Concepts and Formulas for Quick Revision of Heat Transfer

Formula for Heat Conduction:

Q = kA(T1 - T2) / L

where:

A Revision Book of Mechanical Engineering: Concepts & Formulas for Quick Revision-Heat Transfer

by Marie Cirano

5 out of 5

Language	:	English
File size	:	2782 KB
Text-to-Speech	:	Enabled
Enhanced typesetting	:	Enabled
Word Wise	:	Enabled
Print length	:	41 pages
Screen Reader	:	Supported

FREE

• Q is the heat transfer rate (W)
• k is the thermal conductivity (W/mK)
• A is the area of contact (m2)
• T1 and T2 are the temperatures of the objects in contact (K)
• L is the distance between the objects (m)

Formula for Heat Convection:

Q = hA(Ts - Tf)

where:

• Q is the heat transfer rate (W)
• h is the convection heat transfer coefficient (W/m2K)
• A is the surface area of the object exposed to the fluid (m2)
• Ts is the temperature of the object's surface (K)
• Tf is the temperature of the fluid (K)

Formula for Heat Radiation:

Q = εσA(T4 - Ts4)

where:

• Q is the heat transfer rate (W)
• ε is the emissivity of the surface (dimensionless)
• σ is the Stefan-Boltzmann constant (5.67 x 10-8 W/m2K4)
• A is the surface area of the object (m2)
• T is the absolute temperature of the object (K)
• Ts is the absolute temperature of the surroundings (K)

Formula for Specific Heat Capacity:

cp = Q / (mΔT)

where:

• cp is the specific heat capacity (J/kgK)
• Q is the heat absorbed or released (J)
• m is the mass of the material (kg)
• ΔT is the change in temperature (K)

Formula for Thermal Resistance:

R = L / kA

where:

• R is the thermal resistance (m2K/W)
• L is the thickness of the material (m)
• k is the thermal conductivity (W/mK)
• A is the surface area (m2)

Formula for Critical Heat Flux:

qcr = hfgρgσ(ρl - ρg)3/2 / μlL

where:

• qcr is the critical heat flux (W/m2)
• hfg is the latent heat of vaporization (J/kg)
• ρ is the density (kg/m3)
• g is the acceleration due to gravity (m/s2)
• σ is the surface tension (N/m)
• μl is the liquid viscosity (Pa-s)
• L is the characteristic length (m)

Examples of Empirical Correlations:

• Nusselt Number for Laminar Flow in a Tube: Nu = 4.36
• Colburn Factor for Turbulent Flow in a Tube: jH = 0.023Re0.8Prn
• Chilton-Colburn Analogy for Gas Flow: St = jHPr2/3

where:

• Nu is the Nusselt number
• Re is the Reynolds number
• Pr is the Prandtl number
• jH is the Colburn factor
• St is the Stanton number

Types of Heat Exchangers:

• Shell-and-Tube Heat Exchanger: Consists of a series of tubes enclosed in a cylindrical shell.
• Double-Pipe Heat Exchanger: Consists of two concentric pipes, with the fluid entering and leaving through the inner and outer pipes.
• Plate-and-Frame Heat Exchanger: Uses parallel plates separated by gaskets to create flow channels.

A Revision Book of Mechanical Engineering: Concepts & Formulas for Quick Revision-Heat Transfer

by Marie Cirano

5 out of 5

Language	:	English
File size	:	2782 KB
Text-to-Speech	:	Enabled
Enhanced typesetting	:	Enabled
Word Wise	:	Enabled
Print length	:	41 pages
Screen Reader	:	Supported

FREE