1-1 SOLUTIONS MANUAL Fundamentals of Thermal Fluid Sciences 6th Edition Yunus A. Çengel, John M. Cimbala, Afshin J. Ghajar McGraw-Hill, 2022 Chapter 1 INTRODUCTION AND BASIC CONCEPTS PROPRIETARY AND CONFIDENTIAL This Manual is the proprietary property of McGraw-Hill Education and protected by copyright and other state and federal laws. By opening and using this Manual the user agrees to the following restrictions, and if the recipient does not agree to these restrictions, the Manual should be promptly returned unopened to McGraw-Hill Education: This Manual is being provided only to authorized professors and instructors for use in preparing for the classes using the affiliated textbook. No other use or distribution of this Manual is permitted. This Manual may not be sold and may not be distributed to or used by any student or other third party. No part of this Manual may be reproduced, displayed or distributed in any form or by any means, electronic or otherwise, without the prior written permission of McGraw-Hill Education. 1-2 Thermodynamics, Heat Transfer, and Fluid Mechanics 1-1C Why does a bicyclist pick up speed on a downhill road even when he is not pedaling? Does this violate the conservation of energy principle? On a downhill road the potential energy of the bicyclist is being converted to kinetic energy, and thus the bicyclist picks up speed. There is no creation of energy, and thus no violation of the conservation of energy principle. 1-2C An office worker claims that a cup of cold coffee on his table warmed up to 80°C by picking up energy from the surrounding air, which is at 25°C. Is there any truth to his claim? Does this process violate any thermodynamic laws? There is no truth to his claim. It violates the second law of thermodynamics. 1-3C One of the most amusing things a person can experience is that in certain parts of the world, a still car in neutral can go uphill when its brakes are released. Such occurrences are even broadcast on TV. Can this really happen, or is it bad eyesight? How can you verify if a road is really uphill or downhill? A car going uphill without the engine running would increase the energy of the car, and thus it would be a violation of the first law of thermodynamics. Therefore, this cannot happen. Using a level meter (a device with an air bubble between two marks of a horizontal water tube) it can shown that the road that looks uphill to the eye is actually downhill. 1-4C How does the science of heat transfer differ from the science of thermodynamics? Thermodynamics deals with the amount of heat transfer as a system undergoes a process from one equilibrium state to another. Heat transfer, on the other hand, deals with the rate of heat transfer as well as the temperature distribution within the system at a specified time. 1-5C What is the driving force for (a) heat transfer, (b) electric current, and (c) fluid flow? (a) The driving force for heat transfer is the temperature difference. (b) The driving force for electric current flow is the electric potential difference (voltage). (a) The driving force for fluid flow is the pressure difference. 1-6C Why is heat transfer a nonequilibrium phenomenon? Heat transfer is a non-equilibrium phenomena since in a system that is in equilibrium there can be no temperature differences and thus no heat flow. 1-7C Can there be any heat transfer between two bodies that are at the same temperature but at different pressures? No, there cannot be any heat transfer between two bodies that are at the same temperature (regardless of pressure) since the driving force for heat transfer is temperature difference. 1-3 1-8C Define stress, normal stress, shear stress, and pressure. Stress is defined as force per unit area, and is determined by dividing the force by the area upon which it acts. The normal component of a force acting on a surface per unit area is called the normal stress, and the tangential component of a force acting on a surface per unit area is called shear stress. In a fluid, the normal stress is called pressure. Mass, Force, and Units 1-9C Explain why the light-year has the dimension of length. In this unit, the word light refers to the speed of light. The light-year unit is then the product of a velocity and time. Hence, this product forms a distance dimension and unit. 1-10C What is the difference between pound-mass and pound-force? Pound-mass lbm is the mass unit in English system whereas pound-force lbf is the