Operational regimes in a closed loop pulsating heat pipe

Spinato, Giulia; Borhani, Navid; Thome, John R.

doi:10.1016/j.ijthermalsci.2015.11.006

Cited by 57 publications

(18 citation statements)

References 30 publications

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“…Both OHPs have temperature oscillations with characteristic frequencies on-the-order of 10 mHz, which is approximately 2 orders of magnitude lower than those found on OHPs with shorter form factors while undergoing constant heat flux evaporator conditions [44] . This very low frequency operation of the OHP-HE suggests that thin film evaporation, which is a typical mechanism for heat transfer in many OHPs [ 45 , 46 ], may not be the dominant means for phase change of working fluid in the evaporator. Instead, the time scales inherent to fluid oscillations observed herein suggest that boiling heat transfer is more prominent in the OHP-HE evaporator.…”

Section: Resultsmentioning

confidence: 99%

Experimental characterization of an n-pentane oscillating heat pipe for waste heat recovery in ventilation systems

Mahajan¹,

Thompson

Cho

2018

Heliyon

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A tubular oscillating heat pipe (OHP), with long form factor and 1 × 0.5 m2 footprint, was experimentally characterized for passive waste heat recovery via air-to-air heat exchange in a typical Heating Ventilation & Air Conditioning (HVAC) ducting system. Experiments were designed to demonstrate the OHP's ability to utilize otherwise wasted thermal energy to pre-heat or pre-cool air for reducing building energy consumption. Results indicate that the OHP is fully-capable of operating while possessing a relatively long form factor (>1 m) and as a forced convection, air-to-air heat exchanger for waste heat recovery in HVAC systems.

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Section: Resultsmentioning

confidence: 99%

Experimental characterization of an n-pentane oscillating heat pipe for waste heat recovery in ventilation systems

Mahajan¹,

Thompson

Cho

2018

Heliyon

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“…Equation 2 is a common method in heat pipe literature [21,23]. Here, as stated in the previous section, heat input (Q i ) is set and changed via the power supply in a controllable manner.…”

Section: Data Reduction Steps and Uncertaintiesmentioning

confidence: 99%

“…The rapid growth bubble enlarges toward both sides; however, in the heat pipe conditions, heat is applied from evaporator region and thus, an asymmetrical elongation toward condenser region takes place. This phenomenon increases instabilities in the flow passages, and from the heat pipe literature [3,23], it is known that increasing perturbations increases performance of the pulsating heat pipes. When heat further increases (35 W, see Figs.…”

Section: Effects Of Mixing Ratio and Heat Loadmentioning

confidence: 99%

Thermal investigation and flow pattern analysis of a closed-loop pulsating heat pipe with binary mixtures

Markal

Varol

2020

J Braz. Soc. Mech. Sci. Eng.

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The present study basically examines thermal performance and relevant flow phenomena of a flat plate closed-loop pulsating heat pipe (FP-CLPHP) filled with binary mixtures. The heat pipe has eight turns, each of which consisting of asymmetrical channel pairs having cross sections as 2 mm × 2 mm and 1 mm × 2 mm (width × height). Binary mixtures are generated as mixtures of ethanol (E) and pentane (P) with different mixing ratios. Mainly, effects of volume mixing ratio (E/P = 1:1, 1:3 and 3:1), vertical (90°) and horizontal orientation (0°) and filling ratio (30% and 60%) on thermal characteristics are investigated under different heat inputs. For examination of flow dynamics, images are obtained by using a high-speed camera at 1000 fps. The results show that variation of volumetric percentage of each component significantly changes thermal performance. Increasing pentane in the mixture improves the thermal performance, such that heat pipe with mixing ratio of E/P = 1:3 can properly operate even at horizontal position. On the other hand, increasing volume of ethanol in mixture leads to collapse of the FP-CLPHP at both orientations (0° and 90°). Generally, the filling ratio of 30% shows better thermal performance. Complex bubble-liquid interactions and dynamics play critical roles on thermal characteristics. Two novel characteristic phenomena are identified for non-uniform PHPs: (1) flooding phenomenon and (2) asymmetrical rapid bubble growth phenomenon. Keywords Thermal performance • Flow visualization • Bubble dynamics • Heat pipe List of symbols A bi Bubble interface area (m 2) A app Shear force acting area (m 2) D h Hydraulic diameter (m) Q i Heat input (W) Q rh Removed heat via cooling water (W) R th Total thermal resistance (°C W −1) T Temperature (°C) Greek symbols Angle between the heat pipe and horizontal position (°) Dynamic viscosity (Pa s)

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“…Several researchers are performing investigations on non-conventional operating fluids, like nano-fluids (Qu et al, 2010;Aly, 2014), refrigerants (Wang and Jia, 2016;Nazari et al, 2018), inert gases (Spinato et al, 2016) and ionic fluids (Fonseca et al, 2015), surfactant solution (Bastakoti et al, 2018b;Liang et al, 2018), etc., to find novel operating fluids which might enhance the operational performance of PHP. Regarding on surfactant solutions, Liang et al (2018) conjointly discovered thermal performance of PHP with sodium stearate surfactant chemical agent solutions which have better performance results compared with pure water yielded.…”

Section: Introductionmentioning

confidence: 99%

Visualization of bubble mechanism of pulsating heat pipe with conventional working fluids and surfactant solution

Basatakoti

Zhang

et al. 2019

Exp. Comput. Multiph. Flow

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Visualization experiment is a must in realizing functional characteristics of an operational pulsating heat pipe (PHP). So far there is no general formulation which can foretell the complex and chaotic flow nature for every working fluid. Different response of working fluids and their distinct flow nature as well as their behavior can be visualized which thereby helps to understand the operational mechanism of the PHP. In this experiment, tests were conducted in a transparent PHP with 3 conventional working fluids, viz. de-ionized (DI) water, methanol, ethanol, and 300 ppm cetyltrimethyl ammonium chloride (CTAC) solution, each with fill ratio (FR) of 50%. With the help of high speed camera, flow characteristics at different operational stages for each working fluid are captured. Difference in the generation, growth, movement, and flow direction of bubbles are observed and the consequence of combined effects of various thermal properties of the fluid rather than a dominating single property. Start-up characteristics and dominating flow pattern for each fluid are reported in this paper. Moreover, peculiar flow characteristics with 300 ppm CTAC like bubble detachment, movement of cluster of micro-bubbles, and swirling are also presented.

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Operational regimes in a closed loop pulsating heat pipe

Cited by 57 publications

References 30 publications

Experimental characterization of an n-pentane oscillating heat pipe for waste heat recovery in ventilation systems

Experimental characterization of an n-pentane oscillating heat pipe for waste heat recovery in ventilation systems

Thermal investigation and flow pattern analysis of a closed-loop pulsating heat pipe with binary mixtures

Visualization of bubble mechanism of pulsating heat pipe with conventional working fluids and surfactant solution

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