Experimental Investigation of the Thermal Performance of a Wickless Heat Pipe Operating with Different Fluids: Water, Ethanol, and SES36. Analysis of Influences of Instability Processes at Working Operation Parameters

Abstract

In this study, the influences of different parameters on performance of a wickless heat pipe have been presented. Experiments have been carried out for an input power range from 50 W to 300 W, constant cooling water mass flow rate of 0.01 kg/s, and constant temperature at the inlet to condenser of 10 °C. Three working fluids have been tested: water, ethanol, and SES36 (1,1,1,3,3-Pentafluorobutane) with different filling ratios (0.32, 0.51, 1.0). The wall temperature in different locations (evaporation section, adiabatic section, and condenser section), as well as operating pressure inside two phase closed thermosyphon have been monitored. The wickless heat pipe was made of 0.01 m diameter copper tube, which consists of an evaporator, adiabatic, and condensation sections with the same length (0.4 m). For all working fluids, a dynamic start-up effect caused by heat conduction towards the liquid pool was observed. Only the thermosyphon filled with SES36 was observed to have operation limitation caused by achieving the boiling limit in TPCTs (two-phase closed thermosyphons). The geyser boiling effect has been observed only for thermosyphon filled with ethanol and for a high filling ratio. The performance of the thermosyphon determined the form of the heat transfer resistance of the TPCT and it was found to be dependent of input power and filling ratio, as well as the type of working fluid and AR (aspect ratio). Comparison with other authors would seem to indicate that lower AR results in higher resistance; however, the ratio of condenser section length to inside diameter of pipe is also a very important parameter. Generally, performance of the presented thermosyphon is comparable to other constructions.

Effect of adiabatic length on the performance of closed‐loop thermosyphon system

“…When vapor bubble sizes are equal to the inner diameter of the loop pipe, then the geyser boiling phenomenon starts. Also, two important factors that affect the geyser boiling phenomenon are the period of the oscillation and the intensity of the rising and falling of the temperatures of the condenser section and evaporator section 25 …”

“…0.494 0.08 (25) This expression is valid for 700 ≤ (Re) ≤ 3800, 2 ≤ (Pr) ≤ 3.2. This mathematical model is validated by comparing it with the expression reported by Jouhara and Robinson.…”

“…Also, two important factors that affect the geyser boiling phenomenon are the period of the oscillation and the intensity of the rising and falling of the temperatures of the condenser section and evaporator section. 25 Figure 11 indicates the variation of the evaporator and condenser temperature with time at the FR = 0.6 and heat input Q = 0.5 kW. T ew is the evaporator wall temperature; T ev is the evaporator vapor temperature, and T cw is the condenser wall temperature.…”

Assessment of heat transfer and flow characteristics of a two‐phase closed thermosiphon

“…The variety in the evaporator and condenser lengths affects the working characteristics inside the thermosiphon, because the heat flux from the evaporator wall and from the working fluid to the condenser wall varies with the length. Therefore, the same length of the evaporator and condenser sections has been considered to avoid the dry‐out phenomenon 26‐28 . For the two‐phase closed thermosiphon, the specifications, dimensions, and operating conditions are listed as below: Pipe material: copper Pipe inner diameter: 22 mm Pipe outer diameter: 23.8 mm Pipe wall thickness: 0.9 mm Condenser sector: 200 mm Evaporator sector length: 200 mm Tilt angles: 15°, 45°, 75°, and 90° Fill ratios: 0.1, 0.3, 0.5, 0.75, and 0.9 Power inputs: 50, 100, and 250 W Upper and lower caps: insulated Walls: stationary Working fluids: water…”

Experimental Study of Wickless Heat Pipe with Flat Evaporator for Used in Cooling of Electronic Components

“…Where the vapor condenses in the condenser back to liquid and return to the evaporator by the gravity force. [2] Some previous research may be presented this type of heat pipe: Rafal and rzeejczyk, 2018 [3] experimental studied investigation of the thermal performance of a wickless heat pipe. It is study effect of different parameters on performance of straight heat pipe were different working fluid and fill ratio.…”