scholarly journals Combined Visualization and Heat Transfer Measurements for Steam Flow Condensation in Hydrophilic and Hydrophobic Mini-Gaps

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Xi Chen ◽  
Melanie M. Derby
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Mass Flux ◽  
Absolute Error ◽  
Open Loop ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Flow Condensation

Condensation enhancement was investigated for flow condensation in mini-channels. Simultaneous flow visualization and heat transfer experiments were conducted in 0.952-mm diameter mini-gaps. An open loop steam apparatus was constructed for a mass flux range of 50–100 kg/m2s and steam quality range of 0.2–0.8, and validated with single-phase experiments. Filmwise condensation was observed in the hydrophilic mini-gap; pressure drop and heat transfer coefficients were compared to the (Kim and Mudawar, 2013, “Universal Approach to Predicting Heat Transfer Coefficient for Condensing Mini/Micro-Channel Flow,” Int. J. Heat Mass Transfer, 56(1–2), pp. 238–250) correlation and prediction was very good; the mean absolute error (MAE) was 20.2%. Dropwise condensation was observed in the hydrophobic mini-gap, and periodic cycles of droplet nucleation, coalescence, and departure were found at all mass fluxes. Snapshots of six typical sweeping cycles were presented, including integrated flow visualization quantitative and qualitative results combined with heat transfer coefficients. With a fixed average steam quality (x¯ = 0.42), increasing mass flux from 50 to 75 to 100 kg/m2s consequently reduced average sweeping periods from 28 to 23 to 17 ms and reduced droplet departure diameters from 13.7 to 12.9 to 10.3 μm, respectively. For these cases, condensation heat transfer coefficients increased from 154,700 to 176,500 to 194,800 W/m2 K at mass fluxes of 50, 75, and 100 kg/m2 s, respectively. Increased mass fluxes and steam quality reduced sweeping periods and droplet departure diameters, thereby reducing liquid thickness and increasing heat transfer coefficients.

Low Mass Quality Flow Boiling in Microtubes at High Mass Fluxes

2011 ◽  
Vol 3 (4) ◽  
Author(s):  
Mehmed Rafet Özdemir ◽  
Alihan Kaya ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Wall Superheat

In this article, an experimental study on boiling heat transfer and fluid flow in microtubes at high mass fluxes is presented. De-ionized water flow was investigated over a broad range of mass flux (1000 kg/m2s–7500 kg/m2s) in microtubes with inner diameters of  ∼ 250 μm and ∼685 μm. The reason for using two different capillary diameters was to investigate the size effect on flow boiling. De-ionized water was used as working fluid, and the test section was heated by Joule heating. Heat transfer coefficients and qualities were deduced from local temperature measurements. It was found that high heat removal rates could be achieved at high flow rates under subcooled boiling conditions. It was also observed that heat transfer coefficients increased with mass flux, whereas they decreased with local quality and heat flux. Moreover, experimental heat flux data were compared with partial boiling correlations and fully developed boiling correlations. It was observed that at low wall superheat values, there was only a small inconsistency between the experimental data and the conventional partial boiling prediction method of Bergles, while the subcooled and low quality fully developed boiling heat transfer correlation of Kandlikar could fairly predict experimental results at high wall superheat values.

Theoretical Modeling of Vapor Condensation in the Presence of Noncondensable Gas on a Horizontal Tube

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Junhui Lu ◽  
Haishan Cao ◽  
JunMing Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Mass Flux ◽  
Horizontal Tube ◽  
Vapor Condensation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Noncondensable Gas ◽  
Mass Fluxes

Abstract Double-boundary layer theory was adopted to investigate the distributions of the liquid film, gas film, heat transfer coefficient, and condensate mass fluxes around a horizontal tube for vapor condensation with noncondensable gases like steam–air and steam–CO2 mixtures under free convection. The investigation considered the effects of the noncondensable gas concentration, surface subcooling temperature, and pressure. The thicknesses of the liquid and gas films increase gradually along the wall from top to bottom, whereas the local heat transfer coefficient and the condensate mass flux decrease. The film thicknesses do not change significantly around the upper part of the tube but increase sharply around the lower part. The liquid film thicknesses, gas film thicknesses, condensate mass fluxes, and heat transfer coefficients of steam–air systems are compared with those of steam–CO2 systems. The condensate mass flux in the steam–air system is smaller than that of steam–CO2 system under the condition of the same surface subcooling and gas mass fraction because air has more moles of molecules in the mixture than CO2 and the steam more easily diffuses through CO2 than through air. The predicted average condensation heat transfer coefficients agree well with the available experimental data.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

Evaporation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes

2015 ◽  
Author(s):  
Jian-jun Sun ◽  
Jing-xiang Chen ◽  
David J. Kukulka ◽  
Kan Zhou ◽  
Wei Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Smooth Tube ◽  
External Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Enhanced Surface

An experiment investigation was performed using R410A in order to determine the single-phase and evaporation heat transfer coefficients on the outside of (i) a smooth tube; (ii) herringbone tube; and (iii) the newly developed Vipertex enhanced surface 1EHT tube; all with the same external diameter (12.7 mm). The nominal evaporation temperature is 279 K, with inlet and outlet qualities of 0.1 and 0.8. Mass fluxes ranged from 10 to 40 kg m−2s−1. Results suggest that the 1EHT tube has excellent heat transfer performance but a higher pressure drop when compared to a smooth tube. Evaporation heat transfer coefficient for the 1EHT is lower than the herringbone tube and the pressure drop is almost the same.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Flow Boiling in an In-Line Set of Short Narrow Gap Channels

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
D. Janssen ◽  
J. M. Dixon ◽  
S. J. Young ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Flow Boiling ◽  
Coefficient Of Performance ◽  
Narrow Gap ◽  
Transfer Coefficients ◽  
Data Set ◽  
Heat Transfer Fluids ◽  
Heat Transfer Coefficients ◽  
O 10

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at power densities of 1 kW/cm3 and wall heat flux of 3–40 W/cm2. This configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters are 34 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Nonuniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet subcooling, single-phase heat transfer dominates over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 14, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30% in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high ratio of heat transfer to pumping power (coefficient of performance (COP)) is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet subcooling is suggested by the data set for this benchmark multiheater configuration.

Two-Phase Pressure Drop and Boiling Heat Transfer in a Single Horizontal Microchannel

2006 ◽  
Author(s):  
Cheol Huh ◽  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Local Flow ◽  
Heat Transfer Coefficients ◽  
Phase Pressure

With a single microchannel and a series of microheaters made with MEMS technique, two-phase pressure drop and local flow boiling heat transfer were investigated using deionized water in a single horizontal rectangular microchannel. The test microchannel has a hydraulic diameter of 100 μm and length of 40 mm. A real time observation of the flow patterns with simultaneous measurement are made possible. Tests are performed for mass fluxes of 90, 169, and 267 kg/m2s and heat fluxes of from 100 to 600 kW/m2. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient are evaluated and the effects of heat flux, mass flux, and vapor qualities on flow boiling are studied. Both the evaluated experimental data are compared with existing correlations. The experimental heat transfer coefficients are nearly independent on mass flux and the vapor quality. Most of all correlations do not provide reliable heat transfer coefficients predictions with vapor quality and prediction accuracy. As for two-phase pressure drop, the measured pressure drop increases with the mass flux and heat flux. Most of all existing correlations of two-phase frictional pressure gradient do not predict the experimental data except some limited conditions.

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