Modeling of Two-Phase Heat Exchangers With Zeotropic Fluid Mixtures

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
D. Gomse ◽  
T. M. Kochenburger ◽  
S. Grohmann
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Separated Flow ◽  
Modeling Framework ◽  
Two Phase ◽  
Flow Models ◽  
Fluid Mixtures ◽  
Fluid Properties ◽  
Heat Loads ◽  
Simultaneous Heat

Heat exchangers are important components in many engineering applications. This paper proposes a numerical two-phase heat exchanger model with simultaneous heat transfer and pressure drop calculations. The presented model provides a modeling framework compatible with numerous different correlations for both single- and two-phase flow of pure fluids and fluid mixtures. Furthermore, it considers nonconstant fluid properties as well as longitudinal heat conduction and parasitic heat loads, which is particularly relevant in mixed refrigerant cycles for cooling of low-temperature applications. The governing equations are derived and the solution strategy is presented, followed by the model validation against analytical solutions in the corresponding limits. Finally, an exemplary heat exchanger is analyzed using both homogeneous and separated flow models, and the results are compared with experimental data from literature.

Hydrodynamic and Thermal Performance of a Vapor-Venting Microchannel Copper Heat Exchanger

2008 ◽  
Author(s):  
Milnes P. David ◽  
Amy Marconnet ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Exchanger ◽  
Carbon Fiber ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Exchangers ◽  
Single Phase ◽  
Two Phase ◽  
Microchannel Heat Exchanger ◽  
Large Pressure ◽  
Dry Out

Two-phase microfluidic cooling has the potential to achieve low thermal resistances with relatively small pumping power requirements compared to single-phase heat exchanger technology. Two-phase cooling systems face practical challenges however, due to the instabilities, large pressure drop, and dry-out potential associated with the vapor phase. Our past work demonstrated that a novel vapor-venting membrane attached to a silicon microchannel heat exchanger can reduce the pressure drop for two-phase convection. This work develops two different types of vapor-venting copper heat exchangers with integrated hydrophobic PTFE membranes and attached thermocouples to quantify the thermal resistance and pressure-drop improvement over a non-venting control. The first type of heat exchanger, consisting of a PTFE phase separation membrane and a 170 micron thick carbon-fiber support membrane, shows no improvement in the thermal resistance and pressure drop. The results suggest that condensation and leakage into the carbon-fiber membrane suppresses venting and results in poor device performance. The second type of heat exchanger, which evacuates any liquid water on the vapor side of the PTFE membrane using 200 ml/min of air, reduces the thermal resistance by almost 35% in the single-phase regime in comparison. This work shows that water management, mechanical and surface properties of the membrane as well as its attachment and support within the heat exchanger are all key elements of the design of vapor-venting heat exchangers.

Damping of Heat Exchanger Tubes in Two-Phase Flow: Review and Design Guidelines

2004 ◽  
Vol 126 (4) ◽  
pp. 523-533 ◽  
Author(s):  
M. J. Pettigrew ◽  
C. E. Taylor
Keyword(s):  
Heat Exchanger ◽  
Two Phase Flow ◽  
Cross Flow ◽  
Design Guidelines ◽  
Phase Flow ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Design Guideline ◽  
Fluid Properties ◽  
Semi Empirical

Two-phase flow exists in many shell-and-tube heat exchangers such as condensers, evaporators, and nuclear steam generators. Some knowledge on tube damping mechanisms is required to avoid flow-induced vibration problems. This paper outlines the development of a semi-empirical model to formulate damping of heat exchanger tube bundles in two-phase cross flow. The formulation is based on information available in the literature and on the results of recently completed experiments. The compilation of a database and the formulation of a design guideline are outlined in this paper. The effects of several parameters such as flow velocity, void fraction, confinement, flow regime and fluid properties are discussed. These parameters are taken into consideration in the formulation of a practical design guideline.

Modelling the Transient Behaviour of Heat Recovery Steam Generators

1995 ◽  
Vol 209 (4) ◽  
pp. 265-273 ◽  
Author(s):  
P J Dechamps
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Heat Recovery ◽  
Computation Time ◽  
Assisted Circulation ◽  
Steam Generators ◽  
Two Phase ◽  
Linear Heat ◽  
Numerical Predictions ◽  
Equivalent Linear

This paper describes a method used to compute the transient performances of assisted circulation heat recovery steam generators. These heat recovery steam generators are composed of several heat exchangers, each of which is a bundle of tubes. The method presented here treats each heat exchanger in a similar way, replacing the bundle of tubes with an ‘equivalent’ linear heat exchanger. This equivalent linear heat exchanger is then discretized in as many slices as required by the accuracy. The mass and enthalpy equations on each of these control volumes are solved by a fully explicit numerical method, adapted for the special conditions encountered in this kind of problem, allowing a considerable reduction of the computation time compared to other methods. Some emphasis is put on the modifications required to solve the equations for the evaporators because they are two-phase heat exchangers. A model for the steam drums is also presented together with simple models for the main control loops used in such systems. An example is presented in which an existing dual pressure level heat recovery steam generator is started from a cold state. The numerical predictions are in good agreement with measurements.

Second-Law-Based Thermoeconomic Optimization of Two-Phase Heat Exchangers

1987 ◽  
Vol 109 (2) ◽  
pp. 287-294 ◽  
Author(s):  
S. M. Zubair ◽  
P. V. Kadaba ◽  
R. B. Evans
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Unit Cost ◽  
Second Law ◽  
Inlet Temperature ◽  
Two Phase ◽  
Transfer Resistance

This paper presents a closed-form analytical method for the second-law-based thermoeconomic optimization of two-phase heat exchangers used as condensers or evaporators. The concept of “internal economy” as a means of estimating the economic value of entropy generated (due to finite temperature difference heat transfer and pressure drops) has been proposed, thus permitting the engineer to trade the cost of entropy generation in the heat exchanger against its capital expenditure. Results are presented in terms of the optimum heat exchanger area as a function of the exit/inlet temperature ratio of the coolant, unit cost of energy dissipated, and the optimum overall heat transfer coefficient. The total heat transfer resistance represented by (1/U = C1 + C2 Re−n) in the present analysis is patterned after Wilson (1915) which accommodates the complexities associated with the determination of the two-phase heat transfer coefficient and the buildup of surface scaling resistances. The analysis of a water-cooled condenser and an air-cooled evaporator is presented with supporting numerical examples which are based on the thermoeconomic optimization procedure of this paper.

A Review of Prediction Methods for Two-Phase Pressure Loss in Mini/Micro-Channels

2016 ◽  
Vol 24 (01) ◽  
pp. 1630002 ◽  
Author(s):  
Jung Hoon Yun ◽  
Ji Hwan Jeong
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Separated Flow ◽  
Empirical Correlations ◽  
Two Phase ◽  
Flow Models ◽  
Micro Channels ◽  
Extensive Experimental Data ◽  
Phase Pressure

Previous methods and correlations for predicting two-phase frictional pressure loss in mini/micro-channels are reviewed and compared. The empirical correlations are classified into four groups of modeling approaches: Homogeneous equilibrium models (HEMs), separated flow models (SFMs), direct empirical correlations, and flow pattern specific correlations. In order to examine the characteristics of the predictive methods for two-phase pressure loss in mini-channels and to assess the accuracy of the previous models and correlations, extensive experimental data and correlations that are available in the open literature are collected. The 1175 and 1304 experimental data for the two-phase pressure drop for condensing and boiling flows, respectively, are gathered from 15 papers and reports. The results present that the size of the channel significantly influences the pressure drop. The comparison demonstrates that Cicchitti et al.’s two-phase viscosity model is recommended for predicting two-phase pressure loss when the HEM is used. In general, the SFM with the two-phase multipliers of Muller–Steinhagen and Heck and Kim and Mudawar outperforms others for channel diameters of less than 3[Formula: see text]mm.

Modelling Two-Phase Heat Exchanger Performance in the Annular-Mist Flow Regime Considering Entrainment and Deposition Phenomena

2011 ◽  
Author(s):  
Julio C. Pacio ◽  
Carlos A. Dorao
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Regime ◽  
Flow Structure ◽  
Heat Exchangers ◽  
Nucleate Boiling ◽  
Empirical Models ◽  
Uniform Heat Flux ◽  
Two Phase ◽  
Mist Flow

Two-phase flow heat exchangers are main components of large cryogenics, power generation, refrigeration and liquefaction of natural gas plants, both in terms of capital cost and technical challenges. A major challenge in their design is the prediction of local heat transfer coefficients and pressure gradients for the evaporating or condensing fluids. Traditional heat exchanger models are based on one single correlation for predicting the heat transfer in the entire saturated boiling regime, disregarding the flow structure. However, the structure of the flow dictates how the different physical processes (nucleate boiling, convective heat transfer to the liquid and vapour phase, thin film evaporation) interact and contribute to the total heat transfer. In particular, a relevant flow-regime transition for the sizing of heat exchangers is the occurrence of dryout during the evaporation process in the annular-mist flow regime. The objective of this work is to present a three-field model for describing the annular-mist flow considering a liquid film, liquid droplets and a vapor phase, and predicting the occurrence of dryout. The flow structure is affected by the entrainment, deposition and evaporation. These processes are studied on the base of semi-empirical models. The final mathematical model is implemented into an in-house solver. The model is validated with uniform heat flux data available in the open literature. While the model performs well in the case of water flows (within 10% error), the uncertainties are larger for other fluids, probably due to the applicability range of the empirical models. Finally, two numerical examples considering the sensitivity of the input parameters and axial power distribution are studied.

Experimental Study of the Absorption Process of Organic Fluids in a Plate Heat Exchanger

2000 ◽  
Author(s):  
M. Vallès ◽  
M. Bourouis ◽  
D. Boer ◽  
M. Nogués ◽  
A. Coronas ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Cooling Water ◽  
Plate Heat Exchanger ◽  
Absorption Process ◽  
Two Phase ◽  
Plate Heat ◽  
Fluid Mixtures ◽  
Cooling Water Temperature ◽  
Mixing Chamber ◽  
Organic Fluids

Abstract In this paper, the absorption process in a plate heat exchanger with organic fluids has been experimentally investigated. It is well known that the absorber is the key component in absorption systems. The absorber studied consists of an adiabatic mixing chamber and a plate heat exchanger. In the mixing chamber, the solution that is poor in refrigerant is sprayed on the vapor refrigerant. Then, the two-phase mixture that is formed enters into the plate heat exchanger where the absorption process is completed by cooling the solution. Experiments have been performed using the organic fluid mixtures: Methanol-Tetraethyleneglycol dimethylether (TEGDME) and Trifluoroethanol (TFE)-TEGDME. The effect of the solution mass flow rate, the absorber pressure and the cooling water temperature on the absorber performance has been analyzed. The results obtained are discussed in terms of the absorber load, subcooling of the solution at the outlet of the absorber, overall heat transfer coefficient and absorbed mass flux. The information achieved should serve to understand better the absorption process for such mixtures and design an absorber using plate heat exchangers for air conditioning applications.

The Influence of Header Design on Two-Phase Flow Distribution in Plate-Fin Heat Exchangers

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Zhe Zhang ◽  
Sunil Mehendale ◽  
Shengnan Lv ◽  
Hui Yuan ◽  
JinJin Tian
Keyword(s):  
Heat Exchanger ◽  
Water Flow ◽  
Heat Exchangers ◽  
Water Distribution ◽  
Single Phase ◽  
Two Phase Flow ◽  
Flow Distribution ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase

Abstract Fluid flow maldistribution causes deterioration of heat transfer as well as pressure drop penalty in heat exchangers. A test bench was set up to investigate the effect of different header designs on air-water flow distribution in plate-fin heat exchangers (PFHX). Two-phase flow distribution was examined for air Reynolds numbers (ReG) of 28293542 and inlet qualities (x) of 46.3–64.0%. Two-phase flow distribution was seen to be more uneven in the heat exchanger in comparison with single-phase flow, the water distribution being more uneven than that of the air. For a fixed inlet quality, as the air flowrate was increased, the distribution of two-phase flow became increasingly nonuniform, showing a pattern similar to single-phase flow. Furthermore, the air distribution became more even, while the water flow became more unevenly distributed as the inlet quality increased. To mitigate the maldistribution, perforated plates were incorporated in the heat exchanger header. The improved headers significantly aided in distributing the two-phase flow more evenly. At ReG = 2829 and x = 46.3%, the heat exchanger effectiveness was expressed in terms of the unevenness in quality, Sx. The effectiveness decreased as the unevenness of the flow distribution was exacerbated, emphasizing the significance of uniform phase and flow distribution as a key element of heat exchanger design.

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