Thermo Mechanical Engineer

Bristol

Fractile is building silicon, systems and software which will redefine the frontier of AI: running the world’s most advanced models at radically higher speed and lower cost. We have an exceptional team across hardware and software capable of bringing about this change, and we are growing fast to meet demand and deliver our product at scale.

We are seeking a Thermal Engineer with deep experience in data centre or high-density system design, someone who can guide and shape the development of advanced cooling architectures. You might be a mechanical engineer who has specialised in thermal design, or a thermal systems expert with strong modelling and integration experience. Either way, you’ll be comfortable leading design direction and working hands-on with suppliers, prototypes, and test rigs. We are open to a contractor or permanent hires, we are most interested in finding someone who can add real expertise when it’s needed, help define the right path, and guide the build of a robust, production-ready cooling solution.

The Role

You will lead the design of an advanced cooling system for a high-density AI accelerator system destined for data centre deployment. This includes developing the full cooling architecture — from Direct-to-Chip (D2C) liquid cooling through to rack-level thermal management and hybrid liquid-air solutions for host chassis. You’ll collaborate closely with mechanical engineers (internal and external), chip and board designers, and 3rd-party suppliers to define requirements, review designs, and ensure that every aspect of the system — from the cold plate up — meets performance, reliability, and manufacturability goals. We expect you to bring a mix of technical authority, practical design sense, and strong supplier management skills. You may also lead or advise on the development of a thermal test platform to validate solutions in real-world conditions.

Key Responsibilities

Lead the design and specification of an advanced cooling solution for dense AI hardware systems

Work closely with 3rd-party suppliers to define thermal and mechanical requirements and review proposed solutions

Contribute to mechanical system design — specifying chassis interfaces, manifold routing, fittings, and integration details

Model and simulate thermal performance at cold plate, chassis, and rack levels

Develop and/or oversee a test platform to validate cooling concepts and final implementation

Support the design of Direct-to-Chip (D2C) liquid cooling systems, Cold Plates, CDUs, and Hybrid Liquid-Air chassis

Drive design reviews, evaluate trade-offs, and ensure solutions are manufacturable and reliable

Liaise with system, hardware, and data centre teams to ensure the cooling architecture integrates seamlessly into overall system design

Skills & Experience Essential

Bachelor's Degree in Mechanical Engineering

At least 7 years of experience in developing hardware products with thermal design liquid cooling systems for high-performance computing, data centres, or equivalent high-density hardware

Expertise with D2C liquid cooling, cold plate design, and CDU/rack-level systems

Hands-on experience with thermal modelling and simulation tools

Experience taking designs through prototyping, test, and production

Strong collaboration skills — comfortable working across disciplines and with suppliers

Familiarity with thermal-fluid analysis, materials selection, and system reliability principles

Desirable

Experience with AI accelerator or HPC hardware

Background in mechanical engineering — able to support mechanical chassis design and integration

Experience working directly with data centre operators or hyperscale infrastructure teams

Awareness of liquid handling and serviceability considerations in deployed environments

UK-based, or able to work UK hours with occasional on-site collaboration

How we work

Ownership and execution: you will have full agency to drive your work forward

Rapid iteration: we all work directly with top leadership to move from idea to hardware on ambitious timelines

Full-stack engagement: hardware, software, silicon, and modelling teams all work closely together to create a product with generational impact

Optimistic and pragmatic: we possess the will to win, and to do the hard work to get us there

Team player mentality: the mission is bigger than any of us, and we have the curiosity and technical focus to see the best idea shipped, no matter who’s it is

About us

Founded in 2022, team of 70+ which is expanding rapidly

Modern, open offices in London and Bristol

Collaborative, problem-solving culture built on deep curiosity, entrepreneurial initiative and technical fluency

Export control and security clearance

Certain roles may involve working on technologies subject to export restrictions. Applicants may be required to undergo additional eligibility checks to ensure compliance with applicable law.

Essential