Part 2: Hydrogen Turbomachinery Design
Hydrogen is attracting a lot of interest in different circles these days from: propulsion, to energy storage, to personal transportation. The most obvious benefit of hydrogen fuel is a total lack of...
Posts about Engineering
Part 1: Hydrogen and Turbomachinery
Because of its promise as a non-polluting fuel, hydrogen is currently a very popular topic among the energy and turbomachinery communities. If hydrogen is reacted with pure oxygen, the thermal energy...
Critical Speed Maps
This post is about one of the most useful design tools for rotordynamics of turbomachinery: The Undamped Critical Speed Map. A critical speed map can provide a great deal of insight on the potential...
Compressor Design : Axial, Mixed, or Radial?
With so many papers out there, I like to pass the word along when a particularly good one comes my way. My favorite paper for 2021 was titled “SELECTING A COMPRESSOR MERIDIONAL TOPOLOGY: AXIAL,...
Rocket Turbopump Development: Epumps, A Potential Propulsion Game Changer
Dave Japikse, the CEO/Chairman & Founder of Concepts NREC, speaks to e-pumps as a potential propulsion game changer, as well as ongoing rocket turbopump development and design considerations.
Which Type of Turbomachinery is Aerodynamically Easier to Design, a Compressor or Turbine?
In the world of aerodynamics, there are several branches and sub-branches of different types of aerodynamics. In the big picture the field of aerodynamics can be broken down into external and...
Heavy Interest in the Lightest Element: Hydrogen
It’s always interesting to look at the topics of my favorite engineering conferences and see what’s in vogue in a given year. What jumped out at me this year at the ASME TurboExpo was the hot topic...
Meet Claudio Raia
Dave Schowalter, Director of Global Software Sales, introduces you to Claudio Raia, our newest team member and the Managing Director of Concepts NREC Europe. Welcome Claudio!
To The Question of sCO2 Compressor Upstream Conditions Selection
The compressor is generally one of the most sensitive components of an sCO2 cycle. This makes it a challenge to design a robust compressor while keeping the thermodynamic cycle close to optimal.
Preliminary Design Considerations of Zero Reaction Stages in Turbines
Low reaction stages are often used as control stages of steam turbines, ORC turbines, drive and rocket turbopump turbines. Some of the benefits of low reaction stages vs higher reaction stages are:
How Does Rocket Engine Cycle Selection Impact the Design of the Associated Turbopump Assembly?
For lower thrust rocket engine designs, either a Gas Generator (GG) cycle or a Dual Expander (DE) cycle can be considered, among others. While each of these cycles has its inherent advantages and...
What Fluid Model Should I Choose?
When starting a turbomachinery design, the first choice an engineer has to make is the thermodynamic model. The actual fluid type (air, water, R1234ze, etc) is usually clear enough, but what model...
What’s the Difference Between ‘Preliminary’ And ‘Detailed’ Design, And How Do These Design Phases Fit Into Your Turbomachinery Design Project?
Whether it’s a compressor, turbine, or an entire rocket turbopump design project we are tackling at Concepts NREC, we typically divide the design project into three phases: (1) scoping or feasibility...
Why are Scoping Studies Necessary for Your Turbomachinery Project?
At Concepts NREC we do a lot of projects from ‘clean sheet’ all the way through manufacturing of prototype hardware. In fact, these types of projects are among the favorite of the engineering staff...
What’s So Hard About Designing A Pump?
Here at Concepts NREC, we work on a wide range of turbomachinery components designed for fluids ranging from gases to liquids, including supercritical fluids like supercritical CO2 which have...
Design Considerations for Turbo Expander Supersonic Turbines with Liquid to Gas-Liquid Flow Transition
A small turbine (for ORC, air liquification processes) , operating with low volumetric flows at inlet and significant pressure ratio in a single stage configuration (to reduce costs) is often...
Using an Economizer in Centrifugal Compressor Chiller Cycles
In the chiller industry, the evolution of centrifugal compressor chiller cycles has led to an interesting and powerful cycle and related compressor configuration which involves reinjection of...
Super Critical CO2 Compressor Design
Super critical carbon dioxide power (sCO2) cycles are attracting a lot of interest these days all over the world. Many initiatives using various levels of private and public funding are in progress...
Turbomachinery Design for Medical Devices Including Compressors, Fans, Blowers, and Pumps
Turbomachinery is used in a very wide variety of industries and applications. While applications like aerospace ‘jet engines’ or powerplant steam turbines are the applications that come to mind...
Flow Analysis of Multi-Staged Axial and Radial Turbomachinery
When designing a turbomachine, the best analytical approach is not necessarily the most accurate method possible, but the one that will generate the best candidate design in the time and budget...
Coupled Optimization of Preliminary Geometry of Two-Stage Low Flow Turbine and Regenerative Rankine Cycle Parameters (Part 2)
This blog article is a follow up for the earlier blog “Coupled Optimization of Preliminary Design Geometry of Low Flow Steam Turbine with Curtis Stage Layout and Rankine Cycle Parameters”, which...
Coupled Optimization of Preliminary Design Geometry of Low Flow Steam Turbine with Curtis Stage Layout and Rankine Cycle Parameters
Designing turbines for low flow Rankine Cycle for steam is challenging due to their small size, manufacturing restrictions, clearances and cost constraints. Such turbines operate at significant...
Coupled Optimization of Cycle Parameters and Preliminary Geometry of Turbofan Engine
In many instances, the design of new turbofan engine is an iterative process of optimizing engine cycle parameters (i.e. thermodynamics) and executing preliminary design geometry of engine...
Putting Entropy to Work
The previous blog, Entropy Happens… Deal with It! ended with the statement, “That’s how Concepts NREC deals with the constraints of the Second Law of Thermodynamics when designing high-efficiency...
Entropy Happens… Deal with It!
If there’s one thing good about sitting in snarled traffic in Boston, it’s that you get to see some very original bumper stickers. The most recent bumper sticker I saw was probably the strangest one,...
Supercritical CO2, CFD, Alligators & Gladiators – Thoughts & Trends from Turbo Expo 2019
I recently got back from my favorite annual conference: ASME’s Turbo Expo. This year, someone thought it would be a good idea to hold it in Phoenix, Arizona…in the summertime. While that’s not the...
In Thermodynamics: “What Goes Around-Comes Around” is a Good Thing
When discussing the efficiency of transforming one form of energy to another, circularity is the way to go. Anyone who has spent even a little time studying engineering thermodynamics knows that the...
Abstracts From Papers Presented at Turbo Expo 2019
Wow, Concepts NREC had a lot going on at this year's ASME Turbo Expo 2019 in Phoenix, AZ! We held our North American CAE User Group Meeting, spoke to over 200 people at our booth, chaired several...
Top Summer Vacations for Turbomachinery Engineers
Summer is almost here, at least in my hemisphere, so here are some of the best places around the world people in the turbomachinery industry might find interesting! Know of another? Share your...
What’s the Difference Between a Fan, a Blower, and a Compressor?
Turbomachinery equipment is generally segmented based on whether it extracts energy (e.g., turbines) or adds energy (e.g., pumps and compressors). The addition of energy is usually used to compress...
How to Design a Wind Turbine Rotor
In my previous blog post, “How the Design of a Wind Turbine Differs from other Types of Turbines”, I showed that the very small pressure drop across the rotor makes wind turbine design different from...
The Ultimate Fluid Model: Non-Equilibrium Modeling
In this blog series, I covered a lot of thermo-fluid options in engineering analysis, from the simplest perfect gas (When Perfect is Good Enough – Perfect Gas Models) and ideal liquid, (Fluid...
The Tesla Turbine – A Solution Looking for the Right Problem
The great engineer, Dr. Nikola Tesla, is best known for his work with alternating current (AC) electricity, but, did you know that he patented a bladeless type of turbomachinery in 1913? Called the...
Fluid Modeling: Liquified
Continuing on the topic from my previous blog, Getting Real – Advanced Real Gas Models, the counterpart to the perfect gas model for liquids is the “ideal liquid” model. The ideal liquid model is...
Getting Real – Advanced Real Gas Models
The Refprop program The calculations in the National Institute of Standards and Technology (NIST) Refprop program are generally considered the most accurate thermo-fluid models available. The...
Going Through a Phase – Modeling Phase Change with Cubics
When fluids undergo a phase change (see Phase Change - Make Mine a Double), it typically has a very significant effect of the flow behavior and energy level of the system. Some examples of this are:...
What do Undergraduates, a Chimney, Renewable Energy and an Open Pit Mine Have in Common?
It sounds like an opening to a joke, but I wanted to share some creative thinking sparked during a field trip to a local gas turbine cogeneration plant with some undergraduate students I teach. The...
Simple Stall - Video Blog - Part 2
Our CTO, Mark Anderson, takes a fundamental look at simple stall and its impact on turbochargers stability and range. This is the second video in this 2-part series. Be sure to watch Part 1 first!
Simple Stall - Video Blog - Part 1
Our CTO, Mark Anderson, takes a fundamental look at simple stall and its impact on turbochargers stability and range. This is the first video in this 2-part series.
Performance Corrections for Compressor Maps
Turbomachinery performance is almost always analyzed and tested with a fixed inflow condition. In other words, the assumption is that the inflow fluid temperature and pressure is defined and...
Water & Turbomachinery - Two Great Things, That Go Great Together
I work with water a lot here at Concepts NREC. Water is frequently the fluid that flows through various types of rotating equipment we design to either release or store energy. Mankind’s fascination...
What's Better than Perfect? Semi-Perfect Gas Models
In a previous blog, Fluid Phenomena Primer: Energy Versus Temperature, Specific Heat, I explained the behavior for gas phase fluids and how the temperature is affected at high energy levels. In...
How the Design of a Wind Turbine Differs from Other Types
Wind power generation is rapidly growing worldwide, and with that growth, demand for wind turbine design engineers is also growing. However, an engineer who has experience designing turbines in most...
Phase Change - Make Mine a Double!
As I’ve always said, there’s as much thermodynamics in a glass of beer, as there is in a power plant. Don't believe me? Read on. Phase change is common phenomena that we see all the time. We’re most...
When Perfect is Good Enough - Perfect Gas Models
What is a perfect gas? A perfect gas is one that has a linear variation in energy with respect to temperature and a linear variation in pressure with respect to temperature at constant volume. The...
Fluid Phenomena Primer: Energy Versus Temperature, Specific Heat
As one might expect, the temperature of a substance typically increases as energy is added to it. This is the case with most substances in all phases. The exception is when a substance crosses to a...
Increases in Temperature Envelopes and Its Implications on Material Selection
Temperature envelopes in the turbomachinery industry are constantly increasing as the state of the art evolves in pursuit of better performance. This means engineers need to design compressors with...
Does Meanline Design Still Make Sense in the Era of CFD and Optimization?
PCs and workstations are getting faster every year, following Moore's Law. With all this power and speed, the “virtual prototyping” of turbomachinery, using CFD simulations and optimization...
Specific Speed Performance Effects
In my last blog, Specific Speed Demystified, I covered the mathematical definition of specific speed and how it relates to flow and work coefficient. The concept of specific speed has been a guiding...
Specific Speed Demystified
In my blog Flow Coefficient and Work Coefficient, I outlined the basic concept behind the flow and work coefficient. These nondimensional parameters are widely used to characterize axial and radial...
Engineering Resolutions for 2019
I am an engineer and teacher, so as the year draws to a close, I like to look back on memorable events where an engineering activity went, or almost went, awry. Luckily all were caught in the nick of...
The Wright Stuff for Turbomachinery
As an engineer, you probably have at least some familiarity with the story of how two bicycle mechanics, named Orville and Wilbur Wright, invented controlled-powered flying machines at Kitty Hawk,...
Reverse Engineering - Going from Part to Art
Have you ever needed to know the exact geometry of a compressor that has been running for years in your process plant? Perhaps you need to analyze how it would perform if the process fluid had to be...
Radial Compressor Geometry Primer - Video Blog
Below is a 4 minute video blog from Mark Anderson, Concepts NREC's Chief Technology Officer, on the geometry of radial compressors. In it, he details the various parts of the compressor wheel,...
20 Great Gifts for Engineers from $10 to $2 Million
Gifts for Engineers can usually be segmented into a few categories: Things you have to put together, science fiction, gaming, new technology, and witty phrases printed on stuff. A Google search of...
Site Selection for Low- and No-Head Hydroelectric Pilot Plants
According to the 2014 Oak Ridge National Laboratory study on untapped hydro-power potential, there is nearly 65 GW of untapped power in America’s waterways. The vast majority of this power remains...
Material Properties - What Really Matters?
As an engineer in the rotating machinery world, it is my job to design things that work for a very long time. To help ensure this, we have evolved the best analytical tools to calculate the stresses...
Splitter Design for Radial Compressors - Video Blog
Below is 3 minute video blog from Mark Anderson, Concepts NREC's Chief Technology Officer, on splitter design for radial compressors. Click on the small thumbnail image below to launch the full-size...
Why are Turbine Blades Twisted?
It’s a straightforward question, but many turbomachinery engineers can’t easily explain the physics behind blade twist. Some shorter high-pressure turbine (HPT) blades appear nearly 2D in shape...
Extending the Operating Range of Centrifugal Compressors
Extending the operating range of centrifugal compressors has been a highly sought-after goal for several decades. In fact, the potential benefits have motivated researchers to develop and put into...
Designing Turbomachinery is like Solving a Rubik's Cube
I think we can all agree that designing turbomachinery is hard. There are just so many moving parts (pun intended) in the design process, and they are all interconnected. When you change the blade...
Trends in Composite Materials for Turbomachinery Applications
The advancement of composite material technologies over the past few decades has contributed to their widespread use in a vast array of aerospace applications. Most applications target weight...
Using Curvature Smoothing for Quality Reconstruction of Blade Sections Using Surface Data Tables
Frequently, there is a need to reconstruct 2D and 3D geometry from reported or measured surface data points. In most cases, the provided surface data include significant amounts of noise for various...
Early Water Handling
I am fascinated by ancient cultures. After my recent visits to Roman ruins in Central Europe (see A Turbomachinery Engineer's Summer Vacation), I began to wonder how far back mankind’s mastery of...
Yellow Ropes
In the mid 1980’s, while serving in the Canadian Air Force, I had the good fortune, on one of my many adventures, to fly into Sondrestrom Air Base in Greenland. The Base is at the head of a beautiful...
A Turbomachinery Engineer's Summer Vacation
This year's ASME Turbo Expo in Norway inspired me to tack on a vacation to explore European cities on my bucket list. Being an engineer, and student of ancient cultures, part of my trip included...
The Slip Factor Model for Axial, Radial, and Mixed-Flow Impellers
Ideally, the exit flow angle for an impeller should be the same as the exit blade metal angle. However, the exit flow angle deviates from the blade guidance at the impeller exit due to the finite...
Engine-Driven Compressor for Maintaining Aircraft Cabin Pressure
Commercial and military aircraft require that preset levels be maintained for aircraft cabin pressure, airflow, temperature, and humidity — regardless of flight altitude and aircraft speed. To...
Avoiding the "Bad Day" in Aerospace
The AS9100 Certification identifies companies who have qualified to manufacture products for the Aerospace Industry. Manufacturers who meet the extensive requirements of the AS9100 Certification...
What Is Pogo and Why Is It Bad For Rockets?
Space launch vehicles can exhibit self-excited longitudinal oscillations, also known as “Pogo” — so named because the phenomenon vibrates the rocket up and down in a manner similar to bouncing on a...
An Initial Look at Conical Diffusers in Turbomachinery Design
Perhaps the most common type of diffuser in turbomachinery is the conical diffuser. This diffuser is found at the exit of every volute as the geometry transitions to the exit flange. This conical...
A Small Taste of Two Papers from Turbo Expo 2018 in Norway
The 2018 ASME Turbo Expo in Lillestrøm, Norway was, as always, a smorgasbord of papers and presentations on the latest and greatest ideas in turbomachinery and gas turbines. Two of our favorites...
Lessons Learnt
Yes, you read that right. Learnt. It’s in the dictionary; look it up if you don’t believe me. I believe it’s one of those words that came over on the Mayflower and found its way into Webster’s early...
Film Cooling In Turbines
Turbine inlet temperature is one of the most critical parameters in the Brayton cycle of gas turbine engines. One way to increase the cycle efficiency is to increase the turbine inlet temperature, as...
Is Laboratory Testing Still Needed for Turbomachinery Development?
Historically, testing has played a critical role in the turbomachinery design process and multiple rounds of “design, test, analyze, repeat” were not uncommon. Today however, the industry seems to...
Is the Supercritical Carbon Dioxide Market Reaching Critical Mass?
There is obviously a huge amount of interest in Supercritical Carbon Dioxide (sCO2) within the energy industry. One reason is because sCO2 Brayton power cycles operate in the same way as other...
Preliminary Sizing of Supersonic Turbines with Partial Admission for Best Performance Using AXIAL™
Many energy recovery, drive cycles (Organic and Steam Rankine cycles) and rocket propulsion cycles require the use of a turbine that operates at low volumetric flow and high-pressure ratio....
Reverse-Brayton Cryocoolers
Perhaps it is because Spring is so slow to come this year, but I have been thinking a lot about refrigeration and the different types of systems there are. Refrigeration systems that operate below...
Optimizing the Radial-to-Axial Duct Geometry for a Gas Turbine Radial Compressor Impeller
Many gas turbines with radial compressors utilize a radial-to-axial inlet duct upstream of the first compressor stage. Aside from the fact that flow in the duct generates aerodynamic losses, the flow...
Electric Pumps for Space Propulsion
The recent success of Rocket Lab, putting small satellites into orbit with its Electron rocket, is a significant milestone in the evolution of space flight. The Electron rocket is powered by a set...
Flow Coefficient and Work Coefficient Applications
In my last blog, I explored the concept of the flow and work coefficient. In this blog, I will explore the practical application of the two parameters in machine selection and optimization.
Flow Coefficient and Work Coefficient
Two often used quantities to characterize turbomachinery are flow coefficient and work coefficient. The two are generally represented as Φ for flow coefficient and φ for work coefficient. The...
What is a Consortium, and Why Would You Join One?
Merriam-Webster’s definition is, “an agreement, combination, or group (as of companies) formed to undertake an enterprise beyond the resources of any one member.” The word is Latin, derived from...
Reaction Versus Impulse Type Turbomachinery
The universe of turbomachinery consists of many different design concepts that are radically different from one another. Each class of machine has a particular flow and power range that is best...
The (Contemporary) Art of Engineering
Boston, MA is known as a walkable city. Boston’s downtown area is very small, relative to those in other cities. However, the walkable size provides you with a special opportunity to explore the many...
Optimizing the Screw Inducer for a Pump
High-efficiency, low-cavitation pumps often require a screw type inducer to treat the inflow to the main radial/mixed flow pump blades. Efficiency and head rise, split between inducer and main pump,...
Leveraging Your Legacy Designs
Engineers, by their very nature, like to design new things. To us, there is an undeniable appeal to creating something no one has ever seen before. However, there are compelling reasons to leverage...
Compressor Design: Influence of the Impeller Exit Blade Angle
During the compressor design process, one of the key optimization steps is to adjust the impeller exit blade angle with the goal of achieving the desired pressure ratio, efficiency and range. When we...
A New Application for Air Brake Dynamometers?
My gym has been crowded with a lot of new people these past couple of weeks. It happens every year in January as people try to stick to their New Year’s Resolution to exercise more. I don’t mind the...
The 5 Why's - A Tool for Effective Problem Solving
A challenge in the engineering profession is that we, too often, look at complex problems as requiring complex solutions. As an example, a customer recently asked Concepts NREC to perform a very...
Robot Engineers?
Wouldn’t it be ironic if the profession that is creating all the robots was eventually replaced by them? It could happen. Engineering is all about applying laws, measurements, facts, and analysis to...
Vibration and Resonance Issues in Turbomachines
Structural vibration is a natural phenomenon exhibited by all structures, by virtue of simply possessing mass and having an associated structural stiffness. Thus, any structure or assembly of...
Getting Carried Away (Literally) with a Hobby - How I Ended up with a Helicopter
How did I get from not knowing (or caring) anything about home-built aircraft to owning a gas turbine powered helicopter? As you might imagine, it’s complicated.
Ground Source Heat Energy Storage for Power Generation
Have you ever been to the beach on a very hot day? Then I am sure you noticed that the sand is very, very hot, uncomfortably so. Congratulations, you have had first-hand experience with ground source...
When the Dream Turns Into a Nightmare: Resilient Power for Island Economies
Who has not dreamed of living on an island? You’re getting away from it all, walking alone along a secluded beach, as the ocean gently laps at shore…ahhhh. Excuse me – I have to go search for...
Off-Highway Turbochargers
The turbocharger is a very mature device that has been refined over the past 100+ years to achieve the right compromise between competing requirements. Efficiency, boost pressure, and range are all...
Full Disclosure on Non-Disclosure Agreements
If you are working in a technical field as an engineer, and odds are you do, if you are reading this blog, then you have almost certainly come across a few Non-Disclosure Agreements (NDAs). You have...
We Are All Being Robbed! Some Thoughts on Energy Heat Recovery
There are not many people who would argue that if you only received 30% of a commodity that you need to purchase every day to enable you to have your share of “…life, liberty and the pursuit of...
What Next for Wider Flow Range Centrifugal Compressors?
Flow range is an essential consideration in the design of any centrifugal compressor system, regardless of the application. Adequate flow range is necessary, not only to assure that various...
Getting your Bearings – Challenges of Selecting the Right Bearing for the Job
Bearing selection is an interesting concept. Can you really select the bearing – or does the bearing select you? It seems that we have come to understand where to use bearings by where they have been...
Protecting New Ideas: Navigating the Corporate IP Landscape of Today
An engineer named Victor makes a few final adjustments to his novel radial compressor design just before midnight. With a deep breath, he clicks the “Save” button and pushes back from his desk. He...
Measuring Aerodynamic Blockage
Aerodynamic blockage is a comparatively simple parameter to measure and reveals important aerodynamic performance data. Aerodynamic blockage is directly related to the displacement thickness concept...
When and Why You Should Hire an Expert
Every company in the turbomachinery industry needs robust technical expertise to survive in this very mature business. Whether you make a rotating component or use one in a product, your in-house...
Important Considerations When Designing a Volute
When designing a new compressor or pump, most of the focus is put on the impeller and diffuser because they are the elements that are responsible for the work input and its conversion from kinetic...
Design Tradeoffs and Compromises in Integrally Geared Turbomachinery
When designing turbomachines, the quality of the final product can often be improved by implementing a holistic approach to the engineering process. As with many complex mechanical systems there are...
How to Design a Pump for Reduced NPSH
Cavitation occurs in a pump when the bulk liquid pressure starts to approach the vapor pressure of the liquid, and cavities of vapor form as seen in Figure 1. This figure shows the inlet of a...
Turbomachinery is the Key for Sustainable Development
While common sense might lead one to conclude otherwise, increasing energy consumption worldwide is a good thing. Higher per capita energy consumption is associated with a higher quality of life:...
Converting Chiller Compressors to the New Generation of Low GWP Refrigerants
The chiller industry is under tremendous pressure to convert to new, more environmentally friendly refrigerants. This change is driven by new global regulations including, the Montreal Protocol and...
Multidisciplinary Optimization of Turbocharger Turbine with Non-Radial Blades for Two Operating Points
The turbine of an automotive turbocharger is subject to a wide and demanding range of requirements and constraints. High efficiency is required to reduce the pumping work of the engine that can make...
A Cross-Over SCO2 System Application
The 2015 Paris Climate Talks (COP21) were successful in achieving consensus from 196 countries that climate change must be given significant attention. There was a particular focus on the release of...
Turbocharger Market – Is There Room for Growth?
The recent announcement that Bosch Mahle Turbosystems is up for sale demonstrates just how difficult it is to succeed in the mainstream turbo market that is already served by very well established...
How Manufacturing Methods Impact Performance 3 Examples
Some of my other blogs have touched on how important it is to consider manufacturing methods during the design phase. This one will show exactly how manufacturing methods impact performance. We will...
Designing Gas Turbines - It Really Requires Rocket Science
Engineers who design aircraft engines face a conundrum. Gas turbines in aircraft engines have to operate at very high temperatures for thermal efficiency and power output. These high temperatures put...
Current Issues Facing the Global Pump Industry
The Global Pump Industry
Sysyphean Task of Energy Storage
Sisyphus in Greek Mythology was condemned to eternally roll a large rock up a hill only to watch it crash to the bottom. The myth lives on today with the term Sisyphean that refers to tasks that are...
Extremely High Suction Performance Pump Inducers
The path to better operation stability and robustness High suction performance pump inducers are critical to important industrial and advanced aerospace applications where the required inlet pressure...
The CN300: Converting Low Temperature Heat to Electric Power
Concepts NREC introduces licensing for its new compact, high-speed, hermetically sealed turbogenerator. Nominally rated for 300 kWe, the CN300 is designed for converting low temperature heat to...