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• Novel mathematical model to predict the heat transfer rate of skin condensers. • Experimental validation with eigth hot-wall condenser designs. • Adhesive tape has the strongest impact on the heat exchanger performance. This paper comes out with an investigation of the thermal performance of skin-type hot-wall condensers for household refrigeration applications. Eight different hot-wall condensers were manufactured and installed in identical refrigerators. The condenser samples were constructed by varying the following design parameters: (i) adhesive tape (aluminum or polyethylene), (ii) tube O.D. (4.00 or 4.76 mm), (iii) total length (10 or 11.5 m) and (iv) condenser positioning. The refrigerators were placed inside a climate-controlled chamber and tested in steady-state conditions. A mathematical model that takes into account the heat transfer not only to the surroundings but also to the refrigerated compartments was also put forward. The model predictions were compared to the experimental data when deviations within the ±10% bounds were achieved. It was found that the adhesive tape thermal conductivity and the tube-outer sheet contact area have the strongest impact on the condenser performance. It was also found that the polyethylene tape increases the condensing pressure, due to its low thermal conductivity and thus to the smaller useful heat transfer area. It was thus concluded that the refrigerator foaming process must be carried out with an extreme care to avoid any negative impact on the tube-outer sheet contact resistance. Finally, it was noted that the heat transfer to the refrigerated compartments is directly affected by the condenser positioning and the thermal insulation thickness. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an advanced switched modeling approach for vapor compression cycle (VCC) systems used in Air Conditioning and Refrigeration. Building upon recent work (), a complete dynamic VCC model is presented that is able to describe the severe transient behaviors in heat exchangers (condenser/evaporator), while maintaining the moving-boundary framework, under compressor shut-down and start-up operations. The heat exchanger models retain a constant structure, but accommodate different model representations. Novel switching schemes between different representations and pseudo-state variables are introduced to accommodate the transitions of dynamic states in heat exchangers while keeping track of the vapor and liquid refrigerant zones during the stop–start transients. Two model validation studies on an experimental system show that the complete dynamic model developed in Matlab/Simulink can well predict the system dynamics in shut-down and start-up transients. [Copyright &y& Elsevier]

Abstract: This paper reports on the experimental research conducted to study the condensation of ammonia on smooth and integral-fin (32fpi) titanium tubes of 19.05mm outer diameter. Experiments were carried out at saturation temperatures of 30, 35, 40 and 45°C and wall subcoolings from 1 to 8°C. The results show that the condensation coefficients on the smooth tubes are well predicted by the Nusselt theory with an average error of +0.66% and within a deviation between −6.6% and +8.3%. The enhancement factors provided by the integral-fin tubes range from 0.77 to 1.22. The low enhancement factors are due to the high condensate retention between fins, which brings about flooded fractions of the tube perimeter from 62.9% to 73.2%, and the low thermal conductivity of titanium. The Briggs and Rose [1994. Effect of fin efficiency on a model for condensation heat transfer on a horizontal, integral-fin tube. Int. J. Heat Mass Transfer 37, 457–463.] model, which accounts for the conduction in the fins, predicts the experimental data with a mean overestimation of 20%. The analysis of the partial thermal resistances in the overall heat transfer process points out the convenience of enhancing the outside ammonia condensation when high water velocities are considered inside the tubes. [Copyright &y& Elsevier]

Abstract: Microchannel (or mini-channel) heat exchangers are drawing more attention because of the potential cost reduction and the lower refrigerant charge. Serpentine microchannel heat exchangers are even more compact because of the minimized headers. Using the serpentine microchannel condenser, some thermodynamically good but flammable refrigerants like R-290 (Propane) can be extended to more applications. To well size the serpentine microchannel condensers, a distributed-parameter model has been developed in this paper. Airside maldistribution is taken into account. Model validation shows good agreement with the experimental data. The predictions on the heating capacity and the pressure drop fall into ±10% error band. Further analysis shows the impact of the pass number and the airside maldistribution on the condenser performance. [Copyright &y& Elsevier]