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A comprehensive equation to determine the rate of local entropy generation in multicomponent, reacting, laminar fluid flow involving heat and mass transfer is formulated based on species-average velocity in a multicomponent continuum. The entropy-generation equation developed in this study suggests that species diffusion induces a diffusive-viscous effect, heretofore not reported in the literature, which could contribute significantly to entropy generation in multicomponent fluid systems, and that entropy generation in a multicomponent system exceeds that in a single-component fluid system having similar velocity and temperature distributions because a greater number of irreversible processes, such as species diffusion, chemical reaction, and the Soret and Dufour effects, are involved. Under appropriate conditions, if the diffusive-viscous effect is neglected, the entropy-generation equation of this study reduces to those reported in the literature for simpler fluid systems based on mean flow.

While Kolmogorov complexity is the accepted absolute measure of information content in an individual finite object, a similarly absolute notion is needed for the information distance between two individual objects, for example, two pictures. We give several natural definitions of a universal information metric, based on length of shortest programs for either ordinary computations or reversible (dissipationless) computations. It turns out that these definitions are equivalent up to an additive logarithmic term. We show that the information distance is a universal cognitive similarity distance. We investigate the maximal correlation of the shortest programs involved, the maximal uncorrelation of programs (a generalization of the Slepian-Wolf theorem of classical information theory), and the density properties of the discrete metric spaces induced by the information distances. A related distance measures the amount of nonreversibility of a computation. Using the physical theory of reversible computation, we give an appropriate (universal, antisymmetric, and transitive) measure of the thermodynamic work required to transform one object in another object by the most efficient process. Information distance between individual objects is needed in pattern recognition where one wants to express effective notions of "pattern similarity" or "cognitive similarity" between individual objects and in thermodynamics of computation where one wants to analyze the energy dissipation of a computation from a particular input to a particular output. Index Terms - Algorithmic information theory, description complexity, entropy, heat dissipation, information distance, information metric, irreversible computation, Kolmogorov complexity, pattern recognition, reversible computation, thermodynamics of computation, universal cognitive distance.

An approximate method for calculation of the hourly output of a solar still over a 24-hour cycle has been studied. The hourly performance of a solar still is predicted given the values of the insolation, ambient temperature, wind heat-transfer coefficient, water depth, and the heat-transfer coefficient through base and sides. The proposed method does not require graphical constructions and does not assume constant heat-transfer coefficients as in the previous methods. The possibility of using the values of the heat-transfer coefficients for the preceding time interval in the heat balance equations is examined. In fact, two variants of the basic method of calculation are examined. The hourly rate of evaporation is obtained. The results are compared to those obtained by numerical solution of the complete set of heat balance equations. The errors from the approximate method in prediction of the 24-hour output are within + or - 1.5 percent of the values from the numerical solution using the heat balance equations. The range of variables covered is 5 to 15 cms in water depth, 0 to 3 W/m squared K in a heat-transfer coefficient through base and sides, and 5 to 40 W/m squared K in a wind heat-transfer coefficient.

It has been suggested that the sign of charge acquired by a riming graupel pellet during ice crystal interactions depends on its surface state being negative when it is evaporating and positive when growing by vapor diffusion. Experiments were conducted to determine the surface states of riming cylinders in two previous laboratory studies of thunderstorm electrification. Calculations of the heat balance of the simulated graupel pellets are considered in terms of experimental measurements of the charge transferred under similar conditions. The results show that the contribution from in-cloud supercooled droplets is not always adequate to enable the graupel surface to grow by vapor diffusion in all laboratory cloud conditions where it acquires a net positive charge. It is suggested that factors such as the vapor fields around droplets freezing on its surface and the shape and surface roughness of the graupel may play important roles in determining the surface state and hence the overall sign of the charge transfer. Furthermore, the graupel charges negatively under specific conditions where it is clearly growing from the vapor, confirming that it is imperative to consider the relative growth rate of the two interacting surfaces rather than that of the graupel alone. It is concluded that, during the interaction of two ice particles, the positive charge is generally acquired by the surface that is growing faster or evaporating slower at the point of impact. A suitable physical mechanism may be provided by the liquidlike layer hypothesis of Baker and Dash, and it is suggested how it may be extended to include the cases when one or both of the surfaces are evaporating.

The problem of excessive heat buildup in a heat diffusion supported thermosetting process may lead, especially in the case of thick composite profiles, to compromised quality or even thermal degradation of the final product. A computer simulation of a real manufacturing process demonstrates this intrinsic weakness of the conventional manufacturing process by showing nonuniformities in the degree of cure development and a temperature inversion at the end of the processing cycle. Those nonuniformities in thermal expansion and contraction may be avoided by heating the composite uniformly throughout the whole cross section. This can be achieved with the help of electromagnetic irradiation. The electric energy absorption and, hence, conversion to heat takes place uniformly in the whole bulk of the material, regardless of the position. In effect, one can expect that the uniformly fast cured composite features superior mechanical properties over that of a composite that is conventionally processed.

This paper deals with the thermal management of a TBGA chip carrier package. In TBGA packages the backside of the chip is available for heat sink or heat spreader (cover plate) attach. By attaching a heat sink directly to the chip and using a thin layer of high thermal conductivity adhesive, a very low internal thermal resistance can be achieved. The package is attached to an organic card and placed vertically in a channel. A three-dimensional conjugate heat transfer model is used, accounting for conduction and radiation in the package and card and convection in the surrounding air. A simplified turbulence model is developed to predict temperatures in the low Re turbulence regime. A parametric study is performed to evaluate the effects of card design, air velocities, interconnect thermal conductivities and thermal radiation on the chip junction temperatures. An experimental study was also conducted to verify the model. Even though the geometry is highly complex due to the multilayer construction of the module and the card, agreement between the model and the experimental measurement is excellent. It was shown that radiation heat transfer can be an equally significant mode as convection in the natural convection regime. [S1043-7398(00)01302-5]

This paper presents a solution methodology for the optimal placement of convectively and conductively air-cooled electronic components on planar printed wiring boards considering thermal and electrical/cost design objectives. The methodology combines the use of a heat transfer solver for the prediction of the temperature distribution among the electronic components and a genetic algorithm for the adaptive search of optimal or near optimal solutions and a multiobjective optimization strategy (Pareto optimization and multiattribute utility analysis). After proper validation of the elements of the solution methodology (heat transfer solver/genetic algorithm) in isolation, the methodology under consideration is tested using a placement problem (case study) that considers as optimization criteria the minimization of an estimate of the failure rate of the system of components due to thermal overheating (via an Arrhenius relation) and the minimization of the total wiring length given some interconnectivity requirements. Results corresponding to the case study are presented and discussed for both Pareto optimization and multiattribute utility analysis. [S1043-7398(00)00801-X]

Wearable computers are rugged, portable computers that can be comfortably worn on the body and easily operated for maintenance applications. The recently developed process of Shape Deposition Manufacturing has created the opportunity to embed the electronics of wearable computers in a polymer composite substrate. As both a protective outer case and a conductive heat dissipating medium, the substrate satisfies two basic constraints of wearable computer design: ruggedness and cooling efficiency. One such application of embedded electronics is the VuMan3R, a wearable computer designed and manufactured at Carnegie Mellon University for aircraft maintenance. This paper combines finite element numerical simulations, physical experimentation, and analytical models to understand the thermal phenomena of embedded electronic design and to explore the thermal design space. Numerical models ascertain the effect of heat spreaders and polymer composite substrates on the thermal performance, while physical experimentation of an embedded electronic artifact ensures the accuracy of the numerical simulations and the practicality of the thermal design. Analytical models using thermal resistance networks predict the heat flow paths within the embedded electronic artifact as well as the role of conductive fillers used in polymer composites. [S1043-7398(00)00102-X]

This paper introduces an algorithm that focuses on the placement of the power dissipating chips for multichip module applications. The main design issue is addressed on the chip placement to achieve uniform thermal distribution. Our approach to the placement problem is based on the modified force-directed placement method. The proposed thermal force-directed placement method is to relate the force equations to the power dissipation values of the individual bare chip. Examples of multichip placement are presented. The finite element simulation results are also investigated and compared with quadrisection placement methods. [S1043-7398(00)01002-1]