Heat rejection with mechanical pumped cooling loop for lunar surface nuclear reactor power system

The investigation of relation between radiative and convective heat transfer coefficients at the ceiling in a cooled ceiling room

Numerical evaluation of the convective and radiative heat transfer coefficients for preterm neonate body segments inside an incubator

New approach relevant to total heat transfer coefficient including the effect of radiation and convection at the ceiling in a cooled ceiling room

Nuclear power systems will be required to provide much greater power levels for both civilian and defense space activities in the future than an currently needed. Limitations on the amount of usable power from radioisotope thermal generators and the limited availability of radioisotope heat source materials lead directly to the conclusion that nuclear power reactors will be needed to enhance the exploration of the solar system as well as to provide for an adequate defense. Lunar bases and travel to the Martian surface will be greatly enhanced by the use of high levels of nuclear power. Space based radar systems requiring many kilowatts of electrical power can provide intercontinental airline traffic control and defense early warning systems. Since the, figure of merit used in defining any space power system is the specific power, the decrease in die mass of any reactor system component will yield a tremendous benefit to the overall system performance. Also, since the heat rejection system of any power system can make up a large portion of the total system mass, any reduction in the mass of the heat rejection radiators will significantly affect the performance of the power system. Composite materials which combine the high strength, flexibility, and low mass characteristics of Si% based fibers with the attractive compatibility and heat transfer features of metallic foils, have been proposed for use m a number of space radiator applications. Thus, the weave of the fabric and the high strength capability of the individual fibers are combined with the high conductivity and chemical stability of a metallic liner to provide a light weight, flexible alternative to heavy, rigid, metallic radiator structural containers. The primary focus of this investigation revolves around two applications of the fabric composite materials, notably a fabric heat pipe radiator design and the Bubble Membrane Radiator concept.

Thermally activated building systems (TABS) are one of the most commonly utilised structural cooling methods in construction industries. This method of structural cooling has pipes encapsulated in building surfaces. This investigation analyses the internal convective heat transfer coefficient (CHTC) and radiative heat transfer coefficient (RHTC) for TABS in tropical conditions. The overall heat transfer coefficient is experimentally evaluated with HFP01 heat flux sensors and wet bulb globe thermometers. Calculated and actual CHTC were compared with the interrelationship available in the referred literature and with the constant value recommended by the standard. The results from the measurements indicate that the average CHTC and RHTC are 2.66 W/m2K and 5.7 W/m2K, and it conforms with EN ISO 6946 standards for tropical climates. The CHTC was also quantified with many correlations developed in the scientific literature to determine the best model for the TABS environment. From statistical error analysis, it was determined that Khalifa and Marshall's model was suited with the most minor error of 3 % compared to the other models.

Heat transfer study of external convective and radiative coefficients for building applications

Combined heat transfer characteristics were obtained numerically for three-dimensional natural convection and thermal radiation in a long and wide vertical porous layer with a hexagonal honeycomb core. We assumed that the porous layer was both homogeneous and isotropic. The pure Darcy law for fluid flow and Rosseland's approximation for radiation were used. The numerical methodology was based on an algebraic coordinate transformation technique and the transformed governing equations were solved using the SIMPLE algorithm. The effect of radiation on the heat transfer characteristics was investigated over a wide range of radiation numbers and temperature ratios for two Darcy-Rayleigh number values (Ra * = 100 and 1000) and for a fixed aspect ratio of H/L = 1. The results are presented in the form of combined radiation and convection heat transfer coefficients and are compared with the corresponding values for pure natural convection.

<div class="htmlview paragraph">The increasing need for higher electrical power levels for military and scientific space purposes has spurred development of energy conversion systems with higher efficiencies than the traditional solar array. Numerous nuclear options are currently under development. These fuels eliminate the need for large deployable solar arrays or concentrators, allow unrestricted pointing and maneuvering, and are inherently less susceptible to natural and threat environments; they are the only viable energy source for outer planetary exploration. Fission reactors are the most desirable nuclear source for electric power levels above 10 kW. Radioisotope sources have been used in conjunction with thermoelectrics up to 1 kWe for planetary exploration. However, for radioisotope systems in the 1 to 10 kWe range, a much higher conversion efficiency is required. For over 15 years, NASA and the Department of Energy (DOE) have been developing closed cycle turbo-alternator (dynamic) power conversion systems for space use. The Air Force and DOE are jointly developing such a system under the Dynamic Isotope Power System (DIPS) program.</div> <div class="htmlview paragraph">Two closed dynamic cycles are being evaluated for use as part of the DIPS system. They are the Closed Brayton Cycle (CBC) which uses an inert (single phase) gas as the working fluid. The other system is the Organic Rankine Cycle (ORC) which utilizes the phase change properties of the working fluid. Each has a significantly different effect on the design of a radiative heat rejection system, primarily because of the temperature variation of the CBC single phase heat rejection versus the nearly constant temperature two-phase (condensing) ORC heat rejection. The heat rejection system plays an important role, since the power conversion efficiency is strongly dependent on the heat rejection temperature. The lower the rejection temperature, the higher the efficiency. However, the radiator area requirement increases as the rejection temperature is reduced. On a weight optimization basis both systems are comparable, however, the ORC system requires more radiator area for the same cycle efficiency. With the design requirement that the radiator be mounted around the circumference of the vehicle, available area is limited. Therefore, the heat rejection system design may not be a clear-cut weight optimization but rather a matter of area reduction at minimum penalty to efficiency and weight.</div> <div class="htmlview paragraph">The paper presents the results of an optimization study performed on the heat rejection system for a space based ORC power system using an isotope heat source. The radiator sizing depends on the heat rejection temperature, radiator configuration, and radiator properties such as the fin effectiveness, emissivity, and absorptivity. The optimization analysis to evaluate the effect of each of these parameters on the system weight and area is presented.</div>

In October of 2002, The Power and Propulsion Office and The Risk Management Office of NASA Glenn Research Center in Cleveland, Ohio began developing the reliability, availability, and maintainability (RAM) engineering approach for the Space Nuclear Propulsion and Power Systems Project. The objective of the Space Nuclear Power and Propulsion Project is to provide safe and reliable propulsion and power systems for planetary missions. The safety of the crew, ground personnel, and the public has to be the highest priority of the RAM engineering approach for nuclear powered space systems. The project will require a top level reliability goal for substantial mission success in the range from 0.95 to 0.98. In addition, the probability of safe operation without loss of crew, vehicle, or danger to the public, cannot be less than 0.9999. The achievement of these operational goals will require the combined application of many RAM engineering techniques. These include: advanced reliability, availability, and maintainability analysis, probabilistic risk assessment that includes hardware, software, and human induced faults, accelerated life testing, parts stress analysis, and selective end to end sub-system testing. Design strategy must involve the selection of parts and materials specifically to withstand the stresses of prolonged operation in the space and planetary environments with a wide design margin. Interplanetary distances and resulting signal time delay drive the need for autonomous control of major system functions including redundancy management.

A model has been developed to calculate the heat transfer coefficients from the fuel rods to the steam-droplet mixture typical of Boiling Water Reactors under Emergency Core Cooling System (ECCS) operation conditions during a postulated loss-of-coolant accident. The model includes the heat transfer by convection to the vapor, the radiation from the surfaces to both the water droplets and the vapor, and the effects of droplet evaporation. The combined convection and radiation heat transfer coefficient can be evaluated with respect to the characteristic droplet size. Calculations of the heat transfer coefficient based on the droplet sizes obtained from the existing literature are consistent with those determined empirically from the Full-Length-Emergency-Cooling-Heat-Transfer (FLECHT) program. The present model can also be used to assess the effects of geometrical distortions (or deviations from nominal dimensions) on the heat transfer to the cooling medium in a rod bundle.

A set of design considerations is proposed for nuclear power systems to provide power on the Moon or Mars. Setting the initial requirements is extremely important since they govern the choices that determine the final design. In addition, the choice of reactor and its operating conditions depends on details of the energy conversion and heat rejection systems, which must be studied in tandem. Refractory materials are not suitable for the primary pressure boundary for the reactor due to their susceptibility to chemical attack from particles of regolith on the Moon and Mars or by the carbon dioxide atmosphere on Mars. High nickel superalloys would be acceptable in these environments, but their limited creep strength at elevated temperatures limits reactor outlet temperature to about 1150 K or less. This temperature restriction results in the mass of a gas cooled reactor coupled to a Brayton power conversion system being somewhat lighter than that of a liquid metal‐cooled reactors coupled to a Brayton power conversion system. The mass of a liquid metal‐cooled reactor coupled to an advanced Stirling power conversion system would be in between that of the gas and liquid metal cooled systems which use Brayton power conversion.

Nuclear transport power systems (NTPS) can provide solving such important science, commerce and defense tasks in space as radar surveillance, information affording, global ecological monitoring, defense of Earth from dangerous space objects, manufacturing in space, investigations of asteroids, comets and solar systems’ planets (Kuzin et al. 1993a, 1993b). The creation of NTPS for real space systems, however, must be based on proved NTPS effectiveness in comparison with other power and propulsion systems such as, nonnuclear electric‐rocket systems and so on. When the NTPS effectiveness is proved, the operation safety of such systems must be suited to the UN requirements for all stages of the life cycle in view of possible failures. A nuclear transport power module provides both a large amount of thermal and electrical power and a long acting time (about 6–7 years after completing the delivery task). For this reason such module is featured with the high power supplying‐mass delivery effectiveness and the co...

Axisymmetric radiative heat transfer calculations for flows in chemical non-equilibrium

Nuclear Power Systems for Advanced High-Powered Communications Satellites

Net power and energy output of the German LWR nuclear power system