Condenser Tubes Research Articles

Cuff leakage caused by automatic cuff pressure monitor and water condensation in the inflation tube of Microcuff® endotracheal tube.

Cuff leakage caused by automatic cuff pressure monitor and water condensation in the inflation tube of Microcuff® endotracheal tube.

Analysis of air-steam condensation tests on a vertical tube of the passive containment cooling system under natural convection

This paper presents an analytical study of the air-steam condensation on a vertical tube of a passive containment cooling system under natural convection conditions. From JNU (Jeju National University) condensation tests, the heat transfer coefficient (HTC) of steam condensation in the presence of air was measured on an outer surface of a cylindrical tube of 40 mm in outer diameter and 1.0 m in length. Using the experimental results from the JNU tests and those obtained in MIT, TIT, and UW-Madison, the validity of empirical correlations to determine condensation HTCs on condenser tubes with different lengths was evaluated. In addition, the mechanistic models using the heat and mass transfer analogy were applied to calculate the condensate rate of air-steam mixture. Combined with a couple of empirical heat transfer expressions for heat and mass transfer analogy, three different formulations to compute the vapor mass flux were applied and their prediction results were compared to the experimental results by JNU tests and MIT tests. The experimentally determined Sherwood number was also presented for both experiments, provided one employs the Collier/Stephan modeling to calculate the mass transfer rate by air-steam condensation.

In-tube thermodynamic analysis on incomplete/complete condensation in finned tube condensers using a conjugate heat transfer model

Considering both the incomplete and complete condensation, a conjugate-model-based approach is developed to characterize the distributed thermodynamic development inside finned tube condensers. Applied to an engineering oval finned tube, the approach verifies the in-tube flow pattern as annular and river in incomplete and complete condensation respectively; furthermore, quantifies and compares the varying characteristics of cooling wall temperature, condensation heat flux, condensation HTC, film thickness, wall shear in the two condensation.In incomplete condensation, the condensation HTC increases slowly with the condensation approaching, unaffected by the steam quality, or film Reynolds number. With regarding complete condensation, an immediate decline of cooling wall temperature, and condensation heat flux and HTC is observed at the end of condensation, one easy-freezing location is marked for the safety operation of condensers, and the backflow of air is found at the vapor outlet. Concerning the phase change section, due to a much lower cooling wall temperature, the complete condensation provides a much greater condensation heat flux, but a nearly equivalent condensation HTC, as comparing to the incomplete mode.The approach is beneficial in designing an enhanced finned tube and operating a field condenser efficiently.

Analysis of Heat Transfer Characteristics of Shell-and-Tube Condenser

In order to enhance operating efficiency of power plants and reduce operating costs of power plants, it is necessary to study heat transfer characteristics of shell-and-tube condensers. A model of shell and tube condenser was built through Simulink software in this paper. The correlations of Tin, Vc, Gs with K of the condenser, heat exchange capacity of condenser, and condensation was established, also the impact of these factors on heat transfer characteristics of condenser was analyzed. The calculation results show that the higher Tin and Gs is, the higher K of the condenser is, and the lower the heat exchange capacity and condensation of the condenser are. With the increase of Vc, and K, the heat exchange capacity and condensing volume of condenser are increased.

Assessment of RELAP5 code model to simulate U-shaped heat pipe performance for heat sink

One of important component in a high temperature gas cooled reactor (HTGR) is reactor cavity cooling system (RCCS). The function of the RCCS is to remove the heat going out from the reactor pressure vessel. On the other hand, the use of passive system is highly considered in the nuclear reactor design, including in the HTGR design. The heat pipe is one of the passive apparatus. This current study deals with the research on the use of heat pipe to the RCCS design. As part of the study, the performance of U-shaped heat pipe will be assessed both through an experiment and numerical simulation methodology. The objective of this study is to assess the validity of the RELAP5 code model to simulate a U-shaped heat pipe performance. A small U-shaped heat pipe with fins in the condenser part is modelled using the RELAP5/SCDAP code. The result of simulation shows that the heat pipe could removed the heat received in the evaporator to the environment through the condenser of that heat pipe. The phenomena of evaporation and condensation are identified during heat removal. However, the steady state condition is not obtained until the end of the calculation. The calculated thermal resistance of the heat pipe is approx. 0.01258 °C/W. It is concluded that the model could simulate reasonably the heat pipe performance. The model needs to be improved, especially for the finned tube condenser.

Improving the performance of the condenser fan in a subway train against the effects of crosswind flow by placing barriers

In this paper, the effect of crosswind flow and barrier placement on the performance of the condenser fan in a subway train is investigated. In addition, the amount of heat transfer on the condenser tubes is also analyzed. At different velocities of the train, variations in the velocity profile and drag force are determined for various geometries including triangular, rectangular, symmetric triangular barriers, and a barrier with parallel lines outside of the fan. Navier–Stokes, energy equations, and k– ω turbulence model have been used for the numerical modeling of the turbulent and incompressible flow. The results show that due to the created vortices behind the triangular and rectangular barriers, a negative velocity on the outflow of the fan is observed. Also, the symmetric triangular barrier minimizes the rotational flow on the top of the fan, and parallel paths have the most impact on the improvement of the fan's performance due to the elimination of all rotating flows. Finally, variations in temperature on the condenser tubes in the presence of barriers that are placed in the middle gap between the holes on the top of the condenser tubes are determined. These barriers move the crosswind flow toward the condenser tubes and decrease the output air temperature of the condenser.

Experimental and theoretical investigation on a radiative flat heat pipe heat exchanger

Abstract Large amounts of heat are rejected by hot steel when it is cooling during the manufacturing process. In an earlier investigation a flat heat pipe (FHP) was constructed and tested in a factory for recovering this heat loss from steel wires by radiation and convection. In this paper, the performance of the FHP was examined by testing it at different configurations. In parallel a theoretical study was conducted. The FHP consisted of 14 stainless steel tubes connected by a bottom collector and a shell and tube condenser top header. The heat transfer area was increased by attaching a stainless steel at the back of the tubes. The effect of the back panel on heat recovery was examined by testing the FHP with the back panel and without it. In addition, the effects of the emissivity and absorptivity of the FHP surface on the thermal performance were investigated by testing the FHP both painted with high temperature black paint and with it unpainted. A theoretical modelling tool based on thermal network modelling was built. The theoretical prediction of the thermal performance of the FHP represented by the amount of heat recovery was compared with the experimental findings. The results of the FHP thermal performance were compared for four cases. The results indicated that heat recovery was greatly increased by painting the surface with thermal black paint. Furthermore, the back panel has a significant influence on the magnitude of heat recovery.

Reconsideration of correlation for condensation outside a vertical tube in the presence of noncondensable gas

A correlation of the condensation heat transfer coefficient (HTC) on the exterior surface of a vertical tube in the presence of noncondensable gas is reconsidered taking into account temperature variation of the tube and the coolant. We derive a heat transfer model of the condenser tube by employing energy conservation and the HTCs of the outside and inside of the tube. For the condensation HTC, two different suction factors are examined. We estimate a correction factor of the condensation HTC by fitting a numerical solution of the model into experimental data. As a result, it is shown that the correction factor depends on the suction parameter. Furthermore, we show that the correction factor inevitably diverges at no subcooling because of the heat and mass transfer analogy (HMTA). To resolve this problem, we propose a simplified expression for the condensation HTC without HMTA. Finally, a double layer model, where the concentration boundary layer around the condensing surface is composed of viscous and diffusive sublayers, is developed as a generalization of the two suction factors. The variation of the correction factor against the suction parameter can be explained by the double layer model.

Condensation heat transfer enhancement using steam-ethanol mixtures on horizontal finned tube

Condensation of steam-ethanol mixtures was investigated experimentally on instrumented, finned copper tube. The tube had length 70 mm, fin root diameter 12.7 mm. Height, thickness and inter-fin space was of rectangular fins was 1.6 mm, 0.5 mm and 0.6 mm. Concentration of ethanol by mass in the boiler when cold prior to the start-up were 0.025, 0.05, 0.1, 0.5 and 1.0%. Experiments were conducted over a range of vapor-to-surface temperature difference at three pressures of 14 kPa, 55 kPa and atmospheric. Maximum upstream vapor velocity on condensing finned test tube at atmospheric pressure and 14 kPa was 7.5 and 15.0 m/s respectively. Heat transfer enhancement as compared to pure steam of around 3 times was obtained over a range of vapor to surface temperature difference. Results have been compared with the available data for pure steam condensation on finned tube and steam-ethanol condensation on the smooth tube under same conditions of pressure, vapor velocity and vapor to surface temperature difference. Photographs showing increase of retention angle due to ethanol are included in the paper.

An Experimental Investigation of Flow Patterns During Condensation of HFC Refrigerants in Horizontal Micro-Fin Tubes

Condensation heat transfer coefficients and flow regimes in two different horizontal micro-fin tubes are examined during the condensation of refrigerants R-134a and R-410A. The present investigation has focused on determination and prediction of condensation heat transfer coefficients and finding the interrelation between heat transfer coefficients and the prevailing flow regimes. During flow visualization, flow regimes have been captured using borosilicate glass tube at inlet and outlet of the test condenser using high speed digital camera. Stratified, stratified wavy, wavy annular, annular, slug and plug flows have been observed at different mass fluxes and vapor qualities of the refrigerants. The observed flow regimes are compared with the existing flow regime maps proposed by Breber et al. [Prediction of horizontal tube side condensation of pure components using flow regime criteria, J. Heat Transfer 102 (1980) 471–476], Tandon et al. [A new flow regime map for condensation inside horizontal tubes, J. Heat Transfer 104 (1982) 763–768.] and Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] flow regime map shows good agreement with experimental data.

CFD multiphase modelling of the acetone condensation and evaporation process in a horizontal circular tube

With increasing demands on energy efficiency, the use of low grade waste heat using vapour absorption refrigeration systems (VARS) are receiving renewed interest. One idea is to use the combination of acetone and zinc bromide as the salt solution, which allows use of temperatures in the order of 10 s of °C above ambient conditions. This work numerically models acetone phase change in the evaporator and condenser in order to indicate how improvements can be made in these components of the system. ANSYS® Fluent finite volume method CFD is used to produce volume of fluid (VOF) and mixture multiphase flow models to investigate the evaporation and the condensation of acetone in a horizontal circular tube. Different velocities and temperatures were taken in each process to explore the effect of these variables in the system. A user defined function (UDF) is used to calculate the volume fraction of the phases. For the evaporation case, the heat transfer coefficient increases with increasing velocity and the temperature difference between the inlet flow and the wall, as expected. The mass transfer rate decreases with increasing the flow rate or decreasing the wall temperature, from 0.045 kg/m3·s at 0.01 m/s to 0.016 kg/m3·s at 0.06 m/s and it drops from 0.044 to 0.023 kg/m3·s by reducing the temperature just from 300 to 298 K. There is a reduction in specific heat transfer to the liquid despite the higher wall heat transfer coefficient. In the condenser, vapour quality decreases along the tube as liquid acetone is created when the flow rate is reduced. Vapour volume fraction at the outlet section drops from 0.74 to 0.168 by increasing the ingoing velocity from 0.01 to 0.06 m/s. Increasing the rate of condensation will increase the liquid supplied to the evaporator, which increases the evaporation rate and then increases the performance of the VARS. This demonstrates the importance of controlling the temperature and the flow rate in the VARS for generating more refrigerant in the vapour generator.

Study of selective condensation for woody biomass pyrolysis oil vapours

The quality of oil produced from the pyrolysis of biomass is a function of many factors, including the type and extent of the condensing system. In this work, we designed a two-stage fractionation system intermediate/fast pyrolysis in a 2–4 kg/h auger reactor to determine the impact of removal of water and low molecular weight acidic compounds on the quality of the oil and the nature of the fractions recovered. The auger reactor two-stage fractionation system consists of two shell and tube condensers in series with an ESP. The first condenser coolant temperature was varied between 50 and 90 °C, while the second condenser temperate was kept constant at 4 °C. GC-FID analysis show that acetic acid which contributes to bio-oil acidity and other light ends such as methanol, glycolaldehyde, and acetol are entirely removed from the first condenser product at a coolant temperature of 90 °C. The product has a low water content (6 wt%), a low acid content (34 mg KOH/g), and a high heating value (approximately 28 MJ/kg). The two-stage fractional system improves bio-oil fuel quality compared to a bio-oil produced from a traditional condenser system. However, the viscosity of the bio-oil approximately doubled as the first condenser coolant temperature increased from 50 to 70 °C and subsequently limits its applications.

Heat transfer characteristics of plug-in oscillating heat pipe with binary-fluid mixtures for electric vehicle battery thermal management

The development of highly-efficient, cost-effective, and reliable cooling schemes of electric vehicle (EV) battery is still a big challenge for massive commercialization of EVs. In this work, a proof-of-concept plug-in oscillating heat pipe (OHP) with flat-plate evaporator and tube condenser has been developed and experimentally tested for the potential applications in EV battery thermal management. Pure water, ethanol, and binary-fluid mixtures of them at different mixing ratios (MRs) ranging from 1:1 to 4:1 were used at volumetric filling ratios (FRs) of 30%, 40% and 50%. Owing to the zeotropic properties in phase transition and the complex molecular interactions between the ethanol component and water component, the OHP charged with ethanol-water mixtures exhibited better start-up and heat transfer performance. The average battery pack temperature could be controlled below 46.5 °C under the power input of 56 W. Besides, well-satisfied temperature uniformity was achieved on the battery module and the maximum temperature differences were mostly in the range of 1–2 °C. The complementary features for ethanol-water mixture thermo-physical properties and temperature/concentration gradients induced mass transport account for the OHP performance improvement. The novel plug-in OHP associated with desirable heat transfer performance provides a promising candidate for battery thermal management system.

Heat Transfer Analysis of Conventional Round Tube and Microchannel Condensers in Automotive Air Conditioning System

In this paper, an experimental analysis of conventional air-cooled and microchannel condensers in automotive vapor compression refrigeration cycle concerning heat transfer coefficient and energy using R134a as a refrigerant was presented. The performance of two condensers and cycles tested regarding ambient temperature which it was varied from 40oC to 65oC, while the indoor temperature and load have been set to be 23oC and 2200 W respectively. Results showed that the microchannel condenser has 224 % and 77 % higher refrigerant side and air side heat transfer coefficient respectively than the coefficients of the conventional condenser. Thus, the COP, in case of using the microchannel condenser, was found to be 20 % higher than that of the conventional cycle. Also, the microchannel condenser has a 50 % smaller volume than the conventional. Therefore, it provides more space in the car engine container occupied with other components.

A comprehensive understanding of enhanced condensation heat transfer using phase separation concept

A comprehensive analysis of enhanced condensation with phase separation concept is presented, for which mesh-membrane-tube (MMT) is suspended in a tube. A twill Dutch weaved mesh screen and two plain Dutch weaved mesh screens are used to fabricate MMT. Our study reveals that liquid leakage across MMT not only keeps better condensation on condenser wall, but also decreases pressure drop rise penalty. To modulate stratified-flow, the #1 MMT with smallest dp has the largest capillary force to pump liquid towards core region to expose more condenser surface with vapor, where dp is pore diameter. To modulate annular-flow, finest mesh wires of #1 MMT ensure the best wetting to liquid to prevent condenser wall from being impacted by satellite droplets. These mechanisms explain the best performance of #1 MMT, reaching a maximum heat transfer enhancement ratio of 1.82. The three MMTs share a single curve of nozzle discharge coefficient versus Reynolds number. The similar performance of #2 and #3 MMTs is due to identical dp/φ, where φ is mesh open porosity. Fine mesh wires and small mesh pores are suggested to enhance condensation heat transfer. MMT are recommended to be used in condenser tube upstream when vapor mass qualities larger than 0.1.

Performance prediction of finned air-cooled condenser using a conjugate heat-transfer model

Finned air-cooling condensers save a significant amount of water in Rankine cycle power plants; however, their heat-removal capability is difficult to predict due to the condensation in finned tubes resulting from the coupled heat transfer between vapor and cooling air fluid. This study develops a conjugate-model-based approach to characterize the thermal-hydraulic development by the transverse flow of vapor and cooling air in a finned tube, and to quantify effects of varying vapor and cooling air operation on the in-tube condensation and out-tube air convection. The approach proposes all uncoupled conditions of a conjugate model on the heat-exchange interfaces, which guarantees that the temperature and heat flux are equal everywhere on the finned tube. Applied to an engineering finned tube, the model verifies that a high vapor mass flux likely reduces the condensation level, and the effect of non-condensable gases with the inlet mass fraction of 0–5% is negligible to the vapor condensation; an increase of cooling air velocity enhances the performance of both vapor condensation and cooling air convection effectively, and a decrease of atmosphere pressure reduces them obviously. The approach is beneficial in designing an enhanced finned tube and operating a field condenser efficiently.

Performance Evaluation of Wick Cooled Condenser in Vapor Compression Refrigeration System

Presently, the reduction in energy consumed by an air conditioner working on a vapor compression refrigeration cycle is a major issue. Application of evaporative cooling on a small-scale refrigeration and air conditioning system is limited due to its larger size and economy. In the present work, porous wick cloth is used on the condenser tube which is combined with direct evaporative cooling. Evaporation of fluid entrapped in the pore of wick cloth increase the heat transfer rate. The effect of evaporative cooling of the condenser on the performance of the air conditioner is experimentally investigated. The result shows about 32.4% enhancement in COP with a maximum ambient temperature of 35°C and 10-11% reduction in energy consumption and relative humidity about 21-26%. Refrigeration effect increased up to 30.6% with respect to the water cool condenser.

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.

Two phase heat transfer and flow regimes of R-134a and R-410A during condensation in horizontal micro-fin tubes

Two phase heat transfer and flow regimes of R-134a and R-410A during condensation in horizontal micro-fin tubes

Thermo-hydraulic model for steam condensation in a large, inclined, flattened-tube air-cooled condenser

A thermo-hydraulic model for calculating capacity, heat transfer coefficient and void fraction of an inclined air-cooled steam condenser is presented. The condenser tube has an elongated-slot cross-section, with inner dimensions of 214 × 16 mm. The model was developed for a 10.7 m-long tube, and validated by comparison with experiments in a 5.7 m-long tube. The model is for downward inclination angles from 0 to 90°, with co-current vapor and condensate flow. The cooling air is in cross flow.This model is developed based on existing models for inclined, stratified-flow condensation. These have been adapted to the flattened-tube air-cooled condenser geometry and conditions. The model couples both air- and steam-side behavior in order to accurately resolve the variations in heat transfer coefficients, temperatures, and heat flux. On the steam side, the model is for stratified flow, and separates the flow into two sections: a falling film along the wall, and an axially-flowing condensate river along the tube bottom. The axially-flowing condensate river is modeled using open-channel-flow theory. On the air side, heat transfer coefficient is determined from a combination of empirical correlation and CFD.The model and experimental results show agreement within 5% for capacity and 20% for void fraction for all tube inclinations.