Air-side heat transfer and pressure drop characteristics of accelerated flow evaporators

We investigate an alternative tube-fin evaporator design (accelerated flow evaporator, AFE) in which the air-side local heat transfer coefficient is increased due to a progressive reduction of the free-flow area. For a given heat transfer rate, this enhancement is expected to partially compensate the decrease in surface area, which reduces the evaporator material cost. The air-side thermal-hydraulic behavior of nine AFEs was determined experimentally, and a calculation method that relies on j and f correlations for plain tube-fin heat exchangers and on mass and momentum balances has been proposed. The method enables the calculation of the by-pass fraction associated with the air stream through the clearance between the tube bank and the outer edge of the fins. The agreement between the model, which introduces no additional fitting parameters, and the experiments is within ±10% for all heat transfer data and ±15% for the majority of the pressure drop data.