Engineering topics

Juhasz, Albert J.

Publications and source records attributed to Juhasz, Albert J..

43 records · Page 3

NASA NTRS1991

Advanced radiator concepts feasibility demonstration

An innovative pumped loop concept for 600 K space power system radiators is under development utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup. The melting/freezing process of Li in a NaK flow was studied experimentally to demonstrate the Li/NaK radiator feasibility during startup (thawing) and shutdown (cold-trapping). Results of the vapor grown carbon fiber/composite thermal conductivity measurements are also presented.

Rhee, Hyop S.↗

NASA NTRS1991

Heat-pipe transient model for space applications

A two-dimensional model is developed for simulating heat pipes transient performance following changes in the input/rejection power or in the evaporator/condenser temperatures. The model employs the complete form of governing equations and momentum and energy jump conditions at the liquid-vapor interface. Although the model is capable of handling both cylindrical and rectangular geometries, the results reported are for a circular heat pipe with liquid lithium as the working fluid. The model incorporates a variety of other working fluids, such as water, ammonia, potassium, sodium and mercury, and offers combinations of isothermal, isoflux, convective and radiative heating/cooling conditions in the evaporator and condenser regions of the heat pipe. Results presented are for lithium heat pipes with exponential heating of the evaporator and isothermal cooling of the condenser.

Tournier, Jean-Michel↗

NASA NTRS1990

Two-dimensional simulation of a two-phase, regenerative pumped radiator loop utilizing direct contact heat transfer with phase change

An innovative pumped loop concept for 600 K space power system radiators utilizing direct contact heat transfer, which facilitates repeated startup/shutdown of the power system without complex and time-consuming coolant thawing during power startup, is under development. The heat transfer process with melting/freezing of Li in an NaK flow was studied through two-dimensional time-dependent numerical simulations to characterize and predict the Li/NaK radiator performance during startup (thawing) and shutdown (cold-trapping). Effects of system parameters and the criteria for the plugging domain are presented together with temperature distribution patterns in solid Li and subsequent melting surface profile variations in time.

Rhee, Hyop S.↗

NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overalll system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1880 kg/cu m.

Juhasz, Albert J.↗

NASA NTRS1987

Reliability and mass analysis of dynamic power conversion systems with parallel or standby redundancy

A combinatorial reliability approach was used to identify potential dynamic power conversion systems for space mission applications. A reliability and mass analysis was also performed, specifically for a 100-kWe nuclear Brayton power conversion system with parallel redundancy. Although this study was done for a reactor outlet temperature of 1100 K, preliminary system mass estimates are also included for reactor outlet temperatures ranging up to 1500 K.

Juhasz, Albert J.↗

NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overall system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1800 kg/cu m).

Juhasz, Albert J.↗

NASA NTRS1986

Alternative power generation concepts for space

Trade and optimization studies that highlight the potential of solar and nuclear dynamic systems relative to photovoltaic power systems are summarized. The solar dynamic case is the LEO Stirling system, while the nuclear system is the SP-100 system goal. Nuclear systems have the potential for the lightest weight, least area, sunlight independent, radiation-durable system. Solar dynamic systems pose a stiff challenge to photovoltaic systems in the midaltitudes because of their insensitivity to the Van Allen radiation belts. While the initial operational capability space station power system is only slightly superior to the SOA PV system, with development focused on the key technologies, advanced solar dynamic systems are fully competitive in LEO midaltitudes with the advanced photovoltaic systems. Advances in energy storage systems (100 Whrs/kg required) are essential.

Brandhorst, Henry W., Jr.↗