Mixers combine material streams, while splitters divide one stream without changing its thermodynamic state or composition. The public classes are in neqsim.process.equipment.mixer and neqsim.process.equipment.splitter.

Capabilities

Class Use
Mixer Combine two or more streams and calculate an outlet state
StaticMixer Use the alternative static-mixing implementation
Splitter Divide one stream by relative factors or specified outlet flow rates

The stream accessors return StreamInterface. Keep that interface type unless a downstream API specifically requires the concrete Stream class.

Mixer

In its default mode, Mixer applies total mass and component balances and calculates the outlet temperature from an enthalpy balance:

\[\dot{m}_{\mathrm{out}}=\sum_i \dot{m}_i\] \[\dot{H}_{\mathrm{out}}=\sum_i \dot{H}_i\]

For component $j$, the outlet mole fraction is molar-flow weighted:

\[x_{j,\mathrm{out}}= \frac{\sum_i \dot{n}_i x_{j,i}}{\sum_i \dot{n}_i}\]

Here, $\dot{m}$ is mass flow, $\dot{n}$ is molar flow, $\dot{H}$ is enthalpy flow, and $x_j$ is mole fraction.

Complete mixer example

import neqsim.process.equipment.mixer.Mixer;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.equipment.stream.StreamInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemSrkEos richFluid = new SystemSrkEos(300.0, 30.0);
richFluid.addComponent("methane", 0.80);
richFluid.addComponent("ethane", 0.15);
richFluid.addComponent("propane", 0.05);
richFluid.setMixingRule("classic");

Stream richGas = new Stream("rich gas", richFluid);
richGas.setFlowRate(5000.0, "kg/hr");
richGas.run();

SystemSrkEos leanFluid = new SystemSrkEos(310.0, 32.0);
leanFluid.addComponent("methane", 0.95);
leanFluid.addComponent("ethane", 0.04);
leanFluid.addComponent("propane", 0.01);
leanFluid.setMixingRule("classic");

Stream leanGas = new Stream("lean gas", leanFluid);
leanGas.setFlowRate(3000.0, "kg/hr");
leanGas.run();

Mixer mixer = new Mixer("M-100");
mixer.addStream(richGas);
mixer.addStream(leanGas);
mixer.run();

StreamInterface mixedGas = mixer.getOutletStream();
double mixedFlowKgPerHour = mixedGas.getFlowRate("kg/hr");
double mixedTemperatureC = mixedGas.getTemperature("C");

The example produces $8000\ \mathrm{kg/h}$. A focused documentation test verifies the flow, enthalpy closure, component result, and pressure diagnostics.

Pressure behavior and diagnostics

Mixer sets the outlet pressure to the lowest active inlet pressure. It does not provide an independent setOutletPressure specification. If active inlet pressures differ by more than the configured tolerance, the calculation continues at the lowest pressure and records a diagnostic:

mixer.setPressureMismatchTolerance(0.5);
mixer.run();

boolean pressureMismatch = mixer.isPressureMismatch();
double pressureSpreadBar = mixer.getInletPressureSpread();
double minimumInletPressureBara = mixer.getMinInletPressure();
double maximumInletPressureBara = mixer.getMaxInletPressure();

A material mixer is not a hydraulic pressure-drop model. Use an upstream valve, compressor, pump, or pipeline model when pressure equalization or pressure loss must be represented explicitly.

Specified outlet temperature

setOutletTemperature(double) is available and expects kelvin. It changes the calculation from the default enthalpy-balanced mode to a specified-temperature TP flash:

mixer.setOutletTemperature(305.15);
mixer.run();

Use this mode only when the outlet temperature is an imposed boundary condition. For an auditable heating or cooling duty, retain the energy-balanced mixer and add a downstream Heater or Cooler.

Splitter

Splitter clones the inlet thermodynamic state and composition into each outlet and changes only the amount of material. For normalized split factors $f_k$:

\[\dot{m}_k=f_k\dot{m}_{\mathrm{in}}, \qquad \sum_k f_k=1\]

Relative split factors

setSplitFactors treats its values as relative weights. It clamps negative values to zero and normalizes the remaining weights, so at least one value must be positive. The values do not have to sum to one. For example, {7.0, 3.0} becomes {0.7, 0.3}.

The following splitter snippets continue from mixedGas, which is created in the complete mixer example above.

// Continue from the complete mixer example above.
Splitter splitter = new Splitter("SP-100", mixedGas, 2);
splitter.setSplitFactors(new double[] {7.0, 3.0});
splitter.run();

StreamInterface product = splitter.getSplitStream(0);
StreamInterface recycle = splitter.getSplitStream(1);

Specified flows and remainder outlets

Use setFlowRates when one or more outlet flow rates are known. Splitter.REMAINDER (equal to -1.0) marks an outlet that receives material left after the fixed demands:

// Continue from the complete mixer example above.
Splitter distributor = new Splitter("distribution splitter", mixedGas, 2);
distributor.setFlowRates(
    new double[] {2500.0, Splitter.REMAINDER},
    "kg/hr");
distributor.run();

StreamInterface fixedDemand = distributor.getSplitStream(0);
StreamInterface remainingFlow = distributor.getSplitStream(1);

If several outlets use Splitter.REMAINDER, they share the leftover flow equally. If fixed positive demands exceed the inlet flow, NeqSim scales them proportionally to the available flow and assigns zero to remainder outlets. Other negative fixed-flow values are invalid and are clamped to zero.

Static mixer

StaticMixer supports the same multi-inlet connection pattern but uses its own mixing implementation. This snippet reuses richGas and leanGas from the complete mixer example:

// Continue from the complete mixer example above.
StaticMixer staticMixer = new StaticMixer("MX-101");
staticMixer.addStream(richGas);
staticMixer.addStream(leanGas);
staticMixer.run();

StreamInterface staticMixerOutlet = staticMixer.getOutletStream();

StaticMixer does not expose a setPressureDrop method. Add a valve or pipe model when the pressure loss through a physical mixing element is part of the engineering question.

Validation checklist