Cryogenic flow meter

Measuring the flow of cryogenic liquids like liquid nitrogen (LN₂) or liquefied natural gas (LNG) is one of the most demanding tasks in industrial instrumentation. Defined as liquids below -150°C (-238°F), these fluids present a unique set of challenges that can cause standard flow meters to fail. For applications where accuracy and safety are non-negotiable, the Coriolis mass flow meter has emerged as the definitive solution.

This guide explains the challenges of cryogenic measurement, details the specialized design of Coriolis flow meters for these applications, and provides essential installation guidance.

The Unique Challenges of Cryogenic Flow Measurement

Why do so few flow meters work reliably at these ultra-low temperatures? The reasons are rooted in physics:

×  Mechanical Seizing: Flow meters with moving parts are highly susceptible to failure. The extreme cold can cause components like the bearings in a turbine flow meter or the rotors in an oval gear flow meter to contract, seize, or freeze due to trace amounts of moisture, bringing measurement to a complete halt.

×  Material Embrittlement: Standard metals and elastomers become brittle and can fracture when exposed to extreme cold.

×  Fluid Flashing: Cryogenic liquids exist close to their boiling point. Any pressure drop within the meter can cause the liquid to instantly vaporize or "flash," leading to inaccurate, two-phase flow readings.

×  Drastic Density Changes: The density of a cryogenic liquid changes significantly with the slightest shift in temperature. This is a critical issue for volumetric meters (like turbine or variable area), as their readings can become highly inaccurate.

The Coriolis Meter: The Ultimate Cryogenic Solution

A Coriolis mass flow meter is the ideal technology because it measures mass directly. The mass of a fluid does not change, whether it's a liquid or a gas. This fundamental principle makes its measurement immune to the density and phase changes that plague other technologies.

Engineered for the Extreme: Special Design Features

Coriolis meters for cryogenic service are not standard instruments; they are purpose-built with specific features to handle the intense cold:

√  Specialized Materials: The wetted parts, especially the measuring tubes, are constructed from specific grades of stainless steel (316L) that maintain their strength and ductility at temperatures as low as-200°C (-328°F).

√ Vacuum-Insulated Sensor Housing: A key feature is the vacuum jacket that surrounds the sensor. This acts as a thermal barrier, preventing the buildup of ice and frost on the exterior of the sensor. This ensures the vibrating tubes do not freeze up and can oscillate freely, which is critical for accurate measurement. This provides powerful thermal insulation, preventing ambient heat from reaching the fluid. This minimizes unwanted vaporization and stops a thick layer of ice from forming on the sensor, which would otherwise interfere with the precise vibrations required for measurement.

√ Stress-Resistant Construction: The entire sensor is designed to safely handle the thermal stresses caused by the contraction of metal during the cool down process.

√ These advanced instruments provide more than just mass flow. They also offer a real-time temperature display directly on the meter, providing another vital process variable without the need for a separate temperature sensor.

Key Cryogenic Applications

• The accuracy and reliability of these specialized meters make them essential for a wide range of industries:
• Industrial Gases: Measuring liquid nitrogen (LN₂), liquid (LOX), liquid argon (Ar), and liquid CO₂ for production, distribution, and process use.
• Energy: Custody transfer and process monitoring of Liquefied Natural Gas (LNG) and Liquefied Petroleum Gas (LPG).
• Aerospace: Precise measurement of cryogenic propellants like liquid hydrogen and LOX.
• Food & Medical: Dosing of LN₂ for flash freezing in the food industry and for cryopreservation in medical applications.

How to Install a Cryogenic Coriolis Flow Meter

Proper installation is critical to ensure the meter performs accurately and safely.

Cryogenic Flow meter install position for liquid measurement

Cryogenic Flow meter install position for gas measurement

1. Mounting Orientation and Location:
The meter should be installed at a low point in the pipeline to ensure it remains full of liquid and does not trap gas bubbles.
It is crucial to install the meter so the measuring tubes are self-draining to prevent any trapped liquid from vaporizing and causing pressure spikes when the line warms up. Always consult the manufacturer's manual for the recommended orientation.

2. Insulation is Key:
The entire sensor body and adjacent piping should be thoroughly insulated with high-quality cryogenic insulation (e.g., polyurethane foam, vacuum-insulated piping). This maintains the liquid state of the fluid and ensures measurement stability.

3. Controlled Cooldown Procedure:
Never introduce the cryogenic liquid into a warm meter suddenly. This can cause a "thermal shock," damaging the sensor. The system should be cooled down slowly and in a controlled manner by gradually introducing the liquid or cold gas.

4. Protect the Electronics:
Ensure the transmitter (the electronics housing) is mounted in a way that protects it from the extreme cold. Cryogenic models often feature an extended neck between the sensor and transmitter to provide a thermal buffer.

Technical Specifications Overview

By combining a robust, purpose-built design with a fundamental measurement principle, the Coriolis flow meter provides the most accurate and reliable solution for mastering the challenges of cryogenic flow measurement.