4BGroup3

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.

Solution

2221

2121 32

TTTTc

TTb

Km

226

31531538383

104.131538

2

006.0

mK

26104.1006.0 TTK

Solution

mKWKm /2167.1

212167.1

23.0

m

mRT

WKRT /18904.0

WK

Kq

/18904.0

311588

Wq 298.1465

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?

Solution

Solution

21 RRRT When insulator 1 is the better insulator:

Assume L=1m

Solution

On insulator 1:

Solution

On insulator 2:

SolutionWhen 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?

Pin

e

Pre

sse

d C

ork

Con

cret

e

19.1mm

X

50.8mm

Solution

CT 8.172

Solution

SolutionIf 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.]

Solution

SolutionAssume:

Solution

Solution

Solution

SolutionIteration 2:

Solution