Chapter 7, Problem 7.35CU

A domestic water heater holds 189 L of water at 60°C, 1 atm. Determine the exergy of the hot water, in kJ. To what elevation, in m, would a 1000-kg mass have to be raised from zero elevation relative to the reference environment for its exergy to equal that of the hot water? Let To = 298 K, po = 1 atm, g = 9.81 m/s².

At a pressure of 1 bar, a temperature of 17 °C and a mass flow of 0.3 kg/s, air enters a stable insulated compressor and exits at 3 bar, 147 °C. Determine the power required by the compressor and the exergy destruction in kW. Express the exergy disappearance as a percentage according to the power required by the compressor. Changes in kinetic and potential energy will be neglected. dead state; T0=17 °C, P0=1 bar

At steady state, an electric pump motor develops power along its output shaft of 0.7 hp whiledrawing 6 amps at 100 V. The outer surface of the motor is at 150°F. Let T = 40°F.Determine:(b) the exergy flow with input power, exergy flow with output power, magnitude of exergy flowwith heat transfer leaving the motor, and exergy destruction, all in Btu/h.

* Your answer is incorrect. Water within a piston-cylinder assembly, initially at 10 lbf/in.2, 500°F, undergoes an internally reversible process to 80 lbf/in.², 800°F, during which the temperature varies linearly with specific entropy. For the water, determine the work and heat transfer, each in Btu/lb. Neglect kinetic and potential energy effects. W12 m = Q12 = m i 575.85 433.14 Btu/lb Btu/lb

What does the exergy principle state? The exergy of an isolated system can never decreases, but always increases O The exergy of an isolated system can never increases, but always decreases O The exergy of an isolated system can either increases or decreases O None of the above

Define the Mechanisms of exergy transfer.

7.27 Figure P7.27 provides steady-state data for the outer wall of a dwelling on a day when the indoor temperature is maintained at 25°C and the outdoor temperature is 35°C. The heat transfer rate through the wall is 1000 W. Determine, in W, the rate of exergy destruction (a) within the wall, and (b) within the enlarged system shown on the figure by the dashed line. Comment. Let T₂ = 35°C. 20.13, 33-56 Indoor Boundary of enlarged- temperature=25°C T=27C T-3C FIGURE PLAT Outdoor temperature=35°C

Steady-state operating data are shown in the figure below for an open feedwater heater. Heat transfer from the feedwater heater to its surroundings occurs at an average outer surface temperature of 50°C at a rate of 100 kW. Ignore the effects of motion and gravity and let To = 25°C, po = 1 bar. Determine (a) the ratio of the incoming mass flow rates, m/ṁ2. (b) the rate of exergy destruction, in kW. P2 = 1 bar Tz = 400°C 1 ṁy = 0.7 kg/s Pi = 1 bar T, = 40°C Feedwater heater X3 = 25% P3 = 1 bar Tp = 50°C %3D 2)

Answer 94 and 95