The 150-mm-thick wall of a gas-fired furnace is constructed of fireclay brick
(a) How long does it take for the outer surface of the wall to reach a temperature of 750°C’?
(b) Plot the temperature distribution in the va1l at the foregoing lime, as well as at several intermediate times.
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Introduction to Heat Transfer
- Ex1. A piece of chromium steel of length 7.4cm (density=8780kg/m³ ; k = 50w/mK and specific heat cp = 440j/kgK) with mass 1.27kg is rolled into a solid cylinder and heated to a temperature of 600°C and quenched in oil at 36°c. Show that the lumped capacitance system analysis is applicable and find the temperature of the cylinder after 4min. What is the total heat transfer during this period? You may take the convective heat transfer coefficient between the oil and cylinder at 280w/m2k.arrow_forward) Stainless steel ball bearings (ρ = 8085 kg/m3and cp = 0.480 kJ/kgC) having adiameter of 1.22 cm are to be quenched in water at a rate of 1402 per minute.The balls leave the oven at a uniform temperature of 900C and are exposed to air at 300C for a while before they are dropped into the water. If thetemperature of the balls drops to 855C prior to quenching, determine:(i) The rate of heat transfer from the balls to the air; and(ii) The rate of entropy generation due to heat loss from the balls to the air.arrow_forwarda tray of liquid water is placed in a freezer where it cools from 20 deg C to "-5" deg C. what is the total amount of energy needed to freeze per unit of liquid water? the specific heat of ice is half of the specific heat of liquid water. the latent heat of fusion for water is 335 kj/kg include diagramarrow_forward
- 800°C and h = 20 W/m².K. Determine A thick oak wall, initially at 25°C, is suddenly exposed to combustion products for which T the time of exposure required, in s, for the surface to reach the ignition temperature of 400°C. Evaluate the properties of the oak (cross grain) at 300 K. t = i S =arrow_forwardIf a food product is being frozen in a system capable of removing 6200 kJ of thermal energy per product, with the product having a specific heat of 4.1 kJ/kg°C above the freezing temperature of -1.7°C , a latent heat of fusion of 284 kJ/kg, and the product has a specific heat of 2.2 kJ/kg°C below the freezing temperature. If 10.1 kg of product enters the system at 15°C, and exits it with a temperature of –12 °C, what percentage (to the nearest percent) of the full capability of the freezer has been used?arrow_forwardA welding heat source is capable of transferring 160 kJ/min to the surface of a metal part. The heated area is approximately circular, and the heat intensity decreases with increasing radius as follows: 50% of the power is transferred within a circle of diameter = 0.25 cm and 75% is transferred within a concentric circle of diameter = 0.625 cm. What are the power densities in (a) the 0.25 cm diameter inner circle and (b) the 0.625 cm diameter ring that lies around the inner circle? (c) Are these power densities sufficient for melting metal?arrow_forward
- A piece of chromium steel of length 7.4 cm (density = 8780 kg/m^3; k = 50 w/mK and specific heat cp = 440j/kgK with mass 1.27 kg is rolled into a solid cylinder and heated to a temperature of 600 deg C and quenched in oil at 36 deg C. Show that the lumped capacitance system analysis is applicable and find the temperature of the cylinder after 4 min. What is the total heat transfer during the period? You may take the convective heat transfer coefficient between the oil and cylinder at 280 w/m^2 k.arrow_forwardTwo insulated cylinders A and B with volumes VA = 1.2 m³ and VB = 6.4 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= 4.0 x 105 N/m2, TA= 250 K, PB = 2.5 x 105 N/m², Tg = 580 K. The valve is opened to allow the contents in the two cylinders to mix until the pressure equalizes. valve K TEACHER (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. (b) Determine the final pressure. N/m²arrow_forwardThe temperature of the water at the outlet of a three-way mixing valve will most likely be A. equal to the temperature of the water at the hot water inlet. B. lower than the temperature of the water at the cold water inlet. C. higher than the temperature of the water at the hot water inlet. D. higher than the temperature of the water at the cold water inlet.arrow_forward
- Acertain superinsulation material having a thermal conductivity of 2*10^-4 W/m*^ C is used to insulate a tank of liquid nitrogen that is maintained at - 196 degrees * C : 199 kJ is required to vaporize each kilogram mass of nitrogen at this temperature. Assuming that the tank is a sphere having an inner diameter (ID) of 0.52 m, estimate the amount of nitrogen vaporized per day for an insulation thickness of 2.5 cm and an ambient temperature of 21 degrees * C . Assume that the outer temperature of the insulation is 21 degrees * C .arrow_forwardAn ideal gas of 4kg mass (MW=3g/mol and k=2.3) contained in a regulated mass system went through three processes in a cycle, one after the other. The initial conditions for the gas were 20kPa and 310K in the first step, and the pressure was isometrically increased by 30kPa. The gas was heated to 400 degrees Celsius using a technique defined by the equation PV3=C. Upon returning to its previous state, it exhibits polytropic behavior. Calculate the change in entropy for each of the processes.arrow_forward5 An ice chest is constructed of Styrofoam [k = 0.033 W/m · ◦C] with inside dimensions of 25 by 40 by 100 cm. The wall thickness is 5.0 cm. The outside of the chest is exposed to air at 25◦C with h = 10 W/m2 · ◦C. If the chest is completely filled with ice, calculate the time for the ice to completely melt. State your assumptions. The enthalpy of fusion for water is 330 kJ/kg.arrow_forward
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