Condenser under Conditions (original) (raw)
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Heat transfer measurement in a three-phase direct-contact condenser under flooding conditions
Applied Thermal Engineering, 2016
The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct contact condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40°C, 43.5°C and 47.5℃ was the dispersed phase and tap water at a constant temperature (19℃) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct contact column tends to be uniform when the direct contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.
AIChE Journal, 1966
Transfer characteristics are presented for a perforated plate-spray column in which a volatile dispersed phase evaporates while rising in the continuous, counterflowing, immiscible phase. Optimal column heights, volumetric transfer coefficients, holdup, and foam heights are reported as functions of flow rate and temperature approach for a pentane-water system, A comparison with related studies is presented. Recently multiphase exchangers where latent heat rather than sensible heat is transferred between immiscible fluids have been effectively used in water desalination by direct contact freezing. Some of the technical and economical aspects of utilizing these multiphase exchangers were reported by Umano (1), Wiegandt (2, 3) , and others (4). Experimental direct freezing pilot plants (5) are presently in the process of accumulating valuable technical know-how. Unlike the multiphase exchangers, where both the dispersed and the continuous fluids undergo change of phase, three-phase exchangers may be used for heat transfer at various temperature levels. The latter obviously depends on the choice of the transfer fluid. Stagewise operation of three-phase exchangers in a closed evaporation and condensation cycle was recently proposed by Harriott and Wiegandt (6) for simultaneous cooling and heating of sea water and desalined water streams in countercurrent flow. Some experimental data of condensation of methylene chloride in water flowing concurrently in a two-stage packed bed and a single-stage sieve-plate column were reported (6). Limited data were also reported on cocurrent flow evaporation of methylene chloride or pentane in water in a 2-in. diameter column. Wilke et al. (7) studied evaporation of water from sea water flowing concurrently in direct contact with hot Aroclor in an horizontal 3-in. pipe and steam condensation in direct contact with Aroclor in packed columns. Studies of condensation of steam in Aroclor in a simulated cocurrent spray cohmn were also reported (8). Despite increasing interest in technical information on direct contact heat transfer with change of phase, very little is known regarding the basic mechanism and heat transfer characteristics associated with evaporation of dispersions in immiscible liquids. Studies of single-drop evaporation in immiscible liquid media were recently reported by Sideman et al. (9, 10). These, however, may not be directly extended to population of drops, where the onset of nucleation is not simultaneous (and should be dependent on the vapor holdup and degree of turbu
Thermal Science, 2014
An analytical model for the convective heat transfer coefficient and the two-phase bubble size of a three-phase direct contact heat exchanger was developed. Until the present, there has only been a theoretical model available that deals with a single two-phase bubble and a bubble train condensation in an immiscible liquid. However, to understand the actual heat transfer process within the three-phase direct contact condenser, characteristic models are required. A quasi - steady energy equation in a spherical coordinate system with a potential flow assumption and a cell model configuration has been simplified and solved analytically. The convective heat transfer in terms of Nu number has been derived, and it was found to be a function to Pe number and a system void fraction. In addition, the two-phase bubble size relates to the system void fraction and has been developed by solving a simple energy balance equation and using the derived convective heat transfer coefficient expression....
International Communications in Heat and Mass Transfer, 2015
The volumetric heat transfer coefficient of a three-phase direct contact heat transfer condenser has been investigated analytically and experimentally. The experiments were carried out utilising a column of 70 cm in total height and 4 cm inner diameter. The active column height throughout the experiments was taken to be equal to 48 cm. Vapour pentane with three different initial temperatures (40℃, 43.5℃ and 47.5℃) was used as a dispersed phase, while tap water at a constant temperature (19℃) was used as a continuous phase. The variation of the volumetric heat transfer coefficient along the height of the column was measured experimentally and predicted analytically. The effects of the initial dispersed phase temperature, the dispersed mass flow rate and the continuous mass flow rate on the volumetric heat transfer coefficient were tested. The results indicate that the volumetric heat transfer coefficient decreases upon moving up the column, while it increases with an increase in the mass flow rate of either the dispersed phase or the continuous phase. No considerable impact of the dispersed initial temperature on the volumetric heat transfer coefficient was observed under the experimental conditions considered here. Finally, an excellent agreement was achieved between the analytical model and the experimental results.
Advances in Direct Contact Evaporator Design
Chemical Engineering & Technology, 2004
Direct contact evaporators are nonisothermal bubble columns where a hot gas, usually obtained by combustion, is used to heat and vaporize the solvent of a given solution that needs to be concentrated. The design of such equipment has been relied on experimental data or on a simplified method that assumes that the gas leaves the evaporator at equilibrium with the liquid phase, giving no information about the necessary bubbling height to attain such equilibrium conditions. Recent advances in the heat and mass transfer processes during the formation and ascension of superheated bubbles together with simple mass and energy balances in the liquid phase and gas distributor system were used to develop a more detailed design procedure. The accuracy of both design procedures are compared to available experimental data in a direct contact evaporator operating in semibatch mode. The new design method agreed well with the experimental data.
Gas-Liquid Direct-Contact Evaporation: A Review
Chemical Engineering & Technology, 2005
Gas-liquid direct-contact evaporators are characterized by the bubbling of a superheated gas through the solution to be concentrated. In other words, they are nonisothermal bubble columns. Despite their simplicity of construction, these units exhibit rather complex hydrodynamics and, similar to what occurs to isothermal bubble columns, the design of such units still poses a problem. The present paper reviews the literature regarding this kind of equipment, addressing both experimental studies and modeling efforts. The covered issues include classic and potential applications, bubbling regimes, gas holdup and bubble size distributions, as well as mathematical models proposed for simulating the unit. Additionally, pertinent literature on isothermal bubble columns is also discussed. Recommendations are made for future research.
Experimental study on bubble size distributions in a direct-contact evaporator
Brazilian Journal of Chemical Engineering, 2004
Experimental bubble size distributions and bubble mean diameters were obtained by means of a photographic technique for a direct-contact evaporator operating in the quasi-steady-state regime. Four gas superficial velocities and three different spargers were analysed for the air-water system. In order to assure the statistical significance of the determined size distributions, a minimum number of 450 bubbles was analysed for each experimental condition. Some runs were also conducted with an aqueous solution of sucrose to study the solute effect on bubble size distribution. For the lowest gas superficial velocity considered, at which the homogeneous bubbling regime is observed, the size distribution was log-normal and depended on the orifice diameter in the sparger. As the gas superficial velocity was increased, the size distribution progressively acquired a bimodal shape, regardless of the sparger employed. The presence of sucrose in the continuous phase led to coalescence hindrance.
Heat Transfer Engineering, 2017
An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapour at three different initial temperatures (40ºC, 43.5ºC and 47.5ºC), with differing mass flow rates, and tap water at a constant initial temperature (19ºC) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate.
Analytical Modelling of a Spray Column Three-Phase Direct Contact Heat Exchanger
ISRN Chemical Engineering, 2013
An analytical model for the temperature distribution of a spray column, three-phase direct contact heat exchanger is developed. So far there were only numerical models available for this process; however to understand the dynamic behaviour of these systems, characteristic models are required. In this work, using cell model configuration and irrotational potential flow approximation characteristic models has been developed for the relative velocity and the drag coefficient of the evaporation swarm of drops in an immiscible liquid, using a convective heat transfer coefficient of those drops included the drop interaction effect, which derived by authors already. Moreover, one-dimensional energy equation was formulated involving the direct contact heat transfer coefficient, the holdup ratio, the drop radius, the relative velocity, and the physical phases properties. In addition, time-dependent drops sizes were taken into account as a function of vaporization ratio inside the drops, whil...
Experimental investigations on air side heat and mass transfer phenomena in evaporative condensers
International Journal of Heat and Technology, 2017
The evaporative cooling is an energy saving technology and for this reason is widely used both in industrial and civil fields. The heat and mass transfer phenomena occurring inside their tube banks are hard to study and even if many researchers have faced them, further activities need to be carried out. For this reason, this work aims at investigating with an experimental approach the evaporative condensers performance at the tube scale, focusing on the air side where more complex physical interactions occur. A test rig has been set up made of a rectangular transparent channel where electrical heaters simulate the refrigerant side and embedded Pt100 Resistance Temperature Detectors controlled by a PID set and keep constant a given outer surface temperature. Water and air operating conditions are controlled as well, and this allows to carry out a sensitivity analysis depending on all the parameters influencing those thermo-fluid dynamic phenomena. The results show that the cooling rate decreases with the air relative humidity and dry bulb temperature, while increases with water flow rate and temperature. For the testing cases the maximum improvements deriving from increasing water flow rate and temperature are of 37 % and 14 % respectively.