Modeling of thermohydraulic transients in a boiling helium natural circulation loop

Boiling helium natural circulation loops are a cooling option for superconducting magnets. Previous studies on the field have provided a thorough understanding of their steady state behavior in all boiling regimes. Recent experimental research has lead to the understanding of their transient behavior. In particular, it highlights the impact of the thermohydraulic evolution of the circuit on the onset of transient boiling crisis, which represents a limitation of the cooling system. Hence, the need of modeling this aspect of these systems. In this work we present modeling options of two-phase helium loops departing from the homogeneous equilibrium two-phase flow model. Reasonable additional assumptions are introduced to obtain a simplified model and the effect of these assumptions is evaluated by comparison with the solution of the non-simplified equations system. These methods are compared to experimental data to analyze their success and limitations.     

Hydrodynamic characteristics of a horizontal channel with the motion of a two-phase helium flow

Experimental data is presented on the pressure drop in the motion of a two-phase helium flow in a horizontal pipe under adiabatic conditions and with a supply of heat.     

Modeling and performance analysis of a two-phase thermosyphon loop with partially/fully liquid-filled downcomer

Two-phase thermosyphon loops (TPTLs) are extensively used in industries. Numerical simulation is always applied for their configuration design and performance rating. The conventional models are usually developed under large temperature difference, and the fully liquid-filled downcomer are taken for granted. In this study, a generalized model for TPTL is developed, in which the downcomer can be partially liquid filled or fully liquid filled under different conditions. The model is verified by experiments on an air-to-air finned-tube TPTL. Then, it is used to analyze the flow and heat transfer features of a TPTL, under different refrigerant charge and temperature difference. The results show that the downcomer is partially liquid filled in the case of small temperature difference and refrigerant charge. Additionally, the heat transfer rate first increases then decreases with the increase of refrigerant charge, and first increases linearly then increases relatively slowly with the increase of temperature difference.     

Liquid helium transfer with a two-phase jet pump

A new two-phase helium jet pump is described. It may be possible to transfer helium or other cryogenic liquids with a two-phase jet pump that has no moving parts. The pump delivers subcooled liquid for filling the receiver tank without venting. The amount of vapour discharged is about the same as for transfer by receiver-tank venting.     

Thermal resonance in a closed circulation loop

The results of an analytical investigation of transient heat transfer conditions in a closed circulation loop are given. They make it possible to determine the conditions of the resonance increase in the coolant temperature fluctuation amplitude as a function of the temperature variation frequency in the core and the hydrodynamic velocity of heat transfer along the loop.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 61, No. 3, pp. 357–364, September, 1991.     

Performance of a helium circulation system for a MEG

We report the performance of a helium circulation system (HCS) for a magnetoencephalography (MEG) that re-liquefies all the evaporating helium gas using two 1.5 W GM cryocoolers operating at 4.2 K. The MEG with the HCS was used to measure human brain responses for over one and a half years without any noise problems. The noise level is below 10 fT/Hz^1/2 for 2–40 Hz, below 30 fT/Hz^1/2 at 1 Hz, and 200 fT/Hz^1/2 at 50 Hz, which is the power supply frequency. As the amount of liquid helium used decreases less than one percent, the maintenance cost of the MEG becomes less than one-tenth of the previous cost.     

Calculation of circulation characteristics of a two-phase thermosyphon

A new method is described for calculating the circulation characteristics of a thermosyphon with separate vapor and condensate channels. Calculation and experiment are compared.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 3, pp. 424–428, September, 1979.     

Study of jet pumps for circulating a helium two-phase mixture

The operation of a jet pump using a helium, two-phase mixture has been studied. It is shown that for the two-phase region, the relations obtained from the momentum equation are valid only up to the onset of limiting modes, ie until the stream velocity achieves the velocity of sound in any section of the mixing chamber of the jet pump. The experimentally proved method of calculation of the limiting modes is presented in which the velocity of sound in a two-phase stream is determined by thermodynamic theory.     

Experimental study of the drag of a two-phase helium flow in channels

Results are presented from an experimental study of the drag of a turbulent twophase helium flow in a horizontal channel under adiabatic conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 2, pp. 195–201, August, 1982.     

Limiting heat transfer in horizontal two-phase thermosiphon

Experimental results on the heat-transfer crisis in a horizontal thermosiphon with steam heating are outlined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 1, pp. 63–67, January, 1990.     

Thermohydraulic oscillations in a system showing natural circulation of a two-phase coolant

Thermohydraulic oscillations are considered for a wide range in coolant thermophysical parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 3, pp. 419–425, March, 1990.     

Heat transfer to near-critical helium in horizontal channels

Experimental results on heat transfer and pressure losses during a forced motion of helium of near-critical state parameters in a horizontal channel are reported. A method of calculation of temperature and pressure distributions along the channel is proposed.     

An analytical study of two-phase helium flow within a radial rotating duct

A study was made of the behaviour of separated two-phase helium flow within a radial rotating duct. The liquid film thickness, phase velocities, heat-exchange coefficients, pressure and temperature differences were evaluated. The plots obtained for helium flow in thermodynamic equilibrium are used to calculate the radius dependence of pressure and quality at a given rotational frequency and inlet duct conditions. The equilibrium pressure model is presented which describes pressures not too close to the critical values.     

Cooling of horizontal porous tubes by a low temperature helium flow

Heat transport during flow of low temperature helium in a metalloceramic tube is studied. The effect of free convection on temperature fields and Nusselt number is considered. Expressions are presented for evaluation of local heat exchange.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 1, pp. 103–106, July, 1988.     

Critical heat flux for two-phase flow of helium I

This paper describes a study performed to obtain the critical heat flux data on liquid helium I in a vertical tube under forced convection. The pressure of the fluid ranges from 1.1 to 2.0 atm (from 0.11 to 0.20 MN m^?2), and the quality up to 1. The results show that the critical heat flux decreases with increasing pressure and quality.     

Prediction of two-phase pressure gradients of refrigerants in horizontal tubes

Two-phase pressure drop data were obtained for evaporation in two horizontal test sections of 10.92 and 12.00 mm diameter for five refrigerants (R-134a, R-123, R-402A, R-404A and R-502) over mass velocities from 100 to 500 kg/m² s and vapor qualities from 0.04 to 1.0. These data have then been compared against seven two-phase frictional pressure drop prediction methods. Overall, the method by Müller-Steinhagen and Heck (Müller-Steinhagen H, Heck K. A simple friction pressure drop correlation for two-phase flow in pipes. Chem. Eng. Process 1986;20:297–308) and that by Grönnerud (Grönnerud R. Investigation of liquid hold-up, flow-resistance and heat transfer in circulation type evaporators, part IV: two-phase flow resistance in boiling refrigerants. Annexe 1972-1, Bull. de l'Inst. du Froid, 1979) were found to provide the most accurate predictions while the widely quoted method of Friedel (Friedel L. Improved friction drop correlations for horizontal and vertical two-phase pipe flow. European Two-phase Flow Group Meeting, paper E2; June 1979; Ispra, Italy) gave the third best results. The data were also classified by two-phase flow pattern using the Kattan-Thome-Favrat (Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 1: development of a diabatic two-phase flow pattern map. J. Heat Transfer 1998;120:140–7; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 2; new heat transfer data for five refrigerants. J Heat Transfer 1998;120:148–55; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 3: development of a new heat transfer model based on flow patterns. J. Heat Transfer 1998;120:156–65) flow pattern map. The best available method for annular flow was that of Müller-Steinhagen and Heck. For intermittent flow and stratified-wavy flow, the best method in both cases was that of Grönnerud. It was observed that the peak in the two-phase frictional pressure gradient at high vapor qualities coincided with the onset of dryout in the annular flow regime.     

Heat transfer to two-phase flows of helium and nitrogen in vertical channels

Equations are presented for calculation of heat transfer in two-phase convection and well-developed bubble boiling of helium and nitrogen in vertical channels.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 885–892, December, 1986.     

Experimental investigation of heat transfer in the annular channel of a circulation loop

The results of an experimental investigation of heat transfer in the vertical annular channel of a closed circulation heat exchanger are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 5, pp. 777–781, November, 1976.