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.

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.

scholarly journals A Numerical Well-Balanced Scheme for One-Dimensional Heat Transfer in Longitudinal Triangular Fins

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
I. Rusagara ◽  
C. Harley
Keyword(s):  
Heat Transfer ◽  
Differential Equation ◽  
Partial Differential Equation ◽  
Nonlinear Partial Differential Equation ◽  
Transfer Coefficients ◽  
Partial Differential ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
Highly Nonlinear ◽  
Triangular Fin

The temperature profile for fins with temperature-dependent thermal conductivity and heat transfer coefficients will be considered. Assuming such forms for these coefficients leads to a highly nonlinear partial differential equation (PDE) which cannot easily be solved analytically. We establish a numerical balance rule which can assist in getting a well-balanced numerical scheme. When coupled with the zero-flux condition, this scheme can be used to solve this nonlinear partial differential equation (PDE) modelling the temperature distribution in a one-dimensional longitudinal triangular fin without requiring any additional assumptions or simplifications of the fin profile.

Liquid-Vapor Oscillating Flow and Heat Transfer in a U-Shaped Minichannel With Internal Wick Structure

2009 ◽  
Author(s):  
Jiajun Xu ◽  
Yuwen Zhang ◽  
H. B. Ma
Keyword(s):  
Heat Transfer ◽  
Oscillatory Flow ◽  
Oscillating Flow ◽  
Transfer Coefficients ◽  
Oscillating Heat Pipe ◽  
Heat Transfer Coefficients ◽  
Evaporation And Condensation ◽  
Flow And Heat Transfer ◽  
Wick Structure ◽  
Liquid Vapor

Liquid-vapor oscillating flow and heat transfer in a vertically placed oscillating heat pipe (OHP) with a sintered particle wick structure inside are analyzed in this paper. The evaporation and condensation heat transfer coefficients are obtained by solving the microfilm evaporation and condensation on the sintered particles. The sensible heat transfer between the liquid slug and the channel wall are obtained by analytical solution or empirical correlations, depending on whether the liquid flow is laminar or turbulent. The effects of the maximum evaporation and condensation angles on the oscillatory flow, as well as sensible and latent heat transfer are analyzed.

Theoretical Model for Nucleate Boiling Heat and Mass Transfer of Binary Mixtures

2003 ◽  
Vol 125 (6) ◽  
pp. 1106-1115 ◽  
Author(s):  
Ju¨rgen Kern ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Binary Mixtures ◽  
Phase Interface ◽  
Nucleate Boiling ◽  
Interfacial Thermal Resistance ◽  
Transfer Coefficients ◽  
Total Heat Flow ◽  
Heat Transfer Coefficients ◽  
Liquid Vapor

A model is presented to calculate nucleate boiling heat transfer coefficients of binary mixtures. The model includes the governing physical phenomena, such as the variation of the phase interface curvature, the adhesion pressure between wall and liquid, the interfacial thermal resistance as well as the local variation of composition and liquid-vapor equilibrium. Marangoni convection is considered, too. The theoretical background of these phenomena is described and their implementation is explained. The model is verified by comparing calculated heat transfer coefficients of hydrocarbon mixtures with experimental data. Computational and experimental data are in good agreement. In the examples a considerable amount of the total heat flow passes through a tiny thin film area, called micro region, where the liquid-vapor phase interface is attached to the wall. Very high spatial gradients of heat flux and mixture concentration occur interacting with overall heat transfer performance.

Two-Dimensional Study of Heat Transfer and Fluid Flow in a Natural Convection Loop

1982 ◽  
Vol 104 (3) ◽  
pp. 508-514 ◽  
Author(s):  
A. Mertol ◽  
R. Greif ◽  
Y. Zvirin
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Natural Convection ◽  
A Priori ◽  
Two Dimensional ◽  
Transfer Coefficients ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
First Time ◽  
Good Agreement

A study has been made of the heat transfer and fluid flow in a natural convection loop. Previous studies of these systems have utilized a one-dimensional approach which requires a priori specifications of the friction and the heat-transfer coefficients. The present work carries out a two-dimensional analysis for the first time. The results yield the friction and the heat-transfer coefficients and give their variation along the loop with the Graetz number as a parameter. Comparison is also made with experimental data for the heat flux and good agreement is obtained.

Heat-Transfer Measurements in an Inexpensive Supersonic Wind Tunnel: 1—Apparatus and Results for a Laminar Boundary Layer Based on a Simple One-Dimensional Flow Model

1955 ◽  
Vol 22 (3) ◽  
pp. 289-296
Author(s):  
Joseph Kaye ◽  
J. H. Keenan ◽  
G. A. Brown ◽  
R. H. Shoulberg
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Laminar Boundary Layer ◽  
Flow Model ◽  
Transfer Coefficients ◽  
Supersonic Wind Tunnel ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
Dimensional Flow

Abstract Reliable experimental data, obtained at relatively low cost, are presented in the form of heat-transfer coefficients for air moving at supersonic speeds in a round tube. These data are analyzed, interpreted, and compared with available data in the literature. The experimental local heat-transfer coefficients are for laminar, transitional, and turbulent boundary layers. The data for a laminar boundary layer, comprising 17 runs, are discussed here for Mach numbers at tube inlet of 2.8 and 3.0. The range of values of diameter Reynolds number covered is from 20,000 to 100,000 for these laminar-flow tests, while the length Reynolds number extends to about 4,000,000. The computed quantities are obtained on the basis of a simple one-dimensional flow model, but a companion paper will analyze the same data in greater detail on the basis of a two-dimensional flow model.

The Thermodynamic Performance of Liquid-Vapor Separation Air-Cooled Condenser in ORC System at Low Ambient Temperature

2014 ◽  
Author(s):  
Ying Chen ◽  
Wenxian Zheng ◽  
Tianming Zhong ◽  
Nan Hua
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Tube Wall ◽  
Ambient Air ◽  
Working Fluid ◽  
Heat Transfer Area ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermodynamic Performance ◽  
Liquid Vapor

This paper investigated the thermodynamic performance of a novel condenser, liquid-vapor separation condenser (LSC), under the ORC conditions with extreme ambient air temperature. By contrast, a common parallel flow condenser (PFC) with the identical structure of tube and fin, together with the heat transfer area was measured under the same condition. The average condensing temperature was chosen as 35°C, R134a was chosen as the working fluid. The experimental results announced that the in-tube average heat transfer coefficients (AHTCs) of the LSC were 96.7% to 109.1% of the PFC when the initial air temperature varied from −10°C to 10°C, at the R134a inlet mass flux from 437kg/(m2s) to 750kg/(m2s), and heat flux from 3kW/m2 to 5 kW/m2. Specially, the pressure drop was only 35.1% to 53.2% of the PFC under the experiment conditions. The tube wall temperatures of the LSC decreased slower than the PFC. The thermodynamic performance of the LSC was superior to the PFC under the ORC conditions. The result indicates the LSC is a promising condenser in ORC system.

One Dimensional Numerical Study for Thermal Performance of Intermediate Fluid Vaporizer for Liquefied Natural Gas

2014 ◽  
Author(s):  
Z. G. Qu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Liquefied Natural Gas ◽  
Inlet Temperature ◽  
Transfer Coefficients ◽  
One Dimensional ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Capacity ◽  
The Heat Transfer Coefficient

A one-dimensional heat transfer model was established for the three typical parts of Intermediate Fluid Vaporizer (IFV), namely, evaporator, condenser and thermolator used to vaporize liquefied natural gas (LNG). Seawater and propane were applied as heat sources and intermediate working fluid respectively for regasification and cold energy recovery of LNG in an IFV system. Based on the energy balance among the evaporator, the condenser and the thermolator, the heat transfer and thermodynamic model was established and the distribution of temperature of all fluids and heat transfer coefficients were predicted. The effects of several parameters, including the inlet temperature of seawater and LNG, the mass flow of seawater and LNG, the pressure of LNG, on the temperature distribution and heat transfer coefficients were conducted. The results show that the heat transfer capacity of evaporator was enhanced greatly by increasing inlet temperature and inlet mass flow rate of seawater and the thermal resistances in the two sides of evaporator were proportionate, and show that the heat transfer coefficient of condenser increases gradually along flow path and the curve exists convex firstly and another concave with the turning point, and also show that the heat transfer capacity of thermolator decreases gradually with the heat transfer coefficient inside tube keeping consistent along with the flow path and the heat transfer coefficient inside tube was much bigger than heat transfer coefficient outside tube. The results show that the main thermal resistance is the heat transfer of nature gas flowing across the outside tube banks for the thermolator and the propane condensing outside tube for the condenser, respectively.

Sign in / Sign up

Export Citation Format

Share Document