The concept of radiation shielding is well known in modern day to day applications including nuclear reactors to sunblock cream used for human beings. Consider the following image as first lesson on understanding the concept of radiation shielding: Let's try to understand radiation shielding effectiveness by a simple example. Let's consider a thin plate receiving radiations on one side from a radiation source at 650C and radiates on the other face to a surface at 150C. As a first step, determine the temperature of thin plate. For simple analysis, consider emissivity =1 and neglect convection heat flow. In second step, according to your observation, is thin plat an effective radiation shielding material based on information above. Consider the steady-state temperature distributions within a composite wall composed of Material A and Material B for the two cases shown. There is no internal generation, and the conduction process is one-dimensional. Answer the following questions for each case. Which material has the higher thermal conductivity? Does the thermal conductivity vary significantly with temperature? If so, how? Describe the heat flux distribution qx(x) through the composite wall. If the thickness and thermal conductivity of each material were both doubled and the boundary temperatures remained the same, what would be the effect on the heat flux distribution? Case 1: Linear temperature distributions exist in both materials. Case 2: Nonlinear temperature distributions exist in both materials. A high-temperature, gas-cooled nuclear reactor consists of a composite cylindrical wall for which a thorium fuel element (k57W/mK) is encased in graphite (k3W/mK) and gaseous helium flows through an annular coolant channel. Consider conditions for which the helium temperature is T=600K and the convection coefficient at the outer surface of the graphite is h=2000W/m2K a) If thermal energy is uniformly generated in the fuel element at a rate q=108W/m3, what are the temperatures T1 and T2 at the inner and outer surfaces, respectively, of the fuel element? b) Compute and plot the temperature distribution in the composite wall for selected values of q. What is the maximum allowable value of q ? A wire of diameter D=2mm and uniform temperature T has an electrical resistance of 0.01 /m and a current flow of 20A. a) What is the rate at which heat is dissipated per unit length of wire? What is the heat dissipation per unit volume within the wire? b) If the wire is not insulated and is in ambient air and large surroundings for which T= Tsur=20C, what is the temperature T of the wire? The wire has an emissivity of 0.3, and the coefficient associated with heat transfer by natural convection may be approximated by an expression of the form, h=C[(TT)/D]1/4, where C=1.25W/m7/4K5/4. c) If the wire is coated with plastic insulation of 2mm thickness and a thermal conductivity of 0.25W/mK, what are the inner and outer surface temperatures of the insulation? The insulation has an emissivity of 0.9, and the convection coefficient is given by the expression of part (b). Explore the effect of the insulation thickness on the surface temperatures
