Heat 2014 V2


THMT Heat Transfer 2014 V2

Teacher : Raldi A. Koestoer

Issued 24 Oct 2014

Write your name, students no, HP no, email address. Namefile must be your nickname. Use Microsoft excel 2010 (or 2007). Due date submission Thursday 30 Oct 2014 at 12.00 USB copy from coordinator (Aboy) to teacher (do come to my office) . Please look-at your last digit of student number

LD                             Type

1,2,3,4                       AA

5,6,7                           BB

8, 9, 0                        CC

Problem 1

Box of acrylic five mm thick LxWxH 70x50x45 bottom part was replaced with metal heater. Termistance thermometer digital was placed in the middle of the box, and indicate Tb dgC. Surrounding of the room was measured by a thermocouple sensor and showed Tamb dgC. How many Watts of electric-metal heater we need to supply for warming the box so that temp Tb could be achieved and stay constant for long hours. Coef of convection inside and outside were always the same of 5 W/mK

Type         Tb             Tamb

AA             32                 25

BB             34               29

CC             37              30

Problem 2

Steam condenses on the outside pipe constan at inside wall temp 480 dgK. Airflows inside heated by means if force convection. Pipe 2m long, inside diam 2 ins, air velocity V m/sec Pressure 210 kPa. If the mean bulk temp 470 dgK. Deduce a) Coef of heat transfer, and b) The rate of heat transfer per unit area.

AA V=7                      BB V=8                      CC V=9

Problem 3

A tube is heated by means of Forced Convection from an air stream. Length of tube Le ft wall surface at Tw dgF. The flow is measured at aspeed of Fl ft/sec, and it moves through an area measuring 3 in. across. If the air is at a mean bulk temp of Tb dgF and pressure P psia. Calculate a) Pressure drop over the tube length b) Rate of heat from the air c) The coef of heat transfer by which this occurs. Note neglect the effects of any disturbance at the pipe entrance

Type                Le[ft]                Tw[dgF]           Fl[ft/sec]           P[psia] Tb[dgF]

AA                   80                    50                    30                    30                    100

BB                   70                    55                    30                    40                    95

CC                   80                    55                    35                    29                    95

 

Problem 4

Water at Tw dgC flows at the rate of Mf kg per hour. It is used to cool engine oil (Cpo 1900 J per kg dgK) at 250 dgC, which flow at Mo kg per hour. Overall heat transfer coef is hov W/m2 dgK. Calculate the oil outlet temp if the intercooler function in for AA parallel flow and for BB and CC counter-flow. Note: draw a sketch first.

Type                Tw                   Mf                    Mo                   hov

AA                   25                    4000                10000              350

BB                   28                    3000                8000                300

CC                   30                    3000                9000                300

Any question addressed to Koestoer@eng.ui.ac.id or via milis.-

 

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