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Agenda. Heat transfer review What is required to size a heat exchanger Compact heat transfer solutions Plate Heat Exchanger Spiral Heat Exchanger Welded Plate Heat Exchangers Specialty Plate Heat Exchangers Installation Photos Design of Heat Exchanger Solutions Order Flow Process.
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Agenda • Heat transfer review • What is required to size a heat exchanger • Compact heat transfer solutions • Plate Heat Exchanger • Spiral Heat Exchanger • Welded Plate Heat Exchangers • Specialty Plate Heat Exchangers • Installation Photos • Design of Heat Exchanger Solutions • Order Flow Process
Three ways to transfer heat Reflected • Radiation • Electromagnetic waves • When it reaches a body it has 3 options: Absorbed Transmitted • Conduction • Molecular or atomic vibrations • No material transport • Convection • Energy is transferred by the motion and intermixing of small mass elements • Natural convection caused by density difference • Forced convection is man-made (ex., pump)
Flow Principles • Laminar • Conduction: low heat transfer rate • Turbulent • Convection: high heat transfer rate • Film layer at the wall - Conduction- Low heat transfer
Data needed to design a heat exchanger • Flows and temperatures for both sides • Fluid properties including: density, specific heat, thermal conductivity, and viscosity for at least two points. • For condensers and evaporators data such as a condensing curve, boiling point elevation, and/or other parameters may be required. • Process conditions and limitations such as system pressure, potential for fouling or plugging, pressure drop limitations etc. • The supplier may be able to use their experience to assist in determining proper values from above.
Heat Transfer Q = m Cp (T - T ) • Where Q = heat transferred (Kbtu/hr) m = mass flow rate (hot fluid) (lb/hr) C = specific heat (hot fluid) (Btu/lb,F) T = hot fluid entering temperature (F) T = hot fluid leaving temperature (F) HI HO p HI HO
T HI T CO T HO T CI Thermodynamics at work!! Q = m Cp (T - T ) = m Cp (T - T ) HI HO CO CI Temperature Length of Channel
Heat Transfer Q = U A (LMTD) • Where Q = heat transferred U = overall heat transfer coefficient A = heat transfer surface area LMTD = log mean temperature difference
T HI T CO T HO T CI (T -T ) - (T - T ) CO HO CI HI LMTD = (T -T ) CO HI ln (T -T ) HO CI Log Mean Temperature Difference Temperature Length of Channel
Therefore m C (T - T ) U (LMTD) A = HO HI P Determining Heat Transfer Area Q = mCp(T – T ) = U A (LMTD) HI HO Determining Proper “U” value is the key!!
Tube Plate Spiral Items That Effect “U” value and Fouling Tendency • Channel Geometry (turbulence) • Fluid velocity and wall shear • Fluid Properties (particularly viscosity) • *Viscosity also has a major impact on the pressure drop that will be seen in the heat exchanger
Heat Flow Hot Fluid Fouling Layers Cold Fluid Metal Temperature Temperature Temperature Wall Film Boundary Layers 1 U 1 h t k 1 h = + + + Rf Q = U A (LMTD) and
Heat Transfer Basics – Three Wise Men h Nusselt Number Prandtl Number Reynolds Number
T HI T HO T CI Cocurrent Flow Lower LMTD and no temperature cross means less efficiency Temperature T CO Length of Channel