Abstract
This article presents the results of flow visualization studies of Novec refrigerants during condensation in minichannels. Experimental investigation of two-phase flow regimes was conducted in minichannels with internal diameter dh = 2.5, 2.0, 1.2, and 0.5 mm. Images of the two-phase flow structures were analyzed by using the MATLAB algorithm. To calculate void fraction, a two-dimensional areal quantitative stereology technique was used. Observation of flow structures formed during the process of condensation was the major aim of the investigations. The condensation studies were conducted over a wide range of mass flux densities (G = 80–5500 kg/m2s) and saturation temperatures (ts = 30–70 °C). Visualization results and image analysis methods are described in this paper. Based on the experimental results, a flow structure map was constructed and presented.
Highlights
The issues of heat and mass flow are of great importance in current technological development [1,2]
In addition to the study of heat transfer or flow resistance during the condensation process in minichannels, the observation of two-phase flow structures formed in a nonadiabatic flow is of great importance
It consisted of a minichannel made of glass, which was used for the visualization of the two-phase flow of refrigerant during the condensation process
Summary
The issues of heat and mass flow are of great importance in current technological development [1,2]. Nema et al [10] proposed new transition boundaries for individual flow structures, using the database for the condensation of R134a refrigerant in the channels with a hydraulic diameter dh = 1–4.91 mm and mass flow density range G = 150–750 kg/(m2 s). They proved the influence of the channel diameter and heat transfer on the occurrence of some flow structures, by comparing it with adiabatic, air–water, two-phase flow under similar conditions. The proposed flow structure maps are new in this field
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