ME 414 Design Project

Heat Exchanger DesignME 414 Design ProjectCreated and Designed by:Michael StarkJoshua KeithBilly BurdetteBrandon MullenJoseph Listerman

Project GoalsDesign Heat ExchangerCreate a light weight heat exchangerHeat exchange must be as efficient as possibleCost must be kept low as possibleThe size of the heat exchanger must be under design constraint

Project GuidelinesDuring the process of a liquid chemical product, its temperature needs to be reduced by 20 degrees Celsius. Mass flow rate is 220,000 kg/hrFluid enters the heat exchanger at 45 C and should leave at 25 CMaterial properties of this chemical product can be approximated as water

Cooling of the chemical product will be achieved by using treated city waterCity water is available at 20 CMass flow rate is adjustable and one of the design parameters to be selectedExit temperature of city water from the heat exchanger is a function of the selected mass flow rate

Professor ToksoyProject OptimizationMust cool the chemical from 45 C to 25 CHeat exchanger length can not exceed 7 metersHeat exchanger shell diameter can not exceed 2 metersMinimize heat exchanger shell and tube weight hence the costMinimize heat exchanger pressure drop

Professor ToksoyHeat Exchanger Design Inputs for MATLABChemical to be cooled was set as Shell side liquidMass flow rate of cooling water = 220 kg/secShell ID = .889 mShell thickness = 5 mmTube OD = 6.35 mmTube thickness = .457 mmTube Length = 2.88 mBaffle space = .6 mHelical BafflesCounter flowOne shell pass and one tube passAluminum was used for both shell and tube materialsGnielinski equation used for tube side Nusselt correlationSquare tube pitch

Heat Exchanger Design Inputs for MATLAB ExplainedChemical to be cooled was set as shell side liquid In order to keep shell side pressure drop to a minimum we needed to keep the mass flow rate in the shell low. The only way we found of doing this and getting the desired Q was to push the chemical to be cooled through the shell.Mass flow rate of cooling water = 220 kg/sec - For these inputs this calculates out to an average tube side fluid velocity of ~1 m/s which falls within the recommended range of .9 2.4 m/s.Tube OD = 6.35 mm - The small OD was needed to increase the surface area for heat transfer for a given shell ID.Tube thickness = .457 mm - The small tube thickness was needed to increase the heat transfer coefficient and also reduced the total material weight and cost.

Tube Length = 2.88 m - The tube length was increased to increase the calculated Q.Baffle space = .6 m - Although slightly larger then the recommended value of 40-60% of shell ID, .6 m worked well.Helical Baffles A helical baffle will increase the heat transfer coefficient considerably without dramatically increasing pressure drop due to the nature of the flows. Counter flow - Because of the narrow band of temperatures between the two fluids, a counter flow arrangement was used in order to increase the log mean temperature difference between the two fluids without having to increase the mass flow rate of the water to very high levels.Heat Exchanger Design Inputs for MATLAB Explained Cont.One shell pass and one tube pass - One pass was used for both the shell and tube because currently the program does not calculate pressure drop due to multiple passes correctly. We discovered this late into the project and did not have time to fix the issue. If the pressures were calculated properly the water output temperature for one shell pass and two tube passes must stay below 28.33 deg C in order to keep the log mean temperature difference correction factor valid for the given temperature requirements.Aluminum was used for both shell and tube materials - Aluminum was chosen for its excellent heat transfer properties and its reduced weight.Gnielinskis equation used for tube side Nusselt correlation For the calculated Reynolds number of 5800 this correlation is most applicable. Petuhkov Krillovs correlation is used for Reynolds number larger then 104.Heat Exchanger Design Inputs for MATLAB Explained Cont.

Nusselt CorrelationD.O.E. Run 1

D.O.E. Run 1FactorsShell mass flow rateTube lengthShell internal diameterThe most significant affect on heat transfer was tube length, a result of increased surface area.Shell I.D. and tube length had the greatest affect on weight, the larger the shell the more tubes can fit inside. Shell side pressure drop increases with tube length and mass flow rate. Dramatic decrease as shell ID increases.The only factor affecting the tube side pressure drop was tube length.D.O.E. Run 2

D.O.E. Run 2FactorsBaffle SpaceTube ThicknessBaffle CutBaffle spacing has a large affect on q and shell side pressure drop.Tube thickness was the only factor affect HE weight in this DOE.Baffle cut doesnt seem to have any affect on other parameters.We fixed baffle spacing because it heavily influenced shell side pressure drop.

Final D.O.E.

Final D.O.E.Final optimization factorsMass flow rate of the shell fluid fixed to 220 kg/sTube lengthShell internal diameterTube outer diameterWe adjusted the ranges of our chosen factors and ran the DOE again. The mass flow rate only affected the shell side pressure drop at this stage of the design. We chose the shell side mass flow rate based on what we decided would yield reasonable shell outlet temperature using counter flow.

Factorial Design Analysis Heat RateTube length has the largest affect on the heat rate. Shell ID has the smallest relative affect on heat rate.Shell ID had a negative affect on heat rate.This was a result of more tubes decreasing the velocity in the tube.The result is laminar flow inside the tube.

Factorial Design Analysis - P TubeWe can see that tube length has the largest affect on tube side pressure drop.Shell ID has no affect on tube pressure drop.We expected tube OD to have a larger affect on tube side pressure drop.

Factorial Design Analysis - P ShellShell ID had the largest affect on shell side pressure drop.The affect of tube OD on the pressure drop was surprising. We attribute this affect to the 60 triangular pitch tube arrangement.As tube OD grows larger there is more pressure drop in the shell.

Factorial Design Analysis HE WeightThe shell inside diameter has the largest affect on weight.The larger the shell diameter the more tubes we could fit inside, thus increasing weight.Because tube length determines the length of the heat exchanger, it too has a large affect on heat exchanger weight.

Design Optimization - 1The design optimized to our original design. We expected our final tube diameter to be 6.35 mm with a mass flow rate of 220 kg/s. Optimal Tube OD was 8.3mmThe tube length was longer than our original design called for, which was a result of maximizing the q calculated.We set target values for the shell and tube side pressure drops.We set a target range for total weight between 900-1100 kg.Design Optimization - 2

The design optimized to our original design. We expected our final tube diameter to be 6.35 mm with a mass flow rate of 220 kg/s. Optimal Tube OD was 8.3mm, adjusted it to 9.525 mm to coincide with standard tube dimensions.The tube length was longer than our original design called for, which was a result of maximizing the q calculated.We set target values for the shell and tube side pressure drops.We set a target range for total weight between 900-1100 kg.Heat Exchanger Design Output from MATLAB

Heat Exchanger Final DesignTube side mass flow rate of 220 kg/secTube OD set to 9.525 mm, thickness 0.889 mmShell ID set to .889 meters, thickness 5 mmHeat exchanger is a one pass counter flow tube arrangement with helical baffles and optimized tube length of 2.6 m.The ratio between desired and calculated heat rate is 1.00.

Further AnalysisWe believe that cost could be decreased by over-designing the HE and reducing the number of tubes until we got the desired heat ratio. The tube mass flow rate was an important design consideration because the outlet temperature of the shell fluid was completely dependent on it.After performing a macroscopic heat balance, counter flow was chosen because the cold fluid outlet temp was expected to be higher than the hot fluid outlet temp.

Matlab Program ImprovementsCreate program checks in order to eliminate unrealistic designs. If multiple tube passes are used with parallel flow it is possible to calculate a LMTD_CF that is an imaginary number.Provide the operator more detailed information regarding the Nusselt correlations.

Cost SummaryHeat Exchanger Dry Weight730 KgHeat Exchanger & Fluid Weight2287 KgCostOnlineMetals.com$37.00 per 8ft length of aluminum tubingTotal estimated aluminum tubing cost $337,000.00$11.00 per 8ft length of mild steel tubingTotal estimated mild steel tubing cost $100,000.00Instillation and Manufacturing