Condenser Tubes Research Articles

Hydrocarbon condensation in horizontal smooth tubes: Part II – Heat transfer coefficient and pressure drop modeling

In this second part, Part II of a two-part study, data reported in Part I for condensation of hydrocarbons over a wide range of conditions are used to develop models for pressure drop and heat transfer coefficients. The pressure drop model accounts for the pressure drop occurring in the vapor and liquid phases, and due to phase interactions. The model provides improved predictions over existing correlations at lower frictional pressure drop conditions, such as in larger tube diameters and at higher saturation pressures. The data from Part I of this study are also used to develop a physically consistent condensation heat transfer model for horizontal smooth tubes. This model incorporates a novel method to account for the heat transfer through the upper liquid film that typically forms in horizontal tubes. The approach models the evolution of the liquid film from purely horizontal (annular) flow to a combination of vertical (falling film) and horizontal (annular) flow. Moreover, the evolution with quality is modeled continuously without resorting to interpolation between flow regimes. In doing so, this model accurately reflects the observations from flow visualization studies, and is a departure from the approach typically followed in existing correlations. Both models are developed using a database containing only hydrocarbon data (propane and pentane), but are shown to also accurately predict synthetic refrigerant behavior. Special attention is paid to developing a model that is equally applicable to all of the operating conditions in the database, thus equal weighting is given to high pressure and low pressure conditions, and all mass fluxes and tube diameters. The models predict the frictional pressure drop and heat transfer coefficient for the propane database with average deviations of 3% and −1%, respectively.

Estimation of the residual life of steam-turbine condensers based on statistical models

The article presents the results of a study aimed at estimation of the state and prediction of the residual life of steam-turbine condensers on the basis of statistical analysis. The possibility of such evaluation during the operation of steam-turbine plants with accuracy sufficient for practical purposes is demonstrated. It is shown that identification of the operating period, viz., the initial period, the normal operation period, or the period of the lifetime exhaustion, as well as determination of the condenser’s operating time at the moment when the failure of an individual tube occurs, is very important for statistical evaluation of the condenser state. Two statistical models are proposed and comparative analysis of the results calculated by these models for the residual life of the condensers at the Reftinskaya SDPP has been performed. The first model can be used when comprehensive information about the condenser’s operating time before the tubes have failed is available as well as a priori information—or information based on analysis of the condenser tube metal—that the condenser is in its normal operation period. In this case, the fact of exhaustion of the condenser’s lifetime is established by reaching the limit of the failed condenser tubes, which is determined by technical and economic analysis of losses caused by operating the turbine with a reduced heat-exchange surface of the condenser. The distribution function for the operating time of the failed tubes is approximated by a normal distribution. In the cases when no precise information on the condenser tubes’ operating time is available at the thermoelectric power plant (TEPP), the second statistical model based on censored samples is proposed for estimation of the condenser state. An expression to assess the confidence interval that determines the significant difference between the distribution functions for complete and censored operating time values has been derived. It is shown that this model allows prediction of the beginning of the condenser’s lifetime exhaustion period that is 1.5–2.0 years distant from the moment of mass failure occurrences.

RETRACTED: Visualization experiments on the condensation process in the vertical tube condenser of a loop thermosyphon

RETRACTED: Visualization experiments on the condensation process in the vertical tube condenser of a loop thermosyphon

Condensation heat transfer enhancement mechanism for vertical upflows by the phase separation concept at small gravity

In the field of aerospace, minimum and seal of equipments cause the increase in the thermal loading sharply. Due to the lack of driving force, the performance of conventional condenser deteriorates greatly under the small gravity environment, which leads to reduction in the service life of equipments. In this study, a passive condenser, developed on basis of the phase separation concept, is utilized to improve the performance of the condensation heat transfer under the small gravity environment. As a result of the limitation of experiments, the mechanisms of heat transfer enhancement of the phase separation condenser tube are revealed through numerical simulation based on the volume-of-fluid (VOF) method. The following conclusions could be obtained: (1) A novel phase distribution of ‘‘gas near the tube wall and liquid in the tube core’’ is formed. The thin liquid film is indeed created after the flow pattern modulation by inserting mesh cylinder. (2) The condensation quantity for single bubble in the annular region increases about 16 times greater than that in the bare tube region in the case of Jl = 0.0574m/s and Jg = 0.0229m/s. (3) Gas volume fraction affects the parameters of liquid film thickness, bubble length and liquid bridge length. The increase in the gas volume fraction results in the decrease in the evaluation index from 21.56 to 12.82. The evaluation index is defined as the ratio of the condensation quantities per unit tube length of the annular region and the bare tube region.

Heat transfer efficiency and capital cost evaluation of a three-phase direct contact heat exchanger for the utilisation of low-grade energy sources

Low-grade energy cycles for power generation require efficient heat transfer equipment. Using a three-phase direct contact heat exchanger instead of a surface type exchanger, such as a shell and tube heat exchanger, potentially makes the process more efficient and economic. This is because of its ability to work with a very low temperature driving force, as well as its low cost of construction. In this study, an experimental investigation of the heat transfer efficiency, and hence cost, of a three-phase direct contact condenser has been carried out utilising a short Perspex tube of 70cm total height and 4cm internal diameter. Only 48cm was used for the direct contact condensation. Pentane vapour with three different initial temperatures (40°C, 43.5°C and 47.5°C) was contacted with water with an inlet temperature of 19°C. In line with previous studies, the ratio of the fluid flow rates was shown to have a controlling effect on the exchanger. Specifically, the heat transfer efficiency increased virtually linearly with this ratio, with higher efficiencies also being observed with higher flow rates of the continuous phase. The effect of the initial temperature of the dispersed phase was shown to have a lower order impact than flow rate ratio. The capital cost of the direct contact condenser was estimated and it was found to be less than the corresponding surface condenser (shell and tube condenser) by 30 times. An optimum value of the continuous phase flow rate was observed at which the cost of the condenser is at a minimum.

Thermosiphon loop thermal collector for low-temperature waste heat recovery

This paper describes the thermal collector type loop thermosiphon for low-temperature waste heat recovery. Water is used as the working fluid for heat transport at temperatures 100 °C and higher. The loop thermosiphon comprises of a thermal receiver, a condenser, and riser and downcomer tubes. The thermal receiver is made of a cupper plate brazed by meandering heat transfer tube. This receiver collects the thermal radiation from the electric heater at the heat transfer area of 1000 cm2 (40 cm × 25 cm), and transports the heat by vaporization of water to the condenser having heat transfer area of 62 cm2. In the no inclination mode, the thermosiphon is upright so that the thermal receiver and the condenser are placed vertically. In this mode, the effective thermal conductivity exceeds 60 kW/(m K) when the thermal receiver temperature was higher than 125 °C for the water filling ratio α = 30–70%. Although the effective thermal conductivity is deteriorated for the higher filling ratio α = 80% and 90%, the effects from the filling ratio are tiny for α = 30–70%. The experimental tests were also made for the negatively inclined mode where the inlet and exit ports of the receiver were directed downward and for the positively inclined modes where they were directed upward. The tests revealed that the negative inclination almost halted the heat transport. However, the tests also indicated that the positive inclination showed the performance comparable to the no inclination mode for the cases up to the inclination angle 90°.

Experimental investigation on steam flow condensation in the presence of noncondensable gas inside horizontal multi-head spiral channels

An experimental investigation on the heat transfer characteristics of steam flow condensation inside the horizontal circular channel and the horizontal multi-head spiral channels is performed. The effects of the pressure, the water flow rate and the noncondensable gas mass fraction on the flow condensation performance are investigated. Two sets of experimental test sections are established: one is horizontal circular channel (HCC) consisting of an inner condenser tube and an outer cooling jacket, and the other is the horizontal multi-head spiral channels (HMHSC) with a multi-head spiral groove bar in the condenser tube mentioned above. The hot steam flows inside the inner condenser tube and the cooling water flows inside the annular channel in a counterflow direction. The mass flow rate and the local temperature are measured to acquire the average condensation heat transfer coefficient and the condensate mass flow rate. The experimental results indicate that the heat transfer performance of steam flow condensation in the HMHSC is better than that in the HCC under the same condition, and the average enhancement factor of the HMHSC compared against the HCC is about 2.35 times for the average condensation heat transfer coefficient, and 1.25 times for the condensate mass flow rate. Similarly, the average steam-side pressure loss of the HMHSC model is about 1.27 times higher than that of the HCC model under the same experimental conditions. It is obvious that the HMHSC can effectively enhance the heat transfer, while the average steam-side pressure loss will increase correspondingly.

Frictional Pressure Drop Correlations for Single-Phase Flow, Condensation, and Evaporation in Microfin Tubes

Experimental single-phase, condensation, and evaporation (flow boiling) pressure drop data from the literature and our previous studies were collected to evaluate previous frictional pressure drop correlations for horizontal microfin tubes of different geometries. The modified Ravigururajan and Bergles correlation, by adopting the Churchill model to calculate the smooth-tube friction factor and by using the hydraulic diameter in the Reynolds number, can predict single-phase turbulent frictional pressure drop data relatively well. Eleven pressure drop correlations were evaluated by the collected database for condensation and evaporation. Correlations originally developed for condensation and evaporation in smooth tubes can be suitable for microfin tubes if the friction factors in the correlations were calculated by the Churchill model to include microfin effects. The three most accurate correlations were recommended for condensation and evaporation in microfin tubes. The Cavallini et al. correlation and the modified Friedel correlation can give good predictions for both condensation and evaporation. However, some inconsistencies were found, even for the recommended correlations.

Estimation of a tube diameter in a ‘church window’ condenser based on entropy generation minimization

Abstract The internal diameter of a tube in a ‘church window’ condenser was estimated using an entropy generation minimization approach. The adopted model took into account the entropy generation due to heat transfer and flow resistance from the cooling-water side. Calculations were performed considering two equations for the flow resistance coefficient for four different roughness values of a condenser tube. Following the analysis, the internal diameter of the tube was obtained in the range of 17.5 mm to 20 mm (the current internal diameter of the condenser tube is 22 mm). The calculated diameter depends on and is positively related to the roughness assumed in the model.

Viability of integrating forward osmosis (FO) as pretreatment for existing MSF desalting unit

The feed to all Recirculation-multi-stage flash (R-MSF) desalting units in Qatar is pretreated with high temperature additive, which limits its top brine temperature (TBT) to 110°C. The daily capacity of these R-MSF units is about one Million cubic meters (Mm3/d). These units should continue their operation through their life time, (20–30 years). The capacity and performance of these units can be enhanced if Forward osmosis (FO) membrane system is used as pretreatment. The FO membranes can remove the scale constituents in the feed water and allows rising the TBT up to 135°C, and thus increases the capacity of these units. The viability of using FO as feed water pretreatment to an existing operating R-MSF unit is discussed in this paper. A suggested arrangement to use FO as MSF feed pretreatment is presented. Part of the cooling seawater leaving the heat rejection is directed to the FO pretreatment unit as feed solution (FS). The flashing brine leaving the last stage with the maximum brine salt concentration (about 1.5 times of the seawater feed) is directed to the FO unit as draw solution (DS) that absorbs an amount permeate water (D) from the FS while the Ca2+, CO3-, Mg2+, and SO42- are rejected. The diluted DS enters the last stage condenser of the heat recovery section. This arrangement allows to increase the TBT and thus the unit distillate capacity. The potential of calcium sulfate deposite index inside MSF condenser tubes is calculated at different TBTs and different FO recovery ratio. The calculations show that Skillman index in reference MSF (operates at TBT = 110°C) plant is greater than one which indicates the potential of scale deposit formation; however, antiscalant is used to disperse the crystalized scale. The simulation results showed that the potential of scale deposit is decreased as the FO recovery ratio increases due to the increase in divalent ions removal. The MSF can operate at TBT = 135°C safely without calcium sulfate scale at FO recovery ratio of 40%. On the other hand, the increase in the FO recovery ratio, will reduce the osmotic pressure difference across the membrane which requires higher membrane surface area. The impact of feed salinity is investigated, and the results showed that lowering the feed salinity gives better performance of FO unit. The cost of the FO membranes is a major factor in applying the suggested use of the FO as pretreatment for the R-MSF unit. The decision to apply this method depends on the availability and reasonable cost of the FO membranes.

A discussion about the methodology for validating a model of a finned-tube condenser considering different correlations for the heat transfer coefficients and pressure drop

The selection of suitable correlations for calculating heat transfer coefficients and pressure drop plays a fundamental role in the use of semi-empirical models for the simulation of the performance of a heat exchanger. Therefore, a discussion about the best way for validating a condenser model and choosing the best set of correlations for both the heat transfer coefficients and pressure drop is presented. The studies were performed for both the air and refrigerant side in a round tube and plate fin condenser. A test campaign was specially designed to cover a wide range of key parameters, such as air velocity, condensation temperature, refrigerant mass flow rate, and condenser subcooling. The options for defining the boundary conditions in the model and the accuracy metrics are discussed in detail, allowing the identification of the most suitable correlations. By using this set of correlations, the prediction error is within an error band of ±0.4°C for the condensation temperature and ±0.6% in terms of capacity.

Decontamination of discharged aluminum brass condenser tubes of a BWR: evolving the chemical formulation for copper oxide dissolution

Chemical formulations for copper oxide dissolution have been evaluated primarily for the minimum ionic load resulting in the spent formulation along with other desirable qualities. Peroxydisulfuric acid prepared freshly through ion exchange route has shown almost stoichiometric dissolution of the copper oxide as per the acidic oxidative action with efficient kinetics. Stability of the prepared formulation for its application and its effective oxidizing behaviour and aqueous cupric ion stabilizing by its redox product has been established experimentally.

수직 튜브 외벽에서의 증기-비응축성 기체 응축 열전달 실험 연구

To evaluate the heat removal capability of a condenser tube in the PCCS of an advanced nuclear power plant, a steam condensation experiment in the presence of noncondensable gas on a vertical tube is performed. The average heat transfer coefficient is measured on a vertical tube of 40 mm in O.D. and 1.0 m in length. The experiments covers the pressures of 2-4 bar, and the mass fraction of air ranges from 0.1 up to 0.7. From the experimental results, the effects of the total pressure and the concentration of air on the condensation heat transfer coefficient are investigated. The measured data are compared with the predictions by Uchida`s and Tagami`s correlations, and it is revealed that these models underestimate the condensation heat transfer coefficient of the steam-air mixture.

Experimental investigation on heat transfer coefficient during upward flow condensation of R410A in vertical smooth tubes

This paper presents an experimental investigation on condensation of R410A upward flow in vertical tubes with the same inner diameter of 8.02mm and different lengths of 300 mm, 400 mm, 500 mm and 600mm. Condensation experiments were performed at mass fluxes of 103–490 kg m−2s−1. The saturation temperatures of experimental condition were 31°C, 38°C and 48°C, alternatively. The average vapor quality in the test section is between 0.91 and 0.98. The effects of tube length, mass flux and condensation temperature on condensation were discussed. Four correlations used for the upward flow condensation were compared with the experimental data obtained from various experimental conditions. A modified correlation was proposed within a ±15% deviation range.

Experimental and computational investigation of vertical downflow condensation

This explores downflow condensation in a circular tube both experimentally and computationally using FC-72 as a working fluid. A highly instrumented condensation module is used to map detailed axial variations of both wall heat flux and wall temperature, which are used to determine axial variations of the condensation heat transfer coefficient. The experimental results are compared to predictions of a two-dimensional axisymmetric computational model using FLUENT. The study provides detailed construction of the model, including choice of interfacial phase change sub-model, numerical methods, and convergence criteria. The model is shown to yield good prediction of the heat transfer coefficient. The computed temperature profiles exhibit unusual shape, with steep gradient near the annular liquid film interface as well as near the wall, and a mild gradient in between. This shape is shown to be closely related to the shape of the eddy diffusivity profile. These findings point to the need for future, more sophisticated measurements of liquid film thickness, and both velocity and temperature profiles, to both validate and refine two-phase computational models.

볼 여과기 스크린 모듈의 단면 폐쇄효과에 관한 수치해석적 연구

A ball strainer screen module, which is used for a condenser tube cleaning system, is a critical mechanical component for maintaining condenser cleanliness. Despite of this importance, not many research have been focused on this module because of its relatively low usage. Employing CFD, this study examines the implication of fluid velocity change and blockage ratio on the ball strainer screen velocity and the static pressure distribution. Through this study, the impact of blockage in the space between ball strainer screen modules is verified. Also, it is found that the ranges of non-dimensional velocity distribution and static pressure distribution decrease as blockage ratio becomes smaller.

Two phase flow pressure drop in multiport mini-channel tubes using R134a and R32 as working fluids

In this study, two-phase flow pressure drop was experimentally measured in condensation and evaporation fluid flow. Refrigerants R134a and R32 were tested in a multiport extruded aluminium tube (MPEs) with hydraulic diameters of 0.715 and 1.16 mm. Experimental conditions were in a range: mass velocity 200–1229 kg/m2s, heat flux 2.55–70 kW/m2, saturated temperatures (5,7.5,12.5,30,35,40,45,50,55) °C. To do so, two installations have been used. They were constructed at the Technical University of Cartagena Spain, for the study of boiling and condensation in tubes. They are briefly described in this paper jointly with the experiments performed. The experimental data are compared with some well-known correlations which were developed for macro/mini-channel tubes. The homogeneous mixture model slightly underestimates the experimental boiling data. Classic macro-channel correlations: Friedel and Müller-Steinhagen and Heck predict satisfactorily well our experimental pressure drop data. Some of the new correlations specially developed for mini/micro-channels have been tested, finding that Cavallini et al. and Zhang and Webb predict with reasonable accuracy the experimental two-phase flow pressure drop data.

Experimental Investigation of Thermal Performance of a Unique Heat Pipe Array

A novel heat pipe array with multi-evaporators and a shared horizontal exocentric tube condenser was developed and experimentally investigated on its thermal performance and reliability. This uniquely designed heat pipe array was expected to have extensive applications in the fields of solar heat collecting, multichip cooling, waste heat recovery systems, etc. This unique heat pipe array was fabricated with five evaporator tubes vertically arranged in parallel sharing an exocentric horizontal condenser tube. The test facility had been setup and experiments were conducted to investigate the thermal performance of the proposed heat pipe array systematically. Experimental results showed that the heat pipe array had a good thermal performance and an excellent operating stability. Furthermore, the uniquely designed configuration of an exocentric tube condenser and multi-evaporators not only improved vapor–liquid two-phase flow and phase-change heat transfer in the horizontal direction, but also extended the area of condenser and evaporator. The average thermal resistance decreased and the maximum heat transport capacity increased when increasing the length of evaporators. The experimental results also indicated that a maximum thermal performance of the heat pipe array appeared with an evaporator length of 270 mm at an inclination angle of 60 deg and operating temperature of 80°C. In addition, the minimum average thermal resistance and maximum heat transport capacity of this heat pipe array could achieve up to and 1098 W, respectively.

Experimental study of horizontal flattened tubes performance on condensation of R600a vapor

An empirical setup has been established to study heat transfer and pressure drop characteristics during condensation of R600a, a hydrocarbon refrigerant, in a horizontal plain tube and different flattened channels. Round copper tubes of 8.7mm I.D. were deformed into flattened channels with different interior heights of 6.7mm, 5.2mm and 3.1mm as test sections. The test conditions include heat flux of 17kw/m2, mass velocity in the range of 154.8–265.4kg/m2s and vapor quality variation from approximately 10% to 80%. Results indicate that flattening the tubes causes significant enhancement of heat transfer coefficient which is also accompanied by simultaneous augmentation in flow pressure drop. Therefore, the overall performance of the flattened tubes with respect to heat transfer enhancement considering the pressure drop penalty is analyzed. It is concluded that the flattened tube with 5.2mm inner height tube has the best overall performance. Due to the failure of pre-existing correlations for round tube condensation heat transfer, a new correlation is proposed which predicts 90% of the entire data within ±17% error.

Froude number dominates condensation heat transfer of R245fa in tubes: Effect of inclination angles

Condensation heat transfer of R245fa in a tube with the diameter of 14.81mm and length of 1200mm was investigated. The R245fa mass fluxes, inlet vapor mass qualities and inclination angles covered the ranges of 191.3–705.4kg/m2s, 0.191–0.947 and −90° to 90°, respectively. The non-dimensional analysis yielded the importance of inertia force and gravity force to influence condensation heat transfer. Surface tension force played unimportant role. Condensation heat transfer coefficients (h) showed the general increase trend versus inclination angles (θ) and the non-monotonic behavior in the full inclination angle range. The maximum h occurred at θ=30° and −15°. The h values were sensitive to θ near the horizontal positions. The main flow patterns in the condenser tube were stratified-smooth flow, stratified-wavy flow and intermittent flow. For inclined upflow, the liquid layer thickness and interface wave competed with each other to influence heat transfer. An optimal inclination angle existed at which heat transfer coefficients reached maximum. For inclined downflow, condensation heat transfer was balanced by the liquid layer thickness and buoyancy force. The flow was more stable. Heat transfer coefficients were well correlated with the general increase term multiplied by the non-monotonic variation term. The parameters in the correlation depended on the Froude number and vapor mass qualities. The correlation successfully explained the effects of mass fluxes, vapor mass qualities and inclination angles on condensation heat transfer coefficients. Based on the present finding, the condenser is recommended to operate at the inclination angle of −15° or 30°, at which heat transfer coefficients are maximum and pressure drops are minimum. The exactly horizontal flow weakens the condenser performance.