scholarly journals Experimental study on heat transfer characteristics of a modified two-phase closed thermosyphon

2017 ◽  
Vol 21 (6 Part A) ◽  
pp. 2481-2489 ◽  
Author(s):  
Babak Aghel ◽  
Masoud Rahimi ◽  
Saeed Almasi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Experimental Study ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Adiabatic Section

This study investigated the heat transfer characteristics of modified two-phase closed thermosyphon (TPCT) using water as the working fluid. In the modified TPCT, to reduce thermal resistance, a small TPCT was inserted inside the adiabatic section. For both the plain and modified thermosyphons the performances were determined at various heat inputs from 71-960 W. The results showed that the modified TPCT had less temperature difference between the evaporator and condenser sections than the plain one. According to the experimental data, in the modified TPCT, the thermal performance increased up to 20% over that of the unmodified one.

scholarly journals Heat transfer characteristics of miniature two-phase thermosyphons with nanofluids

2020 ◽  
pp. 42-46
Author(s):  
V. Yu. Kravets ◽  
D. I. Hurov
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Carbon Nanotubes ◽  
Synthetic Diamond ◽  
Filling Ratio ◽  
Internal Diameter ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Heat Carriers

This paper presents and analyzes experimental data on the total thermal resistances of two-phase miniature thermosyphons with nanofluids; the geometric parameters of the thermosyphons for all experimental samples are identical: total length 700 mm, internal diameter 5 mm. The following nanofluids used as heat carriers are: aqueous nanofluid based on carbon nanotubes, aqueous nanofluid based on synthetic diamond, and aqueous nanofluid based on amorphous carbon. Much attention is also paid to the influence of the filling ratio on the heat transfer characteristics of the thermosyphons. The influence of filling ratio and types of nanofluid on the performance of miniature closed two-phase thermosyphons is demonstrated.

Effect of Wavy Wall and Plate Bifurcations On Heat Transfer Enhancement in Microchannel

2021 ◽  
Author(s):  
Sathish Kumar D ◽  
Jayavel S
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Working Fluid ◽  
Thin Wall ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Entropy Generation Number ◽  
Transfer Characteristics ◽  
Overall Performance ◽  
Study Heat Transfer

Abstract Miniaturization of electronic components requires compact and effective cooling techniques to dissipate large heat flux without significant increase in pumping power. Microchannel heat sink with liquid as working fluid is a suitable technique for the purpose. In the present study, heat transfer characteristics in presence of vertical bifurcation placed in the downstream of the microchannel passage is studied numerically. Six types of bifurcating plates are considered under two categories: (i) thick-plate and (ii) wavy thin-wall. Water is taken as the working fluid and the flow rate has been varied in the Reynolds number range, 100 = Re = 1000.The effect of bifurcations on pressure drop, heat transfer and the overall thermal resistance are analyzed and compared with those of plane microchannel without bifurcation. The numerical results show that the usage of bifurcation in the microchannel reduces the overall thermal resistance. Field synergy number, entropy generation number and hydro-thermal performance index are calculated to quantify the overall performance improvement in the microchannel with bifurcations. Constant wavy thin-wall bifurcation has been found to improve the overall performance of the microchannel. The detailed geometry of the bifurcation, the resulting convective heat transfer characteristics and percentage improvement in the performance are reported.

Effect of Wick Characteristics on the Thermal Performance of the Miniature Loop Heat Pipe

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Randeep Singh ◽  
Aliakbar Akbarzadeh ◽  
Masataka Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Working Fluid ◽  
Vapor Flow ◽  
Loop Heat Pipe ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Two phase heat transfer devices based on the miniature version of loop heat pipe (LHP) can provide very promising cooling solutions for the compact electronic devices due to their high heat flux management capability and long distance heat transfer with minimal temperature losses. This paper discusses the effect of the wick properties on the heat transfer characteristics of the miniature LHP. The miniature model of the LHP with disk-shaped evaporator, 10 mm thick and 30 mm disk diameter, was designed using copper containment vessel and water as the working fluid, which is the most acceptable combination in electronic cooling applications. In the investigation, wick structures with different physical properties including thermal conductivity, pore radius, porosity, and permeability and with different structural topology including monoporous or biporous evaporating face were used. It was experimentally observed that copper wicks are able to provide superior thermal performance than nickel wicks, particularly for low to moderate heat loads due to their low heat conducting resistance. With monoporous copper wick, maximum evaporator heat transfer coefficient (hev) of 26,270 W/m2 K and evaporator thermal resistance (Rev) of 0.06–0.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700 W/m2 K for hev and 0.08–0.21°C/W for Rev. Capillary structure with smaller pore size, high porosity, and high permeability showed better heat transfer characteristics due to sufficient capillary pumping capability, low heat leaks from evaporator to compensation chamber and larger surface area to volume ratio for heat exchange. In addition to this, biporous copper wick structure showed much higher heat transfer coefficient of 83,787 W/m2 K than monoporous copper wick due to improved evaporative heat transfer at wick wall interface and separated liquid and vapor flow pores. The present work was able to classify the importance of the wick properties in the improvement of the thermal characteristics for miniature loop heat pipes.

Thermal Characteristics of a Circular Finned Thermosyphon Using Different Working Fluids

2014 ◽  
Vol 575 ◽  
pp. 322-328 ◽  
Author(s):  
Narayanan Alagappan ◽  
Narayanan Karunakaran
Keyword(s):  
Experimental Study ◽  
Ethylene Glycol ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Input ◽  
Base Fluid ◽  
Thermal Characteristics ◽  
Working Fluid ◽  
Two Phase ◽  
Evaporation And Condensation

The two-phase closed thermosyphon (TPCT), which is essentially a gravity-assisted wickless heat pipe, utilizes the evaporation and condensation of the working fluid inside the TPCT to transport heat. This experimental study was carried out to understand the thermal performance of circular finned thermosyphon using nanofluid with alcohol and was analyzed, compared with alcohol and base fluid DI water. The concentration of nanoparticle used in this setup was 110mg/lit of TiO2combined with 0.2 ml of ethylene glycol. The heat input (Q) were 10W, 12W, 14 W and 16 W and the orientation 30°, 45°, 60° and 90°.The results demonstrate that TiO2nanofluid with 0.2 ml of ethylene glycol improves the performance through reduction in thermal resistance by 85.86%.

scholarly journals Experimental Study on the Starting-Up and Heat Transfer Characteristics of Pulsating Heat Pipe Under Local Low-Frequency Vibrations

2021 ◽  
Author(s):  
Jing Chen ◽  
Junbiao Dong ◽  
Ye Yao
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Low Frequency ◽  
Heating Power ◽  
Pulsating Heat Pipe ◽  
Heat Transfer Characteristics ◽  
Condensation Section ◽  
Adiabatic Section

This study mainly experimentally investigates and explores the effects of local low-frequency vibrations on the starting-up and heat transfer characteristics of the pulsating heat pipe. A micro motors with the vibration frequency of 200 Hz were imposed on the external surface of evaporation, condensation and adiabatic section of the pulsating heat pipe, respectively, and the starting-up temperature and the average temperatures along the evaporation section as well as the thermal performances of the vibrating heat pipe were experimentally scrutinized under the local vibrations of different positions. The following important conclusions can be achieved by the experimental study: 1) The effect of vibrations at the evaporation section and at the adiabatic section on the starting-up time of pulsating heat pipe is more significant than that at the condensation section. 2) The vibrations at different positions can reduce the starting-up temperature of the pulsating heat pipe. The effect of the vibrations at the evaporation section is the best as the heating power is lower, and the effect of the vibration at the adiabatic section is the best as the heating power is higher. 3) The vibrations at the evaporation section and at the adiabatic section can reduce the thermal resistance of the pulsating heat pipe. However, the vibrations at the condensation section have little effect on the thermal resistance of the pulsating heat pipe. 4) The vibrations at the evaporation section and at the adiabatic section can effectively reduce the temperature of evaporation section of the pulsating heat pipe, but the vibrations at the condensation section have no effect on the temperature of evaporation section of the pulsating heat pipe.

A Critical Review on the Numerical Methods of Two-Phase Flows

2012 ◽  
Author(s):  
Muhammet Balcilar ◽  
Ahmet Selim Dalkiliç ◽  
Ali Çelen ◽  
Nurullah Kayaci ◽  
Somchai Wongwises
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Experimental Data ◽  
Numerical Methods ◽  
Critical Review ◽  
Optimization Techniques ◽  
Numerical Analyses ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics

The two-phase flow processes play a significant role in the heat transfer processes in the chemical and power industry, including in nuclear power plants. This study is a critical review on the determination of the heat transfer characteristics of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the numerical analyses, are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation and evaporation processes in the smooth and enhanced tubes. The theoretical solutions are related to the design of passive containment cooling systems (PCCS) in simplified water boiling reactors (SWBR). A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Fluent CFD program are used in the numerical solution. It is shown that the heat transfer characteristics of laminar and turbulent condensing and evaporating film flows such as heat transfer coefficient and pressure drop can be predicted by means of numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods. Dependency of the output of the ANNs from various numbers of input values is also shown for condensing and evaporating flows.

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