A new ground resistance was developed for use in existing vertical bore heat exchanger VBHEx design algorithms. The new ground resistance accounts for the added heat transfer mode of convection due to groundwater flow by using as its foundation the solution for a moving line heat source. The combined ground resistance is presented in terms of the dimensionless Fourier and Peclet parameters. Results show that significant convection heat transfer may occur within a variety of hydrogeological regimes, particularly when the Peclet number is larger than 0.01. Since the new model captures the influence of groundwater flow, the resulting ground resistance differs markedly from the conduction-only ground resistance currently used in many vertical borehole heat exchanger design algorithms.
A two-dimensional model that describes the temperature and moisture content changes for a bunker storage unit was developed. Various combinations of initial grain temperatures, initial grain moisture contents, and loading dates were used to determine anv advantages or disadvantages of each. Temperature and moisture content contour plots, dry matter loss, and condensation data were analvzed. The effects of only the load'ing dates on dry matter loss appeared to be minimal for all combinations tested. Relatively high dry matter loss values were experienced at the extreme temperature/moisture content combination of 30° C and 15% (w.b.). The combined effect of high initial temperatures and moisture contents resulted in an appreciable amount of moisture migration to the peak of the bunker cross-section making this area more susceptible to spoilage and microbial activity.
An analytical model of transient, simultaneous heat, water, and air transfer is developed in this paper. The resulting governing differential conservation equations are simplified by dimensional analysis and applied to a semi-infinite moist soil with an impermeable heat source at the boundary. Solutions for moisture and temperature distributions are generated numerically for varying surface heat flux and initial moisture content. Difficulties in using a moving boundary approach are discussed. The solutions predict, without using a moving boundary analysis, that a narrow zone with a steep moisture gradient moves through the soil at a rate such that the volume of soil dried per unit surface heat input is constant for a given initial moisture content.
The science of mechanics may trace back to Aristotle (384-322 B.C.) and Archimedes (c. 287-212 B.C.), while thermal science may trace back to the steam engines by Savery in 1697 and Newcomen in 1712 or to the works of Rankine, Clausius, and Lord Kelvin in the 1850s. Both are old sciences where, from time to time, definitions formulated for terms to serve the purpose of previous existing physical understanding are later found inadequate, incorrect, or inconvenient for the description of more complete modern knowledge. Some definitions and conventions in dynamics and thermodynamics are given differently and can be confusing to unsuspecting undergraduate students who are taking them in their curricula. To a certain extent, this is the case with the terms heat, work, potential energy, and conservation of energy. This paper is aimed at pointing out the curvy and bumpy stretches on the road from dynamics to thermodynamics, and vice versa. It is hoped that better inter-disciplinary understanding will enhance effective communication for instructors and better learning for engineering students. I. Concepts of Process, Path, and Heat A process is any change (or transformation) that a system undergoes from one state to another. The series of states through which a system passes during a process is called the path of the process. To describe a process completely in thermodynamics, one needs to specify the initial and final states of the process, the path it follows, and the interactions with the surroundings. A quasi-static, or quasi-equilibrium, process is one which proceeds in such a way that the system remains infinitely close to an equilibrium state all the time.
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