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1.
This paper has dealt with direct contact heat and mass transfer characteristics of air bubbles in a hot water layer. The
experiments were carried out by bubbling air in the hot water layer under some experimental conditions of air flow rate, inlet
air temperature and humidity as a dispersion fluid, and hot water temperature and hot water layer depth as a continuous fluid.
Heat transfer and evaporation of water vapor from hot water to air bubbles occurred during air bubbles ascending into the
hot water. Air bubble flow patterns were classified into three regions of independent air bubble flow, transition and air
bubble combination growth. Non-dimensional correlation equations of direct contact heat and mass transfer between air bubbles
and hot water were derived by some non- dimensional parameters for three regions of bubble flow pattern.
Received on 14 July 2000 / Published online: 29 November 2001 相似文献
2.
The problem of condensation by mixed convection in a vertical channel has been numerically analyzed for an air water system.
The plates of the channel are subjected to uniform but different heat fluxes. The effects of ambient conditions on the condensation
process are investigated. The results show particularly the existence of a particular temperature called inversion temperature
for condensation. This temperature is defined as the temperature above it the condensation rate is higher for a lower vapor
concentration. It was found that this temperature increases with the increase of the ambient pressure and decreases with the
cooling heat flux. 相似文献
3.
This study examines energy transport associated with liquid film condensation in natural convection flows driven by differences
in density due to temperature and concentration gradients. The condensation problem is based on the thin-film assumptions.
The most common compositional gradient, which is encountered in humid air at ambient temperature is considered. A steady laminar
Boussinesq flow of an ideal gas–vapor mixture is studied for the case of a vertical parallel plate channel. New correlations
for the latent and sensible Nusselt numbers are established, and the heat and mass transfer analogy between the sensible Nusselt
number and Sherwood number is demonstrated.
Received on 15 November 1999 相似文献
4.
Udo Dinglreiter 《Heat and Mass Transfer》2011,47(8):991-999
In many industrial processes as well as in air conditioning systems heat and moisture is transferred by rotary heat exchangers
from the warm exhaust air flow to the cold supply air flow. Rotary heat exchangers are classified as sorption rotors, hygroscopic
rotors and condensation rotors. Basic mechanisms of heat and moisture transfer are presented. By means of the condensation
potential as the difference between the moisture content of the warm air flow and the moisture content of the cold air flow
at saturation the humidity transfer at the different rotor types is investigated. The condensation potential as a reference
parameter provides the possibility to describe the influence of various air conditions in exhaust air and supply air flow
on the humidity transfer of different rotary heat exchangers and to compare these rotors with each other. In order to give
an overview of relevant design parameters, the influence of the speed of turning, the flute height of the rotor matrix and
the velocity of the air flow regarding the heat and mass transfer is considered. 相似文献
5.
Direct-contact condensation is studied by injecting steam downward through a pipe and out of the submerged end into a pool of subcooled water. The motion of the steam/water interface is recorded by high-speed movies and systematically classified, based on the injection rate and the pool subcooling. The resulting regime map shows the existence of three main condensation modes as the injection rate is reduced: At a high rate of steam injection an oscillatory jet is observed. At a low rate of injection a phenomenon called “steam chugging,” in which the pool water periodically enters the injection pipe, is observed. At intermediate injection rates an oscillatory bubble exists continuously at the pipe exit. 相似文献
6.
7.
An analysis is made for the influence of the moving condensate film on the mass transfer rate from the gas-vapor mixture to the condensate. The governing energy and mass conservation equations are solved using the Crank-Nicholson method. The results show that the moving condensate film may have a considerable effect on condensation mass transfer. 相似文献
8.
Yu. A. Buevich Yu. A. Korneev 《Journal of Applied Mechanics and Technical Physics》1974,15(4):500-506
Macroscopic equations for the conservation of heat (or the mass of a diffusing impurity) in a continuous medium containing distributed particles of a dispersed phase are formulated neglecting the effect of random fluctuations of the medium and particles by the transfer process. The problem of convective heat conduction or diffusion near an isolated particle is also formulated, the solution of which permits calculation of all the parameters entering into the indicated equations. This problem has been solved in the particular case of small Peclet numbers, which characterize heat and mass exchange in the vicinity of a single particle. 相似文献
9.
Batrice Mdric Pascal Lavieille Marc Miscevic 《Experimental Thermal and Fluid Science》2006,30(8):785-793
An experimental investigation of complete condensation flow is undertaken for a range of mass flow rates between 3.4 and 13.8 kg/m2 s. The associated flow regimes are visualized using an ombroscopic technique. Two major flows are observed (with or without release of bubbles). A critical value of the mass flow rate is obtained at the transition between these two regimes. The visualization also enables a local parameter to be determined: the void fraction. The influence of the presence of a bubbly zone is highlighted by the heat transfer and pressure drops. Finally, the dependence of the critical value of the mass flow rate on the temperature of the secondary flow is obtained. 相似文献
10.
11.
12.
S. S. Kutateladze Institute of Heat Physics, Siberian Branch of the Russian Academy of Sciences. Translated from Prikladnaya
Mekhanika i Tekhnicheskaya Fizika, Vol. 36, No. 6, pp. 102–107, November–December, 1995. 相似文献
13.
V. V. Kuznetsov 《Fluid Dynamics》2011,46(5):754-763
The relations for the temperature, velocity, and pressure fields on the interface between two regions occupied by a liquid
and its vapor are derived from the balance laws. In contrast to the traditional relations, the relations obtained contain
additional terms, responsible for certain physical phenomena on the interface and usually neglected in the force and energy
flux balances. The problem of evaporation of a liquid layer is considered. An exact solution of this problem is constructed
in the one-dimensional formulation. The evaporation rate is calculated for a specific liquid. 相似文献
14.
N. Clerx L. G. M. van Deurzen A. Pecenko R. Liew C. W. M. van der Geld J. G. M. Kuerten 《Heat and Mass Transfer》2011,47(8):981-990
The temperature fields in the center plane of a channel with a square cross-section have been measured. Steam injected at
relatively low mass fluxes through a small hole in one of the walls of the channel condensed intermittently in a small area
close to the inlet. The upstream temperature of the liquid cross-flow, T
L
, the momentum ratio, J, and the Prandtl number proved to be important for the single-phase temperature field induced in the jet further away from
the steam inlet. Jet centerlines of velocity and temperature are measured and positions are compared. Different locations
for J < 100 and low T
L
are explained from dependencies on Reynolds and Prandtl numbers. Next to the jet centerline a second high-temperature zone
was found to occur, close to the wall and downstream of the steam inlet. The importance of capillary forces is investigated
with the aid of 3D CFD computations. 相似文献
15.
Direct Contact Condensation (DCC) of steam in water occurs when steam is introduced into water. It is a phenomenon of high importance in many industrial applications. An important feature of the DCC is the length of the steam plume. Correlations for a steam plume length presently available are accurate only for limited conditions. In this paper, a new two-dimensional steam plume length diagram is presented capable of predicting length accurately for a wide range of conditions. The diagram is validated against experiments. Furthermore, corrections necessary to adopt the diagram for steam injection into a water flow are discussed in the paper. 相似文献
16.
17.
《European Journal of Mechanics - B/Fluids》2003,22(4):391-408
A polynomial expansion procedure and an analytical discrete-ordinates method are used to solve four basic problems, all based on the linearized Boltzmann equation for rigid-sphere interactions, that describe heat transfer and/or evaporation–condensation between two parallel surfaces or for the case of a semi-infinite half space. Relevant to the case of two surfaces, the basic problem of heat transfer driven by a temperature difference at two confining walls described by a general Maxwell gas–surface interaction law (a mixture of specular and diffuse reflection) is solved for the case where different accommodation coefficients can be used for each of the two bounding surfaces. In addition, the classical problem of “reverse temperature gradient” in the theory of evaporation and condensation is also solved for the case of two parallel liquid–vapor interfaces kept at different temperatures. In regard to half-space applications, an evaporation/condensation problem based on a presumed known interface condition and a heat-conduction problem (with no net flow) driven by energy flow from a bounding surface with know properties are each solved with what is considered a high degree of accuracy. 相似文献
18.
The film theory by Ackermann can be applied to simultaneous heat and mass transfer processes, if the mass flux normal to the wall is induced by diffusion. Since this condition mostly is not fulfilled when condensing vapor mixtures, an approximative procedure is developed taking into account the influence of suction in condensation heat transfer. The accuracy of the method turns out to be satisfactory compared with results obtained by numerical analysis. 相似文献
19.
Summary The problem of heat transfer in a two-dimensional porous channel has been discussed by Terrill [6] for small suction at the walls. In [6] the heat transfer problem of a discontinuous change in wall temperature was solved. In the present paper the solution of Terrill for small suction at the walls is revised and the whole problem is extended to the cases of large suction and large injection at the walls. It is found that, for all values of the Reynolds number R, the limiting Nusselt number Nu
increases with increasing R.Nomenclature
stream function
- 2h
channel width
-
x, y
distances measured parallel and perpendicular to the channel walls respectively
-
U
velocity of fluid at x=0
-
V
constant velocity of fluid at the wall
-
=y/h
nondimensional distance perpendicular to the channel walls
-
f()
function defined in equation (1)
-
coefficient of kinematic viscosity
-
R=Vh/
suction Reynolds number
-
density of fluid
-
C
p
specific heat at constant pressure
-
K
thermal conductivity
-
T
temperature
-
x=x
0
position where temperature of walls changes
-
T
0, T
1
temperature of walls for x<x
0, x>x
0 respectively
- = (T – T
1)/T
0 – T
1)
nondimensional temperature
-
=x/h
nondimensional distance along channel
-
R
* = Uh/v
channel Reynolds number
-
Pr = C
p/K
Prandtl number
-
n
eigenvalues
-
B
n()
eigenfunctions
-
B
n
(0)
, ()
eigenfunctions for R=0
-
B
0
(i)
, B
0
(ii)
...
change in eigenfunctions when R0 and small
-
K
n
constants given by equation (13)
-
h
heat transfer coefficient
-
Nu
Nusselt number
-
m
mean temperature
-
C
n
constants given by equation (18)
-
perturbation parameter
-
B
0i
()
perturbation approximations to B
0()
-
Q = B
0/
0
derivative of eigenfunction with respect to eigenvalue
-
z
nondimensional distance perpendicular to the channel walls
-
F(z)
function defined by (54) 相似文献
20.
J. Montlucon 《International Journal of Multiphase Flow》1975,2(2):171-182
The problem of heat and mass transfer around an evaporating water drop located in a superheated steam flow is studied using singular perturbation methods.The perturbation scheme involves three regions and some results concerning the Nusselt number and the drag coefficient of the drop are presented. 相似文献