R-3 Repository :: Browsing by Author "Wierum, Frederic A."

Browsing by Author "Wierum, Frederic A."

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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 Raster scan visibility algorithm for parametric surfaces
(1984) Montgomery, Jerome; Akin, J. E.; Wierum, Frederic A.; Wheeler, Mary F.
A raster scan visibility algorithm is presented for contouring on parametric surfaces. The algorithm entails three-dimensional aspects of coloring, shading, and visibility of points. The approach uses parametric interpolation functions as the primary basis in computations. This technique along with a predictor-corrector method makes contour line tracing on each element more accurate. Continuous color variations on each surface are produced through the use of interpolation functions. The color at every display point can be assigned in proportion to the value of the quantity of interest at that pixel. Shading is included involving several possibilities of the shading rule. They may include ambient light, diffuse reflection, specular reflection, shadows, or transparency. A combination of these may also be included. All of the graphics generated using this algorithm can be displayed on color graphics, as well as, non-color graphics display terminals, and line printers. The algorithm could be used as a segment of a complete computer graphics package.
An efficient computational scheme for solving nonlinear, two-point boundary-value problems via the method of adjoint variables
(1981) Coker, Estelle M.; Miele, Angelo; Bayazitoglu, Yildiz; Wierum, Frederic A.
A method for solving nonlinear differential equations of the form x - (x,t) =, £ t <_ 1, subject to boundary conditions of the form w(x()) = , ÿ(x(l)) = / is developed. It is assumed that t is a scalar, x and are n-vectors, u is a p-vector, and ^ is a q-vector, with p + q ** n. The method is based on the consideration of the performance index P, the cumulative error in the differential equations and the boundary conditions. The differential equations and the boundary conditions are linearized about a nominal function x(t); the linearized system is embedded into a more general system by means of a scaling factor a, <_ a <_ 1, applied to each forcing term. The variations per unit stepsize A(t) = Ax(t)/a are governed by a system of n linear differential equations, subject to p separated initial conditions and q separated final conditions. Then, the system is solved employing the method of adjoint variables. The scaling factor a is determined by a bisection process, starting from a = 1, so as to ensure the decrease of the performance index P. Convergence to the desired solution is achieved when the inequality P £ e is met, where e is a small, preselected number. Two updating schemes are considered, called Scheme (a) and Scheme (b) for easy identification. In Scheme (a), the initial point x() is updated according tox(O) =x() +aA(), and the new nominal function x(t) is obtained by forward integration of the nonlinear differential equations. In Scheme (b), the function xCt) is updated according to x(t) = x(t) + aA(t). Four numerical examples are solved using the ITEL AS/6 computer of Rice University. The computational scheme developed here for the method of adjoint variables is particularly efficient, in that it minimizes the algorithmic work per iteration, namely, the number of integrations to be performed in order to solve the linear, two-point boundary-value problem. In the method developed by Roberts and Shipman (Ref. 4), the number of integrations is n, where n is the number of state variables. In this thesis, we show that the number of integrations can be reduced to q, where q < n is the number of final conditions.
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 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.
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.
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.
Multiple-subarc approach for solving minimax problems of optimal control
(1981) Venkataraman, Panchapakesan; Miele, Angelo; Wierum, Frederic A.; Bayazitoglu, Yildiz
Numerical solutions of minimax problems of optimal control are obtained through a multiple-subarc approach, used as a sequel to a single-subarc approach. The problems are solved by means of the sequential gradient-restoration algorithm. Firsts transformation technique is employed in order to convert minimax problems of optimal control into the Mayer-Bolza problem of the calculus of variations. The transformation requires the proper augmentation of the state vector x(t),the control vector u(t),and the parameter vector ir. As a result of the transformation, the unknown minimax value of the performance index becomes a component of the vector parameter is being optimized. The transformation technique is then employed in conjunction with the sequential gradient-restoration algorithm for solving optimal control problems on a digital computer. The algorithm developed in the thesis belongs to the class of sequential gradient-restoration algorithms. The sequential gradient-restoration algorithm is made up of a sequence of two-phase cycles,each cycle consisting of a gradient phase and a restoration phase. The principal property of this algorithm is that it produces a sequence of feasible suboptimal solutions. Each feasible solution is characterized by a lower value of the minimax performance index than any previous feasible solution. To facilitate numerical implementation, the intervals of integration are normalized to unit length. Several numerical examples are presented to illustrate the present approach. For comparison purposes, the analytical solutions, the single-subarc solutions, and the multiple-subarc solutions are presented. Key Words. MLnimax problems, ndnimax optimal control, numerical methods, continuous approach, single-subarc approach, multiple-subarc approach, transformation techniques, sequential gradient-restoration algorithms.
Onset of convection in fluid layers with nonuniform volumetric energy sources
(1979) Yücel, Adnan (1953-2002); Bayazitoglu, Yildiz; Chapman, Alan J.; Wierum, Frederic A.
The thermal stability of a fluid layer with nonuniform distribution of the volumetric energy sources is studied. The conditions leading to the onset of convective motions in the fluid are determined analytically by linear stability theory. The system considered consists of a fluid layer of infinite horizontal extent which is confined between two rigid parallel boundaries and subjected to general convective boundary conditions. The fluid is heated internally by way of absorption of the external radiation penetrating in the fluid body. The effects of the stabilizing and destabilizing temperature differences at the boundaries and the properties of the bounding surfaces are investigated. Optically thicker layers are found to be more stable.
Sequential gradient-restoration algorithm for mathematical programming problems with inequality constraints
(1983) Sims, Edward Michael; Miele, Angelo; Wierum, Frederic A.; Douglas, Andrew S.
The problem of minimizing a function f(x) of an n-vector x, subject to q equality constraints <{>(x) = and ninequality constraints w(x) _> , is considered. An algorithm of the sequential gradient-restoration type is developed. It involves the alternate succession of gradient phases and restoration phases. For general inequalities, each iteration of the gradient phase and the restoration phase requires the solution of a linear system of order q + n, where q denotes the number of equality constraints and n the number of inequality constraints. The unknowns of the linear systems are the q components of the multiplier X associated with the equality constraints and the n components of the multiplier p associated with the inequality constraints. Considerable simplifications are possible if the inequalities w(x) >_ have a special form. In this connection, the following cases are studied: (PI) lower bounds on x; and (P2) upper and lower bounds on x. If one exploits the special structure of Problems (PI) and (P2) and the properties of diagonal matrices, the algorithmic work per iteration can be reduced considerably. This is due to the fact that the multipliers X and p need not be computed simultaneously, but can be computed sequentially. Specifically, the multiplier X is determined by a linear equation of order q; then, the multiplier pis determined through subsequent multiplications. This means that, for Problems (PI) and (P2), the algorithmic work per iteration is about the same as the algorithmic work per iteration occurring in Problem (P): minimize a function f(x) of an n-vector x, subject to equality constraints (x) = .
Solar image characteristics of solar concentrators
(1979) Phillips, Paul Gregory; Bayazitoglu, Yildiz; Chapman, Alan J.; Wierum, Frederic A.
Solar beams can be concentrated by various optical systems in order to obtain energy at high temperatures. Among the various concentration devices the main criteria for classification deal with the optical systems used. In this work only concentrators using reflecting systems are considered. Host of the previous work done with these concentrators dealt with mathematically well defined systems. The method of analysis of these concentrators was simple but subjected to the problem of having-nonuniform intensity distributions on the absorber. The lack of a uniform intensity profile can disrupt the performance characteristics of the collection system and even ruin the absorber. Changing the geometries of the reflectors could alleviate this problem. The geometries, though, will no longer be mathematicaly well defined. A method of analysis developed in this work will study these mathematically complicated reflectors. Finite elements are used to develop a model for solar concentrators. This model accommodates the size of the solar disk when considering the incident field, and can also study complex reflector and absorber geometries. The present work has some limitations such that it is not general enough to handle many types of concentrators. These concentrators include secondary concentrators of double reflector systems and any other system that deals with ill-defined or broad incident fields. The model has been developed so that improvements in relaxing its limitations can be made. The method of analysis makes use of simple analytic geometry for the solution of specular reflections. All elements are assumed to be planar and specular properties are interpolated over the elements. The use of these elements is studied in three different models and only one of them is used in the final computer program. Two of these models use a type of ray tracing technique. This involves subdividing the incident field into small beams. Each beam is represented by a ray, and the ray is traced through all its reflections. The first method uses only one ray per element and does not lend itself well to accounting for solar size. The second method divides the beam on a reflector element into nine rays. This method is better at accounting for solar size. The specular factor model is the final variation of use of the basic analysis. It uses specular factors which are analogous to view factors for diffuse radiation to anlayze solar concentrators. The results are very accurate for single reflections. The second of the foregoing ray tracing models is chosen for use in the computer program. These results are compared with the previous works and some original results dealing with conical reflectors are examined. Although improvements in the division of the beam into nine rays and in handling various incident fields need to be made, the developed model and its computer application work quite well.
The effect of T-tail empennage geometry on the directional and lateral stability derivatives
(1977) Howard, Roland M.; Wierum, Frederic A.
The advent of the utilization of the T-tail in light aircraft design requires that new consideration be given as to the effect of imposed loads on the empennage and on the stability derivatives, each of which is greatly influenced. This thesis presents the results of wind tunnel tests of a model consisting of a fuselage, a vertical fin, and a horizontal stabilizer. Five different horizontal stabilizers (T-tails), each with a different aspect ratio and longitudinal position were tested. Theoretical calculations are compared with the test results, and discussion given as to the optimization of these geometric parameters.
Thermal comfort study of one window-walled room
(1979) Smith, Jan Preston; Chapman, Alan J.; Beckmann, Herbert K.; Wierum, Frederic A.
Human comfort as a function of location in a room with one window wall at a temperature different from the other walls is studied. Computer models of the radiant field in a room and of the thermal response of the human body are used to obtain the experimental data. The factors affecting human comfort in a typical office room with one wall exposed to common northern United States winter temperatures are discussed in detail. The computer programs utilized in this research are described and their appropriateness as models is justified with current thermal environmental information. The parameters of the research are outlined, and a description of the goals and assumptions is given. The conclusions reached from the research are documented in graphs and text.
Thermal properties of frozen saline soils
(1984) Jordan, Jonathan D.; Chapman, Alan J.; Wierum, Frederic A.; Walker, William F.
The thermal properties of three soils have been studied to ascertain the effects of saturating the soils with saline water. The frozen state is the primary area studied, although data during and after a phase change in the soils is also presented. The thermal properties evaluated include the thermal conductivity and thermal diffusivity, measured by means of the transient thermal probe technique, in which a metal probe is inserted into a cylindrical soil sample. This technique allows the simultaneous determination of the two thermal properties by recording the temperature response at two locations in the sample to an ideal line heat source from the probe. The experimental apparatus is described and the results are compared to several theoretical predictive methods of calculating the thermal conductivity of soils. The data from the phase change region were determined to be inconclusive and the results of the unfrozen soil were too few to find representative results. The results from frozen.state show very little effect from the salinity of the porewater. Any effects seem to be less than the accuracy of the experiment itself. The predictions from the theoretical models support this conclusion. Finally, recommended values for the thermal properties of the frozen soils are given as independent of both the temperature and porewater salinity for the ranges considered in this work.

Browsing by Author "Wierum, Frederic A."

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