Engineering lesson
Explore gas slip and its effect on a thermal pressure profile
Gas slip changes phase occupancy and in-situ density, which can feed back into pressure and thermal behavior. A slip closure is an additional model assumption, not a consequence of equilibrium phase fraction alone.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Couple the local state deliberately
The supported thermal profile updates pressure, temperature and phase behavior along its documented path. Its drift parameters determine how equilibrium phase amounts map into flowing occupancy.
A vapor mole fraction from a flash is not gas holdup. Converting amount to local volume and accounting for relative phase motion are separate steps.
Vary one closure parameter
The recorded study changes drift velocity while retaining feed, inlet state, geometry, heat transfer and the other closure inputs. Endpoint differences therefore describe that model sensitivity.
They do not establish a universal gas-slip correlation or prove a particular flow regime.
Check conservation and solver scope
Read pressure, temperature, phase balances and numerical warnings together. A plausible endpoint can conceal an invalid local state if diagnostics are ignored.
The lesson selects among actual solved cases; it does not interpolate a new coupled profile or claim that the small interaction replaces the workflow.
Explore the example
Original recorded synthetic cases solved with the site's hydrocarbon-slip-thermal-profile engine. The full inputs, outputs and diagnostic rows are in the downloadable JSON. These are discrete solved states; the lesson does not interpolate a new solve.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Prescribed upward gas drift speed (m/s) = 0.2. Outlet absolute pressure (MPa(a)): 4.89813048; Outlet equilibrium temperature (K): 319.951783.
- Outlet absolute pressure (MPa(a))
Worked example
Slip-Aware Hydrocarbon Thermal Pressure Profile Calculator
Fixed controls: Inlet absolute pressure = 5 MPa(a); Inlet equilibrium temperature = 330 K; Pipe inside diameter = 0.1 m; Total mass flow rate = 1 kg/s; Distance along flow = 50 m; Prescribed inside-area heat-transfer coefficient = 100 W/(m2.K); Constant surrounding absolute temperature = 300 K; Prescribed Darcy friction factor = 0.02 dimensionless; Prescribed vertical drift distribution coefficient = 1.2 dimensionless; Methane feed mole fraction = 0.5 dimensionless; Ethane feed mole fraction = 0.15 dimensionless; Propane feed mole fraction = 0.15 dimensionless; n-Butane feed mole fraction = 0.1 dimensionless; n-Pentane feed mole fraction = 0.05 dimensionless; n-Hexane feed mole fraction = 0.05 dimensionless.
Relation and unit basis
G=mass rate/pipe area; wg is local PR equilibrium vapor mass fraction, not molar beta. jg=G*wg/rhog and jl=G*(1-wg)/rhol. alpha=jg/[C0*(jg+jl)+vd], ug=jg/alpha, ul=jl/(1-alpha). HEM fixes C0=1, vd=0. Holdup density=alpha*rhog+(1-alpha)*rhol. Momentum flux M=G*(wg*ug+(1-wg)*ul), total specific static/kinetic energy E=h+0.5*(wg*ug^2+(1-wg)*ul^2).; Implicit trapezoidal balance: d(p+M)/ds=-fD*G^2/(2*D*holdup_density)-holdup_density*g*sin(theta). dE/ds=pi*D*U/mass_rate*(Te-T)-g*sin(theta). Slip profile is vertical upward only. Solve both for p and T using SciPy bounded least squares, then repeat at 10 and 20 steps and audit integrated heat, friction, elevation and flux changes.
Prescribed upward gas drift speed is varied within the supported input range. Six components C1-C6, normal C4-C6, classical PR and all kij=0. No water, isomers, sour gas, heavy fractions, reactions, solids or volume translation. Use the expanded-mixture tools for their explicitly supported alternatives, not by inserting a new species in these fixed feed slots.
1. Define the baseline
Prescribed upward gas drift speed (m/s) = 0.2
Fixed controls: Inlet absolute pressure = 5 MPa(a); Inlet equilibrium temperature = 330 K; Pipe inside diameter = 0.1 m; Total mass flow rate = 1 kg/s; Distance along flow = 50 m; Prescribed inside-area heat-transfer coefficient = 100 W/(m2.K); Constant surrounding absolute temperature = 300 K; Prescribed Darcy friction factor = 0.02 dimensionless; Prescribed vertical drift distribution coefficient = 1.2 dimensionless; Methane feed mole fraction = 0.5 dimensionless; Ethane feed mole fraction = 0.15 dimensionless; Propane feed mole fraction = 0.15 dimensionless; n-Butane feed mole fraction = 0.1 dimensionless; n-Pentane feed mole fraction = 0.05 dimensionless; n-Hexane feed mole fraction = 0.05 dimensionless.
2. Select the relation
G=mass rate/pipe area; wg is local PR equilibrium vapor mass fraction, not molar beta. jg=G*wg/rhog and jl=G*(1-wg)/rhol. alpha=jg/[C0*(jg+jl)+vd], ug=jg/alpha, ul=jl/(1-alpha). HEM fixes C0=1, vd=0. Holdup density=alpha*rhog+(1-alpha)*rhol. Momentum flux M=G*(wg*ug+(1-wg)*ul), total specific static/kinetic energy E=h+0.5*(wg*ug^2+(1-wg)*ul^2).; Implicit trapezoidal balance: d(p+M)/ds=-fD*G^2/(2*D*holdup_density)-holdup_density*g*sin(theta). dE/ds=pi*D*U/mass_rate*(Te-T)-g*sin(theta). Slip profile is vertical upward only. Solve both for p and T using SciPy bounded least squares, then repeat at 10 and 20 steps and audit integrated heat, friction, elevation and flux changes.
Prescribed upward gas drift speed is varied within the supported input range. Six components C1-C6, normal C4-C6, classical PR and all kij=0. No water, isomers, sour gas, heavy fractions, reactions, solids or volume translation. Use the expanded-mixture tools for their explicitly supported alternatives, not by inserting a new species in these fixed feed slots.
3. Substitute the values
v_d = 0.2 m/s; with the fixed controls above, the workflow evaluates Outlet absolute pressure = 4.89813048 MPa(a); Outlet equilibrium temperature = 319.951783 K
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Outlet absolute pressure (MPa(a)) = 4.89813048; Outlet equilibrium temperature (K) = 319.951783
Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation. Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range. Short uniform interval 0.1-500 m, interior 0.101-9.99 MPa(a), 181-449 K, phase speed <=100 m/s and acceleration determinant >=0.5. Vertical upward only, C0=1-1.5 and vd=0-3 m/s supplied by the user; no regime-dependent fit or countercurrent flow. A failed trial or refinement rejects the entire profile. Constant prescribed U, Darcy factor and surroundings; no transient formation/wall thermal history, changing area, fittings, reactions, water, heavy ends, metastable phase delay or two-way reservoir coupling. Slip calculations require vapor/liquid coexistence with mass quality strictly between 0.001 and 0.999 at every trial; constant C0/drift parameters cannot be extended through a disappearing phase. HEM alone permits single-phase continuation. Numerical closure does not establish a field-valid physical correlation.
Result and interpretation
Outlet absolute pressure (MPa(a)) = 4.89813048; Outlet equilibrium temperature (K) = 319.951783
Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation. Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range. Short uniform interval 0.1-500 m, interior 0.101-9.99 MPa(a), 181-449 K, phase speed <=100 m/s and acceleration determinant >=0.5. Vertical upward only, C0=1-1.5 and vd=0-3 m/s supplied by the user; no regime-dependent fit or countercurrent flow. A failed trial or refinement rejects the entire profile. Constant prescribed U, Darcy factor and surroundings; no transient formation/wall thermal history, changing area, fittings, reactions, water, heavy ends, metastable phase delay or two-way reservoir coupling. Slip calculations require vapor/liquid coexistence with mass quality strictly between 0.001 and 0.999 at every trial; constant C0/drift parameters cannot be extended through a disappearing phase. HEM alone permits single-phase continuation. Numerical closure does not establish a field-valid physical correlation.
Only drift velocity changes among recorded coupled-profile cases.
Exact scenario data
Original recorded synthetic cases solved with the site's hydrocarbon-slip-thermal-profile engine. The full inputs, outputs and diagnostic rows are in the downloadable JSON. These are discrete solved states; the lesson does not interpolate a new solve.
| Prescribed upward gas drift speed (m/s) | Outlet absolute pressure (MPa(a)) | Outlet equilibrium temperature (K) |
|---|---|---|
| 0 | 4.917124 | 320.0225 |
| 0.1 | 4.907038 | 319.985 |
| 0.2 | 4.89813 | 319.9518 |
| 0.3 | 4.890204 | 319.9222 |
| 0.4 | 4.883105 | 319.8957 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. Can a flash vapor mole fraction be pasted directly into a holdup field?
Show the worked answer
No. The fraction bases differ, and a slip model can change the occupied volume further.
2. Reproduce the baseline Outlet absolute pressure (MPa(a)) without rounding intermediate values.
Show the worked answer
v_d = 0.2 m/s; with the fixed controls above, the workflow evaluates Outlet absolute pressure = 4.89813048 MPa(a); Outlet equilibrium temperature = 319.951783 K. Outlet absolute pressure (MPa(a)) = 4.89813048. Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation. Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range. Short uniform interval 0.1-500 m, interior 0.101-9.99 MPa(a), 181-449 K, phase speed <=100 m/s and acceleration determinant >=0.5. Vertical upward only, C0=1-1.5 and vd=0-3 m/s supplied by the user; no regime-dependent fit or countercurrent flow. A failed trial or refinement rejects the entire profile. Constant prescribed U, Darcy factor and surroundings; no transient formation/wall thermal history, changing area, fittings, reactions, water, heavy ends, metastable phase delay or two-way reservoir coupling. Slip calculations require vapor/liquid coexistence with mass quality strictly between 0.001 and 0.999 at every trial; constant C0/drift parameters cannot be extended through a disappearing phase. HEM alone permits single-phase continuation. Numerical closure does not establish a field-valid physical correlation.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Prescribed upward gas drift speed (m/s) changes from 0 to 0.4. Other controls remain as stated in the premise. Outlet absolute pressure (MPa(a)) changes from 4.91712361 to 4.88310503.
4. What would be needed to apply this example to a different physical system?
Show the worked answer
Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. Prescribed upward gas drift speed is varied within the supported input range. Six components C1-C6, normal C4-C6, classical PR and all kij=0. No water, isomers, sour gas, heavy fractions, reactions, solids or volume translation. Use the expanded-mixture tools for their explicitly supported alternatives, not by inserting a new species in these fixed feed slots. Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation. Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range. Short uniform interval 0.1-500 m, interior 0.101-9.99 MPa(a), 181-449 K, phase speed <=100 m/s and acceleration determinant >=0.5. Vertical upward only, C0=1-1.5 and vd=0-3 m/s supplied by the user; no regime-dependent fit or countercurrent flow. A failed trial or refinement rejects the entire profile. Constant prescribed U, Darcy factor and surroundings; no transient formation/wall thermal history, changing area, fittings, reactions, water, heavy ends, metastable phase delay or two-way reservoir coupling. Slip calculations require vapor/liquid coexistence with mass quality strictly between 0.001 and 0.999 at every trial; constant C0/drift parameters cannot be extended through a disappearing phase. HEM alone permits single-phase continuation. Numerical closure does not establish a field-valid physical correlation.
Before using the result
- Separate phase amount from occupancy.
- Record drift closure parameters.
- Inspect local and endpoint diagnostics.
Every flash trial must remain at 180-450 K and 0.1-10 MPa absolute, with consistent mole fractions summing to one. Near-critical, vanishing-phase or failed closure states are rejected. Single-phase states are not given an invented vapor quality. Independent engine agreement is not experimental validation. Instantaneous equilibrium and the documented steady balance only. No machinery efficiency, transient behavior, separator sizing, phase residence time, mechanical safety approval or claimed field calibration. A rejected or unbracketed root is not extrapolated into an unsupported range. Short uniform interval 0.1-500 m, interior 0.101-9.99 MPa(a), 181-449 K, phase speed <=100 m/s and acceleration determinant >=0.5. Vertical upward only, C0=1-1.5 and vd=0-3 m/s supplied by the user; no regime-dependent fit or countercurrent flow. A failed trial or refinement rejects the entire profile. Constant prescribed U, Darcy factor and surroundings; no transient formation/wall thermal history, changing area, fittings, reactions, water, heavy ends, metastable phase delay or two-way reservoir coupling. Slip calculations require vapor/liquid coexistence with mass quality strictly between 0.001 and 0.999 at every trial; constant C0/drift parameters cannot be extended through a disappearing phase. HEM alone permits single-phase continuation. Numerical closure does not establish a field-valid physical correlation.
Continue learning
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Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.