Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 4: Q. 4.12 (page 129)

Explain why a rectangular PVcycle, as considered in Problems 1.34 and 4.1, cannot be used (in reverse) for refrigeration.

Short Answer

Expert verified

The rectangular PV cycle doesn't show the property of The range of temperature at which working substance absorbs heat must be less than the range off temperature at which working substance rejects heat. Therefore it cannot be used for refrigeration.

Step by step solution

01

Concept Introduction

For cyclic process, PV diagram is a closed loop. The area of the PV diagram represents the amount of work done during the process.

02

Explanation

The range of temperature at which working substance absorbs heat must be less than the range off temperature at which working substance rejects heat. Since the rectangular PV cycle doesn't show this property, therefore it cannot be used for refrigeration.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Recall Problem 1.34, which concerned an ideal diatomic gas taken around a rectangular cycle on a PVdiagram. Suppose now that this system is used as a heat engine, to convert the heat added into mechanical work.

(a) Evaluate the efficiency of this engine for the case V2=3V1,P2=2P1.

(b) Calculate the efficiency of an "ideal" engine operating between the same temperature extremes.

An apparent limit on the temperature achievable by laser cooling is reached when an atom's recoil energy from absorbing or emitting a single photon is comparable to its total kinetic energy. Make a rough estimate of this limiting temperature for rubidium atoms that are cooled using laser light with a wavelength of 780 nm.

Suppose that the throttling valve in the refrigerator of the previous problem is replaced with a small turbine-generator in which the fluid expands adiabatically, doing work that contributes to powering the compressor. Will this change affect the COP of the refrigerator? If so, by how much? Why do you suppose real refrigerators use a throttle instead of a turbine?

A heat pump is an electrical device that heats a building by pumping heat in from the cold outside. In other words, it's the same as a refrigerator, but its purpose is to warm the hot reservoir rather than to cool the cold reservoir (even though it does both). Let us define the following standard symbols, all taken to be positive by convention:
Th=temperature inside buildingTc=temperature outsideQh=heat pumped into building in1dayQc=heat taken from outdoors in1dayW=electrical energy used by heat pump in1day
(a) Explain why the "coefficient of performance" (COP) for a heat pump should be defined as Qh / W.
(b) What relation among Qh , Qc, and W 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 Th and Tc alone.
(d) Explain why a heat pump is better than an electric furnace, which simply converts electrical work directly into heat. (Include some numerical estimates.)

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 1kgof fluid, and are measured relative to an arbitrarily chosen reference state, the saturated liquid at -40°c. Excerpted from Moran and Shapiro (1995).
See all solutions

Recommended explanations on Physics Textbooks

Electric Charge Field and Potential

Read Explanation

Quantum Physics

Read Explanation

Astrophysics

Read Explanation

Measurements

Read Explanation

Electricity

Read Explanation

Engineering Physics

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free