Effect of active and passive cooling on the thermo-hydrodynamic behaviors of the closed-loop pulsating heat pipes

Closed-loop pulsating heat pipes (CLPHPs) are a new type of two-phase heat transfer devices that can transfer considerable heat in a small space via two-phase vapor and liquid pulsating flow and work with various types of two-phase instabilities so the operating mechanism of CLPHP is not well understood. In this work, two CLPHPs, made of Pyrex, were manufactured to observe and investigate the flow regime that occurs during the operation of CLPHP and thermal performance of the device under different laboratory conditions. In general, various working fluids were used in filling ratios of 40%, 50%, and 60% in horizontal and vertical modes to investigate the effect of thermo-physical parameters, filling ratio, nanoparticles, gravity, CLPHP structure, and input heat flux on the thermal performance of CLPHP. The results indicate that three types of flow regime may be observed given laboratory conditions. Each flow regime exerts a different effect on the thermal performance of the device. There is an optimal filling ratio for each working fluid. The increased number of turns in CLPHP generally improves the thermal performance of the system reducing the effect of the type of the working fluid on the aforementioned performance. The adoption of copper nanoparticles, which positively affect fluid motion, decreases the thermal resistance of the system as much as 6.06–42.76% depending on laboratory conditions. Moreover, gravity brings about positive changes in the flow regime decreasing thermal resistance as much as 32.13–52.58%.

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Flat plate solar water heater with closed-loop oscillating heat pipes

Thermal Science ◽

10.2298/tsci200713192c ◽

2021 ◽

pp. 192-192

Author(s):

Piyanun Charoensawan ◽

Patomsok Wilaipon ◽

Nopparat Seehawong

Keyword(s):

Flat Plate ◽

Flow Rate ◽

Thermal Performance ◽

Closed Loop ◽

Water Flow Rate ◽

Heat Pipes ◽

Solar Water Heater ◽

Water Heater ◽

Solar Water ◽

Irradiation Intensity

The flat plate solar water heater, using the closed-loop oscillating heat pipes (CLOHP), was constructed and investigated. The flat plate collector consisted of 10 pipes of CLOHP and the collector area was 1.5?1 m2. Each CLOHP was made of a copper capillary tube with a 1.5 mm inner diameter, a 2.8 mm outer diameter and had 20 turns. The distilled water was used as the working fluid with a filling ratio of 50% the tube?s total internal volume. The evaporator section of the CLOHP was placed on the absorber plate of the collector, and its condenser section was wrapped around the copper tube, in which hot water flowed through. The solar water heater was tested under the solar simulator with halogen lamps generating the uniform artificial solar energy. The irradiation intensity and the water flow rate of the solar water heater were adjusted. It was found that the thermal performance of the solar water heater clearly improved with an increase in the irradiation intensity from 480 to 1086 W/m2. However, the water flow rate in the range of 1.5-3.0 L/min, had a thermal performance that was slightly different. The thermal efficiency of 0.67 was archived at the high irradiation intensity of 947-1086 W/m2. Moreover, the mathematical model to predict the thermal efficiency of the flat plate solar water heater with the CLOHPs was obtained.

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A High Performance Semi-Passive Cooling System: The Pulse Thermal Loop

Volume 3 ◽

10.1115/ht-fed2004-56457 ◽

2004 ◽

Cited By ~ 3

Author(s):

Mark M. Weislogel ◽

Michael A. Bacich

Keyword(s):

Heat Transport ◽

High Performance ◽

Driving Forces ◽

Cooling System ◽

Heat Pipes ◽

Thermal Control ◽

High Heat ◽

Transport Systems ◽

Passive Cooling ◽

Cooling Systems

Over the past decade, the search for and development of high performance thermal transport systems for a variety of cooling and thermal control applications have intensified. One approach employs a new semi-passive oscillatory heat transport system called the Pulse Thermal Loop (PTL). The PTL, which has only recently begun to be characterized, exploits large pressure differentials from coupled evaporators to force (pulse) fluid through the system. Driving pressures of over 1.8MPa (260psid) have been demonstrated. Other passive cooling systems, such as heat pipes and Loop Heat Pipes, are limited by capillary driving forces, typically less than 70kPa (10psid). Large driving forces can be achieved by a mechanically pumped loop, however, at the expense of increased power consumption, increased total mass, and increased system cost and complexity. The PTL can be configured in either active or semi-passive modes, it can be readily designed for large ∼ O(100kW) or small ∼ O(10W) heat loads, and it has a variety of unique performance characteristics. For low surface tension dielectric fluids such as R-134a, the PTL system has over a 10-fold heat carrying capacity in comparison to high performance heat pipes. Data accumulated thus far demonstrate that the PTL can meet many of the requirements of advanced terrestrial and spacecraft cooling systems: a system that is robust, ‘semi-passive,’ high flux, and offers high heat transport thermal control while remaining flexible in design, potentially lightweight, and cost competitive.

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