Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

Example 11.2 On a summer day, in Phoenix, Arizona, the inside room temperature is maintained at 68F

while the outdoor air temperature is a sizzling 110F. What is the outdoor-indoor temperature

difference in (a) degree Fahrenheit, (b) degree Rankine, (c) degree Celsius, and (d) Kelvin?

Is a 1temperature difference in Celsius equal to a 1temperature difference in Kelvin, and is

a1temperature difference in Fahrenheit equal to a 1temperature difference in Rankine?

If so, why?

We will first answer these questions the long way, and then we will discuss the short way.

(a)

(b)

Note that the temperature difference expressed in degrees Fahrenheit is equal to the tempera-

ture difference expressed in degrees Rankine.

(c)

(d)

Note that the temperature difference expressed in degrees Celsius is equal to the temperature

difference expressed in Kelvin.

It should be clear by now that a 1temperature difference in Celsius is equal to a 1

temperature difference in Kelvin, and a 1temperature difference in Fahrenheit is equal to a

1  temperature difference in Rankine. Of course, this relationship is true because when you are

computing the difference between two temperatures and converting to the absolute tempera-

ture scale, you are adding the same base value to each temperature. For example, to compute

the temperature difference in degrees Rankine between two temperaturesT 1 andT 2 given in

degrees Fahrenheit, you first add 460 to each temperature to convertT 1 andT 2 from degrees

Fahrenheit to degrees Rankine. This step is shown next.

T 1 1 °F 2  460 T 2 1 °F 2  460

T 1 1 °R 2 T 2 1 °R 2  3 T 1 1 °F 2  4604  3 T 2 1 °F 2  4604

d d

T 1 1 °R 2 T 2 1 °R 2

ToutdoorTindoor316.3 K293 K23.3 K

Tindoor 1 K 2 Tindoor 1 °C 2  273  20  273 293 K

Toutdoor 1 K 2 Toutdoor 1 °C 2  273 43.3 273 316.3 K

ToutdoorTindoor43.3°C20°C23.3°C

Tindoor 1 °C 2 

5

9

1 Tindoor 1 °F 2  322 

5

9

168  322 20°C

Toutdoor 1 °C 2 

5

9

1 Toutdoor 1 °F 2  322 

5

9

1110  322 43.3°C

ToutdoorTindoor570°R528°R42°R

Tindoor 1 °R 2 Tindoor 1 °F 2  460  68  460 528°R

Toutdoor 1 °R 2 Toutdoor 1 °F 2  460  110  460 570°R

ToutdoorTindoor110°F68°F42°F

314 Chapter 11 Temperature and Temperature-Related Parameters

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