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Energy Analysis of Control Volumes at Steady
Chapter 4, Problem 76P(choose chapter or problem)
Steam enters a heat exchanger operating at steady state at \(250 \mathrm{kPa}\) and a quality of 90% and exits as saturated liquid at the same pressure. A separate stream of oil with a mass flow rate of \(29 \mathrm{~kg} / \mathrm{s}\) enters at \(20^{\circ} \mathrm{C}\) and exits at \(100^{\circ} \mathrm{C}\) with no significant change in pressure. The specific heat of the oil is \(c=2.0 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\). Kinetic and potential energy effects are negligible. If heat transfer from the heat exchanger to its surroundings is 10% of the energy required to increase the temperature of the oil, determine the steam mass flow rate, in \(\mathrm{kg} / \mathrm{s}\).
Questions & Answers
QUESTION:
Steam enters a heat exchanger operating at steady state at \(250 \mathrm{kPa}\) and a quality of 90% and exits as saturated liquid at the same pressure. A separate stream of oil with a mass flow rate of \(29 \mathrm{~kg} / \mathrm{s}\) enters at \(20^{\circ} \mathrm{C}\) and exits at \(100^{\circ} \mathrm{C}\) with no significant change in pressure. The specific heat of the oil is \(c=2.0 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\). Kinetic and potential energy effects are negligible. If heat transfer from the heat exchanger to its surroundings is 10% of the energy required to increase the temperature of the oil, determine the steam mass flow rate, in \(\mathrm{kg} / \mathrm{s}\).
ANSWER:Step 1 of 5:
Steam enters a heat exchanger and becomes a saturated liquid at the given constant pressure. A different oil steam enters at different temperature and exit with increased temperature and no pressure changes occur. The mass flow rate of the oil is given and the exchange of heat between the exchanger and surrounding is given. We are going to find the mass flow rate of the steam.
The pressure of steam P1 = P2 = 250 kPa = 2.5 bar
The quality of steam x = 0.90
The mass flow rate of the oil 3 = 29 kg/s
The initial temperature of oil T3 = 20°C = 293 K
The final temperature of oil T4 = 100°C = 373 K
The specific coefficient of oil c = 2.0 kJ/kg· K