Fluids / Mechanical Engineer, R&D

Fluidstack; Austin (TX); On-site; USD 120,000 - 180,000; Full time

Job summary

Fluidstack is seeking a highly skilled engineer for the Thermofluids R&D Team in Austin. You will define machine cycle models, size heat exchangers, and design the fluid system including piping and relief paths to support gigawatt-scale compute infrastructure.

You will simulate cycle performance, calibrate models against datasheets and test data, and report gaps clearly. The role emphasizes holding open questions, and working across heat transfer challenges in a fast-paced environment.

Qualifications

• You’ve built a thermodynamic cycle model from fluid properties.
• You’ve sized real heat exchangers against published correlations.
• You’ve calibrated a model against a machine datasheet or test data and reported the gap honestly.
• You’ve written the analysis that changed a design decision.
• You’ve sized a relief path and signed off that the system was protected.
• You’ve held a result open when it was still open, instead of closing it early to be helpful.

Responsibilities

• Define the machine cycle model and set working fluid, pressures, temperatures, and flows.
• Design heat exchangers with very large surface areas and arrange the fluid system accordingly.
• Develop piping, valves, headers, relief and isolation sizing to meet pressure-drop budgets.
• Run trades on air-side temperature rise, face velocity, and subcooling; derive operating points from exchanger ratings.
• Take cycle predictions to the test stand and reconcile with measured COP.

Skills

Thermodynamic modeling

Heat exchanger sizing

Fluid systems design

Two-phase flow

Data center cooling

Tools

CoolProp

REFPROP

Cavallini

Gnielinski

Wang

Job description

About Fluidstack

We exist to make humanity more free. For most of human history, you farmed or you starved. Technology gave people more time for the things they wanted to do, instead of things they had to do. Powerful AI will be the biggest lever for human choice we've ever built - but only if models are aligned with what humanity actually wants. There are groups building AI who don't share these goals. Whoever deploys frontier compute infrastructure fastest will decide whether AI expands human freedom or shrinks it.

We're singularly focused on delivering 10 to 100s of GWs of compute faster than anyone else, rethinking every layer of the stack. We acquire power, design and build data centers, and operate them - with teams spanning hardware and software. Speed and scale are our key differentiators. Come be a part of building civilization-scale infrastructure for AI.

How We Operate

• Be a barrel. Full autonomy. Own things end to end, take on scope without being asked, no permission required to operate outside your core role.

• Insane urgency. We drive everything forward as fast as possible.

• Reason from first principles. Challenge every assumption. Zero analogy thinking, no egos, the best idea wins.

• Love of the game. The frontier of AI is the most interesting problem of our time. We put in long hours at high intensity to push the frontier forward.

• Build something that actually matters. If you're going to spend your time, spend it on something that matters to the world.

The Thermofluids R&D Team

Examples of key problems the team is working on

• Reject 10s of GW of heat, starting now. Fluidstack is targeting 10s of GW of compute over the next two years. Every watt of it becomes heat that has to go somewhere, and no cooling team has ever been asked to open at that scale rather than grow into it.

• Design and build the machines, because nobody can supply them. The merchant compressor market cannot deliver at this rate, and the vendor base behind today’s chillers will not scale to gigawatts. We are taking compressor and chiller design in house, working on machine architectures nobody sells today, and going from blank sheet to production faster than this industry thinks is possible.

• Own every thermofluids problem behind the fleet, not just the chiller. Working fluid and cycle architecture, heat exchangers at a scale that dominates the cost of the plant, two-phase heat transfer at the chip, and thermal energy storage. All of it is open, and whatever this team lands gets built thousands of times.
  

Role Scope

• Define what the machine has to be, owning the cycle model that sets the working fluid and the pressures, temperatures and flows the compressor, turbine and exchangers are designed against.

• Design heat exchangers with surface areas running into millions of square meters, among the largest single drivers of a data center’s physical footprint.

• Design the fluid system around the machine: piping, valves, headers, relief and isolation, sized against the pressure-drop budget the cycle can afford and the pressures the fluid actually runs at.

• Run the trades that decide the machine: air-side temperature rise, face velocity and subcooling. Derive the operating points from coupled exchanger ratings rather than asserted approach temperatures, so infeasible designs get caught in the model instead of in hardware.

• Take the cycle predictions onto the test stand and reconcile them against measured COP, then say plainly where the model was wrong.

What We're Looking For

The below is a starting point. We always make space for exceptional people, so if you don't fit this role exactly, tell us where you would.

• You’ve built a thermodynamic cycle model from fluid properties up and defended its assumptions to someone actively trying to break it.

• You’ve sized real heat exchangers against published correlations, and you’ve caught a case where the correlation belonged to a different geometry than the one in front of you.

• You’ve calibrated a model against a machine datasheet or test data and reported the gap honestly rather than tuning until it disappeared.

• You’ve written the analysis that changed a design decision, in a form that people who never ran the code could read and act on.

• You’ve sized a relief path and been the one who signed off that the system was protected.

• You’ve held a result open when it was still open, instead of closing it early to be helpful.

• Bonus: Vapor-compression and transcritical cycles (chillers, heat pumps, refrigeration). Propulsion and cryogenic fluid systems (feed systems, regenerative cooling, two-phase transport). Piping and relief design for high-pressure fluid systems. Real-gas properties and two-phase heat-transfer correlations (CoolProp, REFPROP, Cavallini, Gnielinski, Wang). Data center thermal architecture (CDUs, dry coolers, direct-to-chip).

We are committed to pay equity and transparency.

Fluidstack is an Equal Employment Opportunity Employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, sex, national origin, sexual orientation, gender identity, disability and protected veterans’ status, or any other characteristic protected by law. Fluidstack will consider for employment qualified applicants with arrest and conviction records pursuant to applicable law.

You will receive a confirmation email once your application has successfully been accepted. If there is an error with your submission and you did not receive a confirmation email, please email [e-mail] with your resume/CV, the role you've applied for, and the date you submitted your application-- someone from our recruiting team will be in touch.