# Heat THE

Heat Transfer Class (Mech Engineering, Raldi A. Koestoer)

Take Home Examination

Please write your  Name, Stud Number, Handphone, Email.

Submission date : Thursday , 12 November 2013 at 16.00. From member to Michel and then Michel transfer the folder to teacher. Filename  must be your nickname. Copy-paste will be punished severely, this is an individual test.

Your text format should be better in MSWord 2007. Look at your last digit of stud number, if your digit include in 0 to 3 you must use the A data, for 4 to 6 use B data, for 7 to 9 use C data.

You can use any data table  for the empirical formulation concerning  Nu, Gr, Re, Pr, Ra or other physical properties, from books, documents, or address in web,  but you should have to mention the reference.

Number one.

The composite wall  of a furnace consist  of steel plate and L1 cm thick refractory wall separated by L2 cm  air gap. Estimate the inside temperature of the refractory wall when the steel plate and  ambient temperature are T1 dgC and  T2 dgC, respectively. The  thermal conductivity of the refractory wall is 0.05 Btu/hr.ft.dgF (pls convert to SI unit). Assume there is no convective heat transfer in the air gap.

(guidance: the heat transfer  to  the ref wall from the steel plate occurs by radiation only, further transfer through the ref wall  by conduction to the outside air, sketch the position first).

A : L1 24 cm. L2 48 cm, T1 500, T2 35.

B : L1 30 cm, L2 40 cm, T1 700, T2 32.

C : L1 30 cm, L2 48 cm, T1 900, T2 28.

Number two.

Consider a heating chamber with 1 meter high vertical wall. The wall surface temperature  is T1 dgC and the ambient is  T2 dgC.

Find the convective heat transfer coefficient and the rate  of heat transfer per unit surface area of the wall. Neglect radiation heat transfer. (Select yourself the properties of air at 1 atm absolute).

A: T1 300  T2 40

B: T1 450  T2 30

C : T1 600  T2 40

Number three.

Determine the radiant heat flux transferred between 2 parallel planes of dimension h  m, L  m, w m. Temp of the planes are T2 K and T1 K . The surrounding will be considered the third surface with T3 0K (Zero K). The emissivities of the planes are e1 0.4 and e2 0.7.

A : h 1,5   L 3,0  w 3,0  T2 900  T2 1100

B : h 2       L 2,5  w 4,0  T2 600  T1 700

C : h 4       L 2,5  w 4,0  T2 600  T1 900

Number four.

Water (Cpw =4181 J/kg dgK) at 20 dgC at the rate of M1 Kg/hr  It is used to cool engine oil (Cpo = 1900 J/Kg dgK) at T1 dgC, which flows at M2 Kg/hr. The overall heat transfer coefficient is 300 W/m2 dgK.

Calculate the oil outlet temperature if the coaxial intercooler function in (PF Parallel Flow or CF Counter Flow). Coaxial intercooler is a double tube concentrice.

A : M1 4000  T1 205  M2 11000   PF

B : M1 6000  T1 175   M2  8000   CF

C : M1 4000  T1 205  M2 11000   CF

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