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Chapter:

Dimensional-Analysis

1. A centrifugal pump which circulates a hot liquid metal at 500 degree Celsius is driven by a 3600 rpm electric motor. The motor is coupled to pump impeller by a horizontal steel shaft of dia 25 mm. Let us assume motor temperature as 60 degree Celsius with ambient air at 25 degree Celsius, what length of shaft should be specified between motor and pump? It may be presumed that rmal conductivity of shaft material is 35W/m K and that convective film coefficient between steel shaft and ambient air is 15.7W/square m K


Hint Answer

2. Analysis of heat flow from finned surface is made with following assumptions
(i) Uniform heat transfer coefficient, h over entire fin surface
(ii) No heat generation within fin generation
(iii) Homogenous material
Identify correct option


Hint Answer

3. An array of 10 fins of anodized aluminum (k = 180W/m K) is used to cool a transistor operating at a location where ambient conditions correspond to temperature 35 degree Celsius and convective coefficient 12W/square m K. The distance AB is 3 mm, EF is 0.4 mm. The length of fin is 5 mm and has its base at 60 degree Celsius. Find power dissipated by fin array?
An array of 10 fins of anodized aluminum (k = 180W/m K) is used to cool a transistor operating at a location where ambient conditions correspond to temperature 35 degree Celsius and convective coefficient 12W/square m K. The distance AB is 3 mm, EF is 0.4 mm. The length of fin is 5 mm and has its base at 60 degree Celsius. Find power dissipated by fin array?\r\n


Hint Answer

4. Find value of corrected length for rectangular fin?
Where, b is width and t is length of fin


Hint Answer

5. It is said that fins can take a variety of forms
(i) Longitudinal fins of rectangular cross section attached to a wall
(ii) Cylindrical tubes with radial fins
(iii) Conical rod protruding from a wall
Identify correct statement


Hint Answer

6. The rate of heat transfer from fin in case of fin insulated at tip is


Hint Answer

7. If heat conducted into element at plane x is Q X = – k A C (d t/d x) X. Then heat conducted out of element at plane (x + d x) is


Hint Answer

8. A rod of 10 mm square section and 160 mm length with rmal conductivity of 50W/m K protrudes from a furnace wall at 200 degree Celsius with convective coefficient 20 W/ square m K. Make calculations for heat convective up to 80 mm length


Hint Answer

9. For steady flow of heat along a rod, general equation is
d2α/dx 2 – m 2 α = 0
The value of constant m is


Hint Answer

10. A steel rod (k = 30 W/m degree) 1 cm in diameter and 5 cm long protrudes from a wall which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an environment with h = 50 W/m2 degree and t a = 30 degree Celsius. Calculate rate of heat dissipation


Hint Answer

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Heat Transfer from Extended Surfaces

A centrifugal pump which circulates a hot liquid metal at 500 degree Celsius is driven by a 3600 rpm electric motor. The motor is coupled to pump impeller by a horizontal steel shaft of dia 25 mm. Let us assume motor temperature as 60 degree Celsius with ambient air at 25 degree Celsius, what length of shaft should be specified between motor and pump? It may be presumed that rmal conductivity of shaft material is 35W/m K and that convective film coefficient between steel shaft and ambient air is 15.7W/square m K

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Analysis of heat flow from finned surface is made with following assumptions
(i) Uniform heat transfer coefficient, h over entire fin surface
(ii) No heat generation within fin generation
(iii) Homogenous material
Identify correct option

;

An array of 10 fins of anodized aluminum (k = 180W/m K) is used to cool a transistor operating at a location where ambient conditions correspond to temperature 35 degree Celsius and convective coefficient 12W/square m K. The distance AB is 3 mm, EF is 0.4 mm. The length of fin is 5 mm and has its base at 60 degree Celsius. Find power dissipated by fin array?
An array of 10 fins of anodized aluminum (k = 180W/m K) is used to cool a transistor operating at a location where ambient conditions correspond to temperature 35 degree Celsius and convective coefficient 12W/square m K. The distance AB is 3 mm, EF is 0.4 mm. The length of fin is 5 mm and has its base at 60 degree Celsius. Find power dissipated by fin array?\r\n

;

Find value of corrected length for rectangular fin?
Where, b is width and t is length of fin

;

It is said that fins can take a variety of forms
(i) Longitudinal fins of rectangular cross section attached to a wall
(ii) Cylindrical tubes with radial fins
(iii) Conical rod protruding from a wall
Identify correct statement

;

The rate of heat transfer from fin in case of fin insulated at tip is

;

If heat conducted into element at plane x is Q X = – k A C (d t/d x) X. Then heat conducted out of element at plane (x + d x) is

;

A rod of 10 mm square section and 160 mm length with rmal conductivity of 50W/m K protrudes from a furnace wall at 200 degree Celsius with convective coefficient 20 W/ square m K. Make calculations for heat convective up to 80 mm length

;

For steady flow of heat along a rod, general equation is
d2α/dx 2 – m 2 α = 0
The value of constant m is

;

A steel rod (k = 30 W/m degree) 1 cm in diameter and 5 cm long protrudes from a wall which is maintained at 10 degree Celsius. The rod is insulated at its tip and is exposed to an environment with h = 50 W/m2 degree and t a = 30 degree Celsius. Calculate rate of heat dissipation

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