It’s an Uncertain World

Brent Cullimore

You are hiking in the Serengeti. A twig snaps in bushes a few feet away from you. Is it the wind, or a lion?

As someone whose ancestors jumped to a worst-case conclusion (and as a result were less likely to become someone else’s lunch), we humans instinctively react with alarm in an uncertain situation. Fear of uncertainty is rarely warranted in the modern world, where stress hormones are more likely to shorten your life than to extend it.

The Wild West of Thermal Engineering

Brent Cullimore

Let me start by confessing that I don’t know much about Bitcoin, much less Bitcoin mining. I’m not even sure you can refer to them as ‘Bitcoins’ if you have two of them. You certainly can’t rub them together and make sparks. (They are sparks, if you think about it!)

Who are Thermal Engineers? You might be one!

Brent Cullimore

I admit that I have chafed in the past at being called a thermal engineer. I have degrees in Mechanical Engineering and in Thermosciences. I consider myself more of a fluid/thermodynamics type: I love bubbles, and I think it is a sin if you stir cream into your coffee too fast and miss all the cool eddies. One of my hopes is to visit the grave of Boltzmann, where his legendary equation describing the entropy of systems like tossed coins is inscribed above his headstone, S = k * log(W).

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.