Abstract
This paper presents a critical analysis of possible data reduction procedures for the evaluation of local heat transfer coefficient during flow boiling experiments. The benchmark method using one-dimensional (1-D) heat transfer in a heated tube was compared to a new data reduction method in which both radial and circumferential contributions to the conductive heat transfer inside a metal tube are considered. Using published experimental flow boiling data, the circumferential profiles of the wall superheat, inner wall heat flux, and heat transfer coefficients were independently calculated with the two data reduction procedures. The differences between the two methods were then examined according to the different heat transfer behavior observed (symmetric or asymmetric), which in turn was related to the two-phase flow regimes occurring in a channel during evaporation. A statistical analysis using the mean absolute percentage error (MAPE) index was then performed for a database of 417 collected flow boiling data taken under different operating conditions in terms of working fluid, saturation temperature, mass velocity, vapor quality, and imposed heat flux. Results showed that the maximum deviations between the two methods could reach up to 130% in the case of asymmetric heat transfer. Finally, the possible uses of the two data reduction methods are discussed, pointing out that the two-dimensional (2-D) model is the most reliable method to be employed in the case of high-level modeling of two-phase flow or advanced design of heat exchangers and heat spreader systems.
Highlights
Refrigeration and air conditioning are both receiving particular attention nowadays, with the two fields being under the strict control of several ongoing policies and regulations concerning the environment
A statistical analysis using the mean absolute percentage error (MAPE) index was performed for a database of 417 collected flow boiling data taken under different operating conditions in terms of working fluid, saturation temperature, mass velocity, vapor quality, and imposed heat flux
We focused on possible methods to evaluate the local heat transfer coefficient in a single metal tube, in which multiple thermocouples were fixed on the external surface for measurement single metal tube, in which multiple thermocouples were fixed on the external surface for ofmeasurement the outer walloftemperature; thetemperature; heat flux wasthe imposed by was means of electrical current directly applied the outer wall heat flux imposed by means of electrical current on the channel itself
Summary
Refrigeration and air conditioning are both receiving particular attention nowadays, with the two fields being under the strict control of several ongoing policies and regulations concerning the environment. The European Union’s regulations on fluorinated gases, known as the EU F-Gas Regulation [3], pushes toward a consistent reduction of greenhouse gas emissions and promotes the utilization of eco-friendly refrigerants. In this dynamic context, the correct design of heat exchangers (i.e., evaporators) is the key factor for fair estimation and optimization of system performance [4]. The correct design of heat exchangers (i.e., evaporators) is the key factor for fair estimation and optimization of system performance [4] This requires dedicated, reliable experiments to obtain more, new high-quality two-phase heat transfer data. It is possible to develop new heat transfer prediction methods or modify the existing ones, which are mostly calibrated on conventional fluids and may not be sufficiently precise when used outside the operating conditions on which they have been based [5,6]
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