RE: CRYOGENICS & APPLICATION OF CRYOGENICS AS ROCKET PROPELLANTS
K. Pandu Ranga Vara Prasad
M.D.V.S. Nageswara Rao
CRYOGENICS.doc (Size: 1.06 MB / Downloads: 301)
Cryogenics is a branch of Thermal Engineering that deals with production and maintenance of very low temperatures for specific purposes. We discuss about the Definition, Application of Cryogenics, Cryogenic Propellants, Production of Cryogenic Propellants, Storage, Utilization, Safety and Cryo Engine specifications used in Rockets. In brief, we are introducing the concept of cryogenics and its technology considering Propellants as the basic application. Cryogenics is a new branch of engineering under Refrigeration, which has a vast area of application as we come to know about each under the discussion. It is basically about the liquifaction of the gases (permanent gases such as Hydrogen, Oxygen, Nitrogen etc.), which have boiling points well below the logical dividing line of –1800C (93.15K). Hence, all substances that deal with maintenance of very low temperatures, below the dividing line are termed as cryogenics.
Cryogenics by definition is that branch of Physics or Engineering that deal with the substances that need to be maintained at temperatures below that of the logical dividing line of –1800C (93.15K). It is the recent technological advancement in the field of Medicine, Aerospace, Metallurgy and Preservation of biological objects.
Classification of cryogenic substances:
Each cryogenic liquid has its own specific properties but most cryogenic liquids can be placed into one of three groups: Inert Gases, Flammable Gases, Oxygen.
• Under Inert cryogenic liquids we have Liquid Nitrogen (LN2), Liquid Helium (LHe).
• For flammable cryogenic liquids we have Liquid Hydrogen (LH2), Liquid Methane and Liquid Carbon-monoxide.
• We have supporters of combustion in cryogenic liquids too, we have Liquid Oxygen (LOX) under this category.
Cooling requirement of Cryogenics:
It can be achieved by mainly three methods,
• By Transfer of Heat
• By External Work
• By Isenthalpic Expansion
By transfer of heat:
Substances can be cooled to cryogenic temperatures by transferring heat from a cold gas stream by using flat plate heat exchangers. A matrix of flat plate and corrugated fins can be used for the construction of the Heat exchanger.
By External Work:
Adiabatic expansion of a gas in a turbine or reverse engineering as in case of a reciprocating engine can be applied to produce the required low temperature. Thus as it explains itself, we need a refrigerant which has a boiling point lesser than the required temperature as a working fluid to accomplish the same.
We are familiar with the Joule-Thompson effect. The working temperature and pressure must be well within the Inversion curve of the specified gas. However, this process is highly ideal, and its practicably too far from reality
Expansion system can be applied by the use of a Brayton cycle engine working under the reverse. A Turbo-Expander can also be used to accomplish the above same. A Linde's valve can be used for higher efficiency in cooling. It employs a Heat Exchanger, a Joule-Thompson valve and a compressor to achieve the cooling effect. Also a Claude cycle can be applied for the above same.
It has a vide area of application as mentioned above in various fields
1. In the field of medicine, it is used for cooling drugs and production of active ingredients for satin drugs at around –1000C.
2. In surgical instruments it is used to freeze knives, which help in freezing and clotting blood during surgery
3. It is used in mechanical manufacturing for changing the microstructure of components; by tempering, hardening, etc. this increases the strength of the components.
4. Metals treated with cryogenic products are used in Racing cars, Musical instruments, knives razor blades, brake rotors, etc. due to their high strength.
5. Soft and elastic metals become brittle on excessive cooling, thus cryogenics helps in machining of soft metals. (Milling, Grinding, etc.,)
6. Used to liquify hydrogen and oxygen that are used as propellants for rockets and aviation industries.
7. In preservation of biological cells and tissues used under microbiology, biotechnology and tissue culture.
8. Used for production of liquid nitrogen that is used to cool micro controllers of super computers.
The propellants used in the present day rockets are divided into three categories, the solid propellants (HTPB), the liquid propellants (Hypergolic), and the cryogenic propellants (LH2 & LOX). Liquid Hydrogen and Liquid Oxygen are the two main cryogenic propellants, where the LH2 is the fuel and the LOX is the oxidizer. These cryogenic propelled engines are also used in aviation industries, more common in the Lockheed Martin fleet. It is a clean fuel and produces only water as the byproduct liberating large quantities of heat.