What is meant by semi-infinite solids? In semi-infinite solids, at any instant of time ,there is always a point where the effect of heating or cooling at one of its boundaries is not felt at all. At this point the temperature remains unchanged. In semi infinite solids, the biot number values is What is meant by infinite solid? A solid which extends itself infinitely in all directions of space is known as infinite solid.
In infinite solids, the biot number value is in between 0. It is defined as the ratio of internal conductive resistance to the surface conductive resistance. What are the factors affecting the thermal conductivity? Moisture 2. Density of material 3. Pressure 4. Temperature 5. Structural of material Explain the significance of thermal diffusivity.
The physical significance of thermal diffusivity is that it tells us how fast heat is propagated or it diffuses through a material during changes of temperature with time What are Heislers charts? In Heislers chart, the solutions for temperature distributions and heat flows in plane walls, long cylinders and spheres with finite internal and surface resistance are presented. Heislers charts are nothing but a analytical solutions in the form of graphs. Dimensional analysis is a mathematical method which makes use of the study of the dimensions for solving several engineering problems.
This method can be applied to all types of fluid resistance, heat flow problems in fluid mechanics and thermodynamics. State Buckinghams theorem. Buckinghams theorem states as follows: If there are n variables in a dimensionally homogeneous equation and if these contain M fundamental dimensions, then the variables are arranged into n-m dimensionless terms.
These dimensional terms are called Buckinghams theorem What are all the advantages of dimensional analysis? It expresses the functional relationship between the variables in dimensional terms. It enables getting up a theoretical solution in a simplified dimensional form. The results of one series of test can be applied to alarge number of other similar problem with the help of dimensional analysis What are all the limitations of dimensional analysis? The complete information is not provided by dimensional analysis. It only indicates that there is some relationship between the parameters.
No information is given about the internal mechanism of physical phenomenon. Dimensional analysis does not give any clue regarding the selection of variables. Define Reynolds number Re It is defined as the ratio of inertia force to viscous force. Inertia force Viscous force. Define Prandtl number Pr It is the ratio of the momentum diffusivity to the thermal diffusivity.
It is defined as the ratio of the heat flow by convection process under an unit temperature gradient to the heat flow rate by conduction under an unit temperature gradient through a stationary thickness L of meter. Define Grashof number Gr. It is defined as the ratio of product of inertia force and buoyancy force to the square of viscous force Define Stanton number St It is the ratio of Mussels number to the product of Reynolds number and Prandtl number.
The fluids which obey the Newtons law of viscosity are called Newtonians fluids and those which do not obey are called non Newtonian fluids.
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What is meant by laminar flow and turbulent flow? Laminar flow: Laminar flow is sometimes called streams line flow. In this type of flow , the fluid moves in layer and each fluid particle follows a smooth continuous path. The fluid particals in each layer remain in an orderly sequence without mixing with each other. Turbulent flow: In addition to the laminar type of flow , a distinct irregular flow is frequently observed in nature.
This type of flow is called turbulent flow. The path of any individual particle is zig-zag and irregular. What is hydro dynamics boundary layer? Convection is a process of heat transfer that will occur between a solid surface and a fluid medium when they are at different temperatures. What is meant by free or natural convection?
If the fluid motion is produced due to change in density resulting from temperature gradients, the mode of heat transfer is said to be free or natural convection. What is forced convection? If the fluid motion is artificially created by means of an external force like a blower of fan ,that type of heat transfer is known as forced convection.
What is the form of equation used to calculate transfer for flow through cylindrical pipes? What are the dimensional parameters used in forced convection? Reynolds number Re 2. Nusselt Number Nu 3. Prandtl number Pr Define boundary layer thickness.
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In the boundary layer concept the flow field over a body is divided into two regions: A thin region near the body called the boundary layer where the velocity and the temperature gradients are large. The region outside the boundary layer where the velocity and the temperature gradients are very nearly equal to their free stream values. Define displacement thickness. The displacement thickness is the distance, measured perpendicular to the boundary, by which the free stream is displaced on account of formation of boundary layer.
Define momentum thickness. The momentum thickness is defined as the distance through which the total loss of momentum per second be equal to if it were passing a stationary plate. Define energy thickness. The energy thickness can be defined as the distance, measured perpendicular to the boundary of the solid body ,by which the boundary should be displaced to compensate for the reduction in kinetic energy of the flowing fluid on account of boundary layer formation. The change of phase from liquid to vapour state is known as boiling What is meant by condensation?
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The change of phase from vapour to liquid state is known as condensation. Give the application of boiling and condensation. Boiling and condensation process finds wide application as mentioned below. Thermal and nuclear power point 2.
Refrigeration systems. Process of heating and cooling.
Air conditioning system. What is meant pool boiling? If heat is added to a liquid from a submerged solid surface, the boiling process is referred to as pool boiling. In this case the liquid above the hot surface is essentially stagnant and it motion near the surface is due to free convection and mixing induced by bubble growth and detachment. What are the modes of condensation?
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There are two modes of condensation 1. Film wise condensation. Drop wise condensation What is Film wise condensation? The liquid condensate wets the solid surface, spread out and forms a continuous film over the entire surface is known as film wise condensation. What is Drop wise condensation? The vapour condenses into small liquid droplets of various sizes which fall down the surface in a random fashion.
What is heat exchange? The heat exchange is defined as equipment which transfers the heat from a hot fluid to a cold fluid. What are the types of heat exchanger? The types of heat exchanger are as follows. Direct contact heat exchangers. Indirect contact heat exchangers 3. Surface heat exchangers 4. Parallel flow heat exchanger What is meant by in direct contact heat exchangers? In this type of heat exchangers, the transfer of heat between two fluids could be carried out by transmission through a wall which separates the two fluids What is meant by Regenerators?
In this type of heat exchangers, hot and cold fluids flow alternately through the same space.
Examples: IC engines, Gas turbine. What is meant by Recuperators or surface heat exchangers? This is the most common type of heat exchangers in which the hot and cold fluid do not come into direct contact with each other but are separated by a tube wall or a surface Examples: Automobile radiators, Air pre heaters , economizers. In this type of heat exchangers, hot and cold fluids move in the same direction.