A water steam at a pressure of 8 kPa and a quality of 94% enters at shell-and-tu
ID: 2994918 • Letter: A
Question
A water steam at a pressure of 8 kPa and a quality of 94% enters at shell-and-tube heat exchanger where it condenses on the outside wall of tubes through which cooling water flows, exiting as saturated liquid at 8 kPa. The mass flow rate of the condensing steam is 94 kg/s. Cooling water enters the tubes at 18 oC and exits at 38 oC with negligible change in pressure. Neglecting stray heat transfer and ignoring kinetic and potential energy effects, determine the mass flow rate of cooling water for steady state operation. A water steam at a pressure of 8 kPa and a quality of 94% enters at shell-and-tube heat exchanger where it condenses on the outside wall of tubes through which cooling water flows, exiting as saturated liquid at 8 kPa. The mass flow rate of the condensing steam is 94 kg/s. Cooling water enters the tubes at 18 oC and exits at 38 oC with negligible change in pressure. Neglecting stray heat transfer and ignoring kinetic and potential energy effects, determine the mass flow rate of cooling water for steady state operation. A water steam at a pressure of 8 kPa and a quality of 94% enters at shell-and-tube heat exchanger where it condenses on the outside wall of tubes through which cooling water flows, exiting as saturated liquid at 8 kPa. The mass flow rate of the condensing steam is 94 kg/s. Cooling water enters the tubes at 18 oC and exits at 38 oC with negligible change in pressure. Neglecting stray heat transfer and ignoring kinetic and potential energy effects, determine the mass flow rate of cooling water for steady state operation. A water steam at a pressure of 8 kPa and a quality of 94% enters at shell-and-tube heat exchanger where it condenses on the outside wall of tubes through which cooling water flows, exiting as saturated liquid at 8 kPa. The mass flow rate of the condensing steam is 94 kg/s. Cooling water enters the tubes at 18 oC and exits at 38 oC with negligible change in pressure. Neglecting stray heat transfer and ignoring kinetic and potential energy effects, determine the mass flow rate of cooling water for steady state operation.Explanation / Answer
From water-steam properties:
At P1 = 8 kPa and quality x1 = 0.94 we get h1 = 2430 kJ/kg
At P2 = 8 kPa and x2 = 0 (saturated liquid) we get h2 = 174 kJ/kg
Change in enthalpy = m*(h1 - h2)
= 94*(2430 - 174)
= 212064 kJ
Change in enthalpy of cooling water = m_cool*Cp*(T2 - T1)
= m_cool*4.18*(38 - 18)
= 83.6*m_cool kJ
Equating both, 83.6*m_cool = 212064
m_cool = 2536.65 kg/s
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