Heat Transfer and Pressure Drop Characteristics of Condensation for R410A in a 3.78mm Circular Tube Under Normal and Micro Gravity

2016 ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li ◽  
Tom I.-P. Shih ◽  
Yonghai Zhang ◽  
Yanping Shi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Transfer Coefficients ◽  
Bottom Part ◽  
Vapor Interface ◽  
Heat Transfer Coefficients ◽  
Micro Gravity ◽  
Liquid Vapor

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 3.78 mm) under normal and micro gravity are investigated numerically. The Volume of Fluid method is used to acquire liquid-vapor interface, while the low-Reynolds form of the Shear Stress Transport k∼ω (SST k∼ω) model is adopted to taking turbulent effect into account. The results indicate that the heat transfer coefficients decrease with increasing gravity accelerations, while the frictional pressure gradients increase with increases in gravity accelerations. The liquid film accumulates at the bottom of the tube, leading to a very thin liquid film attached to the upper part of inner tube wall. This accumulation effect decreases with decreases in gravitational accelerations. A more symmetrical liquid-vapor interface is obtained at lower gravity. The average liquid film thickness is nearly the same for different gravity accelerations at the same vapor quality (δave≈56 μm at x = 0.9 and δave≈230 μm at x = 0.5). The local heat transfer coefficients increase with increasing gravity at the top of the tube and decrease with increases in gravity at the bottom, while the bottom part of the tube has a limited contribution to the global heat transfer coefficient for stratified flow regime. The numerical data obtained under normal gravity agree well with well-known empirical correlations.

Heat Transfer Coefficients and Lifetimes of Micro-Droplet Evaporation in the Transition Regime

2012 ◽  
Author(s):  
Michael S. Hanchak ◽  
Alejandro M. Briones ◽  
Jamie S. Ervin ◽  
Larry W. Byrd
Keyword(s):  
Heat Transfer ◽  
Droplet Radius ◽  
Transition Regime ◽  
Volume Data ◽  
Transfer Coefficients ◽  
Vapor Interface ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
Hot Surface ◽  
Liquid Vapor

The goal of the present work is to determine the heat transfer characteristics of evaporating micro-droplets of water from a hot surface. To accomplish this, a one-dimensional, finite-difference model is used to simulate the transport of water vapor and energy from the droplet’s liquid-vapor interface toward and inside the hemispherical, gaseous region surrounding the droplet. The model incorporates a transition regime correction to the kinetic theory evaporative mass flux. The transition regime correction, a multiplier applied to the kinetic flux, is a function of the Knudsen number, the ratio of molecular mean free path to the droplet radius. The transition regime encompasses droplet sizes for which neither the kinetic model of evaporation nor the hydrodynamic continuum theory is entirely appropriate. The model simulates the liquid phase as one-dimensional conduction between the hot surface and the liquid-vapor interface. Previously, we validated our model against measured volume data as a function of time for several evaporating droplets. Using the model, overall heat transfer coefficients and total evaporation times are determined. Linear fits of both are provided against dimensional groupings of initial droplet volume and surface temperature superheat.

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.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

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.

Measurements of Developing and Fully Developed Heat Transfer Coefficients along a Periodically Interrupted Surface

1979 ◽  
Vol 101 (2) ◽  
pp. 211-216 ◽  
Author(s):  
N. Cur ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Plate Thickness ◽  
Turbulent Regime ◽  
Duct Flow ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Interrupted Surface

The heat transfer and pressure drop characteristics for an array of colinear, equally spaced plates aligned parallel to the flow in a flat rectangular duct have been studied experimentally. The periodic interruptions (i.e., the gaps between the plates) preclude the attainment of hydrodynamic and thermal development of the type that is encountered in conventional duct flows, but a periodic fully developed regime can exist. Measurements of the heat transfer coefficients for the successive plates of the array affirmed the periodically developed regime and demonstrated the developmental pattern leading to its attainment. The thickness of the plates in the array was varied parametrically. In general, the Nusselt number increases with plate thickness. Thickness-related increases in the fully developed Nusselt number of up to 65 percent were encountered. The presence of the interruptions serves to augment the heat transfer coefficients. In the fully turbulent regime, the heat transfer coefficients are on the order of twice those for a conventional duct flow. The pressure drop also increases with the plate thickness.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

Experimental Study on Forced Convection Heat Transfer Inside Horizontal Tubes in an Absorption/Compression Heat Pump

2002 ◽  
Vol 124 (5) ◽  
pp. 975-978 ◽  
Author(s):  
Li Yong and ◽  
K. Sumathy
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Forced Convection ◽  
Experimental Results ◽  
Working Fluid ◽  
Large Temperature ◽  
Absorption Process ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients

Quasi-local absorption heat transfer coefficients and pressure drop inside a horizontal tube absorber have been investigated experimentally, with R-22/DMA as the working pair. The absorber is a counterflow coaxial tube-in-tube heat-exchanger with the working fluid flowing in the inner tube while the water moves through the annulus. A large temperature gliding has been experienced during the absorption process. Experimental results show that the heat transfer coefficient of the forced convective vapor absorption process is higher compared to the vertical falling film absorption. A qualitative study is made to analyze the effect of mass flux, vapor quality and solution concentration on pressure drop and heat transfer coefficients. On the basis of the experimental results, a new correlation is proposed whereby the two-phase heat transfer is taken as a product of the forced convection of the absorption and the combined effect of heat and mass transfer at the interface. The correlation is found to predict the experimental data almost within 30 percent.

Instantaneous Optical Measurement of the Temperature at the Interface Between a Wall and a Thin Liquid Film

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Brian E. Fehring ◽  
Roman W. Morse ◽  
Jason Chan ◽  
Kristofer M. Dressler ◽  
Evan T. Hurlburt ◽  
...  
Keyword(s):  
Laser Beam ◽  
Liquid Film ◽  
Solid Wall ◽  
Incident Angle ◽  
Thin Liquid Film ◽  
Index Of Refraction ◽  
High Temporal Resolution ◽  
Flow Measurements ◽  
Vapor Interface ◽  
Liquid Vapor

Abstract Instantaneous temperature measurements at the interface between a solid wall and a thin, unsteady liquid film are performed using thermoreflectance, a nonintrusive optical technique with high temporal resolution. A laser beam is directed at a wall–liquid interface, and the intensity of the light reflected at that interface is measured by a photodiode. The intensity of the reflected light varies with the index of refraction of the liquid at the wall. The index of refraction is a function of temperature, which enables the instantaneous measurement of the wall temperature. In the presence of thin liquid films, reflections from the liquid–vapor interface at the free surface of the film generate noise in the measurements. We demonstrate that orienting the laser beam at a large incident angle, close to total internal reflection, minimizes noise from the liquid–vapor interface while increasing the sensitivity of the measurement. The thermoreflectance technique is validated in an unsteady two-phase annular flow. Measurements of temperature fluctuations less than 1 K in amplitude are achieved, with an uncertainty of 0.1 K.

Measurements of Mean Heat Transfer Coefficients for Turbulent Forced Convection in a Rectangular Duct With Uniformly Spaced Plate Inserts

2009 ◽  
Author(s):  
Lorena Camargo ◽  
Matthew Gitsham ◽  
B. Rabi Baliga
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Experimental Technique ◽  
Parameter Analysis ◽  
Electrical Heating ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Bottom Part ◽  
Heat Transfer Coefficients ◽  
Heated Plates

An experimental investigation of turbulent forced convection from single and multiple heated plates in the spatially-periodic fully-developed region of air flows in a straight rectangular duct with uniformly spaced plate inserts is described. The focus in this work is on measurements of temporally- and spatially-averaged heat transfer coefficients on the surfaces of the aforementioned plates. The experimental technique is based on a lumped parameter analysis. Six different heated plates were specially designed, constructed, and instrumented for this work. Each of these heated plates was made up of a central metal section (brass, aluminum, or copper) and two plastic end sections (Ertalyte): the metal section was constructed from a top part and a bottom part, with grooves milled in the bottom part to accommodate three thermocouples and an electrical heating wire; the plastic sections were used to reduce the rates of heat loss from the ends to negligible amounts compared to that due to forced convection from the lateral surfaces of the metal section to the air. The Reynolds number used in the presentation of the results is based on the time-mean average streamwise velocity in the minimum cross-sectional area of the duct and a hydraulic diameter: its values ranged from 2,000 to 30,000. Details of the experimental technique used and the results obtained are presented and discussed.

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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