Explanation The sensible heat generated by the total students is expressed as, Q ˙ gen,sensible = q ˙ gen,sensible × no .of students = q ˙ gen,sensible × 150 = 150 ( q ˙ gen,sensible ) (I) Here, the sensible heat generated by each student is q ˙ gen,sensible . The total sensible heat generated in the class room is expressed as, Q ˙ total,sensible = Q ˙ gen,sensible + Q ˙ lighting (II) Consider the class room as the imaginary duct and the chilled air passes through in it. The total sensible heat generated is transferred to the chilled air. And also the air flows at steady state. The mass flow rate of air ( m ˙ air ) is as follows. m ˙ 1 = m ˙ 2 = m ˙ air Write the energy rate balance equation for one inlet and one outlet system. { [ Q ˙ 1 + W ˙ 1 + m ˙ ( h 1 + V 1 2 2 + g z 1 ) ] − [ Q ˙ 2 + W ˙ 2 + m ˙ ( h 2 + V 2 2 2 + g z 2 ) ] } = Δ E ˙ system (III) Here, the rate of heat transfer is Q ˙ , the rate of work transfer is W ˙ , the enthalpy is h and the velocity is V , the gravitational acceleration is g , the elevation from the datum is z and the rate of change in net energy of the system is Δ E ˙ system ; the suffixes 1 and 2 indicates the inlet and outlet of the system. The system is at steady state. Hence, the rate of change in net energy of the system becomes zero. Δ E ˙ system = 0 Neglect the work transfer, potential and kinetic energies. The Equations (III) reduced as follows. [ Q ˙ 1 + 0 + m ˙ air ( h 1 + 0 + 0 ) ] − [ 0 + 0 + m ˙ air ( h 2 + 0 + 0 ) ] = 0 Q ˙ 1 + m ˙ air h 1 − m ˙ air h 2 = 0 Q ˙ 1 = m ˙ air ( h 2 − h 1 ) (II) The change in enthalpy ( h 2 − h 1 ) is expresses as follow. h 2 − h 1 = c p ( T 2 − T 1 ) Here, the specific heat is c p , the exit temperature is T 2 and the inlet temperature is T 1

9th Edition

ISBN: 9781264446889

Author: CENGEL

Publisher: MCG

See similar textbooks

Concept explainers

Properties of Pure Substances

A substance with fixed chemical composition throughout is called a pure substance like water, air, and nitrogen. A pure substance does not have to be a single element or compound. A mixture of two or more phases of a pure substance is also a pure substan…

Videos

Question

Chapter 5.5, Problem 171RP

To determine

The required flow rate of air, in kg/s that needs to be supplied to the room to keep the average temperature of the room as constant.

Expert Solution & Answer

Want to see the full answer?

Check out a sample textbook solution

See solution

Chapter 5.5, Problem 170RP

Chapter 5.5, Problem 172RP

Students have asked these similar questions

A classroom type room with 45students taking an exam in thermodynamics is expected to release a body heat of about 8kJ/hr per person. In order to compensate this heat dissipation, an air-conditioning unit is to be installed. If specific heat capacity and density of air is 1.0062kJ/kg-K and 1.2kg/m3, determine the volume of air flow required in examination room if the air is to be cooled down from 290C to 200C. a. 8.5177Li/s b. 9.1262Li/s c. 9.2022Li/s d. 9.0501Li/s

In adiabatic process, the system has Q=max. value O W=0 O Q=0 O U-0 O * A vertical piston-cylinder device contains water and is being heated on top of a range. During the process, 65 Btu of heat is transferred to the water, and heat losses from the side walls amount to 8 Btu. The piston rises as a result of evaporation, and 5 Btu of work is done by the vapor. Determine the change in the energy of the water .for this process 61 Btu O 52 Btu 55 Btu 60 Btu * hp compressor in a facility that operates at full load-75 for 2500 h a year is powered by an electric motor that has an efficiency of 93 percent. If the unit cost of electricity is $0.11/kWh, the annual electricity cost of this :compressor is 16,540 $ 19,180 $ O 5,380 $ O 14,300 $ O barometric pressure or 1 atmospheric 1 pressure is equal to 1.019 kgf/cm2 1 kgf/cm2 0.9 kgf/cm2 0 kgf/cm2 O

A classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360kJ/h. There are 10 light bulbs in the room, each with a rating of 100W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.

Chapter 5 Solutions

THERMODYNAMICS LLF W/ CONNECT ACCESS

Ch. 5.5 - Name four physical quantities that are conserved...Ch. 5.5 - Define mass and volume flow rates. How are they...Ch. 5.5 - Does the amount of mass entering a control volume...Ch. 5.5 - Consider a device with one inlet and one outlet....Ch. 5.5 - The ventilating fan of the bathroom of a building...Ch. 5.5 - Air enters a 16-cm-diameter pipe steadily at 200...Ch. 5.5 - A steam pipe is to transport 200 lbm/s of steam at...Ch. 5.5 - A garden hose attached with a nozzle is used to...Ch. 5.5 - A steady-flow compressor is used to compress...Ch. 5.5 - Air enters the 1-m2 inlet of an aircraft engine at...

Knowledge Booster

Learn more about

Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.

The required flow rate of air, in kg/s that needs to be supplied to the room to keep the average temperature of the room as constant.

Solution Summary: The author explains the required flow rate of air, in kg/s, that needs to be supplied to the room to keep the average temperature as constant. The total sensible heat generated in the class room is

Concept explainers

Videos

The required flow rate of air, in kg/s that needs to be supplied to the room to keep the average temperature of the room as constant.

Want to see the full answer?

Chapter 5 Solutions