Cryogen transfer

As stated, one of the reasons for using a vacuum is to remove oxygen from a system so that air-sensitive compounds will not react. If that is your primary concern and you do not need to use cryogenic transfer for movement of compounds within the vacuum line, there may not be a need to equip your lab with an ultrahigh-vac-uum system. 

Liquid cryogen transfer lines should be designed so that liquid cannot be trapped in any nonvented part of the system. Experiments in supercritical fluids include high pressure and should be carried out with appropriate protective systems. 

Equation (18) shows that in a constant volume, constant pressure ullage in which the gas cools only by contact with the walls, the average wall temperature varies as the reciprocal of the average gas temperature. This functional relation between and as given by (17) and (18) has been checked with data taken in several cryogenic transfer systems operatedat ADL [1,2,3], Excellent agreement was obtained. 

J. Burke, W. Byrnes, A. Post, and F. E. Ruccia, "Pressurized Cool-down of Cryogenic Transfer Line," Advances in Cryogenic Engineering, Vol. 4, K. D. Timmerhaus, (ed.). Plenum Press, Inc., New York (1960). 

It is believed that the test program outlined in this paper established the feasibility of using pumps for large scale cryogenic transfer systems. In addition, it is of interest that water testing established performance levels which w re met during actual operation on liquid oxygen. 

A Liquid Air Device for Cooling the Wearer of a Totally Enclosed Liquid Rocket Propellant Handler s Suit (4) 196 Pressurized Cooldown of Cryogenic Transfer Lines (4) 378... 

Transfer of Liquid Hydrogen through Uninsulated Lines (5) 103 Flexibility Considerations for the Design of Cryogenic Transfer Lines (5) 111 LIQUEFIERS [see also COOLING,REFRIGERATORS, REFRIGERATION]... 

The first unit is a medium pressure liquid oxygen transfer pump designed for 35 gpm and a 600 foot head rise at 8400 RPM. This unit was designed and manufactured by Turbocraft for the Cambridge Corporation, The other unit is one of the Turbocraft Company s line of close-coupled cryogenic transfer pumps. This unit was supplied as a transfer pump on a Corps of Engineers, 9-ton LOX trailer. Its operating point is 150 gpm with a 125 foot head rise at 3500 RPM,... 

It is quite conceivable that in a short, heavy-wall line, the liquid may reach the end of the line before the line wall temperature has reached equilibrium. However, it is felt that the proposed model applies to most conventional cryogenic transfer lines. 

The above method ass imes an infinite heat transfer coefficient on the fluid side of the concentrated mass, and hence tends to overestimate the percentage cooldown. Additional accuracy might be obtained if the method of calculation were refined to account for finite heat transfer coefficients. A refinement of this type might be helpful in those situations in which the heat input from the partial cooldown of concentrated masses is large in comparison with the heat input from the complete cooldown of the distributed mass. However, it is felt that for most conventional cryogenic transfer lines the assumption of an infinite coefficient is adequate to obtain a reasonable approximation of cooldown mass. 

A method for calculating the pressurized cooldown time of cryogenic transfer lines has been developed. This method has been found to be in good agreement with test data obtained over a fairly wide range of operating conditions in a small-scale pressurized transfer system. The analysis presented should prove to be useful for estimation of the time required for the pressurized cooldown of conventional cryogenic transfer lines. 

D. C. Bowersock, R. W. Gardner, and R. C. Reid, "Pressurized cooldown of cryogenic transfer lines," 1958 Cryogenic Engineering Conference Proceedings. 

FLEXIBILITY CONSIDERATIONS FOR THE DESIGN OF CRYOGENIC TRANSFER LINES... 

Bowing occurs in cryogenic transfer pipingwhen the pipeline is only partially full of liquid. Such a condition occurs during a normal operating cycle of a missile system when liquid trapped between valves is allowed to boil off. Experimental data[l] from tests on 8-in. and 12-in. uninsulated stainless steel thin-walled pipes partially full of liquid nitrogen indicated that the temperature distribution across the pipeline vertical diameter was as shown in Fig. 1. With the pipe half filled with liquid, the top fibers of the pipe did not cool substantially below room ambient temperature at steady state, while the bottom fibers of the pipe were at liquid temperature. As a result of this extreme temperature gradient, the pipeline tends to bow. For example, a partially full 8-in.-diameter 30-ft cantilevered section of pipe would deflect 35 in. at the free end. 

Cryogenic transfer lines can be grouped into three major categories (1) uninsulated lines, (2) foam-insulated lines, and (3) vacuum-insulated lines. The latter category can be subdivided into evacuated powder-insulated lines, high vacuum-insulated lines, and MLI-insulated lines. 

Frequently, cryogenic transfer lines may be economically insulated with foam such as polystyrene and polyurethane or fibrous material such as glass wool. These insulations when properly applied with a vapor barrier may significantly reduce the heat inleak and prove feasible for use with cryogens at temperatures as low as that of liquid nitrogen. If the insulation is free of condensed air, the steady-state heat flux to the foam or fibrous-insulated line may be determined from... 

Another concern of a cryogenic transfer line designer is thermal contraction because the inner line is cooled from ambient to cryogenic temperatures while the outer line remains at room temperature. The degree of thermal contraction from room temperature to liquid hydrogen temperature for a copper pipe is about 0.033 m for each 10 m of pipe length. 

Fig. 7.32. Bolted-flange joint for cryogenic transfer line.

Fig. 7.33. Schematic of typical bayonet joint for cryogenic transfer line. Legend 1, outer line, vacuum shell 2, line coupling 3, warm temperature O-ring seal 4, static gas leg 5, vacuum insulation space 6, vacuum barriers 7, additional liquid seal and 8, liquid line.

Unfortunately, however, the problem of analytically predicting two-phase flow behavior is complicated by the mass transition, usually from the liquid to the vapor, that results from the heat influx into the pipe and from pressure changes. Moreover, the liquid and vapor are quite frequently not in equilibrium, and this introduces additional variables into the prediction. In attempting to describe two-phase flow in a cryogenic transfer line, one must first realize that the flow in the vapor phase may be laminar or turbulent, and the flow in the liquid phase may be similar to or different from the gas. Further, this flow pattern may be altered by the incline of the pipe and by the heat influx or pressure drop. 

Using the saturation rule, determine the pressurization mass requirement for a nominal 117.77 m liquid oxygen storage vessel with a 10% ullage volume. The pressurization is to be maintained at 405 kPa for a 30-min transfer period at a rate of 0.025 m s. Assume that the vessel initially contains 106 m of liquid oxygen at a pressure of 101.3 kPa before it is suddenly pressurized to initiate the cryogen transfer. 

Solubility. This column gives the solubility of the window in water, at room temperature. The values provided are in grams of window material that will dissolve in 100 g of water. Where that information was not readily available, comments on the relative effect of water are provided. Solubility is of interest since water from the air often condenses on dewars or cryogen transfer lines, and it may be difficult to avoid getting some water on the window. 

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