Liquid Ethylene Density Calculator | DIPPR Correlation

What is the liquid ethylene density calculator?

The liquid ethylene density calculator estimates the density of liquid ethylene (C₂H₄) from its temperature and pressure. It uses a DIPPR correlation, a standard equation used across the chemical engineering industry to predict how liquids behave. The tool works for temperatures from 104 K to 282 K and pressures from 1 bar to 100 bar.

Ethylene is a gas at room temperature. Producers cool it to cryogenic temperatures, below about -104°C (169 K) at atmospheric pressure, to keep it liquid for storage and transport. Liquid ethylene packs far more mass into the same volume than the gas, which is why plants store and ship it as a liquid. Knowing its density at a given temperature and pressure matters for sizing storage tanks, checking pipeline flow, and balancing mass in a plant.

Liquid ethylene density formula

The calculator uses DIPPR Equation 105, a correlation built from experimental measurements of saturated liquid density. It first finds the molar density at the chosen temperature, then converts that to mass density, then adjusts for pressure.

Step 1: Molar density at the reference pressure

$\rho_m = \frac{A}{B^{\,1 + \left(1 - \frac{T}{T_c}\right)^{D}}}$

Step 2: Convert to mass density

$\rho_{ref} = \rho_m \times M$

Step 3: Adjust for pressure

$\rho = \rho_{ref} \times \left[1 + \kappa \left(P - P_{ref}\right)\right]$

Where:

$A$, $B$, $T_c$, and $D$ are fitted constants for ethylene, not physical measurements a user enters. The calculator only asks for temperature and pressure.

Density is more sensitive to temperature than to pressure. Liquids barely compress, so the pressure term only shifts the result by a small percentage even across the calculator's full 1-100 bar range. Temperature, by contrast, drives most of the change in density.

How to calculate liquid ethylene density: worked example

Find the density of liquid ethylene at 200 K and 50 bar.

Step 1. Compute the temperature term:

$1 - \frac{200}{282.34} = 0.2916$

Step 2. Raise it to the power $D = 0.29147$:

$0.2916^{0.29147} = 0.6983$

Step 3. Add 1 and raise $B$ to that power:

$0.27657^{\,1.6983} = 0.11273$

Step 4. Divide $A$ by that result, then multiply by the molar mass:

$\rho_{ref} = \frac{2.0961}{0.11273} \times 28.054 = 521.6345 \text{ kg/m}^3$

This is the density at the reference pressure of 1 bar (0.1 MPa). The calculator carries this value at full precision into the next step; rounded for display, it is 521.63 kg/m³.

Step 5. Apply the pressure correction for 50 bar (5 MPa) to the unrounded reference density:

$\rho = 521.6345 \times \left[1 + 0.00125 \times (5 - 0.1)\right] = 524.83 \text{ kg/m}^3$

The calculator returns 524.83 kg/m³ for 200 K and 50 bar.

More examples

The table shows the pattern clearly. Moving from 150 K to 250 K at a fixed 10 bar drops density by about 175 kg/m³, a 29% decrease. Moving from 10 bar to 100 bar at a fixed 200 K raises density by only about 6 kg/m³, roughly 1%. Temperature change has far more effect than pressure change over the ranges this tool covers.

Valid input ranges

The calculator accepts temperatures from 104 K to 282 K and pressures from 1 bar to 100 bar.

• Below 104 K, ethylene approaches its freezing point and the correlation is not validated.
• Above 282 K, the temperature nears ethylene's critical temperature (282.34 K), the point above which liquid and gas become indistinguishable. The correlation cannot describe this region.
• Outside 1-100 bar, the pressure correction term has not been validated and results may be unreliable.

Entering values outside these ranges produces a validation error rather than a result.

Why liquid ethylene density matters

Density calculations support several everyday tasks in chemical plants:

• Storage tank sizing. Liquid ethylene expands as it warms. Tanks must have enough headspace to handle that expansion safely.
• Pipeline and pump design. Pressure drop and pump suction calculations both depend on the density of the liquid moving through the line.
• Mass balance. Flow meters often measure volume, not mass. Converting volume to mass requires an accurate density value.
• Custody transfer. When ethylene changes hands between a supplier and a buyer, volume measurements convert to mass using density, which directly affects the amount billed.

Limitations

This correlation is an estimate, accurate to roughly ±2% within its valid range, based on the underlying DIPPR fit to experimental data. It is not a substitute for a full equation of state near the critical point, for mixtures of ethylene with other gases, or for safety-critical calculations that require certified reference data, such as the NIST REFPROP database.

Frequently asked questions

What is liquid ethylene density measured in? The calculator reports density in kilograms per cubic meter (kg/m³), the standard SI unit for density in chemical engineering.

What temperature and pressure units does the calculator use? Temperature in Kelvin (K) and pressure in bar. To convert from Celsius, add 273.15. To convert from psi to bar, multiply by 0.06895.

What is DIPPR Equation 105? DIPPR Equation 105 is a standard mathematical form used to fit experimental saturated-liquid density data as a function of temperature. DIPPR stands for the Design Institute for Physical Properties, a research consortium that compiles and validates property data for industrial chemicals.

Why does pressure barely change the density? Liquids resist compression far more than gases do. The pressure correction in this calculator, based on an isothermal compressibility of 0.00125 per MPa, shifts density by only a few kg/m³ even across the full 1-100 bar range.

Can this calculator be used for ethylene gas? No. It only models the liquid phase. Gas-phase ethylene needs a different set of equations, such as a compressibility-factor or equation-of-state model.

How accurate is this calculator near the critical temperature? Accuracy drops as temperature approaches 282.34 K, the critical temperature used in the correlation. Near that point, small temperature changes cause large, hard-to-predict swings in density, and the correlation is not designed for that region.

References

1. Design Institute for Physical Properties (DIPPR), sponsored by the American Institute of Chemical Engineers (AIChE). DIPPR Project 801 database.
2. National Institute of Standards and Technology (NIST) Chemistry WebBook, Standard Reference Database Number 69.
3. Poling, B.E., Prausnitz, J.M., & O'Connell, J.P. (2001). The Properties of Gases and Liquids (5th ed.). McGraw-Hill.