Oscillating Heat Pipes (OHPs) are passive, two-phase heat transfer devices featuring serpentine channels filled with a working fluid. Their simple construction, low cost, flexible form factor, miniaturization potential, and exceptional heat transfer capabilities make them one of the most promising solutions for thermal management across a wide range of applications, including electronic cooling, photovoltaic systems, automotive batteries, spacecraft thermal control, wastewater heat recovery, solar desalination, and cryogenics.
In this project, three tubular OHP devices from scratch were fabricated in MREL lab for thermal management solutions, each featuring transparent adiabatic section to enable visualization of internal flow dynamics. The system is equipped for comprehensive diagnostics, including infrared thermography, high-speed video capture, and simultaneous temperature and pressure measurements. This project was conducted as a part of my PhD dissertation research work.
Key Achievements:
Designed and fabricated a one-dimensional OHP optimized to relate the OHP performance to single fluid property— equivalent thermal conductivity and it's accurate and reliable estimation
Conducted synchronized experiments using high-speed and IR cameras along with integrated temperature and pressure sensors
Tested four working fluids (DI water, Methanol, Ethanol and FC-72) across 31 different heat input conditions
Acquired over 124,000 images for flow regime analysis and machine learning-based predictive modeling
Achieved a record-high effective thermal conductivity (~16× that of copper), exceeding any known solid material
Demonstrated superior heat transfer performance over copper and silver even at low heat input levels
Developed novel criteria to characterize and predict OHP operation failure based on thermodynamic and thermal analyses - addressing a long-standing gap in the field where failure could not be estimated prior to extensive experimental testing
Designing OHPs remains a challenge due to complex two-phase flow behavior. Traditional methods using CFD models face trade-offs between accuracy, cost, and time. Machine learning shows promise but demands extensive experimental data, which is costly and time-consuming to obtain. Thus, design of OHP is still considered as one of the unsolved issues in OHP community.
In our study, we introduce a simple and low-cost design criterion based on a single fluid property of OHP—equivalent thermal conductivity—measured from an ideal tubular OHP with a truly adiabatic section. This is linked to the target OHP design through a variable dependent on surface wettability. The OHP is modeled as a conduction-based system and simulated in COMSOL Multiphysics to predict temperature distribution across varying heat loads and working fluid. This project was conducted as part of my PhD dissertation research work.
Key Achievements:
Validated for two different working fluids (DI water, FC-72) for 7 different total heat inputs
Low cost and time of operation
Simple and scalable modeling approach
Reliable estimation of thermal conductivity for target OHP design
Based on design predictions, an embedded oscillating heat pipe (OHP) was fabricated in MREL lab on a copper substrate with a polycarbonate top to enable real-time visualization of the working fluid flow. This configuration allowed for detailed image analysis of internal flow regimes, focusing on the behavior of liquid slugs and vapor plugs. Key flow characteristics such as poistion and length, size distribution and volumetric frequency of liquid slug and vapor plug were extracted to and analyzed to evaluate performance metrics. This project was conducted as a part of my PhD dissertation research work
Key Achievements:
Experimentally validated the OHP design predictions across all working fluids and heat input conditions, with results showing a close match
Achieved a 55% reduction in thermal resistance compared to a solid copper block
Found that the occurrence frequency of smaller-sized liquid slugs and vapor plugs increases with higher heat input, showing a strong interdependence between flow size distribution and thermal performance
A single-loop micro oscillating heat pipe (OHP) is fabricated on a silicon wafer using photolithography at the Cornell NanoScale Science and Technology Facility (CNF) and tested in MREL lab. The device features 225-micron hydraulic diameter channels and is bonded with transparent borosilicate glass from top for flow visualization. The device is equipped with highly synchronized pressure transmitters and thermocouples along with high-speed and infrared camera for data acquisition and the OHP was tested under various heat inputs and working fluids. This project is a part of my PhD dissertation research work
Status: Work in Progress
Electrospray cooling is a promising technique for managing heat in compact electronics due to its potential for localized, high heat flux removal. However, a major limitation is its inherently low flow output and high operating voltage.
This work combines simulation and experimentation. Electrostatic field and spray particle evolution simulations were performed using the Lagrangian model in COMSOL Multiphysics, and electrospray nozzles were fabricated and tested based on the simulation conditions. The experimental results were used to validate the simulations. These simulations provided key insights into droplet trajectories, field strengths, and emitter behavior, which are critical for optimizing emitter configuration and spacing.
Two approaches were used to increase the flow output:
Enhancing a single nozzle: A cap made of ABS material was added to a single electrospray nozzle to increase flow output and reduce voltage during the operation.
Multiplexing the nozzle array: An array of multiple nozzles was used to increase the overall flow rate. However, the electrostatic field strength at the end-side nozzles was lower due to asymmetry, causing irregular spray behavior. To address this, metallic caps were added to the side nozzles to maintain a uniform electric field. COMSOL simulations were used to optimize the size and position of these caps. This project was conducted as part of my Master’s thesis research.
Key achievements:
Flow rate increased by a factor of 12×
Operating voltage reduced by a factor of 5.4×
Irregular flow at side nozzles successfully corrected using metallic caps