Performance analysis of air-cooled condenser using micro-fin tubes

Abstract

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.

In-tube condensation is quite common in refrigeration and air-conditioning applications. It is the binding choice for air-cooled and evaporative condensers. In-tube condensation is often thought of as a process of film-wise condensation of a vapor inside a tube. Since augmentation can result in smaller and more efficient devices, potential savings are quite substantial. An experimental program designed to investigate potential augmentation techniques has been carried out worldwide as part of a large study of in-tube condensation. Copper circular smooth or enhanced tubes with plate aluminum fins on the air side (fin-and-tube heat Exchangers) are the usual geometry in aircooled condensers. Enhanced tubes such as micro fin tubes are typically made of copper and have an outside diameter from 4 to 15 mm, a single set of 50-70 fins with helix angle from 6 to 30°, fin height from 0.1 to 0.25 mm, triangular or trapezoidal fin shapes with an apex angle from 25 to 90°. Air-cooled condensers operate at a greater condensing temperature than water-cooled condensers; hence the compressor (and the refrigeration system) delivers 15 to 20% lower capacity. Therefore one has to use a larger compressor. At the same time, the compressor consumes greater power. Hence the air-cooled system has a lower overall energy efficiency. This paper manly emphasis on increase in overall performance of the air-cooled condenser. The objective of this study is to analyze the theoretical performance of air-cooled condensers using micro-fin tubes. The enhancement factor (ratio of heat transfer coefficient of micro-fin tube to heat transfer coefficient of plane tube) considered to be 1.5. The overall performance of condenser for different refrigerants has also been studied. The refrigerants used for study are R-134a, R-404a and R-22.The performance of condenser is analyzed for 550 C condensing temperature because most of the air cooled condensers in India are working on this condensing temperature. The % saving in fan power is estimated upto 90%with the use of micro-fin tubes, 29% reduction in compressor power; and 17% increase in cooling capacity, on the other hand the % reduction in size of condenser is up to 32%. It is also found that the performance of condenser also varies with the refrigerant used.