Jennifer Tansey 12/15/11
Introduction / Background A common type of condenser used in steam plants is a horizontal, two- pass condenser Steam enters the condenser through an inlet at the top of the condenser and passes downward over a horizontal tube bundle The tube bundle is made up of individual tubes through which a cooling medium circulates to condense the steam Typically the tubes in the top half of the tube bundle are the “cold” first-pass and the tubes in the bottom half are the “warmer” second- pass
Problem Description The objective of this project is to analyze the tube configuration in a bundle to determine the best arrangement of tubes for the maximum amount of heat transferred to the circulating water The six configurations shown are analyzed The dark blue denotes the first-pass tubes and the light blue denotes the second-pass tubes
Performing the Analysis A heat and mass transfer algorithm was created to determine the outlet temperature of the circulating water for the six cases Set and/or calculated all geometric, material and thermodynamic properties Created a velocity profile for the tube bundle, thus allowing a velocity to be calculated for each row of tubes Evaluated all six cases for the same operating conditions and initial parameters, iterating for each pass in each case until values for the heat flux, interface temperature and outer wall temperature converged Solved for the outlet circulating water temperature after the first and second-passes for each case
Post-Processing Compiled the converged results for the heat flux, interface temperature and outer wall temperature for all six cases Calculated and plotted the temperature distribution over the length of the tube bundle for both the first and second-passes using an averaged circulating water temperatures Compared the circulating water temperatures for: All first-pass tubes Average outlet temperature Average temperature along the tubes All second-pass tubes Average outlet temperature Average temperature along the tubes
Post-Processing Performed an energy balance to ensure that the iterative algorithm produced accurate results Took into account the change in energy in the system due to: Net loss in energy in the mixture Net gain in energy in the circulating water Net gain in energy in the condensate formed Net gain in energy in the tube walls Showed less than 3% error, which can be attributed to the assumptions and simplifications made in the analysis
FLOW3D Modeling Created input files for all six cases in FLOW3D to simulate the velocity contours and steam temperature contours Used the velocity profile from FLOW3D in Excel to repeat the algorithm with the new velocity profile Analyzed and compared the results from the velocity profile created in the algorithm and the velocity profile obtained from FLOW3D
Example of FLOW3D Velocity Contours
Example of FLOW3D Temperature Contours Temperature (K) Condenser Height (m) Condenser Width (m)
Conclusions Mehrabian-based velocity profile increases through the tube bundle FLOW3D-based velocity profile decreases through the tube bundle The cases that exhibit the most heat transfer to the circulating water in the first-pass are those that experience the highest steam velocity Cases 2 and 4 for a Mehrabian-based velocity Cases 1 and 3 for a FLOW3D-based velocity The circulating water temperatures tend to converge at the outlet of the second-pass tubes The velocity profile is independent of the heat transfer due to the tube configuration within the bundle The magnitude of the velocity is proportional to the amount of heat transferred
Future Work The FLOW3D simulations could be refined to more accurately compare the results obtained The FLOW3D grid that was generated was relatively coarse and the flow was assumed laminar in order to expedite simulating all six cases A higher grid resolution and assuming a turbulent steam mixture flow through the bundles would each increase the predicted maximum velocity through the tubes