scholarly journals Concentration Probe Measurements in a Mach 4 Nonreacting Hydrogen Jet

2003 ◽  
Vol 125 (4) ◽  
pp. 628-635 ◽  
Author(s):  
D. R. Buttsworth ◽  
T. V. Jones
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
New Technique ◽  
Stagnation Temperature ◽  
Pitot Pressure ◽  
Different Temperatures ◽  
Probe Measurements

A new probe technique is introduced for the measurement of concentration in binary gas flows. The new technique is demonstrated through application of the probe in a Mach 4 nonreacting jet of hydrogen injected into a nominally quiescent air environment. Previous concentration probe devices have mostly used hot wires or hot films within an aspirating probe tip. However, the new technique relies on Pitot pressure and stagnation point transient thin film heat flux probe measurements. The transient thin film heat flux probes are operated at a number of different temperatures and thereby provide stagnation temperature and heat transfer coefficient measurements with an uncertainty of around ±5 K and ±4% respectively. When the heat transfer coefficient measurements are combined with the Pitot pressure measurements, it is demonstrated that the concentration of hydrogen within the mixing jet can be deduced. The estimated uncertainty of the reported concentration measurements is approximately ±5% on a mass fraction basis.

Noninvasive Method to Measure Thermal Energy Flow Rate in a Pipe

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Mohammed A. Alanazi ◽  
Thomas E. Diller
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Energy ◽  
Thermal Contact ◽  
Heat Flux Sensor ◽  
Accurate Estimation ◽  
Fluid Temperature

Abstract A noninvasive, thermal energy flowrate sensor based on a combination of heat flux and temperature measurements is developed for measuring the volume flowrate and the fluid temperature in a pipe. The sensor is covered by a thin-film heater and clamped onto the outer surface of the pipe. Two types of thin-film thermocouple elements are compared to minimize the thermal contact resistance R″ between the thermocouple and the surface of the pipe. A thin, flexible thermopile heat flux sensor (PHFS) is mounted over the thermocouples. A one-dimensional transient thermal model is applied before and during activation of the external heater to provide estimates of the fluid heat transfer coefficient h. The results are correlated with the volume flowrate Q and the fluid temperature Twc. Several different parameter estimation codes are used to estimate the optimal parameters by using the minimum root-mean-square (rms) error between the analytical and experimental sensor temperature values. The experiments are completed over a range of volume flowrates—1.3 gallons/min to 14.5 gallons/min. Encouraging measurement results give good correlation, repeatability, and sensitivity between the heat transfer coefficient h and the volume flowrate Q with an accurate estimation of the fluid temperature Twc. The resulting noninvasive thermal energy flowrate sensor can be used to estimate the volume flowrate and the fluid temperature in a variety of applications.

scholarly journals Experimental Determination of the Heat Transfer Coefficient of Real Cooled Geometry Using Linear Regression Method

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 180
Author(s):  
Asif Ali ◽  
Lorenzo Cocchi ◽  
Alessio Picchi ◽  
Bruno Facchini
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Linear Regression ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
External Surface ◽  
Internal Surface ◽  
Regression Method ◽  
Thermal Transient

The scope of this work was to develop a technique based on the regression method and apply it on a real cooled geometry for measuring its internal heat transfer distribution. The proposed methodology is based upon an already available literature approach. For implementation of the methodology, the geometry is initially heated to a known steady temperature, followed by thermal transient, induced by injection of ambient air to its internal cooling system. During the thermal transient, external surface temperature of the geometry is recorded with the help of infrared camera. Then, a numerical procedure based upon a series of transient finite element analyses of the geometry is applied by using the obtained experimental data. The total test duration is divided into time steps, during which the heat flux on the internal surface is iteratively updated to target the measured external surface temperature. The final procured heat flux and internal surface temperature data of each time step is used to find the convective heat transfer coefficient via linear regression. This methodology is successfully implemented on three geometries: a circular duct, a blade with U-bend internal channel, and a cooled high pressure vane of real engine, with the help of a test rig developed at the University of Florence, Italy. The results are compared with the ones retrieved with similar approach available in the open literature, and the pros and cons of both methodologies are discussed in detail for each geometry.

Theoretical Analysis of Thin Film Evaporation in the Wicks of Loop Heat Pipes

2021 ◽  
pp. 1-14
Author(s):  
Bingyao Lin ◽  
Nanxi Li ◽  
Shiyue Wang ◽  
Leren Tao ◽  
Guangming Xu ◽  
...  
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pore Size ◽  
Momentum Conservation ◽  
Loop Heat Pipes ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Quantity Of Heat

Abstract In this paper, a thin film evaporation model that includes expressions for energy, mass and momentum conservation was established through the augmented Young-Laplace model. Based on this model, the effects of pore size and superheating on heat transfer during thin film evaporation were analyzed. The influence of the wick diameter of the loop heat pipe (LHP) on the critical heat flux of the evaporator is analyzed theoretically. The results show that pore size and superheating mainly influence evaporation through changes in the length of the transition film and intrinsic meniscus. The contribution of the transition film area is mainly reflected in the heat transfer coefficient, and the contribution of the intrinsic meniscus area is mainly apparent in the quantity of heat that is transferred. When an LHP evaporator is operating in a state of surface evaporation, a higher heat transfer coefficient can be achieved using a smaller pore size.

Heat Transfer Coefficient Characterization for Large Aspect-Ratio Thin Films in Film-Riding Seals

2018 ◽  
Author(s):  
James A. Tallman ◽  
Rahul A. Bidkar
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Thin Films ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Test Data ◽  
Face Seal ◽  
Cfd Model ◽  
Low Leakage

Low-leakage film-riding seals are a key enabling technology for utility-scale supercritical carbon dioxide (sCO2) power cycles. Fluid film-riding rotor-stator seals (operating with sCO2 as the working fluid) are designed to track rotor movements and provide effective sealing by maintaining a tight operating clearance (of the order of several microns) from the spinning rotor. Thin film-riding seals generate viscous shear heat during high-speed operation, and the reliable operation of such thin-film seals depends critically on the designer’s ability to control the thermal deformations of the seal/rotor bearing face, which in turn are tied to the designer’s ability to understand and predict the heat transfer across the seal bearing face. In this paper, we develop a simple axisymmetric thermal-mechanical model of a typical face seal to highlight how the uncertainty in heat transfer coefficient (HTC) on the seal bearing face drives uncertainty in seal deformation predictions, especially when the HTCs are an order of magnitude lower than those predicted with duct-based Dittus-Boelter correlations. This uncertainty in seal bearing face HTCs drives the need for an experimental quantification of HTCs in high-aspect ratio thin films associated with low-leakage film-riding seals. In this paper, we describe a non-rotating experimental test rig designed for estimating the HTCs on the seal bearing face using a shim-heater technique along with IR-camera-based temperature measurements. The experimental set-up consists of a thin metal shim (representing the seal bearing face) forming one wall of a pressurized duct with geometric similarity to a typical thin film of a face seal. Pressurized airflow past the shim is used to simulate the flow field expected in a non-rotating seal. The HTC test data for a non-rotating film (as against the actual seal film with rotating fluid) are lower than the actual seal, and establish a lower bound on the HTCs. This is especially useful for bounding the seal deformation uncertainty, which is vulnerable to the HTCs in the low-HTC regime. We present representative test data that is non-dimensionalized using radial-flow-based Reynolds number and compare these HTC estimates both with the predictions of Dittus-Boelter type correlations, and with the predictions of a 3D computational fluid dynamics (CFD) model. The purpose of the CFD model is to develop a HTC prediction tool for such thin-film surfaces, and the test data are used for validating this predictive model.

Numerical Simulation of Convective Heat Transfer in a Spark Ignition Engine

2008 ◽  
Author(s):  
Arash Mohammadi ◽  
Seyed Ali Jazayeri ◽  
Masoud Ziabasharhagh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Combustion Chamber ◽  
Spark Ignition Engine ◽  
Cylinder Wall ◽  
Single Cylinder Engine ◽  
Crank Angle ◽  
Exhaust Valves

A computational fluid dynamics code is applied to simulate fluid flow and combustion in a four-stroke single cylinder engine with flat combustion chamber geometry. Heat flux and heat transfer coefficient on the cylinder head, cylinder wall, piston, intake and exhaust valves are determined. Result for a certain condition is compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurement in the literature and close agreement is observed. It is observed that the value of heat flux and heat transfer coefficient varies considerably in different positions of the combustion chamber, but the trend with crank angle is almost the same.

Nanoparticle aggregation kinematics on the quadratic convective magnetohydrodynamic flow of nanomaterial past an inclined flat plate with sensitivity analysis

2021 ◽  
pp. 095440892110562
Author(s):  
AS Sabu ◽  
Joby Mackolil ◽  
B Mahanthesh ◽  
Alphonsa Mathew
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Sensitivity Analysis ◽  
Heat Transfer Coefficient ◽  
Heat Source ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Inclined Plate ◽  
The Impact ◽  
The Heat Transfer Coefficient

The study focuses on the aggregation kinematics in the quadratic convective magneto-hydrodynamics of ethylene glycol-titania ([Formula: see text]) nanofluid flowing through an inclined flat plate. The modified Krieger-Dougherty and Maxwell-Bruggeman models are used for the effective viscosity and thermal conductivity to account for the aggregation aspect. The effects of an exponential space-dependent heat source and thermal radiation are incorporated. The impact of pertinent parameters on the heat transfer coefficient is explored by using the Response Surface Methodology and Sensitivity Analysis. The effects of several parameters on the skin friction and heat transfer coefficient at the plate are displayed via surface graphs. The velocity and thermal profiles are compared for two physical scenarios: flow over a vertical plate and flow over an inclined plate. The nonlinear problem is solved using the Runge–Kutta-based shooting technique. It was found that the velocity profile significantly decreased as the inclination of the plate increased on the other hand the temperature profile improved. The heat transfer coefficient decreased due to the increase in the Hartmann number. The exponential heat source has a decreasing effect on the heat flux and the angle of inclination is more sensitive to the heat transfer coefficient than other variables. Further, when radiation is incremented, the sensitivity of the heat flux toward the inclination angle augments at the rate 0.5094% and the sensitivity toward the exponential heat source augments at the rate 0.0925%. In addition, 41.1388% decrement in wall shear stress is observed when the plate inclination is incremented from [Formula: see text] to [Formula: see text].

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