High Energy Density Modular Heat Exchangers through

Design, Materials Processing, and Manufacturing Innovations

PI: A.D. Rollett, Carnegie Mellon University

co-PI V. Narayanan, University California Davis

The proposed technology solves the challenge of high efficiency, high temperature

recuperators with a novel design combined with state of the art 3D printing and surface

roughness reduction in the internal passages. This will enable efficient and power dense

power generation cycles for applications in transportation, electricity generation and

industrial sectors.

Project Vision

Project Overview

Context/history of the project

Collaborations between: CMU and UC Davis; HEXCES and UC Davis; CMU and NETL; CMU and

CSM; UCD and ExtrudeHone

Fed. funding: $2.4YM

Length 36 mo.

Team member Location Role in project

Carnegie Mellon U Pittsburgh, PA Lead, 3D Printing, Materials, Tech. Xfer.

U Calif. Davis Davis, CA Heat Exchanger (HX) Design, Testing

HEXCES Rancho Cordova,

CA

HX Design, Code Compliance

Natl. Energy Techn. Lab. Albany, OR Materials testing: creep, oxidation

General Electric Niskayuna, NY ECM internal smoothing, powder removal

Extrude Hone Irwin, PA AFM internal smoothing, powder removal

CO School Mines (CSM) Golden, CO Dissolution smoothing, powder removal

Metal Powder Works Pittsburgh, PA Small lot powder production

Innovation, Objectives, Final Deliverable

‣ Final deliverable: 50 kW sCO2 recuperator.

‣ Targeted application: transportation, electricity generation and industrial sectors.

‣ Innovation:

– HX design that results in massively parallel flow networks within the heat exchange core and headers;

– Optimization of feature resolution in AM of Ni-alloy powders;

– Optimization of material selection and AM processing for maximal creep strength;

– Post processing for reduction of AM surface roughness with directed electrochemical and abrasive flow machining;

– Use of process-based cost model for prediction and reduction of cost.

6x capacity scale up

Features:

1. Diverging pin array on hot (low

pressure) side

2. Counter-flow headers and

manifolds

Heat Exchanger Design

‣ The proposed AM HX design invokes the principles of parallelization and continuous flow redevelopment in the headers and within HX core.

‣ Novel aspects: Modular HX architecture that permits

– Counter flow heat exchanger, including in headers

– Low pressure drop on hot (low pressure drop) side

‣ Anticipated performance metrics: see Table

‣ Projected cost: TBD, will derive from process based cost model (PCBM)

3

Metric State of

the Art

Proposed

Heat exchanger

mass-based

volumetric density

5 MW/m3 8 MW/m3

Hot side inlet

temperature

< 800 °C Aiming for

850 °C

High Temperature

(850 oC) Ultimate

Tensile Strength

Alloy 625

UTS ~100

MPa

MHA-3300

UTS ~350

MPa

Materials

‣ Main material: MHA 3300, excellent creep

properties and known to be printable in laser

powder bed fusion systems.

– Alternative/backup: MAR-M247

‣ TRL for MHA 3300 is 3 (proof of concept)

– TRL for MAR-M247 is 9 (fully developed)

‣ Thermo-mechanical properties: see example

of creep curve.

4

Creep curve for printed MHA 3300 at 850 °C, 157 MPa

Manufacturing Process: LPBF

‣ We will manufacture our heat exchanger for this project using Laser Powder Bed Fusion (LPBF).

‣ Technology readiness level for LPBF is 9, e.g., for rocket engine components.

‣ Main characteristics: layerwise printing, 20 µm per layer. Advantages: near-arbitrary shapes possible, far more flexible than prior lamination technology

‣ Main anticipated challenges are: a) powder removal and b) avoidance of cracking during printing

‣ Mitigation: test 3 different technologies for powder removal and smoothing + use an alloy with excellent creep properties and known printability

5

The penultimate design, right, had an abrupt transition in

cross-section that caused thermal distortion and failure of the

build. The final design, left, had a transition in cross-section

that allowed it to build (very) successfully.

Penultimate

design

Final

design

Example of LPBF printed HXs from prior CMU-UCD project

Prior Experience in AM

HX Design and Expts.

• Small-scale (~1kW) AM HX

for high temperature waste

heat recovery using IN718.

• The HX design was for a

sCO2 working pressure of

200 bar and a flue gas

temperature of 550 °C.

Rasouli, E., Subedi, S., Montgomery, C., Mande, C.

W., Stevens, M. M., Narayanan, V., and Rollett, A. D.,

(2018) “A primary Supercritical CO2 heat exchanger

for waste heat recovery”, Paper 38, 6th International

sCO2 Power Cycles Symposium

ST

EE

L-

Sup

erc

ritical C

O2 T

he

rmal

Energ

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nha

ncem

ent

Labora

tory Existing

capabilities

Pressure and temperature testing

250 bar and 800 °C-static as well as cyclic; fluid used is pressurized nitrogen –no flow within HX channels

Thermofluidic tests

sCO2 is working fluid;

single side of HX at up to 200 bar; other side can be waste heat; with small modifications two sides of HX at equal pressures and heat loads up to 20 kW can be tested; inlet temperature to HX: 600 °C

sCO2 testing facility

Technology-to-Market Strategy

‣ The team will develop a process based cost model (PBCM) to assess the cost of producing the

HX by AM. The PBCM will be spreadsheet-based or use decision analysis tools such as Analytica,

which allow easy visualization and modification of how the different steps of a production process

link together, as well as the exploration of how uncertainty is propagated through the process. As a

baseline, a PCBM for micro-lamination approach for IN738 or MHA3300 will be developed with

assistance from our industry partner in the project.

‣ Plan to commercialize the developed technology: the team will identify potential customers and

potential fabricators (i.e., suppliers of printed parts).

‣ Approach to market: work with partner companies in CMU’s NextManufacturing Center, outreach

to other companies

‣ Anticipated first markets: transportation, electricity generation and industrial sectors.

8

Task Outline

‣ KEY TASKS, CHALLENGES

‣ Design of recuperator (HX) : 2 stages of capacity

‣ Choice of material: find an alloy that is printable (non-cracking) and has the

required high temperature strength

‣ Fabrication of recuperator components: 2 stages of capacity. Also test articles

‣Measurement of creep strength, corrosion

‣ Powder removal from internal passages + surface smoothing: 3 different

technologies

‣ Go/No-Go stages are based on the above

9

Anticipated Challenges and Potential Partnerships

‣ Risk of surface roughness causing too high pressure drop:

We will mitigate this by the planned inclusion of two different technologies for smoothing of internal

passages. A key design feature is to reduce pressure drop on hot side.

‣ The HX design is chosen for reduced pressure drop; an additional benefit of the design is

enhanced heat transfer coefficient. We will mitigate the risk in design by performing separate

effects tests on flow and heat transfer through diverging pin arrays.

‣ The risk of inadequate creep strength in the printed parts is challenging because of the absence of

an established superalloy with the required properties and available in powder form with recipes

for printing in standard machines.

We will mitigate via the novel MHA 3300 alloy and by researching LPBF approaches to M247.

‣ We have established several partnerships to address these challenges with powder suppliers and

with technology providers for internal smoothing.