Effect on Noncondensible Gas and Evaporator Mass on Loop Heat Pipe Performance

Applied Thermal Engineering

Shen

et al. 2020

The coupling effect of evaporator/condenser elevations and non-condensable gas (NCG) on the performance of a loop heat pipe (LHP) operating in gravitational field was investigated experimentally. Ammonia and nitrogen were selected as the working fluid of LHP and the simulated gas of NCG, respectively. The experiments were conducted at three kinds of evaporator/condenser elevations, namely zero elevation, adverse elevation and positive elevation. Experimental results show that NCG will cause an increase in operating temperature, but the trends varies at different evaporator/condenser elevation elevations. The temperature rises caused by NCG at the zero and adverse elevations are negatively correlated with heat load, and the maximum temperature increments are both at the minimum heat load of 15 W, but the influence of NCG is less at adverse elevation. On the other hand, at favorable elevation, the temperature rise exhibits different characteristics in different LHP operation modes, i.e., positively correlated with heat load in gravity driven mode and negatively in capillaritygravity co-driven mode, and the transition heat load is 60 W. For an LHP that has already contained a certain amount of NCG, functioning at favorable elevation could eliminate the adverse effects of NCG on operating temperature and heat transfer performance to some extent. Furthermore, it is found that the presence of NCG and adverse elevation appears to inhibit the backflow during startup and improve startup stability. These results might have reference significance for the design and installation of the LHP for terrestrial applications.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of evaporator/condenser elevations on a loop heat pipe with non-condensable gas

Wang

Applied Thermal Engineering

Shen

et al. 2020

“…In recent years, a few studies about the NCG effect on the performance of LHP have been conducted, and corresponding solutions have been studied as well. Ref [13] and Ref [14] studied the impacts of NCG on the steady state characteristics of LHP by injecting NCG into LHP quantificationally. Experiments showed that the operation of LHP was insensitive to the presence of NCG compared with conventional heat pipes, but NCG would increase the startup time and operating temperature.…”

Section: Introductionmentioning

confidence: 99%

Effect of evaporator tilt on a loop heat pipe with non-condensable gas

Wang

International Journal of Heat and Mass Transfer

Shen

et al. 2019

ReuseThis article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can't change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Abstract: The coupling effect of non-condensable gas (NCG) and evaporator tilts on the steady state operation of a loop heat pipe (LHP) was investigated both experimentally and theoretically in this work. Nitrogen was injected quantitatively into an ammonia-stainless steel LHP to simulate NCG, and the steady state characteristics of the LHP were studied under three typical evaporator tilts. According to the experimental results, the main conclusions below can be drawn. (1) The temperature is the highest under adverse tilt and the lowest under favorable tilt no matter whether there is NCG in LHP. (2) The existence of NCG could cause the increase of temperature under all three typical evaporator tilts, but the temperature increment caused by NCG seems to be relatively small under adverse tilt. (3) The increments of the temperature caused by NCG display different patterns under different tilts. Theoretical analysis was conducted to explain the results: the temperature under the coupling effect of NCG and evaporator tilt was determined by the energy balance between the heat leak from evaporator to compensation chamber and the cooling capacity of returning subcooled liquid. With the increase of heat load, the augmentation of heat leak caused by NCG and the enhancement of subcooled liquid cooling effect were incongruent. The coupling effect of NCG and evaporator tilts should be considered in the terrestrial application of LHP.

“…Power increment test 3.2.1 Operation under horizontal orientationFigure 10shows the temperature changes of some key points along the loop during the power increment test, where the ambient air was used as the heat sink with a constant temperature of about23 , and the evaporator, CC and condenser were placed in a horizontal plane, i.e., no adverse elevation existed.According toFig. 10, when the input power to the film heater was increased from 30 to 60 W, the steady-state operating temperature of the evaporator wall first dropped from 46.0 to 38.2 while when the input power was increased from 60 to W gradually with an interval of 30 W, the evaporator wall temperature always kept increasing.…”

mentioning

confidence: 99%

Quiet power-free cooling system enabled by loop heat pipe

Bai

Applied Thermal Engineering

et al. 2019

Loop heat pipe (LHP) is a quite promising two-phase heat transfer device, holding significant application potential in the modern electronics cooling. In this work, a LHP-based cooling system has been developed, which features no power consumption and no noise, taking full advantage of LHP's efficient longdistance heat transport capability. The heat source was simulated by a film electric resistance heater, which was connected to the cylindrical evaporator of the LHP through an aluminum saddle. The condenser line was embedded into the bottom surface of a fin radiator with a relatively large volume, where heat dissipation to the ambient was completely in the form of air natural convection. Extensive experiments on this cooling system were conducted, mainly focusing on its startup and system thermal resistance. Experimental results show that this cooling system can successfully realize the startup with a very small heat load. With the film heater temperature not exceeding 80 , this cooling system can dissipate a heat load up to 150 W to the ambient at a temperature about 24 , corresponding to a system thermal resistance about 0.30 /W. In addition, this cooling system exhibited very strong anti-gravity capability. With an adverse elevation of 0.5 m, the cooling system can realize normal operation, and no obvious performance decay was observed except an increased operating temperature at small heat loads.