Surface condenser practice — In steam power-plant condensers, steam is routed on the shell side and cooling water through the tubes. Which reason best supports this configuration?
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AThe steam condensation rate is always smaller than the water flow rate.
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BMaintaining vacuum on the tube side is more difficult than on the shell side.
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CHigh water velocity can be achieved conveniently in tubes to raise the overall heat-transfer coefficient (water has low specific volume compared to steam).
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DThe condenser doubles as a storage drum for condensate.
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ETube leaks are preferable because air ingress helps deaeration.
Answer
Correct Answer: High water velocity can be achieved conveniently in tubes to raise the overall heat-transfer coefficient (water has low specific volume compared to steam).
Explanation
Introduction:Condenser design balances heat-transfer performance, pressure containment, vacuum integrity, and maintainability. A standard configuration places the condensing steam on the shell side and circulates cooling water through the tubes. This question asks for the key engineering rationale behind that choice.
Given Data / Assumptions:
- Surface condenser under vacuum on the steam side.
- Cooling water available at significant flow rates and moderate pressures.
- Tube bundles sized to achieve desired overall coefficient U and allowable pressure drops.
Concept / Approach:Water has a much lower specific volume than steam and can be pumped to relatively high velocities inside tubes. Higher tube-side velocities enhance the tube-side film coefficient, increasing the overall heat-transfer coefficient U and mitigating fouling. Steam on the shell side facilitates accommodating large volumetric changes during condensation, distribution over the bundle, and maintenance of vacuum. While vacuum integrity considerations also favor locating vacuum on the shell side (option b is partly true), the widely cited performance reason is the ability to run cooling water at high velocity inside tubes.
Step-by-Step Solution:Identify performance lever: raise U by increasing tube-side velocity of water.Assign phases: water in tubes; steam on shell to condense over the bundle.Select the option that directly states this heat-transfer advantage.
Verification / Alternative check:Design manuals specify target water velocities (e.g., 1–2 m/s) to boost tube-side coefficients while controlling erosion, affirming that tubes are the convenient path for velocity control.
Why Other Options Are Wrong:
- (a) Mass-rate comparison is not the decisive reason.
- (b) Vacuum argument is valid but secondary in many presentations; (c) more directly addresses U and velocity control.
- (d) Storage is not a design objective.
- (e) Air ingress is harmful; leaks degrade vacuum and performance.
Common Pitfalls:Overlooking fouling/erosion limits when increasing water velocity; ignoring tube material selection relative to water chemistry.
Final Answer:High water velocity can be achieved conveniently in tubes to raise the overall heat-transfer coefficient (water has low specific volume compared to steam).