Line Chilldown

Line Chilldown Using Liquid Hydrogen and Liquid Nitrogen

This validation case compares SINDA/FLUINT and FloCAD® predictions with a 1966 test by the National Bureau of Standards (NBS, now National Institute of Standards and Technology, NIST). In the NBS tests, a pressurized dewar containing either LN2 or LH2 was isolated from an empty 200ft (61m) line (open to the atmosphere) by a valve. At time zero, the valve between the dewar and the line was opened, and cryogenic liquid was allowed to flow until the line was completely full and liquid was discharged from open end of the pipe.

Test Set-up

Comparison with Test Data

Liquid (Normal) Hydrogen, Comparison with Figure 7

Differences between parahydrogen and normal hydrogen are explored, since the exact composition of the hydrogen is unknown. The importance of uncertainties in heat transfer and pressure drop correlations, copper alloy properties (also unknown), dewar pressure, and even the roughness and manufacturing tolerance of the tubing is explored. This study demonstrates automated calibration to test data, and investigation of sensitivities.

Click here to fetch the Cryogenic Cooldown Validation from our User Forum

Download the full Line Chilldown Validation report

See also LNG chilldown of a flexible composite hose

dispersed vs. coalesced front

Tuesday, June 26, 2018, 1-2pm PT, 4-5pm ET

This webinar describes flat-front modeling, including where it is useful and how it works. A flat-front assumption is a specialized two-phase flow method that is particularly useful in the priming (filling or re-filling with liquid) of gas-filled or evacuated lines. It also finds use in simulating the gas purging of liquid-filled lines, and in modeling vertical large-diameter piping.

Prerequisites: It is helpful to have a background in two-phase flow, and to have some previous experience with FloCAD Pipes.

Register here for this webinar

FloCAD model of a loop heat pipe

Since a significant portion of LHPs consists of simple tubing, they are more flexible and easier to integrate into thermal structures than their traditional linear cousins: constant conductance and variable conductance heat pipes (CCHPs, VCHPs). LHPs are also less constrained by orientation and able to transport more power. LHPs have been used successfully in many applications, and have become a proven tool for spacecraft thermal control systems.

However, LHPs are not simple, neither in the details of their evaporator and compensation chamber (CC) structures nor in their surprising range of behaviors. Furthermore, there are uncertainties in their performance that must be treated with safety factors and bracketing methods for design verification.

Fortunately, some of the authors of CRTech fluid analysis tools also happened to have been involved in the early days of LHP technology development, so it is no accident that Thermal Desktop ("TD") and FloCAD have the unique capabilities necessary to model LHPs. Some features are useful at a system level analysis (including preliminary design), and others are necessary to achieve a detailed level of simulation (transients, off-design, condenser gradients).

CRTech is offering a four-part webinar series on LHPs and approaches to modeling them. Each webinar is designed to be attended in the order they were presented. While the first webinar presumes little knowledge of LHPs or their analysis, for the last three webinars you are presumed to have a basic knowledge TD/FloCAD two-phase modeling.

Part 1 provides an overview of LHP operation and unique characteristics
Part 2 introduces system-level modeling of LHPs using TD/FloCAD.
Part 3 covers an important aspect of getting the right answers: back-conduction and core state variability.
Part 4 covers detailed modeling of LHPs in TD/FloCAD such that transient operations such as start-up, gravity assist, and thermostatic control can be simulated.