Principal Thermal Mechanical Engineer

Overview

At Jet Cool, a Flex company, we're at the forefront of liquid cooling innovation, delivering advanced solutions that empower our partners in AI and high-performance computing. United by a shared purpose, our teams are pushing the limits of what's possible and tackling complex challenges.

A career at Jet Cool offers the opportunity to make a real impact by helping build smarter, more sustainable data centers. Together, we're not just advancing technology — we're redefining cooling standards to create a more sustainable tomorrow.

To support our extraordinary teams who build great products and contribute to our growth, we're looking to add a Principal Thermal Mechanical Engineer located in Littleton, MA
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Reporting to the Mechanical Development Associate Principal Engineer
, the Principal Thermal Mechanical Engineer will play a pivotal role in the early phases of product development and serve in a guidance capacity through product maturation. Our products drive sustainability across the data center infrastructure by allowing higher coolant temperatures and by driving more complete heat capture for liquid cooling. The Principal Mechanical Engineer will provide technical leadership, mentorship, and hands-on expertise in mechanical design, fluid dynamics, and heat transfer, and will also work closely with customers in communicating the art of the possible with Jet Cool technology and building a strong customer relationship on a technical level.

• Lead the architecture, design, analysis, and optimization of complex fluid and thermal systems—including pumps, fluids, tubing, heat exchangers, and associated components—for advanced computing and processing platforms.
• Own mechanical and fluid system deliverables from concept through production, ensuring designs meet performance, reliability, manufacturability, and compliance requirements.
• Serve as a technical partner to customers and external collaborators, supporting system-level integration of fluid solutions into broader product architectures.
• Drive simulation, analysis, and test efforts to validate fluid flow, pressure drop, thermal performance, and material compatibility across operating conditions.
• Develop, review, and approve engineering requirements, specifications, and technical documentation in accordance with applicable industry standards and regulatory expectations.
• Lead and influence design reviews, presenting technical tradeoffs, risks, and recommendations to cross-functional teams, customers, and senior stakeholders.
• Identify technical gaps and emerging challenges, advocate for targeted research and development, and lead exploratory efforts that build foundational knowledge and intellectual property.
• Establish and promote best practices in fluid system design, analysis, and documentation, contributing to a strong engineering culture and continuous improvement.
• Provide technical leadership, mentorship, and guidance to engineers across experience levels, supporting professional development and raising overall team capability.
• Contribute to new product innovation by evaluating emerging technologies, industry trends, and alternative architectures to drive differentiated fluid system solutions.
• Support the resolution of complex technical issues throughout the product lifecycle, including development, qualification, production, and field support as needed.

• Minimum of 7+ years of experience designing and engineering fluid systems in data center thermal management and cooling, automotive, medical, or nuclear industries, including at least 3+ years of direct experience with Coolant Distribution Units (CDUs).
• Deep expertise in fluid dynamics, thermodynamics, and heat transfer, with strong application of first principles engineering.
• Proven track record of new product development in thermal or fluid systems, including concept development, performance analysis, validation testing, and experimental design.
• Strong analytical and problem solving capabilities, with demonstrated ability to troubleshoot and optimize complex fluid systems across development and production phases.
• Demonstrated technical leadership…