Thermo Mechanical Engineer

About Fractile

Fractile was founded in 2022 on the bet that, eventually, the world’s most capable AI systems would be limited in their impact by the time taken to produce useful outputs. We bet everything on the logical conclusion: that the only way to truly unlock this latent value, to make speed viable at scale, was to radically re-invent the hardware that we run our frontier AI models on. Ever since, we have been building chips and systems that tackle this problem: how to efficiently generate output at thousands of tokens per second, while handling the complexity and capacity challenges of operating large models at very long contexts.

 

The workloads that push to the limits of the current frontier are already transformational; it is the technical and economic limits on inference speed that are constraining progress. The defining work of the 21st century will be marked by the engine of inference delivering immense and diffuse chains of intellectual inquiry, in drug discovery, in software engineering, in materials discovery, in any field where progress is driven by deep reasoning and intelligence to resolve complex problems.

 

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.

What We Offer

• Competitive salary: A competitive salary reflective of your experience and the specialist nature of the role.

• Equity & Ownership: meaningful equity so everyone shares in the value creation

• Benefits: Private Medical, Dental and Vision, Contributory Pension, 25 Days holiday plus bank holidays and Life/Critical Illness Insurance.

• Diverse & fun office: we believe the hardest problems get solved by the broadest range of minds. We are committed to Equal Employment Opportunity through attracting and retaining a diverse team and building an inclusive environment.

Fractile is seeking to increase the clock speed of global progress, one chip at a time. We’ve recently raised $220M from investors including Founders Fund and Accel and our most important work lies ahead. Join us!

 

Export controls

Our work involves technologies subject to UK, US and other international export control regulations. Certain roles may require additional eligibility checks to ensure compliance with applicable law. We'll be transparent about this throughout the hiring process.