传热学chap4第4稳态传导.pdf

Chapter 4 Unsteady-State Conduction 4-1 Introduction Steady-State: T =f (x, y, z) → T =f (x) → T = ax+b Unsteady-State: T =f (, x, y, z) → T =f (, x) → T = ? If a solid body is suddenly subjected to a change in environment, some time mus apse (流逝) before equilibrium temperature condition will prevail (建立) in the body. We refer to the equilibrium condition as the steady state and calculate the temperature distribution and heat transfer by methods described haps. 2. Chapter 4 Unsteady-State Conduction 4-1 Introduction The upper figure shows the temperature change in a ne while the left side is T1 H suddenly kept at temperature T , and the 1 G right side i posed to a fluid of temperature T E i T , which is the same as the initial AB C i temperature. The lower figure shows the temperature Ti change for a ne initially at a uniform temperature T , at time zero the surfaces are i suddenly lowered to T = T . T1 1 2L Consider an infinite ne of thickness 2L. The ne is initially at a uniform temperature T and at time zero the i surfaces are suddenly lowered to T = T . 1 Differential equation: