scholarly journals Heat Transfer Coefficient Determination during FC-72 Flow in a Minichannel Heat Sink Using the Trefftz Functions and ADINA Software

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6647
Author(s):  
Magdalena Piasecka ◽  
Beata Maciejewska ◽  
Paweł Łabędzki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Transfer Problem ◽  
Heat Transfer Problem ◽  
Heated Wall ◽  
Inlet Temperature ◽  
Transfer Coefficients ◽  
Flowing Fluid

This work focuses on subcooled boiling heat transfer during flow in a minichannel heat sink with three or five minichannels of 1 mm depth. The heated element for FC-72 flowing along the minichannels was a thin foil of which temperature on the outer surface was measured due to the infrared thermography. The test section was oriented vertically or horizontally. A steady state heat transfer process and a laminar, incompressible flow of the fluid in a central minichannel were assumed. The heat transfer problem was described by the energy equations with an appropriate system of boundary conditions. Several mathematical methods were applied to solve the heat transfer problem with the Robin condition to determine the local heat transfer coefficients at the fluid/heated foil interface. Besides the 1D approach as a simple analytical method, a more sophisticated 2D approach was proposed with solutions by the Trefftz functions and ADINA software. Finite element method (FEM) calculations were conducted to find the temperature field in the flowing fluid and in the heated wall. The results were illustrated by graphs of local heated foil temperature and transfer coefficients as a function of the distance from the minichannel inlet. Temperature distributions in the heater and the fluid obtained from the FEM computations carried out by ADINA software were also shown. Similar values of the heat transfer coefficient were obtained in both the FEM calculations and the 1D approach. Example boiling curves indicating nucleation hysteresis are shown and discussed.

Meshless Local Petrov-Galerkin Method for Heat Transfer Analysis

2013 ◽  
Author(s):  
Singiresu S. Rao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Transfer Problem ◽  
Radiation Heat Transfer ◽  
Heat Transfer Problem ◽  
Radiation Heat ◽  
Mlpg Method ◽  
Transfer Problems

A meshless local Petrov-Galerkin (MLPG) method is proposed to obtain the numerical solution of nonlinear heat transfer problems. The moving least squares scheme is generalized, to construct the field variable and its derivative continuously over the entire domain. The essential boundary conditions are enforced by the direct scheme. The radiation heat transfer coefficient is defined, and the nonlinear boundary value problem is solved as a sequence of linear problems each time updating the radiation heat transfer coefficient. The matrix formulation is used to drive the equations for a 3 dimensional nonlinear coupled radiation heat transfer problem. By using the MPLG method, along with the linearization of the nonlinear radiation problem, a new numerical approach is proposed to find the solution of the coupled heat transfer problem. A numerical study of the dimensionless size parameters for the quadrature and support domains is conducted to find the most appropriate values to ensure convergence of the nodal temperatures to the correct values quickly. Numerical examples are presented to illustrate the applicability and effectiveness of the proposed methodology for the solution of heat transfer problems involving radiation with different types of boundary conditions. In each case, the results obtained using the MLPG method are compared with those given by the FEM method for validation of the results.

scholarly journals The heat transfer coefficient determination with the use of the Beck-Trefftz method in flow boiling in a minichannel

2018 ◽  
Vol 180 ◽  
pp. 02099 ◽  
Author(s):  
Kinga Strąk ◽  
Beata Maciejewska ◽  
Magdalena Piasecka
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Transfer Problem ◽  
Heat Conduction Problem ◽  
Flow Boiling ◽  
Inverse Heat Conduction Problem ◽  
Heated Wall ◽  
Trefftz Method

In this paper, the solution of the two-dimensional inverse heat transfer problem with the use of the Beck method coupled with the Trefftz method is proposed. This method was applied for solving an inverse heat conduction problem. The aim of the calculation was to determine the boiling heat transfer coefficient on the basis of temperature measurements taken by infrared thermography. The experimental data of flow boiling heat transfer in a single vertical minichannel of 1.7 mm depth, heated asymmetrically, were used in calculations. The heating element for two refrigerants (FC-72 and HFE-7100, 3M) flowing in the minichannel was the plate enhanced on the side contacting with the fluid. The analysis of the results was performed on the basis of experimental series obtained for the same heat flux and two different mass flow velocities. The results were presented as infrared thermographs, heated wall temperature and heat transfer coefficient as a function of the distance from the minichannel inlet. The results was discussed for the subcooled and saturated boiling regions separately.

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.

Flow Boiling of Refrigerants Inside a Single Circular Minichannel

2008 ◽  
Author(s):  
Stefano Bortolin ◽  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Test Tube ◽  
Inlet Temperature ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

The present paper reports the heat transfer coefficients measured during flow boiling of HFC-32 and HFC-134a in a 0.96 mm diameter single circular channel. The test runs have been performed during vaporization at around 30°C saturation temperature, correspondent to 19.3 bar for R32 and 7.7 bar for R134a. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. The quality of the inner surface of the test tube has been measured to check the influence of surface roughness on the heat transfer coefficient. The flow boiling data taken in the present test section is presented and discussed, with particular regard to the effect of heat flux, mass velocity, vapor quality and fluid properties.

scholarly journals Time-Dependent Heat Transfer Calculations with Trefftz and Picard Methods for Flow Boiling in a Mini-Channel Heat Sink

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1832
Author(s):  
Magdalena Piasecka ◽  
Sylwia Hożejowska ◽  
Beata Maciejewska ◽  
Anna Pawińska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Time Dependent ◽  
Heated Wall ◽  
Trefftz Method ◽  
Mini Channels ◽  
The Heat Transfer Coefficient

The intensification of heat transfer using two-phase boiling flow in mini-channels is widely used to dissipate the high heat fluxes in miniaturized electronic devices. However, the process itself is not fully recognized and still requires experimental studies and developing computation methods appropriate for them. The main aim of this work was the mathematical modeling of time-dependent heat transfer process in FC-72 flow boiling in a mini-channel heat sink with five parallel mini-channels of 1 mm depth. Channels have an asymmetrically heated wall while its outer temperature was measured by infrared thermography. The opposite wall of the mini-channels was transparent, helping to record flow patterns due to a high-speed digital camera. The objective of the numerical calculations was to determine the heat transfer coefficient on the wall-fluid contact surface from the Robin boundary condition. The problem was solved using methods based on the Trefftz-type functions. Three mathematical methods were applied in calculations: the FEM with Trefftz type basis functions, the Classical Trefftz Method, and the Hybrid Picard-Trefftz Method. The results were compared with the values of the heat transfer coefficient obtained from theoretical correlations from the literature.

scholarly journals COMPARATIVE ANALYSES OF THE THERMAL PERFORMANCE OF REFRIGERANTS R134A, R245fa, R407C AND R600a DURING FLOW BOILING IN A MICROCHANNELS HEAT SINK

2018 ◽  
Vol 17 (2) ◽  
pp. 57
Author(s):  
H. L. S. L. Leão ◽  
D. B. Marchetto ◽  
G. Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A comparative study of the performance of of refrigerants R134a, R407C, R245fa and R600a during flow boiling was performed for a 123x494 µm2 heat sink composed of 50 parallel rectangular microchannels. Heat transfer experimental results for heat fluxes up to 310 kW/m2, mass velocities from 300 to 800 kg/(m2 s), liquid subcoolings of 5 and 10 °C and saturation temperature close to 30 ºC were obtained. Global heat transfer coefficients (footprint) up to 10 kW/(m2 °C) were found. The liquid superheating necessary for the onset of nucleate boiling (ONB) was also characterized, and the fluids R245fa and R407C presented the highest and lowest, respectively, superheating to trigger the boiling process. Moreover, for a fixed averaged vapor quality, the average effective heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The refrigerants R600a and R407C presented the highest and the lowest heat transfer coefficients, respectively. Five heat transfer predictive methods from literature provided accurate predictions of the data for R134a, R245fa and R600a, capturing most of the data trends. No one method provided accurate predictions of the heat transfer coefficient data of R407C.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

scholarly journals Adiabatic Effectiveness and Heat Transfer Coefficient of Shaped Film Cooling Holes on a Scaled Guide Vane Pressure Side Model

2004 ◽  
Vol 10 (5) ◽  
pp. 345-354 ◽  
Author(s):  
Jan Dittmar ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Guide Vane ◽  
Inlet Temperature ◽  
Test Model ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

The demand of improved thermal efficiency and high power output of modern gas turbine engines leads to extremely high turbine inlet temperature and pressure ratios. Sophisticated cooling schemes including film cooling are widely used to protect the vanes and blades of the first stages from failure and to achieve high component lifetimes. In film cooling applications, injection from discrete holes is commonly used to generate a coolant film on the blade's surface.In the present experimental study, the film cooling performance in terms of the adiabatic film cooling effectiveness and the heat transfer coefficient of two different injection configurations are investigated. Measurements have been made using a single row of fanshaped holes and a double row of cylindrical holes in staggered arrangement. A scaled test model was designed in order to simulate a realistic distribution of Reynolds number and acceleration parameter along the pressure side surface of an actual turbine guide vane. An infrared thermography measurement system is used to determine highly resolved distribution of the models surface temperature. Anin-situcalibration procedure is applied using single embedded thermocouples inside the measuring plate in order to acquire accurate local temperature data.All holes are inclined 35° with respect to the model's surface and are oriented in a streamwise direction with no compound angle applied. During the measurements, the influence of blowing ratio and mainstream turbulence level on the adiabatic film cooling effectiveness and heat transfer coefficient is investigated for both of the injection configurations.

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