Summary

The development of compact heat exchangers for domestic refrigeration applications has been the focus of several studies thanks to its impact in reducing material costs and energy consumption. It also allows for a more effective usage of the space occupied by the cooling system components, which increases the net storage volume of the refrigerator without changing the external dimensions of the product. Due to its low manufacturing cost, wire-on-tube heat exchangers are still the most advantageous condenser type for household refrigeration applications where, traditionally, natural convection is the dominant heat transfer mode. However, for high cooling capacity applications, the potential benefits of more compact forced convection wire-on-tube condensers illustrated above seem to overcome the costs and energy consumption involved in pumping the external air through the condenser. The starting point of the present work was a literature search for compact wire-on-tube heat exchanger configurations which would be subsequently evaluated on the basis of its thermal-hydraulic performance. The configuration chosen for a more in-depth analysis (Ohgaki, 2002) was the one with the largest heat transfer area per unit volume. The main geometric parameters were identified, namely, the number of tube passes, the radial, longitudinal and wire spacings, and their effect on the thermal-hydraulic performance has been assessed by means of the construction and testing of sixteen prototypes. An open-loop wind-tunnel calorimeter was designed and built, and measurements of thermal conductance and pressure drop on the air side were carried ou for values of air flow rate typical of those found in forced convection condensers. The data were correlated in terms of dimensionless parameters like the Colburn j-factor and the Fanning friction factor. The coefficients of the correlations were regressed based on the geometric parameters using the method proposed by Montgomery (2001). The agreement with the experimental data presented maximum errors of 9.4% for the heat transfer and 14.2% for the pressure drop. Finally, a quantitative analysis to provide the most viable configuration from the point of view of the application is discussed.

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