Turboexpander: Alternative Fueling 

Concept for Fuel Cell Electric Vehicle 

Fast Fill

Matthew Post (PI) and Daniel Leighton

National Renewable Energy Laboratory

April 30th, 2019

DOE Hydrogen and Fuel Cells Program 

2019 Annual Merit Review and Peer Evaluation Meeting

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

Project ID # H2039 
NREL | 2

Overview

• Project start date: 10/01/18

• Project end date: 06/01/19

• Total project budget: $225K

– Total recipient share: $125K

– Total federal share: $100K

– Total DOE funds spent*: 

$75K

* As of 3/01/19

• Other Fueling Site/Terminal 

Operations 

• Reliability and Costs of 

Gaseous Hydrogen 

Compression

Timeline and Budget Delivery Technical Barriers

• Toyota Motor Sales

• Honda R&D Americas, Inc.

Partners
NREL | 3

Relevance: Problem Statement
NREL | 4

Relevance: Hydrogen T-S Diagram

Isentropic compression of volume “a”

Isenthalpic 

expansion of 

volume “b”

Interim state 

at 200 bar

Final state 

at 800 bar

°K

(107 °C)

(27 °C) Initial state 

at 100 bar

Heating of volume “a” and “b” are depicted on a T-S diagram, volumes 

will mix in the cylinder resulting in temperature which is “average” of 

the two volumes (mixing rate will depend on turbulent velocity)

Source: “Selected Cryogenic Data 

Notebook, Section III Properties of 

Hydrogen”, Jensen et. al., BNL 

10200-R, Revised August 1980
NREL | 5

Relevance: Joule Thomson Expansion

• Joule Thomson coefficient is 

negative when operating within 

the pressures and temperatures 

experienced at a hydrogen 

dispenser (μ<0)

• Negative Joule Thomson 

coefficient will result in heating 

of the hydrogen across an 

isenthalpic expansion (control 

valve)

• Joule Thomson Effect Definition 

(Encyclopedia Britannica): “The 

change in temperature that 

accompanies expansion of a gas 

without production of work or 

transfer of heat.”

-40°C (233°K)

85°C (358°K)

850 Bar

H2 Dispensing 

Operating Envelope

The blue box in the chart represents the range of 

temperatures and pressures in a hydrogen dispenser. 

Hydrogen is completely outside of the box which 

means a control valve will only heat the gas.
NREL | 6

Relevance: Temperature Rise Effects –

Comparison to CNG Compression Heating

CNG fast fill fueling shows a temperature rise under most conditions 

even though methane has a positive Joule Thomson Coefficient 

(i.e. cools as it expands through the control valve)

Hydrogen will heat similarly as it compresses in a cylinder and will also 

heat as it expands through a control valve unless work is extracted.

Source: “Modeling the Fast Fill Process in Natural Gas Vehicle 

Storage Cylinders”, K. Kountz, Institute of Gas Technology, 1994
NREL | 7

Relevance: Isentropic Compression & 

Isenthalpic Expansion

Va, Pa, Ta Vb, Pb, Tb

Frictionless Piston

Isenthalpic Joule 

Thomson Expansion 

across control valve

Pa < Pb

Gas in the cylinder is assumed to be undergoing isentropic compression, 

while the gas entering the cylinder is undergoing an isenthalpic expansion

“Hydrogen Supply” “Vehicle Cylinder”
NREL | 8

Relevance: HyTransfer Fill Temperature

Initially, gas in the cylinder heats rapidly due to 1) high ∆P across 

throttling valve and 2) high ∆T of isentropic compression in cylinder
NREL | 9

Approach: Project Objectives

Drag Turbine Design/Build

• Proof of concept

• TRL 2 or 3

• Drag turbine type

• Efficiency is about 40% maximum

• Gas temperature can approach 

-40°C at the beginning of a fill

• Device is easier to manufacture

• Device is designed for testing 

proof of concept

• Built and tested at NREL

• Results and findings will be 

summarized in a report

Turboexpander Modeling

• Modeling will be integrated into 

NREL’s Frontier Fueling Model 

• A turboexpander plugin module is 

being created

• Module will include both drag and 

radial inflow turbine types

• Sizing data are being used to 

create the turboexpander module

• Module will be revisited after 

proof of concept testing

• Model will be used in further 

projects for sizing and design
NREL | 10

Approach: Turboexpander Concept

At worst case 40°C ambient temperature conditions, a 40% efficient turbine (in green) 

is capable of achieving -40°C precooled temperatures while the currently used control 

valve (in blue) heats the gas to more than 80°C at the point of expansion.

Temperature at the point of 

expansion as a fill progresses 
NREL | 11

Approach: Turboexpander Concept

Turbine energy can be recovered by coupling to an auxiliary compressor which may 

show system level improvements over an electric generator power recovery concept
NREL | 12

Accomplishments: Drag Turbine Selection

Blade Diameter = 0.75 inches

Spin Speed = 200K RPM

Using the NsDs turbine chart, a drag turbine design (circled) was 

selected for the proof of concept project

Three diameter sizes were overlaid on the 

selection diagram under the conditions 

Source: “How to Select Turbomachinery For Your Application”, that would be found in a dispenser

K. Nichols, Barber Nichols
NREL | 13

Accomplishments: Drag Turbine Sizing

• Inlet Nozzle

– Gas inlet speed needs to be 5x the tip velocity of 

the blade

– Nozzle sizes were identified and can be changed 

as needed

• Ball Bearings

– NREL is working with a ball bearing manufacturer

– Off-the-shelf bearings will be used and sent back 

for analysis

• Shaft Sizing

– Shaft diameter was calculated based on expected 

torque

• Housing Material Selection

– 1/8 Hardened Cold Worked 316L Stainless steel 

was selected

– Material is often used in high pressure hydrogen 

applications

• Machining Tolerance

– Critical tolerances will be machined to 0.002 inch 

tolerance

Flow path volume increases 

allowing expansion of the fluid

Flat blade design

Image Source: ”Study of Turbine and Turbopump Design Parameters. Volume II. A 

Study of High Pressure Drag Turbines Using Compressible Fluids. Final Report for 

Period February 1, 1958 through January 30, 1960”, R. Spies, Sunstrand Turbo, 1960
NREL | 14

Accomplishments: Drag Turbine Loading

• A turbine needs a load to function 

properly and can be removed as:

– Electricity

– Pressure

– Heat

– Motion

• The project utilizes a compressor 

wheel on the same shaft to add a 

load by building pressure.

• An electric generator load was 

considered, but a high pressure and 

high speed feedthrough is required 

and may be a future consideration.

Compressor Wheel

Drag Turbine Blade

Conceptual Design
NREL | 15

Accomplishments and Progress: Responses to 

Previous Year Reviewers’ Comments

• This project was not previously reviewed.
NREL | 16

Collaboration and Coordination

Institution Role

National Renewable Energy Laboratory

Matthew Post, Daniel Leighton

Project coordination, design/build and modeling of a 

turboexpander device, and testing the device

Toyota Motor Company Cost share partner for the design/build portion of the project

Honda R&D Americas, Inc. Cost share partner for the modeling portion of the project
NREL | 17

Future Work: Test Installation

Hydrogen Inlet

To Cylinders

To Vent

Expander Compressor

Stem Valve

Relief Valve

• The turboexpander device will use a compressor wheel on the same 

shaft as the turboexpander to supply a load.

• Both the expander and compressor sides of the device will be supplied 

with the same pressure to minimize cross flow of hydrogen.

• Valves on the outlet of the compressor side will control the load applied 

to the turboexpander and can be varied for testing.

Any proposed future work is subject to change based on funding levels.
NREL | 18

Future Work: Test Installation

• NREL will test performance of the 

turboexpander using the Flow 

Meter Benchmarking Apparatus.

• Equipment is rated for dispenser 

pressure and has pressure control 

valves found in dispensers.

• Test stand has temperature and 

pressure measurement at four 

points in the flow path.

• The cooled hydrogen fills into 

cylinders with temperature and 

pressure measurement capability.

Any proposed future work is subject to change based on funding levels.
NREL | 19

Summary

• A turboexpander is capable of cooling pressurized hydrogen 

gas as it drops in pressure from the station supply

• NREL was awarded a project under the DOE CRADA Call to 

investigate the performance of a turboexpander device

• NREL has designed and is building a proof of concept device 

• A drag turbine will be used in this project

• Test results will be published and will be used in future projects

• A successful project will bring the technology to TRL 2 or 3

• Separate FOA Project Awarded:

– NREL and SNL have partnered with Creare LLC for the 

design/build of a lab scale system validation device

– NREL will test the device and report on the results

– A successful project will bring the technology to TRL 4 or 5

Any proposed future work is subject to change based on funding levels.
www.nrel.gov

NREL/PR-5400-73527

Thank You

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable 

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Sandia National 

Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions 

of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s 

National Nuclear Security Administration under contract DE-NA0003525. Funding provided by U.S. Department of 

Energy Office of Energy Efficiency and Renewable Energy Fuel Cell Technologies Office. The views expressed in the 

article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and 

the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a 

nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or 

allow others to do so, for U.S. Government purposes.
Technical Back-Up Slides
NREL | 22

Concurrent Projects: Project Objectives

CRADA Call Project

• Proof of concept

• TRL 2 or 3

• Drag turbine type

• Efficiency is about 40% maximum

• Gas temperature can approach 

-40°C at the beginning of a fill

• Device is easier to manufacture

• Device is designed for testing 

proof of concept

• Built and tested at NREL

• Modeling at NREL will focus on 

system level integration

FOA Project

• Laboratory scale system validation

• TRL 4 or 5

• Turbine type to be determined

• Efficiency can approach 70%

• Gas temperature can be much 

lower than -40°C 

• Device is more complex

• Device will address issues of 

dispenser installation

• Built at Creare and tested at NREL

• Modeling at Sandia will focus on 

ultimate heating of the cylinder
NREL | 23

Concurrent FOA Project: Sandia Modeling

• MassTran tank filling model and previous validation efforts 

were reviewed

• Validation needs were assessed and was determined that the 

NetFlow wall conduction model needs to be added to 

MassTran

Left: Comparison of measured and computed gas mass-average temperatures. 

Right: Comparison of measured and computed interior wall temperatures.

MassTran, developed 

at Sandia National 

Laboratories, will be 

used to model the 

tank filling and will 

inform the 

turboexpander 

design efforts. 

Any proposed future work is subject to change based on funding levels.
NREL | 24

Concurrent FOA Project: Sandia Modeling

Comparison of measured and computed temperature 

(left) and pressure (right) for a maximum pressure of 

300 psi (top), 3000 psi (middle), and 6000 psi (bottom)

Next steps for Sandia 

turboexpander modeling

• Incorporate the wall heat transfer 

model into the MassTran package.

• Implement a method to select 

time steps needed to avoid 

temperature overshooting. 

• Repeat validation scenarios to 

ensure models can be used for 

temperature predictions during 

fast fillings.

• Validate MassTran using HySTEP

data, which consists of fast filling 

of hydrogen tanks.

• Simulate tank heating for 

turboexpander supplied hydrogen 

(transient temperature and 

pressure H2 entering tank). 

Any proposed future work is subject to change based on funding levels.