System of nomograms for calculation Grashof number Gr
graph-analytical calculation of the Grashof criterion (Grashof criterion)
The Grashof number (Grashof criterion) characterizes the ratio of the lift force arising from the thermal expansion of the gas to the viscous forces.
Formula for calculating the Grashof criterion
Gr = g · β · L3 · Δt / υ2
Scheme of the nomogram system for calculating the Grashof criterion
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Notations
in the formula and on the nomograms for the graphoanalytical calculation of the Grashof criterion
g
- free fall acceleration, m/s2;
L
- the characteristic size, mm;
b
- coefficient of volumetric expansion, 1/K;
Δt
- temperature pressure, K;
n
- coefficient of kinematic viscosity, m2/h.
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The volumetric thermal expansion coefficient β characterizes the relative change in body volume when its temperature changes by one degree (at constant pressure).
Viscosity is the state of "internal friction" of a substance (friction between layers of a liquid or gas), which is expressed in the "internal resistance" of a liquid to the process of its movement, more precisely, the resistance to the movement of some layers of a liquid relative to others.
The coefficient of kinematic viscosity υ characterizes the viscous state of a substance, taking into account the influence of gravity.
Franz Grashof (1826-1893) - German scientist, after whom the Grashof number is named,
Professor at the Department of Applied Mechanics and Machine Theory at the Karlsruhe Polytechnic, Founder of the Society of German Engineers.
Nomogram systems for determining the Grashof criterion
Ranges of parameters on systems of nomograms:
Δt - (1 ... 3001) K
b - (0.3 ... 5)·10-3 1/K
n - (0.001 ... 3) m2/h
L - (0.2 ... 10) mm
Gr - 0.2 ... 220
Topic of this section: Graph-analytical calculation of the Grashof number
graphic-analytical systems
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