Final control questions on the subject “heat engineering” The purpose and function of the subject. Working parameter. Status parameters. Base words and phrases

 
Base words and phrases: temperature area, gradient, Fure, wall, thermal conductivity, flow, 
thermal resistance 
Heat conduction is the vibration of microparticles of the body 
heat is transferred through movement. Thermal conductivity 
occurs mainly in solids. Heat in heat conduction 
in the collision of molecules with different energies in gases, 
free electricity in metals in the vibration of molecules in liquids 
heat is transferred as a result of diffusion. 

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Convection occurs only in liquids and gases. Z saws 
The phenomenon of displacement due to movement is called convection. 
Heat is convective when conduction and convection occur at the same time 
called heat transfer. 
There are 2 types of convection: free and forced convection. Free 
convection occurs due to the density difference, forced convection 
and it happens under the influence of an external force (with the help of a pump, fans). 
In the radiation method, heat is transmitted using electromagnetic waves 
Temperature field. To the set of temperatures at different points of the body 
is called the temperature field. 
t= f(x,y,z,r) 
r is time. 
The temperature field is divided into 2 different states: 
1) area of stable temperature m (temperature does not change over time); 
2) unstable temperature field (temperature changes over time). 
The temperature field m is three-dimensional t=f(x,y,z), two-dimensional t = f(x,y) 
and one-dimensional t = (x) will be 
Temperature gradient. If we connect the points of the body with the same temperature, 
an isothermal surface is formed. 2 isothermal surfaces: temperature t and multiple At 
Let's consider a surface with a temperature of These surfaces are with each other 
does not intersect. If we transfer different directions from point A to the isothermal surface, 
temperature change is different. Normal to the isothermal surface 
If we cross the route, the temperature change will be higher. 
Distance along the normal between isotherms of temperature change (At). 
The ratio of An to is called the temperature gradient 
Differential equation of heat transfer. Heat 
quantities involved in heat transfer through conduction 
differential equation of heat transfer between the relationship 
determines. 
α is the coefficient of thermal conductivity 
Laplace operator 
qv is the body's internal heat source
Single value conditions. Apply the differential equation to a concrete event 
you need to know the single-valued terms to achieve this. 
1. Geometric condition (body dimensions, structure); 
2. Physical condition (physical properties of the body); 
3. Time condition (stable, unstable state); 
4. Boundary conditions: 
I order boundary condition t = f (x,y,z, g ); 
II order boundary condition q = f (x,y, z, g); 
III order boundary condition liquid temperature: tc1> , tc2 

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Fourier's law: Fourier's law of heat conduction states that the rate of heat conduction 
through a material is proportional to the temperature gradient and the cross-
sectional area of the material. 
21. Thermal conductivity of a flat single layer wall