on pressure drops across the distributor
Proposta di una procedura automatizzata per guidare le P.A. nell’efficientamento energetico, economico e ambientale delle strutture esistenti e operanti sul territorio
No full textViene presentato il risultato dello studio condotto presso l’Università degli Studi di Genova per conto del Comune di Cogorno (Ge) in tema di riqualificazione energetica, ambientale ed economica delle strutture esistenti sul territorio dei comuni italiani di medie e piccole dimensioni. Si propone un simulatore in grado di offrire un supporto decisionale agli amministratori locali nelle scelte di riqualificazione delle strutture esistenti senza aggravio di costi a priori per lo studio preventivo di fattibilità.
A smart tool to guide P.A.s’ local authorities towards energetic, economic and environmental optimization of existing buildings
The paper presents the study conducted by the University of Genoa with the City of Cogorno (Ge) in terms of upgrading the energy, environmental and economic efficiency of existing buildings present in Italian municipalities of medium and small size. An easily usable simulator can provide a quick and accurate decision support for local administrators
PHASE SPLIT IN PARALLEL VERTICAL CHANNELS IN PRESENCE OF A VARIABLE DEPTH PROTRUSION HEADER
No full textThe air and water flow distribution are experimentally studied in a test section simulating a heat exchanger composed by a round header and 16 parallel upward channels. The effects of the tube protrusion depth as well as the gas and liquid superficial velocities are investigated and the results are compared with previous data. A new fitting solution to be inserted in the header has been developed based on previous findings by the Authors. The fitting geometry belongs to the family of the protruding pipes but the protruding depth has been varied along the header in order to cope with expected liquid and gas mass flow rates in the parallel channels. The flow at the header inlet is intermittent and annular and water and air have been employed as two phase mixture. The new header fitting demonstrated to yield meaningful improvements in phase distribution in terms of either dimensionless liquid and gas flow ratios or standard deviation of phase flow ratio (the overall performance parameter STD2 here presented decreased by 64%) when compared to the previous configurations
Un’apparecchiatura per la misura simultanea di emittenza e calore specifico di materiali solidi
No full textDescrizione di una tecnica sperimentale per la misura simultanea dell'emittenza termica del calore specifico per materiali solid
Effects of The Presence of Protrusions on The Air-Water Distribution in Parallel Vertical Channels
No full textUniform fluid and phase distribution is essential for efficient operation of engineering equipment such as plate heat exchangers, reactors, mixers where two phases are flowing together. Even though the principles of single phase distribution in parallel channels have been studied for more than three decades, further work is needed when a mixture is present, since to date many process equipment still suffer from uneven distribution of phases inside them. In this paper an experimental investigation is devoted to establish the influence of the operating conditions and of the header geometry on the phase/mass distribution into parallel vertical channels. The study is carried out with air-water mixtures and it is based on the measurement of gas and liquid flow rates in individual channels. The liquid and gas superficial velocities range from 0.2-1.2 and 1.5-16.5 m/s, respectively. In order to control the flow distribution in the channels, the header has been modified by introducing a number of protrusion pipes, whose protrusion height can be varied. The effects of presence of the protruded pipes into the header are analysed in terms of liquid and gas flow ratios and normalised standard deviation of phases and the present results are compared with previous ones obtained in different conditions of header geometry
Distribution of Air-Water Mixtures in Parallel Vertical Channels as an Effect of the Header Geometry
No full textUneven phase distribution in heat exchangers is a cause of severe reductions in thermal performances of
refrigeration equipment. To date, no general design rules are available to avoid phase separation in manifolds
with several outlet channels, and even predicting the phase and mass distribution in parallel channels
is a demanding task. In the present paper, measurements of two-phase air–water distributions are
reported with reference to a horizontal header supplying 16 vertical upward channels. The effects of
the operating conditions, the header geometry and the inlet port nozzle were investigated in the ranges of liquid and gas superficial velocities of 0.2–1.2 and 1.5–16.5 m/s, respectively. Among the fitting devices used, the insertion of a co-axial, multi-hole distributor inside the header confirmed the possibility of greatly improving the liquid and gas flow distribution by the proper selection of position, diameter and number of the flow openings between the supplying distributor and the system of parallel channels connected to the header
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