Views: 0 Author: Site Editor Publish Time: 2025-01-21 Origin: Site
Start with understanding the requirements:
Type of fluids: Identify the hot and cold fluids.
Flow rates: Determine the mass or volumetric flow rates.
Inlet and outlet temperatures: Define the temperature change required for each fluid.
Heat duty: Calculate the amount of heat to be transferred (Q = m * Cp * ΔT).
Pressure drop limits: Ensure pressure drops for both fluids stay within allowable limits.
Material constraints: Consider material compatibility with fluids and operating conditions.
Operating conditions: Include operating pressures, temperatures, and fouling factors.
Choose the type of shell and tube heat exchanger based on:
Flow configuration: Counterflow, parallel flow, or crossflow.
Tube arrangement: Fixed tube sheet, U-tube, or floating head.
Tube pattern: Square or triangular pitch for tube arrangement.
Passes: Number of tube and shell passes (e.g., 1-2, 2-4 passes).
Use the Log Mean Temperature Difference (LMTD) or NTU-Effectiveness method to determine the heat exchanger size.
Calculate LMTD:
where ΔT1and ΔT2 are the temperature differences at each end.
Determine overall heat transfer coefficient (U):
Account for heat transfer through tubes, fouling factors, and fluid film resistances:
where h1,h0 are heat transfer coefficients, t is wall thickness, k is thermal conductivity, and Rf is fouling resistance.
Determine required surface area (A):
Q=U⋅A⋅LMTDQ
Tube Design: Choose tube diameter, thickness, and length. Common sizes: 12.7–50.8 mm OD, lengths 1.2–6 m.
Shell Design: Decide on shell diameter and baffle spacing. Typical baffle spacing is 20–50% of shell diameter.
Tube Sheet Design: Ensure proper tube sheet thickness and hole arrangement.
Nozzles and Supports: Size inlet/outlet nozzles for both fluids, and design supports for structural integrity.
Calculate pressure drops for shell-side and tube-side:
Shell-side pressure drop:
Tube-side pressure drop:
Ensure the calculated values meet system requirements.
Choose materials compatible with operating conditions and fluids:
Tubes: Stainless steel, copper, titanium.
Shell: Carbon steel, stainless steel.
Optimize the design for cost, weight, size, and efficiency:
Reduce fouling by choosing appropriate flow rates and materials.
Ensure proper maintenance access and cleanability.
Leverage specialized heat exchanger design software (e.g., Aspen HYSYS, HTRI) for detailed analysis and optimization.
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