Thermo Mechanical Engineer

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.