Condensation of pure fluids in downflow on horizontal integral low-fin tube bundles.
Abstract:ESDU 01009 provides a method for predicting the local condensate film coefficient for the downflow of a pure vapour or azeotropic mixture over horizontal integral low-fin tubes and tube bundles, typically in TEMA X-shells. The condensation rate on integral low-fin tubes is greater than that on plain tubes of the same nominal outside diameter. Use of low-fin tubing will therefore usually enable the size (tube length and/or bundle diameter) and hence the weight of a condenser for a suitable duty to be reduced compared with the equivalent plain tube unit. Replacement of plain tubes with integral low-fin tubes of the same overall diameter is often a cost-effective solution when plant up-rating is being considered. They are used to maximum advantage in the condensation of low surface tension fluids such as refrigerants and light hydrocarbons and are commonly specified for refrigeration and air conditioning plant. Low-fin tubing is increasingly specified for condensers in the process industries generally.A step-by-step calculation method is presented that can, for example, be used to check the adequacy of a design to meet a performance requirement or to estimate the outlet conditions from a given condenser. The calculation method is applicable to those cases where the saturation temperature over the length of the condensing path remains approximately constant. The method covers gravity-controlled flows, flows with high vapour shear and high and low thermal conductivity tube materials. Bundle pressure drops are not calculated; it is assumed that they are negligible in gravity-controlled downflows (as opposed to shear-controlled flows), with the dominant pressure drop occurring across the inlet nozzle. Typical correlation plots show that the available data correlate mostly within 20 per cent for both single tubes and in-line and staggered tube bundles. For a range of condensing fluids, the data cover a wide range of vapour side temperature difference, vapour Reynolds number and fin configurations. The use of the calculation procedure is illustrated by a practical worked example, and the background to the method is presented in Appendices.
|Data Item ESDU 01009