David C. Deisenroth and Michael M. Ohadi

Thermal Management of High-Power Density Electric Motors for Electrification of Aviation and Beyond

Enhanced cooling, coupled with novel designs and packaging of semiconductors, has revolutionized communications, computing, lighting, and electric power conversion. It is time for a similar revolution that will unleash the potential of electrified propulsion technologies to drive improvements in fuel-to-propulsion efficiency, emission reduction, and increased power and torque densities for aviation and beyond. High efficiency and high specific power (kW/kg) electric motors are a key enabler for future electrification of aviation. To improve cooling of emerging synchronous machines, and to realize performance and cost metrics of next-generation electric motors, electromagnetic and thermomechanical co-design can be enabled by innovative design topologies, materials, and manufacturing techniques. This paper focuses on the most recent progress in thermal management of electric motors with particular focus on electric motors of significance to aviation propulsion.

David M. Hymas, Martinus A. Arie, Farah Singer, Amir H. Shooshtari, and Michael M. Ohadi

An Additively Manufactured Polymer Composite Heat Exchanger for Dry Cooling Applications

The work presented in this paper focuses on the design and thermal characterization of a novel polymer composite heat exchanger (HX) produced by an innovative additive manufacturing process. The heat exchanger represents a gas to liquid configuration in which the gas side removes heat from the liquid side in a cross-flow arrangement. The novel HX utilizes a cross media approach in which, unlike the conventional HXs, the hot and cold sides are directly connected to each other through high conductivity metal fiber fins on the gas side protruding through the walls of the liquid side, thus eliminating the wall resistance separating the hot and cold sides. The HX demonstrates superior thermal performance at reduced pressure drops while also benefiting from the lighter weight and the lower cost that the polymer structure introduces. A 350-W water-to-air heat exchanger was fabricated using a fused filament fabrication (FFF) technique with a novel/patent pending printer head which was developed to produce the metal fiber composite structure of the heat exchanger.

David M. Hymas, Martinus A. Arie, Farah Singer, Amir H. Shooshtari, and Michael M. Ohadi

Enhanced Air-Side Heat Transfer In An Additively Manufactured Polymer Composite Heat Exchanger

The present study builds upon our prior work in integrating additive manufacturing into next-generation heat/mass exchanger devices. In this paper, we will report an analysis of the fabrication, testing, and performance of an additively manufactured polymer composite heat exchanger. This heat exchanger utilizes a novel approach to achieve enhanced airside heat transfer coefficients and overall mass reduction. This device relies on the Cross-Media Fiber concept where two fluid flows are thermally linked by high-conductivity fins, passing through a low-conductivity channel wall. Through this, the authors have met the required pressure containment, coefficient of performance, and heat flow rate targets, which were 28 psig, 100 and 150 W respectively. The advances that are discussed throughout this paper have allowed this novel polymer composite heat exchanger to be produced through a newly developed form of additive manufacturing that can potentially lead to the economical production of large scale Cross-Media Fiber heat exchangers.

Martinus Adrian Arie, Amir Shooshtari, Michael Ohadi

Air Side Enhancement of Heat Transfer in an Additively Manufactured 1 kW Heat Exchanger for Dry Cooling Applications

Additive manufacturing is a fast-growing technique due to its ability to fabricate complex objects layer by layer from a preprogrammed digital model. Additive manufacturing can greatly enhance the heat exchanger manufacturing field, as it makes possible the fabrication of complex heat exchanger designs that are challenging to fabricate using conventional methods. In the present work, an air-to-water manifold-microchannel heat exchanger made of titanium alloy (Ti64) with size of 15 cm x 15 cm x 3.2 cm was fabricated using direct metal laser sintering (DMLS) additive manufacturing technique. The manifoldmicrochannel feeds the fluid flow into an array of parallel microchannels for better flow distribution as well as short flow travel length, thus yielding significantly enhanced heat transfer performance with low pressure drop penalty. Upon successful fabrication, the heat exchanger was experimentally tested, and the results were analyzed against conventional heat transfer surfaces. Based on the experimental results, for the case where the heat exchanger heat flow rate is 900 W, air-side Reynolds number is less than 100 and the temperature difference between the inlet air and water temperature is 27.5 oC, heat transfer coefficient of 180 W/m2K and pressure drop of 100 Pa are observed. Compared to the conventional surfaces like wavy fin, louvered fin, and plain plate fins, up to 80%, 120%, and 190% improvement in air-side heat transfer coefficients were recorded, respectively, with an air-side pressure drop of less than 100 Pa. The results strongly suggest that additive manufacturing could be implemented for materials and complex designs that are otherwise difficult to fabricate with conventional technologies.

Martinus A. Arie, Amir H. Shooshtari, Michael M. Ohadi

Experimental characterization of an additively manufactured Heat Exchanger for dry cooling of power plants

Applied Thermal Engineering, 2018, 129 187-198.

Air-cooled heat exchangers for power plant cooling are receiving much attention lately, as they require little or no water for cooling when compared to water-cooled systems. This paper focuses on the design, fabrication, and experimental characterization of a novel additively manufactured air–water heat exchanger for dry cooling of power plants. The heat exchanger consists of manifold-microchannels on the air side and rectangular channels on the water side in a cross-flow configuration. By using additive manufacturing, the manifold-microchannel heat exchanger can be fabricated as a single component, which eliminates the assembly process. Three prototype heat exchangers were fabricated using direct metal laser sintering (DMLS) out of stainless-steel (SS17-4), titanium alloy (Ti64), and aluminum alloy (AlSi10Mg). Air-side heat transfer coefficients in the range of 100–450 W/m2 K at pressure drops of 50–2000 Pa were recorded for the titanium alloy heat exchanger for air flow rate ranging from 1.89 L/s to 18.9 L/s. Based on our analysis and compared to conventional heat exchangers, the performance of this manifold-microchannel heat exchanger was superior. Compared to wavy fin and plain plate fin heat exchangers, up to 30% and 40% improvement, respectively, in gravimetric heat transfer density was recorded for the entire range of experimental data. Compared to state-of-the-art dry cooling, nearly 27% improvement in gravimetric heat transfer density was noted at air-side coefficient of performance (COPair) of 172.

Xiang Zhang, Ratnesh Tiwari, Amir H. Shooshtari, Michael M. Ohadi

An additively manufactured metallic manifold-microchannel heat exchanger for high temperature applications

Applied Thermal Engineering, 2018.

This work presents an additively manufactured manifold-microchannel heat exchanger made of Inconel 718 and experimentally tested for high temperature aerospace applications. The heat exchanger core with a size of 66mm×74mm×27mm was fabricated as a single piece through the direct metal laser sintering process. A minimum fin thickness of 180 μm was achieved. Successful welding of additively manufactured headers with the heat exchanger core and conventionally manufactured flanges was demonstrated through the fabrication of the unit. The heat exchanger was tested using nitrogen (N2) on the hot-side and air on the cold-side as the working fluids. The experimental tests were conducted at 600 °C on the hot-side and 38 °C on the cold-side. A maximum heat duty of 2.78 kW and a maximum overall heat transfer coefficient of 1000 W/m2K were achieved during the experiments. The decent agreement between the experimental and the numerical results demonstrates the validity of the numerical analysis model used for heat transfer and pressure drop prediction of the additively manufactured manifold-microchannel heat exchanger. Compared to conventional plate fin heat exchangers, nearly 25% improvement in heat transfer density—the ratio between heat duty and mass (Q/m)—was noted at a coefficient of performance (COP) of 62.

Hadi Keramati, Fabio Battaglia, Martinus A. Arie, Farah Singer, and Michael M. Ohadi

Additive Manufacturing of Compact Manifold-Microchannel Heat Exchangers utilizing Direct Metal Laser Sintering

Annual Review of Heat Transfer, Vol. 10.

Direct Metal Laser Sintering is a metal additive manufacturing technique which uses a laser to fuse metal powders, layer by layer to form a 3D object. In this study, Direct Metal Laser Sintering is used to fabricate compact high temperature manifold-microchannel heat exchangers.
Compared to the state of the art heat exchangers, manifoldmicrochannel heat exchangers have been proven to yield superior performances. However, fabrication of manifoldmicrochannel heat exchangers using conventional fabrication methods is a challenge due to their complex geometry. Additive manufacturing processes, like Direct Metal Laser Sintering, allow fabricating the manifold-microchannel heat exchanger as a single component, which significantly simplify its production process. In order to fully utilize the performance potential of manifold-microchannel heat exchangers, small fins (0.1-0.2 mm) and channels (0.2-0.3 mm) are required. In this study, three different machines were used to study the effect of geometries and printing parameters, such as laser power, powder size, and layer thickness, on the fins and channel size of the fabricated microchannel heat exchangers. A comprehensive study has been performed to achieve fin thickness as small as 0.110 mm. Pressure containment tests were also performed to evaluate the minimum base thickness that can hold the designed pressure. A 3”􀵈3”􀀃􀵈3” size microchannel heat exchangers was then successfully fabricated with straight fins of 0.133 mm out of Maraging Steel, and a 4”􀵈4”􀀃􀵈4” size microchannel heat exchangers was successfully fabricated with fin size of 0.22mm out of Inconel 718. The results thus pave the way for more advancements in optimized additive manufacturing of next-generation heat exchangers.

Martinus A. Arie, Amir H. Shooshtari, Ratnesh Tiwari, Serguei V. Dessiatoun, Michael M. Ohadi, Joshua M. Pearce

Experimental characterization of heat transfer in an Additively manufactured polymer Heat Exchanger

Applied Thermal Engineering, 113 (2017) 575-584.

In addition to their low cost and weight, polymer heat exchangers offer good anticorrosion and antifouling properties. In this work, a cost effective air-water polymer heat exchanger made of thin polymer sheets using layer-by-layer line welding with a laser through an additive manufacturing process was fabricate and experimentally tested. The flow channels were made of 150 lm-thick high density polyethylene sheets, which were 15.5 cm wide and 29 cm long. The experimental results show that the overall heat transfer coefficient of 35–120 W/m2 K is achievable for an air-water fluid combination for air-side flow rate of 3–24 L/s and water-side flow rate of 12.5 mL/s. In addition, by fabricating a very thin wall heat exchanger (150 lm), the wall thermal resistance, which usually becomes the limiting factor on polymer heat exchangers, was calculated to account for only 3% of the total thermal resistance. A comparison of the air-side heat transfer coefficient of the present polymer heat exchanger with some of the commercially available plain plate fin heat exchanger surfaces suggests that its performance in general is superior to that of common plain plate fin surfaces.

 M.M. M. Ohadi, J. Darabi, B. Roget

Electrode Design, Fabrication, and Materials Science for EHD-Enhanced Heat and Mass Transport

Annual Review of Heat Transfer, Vol. 10.

The Electrohydrodynamic (EHD) technique is a new and promising technique which has demonstrated proven potential for significantly reducing heat exchanger size/volume while providing on-line/on-demand control for heat transfer surface heating/cooling. Proper electrode is a key element of successful implementation of the EHD technique in practical applications. The main objective of the present chapter is to further advance understanding of the EHD phenomena, particularly as it relates to factors contributing to an optimal electrode design for momentum and energy exchange in single-phase and phase-change processes of significance to energy conversion, refrigeration, power, and process industries. Issues such as electrode geometry, orientation and material, as well as any long-term effects on the system reliability and operational performance are of particular interest. The information presented in this chapter includes our own work as well as other worldwide investigations. The most recent and advanced information is generally given preference. Specific emphasis is placed on single-phase of flow of gases and liquids and two-phase, boiling and condensation processes. In this work, first the fundamental equations governing the EHD body force are described and the mechanisms involved in heat transfer enhancement are explained. Then, the electrode geometries investigated are reviewed and summarized in a tabulated, easy-to-follow format. Where possible schematic diagrams for particular electrodes are depicted for ease of understanding. Finally, the advantages and disadvantages of each design are discussed, and the optimum electrode/heat transfer configurations for a given application are identified.

Xiang Zhang, Hadi Keramati, Dr. Martinus Arie, Dr. Farah Singer, Dr. Ratnesh Tiwari, Dr. Amir Shooshtari, and Dr. Michael M. Ohadi

Recent Developments in High Temperature Heat Exchangers: A Review

Frontiers in Heat and Mass Transfer (FHMT), 11, 18 (2018)

Heat exchangers are key components of most power conversion systems, a few industrial sectors can particularly benefit from high temperature heat exchangers. Examples include conventional aerospace applications, advanced nuclear power generation systems, and high efficiency stationary and mobile modular fossil fuel to shaft power/electricity conversion systems. This paper provides a review of high temperature heat exchangers in terms of build materials, general design, manufacturing techniques, and operating parameters for the selected applications. Challenges associated with conventional and advanced fabrication technologies of high temperature heat exchangers are discussed. Finally, the paper outlines future research needs of high temperature heat exchangers.

David C. Deisenroth, Ramin Moradi, Amir H. Shooshtari, Farah Singer, Avram
Bar-Cohen & Michael Ohadi

Recent Review of Heat Exchangers Enabled by Polymer and Polymer Composite Additive Manufacturing

Heat Transfer Engineering (2017)

 A review of heat exchangers enabled by polymer additive manufacturing showed that polymer additive manufacturing can enable novel designs in metal/polymer composites, ceramic, and polymer heat exchangers by using the polymer as a geometrically complex sacrificial core in the manufacturing process. Polymer heat exchangers can also be directly constructed by polymer additive manufacturing within a single machine. In addition, the unique properties of polymers enable manufacturing of heat exchangers with properties that may otherwise not be possible via gel casting, conformal deposition, fused filament fabrication, and layer welding. A chart of heat exchangers enabled by polymer additive manufacturing is included in Table 3. The properties of polymers may furthermore make possible heat exchangers with low weight, antifouling, anticorrosion, and decreased manufacturing

F. Singer, D. C. Deisenroth, D. M. Hymas, S. V. Dessiatoun, and M. M. Ohadi

Additively Manufactured Copper Components and Composite Structures for Thermal Management

Recently additive manufacturing (AM) has brought significant innovation to thermal management devices and electronics. Among the most influential innovations are additively manufactured copper/copper alloy components and composites that benefit from the superior thermal, electrical and structural properties of the material. Cu is widely used in electronics, HVACR, radiators, charge air coolers, brazed plate heat exchangers, and oil cooling. Ongoing research is extensively studying, in parallel, Cu properties/characteristics and the different AM process parameters required to enhance the quality of the manufactured Cu components and to optimize their performance/applications. In this paper, we report various AM techniques and AM-based hybrid processes used to produce high-density Cu components. Selective heat exchanger/thermal management applications progress is also reviewed. It is then shown that additively manufactured, dense Cu can generate low mass structures and polymer/metal composites that promise to revolutionize developments in thermal management applications. Studies on the effect of the material properties such as the Cu particle morphology and size distribution are also reported. The major studies that report using Cu to address the challenges of electronics fabrication and cooling, which directly affect system-level performance and reliability, are also discussed. A novel AM process that facilitates microchannel cooling with Cu structures and new processes that allow embedding copper wires into thermoplastic dielectric structures are discussed to further emphasize the potentially transformative advances in additively manufactured electronics and thermal management devices using Cu/Cu alloy composites

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