Purpose
The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of long-chain ...alcohol.
Design/methodology/approach
A long-wave evolution model modified for self-rewetting fluids is used to study the inverse thermocapillary characteristics of an evaporating thin liquid film. The flow attributed to the inverse thermocapillary action is manifested through the streamline plots and the evaporative heat transfer characteristics are quantified and analyzed.
Findings
The thermocapillary flow induced by the negative surface tension gradient drives the liquid from a low-surface-tension (high temperature) region to a high-surface-tension (low temperature) region, retarding the liquid circulation and the evaporation strength. The positive surface tension gradients of self-rewetting fluids induce inverse-thermocapillary flow. The results of different working fluids, namely, water, heptanol and DAS of heptanol, are examined and compared. The thermocapillary characteristic of a working fluid is significantly affected by the sign of the surface tension gradient and the inverse effect is profound at a high excess temperature. The inverse thermocapillary effect significantly enhances evaporation rates.
Originality/value
The current investigation on the inverse thermocapillary effect in a self-rewetting evaporating thin film liquid has not been attempted previously. This study provides insights on the hydrodynamic and thermal characteristics of thermocapillary evaporation of self-rewetting liquid, which give rise to significant thermal enhancement of the microscale phase-change heat transfer devices.
Phase change can dramatically alter the interfacial temperature, resulting in surface tension gradients and consequently causing Marangoni convection. The numerical investigation on Marangoni ...convection of binary fluids in a closed microcavity is accomplished in this paper by using the volume of fluid (VOF) model with source terms added by user defined functions (UDF) due to mass transfer, with detailed velocity and temperature fields. For simple fluid, surface tension decreases with increasing temperature, resulting in thermal Marangoni convection that can drive the liquid leave from hot regions and leading to film dryout. For binary fluids, however, the Marangoni convection could also be caused by concentration gradients, resulting in greatly promoted backflow of the fluid. In particular, for self-rewetting fluids which have unique surface tension characteristics that increase with increasing temperature above a critical value, the Marangoni flow can drive the liquid flow towards hot regions, avoiding film dryout. The influence of non-condensable gas is also considered by providing detailed velocity fields near the contact region and it proves that non-condensable gas can negatively affect the heat and mass transfer.
•For simple fluids, thermocapillary stresses drive the liquid away from hot regions.•For binary fluids, the thermal performance is improved by solutocapillary effect.•For self-rewetting fluids, both the heat and mass transfer are enhanced.•The non-condensable gas could negatively affecting the heat transfer.
This study investigated the use of sintered Nickel powder as the wick material of Loop heat pipe with flat evaporator (Flat loop heat pipe, FLHP) and its effect on the heat transfer performance. Add ...the 1-heptanol into water and form Self-rewetting Fluid (SRF), resulting in the Marangoni effect. The colder liquid can be transport to the heating surface, delaying the occurrence of dry-out and increasing the critical heat load. This paper use Surface tension measurements to measure the change of 1-heptanol SRF, then it was apply to nickel wick FLHP as working fluid to investigate its effect on the heat transfer performance. This study successfully established production process of Nickel wick structure. Results of wick structure for the effective pore radius of 2.6 μm, porosity of 62%, permeability of 5.7 × 10-13m2. Results of Surface tension measurements show that 1-heptanol aqueous solution’s surface tension increases with increasing temperature, Results from applying 0.1% 1-heptanol aqueous solution to FLHP as working fluid. For performance testing show that the critical heat load was 240 W and the total thermal resistance was 0.77 ° C/W. Compared with FLHP with pure water, SRF raised the maximum heat flux of 70%, the total thermal resistance of the system reduces 40%, SRF has the potential to enhance the heat transfer performance of FLHP.
As technology becomes increasingly miniaturized, extremely localized heat dissipation leads to the challenge of how to keep these devices from overheating. A pulsating heat pipe (PHP) is an excellent ...cooling device based on the phase change of a working fluid. Experiments are performed to investigate the thermal performances of a Micro Pulsating Heat Pipe (MPHP) using different working fluids. The MPHP consists of 20 parallel channels made of a copper capillary tube with an internal diameter of 0.8 mm. The MPHP is filled with ethanol, deionized water and an aqueous solution of 1-butanol as working fluids, with different filling ratios (FRs) in the range 40–70 vol.%. The 1-butanol aqueous solution is known as a self-rewetting fluid, i.e. a dilute aqueous solution of alcohols with a number of carbon atoms higher than four (such as 1-butanol and pentanol). The surface tension of self-rewetting fluids decreases gradually with an increase in temperature, reaching a minimum around 60 °C, and subsequently increases gradually at higher temperatures. Therefore, at relatively high temperature self-rewetting fluids flow towards the regions at higher temperature due to the Marangoni effect. This flow should improve the boiling phenomenon, which is very important in the heat transfer mechanism of the MPHP. The experimental results indicate that, in the case of self-rewetting fluid, the stable oscillating motion in the MPHP arises at the heat load regime lower than that with water. In addition, the effective thermal conductivity of the MPHP with the highest concentration of self-rewetting fluid is higher than that with other fluids in the high heat load regime.
Recently, electronics thermal management faces problems in the wake of component miniaturization, which has led to higher demands on heat flux dissipation. Pulsating heat pipe (PHP) can be used for ...cooling devices of electronics because of its potential for removing high heat flux. It is well known that various parameters affect the performance of the pulsating heat pipe. Therefore, many researchers have done research on the improvement of performance. This paper presents heat transfer characteristics of the open-loop pulsating heat pipe (OLPHP) using a self-rewetting fluid as working fluids. The heat transfer characteristic results were obtained by PHP that was made of copper tubes of internal diameters 1.8 mm. On the other hand, flow visualization tests were conducted by the use of a PHP that was made of Pyrex-glass tubes with the dimension of the copper tubes PHP. The experimental results indicate that OLPHP using self-rewetting fluid as working fluids can be observed anomalous liquid film behavior in adiabatic section. Especially, it was found that the liquid film was strong wavy when liquid slug moved to cooling section from heating section. The findings showed that the wavy liquid films and liquid slug behavior contributed to the thermal performance improvement.
This paper discuses the use of self rewetting fluids in the heat pipe. In
conventional heat pipes, the working fluid used has a negative
surface-tension gradient with temperature. It is an ...unfavourable one and it
decreases the heat transport between the evaporator section and the condenser
section. Self rewetting fluids are dilute aqueous alcoholic solutions which
have the number of carbon atoms more than four. Unlike other common liquids,
self-rewetting fluids have the property that the surface tension increases
with temperature up to a certain limit. The experiments are conducted to
improve the heat-transport capability and thermal efficiency of capillary
assisted heat pipes with the self rewetting fluids like aqueous solutions of
n-Butanol and n-Pentanol and its performance is compared with that of pure
water. The n-Butanol and n-Pentanol are added to the pure water at a
concentration of 0.001moles/lit to prepare the self rewetting fluids. The
heat pipes are made up of copper container with a two-layered stainless steel
wick consisting of mesh wrapped screen. The experimental results show that
the maximum heat transport of the heat pipe is enhanced and the thermal
resistances are considerably decreased than the traditional heat pipes filled
with water. The fluids used exhibit an anomalous increase in the surface
tension with increasing temperature.
nema
New experimental results have been obtained on the enhancement of heat transport by a pulsating heat pipe (PHP) using a self-rewetting fluid. Self-rewetting fluids have a property that the surface ...tension increases with temperature unlike other common liquids. In the present experiments, 1-butanol and 1-pentanol were added to water at a concentration of less than 1 wt% to make the self-rewetting fluid. A pulsating heat pipe made from an extruded multi-port tube was partially filled with the self-rewetting fluid mixture and tested for its heat transport capability at different input power levels. The experiments showed that the maximum heat transport capability was enhanced by a factor of four when the maximum heater temperature was limited to 110 °C. Thus, the use of a self-rewetting fluid in a PHP has been shown to be highly effective in improving the heat transport capability of pulsating heat pipes.
Heat dissipation, recovery and accumulation is more and more becoming the limiting factor in the advancement of many energy systems. The conventional heat pipes such as copper grooved heat pipes and ...sintered particle heat pipes have played an important role in the heat dissipation in electronic equipment. Pulsating heat pipe (PHP) is a new type of efficient heat transfer device, which was introduced in the mid-1990s by Akachi. PHP can be used for cooling of electronics because of its potential for removing high heat flux. The capillary effect is indeed provided by the small dimension of the channel, and not by the presence of a wick structure. An experimental study was conducted to investigate heat transfer performance of a closed loop pulsating heat pipe with pure water and aqueous solution of butanol (self-rewetting fluid) under various filing ratios, inclination angles and heat inputs. Self-rewetting fluids have a property that the surface tension increase with increase in temperature. Butanol is added to pure water at 0.1 wt% and 0.5 wt% concentrations to make self-rewetting fluid. The PHP is made of copper tube with inner and outer diameters of 2.0 mm and 3.0 mm, respectively. It is observed that lower thermal resistance is obtained by using aqueous solution of butanol compared with pure water. Also aqueous solution of butanol shows improved performance up to horizontal orientation, when compared with pure water.
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