Abstract
In the paper the results of investigations into HFE-7100 flow boiling heat transfer in a cylindrical minigap a 1 mm wide created between the external glass pipe and the copper pipe were discussed. A cartridge heater located axially heated fluid flowing along the minigap. The cooling fluid temperature and pressure at the inlet and the outlet to/from the minigap and temperature of the heater in 18 points were measured. Two-dimensional mathematical model for heat transfer coefficient determination was proposed. It was assumed that in the test section the heat transfer process was in steady state and the fluid flow was laminar. The temperature of the metal pipe near the heater was assumed to satisfy Laplace’s equation. The problem formulated in this way was solved by two methods: the Fourier transform and the Trefftz method. The working fluid temperature was calculated depending on the flow type: for single phase flow with boiling incipience and for two-phase flow, respectively. The heat transfer coefficient at the fluid – copper pipe interface was calculated due to the Robin condition. Local heat transfer coefficient values obtained from the Fourier transform and from the Trefftz method were similar. Results were presented and discussed.
Highlights
Heat exchangers with minigaps have attracted wide attention from the heat transfer issues due to their prominent ability to remove heat flux from confined spaces
This paper shows the results of research on flow boiling heat transfer during refrigerant flow along an annular minigap [6,7,8]
The calculations were performed with the Fourier transform and the Trefftz method for the following experimental parameters: pressure at the inlet 220 kPa, inlet liquid subcooling 56 K, constant mass flow rate of 0.017 kg/s) and five heat fluxes qw in the range of 8.8÷17.4 kW/m2
Summary
Heat exchangers with minigaps have attracted wide attention from the heat transfer issues due to their prominent ability to remove heat flux from confined spaces. A lot of works have been published to address the issues of heat transfer in flow boiling in minigaps of different geometry. Previous authors’ studies mostly have been performed to evaluate the flow boiling heat transfer in rectangular minichannels, as [1,2,3,4,5]. This paper shows the results of research on flow boiling heat transfer during refrigerant flow along an annular minigap [6,7,8]. The research often abandons the experimental studies in favour of numerical simulations, utilising commercial software, where the experimental results serve the purpose of validation of numerical calculations only, such as, for example, in [12, 13]. Application of commercial software for solving an inverse heat conduction problem (IHCP), as
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