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Abstract
Water flowing on a sprinkled tube bundle forms three basic modes: the Droplet mode (the liquid drips from one tube to another), the Jet mode (with an increasing flow rate, the droplets merge into a column) and the Membrane (Sheet) mode (with a further increase in the flow rate of the falling film liquid, the columns merge and create sheets between the tubes. With a sufficient flow rate, the sheets merge at this stage, and the tube bundle is completely covered by a thin liquid film). There are several factors influencing both the individual modes and the heat transfer. Beside the above-mentioned falling film liquid flow rate, these are for instance the tube diameters, the tube pitches in the tube bundle, or the physical conditions of the falling film liquid. This paper presents a summary of data measured at atmospheric pressure, with a tube bundle consisting of copper tubes of 12 millimetres in diameter, and with a studied tube length of one meter. The tubes are situated horizontally one above another at a pitch of 15 to 30 mm, and there is a distribution tube placed above them with water flowing through apertures of 1.0mm in diameter at a 9.2mm span. Two thermal conditions have been tested with all pitches: 15 °C to 40 °C and 15 °C to 45 °C. The temperature of the falling film liquid, which was heated during the flow through the exchanger, was 15 °C at the distribution tube input. The temperature of the heating liquid at the exchanger input, which had a constant flow rate of approx. 7.2. litres per minute, was 40 °C, or alternatively 45 °C.
Highlights
The experiments described in this paper involved the testing of two temperature differences. It was a range of 15–40 °C and the range of 15–45 °C where the falling film liquid’s temperature T1 at the distribution tube outlet was approximately 15 °C and the temperature of the sprinkled liquid was T3 40 °C or 45 °C at the inlet of an exchanger which consisted of ten tubes
The results of the tube bundle with a grooved surface again do not clearly imply the most convenient pitch with the exception of two areas. They are in the first case the area at the A2 pitch and the thermal gradient 15–45 that reaches the maximum of approx. 5.0 kW m2 K in the flow rate range of 5.0 to 10.0 litres per minute, which is in this particular point almost by 2.0 kW m2 K less in comparison with the rest
This paper presents primary measured values of a heat transfer coefficient at the surface of sprinkled tube bundle consisting of ten tubes positioned horizontally one above another, where the tube pitches have been altered and three various tube surfaces have been tested at two thermal gradients
Summary
These are the Droplet mode (D), the Jet mode (J) and the Membrane (Sheet) mode (S) [1,2,3,4]. With an increasing flow rate of the falling film liquid, the transition from the Droplet to the Jet mode is defined by the formation of one stable column of liquid among the droplets (this transition mode will be hereinafter referred to as the “D→J” mode). The transition from the Jet to the Membrane (Sheet) mode is defined by the connection of two columns and their formation of a small triangular sheet (hereinafter referred to as the “J→S” mode). For the authors of its results achieved under strict laboratory conditions for one to three trumpets and our research deals with the behavior “big tube bundle”
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