water vapor condensing to liquid water is what type of process?

Condensation Process

Condensation processes must exist an essential phenomenon to enhance the heat transfer by supplying the ambient subcooled liquid to the heated surface.

From: Boiling , 2017

SOLVENT RECYCLING, REMOVAL, AND DEGRADATION

KLAUS-DIRK HENNING , ... K.C. GLATZMAIER , in Handbook of Solvents (Second Edition), Volume 2, 2014

Condensation process

Condensation processes are especially suitable for the cleaning of low flow highly concentrated streams of exhaust gas. ³⁶ The entire waste matter gas stream is cooled beneath the dew point of the vapors contained therein, so that these tin can condense on the surface of the estrus exchanger (partial condensation). Theoretically, the achievable recovery rates depend merely on the initial concentration, the purification temperature and the vapor pressure of the condensables at that temperature. In do however, flow velocities, temperature profiles, the geometry of the equipment, etc. play decisive roles, as effects such as mist formation (aerosols), uneven flow in the condensers and uncontrolled water ice germination interfere with the process of condensation and prevent an equilibrium concentration from being reached at the low temperatures.

The Rekusolv process ³⁷ uses liquid nitrogen to liquefy or freeze vapors contained in the frazzle gas stream. In order to reduce the residual concentrations in the exhaust to the legally required limits, it is often necessary to resort to temperatures below −100°C. The Rekusolv process is quite commonly used in the chemical and pharmaceutical manufacture and at recycling plants for solvent recovery.

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SOLVENT RECYCLING, REMOVAL, AND DEGRADATION

KLAUS-DIRK HENNING , ... K.C. GLATZMAIER , in Handbook of Solvents (3rd Edition), 2019

21.1.5.4 Fridge recycling

Condensation process

Condensation processes are especially suitable for the cleaning of low menstruum highly concentrated streams of exhaust gas. ³⁶ The unabridged waste gas stream is cooled below the dew betoken of the vapors contained therein so that these tin can condense on the surface of the estrus exchanger (partial condensation). Theoretically, the achievable recovery rates depend only on the initial concentration, the purification temperature and the vapor pressure of the condensable at that temperature. In exercise, however, catamenia velocities, temperature profiles, the geometry of the equipment, etc. play decisive roles, equally furnishings such every bit mist germination (aerosols), uneven flow in the condensers and uncontrolled ice formation interfere with the process of condensation and foreclose an equilibrium concentration from being reached at the low temperatures.

The Rekusolv procedure ³⁷ uses liquid nitrogen to liquefy or freeze vapors contained in the frazzle gas stream. In guild to reduce the residual concentrations in the exhaust to the legally required limits, it is oftentimes necessary to resort to temperatures below –100°C. The Rekusolv process is quite usually used in the chemical and pharmaceutical industry and at recycling plants for solvent recovery.

Example of solvent recovery in refrigerator recycling ^{36, 37}

In refrigerator recycling plants R11 or pentane is released from the insulating foam of the refrigerator during shredding. Figure 21.1.22. shows the Rekusolv process as it is used past a refrigerator recycling company. At this plant, effectually 25 refrigerators per hour are recycled thereby generating viii kg/h of polluting gases. The Rekusolv found is capable of condensing almost all of this. The unit is designed to operate for 10 to 12 hours before it has to exist defrosted. The plant is operated during the day and is automatically defrosted at night. The concentration of pollutants in the exhaust gas is reduced from 20 to 40 one thousand/m³ to 0.one g/one thousandⁱⁱⁱ – a recovery rate of more than 99.5%.

Figure 21.1.22. Block diagram of the Rekusolv process.

[After references 36,37]

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Target phenomena in nuclear thermal-hydraulics

N. Aksan , in Thermal-Hydraulics of Water Cooled Nuclear Reactors, 2017

6.3.7 Liquid-vapor mixing with condensation

Directly contact condensation of steam on cold water is a very efficient heat removal mechanism which often takes place at very rapid heat and mass transfer rates. Violent pressure oscillations due to the rapid condensation of steam and the resulting volume reductions accept been observed in several situations when a subcooled liquid is brought into intimate contact with steam. For case, such oscillations can take identify at the ECC injection points. The mixing of liquid and vapor has an effect on the magnitude of the interfacial area and consequently, in conjunction with temperature differences between steam and h2o, information technology determines the condensation efficiency. The mixing is mainly influenced past the void fraction and the mass fluxes of steam and water every bit well every bit steam and water temperatures and other properties.

Condensation processes are relevant to reactor safe in that they

•

reduce the reactor primary side pressure beneath the gear up points for low pressure ECCSs by SG secondary side estrus removal and high force per unit area ECCS injection,

•

reduce steam flows which otherwise reduce water delivery to the core due to CCFL, every bit shown by experiments in UPTF (Damerell and Simons, 1993a,b; Riegel, 1990a,b); yet, a higher steam upflow to the condensation location preventing water commitment has occurred in small-scale facilities like LOBI,

•

reduce pressure in the UP region (by means of hot-leg ECC injection) to back up a faster reflood of the core.

Condensation may exist reduced if noncondensable gases, for example, nitrogen from the accumulators, are present, see Section 6.three.25.

The measurement of condensed steam is mainly performed by measurements of mass flow, water inventories, temperatures, pressures, void fractions (gamma-densitometer, pressure deviation). The interfacial area has not yet been measured successfully.

Computer code models describe mixing and condensation in the mode that interphase heat and mass transfer rates are empirically correlated to the catamenia regimes which are assumed to occur (Forge et al., 1988). An interfacial expanse then needs to be specified, which is difficult for all flows except for well defined, gravity-separated flow weather condition (see Section vi.iii.viii). The flow map is not used explicitly in every calculator code, simply implicitly in the transfer laws. Information technology is not clear, if these catamenia regime maps are calibration contained (Lewis et al., 1989; Yadigaroglu et al., 1990).

Interfacial estrus and mass transfer laws and the resulting condensation models are mainly determined past the interfacial surface area models that the computer codes utilise (Fletcher and Schultz, 1992). In the three-dimensional, highly unsteady 2-stage flow situation, interfacial area and surface temperature can change rapidly. Two fluid codes employ an average interfacial surface area over a called numerical prison cell size which, in practice, is orders of magnitude larger than the feature turbulent mixing dimensions or the molecular transfer dimensions of the catamenia in or perpendicular to the main flow directions (eastward.g., turbulent mixing length or thermal boundary layer thickness). Thus predictions of mixing and condensation are oftentimes dependent on the discretization chosen for a problem (Yadigaroglu et al., 1990; Forge et al., 1988; OECD/NEA, 1989). The stability of the calculations is specially sensitive to pressure spikes from artificial water packing.

Liquid-vapor mixing with condensation is of special interest in the core, downcomer, Upwardly, LP, SG mixture bedchamber (PWR) and in the ECC water injection regions in the hot and common cold legs (PWR) (Hafner and Fischer, 1990). The differences in geometry and boundary conditions cause differences in the flow regimes of the different locations. Spray cooling effects for BWRs are covered by Section half-dozen.3.9.ane.

vi.3.7.1 Liquid-vapor mixing with condensation—core

Liquid-vapor mixing in the core occurs during ECC water injection in order to prevent overheating of the core. Subcooled ECC water may enter the core from the common cold injection location via the downcomer and LP or from the hot-leg injection location via the Upward down to the cadre.

Condensation on subcooled water entering the core removes a part of the estrus in the core. Local reduction of steam catamenia and consequently higher h2o delivery under CCF conditions may occur due to condensation in the cadre. Fast h2o delivery to the cadre is essential for emergency core cooling. The PH is relevant for institute with combined injection, Upwards or upper head injection.

6.3.7.2 Liquid-vapor mixing with condensation—downcomer

Subcooled ECC water is injected into the cold legs or into the downcomer directly depending on reactor pattern. The injected water flows down the downcomer, and, on its fashion downward, the water is warmed up mainly due to steam condensing on the water interface.

Direct contact condensation on the ECC water which is injected into the cold legs or directly into the downcomer has an influence on the CCF in the downcomer region. The upward flowing steam is reduced by the condensation rate. Consequently, the h2o downflow rate toward the cadre can increase. The condensation rate over again is dependent on the down water mass menstruation rate. The principal water downflow was observed in UPTF tests beneath the cold legs which are uttermost from the broken common cold leg. In small-scale-calibration facilities like LOBI, still, an opposite effect was observed. Condensation at the accumulator ECC water injection location caused a high steam upflow in the downcomer which prevented water downflow for some time.

Condensation in the cold legs and in the downcomer is ranked as very important for LBLOCA refill in a 4-loop PWR (Wilson et al., 1990).

Steam condensation causes a warm-up of the subcooled ECC water which may reduce pressurized thermal daze (PTS) in the reactor vessel wall, in the example of high pressure ECC water injection.

6.3.vii.3 Liquid-vapor mixing with condensation—Up

Liquid-vapor mixing with condensation is important in the example of Up and hot-leg ECC injection in PWRs and in BWRs. It is highly dependent on the injection device, for instance, whether injection is via spray systems or nozzles in the UP or hot leg.

Condensation in the Upward may subtract the steam binding outcome substantially and consequently may allow faster reflood of the core.

Direct contact condensation on the ECC water in the UP has an influence on the CCF in the Upward and especially in the upper tie plate (UTP) region at the top of the core. The upward flowing steam is reduced by the condensation rate. Consequently, the h2o downflow rate into the core tin increase. The condensation rate is dependent on down water mass catamenia rate.

half-dozen.iii.7.4 Liquid-vapor mixing with condensation—LP

At the end of the blowdown period of a LBLOCA, the depressurization of the reactor coolant arrangement (RCS) allows the ECCS to inject subcooled water into the system. When this cold water comes into intimate contact with the superheated steam or saturated 2-phase mixture intense condensation occurs with associated force per unit area oscillations. The ECCS water volition penetrate the downcomer as described in Section 6.3.7.ii and reach the LP of the vessel. At this instant the refill menses starts. Refill will be terminated when the LP water level reaches the lesser end of the core. Some water could remain in the LP subsequently the blowdown and the amount of water has a high impact on the fuel cladding temperature. Evaporation and the entrainment of liquid droplets, which to some extent laissez passer through the core, limit the fuel cladding temperature. Too some subcooled water could enter the LP from leakage in the control rod drives (BWR) and contribute to the water contents of the plenum.

When the ECCS h2o reaches the LP, the water will partly be evaporated on the superheated mechanical structures but volition likewise contribute to the condensation of the existing saturated or superheated vapor in a complicated manner. The ECCS water has a strongly three-dimensional random distribution when information technology enters the LP because of the CCF in the downcomer. This will become even more pronounced in the LP because of the complex evaporation on irregular shaped and distributed structures and the simultaneous condensation of existing vapor.

Direct-contact condensation ofttimes takes place at very rapid estrus and mass transfer rates. Thus the condensation of vapor can lead to the occurrence of violent pressure fluctuations.

Liquid-vapor mixing in the LP is an of import PH, as it influences the fuel temperature through related entrainment and vaporization processes. The entrained liquid and vapor will partly laissez passer through the cadre and enhance the core HT, and the final cooling of the core.

6.three.7.5 Liquid-vapor mixing with condensation—SG mixing chambers (inlet/outlet plenum)

The SG mixing chambers connect the RCS pipage with the SG tube bundle. Because of the geometrical shape of these chambers high turbulence and constructive mixing can be expected fifty-fifty at rather low flow conditions. Thus the inlet conditions to the tube bundle can in well-nigh cases be assumed fairly uniform across the tube parcel menstruum area.

However, during the course of SBLOCAs, situations occur when the NC in the loops can no longer be sustained considering of the liquid inventory existence bereft to allow flow over the superlative of the U tubes. Consummate stage separation occurs and at further loss of liquid inventory CCF develops in the hot legs. Thus saturated or slightly superheated vapor flows from the core through the hot leg into the SG mixing chamber and up into the tube parcel. If the secondary side of the SG has a temperature lower than the saturation temperature of the main side, condensation of vapor in the tubes volition be initiated. The condensate will autumn back down the tubes due to gravity and CCF will be prevailing in those parts of the U tubes. The liquid will enter the mixing sleeping accommodation in which stratification occurs. Some condensation of the vapor in the chamber can exist expected. The liquid flows "over the edge" of the SG nozzle into the hot leg and back to the core where information technology evaporates. The process is known every bit reflux condensation and can contribute significantly to the cooling of the core.

The condensation in the SG tubes is not probable to be uniform and is too oscillatory in nature because of the behavior of the condensation procedure. As a outcome the condensate period into the mixing bedroom will be quite nonuniform and this along with the stratification volition create multidimensional effects that will take some influence on, for instance, the reflux condensation process. As well it is quite possible that the weather in each SG tin be different, which may contribute to asymmetric behavior of the loops.

At low catamenia or nigh stagnant weather condition the liquid-vapor mixing in the SG mixing chambers will accept some influence on the SG efficiency as a heat sink. In the reflux condensation mode, the detailed processes in the SG tubes will be governed by for instance the multidimensional conditions in the mixing chamber. However, the verbal details of the conditions in the mixing bedroom seem to be of second order importance in most situations because the big HT area of the SGs (sized to remove total power) is more than adequate for decay heat removal. Exceptions tin occur when HT efficiency in the SGs is greatly reduced by the presence of noncondensables or by dryout of the secondary side.

6.3.7.vi ECC injection in hot and cold leg

Depending on the ratio of steam flow rate in the common cold or hot leg to the condensation potential of the ECC water, a stratified flow pattern or a water plug will be established in these legs. Conditions favoring plugging are most likely to establish in a LBLOCA scenario. While the mechanisms of plug onset are the aforementioned during condensation and adiabatic flows, an boosted mechanism takes place during condensation due to the local decrease in pressure in the pipe equally a result of volume reduction of the steam. Plug formation causes an intermittent water delivery to the downcomer or the Upward, respectively. Plug germination delays the h2o delivery to the core region.

Those water plugs which are formed in the hot legs (in spite of the nozzle momentum toward the UP) enter the SG tubes and steam is generated. The increased pressure in the SG pushes the plug toward the Upwards. A new plug is formed after the old plug is delivered to the Upward such that an intermittent h2o delivery to the UP, and later on into the core, occurs.

The temperature of the plug end faces in the cold legs increases up to saturation temperature due to steam condensation. Consequently, the condensation decreases and the plug is delivered to the downcomer. A new plug is formed later on delivery of the onetime 1. This procedure causes an intermittent h2o delivery to the downcomer.

ECC h2o delivery from the hot- and cold-leg injection locations toward the core is essential for effective operation of the ECCS. Small-scale delays in ECC water delivery are produced due to plug formation in the legs.

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Humid and condensation

C. Balaji , ... Sateesh Gedupudi , in Rut Transfer Technology, 2021

11.5 Condensation

The condensation process is the opposite of the boiling process and involves the change of a vapor phase to a liquid phase. But as liquid superheat is required to induce the nucleation of bubbling in boiling, vapor subcooling is required to induce the nucleation of droplets in condensation. If the condensate forms a continuous picture show, and then it is called flick-wise condensation (or only, film condensation), which occurs on wetted surfaces. In drop-wise condensation (or simply, driblet condensation), the vapor condenses into minor liquid droplets of dissimilar sizes that coalesce and fall downwards the cooled surface, and it occurs on non-wetted surfaces. Drop condensation, as seen from the to a higher place definition, offers less thermal resistance, and this results in heat transfer coefficients every bit much as 5 to ten times the values in motion-picture show condensation. Though drop condensation would be preferred to film condensation, it is difficult to achieve or maintain drop condensation. Much of the contempo research focuses on promoting drop condensation using microstructured surfaces, which is beyond the scope of this textbook. Additionally, at that place is a lack of reliable theories of drop condensation.

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Health, Safety and Ecology Issues

M.A. Virji , A.B. Stefaniak , in Comprehensive Materials Processing, 2014

viii.06.three.1 Vapor Condensation

The vapor condensation process consists of two steps: generation of supersaturated vapor of the source material and the subsequent nucleation and growth to form a nanomaterial through rapid cooling. It is a bones process used to industry a wide range of metal and metal oxide particles or quantum dots (0-d structures). A number of variants of this procedure be such equally physical vapor condensation (PVC), inert gas condensation, chemic vapor condensation (CVC), and reactive gas condensation depending on the nucleation process and carrier/reactant gases used (29). The PVC manufacturing procedure starts with the evaporation of a solid precursor cloth or mixture of materials to form a supersaturated vapor in an inert groundwork/carrier gas, resulting in nucleation (conversion of the gaseous cloth into solid particles) and the formation of primary particles (physical method). The gas is and so speedily cooled causing condensation of the gas on the newly generated primary particles (homogeneous nucleation). Particle growth occurs via coalescence (sintering) forming smooth spherical particles, and/or coagulation forming loose agglomerates of variable shapes, depending on the temperature (29). PVC is applied for the synthesis of pure metals, oxides, every bit well equally alloys and composites with command of the evaporation and condensation rates of the precursor cloth to maintain stoichiometry. The CVC process is in many ways similar to the PVC process, merely offers a much wider selection of precursor materials and thus a greater variety of ENMs are produced, peculiarly for low-vapor pressure materials. In the CVC process, nucleation occurs via a series of chemical reactions (chemical supersaturation) such as oxidization, reduction, or pyrolysis, but particle growth processes are similar to PVC (homogeneous) (26,29). Oxygen, carbon monoxide, or methyl hydride may be used as reactive gases to generate metal oxide, carbon-metal compounds (due east.g., tungsten carbide), or composite nanoparticles (due east.g., metallic carbides) (29). Mixtures of organometallic compounds or separately evaporated metals or compounds can exist used to generate multicomponent composites or blend nanoparticles, whose morphology and size are controlled through sintering. Metallic nanoparticles may be stabilized past reaction with dilute oxygen to form a thin oxide trounce over the metallic cadre or with sodium/metal halide reactions to form a common salt-encapsulated metal cadre (to form core–shell structures). Trace contaminants from the chemical reaction may adsorb onto the ENM, and may crave purification. The ENM is harvested from the reactor and this stride may be followed by postprocessing such equally grinding to reduce particle size, separation of textile by particle size, and packaging, which is where worker exposure to ENM is probable to occur (come across Tabular array iii below).

Tabular array three. Vapor phase synthesis methods and their characteristics that may influence worker exposure

Process	ENM	Tasks/activities	Factors and influences	Controls/PPE	References
Vapor condensation
PVC	Metallic	• Operating reactor • Cleaning reactor • Packaging	• #/cmiii increased at reactor commencement-up • #/cm3 decreased as production charge per unit decreased • #/cmiii transiently increased during task • #/cm3 transiently increased during chore	• Non reported • Non reported • not reported	(47)
	Metallic oxide (TiOtwo)	• Operating reactor • Recovering product	• #/cmthree increased at reactor first-upward • #/cm3 increased when reaction temperature increased • #/cmiii increased when powder nerveless	• RPE, smoke hood • RPE, fume hood • RPE, smoke hood	(48)
	Metallic (Ag)	• Operating reactor • Recovering product	• Chiliad cm−3 decreased with distance from torch • #/cm3 increased when system turned off • Thou cm−three increased during transfer to collector	• Negative force per unit area • Automated system
	Carbon (CB)	• Packaging	• #/cmiii increased during bagging • M cm−three increased to a higher place outdoor during bagging	• Non reported • Non reported	(49)
	Carbon (CB)	• Operating reactor • Pelletizing	• M cm−three and #/cm3 of CB did not increment • One thousand cm−3 and #/cmiii of CB did not increment	• Enclosures	(45)
	Metallic (Ag, Mn, Co)	• Cleaning reactor	• 1000 cm−three and #/cmiii increased when LEV off	• RPE, LEV	(50)
	Carbon (CNFs)	• Operating reactor • Drying product	• M cm−iii and #/cm3 increased during task • M cm−three and #/cm3 increased during task	• GEV • GEV	(51)
		• Recovering production	• 1000 cm−3 and #/cm3 increased while dumping in drum	• GEV
	Metallic (Al)	• Cleaning reactor	• M cm−3 and #/cm3 increased while brushing torch • M cm−iii and #/cmiii increased while brushing sleeping accommodation	• Enclosure • Enclosure	(51)
	Carbon (CNFs)	• Drying product • Recovering production • Packaging	• K cm−3 and SA/cm−iii increased if dryer opened • Chiliad cm−3 and #/cm3 increased while dumping in drum • M cm−3 and #/cm3 increased during bagging	• GEV • GEV • GEV	(52)
	Carbon (CNFs)	• Operating reactor	• Yard cm−3 of EC increased during chore • M cm−3 of EC influenced by reactor design • M cm−3 of EC higher than in thermal treatment	• GEV • GEV • GEV	(53)
	Metallic oxide (TiOtwo)	• Operating reactor • Reactor maintenance • Recovering product • Packaging	• #/cmthree and size decreased with precursor feed rate • #/cm3 decreased with altitude from reactor • #/cmiii decreased when smoke hood fan operating • #/cm3 decreased when fume hood door closed • #/cm3 and size lower for furnace reactor than flame • #/cmthree increased during tasks • #/cmthree increased during mechanical recovery • #/cmiii increased as mass handled increased	• Fume hood • Fume hood • Smoke hood • Smoke hood • Fume hood, enclosure • Fume hood • Fume hood	(42)
	Metal oxide (CeO2)	• Operating reactor	• #/cmthree highest during furnace warm up • #/cmthree highest when flame on • M cm−3 and #/cmthree higher within enclosure than out • #/cm3 increased if enclosure door opened	• Enclosure • Enclosure • Enclosure • Enclosure	(54)
Vapor deposition
Thermal-assisted CVD	Carbon (MWCNTs)	• Operating reactor • Weighing product	• M cm−3 below detection limit during task • Thousand cm−three above detection limit during task	• Non reported • Not reported	(55)
	Carbon (MWCNTs)	• Opening reactor • Packaging • Packaging	• #/cm3 increased; attributed to catalyst • #/cmiii increased during treatment of MWCNT • #/cmiii increased during handling of catalyst	• RPE, LEV • RPE, LEV • RPE, LEV	(56)
	Carbon (CNTs)	• Operating reactor • Recovering product	• #/cm3 did non increase during furnace heating • #/cm3 did not increment during CNT growth • #/cm3 did not increment during furnace cool off • #/cm3 did not increment when opening furnace • #/cmthree did not increment when removing substrate • #/cm3 did not increase during recovery of CNT	• No LEV • No LEV • No LEV • No LEV • No LEV • No LEV	(44)
	Carbon (MWCNTs)	• Opening reactor	• #/cm3 increased when exhaust off during job	• LEV	(51)
	Carbon (CNPs)	• Operating reactor • Recovering production	• #/cm3 increased slightly during task • #/cm3 increased significantly during transfer	• Sealed organisation • Sealed organization	(51)
	Carbon (SWCNTs)	• Operating reactor	• #/cm3 increased when run with and without catalyst • #/cm3 decreased when ventilation system on	• Fume hood • Fume hood	(57)
	Carbon (MWCNTs)	• Operating reactor	• #/cm3 slightly higher when run without substrate • #/cmthree increased during production • #/cm3 increased if operated at higher high temperatures • size range narrower when operated at high temperature	• Smoke hood • Fume hood • Fume hood • Fume hood	(57)
	Carbon (DWCNTs,/MWCNTs)	• Operating reactor • Recovering product	• Yard cm−3 of EC increased during task • One thousand cm−three of EC increased during chore	• Enclosure • None	(58)
	Carbon (MWCNTs)	• Operating reactor • Recovering product	• M cm−three of EC increased during task • M cm−iii of EC increased during task	• Enclosure • Enclosure	(58)
Flame synthesis
Aerosol/spray/solid	Metal oxides	• Operating reactor	• #/cm3 increased at reactor start-upwardly • #/cmthree college for 2 flames versus 1 • #/cm3 increased as filter to flame distance increases • #/cmthree increased equally production elapsing increases • #/cm3 increased as forerunner:O2 ratio increases	• RPE, smoke hood • RPE, fume hood • RPE, fume hood • RPE, fume hood • RPE, fume hood	(43)
	Carbon (C60)	• Packaging	• V cm−3 increased during transfer with vacuum	• GEV	(59)
	Metal oxide (TiO2)	• Operating reactor • Opening reactor • Recovering production • Cleaning reactor	• M cm−3 increased during production • #/cm3 increased if system operating • M cm−three increased during transfer • Yard cm−iii attributed to soot increased during task	• Sealed organization • Sealed organization • Sealed organization • Sealed system	(60)
Laser ablation	Carbon (SWCNTs)	• Opening reactor • Recovering production	• #/cmiii did not increase during handling • #/cm3 did non increment during handling	• Not reported • Not reported	(46)
Arc discharge	Carbon (SWCNTs, C60)	• Operating reactor • Cleaning reactor	• #/cm3 inside hood increased during performance • M cm−3 inside hood increased during sweeping	• RPE, fume hood • RPE, smoke hood	(61)

Abbreviations: #/cm³, particle number concentration; Ag, argent; Al, aluminum; C60, fullerenes; CB, carbon blackness; CeO₂, cerium dioxide; CNFs, carbon nanofibers; CNPs, carbon nanopearls; CNTs, carbon nanotubes; Co, cobalt; DWCNTs, double-walled carbon nanotubes; EC, elemental carbon; ENM, engineered nanomaterial; GEV, general exhaust ventilation; LEV, local frazzle ventilation; M cm⁻³, particle mass concentration; Mn, manganese; MWCNTs, multiwalled carbon nanotubes; O_ii, oxygen; PPE, personal protective equipment; RPE, respirator; SA cm⁻³, particle surface expanse concentration; SWCNTs, single-walled carbon nanotubes; TiO_ii, titanium dioxide; V cm^−three, particle book concentration.

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CONDENSERS

R.Westward. Serth , in Process Heat Transfer, 2007

eleven.10.1 The general problem

Analysis of the condensation process for a general multi-component mixture entails a much greater level of complication compared to pure-component condensation. Amidst the factors responsible for the added complexity are the following:

•

As previously noted, multi-component condensation is always non-isothermal, and the condensing range tin can be large (greater than 100°F). Thus, at that place are sensible heat effects in both the vapor and liquid phases. Sensible heat transfer in the vapor phase can have a significant effect on the condensation process due to the depression heat-transfer coefficients that are typical for gases.

•

The compositions of both phases vary from condenser inlet to outlet because the less volatile components condense preferentially. Every bit a result, the physical backdrop of both phases can vary significantly over the length of the condenser.

•

Every bit discussed in the previous section, the condensing bend may be highly nonlinear, invalidating the utilise of the LMTD correction gene for calculating the mean temperature departure.

•

Thermodynamic (equilibrium flash) calculations are required to obtain the condensing curve and decide the phase compositions. Equilibrium ratios (Yard-values) and enthalpies are needed for this purpose, and the mixture may be highly non-ideal.

•

Equilibrium exists at the vapor–liquid interface, not between the bulk phases. Hence, the thermodynamic calculations should be performed at the interfacial temperature, which is unknown.

•

Since the interfacial limerick differs from the bulk phase compositions, there are mass-transfer too as heat-transfer resistances in both the vapor and liquid phases. Therefore, mass-transfer coefficients are needed in addition to rut-transfer coefficients in gild to model the process. Furthermore, the heat and mass-transfer effects are coupled, and the equations describing the transport processes are circuitous. Thus, there are computational difficulties involved, likewise as a lack of information for mass-transfer coefficients.

A rigorous formulation of the general multi-component condensation problem has been presented past Taylor et al. [32]. Due to the inherent complexity of the model, yet, it has non been widely used for equipment blueprint. An gauge method adult past Bell and Ghaly [33] has formed the basis for the condenser algorithms used in virtually commercial software packages. This method is described in the following subsection.

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Gas–Liquid Flows

Guan Heng Yeoh , Jiyuan Tu , in Computational Techniques for Multiphase Flows, 2010

vi.ii.1.ane Inter-Stage Mass Transfer

For vaporization and condensation processes, if the kinetic free energy and viscous piece of work terms (work done at the interface) are neglected, the interfacial mass transfer can be derived through equating equation (2.87) to zero, that is, ζ = 0. The volume-averaged and Favre-averaged quantity $\Gamma {\text{′}}^k$ is and then given past

(6.5) $\Gamma {\text{′}}^k\text{=}\frac{{\displaystyle \sum _{\mathrm{thousand}}\overline{〈q^{\mathrm{grand}}\text{·}\nabla \chi 〉}}}{h_{fk}}\text{=}\frac{\text{net heat transport to interface}}{\text{latent heat of vaporization}}$

Co-ordinate to equation (half-dozen.five), the mass flux due to vaporization or condensation can thus be estimated with the knowledge of the estrus flux on each side of the interface. If the fluid side heat flux to the interface exceeds the vapour side heat flux, vaporization occurs. The contrary is true for condensation. It can also be demonstrated that the fluid side interfacial heat flux tends to dominate the process. To a starting time approximation, the interfacial mass transfer due to vaporization is expressed as

(6.6) $\Gamma {\text{′}}^f\text{=}\frac{\overline{〈q^f\text{·}\nabla \chi 〉}}{h_{fg}}\sim \frac{h_{if}{a}_{if}\text{(}{T}^c\text{-}{T}^{int}\text{)}}{h_{fm}}$

where h_if is the interfacial rut-transfer coefficient of the continuous phase (fluid side), a_if the interfacial area concentration (IAC) (per unit of measurement volume of the mixture), T^c the twice-averaged bulk temperature of the continuous stage and T^int the interfacial temperature (saturation temperature) which is usually taken to exist that in equilibrium with the pressure at the interface.

In equation (6.6), information technology is rather convenient to express the heat-transfer coefficient h_if in terms of a non-dimensional Nusselt number:

(6.7) $Nu\text{=}\frac{h_{if}{\lambda }^c}{D_s}$

where λ^c is the bulk thermal conductivity of the continuous phase and D_s the bubble Sauter bore. The nearly well-tested correlation by Ranz and Marshall (1952), which is based on purlieus-layer theory, may exist employed to ascertain the Nusselt number for a range of bubble Reynolds numbers:

(6.8) $\mathrm{Due\; north}u\text{=}\mathrm{ii}\text{+}\mathrm{0.six}R{e}_b^{0.5}P{r}^{\mathrm{0.iii}}\text{,}0\text{≤}R{e}_b\text{<}200$

From above, the chimera Reynolds number Re_b is evaluated based on the slip velocity betwixt the liquid phase and gas phase and chimera Sauter bore co-ordinate to

(6.nine) $R{e}_b=\frac{{\rho }^c\text{|}{U}^c\text{-}{U}^d\text{|}{D}_s}{{\mu }^c}$

where ρ^c is the density of the continuous phase, U ^c the velocity vector of the continuous phase, U ^d the velocity vector of the disperse phases and μ^c the dynamic viscosity of the continuous phase. The bulk Prandtl number of the continuous stage is defined by

(6.x) $Pr\text{=}\frac{{\mu }^c{C}_p^c}{{\lambda }^c}$

where $C_p^c$ is the bulk specific estrus of constant pressure of the continuous phase. In order to cater for a wider range of bubble Reynolds and Prandtl numbers, the correlations by Hughmark (1967) may be applied instead. They are

(6.11) $Nu\text{=}2\text{+}0.6R{e}_b^{0.5}P{r}^{0.33},0\text{≤}R{e}_b\text{<}776.06,0\text{≤}Pr\text{<}250$

(six.12) $Nu\text{=}2\text{+}0.27R{e}_b^{0.62}P{r}^{0.33},776.06\text{≤}R{\mathrm{eastward}}_b,0\text{≤}Pr\text{<}200$

For some special cases of gas–liquid systems, it may be necessary to prefer other more than sophisticated correlations than those aforementioned.

From Chapter 2, the source of sink term ${\mathrm{Southward}}_{{\mathrm{thou}}^k}^{int}$ in the equation governing the conservation of mass is given by

(6.13) $S_{m^{\mathrm{thou}}}^{int}\text{=}{\displaystyle \sum _{\mathrm{50}\text{=}\mathrm{one}}^{{\mathrm{North}}_p}\text{(}{\dot{g}}_{lk}\text{-}{\dot{m}}_{\mathrm{1000}l}\text{)}}$

On the basis of equation (half dozen.vi), we can thus define ${\dot{m}}_{lk}\text{=}\max \text{(}\text{-}\Gamma {\text{′}}^{\mathrm{50}},0\text{)}$ and ${\dot{m}}_{kl}\text{=}\max \text{(}\Gamma {\text{′}}^{\mathrm{fifty}},0\text{)}$ . For the case where Γ′ ⁵⁰ ≥ 0, that is, a vaporization process, ${\dot{\mathrm{1000}}}_{\mathrm{fifty}\mathrm{grand}}\text{=}0$ and ${\dot{m}}_{k\mathrm{fifty}}\text{=}\Gamma {\text{′}}^l$ whereas for the case where Γ′ ^l ≤ 0, that is, a condensation process, ${\dot{m}}_{lm}\text{=-}\Gamma {\text{′}}^l$ and ${\dot{m}}_{\mathrm{yard}l}\text{=}0$ .

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Numerical study on condensation flow and heat transfer characteristics of hydrocarbon refrigerants in a spiral tube

Weihua Cai , ... Yiqiang Jiang , in Advanced Analytic and Control Techniques for Thermal Systems with Rut Exchangers, 2020

2.iv Adding model of mixture condensation heat transfer

Fig. four shows the condensation process of refrigerant mixture in a tube. Information technology tin be conspicuously seen that, every bit refrigerant mixture condenses, volatile components assemble together near vapor-liquid interface, hindering the condensation of the condensing component, i.east., leading to an additional thermal resistance. Meanwhile, a larger saturation temperature divergence among unlike components causes a larger additional thermal resistance and mixture effect.

Fig. 4. Schematic of condensing process of refrigerant mixture.

The total heat flux through liquid film is expressed by:

(31) $q_{\mathit{tot}}=h_{\mathit{film}}\cdot \left(T_{\mathrm{Southward}}-T_w\right)$

Also, it can be expressed by:

(32) $q_{\mathit{tot}}=h\cdot \left(T_c-T_w\right)$

Heat flux due to oestrus and mass transfer through vapor core can exist calculated as:

(33) $q_{\mathit{core}}=h_{\mathit{cadre}}\cdot \left(T_c-T_S\right)$

where h _film , h _core , and h are liquid flick, vapor core, and mixed heat transfer coefficient, respectively; and T _s , T _c , and T _w are temperature at vapor-liquid interface, vapor core, and wall, respectively.

Combining Eqs. (31)–(33), we easily arrive at:

(34) $\frac{1}{h}=\frac{1}{h_{\mathit{film}}}+\left(\frac{q_{\mathit{core}}}{q_{\mathit{tot}}}\right)\left(\frac{1}{h_{\mathit{cadre}}}\right)$

Co-ordinate to Eq. (34), h is closely related to h _film , h _cadre and q _core /q _tot . h _{moving picture} tin be calculated by a single-component two-phase rut transfer coefficient model.

For h _core and q _core /q _tot , the Argent approach [8,9] has been widely used [v,28–33], where h _core was divers as the smooth gas superficial single-phase heat transfer coefficient h′ _v , and modeled as:

(35) $h_{\mathrm{five}}^{\prime }=0.021\frac{{\lambda }_{\mathrm{five}}}{d}{Re}_v^{0.8}{Pr}_v^{0.43}{\alpha }_v^{-\mathrm{0.nine}}\left(\mathrm{one}+\mathrm{iii.5}\frac{d}{D}\right),{Pr}_v=\frac{{\mu }_5{\mathit{Cp}}_{\mathrm{five}}}{{\lambda }_v},{Re}_{\mathrm{five}}=\frac{\mathit{mxd}}{{\mu }_v}$

The ratio q _core /q _tot can be calculated as:

(36) $Z=\frac{q_{\mathit{cadre}}}{q_{\mathit{tot}}}={\mathit{xCp}}_5{\alpha }_v^{-\mathrm{0.v}}\frac{\mathit{dT}}{\mathit{d\gamma }}$

where dT/dγ is the ratio between temperature and enthalpy and can exist obtained from the temperature-enthalpy bend of refrigerant mixture.

Then:

(37) $h=\frac{h_{\mathit{film}}}{1+h_{\mathit{movie}}\mathrm{\Phi }}$

where:

(38) $\mathrm{\Phi }=\frac{Z}{h_{\mathit{cadre}}}$

where Φ denotes heat and mass transfer resistance in vapor cadre.

Furthermore, considering the two-phase enhancement effect at the interface and mass transfer outcome on vapor-phase heat transfer, Neeraas [v] introduced C _f and θ to correct the calculation of h _core , as follows:

(39) $h_{\mathit{core}}=h_v^{\prime }{C}_f\theta$

where C _f represents two-phase enhancement outcome at the interface, obtained past Cost-Bell'due south method [ten]. θ represents mass transfer effect on vapor-phase heat transfer, calculated by Sardesai'southward correlation [34]. C _f and θ are modeled equally:

(twoscore) $C_f={\left[\mathrm{\Delta }{P}_{f,\mathit{tp}}/\mathrm{\Delta }{P}_{f,v}\right]}^{0.445},\mathrm{\Delta }{P}_{f,v}=\left[\frac{0.3164}{{Re}_{\mathrm{five}}^{0.25}}+0.03{\left(\frac{d}{D}\right)}^{0.5}\right]\frac{{\mathrm{chiliad}}^2{\mathrm{10}}^{\mathrm{two}}}{2{\rho }_{\mathrm{five}}d}$

(41) $\theta =\frac{a}{e^a-1},a=\frac{{\mathit{qCp}}_{\mathrm{five}}}{{\gamma }_{\mathit{lv}}{h}_5^{\prime }{C}_f}$

This method is named the "modified Silverish approach". The process to calculate condensation heat transfer coefficient of mixture is shown every bit follows: (i) because the mixture every bit single-component fluid with the same physical properties averaged, movie heat transfer coefficient (h _picture ) is obtained based on numerical simulations; then (ii) condensation heat transfer coefficient (h) for mixtures is calculated using the "modified Silver approach".

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Chain Polymerization 2

Thomas C. Kendrick , ... James Westward. White , in Comprehensive Polymer Science and Supplements, 1989

25.4.4 The Acidolysis/Condensation Equilibria

The contribution of the condensation process to the kinetics and mechanism of acid polymerization has been determined past studies of the equilibria in cyclic and model linear siloxanes using both CF ₃Then_threeH and CF₃CO_twoH as catalyst. ^68,78,82 Assuming that each ring formed corresponds to the consumption of one monomer unit by acidolysis and neglecting intermolecular condensations, it is estimated that this procedure accounts for ca. x% of the conversion of monomer in the polymerization of a forty% solution of D₃ in dichloromethane. ⁷⁶

The processes depicted in equations (79) through (82), which give rise to silanol and silyl ester functions, are well established and can be readily monitored by ¹⁹F and ¹H NMR spectroscopy. ^68,76,93 GLC techniques ⁸² and IR spectroscopy ⁷⁸ were employed to investigate the homocondensation reaction (80) and to determine the effects of H bonding. The acidolysis of MM was found to be similar to that for cyclosiloxanes but without added complications arising from polymerization of the monomer. With strong protic acids such as CF_threeAnd then₃H the acidolysis step is rate determining and the equilibria favouring the silyl ester are established very chop-chop. However the interaction of siloxanes with the moderately stiff trifluoroacetic acid (TFA) depicted in equations (94) through (97) are more amenable to kinetic analysis.

(94)

(95)

(96)

(97)

The initial rate can exist expressed in terms of the initial concentrations as follows

(98)

The reaction tin can be followed past measuring changes in the acid or ester concentration equally a function of fourth dimension; all the same, this approach gives ascent to some unusual results. Depression apparent orders in monomer (e.k. −1.four for D₃ and null for D₄) and high apparent orders in acid (3.1–3.5) are observed and in common with the polymerization of D₃ by CF_iiiSO_iiiH several other inconsistencies were as well noted. ⁷⁸ For case, the apparent value of the activation energy for acidolysis of the SiO bond is higher for D_iii (56   kJ   mol⁻ⁱ) than for the strainless D_iv (45   kJ   mol⁻¹) and the reactions proceed at similar rates although the solvolytic cleavage of D₃ in alcohol was as much every bit 10^iv times faster. ⁹³ Also the improver of water enhances the rate of conversion to ester whereas proton acceptors such as THF subtract the rate of reaction. Equation (98) fails to account for H-bonding phenomena and the actual concentrations of uncomplexed acid and monomer are considerably less than their initial concentrations.

H bonding and self-clan of TFA with siloxanes and water studied independently past IR spectroscopy and the following equilibria were found to be the most important

(99)

(100)

Values of the initial concentrations of free acid [acid]_f and monomer [monomer]_f were determined experimentally and the kinetics reinterpreted in terms of the expression

(101)

The exponents p and q adamant using equation (101) are now more closely related to the molecularity of the reaction. In the instance of D_three the values of p and q are 3.ane and i.0 respectively, whereas for D₄ they are 3.v and 1.5. Chojnowski and co-workers offer an interpretation based on the number of molecules participating in the transition state. They propose that an H-bonded complex of p molecules of acrid and one or more monomer units, formed by a series of rapid reversible reactions, is capable of ring opening. This complex is also in equilibrium with other non-active H-bonded species and uncomplexed acid co-ordinate to Scheme 5. In the D_three case the active species may exist idea of as a complex of 1 monomer and three acid molecules which can transfer charge hands. The addition of amphiprotic (proton donor or acceptor) species such equally water results in the formation of an even more reactive H-bonded complex, which can take role in extermely fast charge reorganization due to cooperative H bail migration. ⁷⁸ In discussing these systems Sigwalt et al. concur that association phenomena are important and suggest that hydrated acid species containing upwardly to seven molecules of h2o may be responsible for the cleavage of siloxane bonds. Thus water molecules may deed as synergists past increasing the acerbity of the catalyst and the basicity of the siloxane in transient H-bonded polymeric complexes of the type shown in Figure 17.

Scheme 5.

Figure 17. Transient H-bonded polymer complex

The dramatic changes observed on the addition of small quantities of water can now be explained in terms of its upshot on the ease of formation of the H-bonded complex cyclic transition state. With increasing water content a rapid increase in the rate of monomer consumption occurs, which passes through a maximum and ultimately levels off. Rate increases of up to three orders of magnitude were noted for the polymerization of D₃ in the presence of CF₃SO₃H, although the effect is either not observed ⁶⁸ or is less obvious in similar reactions ⁶⁷ involving D₄. These features are also catalyst dependent and are illustrated by a plot of apparent commencement-order charge per unit constant against concentration of added h2o in Figure eighteen. Silanol (as HOMe_twoSiOSiMe₂OH), when added in equivalent amounts, has an identical influence on the kinetics of polymerization of D₃ ⁷⁶ as shown in Figure xix. This supports previous arguments that the dynamic equilibrium between silanol and ester groups in equations (80) through (82) is rapidly established. Nevertheless, neither silanol nor silyl esters are constructive catalysts for the ring opening of siloxanes alone ⁵⁴ and the data in Figures 18 and nineteen advise that the rate extrapolates to nothing for the totally anhydrous system (in do this is never accomplished because siloxane cleavage by acidolysis generates water). Thus as well equally facilitating charge transfer in the H-bonded transition land, water too enhances the rate by increasing the stationary land concentration of free acid. The H-bonded complex is also invoked to explain the negative credible order in monomer observed in the polymerization of anhydrous D_iii because at college levels of monomer the formation of other inactive or less active complexes is encouraged.

Effigy 18. The upshot of h2o on the credible rate of polymerization of D₃ (two   mol   50⁻ⁱ in CH_iiCl₂) by CF_threeSO_threeH at 30   °C (reproduced past permission of Huthig and Wepf Verlag from ref. 76)

Figure 19. The effect of equivalent quantities of water and silanol on the initial rate of polymerization of D₃ (reproduced past permission of Huthig and Wepf Verlag from ref. 76)

Diverse other additives take been evaluated by Sauvet et al. ⁶⁸ and the results may likewise be interpreted in terms of their event on the stationary state concentrations of active species, for example triflic (trifluoromethanesulfonic) anhydride inhibits the polymerization, whereas the silyl ester of CF₃And so_iiiH has an accelerating outcome. Still, in that location are discrepancies, for instance weak acids are said to promote D₃ simply retard D₄ reactions ^58,69,78 and in particular the large furnishings of h2o or silanol are not substantiated by Sauvet's results.

Attempts to chronicle the conclusions drawn from the experiments on the weaker TFA to strong acids such as CF_threeAnd so₃H were fabricated by studying model transesterification equilibrium. ⁸² Equally expected the stronger acids show a higher tendency towards silyl ester formation and their rates of reaction are much higher. The ¹⁹F and ¹H NMR spectra of the CF₃SO₃SiMe_iii/MeCO_iiH organisation for example shows only a single ester species corresponding to the CF_iiiSO₃H ester even at relatively high concentrations of acetic acrid. Additionally, germination of the multi-H-bonded circuitous is favoured with weaker acids and monomers of low basicity merely is non expected to be so meaning in the polymerization with CF₃SO_iiiH. With potent acids and more nucleophillic monomers (due east.g. D₃) protonation followed by reaction of a second siloxane unit, affording a siloxonium agile heart, is more probable to occur. ^72,78 However, despite these differences the overall character of the interdependence of the equilibrium concentrations of reactive species in the two cases has many common features. ⁸²

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Unsaturated Polyester Resins

Johannes Karl Fink , in Reactive Polymers Fundamentals and Applications (Second Edition), 2013

1.ii.4.2 Sequence Distribution of Double Bonds

The polycondensate formed by the melt condensation procedure of maleic anhydride, phthalic anhydride, and 1,two-propylene glycol in the absenteeism of a transesterification catalyst has a non-random structure with a tendency toward blockiness. On the other hand, the distribution of unsaturated units in the unsaturated polyester influences the curing kinetics with the styrene monomer. Segments containing double bonds close together appear to lower the reactivity of the resin due to steric hindrance. This is suggested by the fact that the rate of cure and the terminal caste of conversion increase as the boilerplate sequence length of the maleic units decreases. Due to the influence of the sequence length distribution on the reactivity, the reactivity of unsaturated polyester resins may be tailored by sophisticated condensation methods.

Methods to summate the distributions accept been worked out [46,47]. Monte Carlo methods can be used to investigate the effects of the various rate constants and stoichiometry of the reactants. Besides, structural asymmetry of the diol component and the influence of the dynamics of the ring opening of the anhydride are considered.

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