scholarly journals Heat transfer coefficient, pressure gradient, and flow patterns of R1233zd(E) and R1336mzz(Z) evaporating in a microchannel tube

2022 ◽  
Vol 182 ◽  
pp. 121992
Author(s):  
Houpei Li ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Flow Patterns

Flow Boiling Heat Transfer and Flow Pattern in Rectangular Channel of Mini-Gap

2004 ◽  
Author(s):  
Yang Yang ◽  
Yasunobu Fujita
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Annular Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Gap Size ◽  
Vapor Quality ◽  
Micro Channels ◽  
Mini Channels

Flow boiling in micro- and mini-channels has attracted much attention in recent years. But the phenomena is such confined channels have not been fully understood and explained. Some conclusions reached by different authors are even contradictory. The present research is trying to study some aspects of flow boiling in mini- and micro-channels. In the present paper boiling heat transfer and two-phase flow patterns in rectangular narrow channels were studied. The gap size of the channel was varied as 2, 1, 0.5 and 0.2 mm with the channel width and length being kept at 20 mm and 100 mm, respectively. In the present mini- and micro-channels, four flow patterns were identified; bubbly, intermittent, wavy and annular flow. They can be also divided into several sub-flow patterns. Flow patterns showed strong channel gap size dependence. Smaller gap size deleted bubbly flow, thus induced simpler flow patterns to shift the annular flow at lower vapor quality. The channels can be divided into two groups depending on the gap size; the larger gap group of 2 and 1 mm, and the smaller gap group of 0.5 and 0.2 mm. The larger gap group showed similar heat transfer behavior as conventional size of tubes. The smaller gap group indicated some peculiar phenomena. Heat transfer coefficient in the smaller gap group was relatively high in the low quality region. Then heat transfer coefficient decreased monotonously with increasing vapor quality. This behavior was considered attributable to the micro-bubble generation in the channel corners and an early partial dryout of thin liquid film. Thus the relationship between heat transfer coefficient and flow pattern should be carefully pursued in micro- and mini-channels to develop heat transfer correlations based on flow patterns.

scholarly journals HEAT TRANSFER IN GRADIENT TURBULENT BOUNDARY LAYER

2019 ◽  
Vol 41 (4) ◽  
pp. 19-26
Author(s):  
A.A. Avramenko ◽  
M.M. Kovetskaya ◽  
E.A. Kondratieva ◽  
T.V. Sorokina
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Boundary Layer Separation ◽  
Variable Pressure ◽  
Flow Acceleration ◽  
Longitudinal Pressure Gradient

Effect of pressure gradient on heat transfer in turbulent boundary layer is constantly investigated during creation and improvement of heat exchange equipment for energy, aerospace, chemical and biological systems. The paper deals with problem of steady flow and heat  transfer in turbulent boundary layer with variable pressure in longitudinal direction. The mathematical model is presented and the analytical solution of heat transfer in the turbulent boundary layer problem at positive and negative pressure gradients is given. Dependences for temperature profiles and coefficient of heat transfer on flow parameters were obtained.  At negative longitudinal pressure gradient (flow acceleration) heat transfer coefficient can both increase and decrease. At beginning of acceleration zone, when laminarization effects are negligible, heat transfer coefficient increases. Then, as the flow laminarization increases, heat transfer coefficient decreases. This is caused by flow of turbulent energy transfers to accelerating flow. In case of positive longitudinal pressure gradient, temperature profile gradient near wall decreases. It is because of decreasing velocity gradient before zone of possible boundary layer separation.

Flow Boiling in Minichannels Under Normal, Hyper and Microgravity: Frictional Pressure Loss and Flow Patterns

2007 ◽  
Author(s):  
D. Brutin ◽  
S. Luciani ◽  
O. Rahli ◽  
Ch. LeNiliot ◽  
L. Tadrist
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pressure Loss ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Flow Patterns ◽  
Local Heat Transfer Coefficient ◽  
Parabolic Flights

We present in this paper, flow boiling results obtained during parabolic flights campaigns. The experimental aim is to obtain the local heat transfer coefficient and the influence of gravity on HFE-7100 flow boiling in minichannels. The hydraulic diameter investigated is: 0.84 mm. The influence of hypergravity and microgravity solely on the frictional pressure loss is evidenced in this paper, and explained using the flow patterns.

Vertical Falling Film Evaporation of Pure Refrigerant HCFC123 in a Plate-Fin Heat Exchanger

2013 ◽  
Author(s):  
Junichi Ohara ◽  
Shigeru Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Patterns ◽  
Falling Film ◽  
Fin Efficiency ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

The characteristics of heat transfer and flow patterns are investigated experimentally for the vertical falling film evaporation of pure refrigerant HCFC123 in a rectangular minichannels consisting of offset strip fins. The refrigerant liquid is uniformly supplied to the channel through a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. To observe the flow patterns during the evaporation process directly, a transparent vinyl chloride resin plate is placed as the front wall. The experimental parameters are as follows: the mass velocity G = 28∼70 kg/(m2s), the heat flux q = 20∼50 kW/m2 and the pressure P ≈ 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3 while there is little influence of G and q in the region x ≤ 0.3. From the direct observation using a high speed video camera and a digital still camera, flow patterns are classified into five types. Then the empirical correlation equations for evaporation heat transfer coefficient on a vertical falling film plate fin evaporator with minichannels are proposed. From the physical model to evaluate the heat transfer coefficient of the minichannel surface with fins, the characteristics of fin efficiency is clarified that the average value of fin efficiency is about 0.6 and the distributive characteristics of fin efficiency is roughly inverse of heat transfer coefficient characteristics.

Effects of the Condition of the Approach Boundary Layer and of Mainstream Pressure Gradients on the Heat Transfer Coefficient on Film-Cooled Surfaces

1985 ◽  
Vol 107 (1) ◽  
pp. 99-104 ◽  
Author(s):  
N. Hay ◽  
D. Lampard ◽  
C. L. Saluja
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Adverse Pressure Gradient ◽  
Pressure Gradients ◽  
Favorable Pressure Gradient ◽  
The Heat Transfer Coefficient

This paper describes an investigation of the sensitivity of the heat transfer coefficient under the film to the state of the approach boundary layer for injection through a row of holes on a flat plate. The investigation is done for a range of blowing parameters using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. Additionally, for the same injection geometries, the effect of injection in the presence of mild adverse, mild favorable, and strong favorable mainstream pressure gradients is investigated. The results indicate that the heat transfer coefficient under the film is sensitive neither to the condition of the approach boundary layer nor to the presence of a mild adverse pressure gradient, but it is significantly lowered by a favorable pressure gradient, particularly at low blowing parameters.

Upflow Boiling and Condensation in Rectangular Minichannels

2003 ◽  
Author(s):  
V. V. Kuznetsov ◽  
S. V. Dimov ◽  
P. A. Houghton ◽  
A. S. Shamirzaev ◽  
S. Sunder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

When boiling or condensation occurs inside very small and non-circular channels, capillary forces influence two-phase flow patterns, which in turn determine heat transfer coefficients and pressure drop. A better understanding of the underlying phenomena would be beneficial from the perspective of optimizing the design of compact evaporators and condensers. The thrust of this study was to understand the nature of up-flow boiling and condensation heat transfer in channels with a small gap. It consisted of two parts. The first part included observation of two-phase flow patterns with refrigerant R21 in a test section containing plain fins. The shape of the channels formed between fins was close to rectangular. The test section was placed in a closed refrigerant loop, and it was fabricated with a transparent wall to allow observation of the flow. An electrically heated coil was used to introduce liquid and vapor at the needed quality into the test section. Regimes of slug, froth, annular and cell flow patterns were recognized and the areas of flow pattern were determined. The second part included up-flow boiling and condensation heat transfer measurement with refrigerant R21 in a set of vertical mini-channels consisting of plain fins. An aluminum fin pad was bonded to two dividing aluminum sheets by dip brazing. Heat was supplied to the test section from a thermoelectric module, which utilized the Peltier effect. A thick copper plate was placed between the dividing sheet on each side of the fin passage and the respective Peltier module to establish a uniform wall temperature. Heat transfer coefficient measurements were done under forced flow conditions. Data are obtained for mass flow rates of 30 and 50 kg/m2s under both boiling and condensation modes with wall superheats ranging from 1 to 5K. The dependence of heat transfer coefficient from wall superheat was not observed both for boiling and condensing modes. It shows the primary role of evaporation from thin films in a confined space when the mass flux is small. At low vapor quality the boiling heat transfer coefficients are considerably higher than that for condensation. A high heat flux in ultra thin liquid film area near the channel corner or in the vicinity of liquid-vapor-solid contact line (after the film rupture) supports the high total heat transfer coefficient in evaporation mode. In contrast with evaporation mode, at upflow condensation mode the heat transfer coefficient is strongly dependent on vapor quality. At plug flow regime the vapor velocity determines the condensing heat transfer.

Experimental and Numerical Investigations of Shock-Film Cooling Interaction on a Turbine Blade With Fan-Shaped Cooling Holes

2015 ◽  
Vol 7 (4) ◽  
Author(s):  
S. Xue ◽  
A. Arisi ◽  
W. Ng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Secondary Flows ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Near Surface ◽  
Film Cooling Effectiveness

This paper presents the findings of an experimental and numerical investigation on the shock effect on heat transfer coefficient and film-cooling effectiveness. In this study, coolant was injected on the blade surface through a fan-shaped hole in a transonic cascade. The experimental results indicate that on the film-cooled suction surface of the blade, the shock from the adjacent blade impinging on the suction surface causes the film-cooling effectiveness to drop quickly by 18%, and then stay at a low level downstream of the shock. The shock also causes the local heat transfer coefficient to decrease rapidly by 25%, but then rise back up immediately after the shock. The results from the numerical study supported the film-cooling effectiveness and heat transfer coefficient trends that were observed in the experiment. A detailed analysis of the numerical results reveals that the rapid change of the film-cooling effectiveness is due to the near surface secondary flows, which push the hot mainstream air toward the injection centerline and lifts the low temperature core away from the surface. This secondary flow is a result of a spanwise pressure gradient. The drop in heat transfer coefficient is caused by a boundary layer separation bubble which results from an adverse streamwise pressure gradient at the shock position.

Heat Transfer Coefficient, Pressure Gradient, and Flow Patterns of R1234yf Evaporating in Microchannel Tube

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Houpei Li ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Saturation Temperature ◽  
Heat Mass Transf ◽  
The Heat Transfer Coefficient

Abstract This paper presents the heat transfer coefficient, pressure gradient, and flow pattern of R1234yf in a microchannel tube. Both heat transfer coefficient and pressure gradient are presented against real saturation pressure, while flow pattern captures at the exit of data points are presented in the same plot. The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg m−2s−1, heat flux from 0 to 6 kW m−2, vapor quality from 0 to 1, and inlet saturation temperature from 10 to 30 °C. Comparing the correlations to the HTC measurements at very low quality (about 0.1), Gorenflo, D., and Kenning, D. (2010, Pool Boiling, in: VDI Heat Atlas, 2nd ed, Springer, pp. 757–788) agree with the results. As vapor quality increases, pressure gradient increases. The adiabatic pressure gradient is a strong function of mass flux and saturation pressure (temperature). Flow patterns of R1234yf are also affected by mass flux and saturation pressure. The heat transfer coefficient is a strong function of mass flux and heat flux. The saturation temperature has a smaller effect on HTC in the condition range (10 – 30 °C). Under the test range, the accelerating pressure drop is insignificant compared to friction. Comparing to the results, Mishima, K., and Hibiki, T. (1996, “Some Characteristics of Air-Water Two-Phase Flow in Small Diameter Vertical Tubes,” Int. J. Multiph. Flow, 22(4), pp. 703–712) and Muller-Steinhagen, H., and Heck, K. (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Accessed March 1, 2018)., 20, pp. 297–308.) have small mean absolute error (MAE) to predict local pressure gradient. For the heat transfer coefficient, Sun, L., and Mishima, K. (2009, “An Evaluation of Prediction Methods for Saturated Flow Boiling Heat Transfer in Mini-Channels,” Int. J. Heat Mass Transf, 52(23–24), pp. 5323–5329) and Gungor, K. E., and Winterton, R. H. S. (1986, “A General Correlation for Flow Boiling in Tubes and Annuli,” Int. J. Heat Mass Transf, 29(3), pp. 351–358) have an MAE less than 30%.

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