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augmentation of, in axial flow reboilers, in evaporators,
Estimation of Heat Transfer Coefficients
in forced convective boiling of binary and multicomponent mixtures, in forced convective heat transfer in vertical tubes, in horizontal tubes, in kettle reboilers, in microchannels, outside tubes and tube bundles in crossflow, in pool boiling of binary and multicomponent mixtures, in pool boiling systems,
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Nahme-Griffith number, Nakashima, CY Nanoparticles, for heat transfer augmentation, Naphthalene: Napthenes: National practice, in mechanical design, guide to, Natural convection: Natural draft cooling towers: Natural frequency of tube vibration in heat exchangers, Navier-Stokes equation, Neon: Neopentane: Net free area, in double-pipe heat exchangers, Netherlands, guide to national mechanical design practice, Networks, of heat exchangers, pinch analysis method for design of, Neumann boundary conditions, finite difference method, Nickel, thermal and mechanical properties Nickel alloys, Nickel steels, Niessen, R, Nitric oxide: Nitriles: Nitrobenzene: Nitro derivatives: Nitroethane: Nitrogen: Nitrogen dioxide: Nitrogen peroxide: Nitromethane: m-Nitrotoluene: Nitrous oxide Noise: Nonadecane: Nonadecene: Nonane: Nonene: Nonanol: Nonaqueous fluids, critical heat flux in, Non-circular microchannels: Noncondensables: Nondestructive testing, of heat exchangers Nongray media, interaction phenomena with, Nonmetallic materials: Non-Newtonian flow: Nonparticipating media, radiation interaction in, Nonuniform heat flux, critical heat flux with, Non-wetting surfaces, in condensation augmentation, North, C, No-tubes-in-window shells, calculation of heat transfer and pressure drop in, Nozzles: Nowell, D G, Nucleate boiling:
augmentation of, in axial flow reboilers, in evaporators,
Estimation of Heat Transfer Coefficients
in forced convective boiling of binary and multicomponent mixtures, in forced convective heat transfer in vertical tubes, in horizontal tubes, in kettle reboilers, in microchannels, outside tubes and tube bundles in crossflow, in pool boiling of binary and multicomponent mixtures, in pool boiling systems,
Nuclear industry, fouling problems in, Nucleation: Nucleation sites: Nuclei, formation in supersaturated vapor, Number of transfer units (NTU): Numerical methods: Nusselt: Nusselt-Graetz problem, in laminar heat transfer in ducts, Nusselt number:
O P Q R S T U V W X Y Z
N Nucleate boiling: in evaporators,
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Estimation of Heat Transfer Coefficients

DOI 10.1615/hedhme.a.000275

3.5.7 Estimation of heat transfer coefficients

R. A. Smith, P. D. Hills

This section is in general only intended to give an overview of the heat transfer processes; more detailed information may be found in Section 31 for single phase convective heat transfer, Section 32 for condensation and Section 33 for evaporation and boiling heat transfer.

The overall heat transfer coefficient (U) is the reciprocal of the sum of the five thermal resistances through which the heat must pass; (1) the boiling liquid, (2) the fouling deposited by the boiling liquid, (3) the wall, (4) the fouling deposited by the heating fluid, and (5) the heating fluid. Each resistance may be expressed as the reciprocal of the individual coefficient (α), corrected where necessary to refer to the same area, usually the outside.

\[\label{eq1} \frac{1}{U_{o}}=\frac{1}{\alpha_{c}}\frac{A_{o}}{A_{c}}+r_{f,c} \frac{A_{o}}{A_{c}}+r_{w}\frac{A_{o}}{A_{w}}+r_{f,h}\frac{A_{o} }{A_{h}}+\frac{1}{\alpha_{h}}\frac{A_{o}}{A_{h}} \tag{1}\]

Here, A is the surface area, Af is the fouling resistance and α is the film heat transfer coefficient. The subscripts c, h, o and w refer to cold fluid side, hot fluid side, outside surface and mean wall respectively. Note that if boiling occurs on the outside surface, Ao = Ac whereas if boiling is inside the tubes, Ao = Ah. The estimation of these individual coefficients or resistances is dealt with below. Aw is given by:

\[\label{eq2} A_{w} =\frac{A_{o}-A_{I}}{\ln(A_{o} /A_{I})} \tag{2}\]

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