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E-type shells in shell-and-tube heat exchangers: Ebert and Panchal equation, for crude oil fouling, Eckert number, Eddy viscosity: Eddy diffusivity, of heat, Edge, D, Edwards, D K EEC code for thermal design of heat exchangers, Effective diffusivity, Effective thermal conductivity of fixed beds, Effective tube length in shell-and-tube heat exchangers, Effectiveness of a heat exchanger: Efficiency of fins, Eicosane: Eicosene: Ejectors, in flash distillation plant, EJMA (Expansion Joint Manufacturers Association), standards for expansion bellows Elastic properties of solids: El-Dessouky, H, Electrical enhancement processes, in heat transfer augmentation, Electric fields, effect on properties of rheologically complex materials, Electric fields, in augmentation of condensation, Electrical process heater, specification of, Electrokinetics, for heat transfer augmentation in microfluidic systems, Electromagnetic theory of radiation, Electrostatic fields in augmentation of heat transfer, Elements: Elhadidy relation between heat and momentum transfer, Embedding methods for radiative heat transfer in nonisothermal gases, Embittlement, of stainless steels, Emission of thermal radiation, in solids, Emissivity: Emitting media, interaction phenomena with, Emulsions, viscosity of, EN13445 (European Pressure Vessel Codes), design of heat exchangers to, Enclosures: Energy equation: Energy recovery, maximum, in heat exchanger network design, Enhanced surfaces, fouling in, Enhancement devices: Enlargements in pipes: Enthalpy: Entrainment in annular gas-liquid flow Entrance effects in heat and mass transfer: Entrance lengths, hydrodynamic in pipe flow, Entrance losses for tube inlet in shell-and-tube heat exchanger, Entry losses in plate heat exchangers, Entropy generation and minimisation Environmental impact, of fouling, Eotvos number: Epstein, N, Epstein matrix, for fouling, Equalizing rings, for expansion bellows, Equilibrium interphase: Equilibrium vapor nucleus, Equivalent sand roughness, Ergun equation, for pressure drop in fixed beds ESDU correlations: Esters: Ethane: Ethanol: Ethers: Ethyl acetate: Ethylacetylene: Ethylacrylate: Ethylamine: Ethylbenzene: Ethyl benzoate: Ethyl butanoate: Ethylcyclohexane: Ethylcyclopentane: Ethyl formate: Ethylene: Ethylene diamine: Ethylene glycol: Ethylene oxide: Ethylmercaptan: 1-Ethylnaphthalene: 2-Ethylnaphthalene: Ethyl proprionate: Ethyl propylether: Ettouney, H, Euler number: Eutectic mixtures, condensation of forming immiscible liquids, Evaporation: Evaporative crystallisers, Evaporators:
arrangements for thermal economy, choice of tube diameter for, choice of type of, design aspects, estimation of heat transfer coefficients in, estimation of pressure drop and circulation in,
Estimation of Pressure Drop and Circulation Rate
estimation of surface area in, in Ocean Thermal Energy Conversion (OTEC) systems in refrigeration systems, introduction to, as type of heat exchanger, types,
Exergy, definition of, Exergy analysis, Exit losses for tubes in shell-and-tube exchanger, Expansion bellows, for shell-and-tube heat exchangers: EJMA (Expansion Joint Manufacturers Association), standards for Expansion joints, mechanical design of: Expansion of tubes into tube sheets: Expansion turbine, lost work in, Explosively clad plate, Explosive welding of tubes into tube sheets Explosive expansion joints, Extended surfaces (see also Fins) Externally induced convection, in kettle reboilers, Extinction coefficient, Extinction efficiency, Eyring fluid (non-Newtonian),

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A B C D E
E-type shells in shell-and-tube heat exchangers: Ebert and Panchal equation, for crude oil fouling, Eckert number, Eddy viscosity: Eddy diffusivity, of heat, Edge, D, Edwards, D K EEC code for thermal design of heat exchangers, Effective diffusivity, Effective thermal conductivity of fixed beds, Effective tube length in shell-and-tube heat exchangers, Effectiveness of a heat exchanger: Efficiency of fins, Eicosane: Eicosene: Ejectors, in flash distillation plant, EJMA (Expansion Joint Manufacturers Association), standards for expansion bellows Elastic properties of solids: El-Dessouky, H, Electrical enhancement processes, in heat transfer augmentation, Electric fields, effect on properties of rheologically complex materials, Electric fields, in augmentation of condensation, Electrical process heater, specification of, Electrokinetics, for heat transfer augmentation in microfluidic systems, Electromagnetic theory of radiation, Electrostatic fields in augmentation of heat transfer, Elements: Elhadidy relation between heat and momentum transfer, Embedding methods for radiative heat transfer in nonisothermal gases, Embittlement, of stainless steels, Emission of thermal radiation, in solids, Emissivity: Emitting media, interaction phenomena with, Emulsions, viscosity of, EN13445 (European Pressure Vessel Codes), design of heat exchangers to, Enclosures: Energy equation: Energy recovery, maximum, in heat exchanger network design, Enhanced surfaces, fouling in, Enhancement devices: Enlargements in pipes: Enthalpy: Entrainment in annular gas-liquid flow Entrance effects in heat and mass transfer: Entrance lengths, hydrodynamic in pipe flow, Entrance losses for tube inlet in shell-and-tube heat exchanger, Entry losses in plate heat exchangers, Entropy generation and minimisation Environmental impact, of fouling, Eotvos number: Epstein, N, Epstein matrix, for fouling, Equalizing rings, for expansion bellows, Equilibrium interphase: Equilibrium vapor nucleus, Equivalent sand roughness, Ergun equation, for pressure drop in fixed beds ESDU correlations: Esters: Ethane: Ethanol: Ethers: Ethyl acetate: Ethylacetylene: Ethylacrylate: Ethylamine: Ethylbenzene: Ethyl benzoate: Ethyl butanoate: Ethylcyclohexane: Ethylcyclopentane: Ethyl formate: Ethylene: Ethylene diamine: Ethylene glycol: Ethylene oxide: Ethylmercaptan: 1-Ethylnaphthalene: 2-Ethylnaphthalene: Ethyl proprionate: Ethyl propylether: Ettouney, H, Euler number: Eutectic mixtures, condensation of forming immiscible liquids, Evaporation: Evaporative crystallisers, Evaporators:
arrangements for thermal economy, choice of tube diameter for, choice of type of, design aspects, estimation of heat transfer coefficients in, estimation of pressure drop and circulation in,
Estimation of Pressure Drop and Circulation Rate
estimation of surface area in, in Ocean Thermal Energy Conversion (OTEC) systems in refrigeration systems, introduction to, as type of heat exchanger, types,
Exergy, definition of, Exergy analysis, Exit losses for tubes in shell-and-tube exchanger, Expansion bellows, for shell-and-tube heat exchangers: EJMA (Expansion Joint Manufacturers Association), standards for Expansion joints, mechanical design of: Expansion of tubes into tube sheets: Expansion turbine, lost work in, Explosively clad plate, Explosive welding of tubes into tube sheets Explosive expansion joints, Extended surfaces (see also Fins) Externally induced convection, in kettle reboilers, Extinction coefficient, Extinction efficiency, Eyring fluid (non-Newtonian),
F G H I J K L M N O P Q R S T U V W X Y Z
E Evaporators: estimation of pressure drop and circulation in,
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Estimation of Pressure Drop and Circulation Rate

DOI 10.1615/hedhme.a.000274

3.5.6 Estimation of pressure drop and circulation rate

R. A. Smith and P. D. Hills

The flow rate through the circulation loop of an evaporator determines the heat transfer coefficient in the calandria and also the quality (weight fraction vapour) of the two-phase mixture leaving the calandria, and is a key parameter in the design. In order to determine the circulation, it is necessary to be able to estimate the pressure drop through the circulation loop. This is especially important in a natural circulation evaporator, where the circulation rate must be determined by trial and error so that the head available from the differences between the densities in the riser and downcomer equals the loss due to friction and acceleration around the circulation loop. Computer programs are normally used for this. With assisted and forced circulation it is also necessary to be able to estimate pressure drop so that the head required from the impeller can be estimated.

The estimation of pressure drop in the regions of single-phase flow presents no major problems, and the methods can be obtained from Section 144 and Section 146. The pressure drop in the boiling zone is more important because it is usually greater and always much more difficult to estimate, there being big discrepancies between the various published and proprietary correlations. It is first necessary to be able to estimate the density of a two-phase mixture, for the estimation both of the pressure drop due to acceleration and of the pressure rise or drop due to gravity. Second, the pressure loss due to friction must be estimated. Correlations for two-phase density and friction are given in Section 154.

Two phase fluid flows are liable to be unstable. There are several different forms of instability, and it is important to ensure that the flow in an evaporator will be steady. More information on the subject may be found in Hewitt et al. (1994). Unsteady flow in an evaporator can upset other items of equipment on the plant, and it has a very serious effect in a crystallizing evaporator on the size of the crystals.

It is important when estimating the pressure drop through an evaporator to allow for the effects of the deposition of dirt or scale — see also Section 275.

For single phase flow in clean heat exchanger tubes, the estimated pressure drop is likely to be accurate to within ± 2–3%, assuming the physical properties are known. The pressure drop in a fouled tube may be significantly higher, and may not be estimated correctly by the computer programs used for exchanger design. There are two factors resulting from fouling which are important here.

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