CLASSIFICATIONS OF HEAT EXCHANGER

  • CLASSIFICATION ACCORDING TO TRANSFER PROCESS :1
    • Indirect contact type
      • Direct transfer type
        1. Single phase
        2. Multiphase
      • Storage type
      • Fluidized Bed
    • Direct contact type
      • Immiscible fluids
      • Gas – liquid
      • Liquid – vapor
  • CLASSIFICATION ACCORDING TO NUMBER OF FLUIDS:-
    • Two – fluids
    • Three – fluids
    • N – fluids (N > 3)
  • CLASSIFICATION ACCORDING TO SURFACE COMPACTNESS :-
    • Gas –to- fluid
      1. Compact (β ≥ 700 m2/m3)
      2. Non compact (β < 700 m2/m3)
    • Liquid –to- liquid and phase change
      1. Compact (β ≥ 400 m2/m3)
      2. Non compact (β < 400 m2/m3)
  • CLASSIFICATION ACCORDING TO CONSTRUCTION :-
    • TUBULAR
      • Double-pipe
      • Shell-and-tube
        1. Cross flow to tubes
        2. Parallel flow to tubes
      • Spiral Tube
      • Pipe coils
    • PLATE TYPE
      • PHE (Plate Heat Exchanger)
        1. Gasketed
        2. Welded
        3. Brazed
      • Spiral
      • Plate coil
      • Printed Circuit
    • EXTENDED SURFACE
      • Plate – fin
      • Tube – fin
        1. Ordinary separating wall
        2. Heat – pipe wall
    • REGENERATIVE
      • Rotary
      • Fixed – matrix
      • Rotary hoods
  • CLASSIFICATION ACCORDING TO FLOW ARRANGEMENTS:-
    • Single – pass
      1. Counter flow
      2. Parallel flow
      3. Cross flow
      4. Split-flow
      5. Divided-flow
    • Multipass
      • Extended surface
        1. Cross- counter flow
        2. Cross- parallel flow
        3. Compound flow
    • Shell-and-tube
      1. Parallel counter flow
        • m- shell passes
        • n- tube passes
      2. Split- flow
      3. Divided- flow
    • Plate
      • Fluid 1 m passes
      • Fluid 2 n passes
  • CLASSIFICATION ACCORDING TO HEAT TRANSFER MECHANISMS:-
    • Single- phase convection on both sides
    • Single- phase convection on one side, two- phase convection on other side
    • Two- phase convection on both sides
    • Combined convection and radiative heat transfer

1Classification of heat exchangers (Shah, 1981)

TERMINOLOGY DEFINITION UNIT
Capacity Ratio Ratio of the products of mass flow rate and specific heat capacity of the cold fluid to that of the hot fluid. Also computed by the ratio of temperature range of the hot fluid to that of the cold fluid. Higher the ratio greater will be size of the exchanger
Density It is the mass per unit volume of a material kg/m3
Effectiveness Ratio of the cold fluid temperature range to that of the inlet temperature difference of the hot and cold fluid. Higher the ratio lesser will be requirement of heat transfer surface
Fouling The phenomenon of formation and development of scales and deposits over the heat transfer surface diminishing the heat flux. The process of fouling will get indicated by the increase in pressure drop
Fouling Factor The reciprocal of heat transfer coefficient of the dirt formed in the heat exchange process. Higher the factor lesser will be the overall heat transfer coefficient. (m2.K)/W
Heat Duty The capacity of the heat exchanger equipment expressed in terms of heat transfer rate, viz. magnitude of energy or heat transferred per time. It means the exchanger is capable of performing at this capacity in the given system W
Heat exchanger Refers to the nomenclature of equipment designed and constructed to transmit heat content (enthalpy or energy) of a comparatively high temperature hot fluid to a lower temperature cold fluid wherein the temperature of the hot fluid
decreases (or remain constant in case of losing latent heat of condensation) and the temperature of the cold fluid increases (or remain constant in case of gaining latent heat of vaporization). A heat exchanger will normally provide indirect contact heating. E.g. A cooling tower cannot be called a heat exchanger where water is cooled by direct contact with air
Heat Flux The rate of heat transfer per unit surface of a heat Exchanger W/ m2
Individual Heat transfer Coefficient The heat flux per unit temperature difference across Heat transfer boundary layer of the hot / cold fluid film formed at the heat transfer surface. The magnitude of heat transfer coefficient indicates the ability of heat conductivity of the given fluid. It increases with increase in density, velocity, specific heat, geometry of the film forming surface W/( m2.K)
LMTD Correction factor Calculated considering the Capacity and effectiveness of a heat exchanging process. When multiplied with LMTD gives the corrected LMTD thus accounting for the temperature driving force for the cross flow pattern as applicable inside the exchanger
Logarithmic Mean Temperature difference (LMTD) The logarithmic average of the terminal temperature approaches across a heat exchanger °C
Overall Heat transfer Coefficient The ratio of heat flux per unit difference in approach across a heat exchange equipment considering the individual coefficient and heat exchanger metal surface conductivity. The magnitude indicates the ability of heat transfer for a given surface. Higher the coefficient lesser will be the heat transfer surface requirement W/(m2.K)
Pressure drop The difference in pressure between the inlet and outlet of a heat exchanger/td>

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Specific heat capacity The heat content per unit weight of any material per degree raise/fall in temperature J/(kg.K)
Temperature Approach The difference in the temperature between the hot and cold fluids at the inlet / outlet of the heat exchanger. The greater the difference greater will be heat transfer flux °C
Thermal Conductivity The rate of heat transfer by conduction though any substance across a distance per unit temperature difference W/(m2.K)
Viscosity The force on unit volume of any material that will cause per velocity Pa (Pascal)