Engineering topics

Kulacki, F. A.

Publications and source records attributed to Kulacki, F. A..

5 records

NASA NTRS1980

A numerical investigation of thermal convection in a heat-generating fluid layer

Finite difference solutions of the equations governing thermal convection driven by uniform volumetric energy sources are presented for two-dimensional flows in a rectangular domain. The boundary conditions are a rigid (i.e, zero slip), zero heat-flux lower surface, rigid adiabatic sides, and either a rigid or free (i.e., zero shear) isothermal upper surface. Computations are carried out for Prandtl numbers from 0.05 to 20 and Rayleigh numbers from 5 x 10 to the 4th to 5 x 10 to the 8th. Nusselt numbers and average temperature profiles within the layer are in good agreement with experimental data for rigid-rigid boundaries. For rigid-free boundaries, Nusselt numbers are larger than in the former case. The structure of the flow and temperature fields in both cases is dominated by rolls, except at larger Rayleigh numbers where large-scale eddy transport occurs. Generally, low velocity upflows over broad regions of the layer are balanced by higher velocity downflows when the flow exhibits a cellular structure. The hydrodynamic constraint at the upper surface and the Prandtl number are found to influence only the detailed nature of flow and temperature fields. No truly steady velocity and temperature fields are found despite the fact that average Nusselt numbers reach steady values.

Emara, A. A.↗

NASA NTRS1977

Studies of heat-source driven natural convection: A numerical investigation

Thermal convection driven by uniform volumetric energy sources was studied in a horizontal fluid layer bounded from above by a rigid, isothermal surface and from below by a rigid, zero heat-flux surface. The side walls of the fluid domain were assumed to be rigid and perfectly insulating. The computations were formally restricted to two-dimensional laminar convection but were carried out for a range of Rayleigh numbers which spans the regimes of laminar and turbulent flow. The results of the computations consists of streamline and isotherm patterns, horizontally averaged temperature distributions, and horizontally averaged Nusselt numbers at the upper surface. Flow and temperature fields do not exhibit a steady state, but horizontally averaged Nusselt numbers reach limiting, quasi-steady values for all Rayleigh numbers considered. Correlations of the Nusselt number in terms of the Rayleigh and Prandtl numbers were determined.

Emara, A. A.↗

NASA NTRS1976

The Identification of Scientific Programs to Utilize the Space Environment

A program to identify and develop ideas for scientific experimentation on the long duration exposure facility (LDEF) was completed. Four research proposals were developed: (1) Ultra pure germanium gamma ray radiation detectors in the space environment, intended to develop and demonstrate an X-ray and gamma-ray spectroscopy system incorporating a temperature cyclable high-purity germanium detector and diode heat pipe cryogenic system for cooling, (2) growth, morphogenesis and metabolism of plant embryos in the zero-gravity environment, to investigate if the space environment induces mutations in the embryogenic cells so that mutants of commercial significance with desirable attributes may be obtained, (3) effect of zero gravity on the growth and pathogenicity of selected zoopathic fungi. It is possible that new kinds of treatment for candidiasis, and tichophytosis could eventuate from the results of the proposed studies, and (4) importance of gravity to survival strategies of small animals. Gravitational effects may be direct or mediate the selection of genetic variants that are preadapted to weightlessness.

Kulacki, F. A.↗

NASA NTRS1975

Studies of heat source driven natural convection

Natural convection energy transport in a horizontal layer of internally heated fluid was measured for Rayleigh numbers from 1890 to 2.17 x 10 to the 12th power. The fluid layer is bounded below by a rigid zero-heat-flux surface and above by a rigid constant-temperature surface. Joule heating by an alternating current passing horizontally through the layer provides the uniform volumetric energy source. The overall steady-state heat transfer coefficient at the upper surface was determined by measuring the temperature difference across the layer and power input to the fluid. The correlation between the Nusselt and Rayleigh numbers for the data of the present study and the data of the Kulacki study is given.

Kulacki, F. A.↗

NASA NTRS1974

Studies of heat source driven natural convection

Natural convection energy transport in a horizontal layer of internally heated fluid with a zero heat flux lower boundary, and an isothermal upper boundary, has been studied. Quantitative information on the time-mean temperature distribution and the fluctuating component of temperature about the mean temperature in steady turbulent convection are obtained from a small thermocouple inserted into the layer through the upper bounding plate. Data are also presented on the development of temperature at several vertical positions when the layer is subject to both a sudden increase and to a sudden decrease in power input. For changes of power input from zero to a value corresponding to a Rayleigh number much greater than the critical linear stability theory value, a slight hysteresis in temperature profiles near the upper boundary is observed between the heat-up and cool-down modes.

Kulacki, F. A.↗