Presence Of Non-condensable Gases Research Articles

A droplet model in steam condensation with gas mixtures

A physical and revised mathematical droplet model was proposed for condensation heat transfer process near the cooled solid surface,according to the micro-physical mechanism and thermodynamic characteristics in condensation phase change process. The heat transfer model considering the effect of interfacial effects was used to calculate the temperature of clusters. The mathematical model based on the refined DM homogeneous nucleation model,introducing the wall conditions and making some correlations,was used to calculate the size distribution of clusters,and also describe the effect of the presence of non-condensable gases on the distribution of clusters. The present model explains quantitatively the fact that the presence of small amount of non-condensable gases deteriorate condensation heat transfer performance significantly. The predicted results of the model agree with the experimental results reported in the literature.

Numerical analysis of filmwise condensation in a plate fin-and-tube heat exchanger in presence of non-condensable gas

In the present paper, a numerical model of a fin-and-tube heat exchanger is proposed. The simulation of water vapor condensation in presence of non-condensable gas (air) between two vertical plane plates and in a plate fin-and-tube heat exchanger in a stationary mode is performed using Fluent software. The differential equations that describe the heat and mass transfer were integrated by the finite volume method, in two and three dimensions.

Reflux condensation of flowing vapor and non-condensable gases counter-current to laminar liquid film in a vertical tube

An analytical model using the heat and mass transfer analogy approach was developed for local heat transfer in reflux condensation of flowing vapor and non-condensable gases counter-current to laminar liquid film in a vertical tube. The liquid film model was derived from the two-phase integral momentum equations for counter-current flow. The non-condensable gas effect was accounted for using the diffusion layer theory. The momentum, heat and mass transfer for the liquid and gas phases are coupled together by the shear stress, temperature and gas mass fraction at the two-phase interface, which together with the unknown vapor flow conditions at the outlet of the tube were solved iteratively. The model anticipates that vapor might not necessarily condense completely inside the tube. The root mean square of the theory's relative error is 30% compared with available experimental data. The model provides a mechanism for the safety analysis codes to evaluate reflux condensation in the presence of non-condensable gases.

Turbulent film condensation in the presence of non-condensable gases over a horizontal tube

A numerical model is presented for studying turbulent film condensation in the presence of non-condensable gases over a horizontal tube. Inertia, pressure gradient are included in this analysis, and the influence of turbulence in the proposed two-phase model is considered. The numerical results demonstrate that a very small bulk concentration of non-condensable gas reduces the heat transfer coefficient and film thickness considerably. The local heat flux and film thickness increase as tube surface temperature decreases at any bulk concentration of non-condensable gas. Moreover, inlet velocity increases as film thickness decreases and heat flux increases, a numerical result in agreement with that obtained by Nusselt. Numerical results indicate that average dimensionless heat transfer coefficients are in good agreement with theoretical and experimental data.

Condensation heat transfer characteristic in the presence of noncondensable gas on natural convection at high pressure

The steam–gas pressurizer in integrated small reactors experiences very complicated thermal-hydraulic phenomena. Especially, the condensation heat transfer with noncondensable gas under natural convection is an important factor to evaluate the pressurizer behavior. However, few studies have investigated the condensation in the presence of noncondensable gas at high pressure. In this study, therefore, a theoretical model is proposed to estimate the condensation heat transfer at high pressure using the heat and mass transfer analogy. For the high pressure effect, the steam and nitrogen gas tables are used directly to determine the density of the gas mixture and the heat and mass transfer analogy based on mass approach is applied instead of that based on the ideal gas law. A comparison of the results from the proposed model with experimental data obtained from Seoul National University indicates that the condensation heat transfer coefficients increase with increasing system pressure and with decreasing mass fraction of the nitrogen gas. The proposed model is also compared with other conventional correlations proposed in the literature. The proposed model demonstrates the capability to predict the condensation heat transfer coefficients at high pressure better than any other correlation. Finally, the condensate rate is compared to verify the application of the heat and mass transfer analogy at high pressure. The comparison results confirm that the heat and mass transfer analogy can be applied to evaluate the condensation heat and mass transfer at high pressure.

Effect of electrohydrodynamic (EHD) on condensation of R-134a in presence of non-condensable gas

Effects of applying EHD and non-condensable (NC) gas contents have been experimentally studied on inter-tubular condensation of refrigerant R-134a flow. Applying of electrical field enhances condensing heat transfer coefficient (CHTC), but presence of NC gas in condensing vapour reduces this coefficient. In competition of these two effective parameters on condensation, it can be observed that at higher concentration of NC gas, the effect of electrical field on enhancement of CHTC is greatly reduced. But at lower concentration of NC gas, the effect of electrical field is more considerable, due to thickness of heat transfer boundary layer.

An algorithm for designing a TEMA ‘J’-shell and tube partial condenser

This paper presents an algorithm to design and calculate a rather infrequently used type of heat exchanger, the ‘BJM’ shell and tube partial condenser. The algorithm was developed in a project aimed at the recovery of water and energy in a chemical plant, where gases originated from drying processes contain a high quantity of water vapour with a temperature that allows the heating of some service flows. The heat transfer process implies the condensation of water vapour in the presence of non-condensable gases. Whereas the design procedure of this equipment has not yet become well established, the authors, using previous theoretical grounds, have developed a new algorithm.

Performance of a residential heat pump operating in the cooling mode with single faults imposed

The system behavior of a R410A residential unitary split heat pump operating in the cooling mode was investigated. Seven artificial faults were implemented: compressor/reversing valve leakage, improper outdoor air flow, improper indoor air flow, liquid line restriction, refrigerant undercharge, refrigerant overcharge, and presence of non-condensable gas in the refrigerant. This study monitored eight fault detection features and identified the most sensitive features for each fault. The effect of the various fault levels on energy efficiency ratio (EER) was also estimated. Since the studied system employed a thermostatic expansion valve (TXV) as an expansion device, it could adapt to some faults making the fault less detectable. The distinctiveness of the fault depended on the TXV status (fully open or not).

Theoretical modeling of condensation of steam outside different vertical geometries (tube, flat plates) in the presence of noncondensable gases like air and helium

Condensation of steam coming out from the coolant pipe during a loss of coolant accident (LOCA) plays a key role in removing heat from the primary containment of the advanced nuclear reactor (ANR). The presence of large mass fractions of air ( W air = 0.25–0.9) and a small mass fraction of helium ( W He = 0.017–0.083) reduces the overall heat transfer coefficient (HTC) substantially. The present work emphasizes on the issue that modeling the diffusion of water-vapor through the gas–liquid interface is the key to give good predictions in HTC. In this, condensation conductivity and effective diffusivity plays a key role. Therefore, modifications have been made in the derivation for calculation of condensation conductivity in the case of steam–air mixture and effective diffusivity (in the case of multicomponent mixture). The model validation has been done with the experimental data of Dehbi et al. [Dehbi, A.A., Golay, M.W., Kazimi, M.S., 1991. National Conference of Heat Transfer AIChE Symposium Series, pp. 19–28] and Anderson et al. [Anderson, M.H., Herranz, L.E., Corradini, M.L., 1998. Experimental analysis of heat transfer within the AP600 containment under postulated accident conditions. Nucl. Eng. Des. 185, 153–172] and other analytical models available in the literature [Herranz, L.E., Anderson, M.H., Corradini, M.H., 1998a. The effect of light gases in noncondensable mixtures on condensation heat transfer. Nucl. Eng. Des. 183, 133–150; Herranz, L.E., Anderson, M.H., Corradini, M.L., 1998b. A diffusion layer model for steam condensation within the AP600 containment. Nucl. Eng. Des. 185, 153–172; Peterson, P.F., Schrock, Y.E., Kageyama, T., 1993. Diffusion layer theory for turbulent vapor condensation with noncondensable gases. J. Heat Transf., 115; Dehbi, A.A., Golay, M.W., Kazimi, M.S., 1991. National Conference of Heat Transfer AIChE Symposium Series, pp. 19–28]. Since the validations of the results were found satisfactory, the datasets [Dehbi, A.A., Golay, M.W., Kazimi, M.S., 1991. National Conference of Heat Transfer AIChE Symposium Series, pp. 19–28; Anderson, M.H., Herranz, L.E., Corradini, M.L., 1998. Experimental analysis of heat transfer within the AP600 containment under postulated accident conditions. Nucl. Eng. Des. 185, 153–172] have been compared with a wide range of subcooling and the operating pressures. An extensive comparison has been reported and the results predicted by the present model were found to be satisfactory.

Condensation heat transfer enhancement in the presence of non-condensable gas using the interfacial effect of dropwise condensation

Heat transfer characteristics of dropwise condensation (DWC) were experimentally studied on a vertical plate for a variety of non-condensable gas (NCG) concentration, saturation pressure, and surface sub-cooling degree. As the heat transfer performance was dominated by the vapor diffusion process near the interface of the gas–liquid within the gas phase, the additional thermal resistance of the coating layer may not be strictly limited, a fluorocarbon coating was applied to promote dropwise condensation mode. Compared with the traditional filmwise condensation (FWC), heat and mass transfer with NCG can be enhanced with the dropwise condensation mode. In the present paper, the effect of condensate liquid resistance should not be regarded as the most vital factor to explain the results, but the vapor diffusion process. This is attributed to the liquid–vapor interfacial perturbation motion caused by coalescence and departure of condensate droplets. The results also demonstrated that the feature of droplets departure is the dominant factor for the steam–air condensation heat transfer enhancement.

Analytical thermal hydraulic model for oscillatory condensation of steam in presence of air

An analytical thermal hydraulic model has been developed from fundamental conservation laws, for the process of oscillatory condensation of steam in a pool of water, in presence of non-condensable gas (air). The oscillatory condensation phenomena addressed here is steam chugging, with an emphasis laid on studying the effect of small amount of air present in steam, on the phenomena. The objective of developing the model is to present an approximation of the real phenomena and to obtain an analytical solution. At the outset, a parametric study was conducted by using the developed model to capture and identify the salient features of steam chugging and compare the wave shapes obtained with those available in open literature. Subsequently, the effect of presence of air in steam was studied in detail using the non-condensable gas model. An attempt has been made to show numerically that the presence of a small amount of air in steam would effectively stabilize condensation and prevent inception of chugging. Typical results are presented in this paper to bring out the difference in oscillatory behavior due to presence and absence of non-condensable gas.

A generalized mathematical description for comparative assessment of various horizontal polar tube geometries with regard to external film condensation in presence of non-condensable gases

A generalized mathematical treatment is postulated to investigate the condensation heat transfer performance of horizontal tubes with varying geometries, with the presence of non-condensable gases in the free stream. The governing equations of mass, momentum and energy conservation in the liquid phase are solved semi-analytically, with matching constraints being imposed at the liquid–vapour interface, while the governing equations of energy and species conservation in the vapour phase are solved numerically. An air–water vapour system is considered for demonstrating the mathematical model. Special cases of the model are illustrated with the aid of elliptical and equiangular spiral geometries. It is revealed that the geometrical features of typical polar surfaces can turn out to be favourable in arresting probable drastic reductions in the condensation heat transfer rates that could be otherwise associated with the presence of non-condensable gases in the free stream. The favourable effects induced by polar surfaces become relatively more prominent, as percentage of non-condensable gases in the free stream increases. A geometrical shape function is also ascertained in this regard, which quantifies the extent of this augmentation in the heat transfer performance. In general, it is suggested that polar surfaces with higher values of the shape function over a majority of the azimuthal regime can turn out to be more desired choices for achieving enhanced rates of condensation heat transfer, provided that there are no serious manufacturability constraints.

Experimental Investigation of Enhancement of Dropwise Condensation Heat Transfer of Steam-Air Mixture: Falling Droplet Effect

The presence of noncondensable gas (NCG) in dropwise condensation (DWC) makes a heat transfer mechanism different; in order to get a better understanding of the enhancement mechanism in dropwise condensation with noncondensable gas, the experiments on dropwise condensation, filmwise condensation (FWC), and dropwise-filmwise coexisting condensation (DFC) heat transfer with and without noncondensable gas were performed on specially designed vertical plates. The investigations were concerned with the dynamic behavior of the liquid condensate near the vapor-liquid interface. The experimental results indicated that the heat transfer characteristics of dropwise condensation of pure steam without noncondensable gas were similar to those of the dropwise-filmwise coexisting condensation surface. However, in the presence of noncondensable gas, without the effect of droplets falling onto the vapor-liquid interface, the heat transfer characteristics of the dropwise-filmwise coexisting condensation surface were parallel to those of the filmwise condensation surface, and indeed almost no heat transfer enhancement was found. Compared with the former two condensation modes, the heat-transfer coefficient of dropwise condensation with noncondensable gas was enhanced by 30−80% for the air mole concentration of 0.9% and 4.8%, respectively. The facts cannot be attributed to the effects of reduction of the thermal resistance of the condensate layer and changes in the shape of the condensation surface, which were mainly due to the departure behavior of the condensing droplets, but make a considerable contribution to the overall heat and mass transfer performance.

Improvements in a CFD code for analysis of hydrogen behaviour within containments

The use of CFD codes for the analysis of the hydrogen behaviour within NPP containments during severe accidents has been increasing during last years. In this paper, the adaptation of a commercial multi-purpose code to this kind of problem is explained, i.e. by the implementation of models for several transport and physical phenomena like: steam condensation onto walls in presence of non-condensable gases, heat conduction, fog and rain formation, material properties and criteria for assessing the hydrogen combustion regime expected. The code has been validated against several experiments in order to verify its capacity to simulate the following phenomena: plumes, mixing, stratification and condensation. Moreover, two tests in an integral large enough experimental facility have been simulated, showing that the well-mixed and stratified conditions of the test were reproduced by the code. Finally, an example of a plant application demonstrates the ability of the code in this kind of problems.

Interface conditions governing evaporation of stored liquids in presence of non-condensable gas

Experiments were conducted to determine the variation of interface temperatures during the storage and draining of liquid nitrogen from large containers in the presence of the non-condensable gas. A chilled layer was seen to be formed at the interface in the presence of the non-condensable gas and this layer advanced into the warm liquid at speeds higher than the characteristic speeds associated with thermal diffusion. A theoretical model was developed for the interface temperatures considering the evaporation from the stratified layer in the stored column of liquid. The predictions of the model were shown to compare well with the experimental measurements. A correlation was obtained for the interface temperatures when the proportion of the non-condensable gas was varied.

OS9-8 不凝縮性ガス存在下における凝縮液滴の画像処理計測(OS9 動力エネルギーシステムにおける熱流動,分散と集中の共存)

Dropwise condensation process consist of several discontinuously and irregular process. Therefore, it is difficult for dropwise condensation to analysis of continuously and regular methods as filmwise condensation and another heat transfer phenomenon. It is widely thought that drop growing speed and drop size distribution is paramount importance for construction of dropwise condensation theory. In addition, it is well known that the presence of non-condensable gas is reduced the heat transfer coefficient. However the research of drop growing speed and condensation cycle is not performed a lot. The objective of this study is to measure the drop growing speed and the condensation cycle in the presence of non-condensable gas, and visualization of dropwise condensation process is performed using a digital video camera. In the result of visualization method, it is understandable that the causes with decreases of heat transfer coefficient and amount of heat transfer in the reduction of drop glowing speed.

On various forms of the heat and mass transfer analogy: Discussion and application to condensation experiments

The paper is focused on some of the different forms of the analogy between heat and mass transfer, as they appear in available textbooks and literature on condensation and evaporation. The motivation for the work is the need to clearly point out the assumptions at the basis of each one of them and to quantify the related differences in the application to real experimental data. In fact, the analogy is very often cast in apparently very different forms, whose relation to each other must be carefully understood when a selection among them is performed for a given application. Basing on previous experience in the analysis of heat and mass transfer for passive cooling in light water nuclear reactors, the present work briefly summarises the theoretical bases of the selected forms of the analogy, comparing the related relationships. Then, an experimental activity related to condensation on a flat plate in the presence of noncondensable gases, aimed at providing data for nuclear reactor containment analysis, is presented and the obtained results are processed by the different forms of the analogy to assess the related quantitative differences, thus providing a clearer perspective about the results of their use in engineering applications.

Film condensation in presence of non-condensable gases over horizontal tubes with progressively increasing radius of curvature in the direction of gravity

A theoretical study is executed to investigate the simultaneous influences of reduction in heat transfer rate on account of condensation in presence of non-condensables and its augmentation by the geometry of an horizontal tube surface with increasing radius of curvature in the direction of gravity. The tube surface profile considered for the present work is an equiangular spiral described in a polar form as: R = ae mθ ( a and m being parametric constants). It is observed that a very small bulk concentration (even less than 1%) of the non-condensable gas reduces considerably the heat transfer coefficient. However, there is an enhancement in heat transfer coefficient for condensation over a polar tube surface, as compared to that over a circular tube surface. This enhancement in heat transfer coefficient, with an increase in the value of m (a surface profile parameter), in presence of non-condensables is more than the corresponding proportional enhancement in the same in absence of any non-condensable species.

MODELING AND CONTROL OF AN AUTOREFRIGERATED CSTR POLYMERIZATION REACTOR: IMPACT OF THE NON-CONDENSABLE GASES

The concept of process intensification is applied to a CSTR polymerization reactor, where bulk reactions take place via styrene free-radicals, connected to a semi-flooded horizontal condenser; the aim is to operate the system in a safe and efficient way. The results obtained show that the developed model was able to reproduce the major dynamic characteristics, even with the presence of non-condensable gases. The existence of such gases prevents the reactor from ever reaching a steady-state, as they accumulate in the system, increasing the condenser pressure and the reactor temperature and reducing the contact area and the mass of liquid in the condenser. To overcome this problem, the control strategy of this work proposes a regular purge of the condenser gases in order to avoid a collapse of the system. In this context, different control algorithms were also analyzed and it was concluded that a fast and reliable control of the reactor is only possible when advanced controllers are used.

MODELING AND CONTROL OF AN AUTOREFRIGERATED CSTR POLYMERIZATION REACTOR: IMPACT OF THE NON-CONDENSABLE GASES

The concept of process intensification is applied to a CSTR polymerization reactor, where
bulk reactions take place via styrene free-radicals, connected to a semi-flooded horizontal
condenser; the aim is to operate the system in a safe and efficient way. The results obtained
show that the developed model was able to reproduce the major dynamic characteristics,
even with the presence of non-condensable gases. The existence of such gases prevents
the reactor from ever reaching a steady-state, as they accumulate in the system, increasing
the condenser pressure and the reactor temperature and reducing the contact area and the
mass of liquid in the condenser. To overcome this problem, the control strategy of this
work proposes a regular purge of the condenser gases in order to avoid a collapse of the
system. In this context, different control algorithms were also analyzed and it was concluded
that a fast and reliable control of the reactor is only possible when advanced controllers
are used.