Thermo Package

The chemicals package is a required dependency that provides the chemical database and pure component property correlations.

Key Modules

thermo.chemical

Interface for pure component properties including:

• Temperature-dependent viscosity, density, thermal conductivity
• Vapor pressure and phase behavior
• Heat capacity (Cp, Cv)
• Enthalpy and entropy

thermo.mixture

Mixture property calculations:

• Composition-weighted properties
• Mixing rules for EOS
• Partial molar properties
• Excess properties

thermo.stream

Process stream calculations:

• Mass and energy balances
• Flash calculations (VLE)
• Phase fraction determination
• Enthalpy of streams

thermo.eos

Equation of state implementations:

• Peng-Robinson (PR)
• Soave-Redlich-Kwong (SRK)
• Ideal gas law
• Cubic equations of state

Core Capabilities for Pump Engineering

1. Temperature-Dependent Viscosity

Critical for pump performance across operating temperature ranges.

from thermo.chemical import Chemical

# Water viscosity variation with temperature
water = Chemical('water', T=298.15, P=101325)  # 25°C, 1 atm

# At different temperatures
temps = [20, 40, 60, 80, 100]  # °C
for T_c in temps:
    water.T = T_c + 273.15
    print(f"T = {T_c}°C: μ = {water.mu*1000:.4f} cP, ρ = {water.rho:.1f} kg/m³")

# Output demonstrates viscosity decreasing with temperature:
# T = 20°C: μ = 1.0016 cP, ρ = 998.2 kg/m³
# T = 40°C: μ = 0.6529 cP, ρ = 992.2 kg/m³
# T = 60°C: μ = 0.4665 cP, ρ = 983.2 kg/m³

2. Pump Power Correction for Temperature

Account for viscosity and density changes when pumping at different temperatures.

from thermo.chemical import Chemical

def pump_power_correction(fluid_name, T_design, T_actual, Q, H, eta=0.75):
    """
    Calculate pump power at actual temperature vs design temperature.

    Parameters:
    -----------
    fluid_name : str, chemical name
    T_design : float, design temperature (K)
    T_actual : float, actual temperature (K)
    Q : float, flow rate (m³/s)
    H : float, head (m)
    eta : float, pump efficiency

    Returns:
    --------
    Power correction factor and actual power required
    """
    # Properties at design temperature
    fluid_design = Chemical(fluid_name, T=T_design, P=101325)
    rho_design = fluid_design.rho
    mu_design = fluid_design.mu

    # Properties at actual temperature
    fluid_actual = Chemical(fluid_name, T=T_actual, P=101325)
    rho_actual = fluid_actual.rho
    mu_actual = fluid_actual.mu

    # Power calculation: P = ρ*g*Q*H/η
    g = 9.81  # m/s²
    P_design = rho_design * g * Q * H / eta
    P_actual = rho_actual * g * Q * H / eta

    # Viscosity affects efficiency (simplified)
    # Higher viscosity reduces efficiency
    eta_correction = (mu_design / mu_actual) ** 0.1  # Empirical
    eta_actual = eta * eta_correction
    P_actual_corrected = rho_actual * g * Q * H / eta_actual

    return {
        'P_design': P_design / 1000,  # kW
        'P_actual': P_actual / 1000,  # kW
        'P_corrected': P_actual_corrected / 1000,  # kW
        'rho_ratio': rho_actual / rho_design,
        'mu_ratio': mu_actual / mu_design,
        'eta_correction': eta_correction
    }

# Example: Pumping water at elevated temperature
result = pump_power_correction('water', T_design=298.15, T_actual=353.15,
                                Q=0.05, H=50, eta=0.75)

print(f"Design power: {result['P_design']:.2f} kW")
print(f"Actual power (density only): {result['P_actual']:.2f} kW")
print(f"Actual power (with efficiency): {result['P_corrected']:.2f} kW")

3. Mixture Properties

Essential for pumps handling mixed fluids or process streams.

from thermo.mixture import Mixture

# Ethanol-water mixture (common in chemical processing)
mixture = Mixture(['ethanol', 'water'], ws=[0.3, 0.7], T=298.15, P=101325)

print(f"Mixture density: {mixture.rho:.1f} kg/m³")
print(f"Mixture viscosity: {mixture.mu*1000:.3f} cP")
print(f"Mixture heat capacity: {mixture.Cp:.1f} J/kg·K")

# Compare to pure components
from thermo.chemical import Chemical
ethanol = Chemical('ethanol', T=298.15, P=101325)
water = Chemical('water', T=298.15, P=101325)

print(f"\nPure ethanol: ρ = {ethanol.rho:.1f} kg/m³, μ = {ethanol.mu*1000:.3f} cP")
print(f"Pure water: ρ = {water.rho:.1f} kg/m³, μ = {water.mu*1000:.3f} cP")

4. Vapor Pressure and NPSH Calculations

Determine available NPSH and cavitation risk.

from thermo.chemical import Chemical

def calculate_NPSHa(fluid_name, T, P_suction, z_suction, v_suction):
    """
    Calculate Net Positive Suction Head Available.

    Parameters:
    -----------
    fluid_name : str, chemical name
    T : float, fluid temperature (K)
    P_suction : float, suction pressure (Pa absolute)
    z_suction : float, suction elevation relative to pump (m)
    v_suction : float, velocity at suction (m/s)

    Returns:
    --------
    NPSHa in meters
    """
    fluid = Chemical(fluid_name, T=T, P=P_suction)

    rho = fluid.rho  # kg/m³
    Psat = fluid.Psat  # Vapor pressure, Pa

    g = 9.81  # m/s²

    # NPSHa = (P_suction - Psat)/(ρ*g) + v²/(2g) - z_suction
    pressure_head = (P_suction - Psat) / (rho * g)
    velocity_head = v_suction**2 / (2 * g)

    NPSHa = pressure_head + velocity_head - z_suction

    return {
        'NPSHa': NPSHa,
        'P_suction': P_suction / 1000,  # kPa
        'Psat': Psat / 1000,  # kPa
        'rho': rho,
        'margin': (P_suction - Psat) / 1000  # kPa
    }

# Example: Water at 80°C (elevated temperature)
result = calculate_NPSHa('water', T=353.15, P_suction=150000,
                         z_suction=2.0, v_suction=2.5)

print(f"NPSHa = {result['NPSHa']:.2f} m")
print(f"Suction pressure = {result['P_suction']:.1f} kPa")
print(f"Vapor pressure = {result['Psat']:.1f} kPa")
print(f"Pressure margin = {result['margin']:.1f} kPa")

# Warning if NPSHa is low
if result['NPSHa'] < 3.0:
    print("⚠ WARNING: Low NPSHa - high cavitation risk!")

5. Enthalpy Calculations for Pump Staging

Calculate enthalpy rise and temperature increase in multistage pumps.

from thermo.chemical import Chemical

def pump_temperature_rise(fluid_name, T_inlet, P_inlet, P_outlet, eta):
    """
    Calculate temperature rise due to pump inefficiency.

    Energy not converted to useful work appears as heat in the fluid:
    ΔT = (1-η) * ΔP / (ρ * Cp)

    Parameters:
    -----------
    fluid_name : str
    T_inlet : float, inlet temperature (K)
    P_inlet : float, inlet pressure (Pa)
    P_outlet : float, outlet pressure (Pa)
    eta : float, pump efficiency
    """
    fluid = Chemical(fluid_name, T=T_inlet, P=P_inlet)

    rho = fluid.rho  # kg/m³
    Cp = fluid.Cp  # J/kg·K

    delta_P = P_outlet - P_inlet  # Pa

    # Temperature rise from inefficiency
    delta_T = (1 - eta) * delta_P / (rho * Cp)

    # Recalculate properties at outlet
    T_outlet = T_inlet + delta_T
    fluid_out = Chemical(fluid_name, T=T_outlet, P=P_outlet)

    # Enthalpy change
    H_inlet = fluid.H  # J/kg
    H_outlet = fluid_out.H  # J/kg
    delta_H = H_outlet - H_inlet

    return {
        'T_inlet': T_inlet - 273.15,  # °C
        'T_outlet': T_outlet - 273.15,  # °C
        'delta_T': delta_T,  # K
        'delta_H': delta_H / 1000,  # kJ/kg
        'delta_P': delta_P / 1e6  # MPa
    }

# Example: Multistage boiler feed pump
result = pump_temperature_rise('water', T_inlet=333.15, P_inlet=500000,
                               P_outlet=15000000, eta=0.82)

print(f"Inlet temperature: {result['T_inlet']:.1f} °C")
print(f"Outlet temperature: {result['T_outlet']:.1f} °C")
print(f"Temperature rise: {result['delta_T']:.2f} K")
print(f"Enthalpy rise: {result['delta_H']:.1f} kJ/kg")
print(f"Pressure rise: {result['delta_P']:.1f} MPa")

6. Phase Equilibrium for Multiphase Pumps

Determine if two-phase flow will occur in pump.

from thermo.chemical import Chemical

def check_phase_state(fluid_name, T, P):
    """
    Check if fluid is single-phase or will flash to vapor.
    """
    fluid = Chemical(fluid_name, T=T, P=P)

    Psat = fluid.Psat  # Vapor pressure
    Tsat = fluid.Tb  # Boiling point at 1 atm

    # Determine phase
    if P > Psat:
        phase = "Liquid (subcooled)"
        margin = (P - Psat) / Psat * 100  # % margin
    elif P < Psat:
        phase = "Two-phase or Vapor (FLASHING!)"
        margin = (Psat - P) / P * 100  # % above operating pressure
    else:
        phase = "Saturated liquid"
        margin = 0

    return {
        'phase': phase,
        'T': T - 273.15,
        'P': P / 1000,  # kPa
        'Psat': Psat / 1000,  # kPa
        'margin': margin
    }

# Example: Check if water will flash at pump suction
temps = [40, 60, 80, 100]  # °C
P_suction = 120000  # Pa (1.2 bar absolute)

for T_c in temps:
    result = check_phase_state('water', T=T_c+273.15, P=P_suction)
    print(f"T = {result['T']:.0f}°C, P = {result['P']:.1f} kPa: {result['phase']}")
    if 'subcooled' in result['phase']:
        print(f"  Margin = {result['margin']:.1f}%")
    print()

# Output will show flashing occurs above ~105°C at 1.2 bar

Equation of State Applications

Peng-Robinson EOS for High-Pressure Pumps

from thermo import ChemicalConstantsPackage, PRMIX, CEOSGas, CEOSLiquid, FlashVL
from thermo.interaction_parameters import IPDB

# High-pressure natural gas mixture
constants = ChemicalConstantsPackage.constants_from_IDs(['methane', 'ethane', 'propane'])

# Operating conditions
T = 298.15  # K
P = 10e6  # Pa (100 bar)
zs = [0.85, 0.10, 0.05]  # Mole fractions

# Peng-Robinson EOS
kijs = IPDB.get_ip_asymmetric_matrix('ChemSep PR', constants.CASs, 'kij')
eos_kwargs = {'Tcs': constants.Tcs, 'Pcs': constants.Pcs, 'omegas': constants.omegas, 'kijs': kijs}

gas = CEOSGas(PRMIX, eos_kwargs, HeatCapacityGases=constants.HeatCapacityGases, T=T, P=P, zs=zs)
liquid = CEOSLiquid(PRMIX, eos_kwargs, HeatCapacityGases=constants.HeatCapacityGases, T=T, P=P, zs=zs)

# Flash calculation
flasher = FlashVL(constants, HeatCapacityGases=constants.HeatCapacityGases, gas=gas, liquids=[liquid])
res = flasher.flash(T=T, P=P, zs=zs)

print(f"Temperature: {T-273.15:.1f} °C")
print(f"Pressure: {P/1e6:.1f} MPa")
print(f"Phase: {res.phase}")
if res.phase == 'L':
    print(f"Liquid density: {res.rho_mass():.1f} kg/m³")
    print(f"Liquid viscosity: {res.mu()*1e6:.2f} μPa·s")

Complete Engineering Examples

See examples.py for verified, production-ready examples including:

1. Temperature-viscosity correction for pump curves
2. NPSH calculations with temperature variation
3. Mixture property calculations for blended fuels
4. Enthalpy rise in multistage pumps
5. Flash calculation for pump discharge conditions
6. Chemical database queries

Pump Application Summary

When to Use Thermo Package

1. Temperature-dependent properties: When fluid temperature varies significantly
2. Mixture handling: Pumping blended fluids or process streams
3. High-temperature applications: Boiler feed pumps, thermal oil pumps
4. Cavitation analysis: Accurate vapor pressure for NPSH calculations
5. Multiphase flow: Determining if flashing will occur
6. Energy calculations: Heat balances for pump temperature rise

Integration with Fluids Package

The thermo package complements fluids for complete pump analysis:

• thermo: Provides temperature-dependent properties (ρ, μ, Psat)
• fluids: Uses these properties for hydraulic calculations (friction, head loss)

from thermo.chemical import Chemical
from fluids.core import Reynolds
from fluids.friction import friction_factor

# Get properties from thermo
water = Chemical('water', T=333.15, P=101325)  # 60°C
rho = water.rho
mu = water.mu

# Use in fluids calculations
Re = Reynolds(V=2.0, D=0.1, rho=rho, mu=mu)
f = friction_factor(Re=Re, eD=0.0001)

print(f"At 60°C: Re = {Re:.0f}, f = {f:.5f}")

Common Chemicals Database

Access to 20,000+ chemicals via CAS number or name:

• Industrial fluids (water, oils, glycols)
• Hydrocarbons (methane, propane, gasoline)
• Refrigerants (R-134a, ammonia)
• Acids and bases (HCl, NaOH)
• Organic solvents (ethanol, acetone)

See reference.md for database details and common pump fluids.

Best Practices

1. Always specify both T and P when creating Chemical objects
2. Check phase state before using liquid properties
3. Validate against known data (steam tables, RefProp, NIST)
4. Use appropriate EOS for high-pressure applications (>20 bar)
5. Consider temperature range of correlations (some limited to <150°C)
6. Cache Chemical objects for performance in iterative calculations

Units

All properties in SI units:

• Temperature: K (convert from °C: T_K = T_C + 273.15)
• Pressure: Pa (1 bar = 100,000 Pa)
• Density: kg/m³
• Viscosity: Pa·s (1 cP = 0.001 Pa·s)
• Enthalpy: J/kg
• Heat capacity: J/kg·K

Troubleshooting

Issue: Property returns None

• Cause: Property not available for this chemical or outside valid range
• Solution: Check Chemical.Tmin, Chemical.Tmax for valid temperature range

Issue: Mixture properties unrealistic

• Cause: Missing interaction parameters or invalid composition
• Solution: Verify sum of mass/mole fractions equals 1.0

Issue: Flash calculation fails

• Cause: Initial guess outside valid region or bad EOS parameters
• Solution: Use simpler EOS (ideal gas) or adjust initial T/P estimate

References

• DIPPR 801 Database (AIChE Design Institute for Physical Properties)
• NIST Chemistry WebBook
• Poling, B.E., Prausnitz, J.M., O'Connell, J.P., "The Properties of Gases and Liquids" (5th Edition)
• Perry's Chemical Engineers' Handbook (9th Edition)
• Peng, D.Y., Robinson, D.B., "A New Two-Constant Equation of State" (1976)

Further Reading

• Official documentation: https://thermo.readthedocs.io/
• Chemicals documentation: https://chemicals.readthedocs.io/
• Source code: https://github.com/CalebBell/thermo
• Tutorial notebooks: https://github.com/CalebBell/thermo/tree/master/docs