Steady Temperatures in a Rotating Cylinder—Some Variations in the Geometry and the Thermal Boundary Conditions

1986 ◽  
Vol 108 (3) ◽  
pp. 446-453 ◽  
Author(s):  
B. Gecim ◽  
W. O. Winer

Three cases are studied as variations in the geometry and the thermal boundary conditions pertinent to the classical flash temperature theory. First, the case of multiple surface heat sources is considered. It is shown that the relative location of the sources is the critical factor in predicting the local temperatures at each contact. Second, the case of a short cylinder (or a disk) is analyzed. In addition to the lateral surface boundary conditions, convective cooling from the side faces is considered. It is shown that a considerable reduction in bulk temperature can be achieved by effective cooling from the side faces. Third, the case of a hollow cylinder is studied where, in addition to the outer boundary conditions, uniform internal heating (or cooling) is considered. It is demonstrated that the bulk temperature can be varied significantly by changing the magnitude (and direction) of the internal heat flux. In both the second and the third cases, over a wide range of the pertinent parameters, it is shown that the local temperature rise remains virtually unchanged.

2020 ◽  
Author(s):  
MODI ZHU ◽  
Jingfeng Wang ◽  
Husayn Sharif ◽  
Valeriy Ivanov ◽  
Aleksey Sheshukov

Author(s):  
Andrea Ferrantelli ◽  
Jevgeni Fadejev ◽  
Jarek Kurnitski

As the energy efficiency demands for future buildings become increasingly stringent, preliminary assessments of energy consumption are mandatory. These are possible only through numerical simulations, whose reliability crucially depends on boundary conditions. We therefore investigate their role in numerical estimates for the usage of geothermal energy, performing annual simulations of transient heat transfer for a building employing a geothermal heat pump plant and energy piles. Starting from actual measurements, we solve the heat equations in 2D and 3D using COMSOL Multiphysics and IDA-ICE, and discover a negligible impact of the multiregional ground surface boundary conditions. Moreover, we verify that the thermal mass of the soil medium induces a small vertical temperature gradient on the piles surface. We also find a roughly constant temperature on each horizontal cross-section, with nearly identical values if the average temperature is integrated over the full plane or evaluated at one single point. Calculating the yearly heating need for an entire building we then show that the chosen upper boundary condition affects the energy balance dramatically. Using directly the pipes’ outlet temperature induces a 54% overestimation of the heat flux, while the exact ground surface temperature above the piles reduces the error to 0.03%.


2020 ◽  
Vol 159 ◽  
pp. 103717
Author(s):  
Nikta Iravani ◽  
Peyman Badiei ◽  
Maurizio Brocchini

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