This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Chapter 2 Basic Concepts of Thermodynamics Review Problems 280E The efficiency of a refrigerator increases by 3% per ° C rise in the minimum temperature. This increase is to be expressed per ° F, K, and R rise in the minimum temperature. Analysis The magnitudes of 1 K and 1 ° C are identical, so are the magnitudes of 1 R and 1 ° F. Also, a change of 1 K or 1 ° C in temperature corresponds to a change of 1.8 R or 1.8 ° F. Therefore, the increase in efficiency is (a) 3% for each K rise in temperature, and (b), (c) 3/1.8 = 1.67% for each R or ° F rise in temperature. 281E The boiling temperature of water decreases by 3 ° C for each 1000 m rise in altitude. This decrease in temperature is to be expressed in ° F, K, and R. Analysis The magnitudes of 1 K and 1 ° C are identical, so are the magnitudes of 1 R and 1 ° F. Also, a change of 1 K or 1 ° C in temperature corresponds to a change of 1.8 R or 1.8 ° F. Therefore, the decrease in the boiling temperature is (a) 3 K for each 1000 m rise in altitude, and (b), (c) 3 × 1.8 = 5.4 ° F = 5.4 R for each 1000 m rise in altitude. 282E The average body temperature of a person rises by about 2 ° C during strenuous exercise. This increase in temperature is to be expressed in ° F, K, and R. Analysis The magnitudes of 1 K and 1 ° C are identical, so are the magnitudes of 1 R and 1 ° F. Also, a change of 1 K or 1 ° C in temperature corresponds to a change of 1.8 R or 1.8 ° F. Therefore, the rise in the body temperature during strenuous exercise is (a) 2 K (b) 2 × 1.8 = 3.6 ° F (c) 2 × 1.8 = 3.6 R 236 Chapter 2 Basic Concepts of Thermodynamics 283E Hypothermia of 5 ° C is considered fatal. This fatal level temperature change of body temperature is to be expressed in ° F, K, and R. Analysis The magnitudes of 1 K and 1 ° C are identical, so are the magnitudes of 1 R and 1 ° F. Also, a change of 1 K or 1 ° C in temperature corresponds to a change of 1.8 R or 1.8 ° F. Therefore, the fatal level of hypothermia is (a) 5 K (b) 5 × 1.8 = 9 ° F (c) 5 × 1.8 = 9 R 284E A house is losing heat at a rate of 3000 kJ/h per ° C temperature difference between the indoor and the outdoor temperatures. The rate of heat loss is to be expressed per ° F, K, and R of temperature difference between the indoor and the outdoor temperatures. Analysis The magnitudes of 1 K and 1 ° C are identical, so are the magnitudes of 1 R and 1 ° F. Also, a change of 1 K or 1 ° C in temperature corresponds to a change of 1.8 R or 1.8 ° F. Therefore, the rate of heat loss from the house is (a) 3000 kJ/h per K difference in temperature, and (b), (c) 3000/1.8 = 1667 kJ/h per R or ° F rise in temperature. 285 The average temperature of the atmosphere is expressed as T atm = 288.15 – 6.5 z where z is altitude in km. The temperature outside an airplane cruising at 12,000 m is to be determined....
View
Full
Document
This homework help was uploaded on 04/18/2008 for the course EML 3007 taught by Professor Chung during the Spring '08 term at University of Florida.
 Spring '08
 Chung

Click to edit the document details