Explanation Draw the schematic diagram of the room as shown in figure (1). Write the expression for the volume of the room: V = l b h (I) Here, length of the room is l , width of the room is b , and height of the room is h . Write the formula for the mass of the air. m a i r = P 1 V 1 R T 1 (II) Here, pressure is P 1 , volume is V 1 , gas constant is R , Temperature is T 1 . Write the expression for the change in internal energy of the water. Δ U w a t e r = m c P ( T 2 − T 1 ) (III) Here, mass of the water is m , specific heat at constant pressure is c P , final temperature of the water is T 2 , and temperature of the water is T 1 . Write the expression for the change in internal energy of the air. Δ U a i r = m c v ( T 2 − T 1 ) a i r (IV) Here, mass of the air is m , specific heat at constant volume of the air is c v , final temperature of the air is T 2 , and temperature of the air is T 1 . Express the energy balance equation for closed system. E i n − E o u t = Δ E s y s t e m 0 = ( Δ U ) w a t e r + ( Δ U ) a i r (V) Here, energy transfer in to the control volume is E i n , energy exit from the control volume is E o u t and change in internal energy of system is Δ E s y s t e m . Conclusion: Substitute 4 m for l , 5 m for b , and 6 m for h in equation (I). V = 4 m × 5 m × 6 m =120 m 3 Substitute 95 kPa for P 1 , 120 m 3 for V 1 , 0.2870 kPa ⋅ m 3 kg ⋅ K for R , 15 ° C for T 1 in equation (II) m a i r = 95 kPa × 120 m 3 0

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 4.5, Problem 122RP

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The final equilibrium temperature in the room

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Chapter 4.5, Problem 121RP

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Q1: Determine the length, angle of contact, and width of a 9.75 mm thick leather belt required to transmit 15 kW from a motor running at 900 r.p.m. The diameter of the driving pulley of the motor is 300 mm. The driven pulley runs at 300 r.p.m. and the distance between the centers of two pulleys is 3 meters. The density of the leather is 1000 kg/m³. The maximum allowable stress in the leather is 2.5 MPa. The coefficient of friction between the leather and pulley is 0.3. Assume open belt drive.

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