R-3 Repository :: Browsing by Author "Chapman, Alan J."

Browsing by Author "Chapman, Alan J."

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A fundamental study of spray evaporative cooling
(1979) Grissom, William M.; Wierum, Frederic A.; Chapman, Alan J.; Bayazitoglu, Yildiz
"Spray evaporative cooling" is defined as the mode of spray cooling heat transfer for which no liquid film would form on a heated surface of infinite extent. The heat flux during this mode is simply that required to vaporize all of the impinging spray. The lower surface temperature range limit for the existence of spray evaporative cooling is determined experimentally to be an essentially linear function of the impinging spray mass flux. This suggests a conduction-controlled droplet evaporation mechanism. An analytical model of this form gives fairly good agreement with the experimental measurements at atmospheric pressure. The effect of lowering the surrounding pressure appears to be a decreased "wettability" of the liquid (distilled water) upon the aluminum surface. This would account for the correspondingly lower droplet evaporation times observed. "Spray film cooling" is defined as the mode of spray cooling heat transfer for which a liquid film would exist upon the heated surface. An analysis of this mode is of importance in determining several characteristics of the spray evaporative cooling mode. At atmospheric pressure the mechanism governing spray film cooling appears to be quite similar to that of ordinary pool boiling with little or no dependence upon the liquid film thickness. At vacuum pressures spray film cooling appears to be governed by the simple mechanism of heat conduction through the liquid film, and very much dependent upon the liquid film thickness. The "Leidenfrost State" is defined as the mode in which impinging droplets rebound off of the surface. The initiation of the Leidenfrost state imposes: the upper range limit for the existence of spray evaporative cooling. The surface temperature at which this state is initiated is found to be very much a function of the surrounding pressure. Interestingly, this variation with pressure is such that it counteracts the variation of the lower range limit with pressure, resulting in essentially the same maximum possible heat flux during spray evaporative cooling for all surrounding pressures.
A numerical analysis of coupled solidification and natural convection within a two-dimensional rectangular cavity
(1974) Heuer, Christopher Edward; Chapman, Alan J.
A numerical method is developed to solve a problem of coupled solidification and natural convection within a two-dimensional rectangular cavity. The vertical walls of the cavity are adiabatic while the horizontal walls are isothermal, the upper boundary being maintained below the fusion temperature of the liquid. The solid layer that forms is assumed to have a uniform thickness. The Boussinesq system of equations is used to describe the liquid, and the one-dimensional heat conduction equation is used to describe the solid. The average temperature derivatives at the solid-liquid interface are used to determine its motion. A coordinate transformation based on solid thickness and an alternating direction implicit differencing scheme are the central features of the numerical method. For the limited range of non-dimensional parameters studied, steady state values of solid thickness and heat transfer coefficient as well as stream function and temperature distributions are obtained. It is found that the steady state of the liquid is not affected by the presence of a moving interface during the transient period. Internal natural convection without phase change is then studied to learn more about the details of the flow field.
A numerical study of vortex-shedding suppression in laminar flow about a cylinder near a plane boundary
(1989) Rothberg, Robert Hanks; Chapman, Alan J.
The effect of a nearby plane boundary on vortex shedding from a circular cylinder is investigated for laminar flow. A two-dimensional finite difference numerical technique is used to solve the incompressible Navier-Stokes equations in primitive variable form on a computational mesh that is generated using a body-fitted coordinate transformation. Results are first presented for flows at Reynolds numbers of 80 and 100, based on the cylinder diameter, with the cylinder constrained against movement. Several cases of moving cylinder simulation are also presented for flow at a Reynolds number of 100. Fixed cylinder cases were run initially at both Reynolds numbers for an unbounded cylinder to confirm agreement of the simulation results with experimental evidence. The influence of a nearby plane boundary was investigated through a traverse of gap ratios beginning with a value of 3.0 and concluding with 0.5. Additional attention was focused on the behavior of the flow at gap ratios in the vicinity of the vortex shedding suppression gap ratio. Nearing the plate, a maximum Strouhal period was observed for each flow as suppression was approached. Features of the more viscous flow at the lower Reynolds number occurred at larger gap ratios than for the higher Reynolds number, as expected. The moving cylinder simulations were conducted primarily to demonstrate the capability of the simulator to accommodate the moving boundary of the cylinder. Initial gap ratios were chosen for examination based on the behavior of the fixed cylinder in the vicinity of the gap associated with vortex suppression.
Acceleration of a plasma by an electric and magnetic field
(1962) Wooten, David Clark; Chapman, Alan J.
Experiments were performed using a continuous electromagnetic, or J X B, body force to accelerate the plasma. Argon and helium plasmas were accelerated in a cylindrical channel after a free jet had been established. The specific impulses and efficiencies obtained by expanding helium through an arc-jet-nozzle arrangement is compared to the specific impulses and efficiencies obtained using a continuous electromagnetic field to accelerate the gas. The dependence of the electromagnetic body force upon the accelerating arc current was found, in general, to agree with theoretical predictions.
An approximation procedure for determining configuration factors in radiative heat transfer problems
(1964) Clarke, Robert Cleveland; Chapman, Alan J.
An approximation procedure for determining radiative heat transfer configuration factors has been presented and discussed. The approximation method proposed was applied to several configurations and the results obtained have been presented in graphical form for several variations of the parameters in each case. A detailed discussion of the errors involved in applying the approximation method is also included.
An experimental investigation of an application of a hydraulic analogy to unidimensional diabatic gas flow
(1955) O'Keiff, Gustav M; Chapman, Alan J.
An interactive computer solution for thermal systems
(1985) Reynolds, Frank Fisher; Walker, William F.; Chapman, Alan J.; Wierum, Frederic A.
The Thermal Analysis System is an attempt to automate the analysis of a closed thermodynamic system. A first law analysis is performed on each device in the system using the properties initially entered by the user at selected states. The known data for a problem to be solved is entered via interactive prompts. The program then manipulates the data and attempts to solve the system. If enough data is not known to solve the system completely, all known data is printed out and an error message will appear.
An investigation of the transition from subsonic flow to supersonic flow in a two dimensional nozzle by means of an hydraulic analogy
(1955) Merwin, John Elwood; Chapman, Alan J.
An orthogonal adaptive grid module to complement existing fluid dynamics and heat transfers codes
(1985) Barry, Matthew Robert; Wierum, Frederic A.; Akin, J. E.; Chapman, Alan J.
A versatile, orthogonal adaptive grid scheme for two-dimensional numerical fluid dynamics and heat transfer problems is presented. The scheme employs a one-dimensional adaptation sweep to define one family of physical grid lines. A second sweep then uses a technique called AOT, developed herein, to fit an orthogonal family of lines to the solution-adapted lines. These procedures are fast, require.little core storage, and do not change the original domain boundaries. Each subroutine developed performs a specific function and together they form the adaptive grid module. The versatility of these subroutines allows their usage in various combinations and in either grid direction. Modifications required to implement this scheme into existing fluid dynamics and heat transfer codes, therefore, are minimal. Code documentation and sample applications showing the implementation and versatility of the scheme are presented.
Analysis of pressure drop and heat transfer in the flow of an ethylene glycol solution through a tube cooled by radiation from a rectangular fin
(1966) Gilliam, David McLarty; Chapman, Alan J.
A finite difference numerical analysis is presented concerning the pressure drop and heat transfer in the steady flow of a eutectic ethylene glycol aqueous solution through a tube cooled by radiation from a rectangular fin into an environment at zero degrees Rankine. The temperature dependence of all fluid properties is taken into account. The solution predicts an unusual functional dependence of pressure drop on the mass flow rate: that for lower and lower values of the mass flow rate, the pressure drop through a tube reaches a minimum value and then begins to increase. The application to parallel network flows of the solution of the transport equations for the flow in a single tube is illustrated with two examples. The most accurate numerical solution is compared with a simplified numerical solution which neglects inlet effects and with an approximate analytical solution. The convergence of the numerical method and agreement with experimental data are demonstrated. Finally the FORTRAN programs developed are listed with flow charts and annotations.
Applications of a mathematical model of the human body for determining thermal comfort
(1984) Hill, Gregory Wade; Chapman, Alan J.; Wierum, Frederic A.; Beckmann, Herbert K.
A conceptual description of a current mathematical model of the human body, analyzed in terms of heat transfer, is presented. This model is designed to predict thermal comfort responses of a person exposed to a particular indoor environment. Methods of heat exchange between the body core, the skin, and the surroundings are described. Formulations are also included for two parameters describing the environment-the mean radiant temperature and the convective heat transfer coefficient. Heat transfer equations and computer programs for this model are used to generate data for the study. Three applications for this model are discussed in terms of their effectiveness in achieving thermal comfort: the effect of radiant cooling panels, the effect of ceiling fans, and the effect a change in the person's metabolic rate. In each example, the temperature of the surroundings is displaced from a reference temperature where thermal comfort exists. Efforts to restore the sensation of comfort are examined and the results are illustrated in graphical and tabular form. Conclusions are drawn from the procedure and recommendations for future research are suggested.
Comparative evaluation of alternate flow configurations of three fluid, cross flow, heat exchangers
(1968) Ellis, Wilbert E; Chapman, Alan J.
The performance characteristics of two specific three fluid, cross flow, heat exchanger configurations have been determined; and then evaluated comparatively with other conceivable arrangements previously analyzed. Results have been presented in terms of the temperature effectiveness of two of the fluid streams as a function of heat exchanger size for sets of fixed operating conditions. These results are presented over a wide range of operating parameters for a single pass configuration, but only for selected two pass conditions. Where possible, general conclusions as to the advantages and disadvantages of the configurations analyzed in this effort compared to those previously evaluated are presented. This comparative evaluation was conducted over the entire range of operating parameters analyzed for the single pass, three fluid, cross flow heat exchanger.
Condensation of a dialectic vapor in the presence of a non-uniform electric field
(1965) Holmes, Ronald Edwin; Chapman, Alan J.
Several different electrode configurations have a voltage applied to them. The region between the electrodes is assumed to be free of charges. The differential equation for these configurations, Laplace's equation, is solved in each case either analytically or with an I.B.M. 70140 computer using finite difference techniques. These results are then used to find the available body forces along a flat plate placed between the electrodes. The results are non-dimensionalized and an attempt is made to determine the possible value of each configuration in condensing heat transfer.
Crossed-field acceleration of a supersonic plasma
(1963) Boddie, William Lee; Chapman, Alan J.
An effort was made to obtain further correlation between theoretical and experimental results for continuous Lorentz force acceleration of a partially ionized gas. Four different nozzle-accelerator combinations were evaluated in the course of the research, with considerable differences in the performance of the various designs. In general, however, significant increases in the mass specific impulses and efficiencies were obtained when continuous crossed electric and magnetic fields were used to accelerate the partially ionized gas.
Design of nozzles for partly ionized gases
(1959) Baker, Jerry Robison; Chapman, Alan J.
An analytic expression is obtained for the speed of sound in a partly ionized gas under certain conditions. The method of characteristics is adapted to use this information for the solution of the compressible gas flow potential equation, and the contour of a nozzle which accelerates the gas to a high velocity is calculated graphically to illustrate the application of the method. A modification of Koga's procedure for using a computer to solve the equation is proposed.
Design, construction, and performance testing of a model waste heat rejection radiator
(1978) Johansen, Sigurd A.; Chapman, Alan J.
At present, waste heat from various cooling processes is discharged to. the environment primarily by devices using forced convection heat transfer. An alternative to this method is the use of a heat rejector, exposed to the atmosphere, which transfers heat by radiation and free convection. An experimental model was built, using flat tube-and-fin radiator panels with a model heat load applied to them. The heat transfer behavior of this device was compared to the predictions of a mathematical model which linearized the dependence of the radiative heat transfer on temperature. The tests of the device showed that it rejected significant amounts of heat at relatively low temperatures, and that the mathematical model was successful in predicting the behavior of the experimental apparatus.
Development of an experimental apparatus and method for the determination of thermal conductivity and thermal diffusivity of solid and frozen soils
(1984) Inbody, Michael Andrew; Chapman, Alan J.; Wierum, Frederic A.; Bourland, Hardy M.
Evaporative cooling on a grooved surface
(1980) Yoder, Dwight; Wierum, Frederic A.; Chapman, Alan J.; Bayazitoglu, Yildiz
Spray evaporative cooling defines a mode of heat transfer where the drops evaporate on contact with the heated surface. Since no water accumulates on the surface, the term "dry wall" is used to described the surface condition. If while operating in the drywall mode the surface temperature is lowered, there will be a transition to a point where water will begin to accumulate on the surface. When water begins to accumulate the surface is said to be "flooded". Behavior at this transition point was investigated experimentally to determine the temperatures and corresponding heat flux at which this transition occurred. Several pressure ranges were considered including one below the triple point of water. Additionally, the results using a grooved surface were compared to those using a smooth surface. It was determined that a grooved surface has no effect on the heat transfer.
Experimental determination of the air flow through the individual cylinders of an internal combustion engine
(1955) Lewis, David Warren; Chapman, Alan J.
The overheating of certain cylinders of multicylinder engines is of vital import to those concerned with large power installations. Such overheating results in a loss of power from the engine. Therefore, engines must be underrated by manufacturers or else customers must install power plants which are somewhat oversized. Overheating of certain cylinders of an engine has been attributed to a nonuniform distribution of the pulsating fluid (air or fuel-air mixture) flowing through the individual cylinders of the engine. For this reason, manifolds (intake or exhaust) have been adjudged as the probable cause for overheating. To date, the majority of analytical work applicable to manifolds has been limited to intake manifolds or to steady flow conditions. The experimental work related to nonsteady flow has been limited to the total overall flow of a particular engine. The present work is concerned with the experimental procedure for measuring the pulsating flow through the individual cylinders of an internal combustion engine. Experimentation has been carried out by motoring a three cylinder, two stroke cycle, General Motors Diesel Engine. By motoring the engine with a dynamometer, complications arising from high temperatures and pressures were circumvented. The fluid flow through the individual cylinders was measured with a "Proportional Flow Meter".
Feasibility and optimization studies of finned radiators discharging waste heat to the atmosphere
(1977) Higenyi, James K. D.; Chapman, Alan J.
The steady state performance of radiators, exposed to a clear sky, is investigated. Radiators are subjected to a radiative environment consisting of infra-red and solar radiation. There is also a convective heat exchange between the radiators and the atmosphere. Four surface orientations (South, West, North, and East) are examined. For each surface orientation, six surface inclinations (15°, 3°, 45°, 6°, 75°, and 9° with respect to the horizontal) are considered. Both the daily heat loss and the instantaneous (hourly) heat rejection are considered for the fifteenth day of each month in a year. The climate used is that of Houston, Texas (Latitude 3°N and Longitude 95°W). The feasibility of using radiators to reject heat, for a given environment, depends on the time of the day and the magnitude of the Inlet fluid temperature. It is found that for fluid temperatures equal to or greater than 4°C, radiators oriented in all directions and at any surface inclination reject heat at all times of the year. The optimum surface orientation-inclination is determined by considering the daily total heat loss. In June and July, surfaces oriented to the south reject the greatest amount of heat, followed by radiators facing north, while east and west facing surfaces reject the least heat. For the period August-December-May, north oriented surfaces are superior, with an optimum surface inclination varying between 45° and 9°. In this same period of about ten months, east and west facing surfaces are the next efficient while south oriented surfaces reject the least heat and are inferior to horizontal surfaces.

Browsing by Author "Chapman, Alan J."

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