Principal Thermal Mechanical Engineer

Location: USA, MA, Littleton

Time Type: Full time

Job Description

At JetCool, 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 JetCool 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.

Job Summary

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.

Reporting to the Product Manager the Principal Thermal Mechanical Engineer will play a pivotal role in the early phases of product development and serving 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 but also work closely with customers in communicating the art of the possible with JetCool technology and building a strong customer relationship on a technical level.

What a typical day looks like:

• Lead the initial design, analysis, and optimization of complex fluid systems from concept initial CAD to final detailed CAD and drawing for liquid cooling, including cold plates, pumps, fluids, tubing, and heat exchangers, for the latest computer processing chipsets.
• Collaborate with customer and partner teams to integrate fluid systems into overall product designs.
• Conduct fluid flow simulations, analyses, and tests to ensure efficient and reliable performance of fluid systems under various operating conditions.
• Perform detailed calculations and analysis of fluid dynamics, pressure drops, thermal performance, and material compatibility.
• Develop and review engineering specifications, and documentation for fluid system and heat transfer components and assemblies, ensuring compliance with industry standards and regulatory requirements.
• Assist in maintaining a strong best practice culture and driving additional foundational knowledge and IP through research.
• Identify technical gaps to advocate for research and development and lead research projects, maximizing product impact and benefit.
• Provide technical guidance and mentorship to junior engineers, fostering a culture of continuous learning and development.
• Participate in design reviews, presenting technical findings and recommendations to internal and external stakeholders.
• Contribute to the development of new product concepts and innovations in fluid system design, keeping abreast of industry trends and emerging technologies.
• Support the resolution of technical challenges and issues related to fluid systems throughout the product lifecycle.

The experience we’re looking to add to our team:

• Master's (Thesis required) degree in Mechanical Engineering or related field.
• Minimum of 7 years of post-collegiate experience in designing and engineering fluid systems, preferably within the data center thermal management/ cooling, automotive, medical, or nuclear industries. 
• Minimum of 3 years working at senior or principal engineer level in an industrial setting. 
• Profound expertise in fluid dynamics, thermodynamics, and heat transfer, with a strong foundation in engineering principles.
• Extensive experience in SolidWorks CAD, complex part and assembly drawings, GD&T and DFMs.
• Ability to independently develop product concepts, performance analysis and design experiments. Track record of new product development, preferably thermal fluid products. 
• Strong analytical and problem-solving skills, with the ability to effectively troubleshoot and optimize fluid system performance.
• Excellent communication and documentation skills to convey complex technical concepts to both technical and non-technical audiences.

BO18

What you'll receive for the great work you provide:

• Full range of medical, dental, and vision plans
• Life Insurance
• Short-term and Long-term Disability
• Matching 401(k) Contributions
• Vacation and Paid Sick Time
• Tuition Reimbursement

Application Deadline:

Applications for this job position will be accepted for at least five days following the job posting start date below and continuing until the end date below or until the position is filled. This posting may close sooner due to application volume.

Job Posting Start Date 07-09-2026 Job Posting End Date 10-30-2026

The base pay range for this position is provided below. The final base rate offered will be determined using job-related, non-discriminatory criteria, including but not limited to experience, qualifications, geographic location, education, external market data, and internal equity.

$153,500.00 USD - $211,000.00 USD Annual

Job Category

Design, Process & Technology Engineering

Is Sponsorship Available?

No

JetCool is an Equal Opportunity Employer and employment selection decisions are based on merit, qualifications, and abilities. We do not discriminate based on: age, race, religion, color, sex, national origin, marital status, sexual orientation, gender identity, veteran status, disability, pregnancy status, or any other status protected by law. We're happy to provide reasonable accommodations to those with a disability for assistance in the application process. Please email accessibility@flex.com and we'll discuss your specific situation and next steps (NOTE: this email does not accept or consider resumes or applications. This is only for disability assistance. To be considered for a position at JetCool, you must complete the application process first).