The critical radius of insulation is a counterintuitive concept within the study of heat transfer. The theory states that adding insulation to a cylindrical or spherical object will increase the rate of heat loss rather than decrease it , if the radius (thickness) of the insulation is at its “critical” value.
What is critical radius in thermodynamics?
Therefore there exists one particular radial thickness for the given insulation material, radius of the wire and surrounding conditions which will have maximum conduction and convection heat transfer. That particular radial thickness is called critical radius of insulation.
Is there any importance of critical radius of insulation on spherical reservoir explain?
This is due to the fact the outer surface have always the same area. But in cylindrical and spherical coordinates, the addition of insulation also increases the outer surface , which decreases the convection resistance at the outer surface. ... In the case of cylinders and spheres it is called critical radius.
What is the critical radius of insulation and economic thickness of insulation?
Explanation: Critical radius of insulation = k/h = 0.0825/8 = 0.01031 m = 10.31 mm .
What is meant by critical thickness of insulation explain its significance?
Critical thickness of insulation means maximum heat loss with min thermal resistance . This concept is useful in the situation when surface area of the base object increases with the insulation, i.e., cylindrical and spherical systems.
What is critical radius in thermal insulation?
resistance of insulation, but decreases the convection resistance of the surface because of the increase in the. outer surface area. Due to these opposite effects, a critical radius of insulation is defined as the outer radius . that provides maximum rate of heat transfer .
What is critical radius of insulation?
The critical radius of insulation is the thickness of insulation at which the rate of heat transfer through the body is maximum . It means that the rate of heat transfer increases with an increase in the thickness of insulation up to the critical radius of insulation.
What is critical radius of insulation for Sphere?
The thickness up to which heat flow increases and after which heat flow decreases is termed as Critical thickness. The insulation radius at which resistance to heat flow is minimum and consequently heat flow rate is maximum is called “critical radius”.
What is the value of critical radius of insulation for spherical object?
What is the value of a critical radius? Explanation: Critical radius of insulation = k/h = 0.0825/8 = 0.01031 m = 10.31 mm .
What is the significance of critical thickness of insulation in current carrying conductors?
It reduces the thermal resistance of the insulation and thereby enables theconductor to carry a higher current.
Which is the right expression for critical radius of insulation for cylinder?
r=r1+t (t=thickness of insulation) .
How do you calculate critical thickness?
- r1=0.5mm=0.5×10−3m (Radius of wire)
- r2=1.5mm=1.5×10−3m (Outer radius of insulation)
- Kins=0.5W/mK (Thermal conductivity of insulation material)
- t3=30°C=303K (Atmospheric temperature)
- h=8W/m2K (Convective heat transfer coefficient for surrounding atmosphere)
What is critical radius of insulation Mcq?
Critical Thickness of Insulation MCQ Question 4 Detailed Solution. Concept: The critical radius of insulation r c is the radius up to which the addition of material increases the rate of heat loss and after critical radius addition of heat results in a decrease in heat loss.
What is the critical thickness of insulation on a steam pipe?
| Nominal Pipe Size NPS (inches) Recommended minimum Thickness of Insulation (inches) * | Temperature Range ( o C) | Hot Water High Pressure Steam | < 1′′ 1.0 2.5 | 1 1/4′′ – 2′′ 1.0 2.5 |
|---|
Why is there no critical insulation thickness for a plane wall that has insulation?
From a certain thickness of the insulation the thermal resistivity against conduction increases faster than the heat transfer at the outside of the insulation due to convection. There shouldn’t be a critical thickness for the insulation for a plane wall, because it doesn’t increase the surface of the insulated object .
What is thermal diffusivity and explain its significance?
Thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure . It measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. High diffusivity means heat transfers rapidly.
What is critical radius of nucleation?
Critical radius is the minimum particle size from which an aggregate is thermodynamically stable . ... When these conditions are not satisfied, a rapid creation-annihilation of aggregates takes place and the nucleation and posterior crystal growth process does not happen.
Is the radius increase in hollow cylinder the temperature?
It is observed that the temperature increases when the radius ratio decreases , this obtained result is due to the increasing in the thickness of the hollow cylinder and therefore the thermal resistance will be increased.
Which has high thermal conductivity?
Diamond is the leading thermally conductive material and has conductivity values measured 5x’s higher than copper, the most manufactured metal in the United States. Diamond atoms are composed of a simple carbon backbone that is an ideal molecular structure for effective heat transfer.
What happens when the radius of insulation on a pipe exceeds the critical value?
When the thickness of insulation on a pipe exceeds the critical value the heat flow rate. Options are : Increases .
What is effectiveness of fin?
the ratio of actual heat transferred from fin area to the heat which would be transferred if entire fin area was at base temperature.
Why the heat transfer coefficient is important?
It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. ... The heat transfer coefficient is the reciprocal of thermal insulance . This is used for building materials (R-value) and for clothing insulation.
What is an example of a thermal insulator?
Materials that are poor conductors of thermal energy are called thermal insulators. Gases such as air and materials such as plastic and wood are thermal insulators.
What is unit of thermal diffusivity?
In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI derived unit of m2/hr .
What happens when thermal conductivity becomes infinite?
Super fluids are also unique because they have infinite thermal conductivity. This means that any volume of super fluid, no matter how large, will always be precisely the same temperature throughout.
What is critical radius in material science?
In a collection of supported particles of different sizes, the critical radius is the size of the particle that is in equilibrium with the surrounding adatom concentration . Such a particle neither grows nor shrinks due to Ostwald ripening, whereas larger particles grow and smaller particles shrink.
