{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Heat transfer Chapter 2

# Heat transfer Chapter 2 - Heat transfer ME 431 by Dr Afif...

This preview shows pages 1–3. Sign up to view the full content.

Heat transfer ME 431, by Dr. Afif Hasan ----------------------------------------------------------------------------------------------------------- - Chapter 2 Introduction to conduction Conduction heat transfer in a medium due to temperature gradient is governed by Fourier law of cooling. Heat flux : A q dx dT k q x x = - = q :is normal to the cross section area “A” or direction of heat flow will be always normal to surface of constant temperature.(isothermal surface). In general: n T k q n - = n: is normal to an isotherm. Heat flux is a vector quantity and can be written as T k q - = ) ( z T k y T j x T i k + + - = gradient. Or z y x q k q j q i q + + = Where: ; x T k q x - = ; y T k q y - = ; z T k q z - = k: is independent of direction (same in all directions) or isotropic. Note: Fourier law apply to all matter: liquid, solid, gas 1 dx dT x kA q - = n q x q y q n y x Two- dimensional system Conduction Isotherm

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Heat transfer ME 431, by Dr. Afif Hasan ----------------------------------------------------------------------------------------------------------- - magnitude& mechanism could be different?. Thermal conductivity : From Fourier law, thermal conductivity is defined as: ; x T q k x - = thermal conductivity of solid is larger than that of liquid which is larger than that of gases. As shown in figure 2.4 page 46 “k” of solids may be four orders of magnitude of that of gas . K solid >>K liquid >>K gas. 1-Solids: Conduction in solids due to two mechanisms: (i) lattice vibration waves (ii)Migration of free electrons. Solid comprised of free electrons and atoms bounded in periodic arrangement called the lattice thus thermal energy is transported by both lattice vibration and movement of free electrons. k= k e +k L where; k e : free electron k L: lattice vibration. For pure metals: k e = L 0 T/ ρ e L 0 : Lorenz number ρ e : electrical resistivity, where ρ e = ρ 0+ ρ / T.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern