6.4. Annealing is a process by which steel is reheated and then cooled to make it less brittle.Consider the reheat stage for a 100-mm-thick steel plate (p = 7830 kg/m³, c = 550 J/kg • K, k =48 W/m⚫ K), which is initially at a uniform temperature of T₁ = 200°C and is to be heated to aminimum temperature of 550°C. Heating is effected in a gas-fired furnace, where products ofcombustion at T∞ = 800°C maintain a convection coefficient of h = 250 W/m² ⚫ K on bothsurfaces of the plate. How long should the plate be left in the furnace?

Analyzing the Problem and AssumptionsWe're tasked with determining the time required to heat a steel…

Answered: 6.4. Annealing is a process by which…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

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THERMODYNAMICS A 1.5kW iron has a 0.5 cm thick brass base plate (p=8,310 kg/m3 and cp = 400 J/kg C) with a surface area of 0.03 m^2. At the start, the iron is in thermal equilibrium with the ambient air temperature of 22 degrees Celsius. What is the shortest time required for the plate temperature to reach 200 degrees Celsius if 95 percent of the heat generated in the resistance wires is transmitted to the plate?
8. You place a 1.5 kg block of aluminum that is 45°C in contact with a 2.1 kg block of copper that is 18°C. Both blocks are in an insulated container. The specific heat of aluminum is 0.91 J/K/g and the specific heat of copper is 0.39 J/K/g. What is the final temperature of the two blocks?
6. a. The heat flux applied to the walls of the biomass combustion furnace is 20 W/m2. The furnace walls have a thickness of 10 mm and a thermal conductivity of 12 W/m.K. If the wall surface temperature is measured to be 50oC on the left and 30oC on the right, prove that conduction heat transfer occurs at a steady state!b. Heating the iron cylinder on the bottom side is done by placing the iron on the hotplate. This iron has a length of 20 cm. The surface temperature of the hotplate is set at 300oC while the top side of the iron is in contact with the still outside air. To reach the desired hotplate temperature, it takes 5 minutes. Then it takes 15 minutes to measure the temperature of the upper side of the iron cylinder at 300oC. Show 3 proofs that heat transfer occurs transiently
P34.9 Two parallel metal plates separated by 1 cm are held at 300, and 298 K, respectively. The space between the plates is filled with N2 (or = 0.430 nm² and Cv, m = 5/2 R). Cv.m Determine the heat flux between the two plates in units of W cm².
A steel ball of density 7800 kg/m³ and specific heat 0.47 kJ/kg-K having 10 cm diameter at 300°C is placed in atmosphere at 30°C. Calculate the initial rate of cooling in °C/sec. Assume convective heat transfer coefficient h = 15W / (m ^ 2) - K . Neglect heat loss by radiation.
Solar heating of a house is much more efficientif there is a way to store the thermal energy collected during theday to warm the house at night. Suppose one solar-heated homeutilizes a concrete slab of area 12 m2and 25 cm thick. (a) If thedensity of concrete is 2400 kg>m3, what is the mass of the slab?(b) The slab is exposed to sunlight and absorbs energy at a rate of1.4 * 107J>h for 10 h. If it begins the day at 22 °C and has a specificheat of 750 J>1kg # K2, what is its temperature at sunset? (c) Modelthe concrete slab as being surrounded on both sides (contact area24 m2) with a 2.0-m-thick layer of air in contact with a surface thatis 5.0 °C cooler than the concrete. At sunset, what is the rate atwhich the concrete loses thermal energy by conduction throughthe air layer? (d) Model the concrete slab as having a surface areaof 24 m2and surrounded by an environment 5.0 °C cooler thanthe concrete. If its emissivity is 0.94, what is the rate at which theconcrete loses thermal…
6. A mass of 0.20 kg of metal having a temperature of 100 deg. C is plunged into 0.04 kg of water at 20 deg. C The temperature of the water and metal becomes 48 deg. C. The latent heat of ice at 0 eg. C is 335 kJ/kg-K and the specific heat capacity of water is 4.19 kJ/kg-K. Assuming no heat loss to the surroundings, determine the specific heat capacity of the metal in kJ/kg-K
Determine the heat stored in a concrete floor (10 cm thick, 3.5 m × 4.5 m),initial temperature 60°F, final temperature 80°F.
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Question 1.: A sample of 6.25 kilograms of water at 7.00°C is placed in the freezer. Assuming all energy removed from the freezer is removed from the water, how long does the 1/5 horsepower (HP) motor (1 HP = 746 Watts) have to run to cool all of the liquid to ice at 0.00°C? The freezer has a COP of 5.00. Your challenge: come up with a complete equation solved for the variable in question before you plug in any of the numerical values given above. In this way, you will be prepared to solve for any of the variables! Some questions to consider along the way ... (a.) What is the relationship between power, P (in watts) and work, W (in joules)? What is the variable you are eventually solving for? (b.) What is the relationship between the COP a freezer/refrigerator, and work? (c.) How much energy as heat must be removed from the water to freeze it? What heat pump/refrigerator variable does this value correspond to? freezer run time = S = minutes
2. Two insulated cylinders A and B with volumes VA = 2.0 m³ and VB = 5.8 m³ contain chlorine gas at different pressures and temperatures. The cylinders are insulated (no heat is lost to or gained from the outside) and connected by a valve. Initially, the valve is) closed and the gas in the two cylinders has the following values: PA = 4.0x105 N/m², TA = 210 K, PB = 2.5x105 N/m², TB = 580 K. The valve is opened to allow the contents in the two cylinders to mix until the pressure equalizes. valve B a. Assuming there is no change in the temperatures of the containers themselves, determine the final temperature of the gas in the two cylinders. The atomic mass of chlorine gas is 35.4527 u. (1 u = 1.67377x1027 kg) b. Determine the final pressure?

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