EHD Enhanced Convective Boiling of R-134a in Grooved Channels—Application to Subcompact Heat Exchangers

1997 ◽  
Vol 119 (4) ◽  
pp. 805-809 ◽  
Author(s):  
M. Salehi ◽  
M. M. Ohadi ◽  
S. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Flow Direction ◽  
Reynolds Numbers ◽  
Convective Boiling ◽  
Field Polarity ◽  
Electrical Field Strength ◽  
Compact Heat Exchangers ◽  
R 134A

Electrohydrodynamically (EHD) enhanced flow boiling of refrigerant R-134a inside grooved channels of approximately 1-mm hydraulic diameter was investigated with the objective of addressing the applicability of the EHD technique in highly compact heat exchangers. Two sets of experiments were performed. The first set included experiments in a channel with a smooth heat transfer wall, whereas in the second set a corrugated (enhanced) surface was used. In each case experiments were conducted as a function of the applied electrical field strength, electric field polarity, flow Reynolds number, inlet test section vapor quality, and flow direction (upward, downward, or horizontal). It is demonstrated that in all cases the EHD effect can substantially increase the heat transfer coefficient particularly at low Reynolds numbers and when applied over the enhanced heat transfer wall.

Two Phase Boiling Heat Transfer of Water in Minichannel

2017 ◽  
Author(s):  
Ye Tian ◽  
Wei Huang ◽  
Pengfei Li ◽  
Simin Cao ◽  
Yan Sun
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Absolute Error ◽  
Nuclear Industry ◽  
Working Fluid ◽  
Two Phase ◽  
Compact Heat Exchangers ◽  
Compact Size

Printed Circuit Heat Exchangers (PCHE) is a new type of compact heat exchangers, it will be widely used for nuclear industry due to its higher heat transfer area density, compact size, and design flexibility. The hydraulic diameter of PCHE tubes ranges from 1mm to 2mm which belongs to mini-channel according to Kandlikar and Grande (2003)’s study.[1] In this paper, two-phase flow boiling heat transfer of water in mini-channel is discussed. The most of previous literatures in this field mainly focused on flow boiling of refrigerants, but the main working fluid in PCHE tubes is water. A composite correlation of flow boiling of water through mini-channel has been developed on basis of a database of water in this paper. Mean absolute error (MAE) method is used to evaluate relative error. Comparing with the experimental data, the MAE of the new correlation is 23.4%.

Flow Boiling Heat Transfer Characteristics of R-134a in Horizontal and Vertical Mini-Channels

2010 ◽  
Author(s):  
Sira Saisorn ◽  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Flow Boiling ◽  
Flow Direction ◽  
Experimental Conditions ◽  
Mini Channels ◽  
System Temperature ◽  
Temperature Variable ◽  
R 134A ◽  
Regime Map

Heat transfer experiments are carried out to obtain the data of R-134a during flow boiling in a circular mini-channel having a diameter of 1.75 mm and a length of 600 mm. The DC power supply generating 80 A at 12 V is used to apply heat to the test section. T-type thermocouples are installed at the inlet and outlet of the test section to measure the system temperature. The 10 thermocouples are installed on the top and bottom sides at equal distances along the tube to measure the wall temperature. Variable area type flow meters calibrated specially in the range 0.02–0.2 LPM for R-134a by the manufacturer are used to measure the refrigerant flow rate. A transparent tube is installed to match up with the test section outlet and to serve as a viewing window for visualisation. Two sets of the horizontal flow and vertical upward flow data are analysed. Flow regime map and heat transfer coefficient tend to be dependent with flow direction under the certain experimental conditions.

Application of the Local Assumption for the Design of Compact Heat Exchangers for Boiling Heat Transfer

1984 ◽  
Vol 106 (1) ◽  
pp. 204-209 ◽  
Author(s):  
C. C. Chen ◽  
J. W. Westwater
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Equivalent Diameter ◽  
Compact Heat Exchangers ◽  
Two Fluids ◽  
Flow Oscillations

The design technique of interest here is the use of the local assumption, namely, that the local heat transfer coefficient during flow boiling is uniquely fixed by the local metal-to-liquid, ΔT, and the local fluid velocity. The object of this paper is to show the performance of two new compact heat exchangers that are specifically designed for boiling duty by this technique. These exchangers, from different manufacturers, were brazed aluminum, crossflow devices having core sizes of about 8 × 8 × 8 cm. The equivalent diameter of the flow passages on the boiling side, based on the wetted perimeter, was 0.167 cm. Offset fins gave excellent mixing of the boiling fluid, so homogeneous flow was assumed to prevail. Tests were made with Refrigerant-113 (R-113) at atmospheric pressure in these exchangers installed as thermosiphon reboilers. Heat was provided by condensing steam. The measured mass velocity of the R-113 was from 14 to 750 kg/s m2, the inlet velocity was 0.008 to 0.45 m/s, the calculated homogeneous exit velocity was 0.5 to 20 m/s, the calculated metal-liquid, ΔT, varied from 15 to 120 K, and the heat duty varied from 5.5 to 57 kW. On a volumetric basis, this upper duty is 120,000 kW/m3, a remarkably high duty for the exchange of heat between two fluids. For both exchangers, the agreement between predicted and measured duties was satisfactory as long as no dryout occurred. When dryout occurred, flow oscillations were observed, and the observed heat duty was as much as 40 percent below the predicted value.

Computational Insights Into Air-Side Flow and Heat Transfer in Compact Heat Exchangers

2005 ◽  
Author(s):  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Heat Exchangers ◽  
Three Dimensional ◽  
Computer Experiments ◽  
Transfer Coefficients ◽  
Substantial Impact ◽  
Compact Heat Exchangers ◽  
Thermal Phenomena ◽  
Side Flow

The paper describes two- and three-dimensional computer simulations which are used to study fundamental flow and thermal phenomena in multilouvered fins used for air-side heat transfer enhancement in compact heat exchangers. Results pertaining to flow transition, thermal wake interference, and fintube junction effects are presented. It is shown that a Reynolds number based on flow path rather than louver pitch is more appropriate in defining the onset of transition, and characteristic frequencies in the louver bank scale better with a global length scale such as fin pitch than with louver pitch or thickness. With the aid of computer experiments, the effect of thermal wakes is quantified on the heat capacity of the fin as well as the heat transfer coefficient, and it is established that experiments which neglect accounting for thermal wakes can introduce large errors in the measurement of heat transfer coefficients. Further, it is shown that the geometry of the louver in the vicinity of the tube surface has a large effect on tube heat transfer and can have a substantial impact on the overall heat capacity.

Comparison of 30 Boiling and Condensation Correlations for Two-Phase Flows in Compact Plate-Fin Heat Exchangers

2017 ◽  
Author(s):  
Wenhai Li ◽  
Ken Alabi ◽  
Foluso Ladeinde
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase Flows ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Heat Exchanger Design ◽  
Micro Channels ◽  
Vertical Tubes

Over the years, empirical correlations have been developed for predicting saturated flow boiling [1–15] and condensation [16–30] heat transfer coefficients inside horizontal/vertical tubes or micro-channels. In the present work, we have examined 30 of these models, and modified many of them for use in compact plate-fin heat exchangers. However, the various correlations, which have been developed for pipes and ducts, have been modified in our work to make them applicable to extended fin surfaces. The various correlations have been used in a low-order, one-dimensional, finite-volume type numerical integration of the flow and heat transfer equations in heat exchangers. The NIST’s REFPROP database [31] is used to account for the large variations in the fluid thermo-physical properties during phase change. The numerical results are compared with Yara’s experimental data [32]. The validity of the various boiling and condensation models for a real plate-fin heat exchanger design is discussed. The results show that some of the modified boiling and condensation correlations can provide acceptable prediction of heat transfer coefficient for two-phase flows in compact plate-fin heat exchangers.

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