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Questions and Answers
What is the formula for convection heat transfer rate?
What is the formula for convection heat transfer rate?
Qconv = hAs (Ts - T)
What is the thermal resistance of the surface against heat convection?
What is the thermal resistance of the surface against heat convection?
Rconv = 1 / (hAs)
What is the formula for radiation heat transfer rate?
What is the formula for radiation heat transfer rate?
Qrad = hrad As (Ts^4 - Tsurr^4)
What is the thermal resistance of a surface against radiation?
What is the thermal resistance of a surface against radiation?
What is the unit of convection heat transfer coefficient?
What is the unit of convection heat transfer coefficient?
What is the unit of radiation heat transfer coefficient?
What is the unit of radiation heat transfer coefficient?
What is the formula for convection heat transfer rate in terms of convection resistance?
What is the formula for convection heat transfer rate in terms of convection resistance?
What is the formula for radiation heat transfer rate in terms of radiation resistance?
What is the formula for radiation heat transfer rate in terms of radiation resistance?
What is the concept that can be used to solve heat conduction problems without involving differential equations?
What is the concept that can be used to solve heat conduction problems without involving differential equations?
What is the analogy between heat conduction and electrical circuit problems?
What is the analogy between heat conduction and electrical circuit problems?
What is the geometric shape of the plane wall considered in the problem of one-dimensional steady heat conduction?
What is the geometric shape of the plane wall considered in the problem of one-dimensional steady heat conduction?
What is the relationship between the temperature distribution and the distance x through the wall under steady conditions?
What is the relationship between the temperature distribution and the distance x through the wall under steady conditions?
What is the expression for the rate of conduction heat transfer Qcond,wall through the wall?
What is the expression for the rate of conduction heat transfer Qcond,wall through the wall?
What is the thermal resistance of the wall against heat conduction, Rwall?
What is the thermal resistance of the wall against heat conduction, Rwall?
What is the expression for the heat conduction through a plane wall in terms of thermal resistance?
What is the expression for the heat conduction through a plane wall in terms of thermal resistance?
What are the typical units of thermal resistance, Rwall?
What are the typical units of thermal resistance, Rwall?
What are the two ways heat can be transferred in a solid?
What are the two ways heat can be transferred in a solid?
What happens to heat transfer when a fluid is still (no bulk fluid motion)?
What happens to heat transfer when a fluid is still (no bulk fluid motion)?
What is the role of gases in radiation?
What is the role of gases in radiation?
What is the primary mode of heat transfer in a vacuum?
What is the primary mode of heat transfer in a vacuum?
What is the condition for approximating heat conduction as one-dimensional in a large plane wall?
What is the condition for approximating heat conduction as one-dimensional in a large plane wall?
What is the relationship between convection and conduction in a fluid?
What is the relationship between convection and conduction in a fluid?
What is the primary mode of heat transfer in a liquid?
What is the primary mode of heat transfer in a liquid?
Can a gas between two solid surfaces interfere with radiation?
Can a gas between two solid surfaces interfere with radiation?
What is the main assumption in the heat transfer problem of a single-pane window, considering the temperature variation?
What is the main assumption in the heat transfer problem of a single-pane window, considering the temperature variation?
What is the thermal conductivity of the glass window in the example problem?
What is the thermal conductivity of the glass window in the example problem?
What is the purpose of the heat transfer coefficients h1 and h2 in the single-pane window problem?
What is the purpose of the heat transfer coefficients h1 and h2 in the single-pane window problem?
What is the temperature of the surroundings in the steam pipe problem?
What is the temperature of the surroundings in the steam pipe problem?
What is the assumption made for the thermal conductivity of the wall in the problem of steady one-dimensional heat conduction?
What is the assumption made for the thermal conductivity of the wall in the problem of steady one-dimensional heat conduction?
What is the thickness of the glass wool insulation in the steam pipe problem?
What is the thickness of the glass wool insulation in the steam pipe problem?
What is the rate of heat loss from the steam per unit length of the pipe?
What is the rate of heat loss from the steam per unit length of the pipe?
Why does adding insulation to a wall always decrease heat transfer?
Why does adding insulation to a wall always decrease heat transfer?
What happens to the convection resistance of a cylindrical pipe or a spherical shell when insulation is added?
What happens to the convection resistance of a cylindrical pipe or a spherical shell when insulation is added?
What is the purpose of finned surfaces in heat transfer?
What is the purpose of finned surfaces in heat transfer?
What is the total thermal resistance in the steam pipe problem?
What is the total thermal resistance in the steam pipe problem?
What is the condition required to determine the value of r2 at which Q reaches a maximum?
What is the condition required to determine the value of r2 at which Q reaches a maximum?
What is the temperature of the right surface of the wall at x = L?
What is the temperature of the right surface of the wall at x = L?
What is the effect of adding insulation to a cylindrical pipe on the conduction resistance?
What is the effect of adding insulation to a cylindrical pipe on the conduction resistance?
Why does the heat transfer from a pipe may increase or decrease when insulation is added?
Why does the heat transfer from a pipe may increase or decrease when insulation is added?
What is the expression for the rate of heat transfer from the insulated pipe to the surrounding air?
What is the expression for the rate of heat transfer from the insulated pipe to the surrounding air?
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Study Notes
Convection Heat Transfer
- The convection heat transfer rate (Qconv) can be expressed as: Qconv = hAs (Ts - T) where h is the convection heat transfer coefficient, As is the surface area, Ts is the surface temperature, and T is the fluid temperature.
- The convection resistance (Rconv) of a surface can be expressed as: Rconv = 1 / hAs
Radiation Heat Transfer
- The radiation heat transfer rate (Qrad) can be expressed as: Qrad = hrad As (Ts^4 - Tsurr^4) where hrad is the radiation heat transfer coefficient, As is the surface area, Ts is the surface temperature, and Tsurr is the surrounding temperature.
- The radiation resistance (Rrad) of a surface can be expressed as: Rrad = 1 / hrad As
Heat Transfer Modes
- Conduction, convection, and radiation are the three modes of heat transfer.
- Conduction occurs through a stationary medium, convection occurs through a moving fluid, and radiation occurs through electromagnetic waves.
- The mode of heat transfer depends on the presence or absence of fluid motion and the temperature differences between surfaces.
One-Dimensional Heat Conduction
- Heat conduction through a large plane wall, cylinder, or sphere can be approximated as one-dimensional.
- The thermal resistance of a plane wall can be expressed as: Rwall = L / kA, where L is the thickness of the wall, k is the thermal conductivity, and A is the cross-sectional area.
- The rate of heat conduction (Qcond) can be expressed as: Qcond = kA (T1 - T2) / L, where T1 and T2 are the temperatures on either side of the wall.
Thermal Resistance Concept
- Thermal resistance is analogous to electrical resistance, with temperature difference as the driving force and heat transfer rate as the resulting flow.
- Thermal resistance can be used to analyze heat conduction problems in various geometries, including plane walls, cylinders, and spheres.
Critical Radius of Insulation
- Adding insulation to a wall always decreases heat transfer, but adding insulation to a cylindrical pipe or spherical shell can increase or decrease heat transfer, depending on the dominance of conduction and convection resistances.
- The critical radius of insulation is the radius at which the heat transfer rate reaches a maximum or minimum.
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