Condenser Performance Research Articles

On the dynamic modeling and control of the cold-end system in a direct air-cooling generating unit

Direct air-cooling is considered as a promising technique in power generation because of its distinct water-saving advantages, where ambient air is utilized instead of water, to cool down the exhaust steam in the direct air-cooling condenser. However, the relatively poor heat transfer characteristics and thermodynamic properties of air also brings higher backpressure in the direct air-cooling generating unit compared with conventional water-cooling generating unit, as well as the sensitivity of condenser performance to meteorological and ambient conditions. Therefore, the unit backpressure control for the direct air-cooling generating unit has been a challenging task in the recent years. To this end, a control-oriented mechanism dynamic cold-end system model is built for the direct air-cooling generating unit in this paper. The modified moving boundary method is utilized to capture the dynamic process of exhaust steam condensation in the condenser, wherein a time-variant mean void fraction is adopted to enhance model accuracy and robustness. Validation results with operating data have shown the established model can capture the dynamics of direct air-cooling cold-end system with satisfied accuracy. Based on the established model, a model predictive controller with feedforward compensation is proposed to keep unit backpressure steady at the desired set-point while suppressing the time-varying stochastic ambient temperature disturbances by regulating the rotation speed of fan array appropriately. The simulation results have verified the merits and effectiveness of the proposed strategy in achieving both satisfactory backpressure regulation and disturbance rejection performance.

Calculation of Stator Temperature Field in Water Cooled Synchronous Condenser

When the Synchronous condenser adjusts the reactive power of the grid, it will generate a lot of internal losses. Most of these losses will eventually be converted into heat, which will increase the temperature of each part of the motor, which will hinder the safe operation of the Synchronous condenser. At present, the hollow strands in the stator windings of the water-cooled motor have a structure in which the upper and lower sections are equal. In order to reduce the loss of the inner winding of the Synchronous condenser, this paper proposes a new type of winding structure, that is, the structure of the upper section of the hollow strand is larger than the lower section. Taking a 300Mvar large-scale Synchronous condenser as an example, a two-dimensional electromagnetic field finite element simulation model of stator bars under two structures is established, and the resistance increase coefficient of each strand is calculated. Based on this, a large-scale Synchronous condenser is established. a three-dimensional mathematical model of the stator temperature field, The results show that when the hollow strands adopt different structures with upper and lower sections, the temperature rise at the highest point around the hollow strands is reduced.

Water recovery from stripping gas overhead CO2 desorber through air cooling enhanced by transport membrane condensation

At the CO2 regeneration stage in a CO2 chemical absorption process, the stripping gas (i.e., H2O(g)/CO2) leaving the CO2 desorber is cooled down to return the condensate into the desorber. Mostly the circulating cooling-water is used to provide this cooling duty. In this study, the air-cooling technology enhanced by transport membrane condensation was investigated with the aim of reducing the additional cooling-water duty of the chemical absorption process. A tubular hydrophilic ceramic membrane with the mean pore size of the inner separation layer of 4 nm and the length of 400 mm was used for water recovery from H2O(g)/CO2 using N2 as the sweeping gas. Results showed that the cooling performance of the N2-cooling ceramic membrane condenser is about 4–7 times higher than that of the N2-cooling stainless steel condenser with the same dimensions. For the water recovery from H2O(g)/CO2 using the N2-cooling ceramic membrane condenser, increasing the flow rate and pressure of inlet H2O(g)/CO2 can bring about the increase of the water transfer flux. The water transfer flux can increase with the H2O(g) molar fraction in H2O(g)/CO2 as well. Additionally, the increase of N2 flow rate in addition to the reduction of inlet N2 pressure can enhance the water transfer performance. Moreover, the temperatures of H2O(g)/CO2 and N2 have little impacts on the water transfer flux. Finally, an empirical correlation for predicting the water transfer flux as a function of the key operation variables was proposed for the N2-cooling ceramic membrane condenser. Most of the calculated water transfer flux data are in good agreement with the experimental results with an average absolute deviation of 12.5%.

Experimental study of condensation heat transfer on a horizontal aluminum tube with superhydrophobic characteristic

In this study, we conducted a condensation heat transfer experiment for an observation of the condensation heat transfer performance from a superhydrophobic surface fabricated with the Self Assembled Monolayer (SAM) method. For the experiment of condensation heat transfer, we designed an experimental facility that could compare a superhydrophobic tube and a bare tube under the same conditions. The experiment was conducted according to a condition number defined by the coolant Reynolds number and the saturation pressure, and two repeat tests were carried out to analyze the attached condensation. Each condensation phenomenon was observed by a camera, and the droplet detaching frequency was measured in units of [drops/min]. As a result, the dropwise condensation was observed under the condition #1 and #2 in the superhydrophobic tube, and the performance was improved by about 105% over the bare tube with regard to the average overall heat transfer coefficient. Under the conditions #3 and #4, the flooded condensation was observed, and the performance improved by about 16%. By contrast, the attached condensation with a lower detaching frequency than the flooded condensation was observed under the condition #5, and a performance degradation of about 20% was observed. In addition, the condensation performance was analyzed with a ratio of the condensation thermal resistance to a total thermal resistance. As a result of the condensation thermal resistance, the ratio decreased greatly than that of the bare tube when the dropwise condensation occurred, and it was slightly decreased in the condition of the flooded condensation, and it increased in attached condensation. In the repeat tests, after passing the attached condensation, we observed that the performance of the condition #2 was further decreased compared with the situation after passing only the flooded condensation. From the result, attached and flooded condensation seemed to be related to the droplet pinning depth, and we predicted that the droplet pinning depth of attached condensation would be deeper than that of flooded condensation. In conclusion, attached condensation more seriously affects the condensation performance degradation than flooded condensation. Therefore, it is necessary to understand the condition of attached condensation and to prevent attached condensation phenomenon.

Current State and Trends in the Design and Operation of Water-Cooled Condensers of Steam Turbines for Thermal and Nuclear Power Stations (Review)

A review and analysis are presented of the available foreign publications on the modern methods of design, manufacture, design calculation, and operation of water-cooled condensers for large steam turbines used in Russia and abroad. A list of the world’s leading manufacturers of condensers is presented. The adopted alternative arrangements of condensers concerning the turbine centerline and available condenser design styles are examined. The condensers for turbines manufactured by General Electric and the Leningrad Metal Works (LMZ) are compared by their design characteristics and performance indices. The arrangements of tube bundles used in designing and upgrading condensers in Russia and abroad are presented. Information is given on construction materials of condenser tubes and tube sheets as well as on the methods for tube-to-tube sheet attachment. Data on air removal equipment of the condensers are presented. The basic lines of evolution of steam jet ejectors, water-ring pumps, and hybrid air removal systems are considered. The methods of condenser heat-transfer surface cleaning adopted in Russia and abroad are compared. The data on the number of failures and the basic causes of these failure are presented. The procedures for replacement of tubes during repair or modernization of condensers and the symptoms used to determine the necessity of tube replacement are described. Information derived from the authors' investigations and a review of American publications on the potential for heat transfer enhancement in the condensers through the use of shaped tubes is given. The condenser design methods and standards applicable in Russia and abroad are assessed. The lines of improvement in the design of condensers for modern steam turbines of thermal and nuclear power stations are outlined.

Dynamic Behaviors and Protection Strategy of Synchronous Condenser Integrated Power System Under Non-Full Phase Fault Conditions

When a synchronous condenser connected power network encounters a non-full phase fault, the amplitude of the stator current is severely suppressed by the magnetic field generated inside the synchronous condenser, in which the sensitivity of failure protection of circuit breakers are affected resulting in rejection of failure protection. In severe cases, it may endanger the secure and stable operation of the synchronous condenser and the related equipment. In this paper, dynamic behaviors of a synchronous condenser without/with de-excitation action under non-full phase faults are investigated with the following four contributions: 1) A mathematical model under non-full phase fault conditions is established. The theoretical value of fault currents is calculated when the synchronous condenser is without/with de-excitation action. 2) The inferiority/superiority without/with de-excitation action is analyzed. The tendency of dynamic behaviors of variables, including the phase current, negative-sequence, and zero-sequence currents, after de-excitation action, is obtained. A selection criterion of failure protection is proposed according to the dynamic behaviors of negative- and zero-sequence currents. 3) Based on the consistent characteristics of the theoretical calculation, simulations in PSCAD/EMTDC and recorded on-site data from WaveEx, the fact that the simulation model established in PSCAD/EMTDC can provide an effective verification platform for practical applications and data analysis of a synchronous condenser integrated power grid under non-full phase faults is justified. 4) An improved operational threshold of failure protection of circuit breakers is proposed. It can reduce the rejection operation probability of failure protection, which improves the protection sensitivity and enhances the security of the system operation. The simulation results justify the necessity and reliability of the criterion setting proposed for failure protection.

Molybdenum carbide as an efficient and durable catalyst for aqueous Knoevenagel condensation

Molybdenum carbide showed an efficient performance for the Knoevenagel condensation in aqueous media at room temperature, affording the corresponding products in high yields within a short reaction time.

Ligand geometry controlling Zn-MOF partial structures for their catalytic performance in Knoevenagel condensation

A series of novel Zn-MOFs {1Zn: [Zn(NIA)2(3-bpdh)2]; 2Zn: [Zn(NPA)2(4-bpdh)2H2O]; 3Zn: [Zn2(CHDA)4(3-bpd)2]} were constructed by dicarboxylic acid and N,N′-bis(pyridine-yl-ethylidene)hydrazine. Ligand geometry revealed 1D to 3D Zn-MOF crystal topologies, whose combined-mode could be affected by the conditions. All these conditions affected the micro-nano crystal morphologies, namely 1Zn micro-sheets or nanospheres, 2Zn micro-clusters or micro-stick, and 3Zn micro-clusters or hollowspheres that were obtained. The catalysts exhibited 100% selectivity for Knoevenagel condensation reactions, among which the benzaldehyde conversion rate of the 3Zn hollowspheres was the highest, reaching a peak of 90%.

Condensation heat transfer on nickel tubes: The role of atomic layer deposition of nickel oxide

The search for durable surfaces offering sustainable high rates of condensation is very essential for many applications. Most of the metal surfaces are subject to oxidization when exposed to water vapor and air, as is the case during the condensation under saturation conditions. Due to the relative stability of nickel and nickel oxide (NiO) among other common metals, they were considered herein as the substrates for condensing saturated water vapor under the atmospheric conditions. The main objective of this study was to investigate the influence of NiO layer(s) that would be formed during practical applications on the condensation performance. To mimic such oxide formation, different thicknesses of NiO layers were deposited by atomic layer deposition (ALD) method on the surface of smooth nickel tubes. The influence of the oxide layers on the condensation rate was then experimentally characterized, and the droplet dynamic was analyzed. Due to the presence of the large amount of hydrophobic carbon contents in the deposited NiO-ALD layers, especially at the initial stages of the ALD deposition process, a suitable wettability contrast degree with the corresponding deposited hydrophilic NiO was established. Thus bi-philic wettable surfaces were achieved. The degree of contrast in the wettability was varied by the number of the deposited NiO-ALD layers. It was found that samples with a higher carbon to NiO ratio exhibited a higher condensation heat transfer performance, reaching a maximum heat flux and heat transfer coefficient (HTC) of about 3.9 and 4.2 times that of the filmwise condensation (FWC) at subcooling temperatures of 11.0 °C and 3.5 °C, respectively.

Multi‐channel VSI fed large variable speed asynchronous hydro‐condenser: fault analysis, fault diagnosis and fault tolerant control

Multi-level voltage source inverter (VSI) fed doubly fed induction machine (DFIM) has gained prominence in large rated hydro-generating unit (HU) since it provides part load operation with reduced power converter rating and high dynamic stability. Power converters connected in rotor side control real and reactive power of the unit. This study discusses the condenser operation of variable speed HU (250 MW), to be commissioned in Tehri plant (India), with the power flow diagram. Further, it provides dynamic behaviour and survivability status of the DFIM unit during power converter and control circuit faults where power converter redundancy is not available in large rated DFIM unit. Economic analysis of 250 MW HU under power converter and control circuit failures are also investigated. The present work also explores fault tolerant operation of a 250 MW DFIM unit at open switch fault in converters to increase the continuity of the unit operation which provides additional 2% of reactive power support to the grid compared to the DFIM without power converter redundancy operation. Open switch fault is detected through Park's vector phase currents technique and variation in DC link voltage. The computer simulation results are validated in an experiment carried on 2.2 kW DFIM in the laboratory.

Numerical simulation study of novel air-cooled condenser with lateral air supply

Uneven distribution of internal temperature and air flow field are considered to be the essential defects of the Λ-frame air-cooled condenser (ΛACC) in a power plant. Lateral air supplement to a noble, truncated cone-shaped air-cooled condenser (TCACC) is investigated by mean of numerical simulation to solve these problems fundamentally and improve the performance of the air-cooled condenser (ACC) obviously. A Circular ring, installing at the bottom of the heat transfer surface, the structure of which is optimized. According to compare a series of ACCs in different fan inlet air conditions, the TCACC with a lateral air supply (TCACCL) is obtained for heat transfer and safety. The numerical results indicate that the lateral air supplement is an effective way to improve the thermo-flow performance of TCACC.

Effect of inclination on heat transfer and flow regimes in large flattened-tube steam condensers

An experimental study of convective steam condensation inside a large, inclined, flattened tube used in air-cooled condensers for power plants is presented. This is the fourth of a four-part group of papers. The first three parts (Kang et al., 2017; Davies et al., 2017, 2018) published in the same journal present the facility, pressure drop, void fraction, flow regime and heat transfer results, while this study presents the effects of inclination on heat transfer and flow regimes.The condenser is a flattened steel tube with brazed aluminum fins. The full tube has dimensions 10.72 m × 214 mm × 18 mm. The condenser tube is cut in half lengthwise and covered with a polycarbonate window to perform visualization simultaneously with the heat transfer measurements. The steam is condensed at atmospheric pressure, and cooled by air at a uniform velocity profile. The angle of inclination is varied from horizontal (0°) to 75° downward. Condenser performance is also predicted with a model.The majority of the condenser is found to be in the stratified flow regime for all inclinations tested, with only a short annular section at the inlet of the condenser. The tubes inclined greater than 60° are also found to have stratified-wavy flow near the condenser outlet. Overall condenser U is found to increase with increasing downward inclination angle of the condenser, with a maximum increase of approximately 4% at 75° inclination. This improvement is found to be the result of improved drainage and increased void fraction near the condenser outlet. Mean steam-side heat transfer coefficient1HTC – Heat transfer coefficient1 (HTC) is found to remain constant along the tube, and for the entire condenser, with changes in tube inclination angle. Commonly-used inclined condensation HTC correlations are found to underpredict the magnitude of the experimentally-determined steam-side HTC.

Influence of the degree of superheating on the performance of a R134a condenser by means of experimental and numerical studies

In this investigation the influence of the degree of superheating at the inlet of a R134a condenser on its performance is studied. The degree of superheating is controlled by liquid injection from the condenser outlet by a membrane pump. The physical phenomena of influence are a reduction in the mean temperature difference and an increment in the overall heat transfer coefficient. An experimental rig has been built and a number of operating conditions tested as a function of the compressor capacity, evaporator power and the degree of inlet superheating. A numerical model has been developed for the experimental setup, the result of which has been compared with the experimental data. Additionally, the model has been used to understand the evolution of the heat transfer inside the condenser. It has been concluded that the overall condenser efficiency may slightly increase at high evaporator loads and high compressor capacities.

Enhancement of condensation heat transfer in the presence of non-condensable gas using steam jet method

In this study, the use of the steam jet method to destroy the mixed boundary layer of steam and non-condensable gas (NCG) was researched in order to enhance the condensation heat transfer performance. An experimental facility was designed and manufactured in which steam was injected vertically into a single aluminum tube. Both the initial chamber pressure related to the amount of NCG and the bulk chamber pressure after the normal steam injection were tested. The time and enhancement parameters were obtained, including the steam jet continuance time, the maximum heat transfer enhancement ratio, the average heat transfer enhancement ratio and the average overall heat transfer coefficient. The results of the experiment indicate that after the steam jet injection, the maximum heat transfer enhancement ratio increased by at least 137%, and the average heat transfer enhancement ratio increased by at least 118%. In addition, as the NCG mass fraction increased, the values of the continuance time, maximum heat transfer enhancement ratio, average heat transfer enhancement ratio, and average overall heat transfer coefficient improved. Thus, it was confirmed that the steam jet injection method, under the conditions of an accident in which a large amount of NCG flows into the condenser, can effectively improve the condensation performance. Finally, the idea of a bundle-type condenser which is applied by the steam jet method was proposed.

Capillary-Enhanced Filmwise Condensation in Porous Media.

Condensation is prevalent in various industrial and heat/mass transfer applications, and improving condensation heat transfer has a direct effect on process efficiency. Enhancing condensation performance has historically been achieved via the use of low surface energy coatings to promote the efficient dropwise mode over the typical filmwise mode of condensation. However, low surface tension fluids condense on these coatings in the filmwise mode, and low surface energy coatings are generally not robust at thicknesses required to enhance condensation heat transfer. We present a robust and scalable condensation enhancement method where a high heat transfer coefficient is achieved by leveraging capillary forces within a high thermal conductivity porous wick to promote condensate removal. The capillary pressure is supported by a pump to sustain steady condensate removal, and the high thermal conductivity of the wick decreases the overall thermal resistance. This technique has the potential to enhance condensation for a variety of fluids including low surface tension fluids and is capable of operating in both a gravity and a micro- (or zero-) gravity environment. We highlight key characteristics and enhancements achieved through this capillary-enhanced filmwise condensation technique using a porous media flow model. The model results indicate that increased wick thickness and permeability increase the operational envelope and delay the failure that occurs when the condensate floods the wick. However, increasing the permeability is more favorable as both the heat transfer coefficient and the flooding threshold are increased. The working fluid thermophysical properties determine both the degree of enhancement possible and the relative contributions from gravitational and capillary pressure forces when condensation occurs in the presence of gravity. This study provides fundamental insight into an enhanced filmwise condensation technique and an improved framework for modeling porous media flows with mass addition via condensation.

Noncommutative effects of charged black hole on holographic superconductors

In this paper, we analytically investigate the noncommutative effects of a charged black hole on holographic superconductors. The effects of charge of the black hole is investigated in our study. Employing the Sturm-Liouville eigenvalue method, the relation between the critical temperature and charge density is analytically investigated. The condensation operator is then computed. It is observed that condensate gets harder to form for large values of charge of the black hole.

Experimental condensation study of vertical superhydrophobic surfaces assisted by hydrophilic constructal-like patterns

The effect of hydrophilic constructal-like patterns on the condensate mass flow rate production of superhydrophobic vertical test sections is discussed. The surface patterning, which presents a branching topology, is obtained by coating selected areas of the condensation surface with a commercial product. In total, five different designs were tested, three with a branched topology having coated/clear area fractions of approximately 30%, 50% and 70%, in addition to fully clear and fully coated test sections. The condensation performance of each test section was measured in the presence of non-condensable gases inside a climate-controlled chamber, which allowed independent adjustment of its internal temperature and humidity. Condensation measurements indicate that for some cases, averaged improvements ranged between 7.4% and 17.5% when a test section with an area fraction of 70% is compared with clear and fully coated surfaces, respectively, considering the climate-controlled chamber is kept with a relative humidity of nearly 80%. Additionally, a qualitative image-based analysis of the condensation process revealed that the superhydrophobic/hydrophilic interface arguably aids the droplet detachment and could, potentially, guide/direct the draining flow in real systems.

Study on the application of comprehensive energy-saving improvement scheme for condenser in a subcritical 600 MW unit

At present, the condenser pressure of the current generation unit is generally not up to the design value during operation, which affects the thermal cycle economy of the power plant. For a subcritical 600 MW unit, for every 1 kPa reduction in condenser pressure, about 2.5g/(kW·h) reduction in power supply coal consumption. There are many problems in the operation of the original condenser of a 600 MW unit, which leads to the reduction of thermal efficiency of the unit. After the improvement of condenser tube bundle arrangement, the improvement of water chamber structure and the improvement of vacuum system, the operation effect became better obviously The performance test results of condenser after comprehensive energy-saving improvement show that the condenser pressure was reduced by 1.46 kPa under the same boundary condition compared with that before the improvement. According to the vacuum parameter correction curve of the steam turbine of the subcritical 600MW unit, the vacuum is increased by 1.46 kPa, which can reduce the heat consumption rate of the steam turbine by 94.9 kJ/(kW·h) and reduce the power supply coal consumption by 3.65 g/(kW·h).

Thermo-flow performance analysis of split air conditioner under high-speed winds around buildings

ABSTRACT Air-cooled condensers are predominantly used in condensing units of split air conditioning systems. These units are mostly installed on terraces or on outer walls of buildings. In case of tall buildings, the performance of air-cooled condenser is greatly affected by high-speed winds. Present work deals with a numerical study predicting the influence of high-speed winds on the performance of split air conditioning systems whose condensing units are installed on outer walls of buildings using mounting brackets. Simulation tools viz. ANSYS Fluent and VapCyc are employed in this work in order to obtain air flow and thermal characteristics of the condensing unit. Simulation results show that the thermo-flow performance of the split air conditioning system deteriorates significantly with high-speed winds due to an increase in the temperature of air entering the condensing unit and inferior air flow rates in the condensing unit. It is observed that the cooling capacity and coefficient of performance of the air conditioning system are reduced by 11% and 35%, respectively, when wind speed is 12.3 m/s in comparison with the baseline case.

Nonequilibrium condensation process of a holographic p -wave superconductor

We study the nonequilibrium condensation process of a holographic $p$-wave superconductor model, which is described by Einstein-Maxwell theory coupled with the charged complex vector field in asymptotic anti-de Sitter (AdS) spacetime. By solving the gravitational dynamics in the asymptotic AdS spacetime numerically, we obtain the full time dependent solution of the system, and observe a dynamical process from the perturbed Reissner-Nordstr\om-AdS black hole to the anisotropic black hole with vector hair when the initial black hole temperature is smaller than the critical temperature ${T}_{c}$. By holography, this nonlinear dynamical process is then dual to the phase transition process from a normal state to a $p$-wave superconducting state on the boundary theory. We also investigate the time evolution of the superconducting condensate operator and horizon area.