Magnet for Stirling Cooler (FPSC) – Fast & Deep Freezing
Free Piston Stirling Cooler is a kind of Magnetic Levitation Cooler. It is widely used for precise temperature control for under -100℃.
This is the Stirling Cooler, which we refer to as FPSC (Free Piston Stirling Cooler). The default version of Stirling coolers includes pistons, heat exchangers, and compression spaces. But we are seeing the technology advancements in all industries, and Stirling refrigerators aren’t an exception.
The Stirling Cooler use Helium as a gas, which differs from a compressor, is a cooling system continuously repeats gas compression and adiabatic expansion and uses naturally helium gas as the refrigerant. Helium is a very safe gas. It is entirely harmless to our environment.
The typical use of our Stirling Cooler is deep temperature refrigerators, freezers, but RIGID is also developing a product lineup for use in laboratory equipment, and other equipment used for low temperature distribution of goods.
RIGID, one of the leading Chinese companies in terms of innovation, designed a free piston Stirling cooler – FPSC. The unit takes the entire product to a whole new level where it can save a lot of energy and significantly improve efficiency.
Thanks to that, these units are eco-friendly solutions suitable for all those individuals and corporate clients who want to demonstrate their care for the planet. The new cooler doesn’t contain any CFC, and it is interesting to note that the role of coolant was taken by helium. It is even more impressive that FPSCs use doesn’t need a big amount of helium – it is a small quantity that can do the cooling.
What Is a Stirling Cooler?
The Free Piston Stirling Cooler (FPSC) is an elegant, completely sealed heat transfer system that has only two moving parts (a piston and a displacer), and which can use helium as the working fluid without concern about seal leakage.
The piston is typically driven by an oscillating magnetic field that is the source of the power needed to drive the refrigeration cycle. The magnetic drive allows the piston to be driven without requiring any seals, gaskets, O-rings, or other compromises to the hermetically sealed system.
Claimed advantages for the system include environmental friendliness, cooling capacity, lightweight, compact size, precise controllability, and high efficiency.
Stirling coolers are nothing but cryocoolers that use a Stirling cycle to work. These cooling systems function as standalone units, and you can find them in various sizes.
In most cases, Stirling coolers are tabletop models that can cool down different objects and items to cryogenic temperatures.
Free piston Stirling coolers use a Stirling engine, which has only two parts that move. The unit has a casing made of stainless steel, and all sensitive components are hermetically sealed inside.
Biotech/Pharmaceutical – you can use low temperatures for maintaining chemicals and other pharmaceutical products, including vaccines.
Energy/Chemical – you can create a cryogenic environment and analyze and inspect different chemicals and test reactions of chemicals.
Metrology – if you need to maintain precise temperature, and keep it at the desired low level, these units are the right choice.
Foods/Logistics – if you are doing food delivery, you can keep the food refrigerated to maintain its freshness and deliciousness. Additionally, Stirling coolers can be used in portable freezers.
Medicine/Vaccine – you can use Stirling Cooler for compact and deep freezer. The lowest maximum temperature can reach minus -100℃.
How Does Free Piston Stirling Cooler Work?
Since Free Piston Stirling Coolers (FPSC) are new and revolutionary units, you are probably wondering how they work. Here is a quick explanation.
You have the main body with a fin or cylinder protruding from it. The product uses a heat exchanger to cool the cylinder down. The heat exchange involves repeating compression cycles.
The main body also contains a piston that moves up and down continuously. The material of choice for these pistons is usually stainless steel. The moving of the piston combined with the compression leads to a gas explosion.
The upper compression chamber of the cooling system contains two pistons and balancing floats. The manufacturer uses helium gas to fill the chamber, and a linear motor to drive the piston.
The driving action transfers helium to the 80Hz balancing float. The system can control the difference in temperature at 80C.
You will also find an expansion space on the top of the balancing float. At the same time, compression space is between the piston and the float for balancing. Finally, a helium gas flow channel is the annular space that surrounds the balancing float.
Now, let’s focus on the flow passage. In the expansion space, you will find a cold side cylinder (fin), and the compression space is where the designers put the heat sink. You will also find a regenerator in the space between the heat sink and the cold cylinder fin.
Why would you need a regenerator? The idea is to ensure helium’s heat exchange, as well as capture that heat, store it, and return it to the helium gas.
In case there is something unclear, you can check out the photo above. The picture clearly explains the working principle of a Stirling cooler engine, and you can use it to understand previous paragraphs better.
Here is another photo that can better explain the working principle of a free piston Stirling cooler. It is a 3D image of various components included in the FPSC.
The piston driving frequency is approximately 80Hz. The piston motion creates a pressure differential that drives the displacer.
That differential goes through the refrigerant because it needs to keep a certain phase angle of the displacer to the piston.
In essence, the refrigerant is expanded and compressed by the linear motor that drives the piston. Thanks to that, you have an expansion (cool) space and compression (warm) space. That is the basic explanation of a Stirling cycle.
What makes a free piston Stirling cooler unique? The fact that Rigid added a feature that piston does not have to be physically connected with the displacer. Instead, it has the freedom of moving independently.
A detailed description of the ideal Beta machine cycle is presented in the Engineering Thermodynamics – Chapter 3b web resource. Refer also to the animation of the Beta machine by Matt Keveney – Single Cylinder Stirling Engine, showing clearly the principle of operation.
Apart from Stirling’s original engine, an important early Beta engine is Lehmann’s machine on which Gustav Schmidt did the first reasonable analysis of Stirling engines in 1871. Andy Ross built a small working replica of the Lehmann machine, as well as a model air engine, both based on single cylinder Beta configurations.
Rolf Meijer of Philips, Holland, developed his famous vibrationless rhombic drive Beta engines in the early 1960s. A detailed description of this engine can be found in the Beta model Stirling engine website by Pierre Gras. In 1965 the General Motors Research Labs developed a 7.5kW rhombic drive Stirling engine/generator set GPU-3 (Ground Power Unit) for the US Army. It is described and analyzed in the book by I.Urieli & D.M.Berchowitz – Stirling Cycle Engine Analysis (Adam Hilger, 1984), pages 30 – 40, and since this book is out of print, these pages have been added here for convenience: Rhombic-GPU-3.pdf.
Free Piston Stirling Engines
Probably the most ingenious Stirling engines yet devised are the free-piston engines invented and developed by William Beale at Ohio University in the late 1960s. Legend has it that while teaching about the rhombic drive engine he suddenly realized that “this engine will still run if we simply throw away this complex drive mechanism – Eureka!”. He then formed the company Sunpower, Inc., which has been the leader in the development of free-piston Stirling engines and cryocoolers to this day. Most of Sunpower’s engines are Beta arrangements and employ no mechanical linkage system. The main aspect of the free piston machine is that the output power can be obtained through a linear alternator, allowing the entire system to be hermetically sealed. In fact, this is the only Stirling configuration to reach commercialization in any numbers. This is mainly because it avoids the fatal flaws of the crank, proven again and again over the years to be near-insurmountable – sealing and lubrication.
Can an FPSC Cool Down Items Effectively?
Are you wondering if the Free Piston Stirling Cooler is capable of cooling items effectively?
The answer is yes, but it is important to make sure that heat exchange is one of the features offered by the product’s thermal receiver. It is the way how FPSCs manage to cool down objects near them.
Now that we established how Stirling coolers cool down objects, let’s talk the effectiveness. It may depend on the unit, but the FPSC designed by Rigid needs only two minutes to reach temperatures as low as -80C. We are talking about an environment where the no-load temperature is 25C.
If you want to see the Free Piston cooler designed by Rigid in action, we suggest checking out this video. It is beta testing of the product where the object that the unit cools down reaches -114C.
Who Is the Company Behind the Free Piston Stirling Cooler?
As early as 8 years ago, RIGID has secret research agent in this deep freezing industry. Ever since day one, the company dedicates maximum effort to come up with innovative miniature compressor solutions. The primary idea behind their unit is innovation.
The company is trying to combine an effective solution designed in a portable and compact package. The idea is to reduce the size of cooling units as much as possible while keeping their performance at the highest level.
Rigid uses modern approaches and technologies and utilizes creativity, skill, and knowledge of its engineers to design unique and customized solutions for many applications. The company searches for an ideal ultra-freezing solution. Thanks to that approach, Rigid managed to come up with FPSC units that have versatile uses.
These units have been designed after more than a decade of innovation, leadership, and evolution in developing miniature DC compressors.
Some of the potential applications of DSPCs include home refrigeration, biotech, and pharmaceutical industries.
An extremely interesting free piston engine system developed by William Beale is the free-cylinder water pump. In this engine a heavy internal mass provides the reaction force driving the cylinder which is directly connected to the water pump. It has built in power adjustment and responds to load automatically. All other engines require a transmission and complicated control mechanisms to do this. Furthermore, there is no other mechanical heat engine that I know of that operates from infinite load to zero without either stalling or destroying itself.
Is FPSC a Better Choice Than Compressor Refrigerator?
The short answer is yes, but we always like to explain the issue in detail.
The compact size is the first reason why free piston Stirling coolers are better than cooling systems that utilize vapor compression.
Apart from the small size, you can also expect the system to be lightweight. Thanks to those two characteristics, you will essentially get a portable cooler that you can effortlessly transfer from one location to another.
The overall weight of the complete Stirling Cooler is 4.41 pounds (2 kilograms), which is quite impressive. You can better understand how light this cooling unit is if we tell you that a normal compressor weighs five times as much.
Even if you neglect the obvious sizing advantage, FPSC is better than vapor-compression systems because they are a more efficient solution. Thanks to higher efficiency and better use of energy, they also manage to be eco-friendly.
Additionally, the working fluid of FPSC is helium gas, which is also a positive thing for the environment. Many other cooling solutions utilize R134a and other solutions, which can have a high potential for global warming.
What Are Applications for Free Piston Stirling Cooler?
Here are some suggestions of different ways of using FPSCs:
Direct cooling with conductive connection
Direct cooling with brine
Direct cooling with thermosyphon
Now, let’s take a look at some industries where you can use these units:
Biotech/pharmaceutical – you can use low temperatures for maintaining chemicals and other pharmaceutical products, including vaccines. Freeze drying, preventing byproduct formation, and even cryopreservation are also potential uses of a Stirling cooler.
Energy/chemical – you can create a cryogenic environment and analyze and inspect different chemicals. You can also use the environment created by FPSCs to test reactions of chemicals.
Metrology – if you need to maintain precise temperature, and keep it at the desired low level, these units are the right choice.
Foods/logistics – if you are doing food delivery, you can keep the food refrigerated to maintain its freshness and deliciousness. Additionally, Stirling coolers can be used in portable freezers.
Vaccine/Medicine – you can use Rigid Stirling Cooler for compact and deep freezer. The maximum lowest temperature can reach minus -100
FPSC Stirling Cooler
These applications are merely some suggestions how you can use a free piston Stirling cooler. It is an extremely versatile cooling system that you can use virtually anywhere.
The only important thing is that you need to achieve and maintain an ultra-low temperature of an item, substance, or object. The Stirling cooler will take care of the rest.
Is It Hard to Maintain FPSC?
No, it is not difficult to maintain these cooling units at all. Furthermore, Rigid made maximum effort to ensure the maintenance is effortless.
First of all, FPSC systems are oil-free. That will eliminate the risk of leaks, and make taking care of the unit easier. It also means that free piston Stirling coolers virtually do not require any maintenance.
They are long-term units that will last for years, and during all that time, you don’t have to put it any effort to maintain their longevity. The only thing you should do is to enjoy fast and efficient cooling!
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