Experimental Analysis of Gas Flow Forced Convection in Microtubes

2011 ◽  
Author(s):  
Gian Luca Morini ◽  
Yahui Yang ◽  
Habib Chalabi ◽  
Marco Lorenzini
Keyword(s):  
Cross Sections ◽  
Experimental Analysis ◽  
Gas Flow ◽  
Bulk Temperature ◽  
Gas Flows ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Axial Heat ◽  
The Right

This paper deals with the experimental analysis of forced micro-convection features of heated gas flows through commercial stainless steel microtubes having an inner diameter of 172 μm and 500 μm. The experimental results, in terms of Nusselt numbers, are compared to the classical correlations validated for conventional pipes and to the correlations proposed for gas flows through microtubes under laminar and transitional conditions (Re ∈ [400–3500]). The cross sections of the tested microtubes enabled the analysis of the effects of wall axial heat conduction on the Nusselt number which determines a dependence of the convective heat transfer coefficients on the Reynolds number even in the laminar regime, especially for low inner diameters. It is highlighted in the paper that the effects due to overall heat losses, to viscous dissipation and the problems in the right determination of the axial gas bulk temperature distribution cannot be ignored in the thermal analysis of gas flows through microtubes.

The Rules of Single-Phase Forced Convection in Microchannels

2012 ◽  
Author(s):  
Gian Luca Morini
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Gas Flows ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Liquid Flows ◽  
The University ◽  
Convective Heat Transfer Coefficients

This paper deals with the experimental analysis of forced micro-convection features of liquid and gas flows through microchannels. An overview of the main effects that tends to play an important role on the determination of the Nusselt numbers in microchannels is presented. Some experimental data obtained at the Microfluidics Lab of the University of Bologna together with the main results appeared recently in the open literature are used in order to highlight the characteristics of the convective heat transfer through microchannels with inner diameter from 0.75 mm down to and 0.15 mm. It is shown that the behavior of gas and liquid flows through microchannels in terms of convective heat transfer coefficients can be strongly affected by scaling and micro-effects as by practical issues linked to the geometry of the test rig, fittings, position of the sensors and so on. It is demonstrated that the comparison with the conventional correlations for the prediction of the convective heat transfer coefficients gives good results only if one has verified beforehand that the main scaling and micro-effects are negligible.

Heat Transfer in a Surfactant Drag-Reducing Solution—A Comparison With Predictions for Laminar Flow

2005 ◽  
Vol 128 (6) ◽  
pp. 557-563 ◽  
Author(s):  
Paul L. Sears ◽  
Libing Yang
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Drag Reducing Additive ◽  
Good Agreement

Heat transfer coefficients were measured for a solution of surfactant drag-reducing additive in the entrance region of a uniformly heated horizontal cylindrical pipe with Reynolds numbers from 25,000 to 140,000 and temperatures from 30to70°C. In the absence of circumferential buoyancy effects, the measured Nusselt numbers were found to be in good agreement with theoretical results for laminar flow. Buoyancy effects, manifested as substantially higher Nusselt numbers, were seen in experiments carried out at high heat flux.

scholarly journals Heat Transfer Measurements for Rotating Turbine Discs

1989 ◽  
Author(s):  
G. Qureshi ◽  
M. H. Nguyen ◽  
N. R. Saad ◽  
R. N. Tadros
Keyword(s):  
Heat Transfer ◽  
Coolant Flow ◽  
Flow Conditions ◽  
Transfer Coefficients ◽  
Rotating Disc ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Rotating Discs ◽  
Turbine Disc ◽  
State Technique

To optimise the turbine disc weight and coolant flow requirements, the aspect of improving thermal analysis was investigated. As a consequence, an experimental investigation was undertaken to measure the rates of convective heat transfer. The constant temperature steady state technique was used to determine the local and average heat transfer coefficients on the sides of rotating discs. The effects of coolant flow rates, CW (3000 ≤ CW ≤ 18600) with two types of cavity in-flow conditions and of the rotational speeds, Reθ (from 4×105 to 1.86×106) on the disc heat transfer were studied and correlations developed. For a rotating disc in confined cavities with superimposed coolant flows, Nusselt numbers were found to be higher than those for the free rotating disc without confinement.

Prediction of Heat Transfer Coefficients in Gas Flow Normal to Finned and Smooth Tube Banks

1981 ◽  
Vol 103 (4) ◽  
pp. 705-714 ◽  
Author(s):  
J. C. Biery
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Finned Tube ◽  
Smooth Tube ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Tube Banks

A new method is presented to predict heat transfer coefficients for gas flow normal to smooth and finned tube tanks with triangular pitch. A transformation from the actual tube bank to an equivalent equilateral triangular pitch infinite smooth tube bank (ETP-I-STB) is made. A function of Ch(Ch = NSTNPR2/3NRe0.4) versus (Xt D0)Δ, ratio of transverse pitch to tube diameter for the ETP-I-STB, was developed. The Ch for the equivalent ETP-I-STP then applies to the actual tube bank. The method works with circular finned tubes, smooth tubes, continuous finned tubes, and segmented finned tubes with any triangular pitch. Also, fair predictions were made for in-line tubes with high Reynolds numbers.

Conditions for Equivalency of Countercurrent Vessel Heat Transfer Formulations

1999 ◽  
Vol 121 (5) ◽  
pp. 514-520 ◽  
Author(s):  
R. B. Roemer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Bulk Temperature ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients ◽  
The Difference ◽  
Convective Heat Transfer Coefficients

Previous models of countercurrent blood vessel heat transfer have used one of two, different, equally valid but previously unreconciled formulations, based either on: (1) the difference between the arterial and venous vessels’ average wall temperatures, or (2) the difference between those vessels’ blood bulk fluid temperatures. This paper shows that these two formulations are only equivalent when the four, previously undefined, “convective heat transfer coefficients” that are used in the bulk temperature difference formulation (two coefficients each for the artery and vein) have very specific, problem-dependent relationships to the standard convective heat transfer coefficients. (The average wall temperature formulation uses those standard coefficients correctly.) The correct values of these bulk temperature difference formulation “convective heat transfer coefficients” are shown to be either: (1) specific functions of (a) the tissue conduction resistances, (b) the standard convective heat transfer coefficients, and (c) the independently specified bulk arterial, bulk venous and tissue temperatures, or (2) arbitrary, user defined values. Thus, they are generally not equivalent to the standard convective heat transfer coefficients that are regularly used, and must change values depending on the blood and tissue temperatures. This dependence can significantly limit the convenience and usefulness of the bulk temperature difference formulations.

Experimental Analysis of the Pool Boiling Phenomenon of Sugarcane Juice

2015 ◽  
Vol 789-790 ◽  
pp. 489-495 ◽  
Author(s):  
Daniel Marcelo ◽  
Paul Villar Yacila ◽  
Raúl La Madrid Olivares
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Experimental Analysis ◽  
Electrical Power ◽  
Power Input ◽  
Sugarcane Juice ◽  
Middle Level ◽  
Transfer Coefficients ◽  
Combustion Gases ◽  
Heat Transfer Coefficients

In Peru, jaggery making process has low energy efficiency and it is due to low heat transfer coefficients for natural convection linked to the sugar cane movement generated by the heat exchange between the sugarcane juice and the combustion gases. This low heat transfer coefficients are caused by improper heat exchangers designs. In this work, is performed an experimental analysis that consist in supplie heat to a pot containing sugarcane juice using a hot plate of constant electrical power. This study consist in identify boiling regimes and estimate the heat transfer coefficients linked to natural convection boiling, measuring: (i) the temperature at the bottom of the pot (ii) the temperature at the bottom level of sugarcane juice (iii) the temperature at middle level of sugarcane juice (iv) the temperature at free surface of sugarcane juice (v) rate of water evaporated. The method of linear regression and the correlation of Rohsenow were used for obtaining the values of the heat transfer coefficients ranging from 4088.6 W/m2°C to 12592.8 W/m2°C with power input ranging from 700W to 1300W.

Rotor Cavity Flow and Heat Transfer With Inlet Swirl and Radial Outflow of Cooling Air

1992 ◽  
Author(s):  
F. W. Staub
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Crystal Surface ◽  
Ambient Pressure ◽  
Swirl Flow ◽  
Scale Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Inlet Swirl ◽  
Radial Outflow

To improve the reliability of turbine disc life prediction, experimental verification is required of analytical tools that calculate the flow field and heat transfer coefficients in turbine-stator cavities. As a first step, a full-scale model of the forward cavity of a typical aircraft gas turbine was employed using a high-molecular-weight gas (Refrigerant-12) at ambient pressure and temperature conditions to match the dimensionless parameters at engine conditions. The cavity temperature and selected cavity velocity profiles were measured using electrical heat addition with liquid crystal surface temperature measurement to obtain local disc heat transfer coefficients. A part of the cooling gas flow was added through a rotating inner seal with the remainder added at high angular swirl in the direction of rotation at a larger radius. Rotational Reynolds numbers were varied up to 9×106 with the radial Reynolds number variation up to 9000. A first-order comparison is given of the velocity distribution and disc heat transfer coefficients calculated by a CFD code and the measured values. The disc heat transfer coefficients can be dominated by the inlet swirl flow or by the rotor speed, depending on whether the coolant flow is greater or smaller than that generated by the rotor alone acting as a free disc.

Effects of Channel Height and Bulk Temperature Considerations on Heat Transfer Coefficient of Wetted Surfaces in a Single Inline Row Impingement Channel

2008 ◽  
Author(s):  
Mark Ricklick ◽  
Stephanie Kersten ◽  
V. Krishnan ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Side Wall ◽  
Bulk Temperature ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Jet Impact ◽  
Side Walls

High performance turbine airfoils are typically cooled with a combination of internal cooling channels and impingement/film cooling. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients. However, little work has been done in examining effects on the channel side walls, which may be a major contributor to heat transfer in real world applications. This paper examines the local and averaged effects of channel height and on heat transfer coefficients, with special attention given to the channel side walls. The effects on heat transfer results due to bulk temperature variations were also investigated. High resolution local heat transfer coefficient distributions on target and side wall surfaces were measured using temperature sensitive paint and recorded via a scientific grade charge-coupled device (CCD) camera. Streamwise pressure distributions for both the target and side walls was recorded and used to explain heat transfer trends. Results are presented for average jet based Reynolds numbers between 17,000 and 45,000. All experiments were carried out on a large scale single row, 15 hole impingement channel, with X/D of 5, Y/D of 4, and Z/D of 1, 3 and 5. The results obtained from this investigation will aid in the validation of predictive tools and development of physics-based models.

Effect of Heater Configurations on Transient Heat Transfer for Various Gases Flowing Over a Twisted Heater

2009 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Generation ◽  
Gas Flow ◽  
Generation Rate ◽  
Transient Heat Transfer ◽  
Heat Generation Rate ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Forced convection transient heat transfer coefficients were measured for helium gas and carbon dioxide gas flowing over a twisted heater due to exponentially increasing heat input (Q0exp(t/τ)). The twisted platinum plate with a thickness of 0.1 mm was used as test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q0exp(t/τ). The gas flow velocities ranged from 1 to 10 m/s, the gas temperatures ranged from 313 to 353 K, and the periods of heat generation rate ranged from 46 ms to 17 s. The surface temperature difference and heat flux increase exponentially as the heat generation rate increases with the exponential function. Transient heat transfer coefficients increase with increasing gas flow velocity. The geometric effect of twisted heater in this study shows an enhancement on the heat transfer coefficient. Empirical correlation for quasi-steady-state heat transfer was obtained based on the experimental data. The data for heat transfer coefficient were compared with those reported in authors’ previous paper.

Conjugate Heat Transfer in Air-to-Refrigerant Airfoil Heat Exchangers

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Yutaka Ito ◽  
Naoya Inokura ◽  
Takao Nagasaki
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Exchangers ◽  
Transfer Coefficients ◽  
Exchange System ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Heat Exchange System ◽  
Inverse Heat Transfer ◽  
Transfer Method

A light and compact heat exchange system was realized using two air-to-refrigerant airfoil heat exchangers and a recirculated heat transport refrigerant. Its heat transfer performance was experimentally investigated. Carbon dioxide or water was used as a refrigerant up to a pressure of 30 MPa. Heat transfer coefficients on the outer air-contact and inner refrigerant-contact surfaces were calculated using an inverse heat transfer method. Correlations were developed for the Nusselt numbers of carbon dioxide and water on the inner refrigerant-contact surface. Furthermore, we proposed a method to evaluate a correction factor corresponding to the thermal resistance of the airfoil heat exchanger.

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