Experimental Investigation of Thermal and Hydrodynamic Performances of a Partial Cross-Wavy Recuperator for Microturbine Applications

2012 ◽  
Author(s):  
L. X. Du ◽  
P. Q. Yu ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Experimental Results ◽  
Hydrodynamic Performance ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Efficient

In order to improve the thermal efficiency of the microturbines, the compact and high efficient primary surface heat exchangers are mandatory. Recently, the thermal and hydrodynamic performances of a cross-wavy (CW) primary surface recuperator are experimentally investigated. The recuperator tested in the experiment is only 1/3 part of the whole recuperator which is designed for a 100kW microturbine. The experimental results have shown that the comprehensive thermal and hydrodynamic performances of the CW primary surface recuperator are competitive. The overall heat transfer coefficients and the pressure drops of the recuperator are tested in the experiments. And the range of the Reynolds number is from 150 to 400. The corresponding correlations between heat transfer coefficients and Reynolds numbers and the correlations between friction factors and Reynolds numbers are obtained. The Genetic Algorithm (GA) has been used to separate the coefficients of heat transfer correlations in the hot and cold sides of the partial recuperator by separating the overall heat transfer coefficient without experimentally knowing wall temperatures. In order to improve the hydrodynamic performance, the flow arrangement is also carefully designed. Furthermore, the experimental results have also confirmed that the flow distribution in the recuperator is quite uniform.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Numerical Investigation on the Effect of Transversal Septa on Forced Convection in Circular Tubes

2009 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Circular Tubes ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry, solar energy heater, etc. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. In this paper a numerical investigation is carried out on forced convection in circular tubes with septa heated by constant fluxes and characterized by different shapes. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, when the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa may significantly augment pressure drops. The fluid is air and properties are function of temperature. Septa of the same material of the tube are introduced and several shapes and arrangements are analyzed as well as different Reynolds numbers, baffle spacings and heat fluxes applied on the external surface. The investigation is accomplished by means of the commercial code Fluent. A k-e turbulence model is used with enhanced wall treatment options. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients, friction factors and pressure drops for different values of heat flux, Reynolds numbers and baffle spacings. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow

1981 ◽  
Author(s):  
L. W. Florschuetz ◽  
C. R. Truman ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Circular Jets

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after inpingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

Turbulent Convective Heat Transfer in Forced Cooled Underground Electric Transmission Systems

1985 ◽  
Vol 107 (2) ◽  
pp. 327-333 ◽  
Author(s):  
R. Ghetzler ◽  
J. C. Chato ◽  
J. M. Crowley
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Transfer Coefficients ◽  
Transmission Systems ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Electric Transmission ◽  
Friction Factors ◽  
High Reynolds

Heat transfer and friction factors were experimentally determined in a scale model of high-voltage, pipe-type underground transmission systems for Reynolds numbers to 8000. Dielectric insulating oil (Sun No. 4) with a Prandtl number of 120 was utilized for the coolant. Two ratios of cable to enclosure pipe diameters, corresponding to standard and oversize enclosure pipes, were examined for the three-cable system. Helical wire wrap was included to simulate protective skid wires around the cables. Three configurations of cable positioning were considered—open triangular, close triangular, and cradled. A method of generalizing the heat transfer coefficients was developed and tested for rough pipe cables based on extensions of previous work in the literature. The generalized correlation, without correction factors, was found to be applicable only in two cases with appropriate flow pattens and geometries. Heat transfer to the pipe wall could be correlated by standard methods in the high Reynolds number range.

An Experimental and Numerical Investigation on the Thermal-Hydraulic Performance of Double Notched Plate

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Lei Zhang ◽  
Defu Che
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Local Information ◽  
Transfer Coefficients ◽  
Enhanced Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Friction Factors

The double notched (DN) plate is commonly used in rotary air preheaters, but relevant investigations are rare. Thus, thermal-hydraulic performances of the DN plate are investigated in this paper. A single-blow, transient technique is refined and then used to measure the overall mean heat transfer coefficients and friction factors. A validated numerical method is also utilized to provide local information. The measured results show that the performance of the DN plate approaches that of the double undulated (DU) plate and lies between that of the cross corrugated (CC) plate and the parallel plate. No swirling flow pattern is identified in the predicted velocity fields. Basically, two types of flow are observed: wavy channel flow and pipe flow. High or low Nusselt numbers, Nu, are obtained at the luff or lee side of undulations and notches, respectively. Nu values increase and Nu distributions become more homogenous with increasing Reynolds numbers, Re. A recommendation is made that the DN plate be operated under moderate Re to achieve homogenous and enhanced heat transfer, given the allowable pressure drop.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45 deg Round-Edged Ribs at High Reynolds Numbers

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Nawaf Alkhamis ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Reynolds ◽  
The Cost

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib-roughened square channel, which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2, while spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in the heat transfer due to the ribs at the cost of a higher friction factor, especially at higher Reynolds numbers. Round-edged ribs experience a similar heat transfer coefficient and a lower friction factor compared with sharp-edged ribs, especially at higher values of the rib height. Correlations predicting Nu and f as a function of e/D, p/e, and Re are presented. Also presented are correlations for the heat transfer and friction roughness parameters (G and R, respectively).

Experimental Investigation on Heat Transfer and Pressure Drop in a Microtubine Recuperator With Cross-Wavy Primary Surface Channels

2005 ◽  
Author(s):  
Q. W. Wang ◽  
H. X. Liang ◽  
L. Q. Luo ◽  
J. W. Wang ◽  
Z. P. Huang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Steel Strip ◽  
Reynolds Numbers ◽  
Superior Performance ◽  
Transfer Coefficients ◽  
Corrosion Properties ◽  
Heat Transfer Coefficients ◽  
Hot Gas ◽  
Friction Factors

Compact heat exchangers are used in a wide variety of applications. Typical utilization is a low-cost recuperator for power generation microturbines. In this scenario, a recuperator takes heat from the exhaust gas and preheats the compressor discharge air before it reaches the combustion chamber. To achieve thermal efficiency over 30%, recuperators with high thermal performance surfaces geometries are needed. It has been shown that Cross-Wavy Primary Surface (CWPS) has superior performance and high commercial potential in compact recuperators based on previous studies. In the present study, we successfully implemented a prototype recuperator with CWPS channels for a 100kW microturbine. The material we used in the recuperator core is a 0.12mm-thick stainless steel strip, which has good high-temperature mechanical and corrosion properties. The working mediums are compressed air and hot gas for the two sides of the recuperator. We tested comprehensively the thermal performance of the recuperator in terms of the overall heat transfer coefficients and friction factors vs. Reynolds numbers in the CWPS channels, with Reynolds number ranging from 250 to 400. The exhaust hot gas temperature was much non-uniform, indicating the importance of flow arrangement when designing the recuperator. We also investigated the heat transfer coefficients and friction factors vs. Reynolds numbers, and obtained corresponding correlations.

Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement with Crossflow

1981 ◽  
Vol 103 (2) ◽  
pp. 337-342 ◽  
Author(s):  
L. W. Florschuetz ◽  
C. R. Truman ◽  
D. E. Metzger
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Channel Height ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Circular Jets

Two-dimensional arrays of circular jets of air impinging on a heat transfer surface parallel to the jet orifice plate are considered. The air, after impingement, is constrained to exit in a single direction along the channel formed by the surface and the jet plate. The downstream jets are subjected to a crossflow originating from the upstream jets. Experimental and theoretical results obtained for streamwise distributions of jet and crossflow velocities are presented and compared. Measured Nusselt numbers resolved to one streamwise hole spacing are correlated with individual spanwise row jet Reynolds numbers and crossflow-to-jet velocity ratios. Correlations are presented for both inline and staggered hole patterns including effects of geometric parameters: streamwise hole spacing, spanwise hole spacing, and channel height, normalized by hole diameter. The physical mechanisms influencing heat transfer coefficients as a function of flow distribution and geometric parameters are also discussed.

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