# 4BGroup3

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Published on January 6, 2009

Author: 4ChEAB08

Source: slideshare.net

Group 3 Members: Agno, Jennilyn Balmes, Niña Chan, Armi Samia, Romulo Santos, Olivia

Problem Set No. 3  Compute the heat loss per square meter of surface for a furnace wall 23 cm. thick. The inner and outer surface temperature are 315°C and 38°C respectively. The variation of the thermal conductivity in W/mK, with temperature in °C is given by the following relation: k= 0.006T-1.4x10-6 T2.

 Compute the heat loss per square meter of surface for a furnace wall 23 cm. thick. The inner and outer surface temperature are 315°C and 38°C respectively. The variation of the thermal conductivity in W/mK, with temperature in °C is given by the following relation: k= 0.006T-1.4x10-6 T2.

Solution

Solution

Problem Set No. 11  An insulated steam pipe having an outside diameter of 0.0245 m is to be covered w/ two layers of insulation each having a thickness of 0.0245 m. The average thermal conductivity of one material is approximately four times that of the other. Assuming that the inner and outer surface temperature of the composite insulation are fixed, how much will the heat transfer be reduced when the better insulating material is next to the pipe then when it is the outer layer?

 An insulated steam pipe having an outside diameter of 0.0245 m is to be covered w/ two layers of insulation each having a thickness of 0.0245 m. The average thermal conductivity of one material is approximately four times that of the other. Assuming that the inner and outer surface temperature of the composite insulation are fixed, how much will the heat transfer be reduced when the better insulating material is next to the pipe then when it is the outer layer?

Solution

Solution When insulator 1 is the better insulator: Assume L=1m

Solution On insulator 1:

Solution On insulator 2:

Solution When insulator 2 is the better insulator:

Solution  When insulator1 is the better insulator, lower heat is being transferred for the pipe to the outside environment. (Computations are done regardless of the inner and outer temperature and the actual value of mean thermal conductivity)

Problem  Insulation for a refrigerated food warehouse . It wants to build a cold storage with a 19.1mm inner layer of pine, an intermediate layer Pressed cork and an outer layer of 50.8mm of concrete. The temperature of the wall interior is -17.8 C and the outer surface of 29.4 C in the concrete. The conductivities are averages for the pine, , to cork, , and for concrete The total internal surface area to be used in the calculations is approximately 39m2 (omitting the effects of corners and edges). How thick is the Cork pressing needed to keep the heat loss at 586 W?

Solution Pine Pressed Cork Concrete 19.1mm X 50.8mm

Solution

Solution If overall heat not exceed 586W:

Solution

Problem  Losses of heat with resolution by subsequent approaches. The exhaust gases tube of a heater has an internal diameter of 114.3 mm with walls of ceramics of 6.4mm thick. The average value of k is 1.52. In the outside of this wall an insulator of 102 mm of mineral wool settles. The thermal conductivity of the mineral wool is oC (W/m. K). The inner temperature of the ceramics surface is T1 = 588.7 K and the temperature of the external surface of the insulator is T3=311K. Calculate the loss of heat for 1.5m of pipeline and the interfacial temperature, T2 between the ceramic and the insulator. [Hint: the correct value of Km for the insulation is that evaluated at the mean temp. of. Hence, for the first trial assume a mean temperature of, say, 448K. Then calculate the heat loss and T2. Using this new T2, calculate a new mean temperature and proceed as before.]

 Losses of heat with resolution by subsequent approaches. The exhaust gases tube of a heater has an internal diameter of 114.3 mm with walls of ceramics of 6.4mm thick. The average value of k is 1.52. In the outside of this wall an insulator of 102 mm of mineral wool settles. The thermal conductivity of the mineral wool is oC (W/m. K). The inner temperature of the ceramics surface is T1 = 588.7 K and the temperature of the external surface of the insulator is T3=311K. Calculate the loss of heat for 1.5m of pipeline and the interfacial temperature, T2 between the ceramic and the insulator. [Hint: the correct value of Km for the insulation is that evaluated at the mean temp. of. Hence, for the first trial assume a mean temperature of, say, 448K. Then calculate the heat loss and T2. Using this new T2, calculate a new mean temperature and proceed as before.]

Solution

Solution Assume:

Solution

Solution

Solution

Solution Iteration 2:

Solution