Determination of the heat transfer coefficient distribution on the longitudinal finned tubes in staggered arrangement using inverse and cfd method

Determination of the heat transfer coefficient distribution on the longitudinal finned tubes in staggered arrangement using inverse and cfd method

Cebula, A.
Sobota, T.

2006-09-08

Local heat transfer from a cylinder in tube bank has been extensively studied. In many applications such as design of heat exchangers, detailed information regarding the circumferential and longitudinal variation of heat transfer to a cylinder is required. There are many different methods for measuring local heat transfer like techniques using liquid crystals, thermal paints, heater foils, naphthalene heatmass transfer analogy. All techniques have been widely used with considerable success but they have certain difficulties. An alternative method to obtain the local convective heat transfer coefficient is the inverse procedure. This paper presents results of an experimental study on heat exchanger consisting of finned tube. Tubes have two longitudinal fins which join neighboring tubes, creating membrane panels. The local and mean heat transfer coefficients on the tube circumference were determined using the inverse heat transfer method. Using the inverse methods, the convective heat-transfer coefficient was determined very exactly, reproducing the real two-dimensional temperature distribution in the cross-section of the tube. Determination of the space-variable heat transfer coefficient on a complex shape surface requires the solution of the nonlinear inverse heat conduction problem. The unknown parameters associated with the solution are selected to achieve the closest agreement in a least squares sense between the computed and measured temperatures using the Levenberg-Marquard method. The nonlinear least squares problem is parameterized by expressing the space variation on the heated tube with two longitudinal fins in cross flow. Experiments were performed with an array of vertical tubes arranged in staggered pattern. The design of apparatus and the measurements were performed according to the general guidelines presented in ASHRAE and ARI Standards. Air flow in the open-loop wind tunnel was provided by variable speed radial fan. The air duct is made of galvanised sheet steel and has rectangular cross-section. Heat loses from the duct and heated tube bundle were minimised by insulating the outside surface of the duct with fibreglass mats. As a results of experimental and numerical investigations were obtained distribution of the local heat transfer coefficient on the surface of the membrane and fined tube for various Reynolds numbers and the temperature distribution on their surfaces too. The presented method for determining the local heat transfer coefficient on external tube surfaces is characterized by very high accuracy and can be applied to determine the spatial heat transfer distribution on objects with a complex shape.

heat transfer coefficient
heat exchanger
CFD
convection

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Conference proceedings

conference paper

(c) 2006 Cebula, A.; Sobota, T.