What is critical radius of insulation explain its importance in electrical and thermal system?

What is critical radius of insulation explain its importance in electrical and thermal system?

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.

Why don’t we care about the critical radius of insulation while we insulating the hot water pipes or tanks?

THE CRITICAL RADIUS OF INSULATION. We know that by adding more insulation to a wall always decreases heat transfer. The thicker the insulation, the lower the heat transfer rate. Thus, insulating the pipe may actually increase the rate of heat transfer from the pipe instead of decreasing it when r2< rcr .

How do you find the critical radius of insulation?

1. r1=0.5mm=0.5×10−3m (Radius of wire)
2. r2=1.5mm=1.5×10−3m (Outer radius of insulation)
3. Kins=0.5W/mK (Thermal conductivity of insulation material)
4. t3=30℃=303K (Atmospheric temperature)
5. h=8W/m2K (Convective heat transfer coefficient for surrounding atmosphere)
6. t1=75℃=348K (Temperature of inside surface of insulation)

What is critical radius of insulation and critical thickness?

In a plane wall the area perpendicular to the direction of heat flow adding more insulation to a wall always decreases heat transfer. The thicker the insulation, the lower the heat transfer rate. This is due to the fact the outer surface have always the same area.

Which among the following has maximum value of 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.

Which metal has maximum value of thermal conductivity?

Copper

What is effect of temperature on thermal conductivity of metals?

In pure metals the electrical conductivity decreases with increasing temperature and thus the product of the two, the thermal conductivity, stays approximately constant. However, as temperatures approach absolute zero, the thermal conductivity decreases sharply.

What is the effect of temperature on metals?

Temperature affects metal in numerous ways. A higher temperature increases the electrical resistance of a metal, and a lower temperature reduces it. Heated metal undergoes thermal expansion and increases in volume.

What is the effect of temperature to some materials?

High temperature reduces material stiffness and strength, while low temperature increases material stiffness and strength. Almost all materials creep over time if exposed to elevated temperatures under applied load.

Which temperature does thermal conductivity of water start to fall?

The thermal conductivity exhibits a sharp drop in the temperature interval from the melting point (550 K) up to 650 K. At higher temperatures the thermal conductivity exhibits almost no temperature dependence.

What is the effect of temperature on specific conductivity?

The conductivity invariably increases with increasing temperature, opposite to metals but similar to graphite. It is affected by the nature of the ions, and by viscosity of the water. In low ionic concentrations (very pure water), the ionization of the water furnishes an appreciable part of the conducting ions.

What is the effect of temperature on resistivity?

As temperature rises, the number of phonons increases and with it the likelihood that the electrons and phonons will collide. Thus when temperature goes up, resistance goes up. For some materials, resistivity is a linear function of temperature. The resistivity of a conductor increases with temperature.

Why does conductivity increase with temperature?

An increase in temperature may also cause an increase in the number of ions in solution due to dissociation of molecules. As the conductivity of a solution is dependent on these factors then an increase in the solution’s temperature will lead to an increase in its conductivity.

Does water conductivity change with temperature?

Conductivity is temperature dependent. When water temperature increases, so will conductivity 3. For every 1°C increase, conductivity values can increase 2-4% 3. Temperature affects conductivity by increasing ionic mobility as well as the solubility of many salts and minerals 30.

Why conductivity decreases with increase in temperature?

The electrical conductivity of a metal decreases with the rise in temperature because the positively charged kernels present in the electron sea also acquire mobility and obstruct the movement of valence electrons responsible for conductivity.

What factors do not affect conductivity?

The factor which is not affecting the conductivity of any solution is. Solution : Dilution, temperature and nature of electrolyte affect the conductivity of solution.

What are the factors that affects the conductivity of solution?

There are three main factors that affect the conductivity of a solution: the concentrations of ions, the type of ions, and the temperature of the solution. 1) The concentration of dissolved ions. An electrolyte consists of dissolved ions (such as Na+ and Cl-) that carry electrical charges and can move through water.

What are the factors affecting electrical conductivity?

Factors Influencing Electrical Conductivity

• Metal Content.
• Porosity.
• Clay Content.
• Permeability.
• Skin Depth.

Why does conductivity increase with concentration?

As you increase the concentration of the solution you get more charge carrying ions, so the conductivity increases. But because the ions get closer together they begin to interact and slow each other down so the conductivity per mole of the ions is reduced.

Is conductivity directly proportional to concentration?

Answer: Specific Conductivity decreases with a decrease in concentration. Since the number of ions per unit volume that carry current in a solution decrease on dilution. Hence, concentration and conductivity are directly proportional to each other.

What is the relationship between conductivity and concentration?

The more concentrated a solution is, the higher the conductivity is. In most cases it is a proportional relationship. As the ion concentration increases, the conductivity increases.

Why does conductance decrease at high concentration?

Molar conductance is dependent on the concentration of the electrolyte. When the solution is dilute the number of ions available per unit volume reduces, resulting in the reduction of the conductivity.

Does conductance depend on concentration?

The conductance of such electrolytic solutions depends on the concentration of the ions and also on the nature of the ions present (through their charges and mobilities). Conductance behavior as a function of concentration is different for strong and weak electrolytes.

What is the effect on specific conductance on dilution?

The specific conductivity decreases on dilution. The equivalent conductivity and molar conductivity increases with dilution. The equivalent and molar conductivities tend to accumulate maximum value with increasing dilution.

Is conductivity linear with concentration?

The concentration and mobility of the ions are not independent properties. As the concentration of an ion increases, its mobility decreases. As a consequence, the conductivity increases linearly with respect to the square root of concentration instead of in direct proportion.