Research Student Presentation
DEPARTMENT OF INSTRUMENTATION AND APPLIED PHYSICS
Research Student Presentation
NAME OF THE CANDIDATE : Mr. Nagendra. H. N.
DEGREE : Ph.D.
TITLE OF THE PRESENTATION : Studies on cool-down and fluid quality on the
developed cryogenic transfer line
SUPERVISORS : Dr. Upendra Behera & Dr. N. C Shivaprakash
DATE & TIME : Wednesday, 29th August, 2018 at 3.30 PM.
VENUE : Seminar Hall, Dept. of Instrumentation and Applied Physics
Cryogenic fluid is transferred by specially designed piping systems, from the plant to the storage container and further to the various applications. The transfer of cryogenic fluids such as liquid helium, hydrogen, nitrogen and oxygen is a daily common laboratory and commercial occurrence. Transfer of small quantities of cryogenic fluids through short tubes has been accomplished for several years in the laboratory. Unlike the conventional fluids, vacuum jacketed (with or without super-insulation) transfer lines are needed to minimize the loss of the cryogenic fluid by evaporation and heat transfer. With the advent of the space program, the need arose for transfer lines to handle liquid oxygen and liquid hydrogen. The length for these lines on some test sites is 600 m or more. With longer lines, problems of cool-down with two-phase flow, thermal contraction, bowing of the line under partial fill conditions and many other engineering problems arise. The lines were usually constructed in sections; thus, effective low-heat-in-leak joints were required.
Uninsulated or porous insulated lines are frequently used to transfer liquid air, oxygen and nitrogen for relatively short distance. In fact, the uninsulated line may be the most economical method for short-time, short-distance transfer of these fluids. During the transfer of liquid oxygen and pressurized liquid nitrogen, a layer of frost quickly builds up on the outside of the line, and this frost layer helps insulate the line. During the transfer of sub-cooled liquid nitrogen and liquid hydrogen, however, air condenses on the outside of the line. This condensation causes an increased heat-transfer rate because the latent heat of the air is transferred to the line in addition to the convective heat transfer. Liquid air also tends to wash away some of the frost that is formed initially.
Insulations such as fiberglass, polystyrene foam and polyurethane foam may be applied to the bare line to reduce the heat in-leak and have a fairly inexpensive transfer line at the same time. When these porous insulations are used, a vapor barrier must be applied to the outer surface of the insulation to prevent water-vapor diffusion into the insulation. Condensations of air within the insulation for liquid hydrogen transfer also cause a safety hazard. The condensed air is rich in oxygen, so serious explosions can result if the insulation is combustible. For this reason, one must be especially careful in using porous insulations for liquid hydrogen transfer
Vacuum-insulated lines consist of an inner pipe, in which the liquid flows, concentric to an outer vacuum jacket. The annular space may contain vacuum alone or vacuum with multilayer insulation known as super-insulation. The vacuum-insulated line may be used with any cryogenic fluid from liquid oxygen to liquid helium to attain low-heat transfer. For long-distance, long-time transfer, the vacuum-insulated line is more advantageous than the other types of transfer line.
Vacuum-jacketed lines are usually designed according to the American Standard Code for Pressure Piping. The inner line is sized to withstand the design internal pressure. The outer line must support the collapsing load of atmospheric pressure.
Analytical studies have been conducted for pressure drop, heat load and cool down on rigid and flexible transfer lines. Transfer line has been designed for 2 to 15 LPM of LN2 flow rates. The line operates at 1.34 bar absolute pressure. Transfer line is designed such that it can be disassembled as inner and outer part with the help of the O-ring seals and lock nuts provided at the ends. This enables to evaluate the performance of the developed transfer line for cool-down studies and two-phase flow behavior (void fraction) of the cryogenic fluid for vacuum insulated and/or super-insulated conditions.
The void fraction can be determined by various techniques. Such as Gama ray absorption, X-ray absorption, impedance, optical void probes, capacitive measurement technique and diode based measuring technique. Capacitance type measurement technique is most common and easy technique to find the void fraction. However, it is not easy to manufacture capacitance type flow sensors for cryogenic fluids and are quite challenging. In view of the above, an attempt has been made to develop diode based void fraction measurement sensor to determine the flow characters of the cryogenic fluids in the developed transfer line. The results are quite satisfactory. In addition to this, we are also in the process of developing the capacitance based void fraction measurement sensor.
ALL ARE WELCOME
Date(s) - 29/08/2018
3:30 pm - 5:00 pm
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