scholarly journals Single-phase and two-phase heat transfer in microchannels

2012 ◽  
Author(s):  
Bin Xu
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase ◽  
Two Phase Heat Transfer

Two-Phase Heat Transfer Performance of Dielectric Fluid HFE-7100 Within Multiport Microchannel

2008 ◽  
Author(s):  
Lung-Yi Lin ◽  
Yeau-Ren Jeng ◽  
Chi-Chuan Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Convective Heat Transfer Coefficient ◽  
Dielectric Fluid ◽  
Transfer Performance ◽  
Two Phase ◽  
Two Phase Heat Transfer

This study presents convective single-phase and boiling two-phase heat transfer performance of HFE-7100 coolant within multi-port microchannel heat sinks. The corresponding hydraulic diameters are 450 and 237 μm, respectively. For single-phase results, the presence of inlet/outlet locations inevitably gives rise to considerable increase of total pressure drop of a multi-port microchannel heat sink whereas has virtually no detectable influence on overall heat transfer performance provided that the effect of entrance has been accounted for. The convective boiling heat transfer coefficient for the HFE-7100 coolant shows a tremendous drop when vapor quality is above 0.6. For Dh = 450 μm, it is found that the mass flux effect on the convective heat transfer coefficient is rather small.

Experimental Investigation and Empirical Analysis of Non-Boiling Gas-Liquid Two Phase Heat Transfer in Vertical Downward Pipe Orientation

2012 ◽  
Author(s):  
Swanand M. Bhagwat ◽  
Mehmet Mollamahmutoglu ◽  
Afshin J. Ghajar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Annular Flow ◽  
Single Phase ◽  
Phase Flow ◽  
Upward Flow ◽  
Two Phase ◽  
Reynolds Analogy ◽  
Two Phase Heat Transfer

The non-boiling gas-liquid two phase flow is pertinent to industrial applications like the reduction of paraffin wax depositions in petroleum transport lines, air lift systems and the chemical processes such as ethanol-water fractionation seeking enhanced heat and mass transfer. The non-boiling two phase heat transfer mechanism in horizontal and vertical orientations has been investigated by many researchers. However, till date very little experimental work and investigation has been performed for vertical downward flow. In order to contribute more to this research and have a better understanding of the non-boiling two phase heat transfer phenomenon for this pipe orientation, experimental investigation is undertaken for a vertical downward oriented 0.01252 m I.D. schedule 10 S stainless steel pipe using air-water as fluid combination. The influence of different flow patterns on the two phase convective heat transfer coefficient is studied using experimental measurements of 165 data points for bubbly, slug, froth, falling film and annular flow patterns spanned over the entire range of the void fraction. In general the two phase heat transfer coefficients are found to be consistently higher than that of the single phase flow. This tendency is observed to increase with increase in the gas flow rate as the flow regime migrates from bubbly to the annular flow. The concept of Reynolds analogy as implemented by Tang and Ghajar [1] for horizontal and vertical upward flow is analyzed against the vertical downward flow data collected in the present study. Due to lack of correlations available for predicting the two phase heat transfer coefficient in vertical downward orientation it was decided to perform the quantitative analysis of the seventeen two phase heat transfer correlations available for vertical upward flow. This analysis is concluded by the recommendation of the top performing correlations in the literature for each flow pattern. Based on the pressure drop data and using Reynolds analogy, a simple equation is proposed to correlate the two phase heat transfer coefficient with the single phase heat transfer coefficient.

scholarly journals ОПРЕДЕЛЕНИЕ КОЭФФИЦИЕНТА КОНВЕКТИВНОГО ТЕПЛОПЕРЕНОСА В ГИДРОАККУМУЛЯТОРЕ С ТЕПЛОВЫМ РЕГУЛИРОВАНИЕМ ДЛЯ УСЛОВИЙ НЕВЕСОМОСТИ

2019 ◽  
pp. 10-15
Author(s):  
Полина Сергеевна Коваль ◽  
Эдем Русланович Решитов ◽  
Рустем Юсуфович Турна
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Convective Heat ◽  
Single Phase ◽  
Convective Heat Transfer Coefficient ◽  
Zero Gravity ◽  
Two Phase ◽  
Transfer Processes ◽  
Equilibrium Process ◽  
Two Phase Heat Transfer

In the modern world with the increasing power of spacecraft heat dissipation, the need has arisen to use efficient heat removal systems with two-phase heat transfer contours. Their advantages are determined by the fact that they can carry a much larger amount of heat per unit of consumption than when using a single-phase coolant. The energy consumption of the pump for pumping the coolant is insignificant, and the use of heat exchange during boiling allows you to maintain the temperature of objects almost the entire length of the circuit close to the saturation temperature. All heat transfer processes occurring with a change in the state of aggregation of a substance (boiling, condensation) occur much more intensively than during convective heat exchange in a single-phase liquid. A feature of this system is the change in mass of the coolant in the circuit when changing the operating modes of the two-phase heat transfer system. To regulate the amount of coolant in the circuit, as well as to maintain a predetermined pressure (boiling point), a hydraulic accumulator with thermal regulation (HCA) is used. The actual processes of heat and mass transfer in HCA are non-equilibrium, which complicates the calculation of the thermal control system. This paper describes the concept of a nonequilibrium mathematical model for calculating heat and mass transfer processes in HCA. It is shown that the nonequilibrium of processes can be taken into account by the convective heat transfer coefficient “k” in the mathematical model of HCA: k = 1 corresponds to the absence of convection; k > 100 corresponds to an equilibrium process. Based on the analysis of the flight space experiment for heating HCA, a prediction was made of the value of the convective heat transfer coefficient k under zero-gravity conditions. To assess the influence of the “k” value on the process of regulating the two-phase heat transfer contour under weightless conditions, it is recommended to use the values k = 30 ± 15. In ground-based experiments at high-intensity convection in HCA, processes are much more equilibrium than in zero gravity. It is concluded that the equilibrium process (high values of k) can be considered as more conservative concerning the regulatory process in weightlessness.

scholarly journals АНАЛІЗ ВПЛИВУ ОБСЯГУ ГІДРОАКУМУЛЯТОРУ НА ПРАЦЕЗДАТНІСТЬ ДВОФАЗНОГО КОНТУРУ ТЕПЛОПЕРЕНОСУ СИСТЕМИ ТЕРМОРЕГУЛЮВАННЯ КОСМІЧНОГО АПАРАТУ

2018 ◽  
pp. 24-29
Author(s):  
Павел Григорьевич Гакал ◽  
Геннадий Александрович Горбенко ◽  
Эдем Русланович Решитов ◽  
Рустем Юсуфович Турна
Keyword(s):  
Heat Transfer ◽  
Control System ◽  
Energy Consumption ◽  
Control Systems ◽  
Single Phase ◽  
Thermal Control ◽  
Space Vehicles ◽  
Two Phase ◽  
Thermal Control System ◽  
Two Phase Heat Transfer

The world trend in the development of space vehicles is the expansion of their functionality, which leads to an increase in the power consumption, most of which is allocated in the elements of spacecraft equipment in the form of heat. To remove heat from the equipment elements, transfer it to the heat sink subsystem with subsequent removal to outer space, and also to maintain the required temperature mode of the equipment operation, thermal control systems are used. The increase in the power-to-weight ratio and linear dimensions of new spacecraft in conditions of severe design and weight-and-size limitations leads to a complication and growth of the mass of the system of thermal control of space vehicles. At present, thermal control systems for space vehicles based on single-phase fluid heat transfer loops are used. For space vehicles with an energy consumption of more than 10 kW, thermal control systems based on two-phase heat transfer loops are the most promising. They have a number of advantages in comparison with single-phase thermal control systems: two-phase heat transfer loops can transfer much more heat per unit of flow; the use of heat transfer during boiling allows to maintain the temperature of objects practically on the whole extent of the circuit close to the saturation temperature; the mass of the thermal control system with a two-phase coolant is substantially less than with a single-phase coolant , and the energy consumption of the pump for pumping the coolant is negligible. In this paper, a two-phase heat transfer loop performances are analyzed. The process of increasing the thermal power up to the maximum under conditions of full filling of the accumulator is considered. The study was carried out on an experimental two-phase heat transfer loop with an ammonia. Transient processes associated with an increase in the thermal load from 73 % to 100 % are considered. The obtained data correlate well with the results of the calculation. Based on the results of the analysis, conclusions were made on the operability and stability of the spacecraft thermal control system under these conditions, and recommendations on the choice of the volume of the accumulator are given.

Experimental Investigation of Two-Phase Heat Transfer in a Simulated Cooling Duct of a Piston Engine Cylinder Head

2020 ◽  
pp. 4-15
Author(s):  
O.V. Abyzov ◽  
Yu.V. Galyshev ◽  
A.K. Ivanov
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Experimental Investigation ◽  
Cylinder Head ◽  
Single Phase ◽  
Nucleate Boiling ◽  
Piston Engine ◽  
Two Phase ◽  
Engine Cylinder ◽  
Two Phase Heat Transfer

Liquid cooling of cylinder and piston parts in highly boosted internal combustion engines is generally accompanied by local phase transition phenomena, such as surface nucleate boiling. The heat transfer coefficient of nucleate boiling is several times higher than that of single-phase convection. In order to efficiently exploit the thermal effect of nucleate boiling in cooling systems, simultaneously preventing emergency supercritical modes, a deeper understanding of boiling physics based on full-scale experiments is required. We conducted experimental investigation of heat transfer in a simulated cooling duct of a piston engine cylinder head, using a bespoke motor-free installation. We studied the effects of velocity, flow character and coolant type on the heat transfer, accounting for the presence of congestion regions. Over the course of the experiment, we simulated thermal conditions characteristic of different heat transfer types: single-phase convection, nucleate boiling, the onset of boiling crisis. We used the experimental data to plot the coolant heat flow density as a function of wall temperature for different measuring points situated inside the stream and the turbulent flow regions (congestion regions). We show that the mature nucleate boiling mode is the most favourable in terms of how uniform the temperature field within a part is. The experimental data obtained during the investigation may be used to verify mathematical simulations in the two-phase heat transfer theory, provided the data have been appropriately processed

Heat Transfer of Two-Phase Impinging Jet: Heat Transfer Enhancement

2004 ◽  
Author(s):  
Masahiro Osakabe ◽  
Sachiyo Horiki
Keyword(s):  
Heat Transfer ◽  
Pressure Fluctuation ◽  
Single Phase ◽  
Degradation Mechanism ◽  
Copper Surface ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Enhancement Of Heat Transfer ◽  
Inner Diameter ◽  
Two Phase Heat Transfer

To study the enhancement and degradation mechanism of impinging two-phase heat transfer, air/water two-phase jet was applied on the cooling of copper surface of 30 mm in diameter. The two-phase jet impinged vertically on the horizontal heat transfer surface from capillary nozzle holes of 2, 4 and 6 mm in inner diameter. The non-dimensional heat transfer coefficient (HTC) was defined as the experimental HTC divided with the predictive HTC where the superficial two-phase velocity jG+jL and the physical properties of water were used in the empirical HTC correlation for single-phase flow. The larger non-dimensional HTC and stagnation pressure fluctuation were obtained with the nozzle of larger diameter. The larger nozzle could provide the more significant enhancement of heat transfer and pressure fluctuation with an addition of air. It was considered that the enhancement of heat transfer was due to the stimulation of thermal boundary layer with an addition of air.

Single and Two-Phase Heat Transfer in a Low-Density, 3-Dimensional Microchannel

2005 ◽  
Author(s):  
Mark W. Snyder ◽  
James E. Bryan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Single Phase ◽  
Working Fluid ◽  
Low Density ◽  
Total Resistance ◽  
Two Phase ◽  
Copper Strip ◽  
3 Dimensional ◽  
Two Phase Heat Transfer

A test section was developed to study 3-D microchannel surfaces made from copper strip. Selected results were presented for single and two-phase heat transfer through a low-density, 3-D micro channel using ethanol as the working fluid. Details of the single phase and two-phase heat transfer and fluid flow can be resolved from the experimental data. For 4 selected cases the total resistance was measured to be lower as the flow transitioned to two-phase flow for a given pressure drop. However, as the rate of two-phase heat transfer increased so did the pressure drop fluctuations.

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