Oil - Water Flows

Two Phase Flow in Heat Pipes and Oil & Gas Pipelines: Similarities & Differences

Omar A. Al-SaifSaudi Aramco

NTNU - Department of Energy and Process Engineering

#1OutlineReview of two phase flow in Oil & Gas SystemHeat Pipes IntroductionHeat Pipes ComponentsHeat Pipes LimitationsHeat Pipes TheoryHeat Pipes TypesHeat Pipes Pressure Drop Heat Pipes Start-upsSimilarities with Oil & Gas PipelinesDifferences with Oil & Gas Pipelines#Review of Two Phase Flow in Oil & Gas SystemFluid is normally multi-component; phase envelopePressure ranges (1 100) barTemperature (0 200) CModelling approach:Fluid flow in porous medium in reservoir steady state or transient, (2-D & 3-D)Steady state modelling in pipeline (1-D)Transient modelling in pipeline (1-D)Slug tracking vs. slug capturingVarious flow regimes with different pipe orientationPipe diameters

#Heat Pipes HistoryGaugler in 1944 at General Motors patented the conceptSerious development at NASA Los Alamos Lab in 1964 by Grover & co-workersZero-gravity heat transfer was the main motivationNowadays;Spacecraft & SatellitesElectronics CPUsSolar PanelsCell phone industryIndustrial heat exchangersPipeline Industry: Trans-Alaska oil pipeline, used heat pipe technology. Heat pipes are used in pipeline supports in order to prevent melting of the permafrost, McDonnell Douglas produced 12,000 heat pipes per month

#Heat Pipes IntroductionCapillary-driven two phase heat transfer device, which transfers heat from a heat source to a heat sinkVery high thermal conductivity super-conductorMakes use of the latent heat of vaporization to release heat energyWork with minimal temperature gradientsThree basic components:ContainerWorking fluidCapillary structure Wick

#Heat Pipes IntroductionHeat Pipe Cycle:Heat is absorbed in the evaporator sectionFluid boils to vapor phase & travels to condenser sectionHeat is released at the condenser sectionFluid vapor condenses to liquid phase & flows back to the evaporator through the wick by capillary force

(From Chi, S.W., Heat Pipe Theory and Practice, McGraw-Hill, New York, 1976.)#Capillary Force

#Heat Pipes ComponentsContainer: its function is to isolate working fluid from environment It has to maintain pressure and be compatible with fluidCapillary Structure (Wick): its a porous structure used to generate capillary forcesIts made of steel, aluminum, nickel, copper or ceramicsVarious bore sizes and designs can be produced based on applicationThree important properties:Minimum capillary radius: small to give high capillary forcePermeability: measure of wick resistance to axial flowEffective thermal conductivity: minimize temperature drop across wick

#Heat Pipes ComponentsWorking Fluid:Heat Pipe has a wide range of applications, from cryogenic to very high temperaturesWorking fluids range from:Cryogenic (4 200)K: Helium, Argon, O2 Low (200 550)K: Water, AcetoneIntermediate (450 750)K: Mercury, SulfurHigh (750K & above): Sodium, Lithium Fluid Characteristics:Saturation temperature at operating pressure compatible with heat applicationCompatibility with wick and container materialsHigh thermal conductivityHigh latent heatLow viscosityHigh surface tension high capillary forceWettability of wick & wall material High wettability leads to high capillary force

Reay, D., McGlen, R., & Kew, P. (2013).Heat pipes: theory, design and applications. Butterworth-Heinemann.

#Heat Pipes Components

Main Properties of Heat Pipes working fluids:Surface TensionViscosityLatent Heat

Source: Zohuri, B. (2011).Heat pipe design and technology: A practical approach.

#Heat Pipes Limitations-IZohuri, B. (2011).Heat pipe design and technology: A practical approach.

#Heat Pipes Limitations-IICapillary LimitDepends on permeability of wickDepends on properties of fluidEntrainment LimitShear force vs. surface tension force KH instabilitiesIf shear force exceeds resistive liquid surface tension, vapor flow entrains liquid droplets Could lead to dry out of evaporative sectionBoiling LimitAt high temperatures nucleate boiling might occur in wickThis create bubbles in liquid layerLimit liquid flow & reduces conduction heat transfer from pipe walls to the liquid in the wickZohuri, B. (2011).Heat pipe design and technology: A practical approach.

#Heat Pipes Types-IHeat pipes come in various types and configurations:Two-phase Closed ThermosyphonGravity dominated liquid flowCapillary Driven Heat PipesCapillary dominated liquid flowAnnular Heat PipesVapor flow is distributed over three areasMuch larger evaporation & condensate sectionsIsothermal furnace due to its temp. flattening feature Rotating Heat PipesTwo disks joined at the middleVapor space in the middle & heat is applied at tip of disk and extracted near centerCool down metal cutting tools and electric motors

#Heat Pipes Types-IIGas Loaded Heat PipesNon condensable gas is introduced to control condenser sectionCondenser section varies with amount of heat applied at evaporator sectionNearly constant temp. at evaporator sectionFurnaces & electronicsCapillary Pumped Loop Heat PipesHeat is applied at evaporator and vapor is forced to flow in one directionCondenser condenses vapor in the form of slugsSub-cooler further condenses remaining vaporWick pumps liquid back into evaporatorSpacecraft & electronics very high heat rejection rate

#Heat Pipes Types-IIIPulsating Heat Pipes (PHPs)Two types: looped & un-loopedLong, very small capillary tubes, (less than 5mm), bent many turnsNo capillary structures (wick-less)Pressure difference between condenser & evaporator sections circulates the fluidDue to small diameter, surface tension forces more important than gravitational forces applications in micro-gravity environmentDifferent filling (charge) ratios gives different heat transfer characteristicsWorking fluid thermo-physical properties are very important: surface tension, wettability, conductivityRecently: nano-fluids, self-rewitting and self-rewitting-nano fluids are used to improve heat transfer performanceNano-fluids: suspensions of nano-particles in a base fluid. Enhances conductivitySelf-rewitting fluids: dilute aqueous solutions of alcohols with high no. of carbon atoms. Increase surface tension with temp (Inverse Marangoni effect)Self-rewitting-nano fluids: mixture of bothElectronics cooling, solar collector, spacecraft

#Heat Pipes Types-IVMicro & Miniature Heat PipesMicro heat pipes: Hydraulic Dia.: 10 500 mMiniature heat pipes: Hydraulic Dia.: 0.5 5 mmMicro heat pipes has a single non-circular channel for both liquid & vaporLiquid returns to evaporator by capillary forces occurring in sharp corners of channelLimited application in micro electronics applicationsDue to its extremely small dimensions, difficulties in manufacturingCell phone industry

#Heat Pipes Pressure Drop Calculation

#Heat Pipes Liquid Pressure Drop#Heat Pipes Vapor Pressure Drop

#Heat Pipes Pressure DistributionPressure distribution for low vapor rates, left, shows no pressure recovery

Pressure distribution for high vapor rates, right, shows pressure recovery

Pressure recovery due to inertia pressure gain as vapor flow is stopped

#Heat Pipes Start-upUniform Start-upAxial temperature nearly uniform throughout startup period, figure (a)Normally when working fluid in wick liquid and vapor in the inner sectionExample is water heat pipesFrozen Start-upWorking fluid in wick is initially frozen & vapor space in vacuumExperienced in liquid-metal heat pipes, since liquid metals are at solid state at room temperaturesA temperature smeared front is advancing through the heat pipe sections with time until the axial temperature distribution becomes uniform, figure (b)Gas-Loaded Heat Pipes Start-upFrontal start-up character due to presence of non-condensible gas in gas-loaded heat pipesBefore start-up, vapor space is filled with non-condensible gasAs heat is applied at evaporator, vaporized liquid pushes non-condensible gas throughout heat pipe sections, figure (c)

#Heat Pipes - ModellingStrong coupling between heat transfer and fluid mechanicsVarious modelling approaches:Analytical vs. numerical methodsCompressible vapor vs. incompressible vaporOne dimensional vs. two/three dimensional analysisSteady state vs. transient modellingDifferent Heat Pipes requires different modelling approachConventional heat pipesPulsating heat pipesGas-loaded heat pipesMicro heat pipesNew fluids with special propertiesCFD (3D) modelling of heat pipesPossible due to small scaleShould capture more physicsMinimize the use of correlations#SimilaritiesVarious flow regimes available in bothOil & Gas systems has various flow regimes: stratified, slug, annular, bubblyHeat Pipes has few flow regimes: annular, slugFluid flow in porous mediumLiquid flow in downhole reservoirs in Oil & Gas systemsLiquid flow in capillary structure wickTransient modelling is important to capture the dynamicsStartups, shutdowns, flow rate ramp-ups and ramp-downs, slugging phenomena are all dynamic cases that requires transient simulation in oil and gas systemsSimilarly, startups, slugging, heat flux ramp-ups and ramp-downs are all dynamic cases that requires transient simulation in Heat Pipes

#DifferencesFluid CharacteristicsOil & Gas systems has, most of the time, multi-component fluids where the phase envelope plays an important role in defining the system behaviorHeat Pipes has, mostly, single component fluids that has well defined characteristics and as such has less uncertainties modelling them. Exception are nano-fluids and nano-re-witting fluidsStrong coupling between heat and fluid flow equationsIn oil & gas systems, detailed heat transfer analysis can often be neglected in steady state oil & gas systems. Transient cases however, normally requires heat transfer considerations In Heat Pipes, a detailed heat transfer analysis is required as it drives the whole fluid flow mechanismCapillary ForcesCapillary forces are not considered in the oil & gas pipeline simulations. However, they are considered in oil & gas reservoirsCapillary forces are the main driving mechanism for fluid flow in wickScale of diameter and lengthIn oil and gas pipelines, the pipeline diameter ranges from (4 inch) to (60 inch). The pipeline length ranges from few hundred meters to tens of kilometers. In Heat Pipes, the pipe diameter, ranges from (10 m) to (30 mm). The pipeline length is usually in the order of hundreds of millimeters.

#DifferencesPressure RatingIn oil & gas systems, the operating pressure is usually high, (10 bar) to (100 bar)In Heat Pipes, the operating pressure is usually small, (below 1 bar)Temperature RatingIn oil & gas systems, the operating temperature is usually moderate, (0 C) to (200 C)In Heat Pipes, the operating temperature has a very wide range, (-250 C) to (600 C)CFD (3D) ModellingDue to its smaller scale, the possibility to apply full CFD (3D) modelling in Heat Pipes is largerLimited CFD (3D) modelling in oil & gas pipelines due to its size and therefore computational requirements. However, full scale (3D) reservoir simulations have been applied for many years using super computers at many big oil and gas companiesLab ExperimentsDue to its smaller scale, full scale lab experiments are possible, which provide very important data to calibrate the simulation models. The experiments are conducted using the same working fluid, at similar pressure and temperature conditions and with the same pipe sizeIn oil & gas pipelines, full scale experiments are rare to find. This includes both the pressure rating and pipeline diameters. There exists few high pressure labs but with normally relatively smaller diameter than the ones experienced in field data. Accurate field measurements are rare in literature and normally entail high uncertainties#New Application for Heat PipesLarge temperature across the choke, due to Joule-Thompson effectThis may result in being in hydrate formation regionHeat pipes can be installed to recover heat from upstream to downstreamGas will be travelling with high velocities so residence time can be an issueExternal or internal installation of heat pipes can be madeGOSPReservoir300F200F150F70F

Heat Pipe#Thank You#Heat Pipes Detailed Modeling

#Capillary Force

#

#

Thevapor pressure ofwateris the pressure at whichwater vaporisin thermodynamic equilibrium with its condensed state#