Chapter 2, Problem 2.4DP

Metal spheres, 10 mm in diameter, are to be annealed by heating them to 827°C then allowing them to cool slowly in air at 27°C to the point where they are in thermal equilibrium with the air. 2000 balls are annealed in one hour’s time. What is the total rate of their heat transfer if they are made of steel, lead, or copper? a.Sketch the problem. b.Draw lines identifying the control volume, or control mass. c.Identify the states with numbers, letters, or descriptions such as “in” and “out”. d.Write down the knowns and unknowns. e.Identify what is being asked for. f.State all assumptions.

1. A room has a pine ceiling (k = 0.12 WI(m-Cº) ] that measures 3.0 m x 4.0 m 2.0 cm. On a cold day, the temperature inside the room is 20°C, and the temperature in the attic above is 8°C. If 6.0 cm of glass wool insulation ( k = 0.042 WI(m.Cº) ] were put in above the ceiling, how much energy would be saved in one hour? 2.  2.0-kg block moving with an initial speed of 5 m/s slides on a rough table and is stopped by the force of friction. Assuming that the table and air remain at 24°C, calculate the entropy change of the universe.

1 example each Conductive heat flow through flat surface  Conductive heat flow throw composite wall

2.16 A standard 4-in. steel pipe (ID = 4.026 in., OD = 4.500 in.) carries superheated steam at 1200°F in an enclosed space where a fire hazard exists, limiting the outer surface temperature to 100°F. In order to minimize the insulation cost, two materials are to be (a) Specify the thickness for each insulating mate- rial. (b) Calculate the overall heat transfer coefficient based on the pipe OD. (c) What fraction of the total resistance is due to (1) steam-side resistance, (2) steel pipe resistance, (3) insulation (the combina- tion of the two), and (4) outside resistance? (d) How much heat is transferred per hour per foot length of pipe? used: first a high-temperature (relatively expensive) insulation is to be applied to the pipe, and then magnesia (a less expensive material) will be applied on the outside. The maximum temperature of the magnesia is to be 600°F. The following constants are known: steam-side coefficient h = 100 Btu/hr ft² °F high-temperature insulation conductivity k =…

As shown in the sketh below, a steam pipe of 0.12-m inside diameter is insulated with a layer of calcium silicate. 12. Ts.2} 1. Ts,1} Steam Insulation (a) If the insulation is 17.5 mm thick and its inner and outer surfaces are maintained at T,1 = 800 K and Ts,2 = 490 K, respectively, what is the rate of heat loss per unit length (q') of the pipe, in W/m? (b) Determine the rate of heat loss per unit length (q'), in W/m, and outer surface temperature T.2, in K, for the steam pipe with the inner surface temperature fixed at Ts,1 The outer surface is exposed to an airflow (T = 800 K, inner radius ri = 0.06 m, and outer radius r2 = 25°C) that maintains a convection coefficient of h = 25 W/m2-K and to = 0.1 m. large surroundings for which Tsur = T_ = 25°C. The surface emissivity of calcium silicate is approximately 0.8.

Activity: compile 1 example for each topic: explain: 1. Conductive heat flow through flat surface2. Conductive heat flow throw composite wall3. Conductive heat flow through thick walled tube4. CONDUCTED HEAT FLOW THROUGH THICK SPHERE5. Heat transfer between two fluids separated by walls of a composite tube of solid materials6. Absorption, reflection and transmission

A pipe carries hot molten lead from one part of a factory floor to another. The mass flow rate of lead is 0.05 kg/s. While trying to figure out the heat loss from the pipe, you found that over a 2-m length of he pipe the lead temperature drops from 580 C to 557.C. What is the rate at which thermal energy is being lost from the lead carrying pipe in this 2-m section? Use the property table to find out properties of lead as needed.

2. A rod that is 1.5 m long is made up of 0.75 m copper and 0.75 m aluminum of equal cross- sectional area and joined end to end. The rod is well insulated that there is no heat loss along the sides. The copper end is at 125 °C while the aluminum end is at 25 °C. Assuming a steady-state heat conduction, find the (a) amount of heat conducted per unit time and area of the rod and (b) temperature I at the copper-aluminum interface. (katuminum 240 /s m °C and kcopper = 390 /s m°c)

Some help please (How do I go about this? TIA)...Determine the rate of heat loss per square foot through thr wall of your home if the home is heated to 70F when the outside temperature of -10F. Assume the fiberglass insulation has the same properties as silica glass fiber.