Learning Materials
Features
Discover
Chapter 4: 4.10 (page 129)
Suppose that heat leaks into your kitchen refrigerator at an average rate of 300 watts. Assuming ideal operation, how much power must it draw from the wall?
The power drawn from wall is 57.69 W.
Over 30 million students worldwide already upgrade their learning with Vaia!
All the tools & learning materials you need for study success - in one app.
Get started for free
In a real turbine, the entropy of the steam will increase somewhat. How will this affect the percentages of liquid and gas at pointin the cycle? How will the efficiency be affected?
It has been proposed to use the thermal gradient of the ocean to drive a heat engine. Suppose that at a certain location the water temperature is at the ocean surface and at the ocean floor.
(a) What is the maximum possible efficiency of an engine operating between these two temperatures?
(b) If the engine is to produce of electrical power, what minimum volume of water must be processed (to suck out the heat) in every second?
In an absorption refrigerator, the energy driving the process is supplied not as work, but as heat from a gas flame. (Such refrigerators commonly use propane as fuel, and are used in locations where electricity is unavailable.* ) Let us define the following symbols, all taken to be positive by definition:
Qf= heat input from flame
Qc= heat extracted from inside refrigerator
Qr= waste heat expelled to room
Tf= temperature of flame
Tc= temperature inside refrigerator
Tr= room temperature
(a) Explain why the "coefficient of performance" (COP) for an absorption refrigerator should be defined as Qc / Qf.
(b) What relation among Qf, Qc, and Qr is implied by energy conservation alone? Will energy conservation permit the COP to be greater than 1 ?
(c) Use the second law of thermodynamics to derive an upper limit on the COP, in terms of the temperatures Tf, Tc, and Tr alone.
Liquid HFC-134a at its boiling point at 12 bars pressure is throttled to 1 bar pressure. What is the final temperature? What fraction of the liquid vaporizes?
Table 4.3. Properties of the refrigerant HFC-134a under saturated conditions (at its boiling point for each pressure). All values are for of fluid, and are measured relative to an arbitrarily chosen reference state, the saturated liquid at c. Excerpted from Moran and Shapiro (1995).
Calculate the efficiency of a Rankine cycle that is modified from the parameters used in the text in each of the following three ways (one at a time), and comment briefly on the results: (a) reduce the maximum temperature to ; (b)reduce the maximum pressure to 100 bars; (c)reduce the minimum temperature to .
What do you think about this solution?
We value your feedback to improve our textbook solutions.
Explanations 
Textbooks 
Exams 
GCSE 
IGCSE 
AS 
A Level 
International A Level 
University Admissions Tests 
Flashcards 
Vaia AI 
Notes 
Study Plans 
Study Sets 
Find a job 
Find a degree 
Student Deals 
Magazine 
Mobile App