scholarly journals An experimental study of flow boiling heat transfer of zeotropic mixture R32/R134a in a microchannel heat exchanger

2021 ◽  
Vol 2119 (1) ◽  
pp. 012072
Author(s):  
A. S. Shamirzaev
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Flow Boiling ◽  
Initial Mixture ◽  
Working Fluid ◽  
Absolute Pressure ◽  
Space Technology ◽  
Microchannel Heat Exchanger ◽  
Zeotropic Mixture

Abstract This paper presents experimental data on heat transfer of a binary zeotropic mixture of refrigerants R32/R134a in a microchannel heat exchanger with a high specific surface within a range of parameters that is practically important for the development of cooling systems for microelectronics and space technology. The experiments were carried out in a horizontal heat exchanger with one-sided heating of a copper microchannel plate 20x40 mm, containing 21 rectangular microchannels with a cross-section of 335x930 μm, within the range of mass fluxes from 80 to 250 kg/m2s, and at an absolute pressure in the system ranged from 12 to 14 bar. A zeotropic mixture of refrigerants R32/R134a with a molar concentration of the initial mixture of 65%/35% was used as a working fluid. Experimental data were compared with model-based calculations that take into account the influence of changes in the concentrations of components in the liquid and gas phases.

Visualization of FC-72 Flow Boiling in Parallel- and Counter-Flow Plate Heat Exchangers

2014 ◽  
Author(s):  
Kohei Koyama ◽  
Yuya Nakamura ◽  
Hirofumi Arima
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Flow Pattern ◽  
Void Fraction ◽  
Flow Boiling ◽  
Plate Heat Exchanger ◽  
Parallel Flow ◽  
Working Fluid ◽  
Counter Flow ◽  
Plate Heat

This study investigates FC-72 (Perfluorohexane) flow boiling in a plate heat exchanger. A plate heat exchanger which has a transparent cover plate is manufactured to visualize boiling two-phase flow pattern of the working fluid FC-72 heated by hot water. Titanium is used for heat transfer plate, which has micro pin-fin structure on the heat transfer surface to enhance heat transfer. Experiment is conducted for parallel- and counter-flow arrangements to compare thermal and hydraulic performances. Flow boiling is photographed by a digital camera and instantaneous images are processed to classify flow pattern and to measure void fraction in the heat exchanger. Flow rates and temperatures of FC-72 and hot water at inlet and outlet of the heat exchanger are simultaneously measured to obtain overall heat transfer coefficient. Two-phase flow pattern of FC-72 flow boiling and void fraction along flow direction as well as thermal performance are discussed. Experimental results show that bubbly flow, slug flow, and churn flow are observed for the experimental range of this study. Extent of churn flow in the parallel-flow heat exchanger is larger than that of the counter-flow one due to generated bubbles at upstream region in working fluid channel. Void fraction of the parallel-flow plate heat exchanger increases rapidly compared with that of the counter-flow one due to location of onset of nucleate boiling. Overall heat transfer coefficients for the parallel-flow arrangement is larger than that of the counter-flow due to destruction of thermal boundary layer. The experimental results show that flow arrangement of a plate heat exchanger has the potential to improve its thermal performance.

A Numerical Study of Flow Boiling Heat Transfer of Nanoemulsion in Mini-Channel Heat Exchanger

2018 ◽  
Author(s):  
Jiajun Xu ◽  
Musa Acar ◽  
Naresh Poudel ◽  
Jaime Rios ◽  
Thanh N. Tran
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Boiling Heat Transfer ◽  
Single Phase ◽  
Numerical Study ◽  
Flow Boiling ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Vof Model ◽  
Flow Boiling Heat Transfer

In this study, a numerical study has been performed on the two-phase heat transfer of a new nanostructured heat transfer fluid: Water-in-Polyalphaolefin (PAO) Nanoemulsion Fluid inside a mini-channel heat exchanger using ANSYS FLUENT. Nanoemulsion fluids are liquid suspensions of nanosized droplets, which are part of a broad class of colloidal dispersions. The nanoemulsion fluid can be formed spontaneously by self-assembly, in which these nanodroplets are in fact swollen micelles. To simplify the complexity of the numerical model, the nanoemulsion fluid was then treated as a homogenous fluid during single-phase and only the water vaporizes during the phase change. The volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to solve the continuity, momentum, energy equations in two dimensional domains. The thermophysical properties of the nanoemulsion fluid were measured and used for the current simulation. The results were verified using the experimental results and has shown good agreement. This study has demonstrated the feasibility of simplyig the simulation of flow boiling heat transfer of this new heat transfer fluid through treating it as a homogenous fluid during single-phase convective heat transfer and separating the vapor phase of the nano-micelles during flow boiling. This study has also shown that this Water-in-PAO nanoemulsion could function as a good and alternative conventional working fluid in heat transfer applications.

Heat Exchange Characteristics of a Gas-Gas Counterflow Microchannel Heat Exchanger

2008 ◽  
Author(s):  
K. Koyama ◽  
Y. Asako
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Transfer Rate ◽  
Rectangular Cross Section ◽  
Working Fluid ◽  
Partition Wall ◽  
Transfer Rates ◽  
Pressure Losses ◽  
Microchannel Heat Exchanger

Heat exchange characteristics of a gas-gas counterflow microchannel heat exchanger have been investigated experimentally. The microchannel has a rectangular cross section with 200 μm high and 300 μm wide. Working fluid is air. Reynolds number in the hot passage ranges from 127 to 381, and that in the cold passage ranges from 25 to 381. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure losses. The heat exchange and the pressure loss characteristics of the tested microchannel heat exchanger are discussed. Since the partition wall of the heat exchanger is thick comparing with the microchannel dimensions, a simple heat exchange model, the wall temperature of which is constant, is proposed to predict the heat transfer rate. The predicted heat transfer rates are compared with those of the experimental results and both results agree well.

scholarly journals Experimental analysis and ANN prediction on performances of finned oval-tube heat exchanger under different air inlet angles with limited experimental data

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 968-980
Author(s):  
Xueping Du ◽  
Zhijie Chen ◽  
Qi Meng ◽  
Yang Song
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Correlation Equation ◽  
Tube Heat Exchanger ◽  
Flow Friction ◽  
Air Inlet ◽  
Comparison Results ◽  
Wide Range ◽  
Oval Tube

Abstract A high accuracy of experimental correlations on the heat transfer and flow friction is always expected to calculate the unknown cases according to the limited experimental data from a heat exchanger experiment. However, certain errors will occur during the data processing by the traditional methods to obtain the experimental correlations for the heat transfer and friction. A dimensionless experimental correlation equation including angles is proposed to make the correlation have a wide range of applicability. Then, the artificial neural networks (ANNs) are used to predict the heat transfer and flow friction performances of a finned oval-tube heat exchanger under four different air inlet angles with limited experimental data. The comparison results of ANN prediction with experimental correlations show that the errors from the ANN prediction are smaller than those from the classical correlations. The data of the four air inlet angles fitted separately have higher precisions than those fitted together. It is demonstrated that the ANN approach is more useful than experimental correlations to predict the heat transfer and flow resistance characteristics for unknown cases of heat exchangers. The results can provide theoretical support for the application of the ANN used in the finned oval-tube heat exchanger performance prediction.

Augmented Performance of Flow Boiling Heat Transfer in a Tube With Axial Micro-Grooves and its Augmentation Mechanisms

1999 ◽  
Author(s):  
Lixin Cheng ◽  
Tingkuan Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Axial Direction ◽  
Smooth Tube ◽  
Absolute Pressure ◽  
Transfer Coefficients ◽  
Frictional Pressure Drop ◽  
Flow Boiling Heat Transfer ◽  
Enhanced Tube

Abstract Experiments of upward flow boiling heat transfer with water in a vertical smooth tube and a tube with axial micro-grooves were respectively conducted. Both of the tested tubes have a length of 2.5 m, an inner diameter of 15 mm and an outlet diameter of 19 mm. The tube with axial micro grooves has many micro rectangle grooves in its inner wall along the axial direction. The grooves have a depth of 0.5 mm and a width of 0.3 mm. The tests were performed at an absolute pressure of 6 bar. The heat flux ranged from 0 to 550 kW/m2 and the mass flux was selected at 410, 610 and 810 kg/m2s, respectively. By comparison, flow boiling heat transfer coefficients in the enhanced tube are 1.6 ∼ 2.7 fold that in the smooth tube while the frictional pressure drop in the enhanced tube is slightly greater than that in the smooth tube. The augmentation of flow boiling heat transfer in the tube with axial micro-grooves is apparent. Based on the experimental data, a correlation of flow boiling heat transfer is proposed for the enhanced tube. Finally, the mechanisms of heat transfer enhancement are analyzed.

Flow Boiling Heat Transfer of HFO-1234yf in a Plate-fin Heat Exchanger with Plain Fins

2021 ◽  
Vol 25 (4) ◽  
pp. 87-92
Author(s):  
Chang-Hyo Son ◽  
Jeong-In Yoon ◽  
Sung-Hoon Seol ◽  
Dong-Ik Kang
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Boiling Heat Transfer

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

2012 ◽  
Author(s):  
Lorenzo Cremaschi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Phase ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.

Heat Transfer Coefficient Measurement for Downward-Facing Heat Transfer on Curved Rectangular Water Channel

2016 ◽  
Author(s):  
Jun Yeong Jung ◽  
Yong Hoon Jeong
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Flow Boiling ◽  
Water Channel ◽  
Outer Wall ◽  
Reactor Vessel ◽  
Working Fluid ◽  
Heater Surface ◽  
Ir Camera ◽  
Lower Head

In-Vessel Retention by External Reactor Vessel Cooling (IVR-ERVC) is method of removing the decay heat by cooling reactor vessel after corium relocation, and is also one of severe accident management strategies. Estimating heat transfer coefficients (HTCs) is important to evaluate heat transfer capability of the ERVC. In this study, the HTCs of outer wall of reactor vessel lower head were experimentally measured under the IVR-ERVC situation of Large Loss of Coolant Accident (LLOCA) condition. Experimental equipment was designed to simulate flow boiling condition of ERVC natural circulation, and based on APR+ design. This study focused on effects of real reactor vessel geometry (2.5 m of radius curvature) and material (SA508) for the HTCs. Curved rectangular water channel (test section) was design to simulate water channel which is between the reactor vessel lower head outer wall and thermal insulator. Radius curvature, length, width and gap size of the test section were respectively 2.5 m, 1 m, 0.07 m and 0.15 m. Two connection parts were connected at inlet and outlet of the test section to maintain fluid flow condition, and its cross section geometry was same with one of test section. To simulate vessel lower head outer wall, thin SA508 plate was used as main heater, and test section supported the main heater. Thickness, width, length and radius curvature of the main heater were 1.2 mm, 0.07 m, 1 m and 2.5 m respectively. The main heater was heated by DC rectifier, and applied heat flux was under CHF value. The test section was changed for each experiment. The HTCs of whole reactor vessel lower head (bottom: 0 ° and top: 90 °) were measured by inclining the test section, and experiments were conducted at four angular ranges; 0–22.5, 22.5–45, 45–67.5 and 67.5–90 °. DI water was used as working fluid in this experiment, and all experiments were conducted at 400 kg/m2s of constant mass flux with atmospheric pressure. The working fluid temperatures were measured at two point of water loop by K-type thermocouple. The main heater surface temperatures were measured by IR camera. The main heater was coated by carbon spray to make uniform surface emissivity, and the IR camera emissivity calibration was also conducted with the coated main heater. The HTCs were calculated by measured main heater surface temperature. In this research, the HTC results of 10, 30, 60 and 90 ° inclination angle were presented, and were plotted with wall super heat.

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