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.

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).

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

2009 ◽  
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; spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in heat transfer due to 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 to sharp edged ribs, especially at higher values of rib height. Correlations predicting Nu and f as a function of e/D, p/e and Re are presented. Also presented are correlations for heat transfer and friction roughness parameters (G and R).

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

Heat Transfer from a Plate Elevated above a Host Surface and Washed by a Separated Flow Induced by the Elevation Step

1981 ◽  
Vol 103 (3) ◽  
pp. 441-447 ◽  
Author(s):  
E. M. Sparrow ◽  
F. Samie ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Active Surface ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Reynolds Number Flow ◽  
Heat Transfer Coefficients ◽  
High Reynolds

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for a thermally active surface elevated above a parallel host surface. The step-like blockage associated with the elevation causes flow separation and recirculation on the forward portion of the thermally active surface. Four parameters were varied during the course of the experiments, including the angle of attack of the oncoming airflow relative to the surface, the step height, the extent of the host surface which frames the active surface (i.e., the skirt width), and the Reynolds number. Flow visualization studies, performed with the oil-lampblack technique, showed that the streamwise extent of the separation zone increases with decreasing angle of attack, with larger step heights and skirt widths, and at higher Reynolds numbers. At larger angles of attack, separation does not occur. The experimentally determined heat transfer coefficients were found to increase markedly due to the flow separation, and separation-related enhancements as large as a factor of two were encountered. The enhancement was accentuated at small angles of attack, at large step heights and skirt widths, and at high Reynolds numbers. A main finding of the study is that the separation-affected heat transfer coefficients are generally greater than those for no separation, so that the use of the latter may underestimate the heat transfer rates. For an application such as a retrofit solar collector, such an underestimation of the wind-related heat loss would yield an optimistic prediction of the collector efficiency.

Pressure Drop and Heat Transfer in a Duct With Triangular Cross Section

1960 ◽  
Vol 82 (2) ◽  
pp. 125-136 ◽  
Author(s):  
E. R. G. Eckert ◽  
T. F. Irvine
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Cross Section ◽  
Flow Region ◽  
Isosceles Triangle ◽  
Transfer Coefficients ◽  
Round Tube ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Friction Factors

Friction factors have been measured for a duct whose cross section has the shape of an isosceles triangle with a side ratio 5 to 1 in the fully developed flow region for laminar, transitional, and turbulent conditions. In addition, local and average heat-transfer coefficients and the temperature field in the duct wall have been determined for the condition of constant heat generation per unit volume of the duct walls. Friction factors in laminar flow agreed well with analytical predictions. In the turbulent flow range they were by 20 per cent lower than values calculated from relations for a round tube with the use of the “hydraulic diameter.” Heat-transfer coefficients averaged over the circumference of the duct were only half as large as values calculated from round tube relations in the Reynolds number range from 4300 to 24,000. The measurements also revealed that thermal starting lengths were in excess of 100 diameters. In round tubes a length of 10 to 20 diameters has been found sufficient to develop the temperature field.

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 Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Nawaf Y. Alkhamis ◽  
Akhilesh P. Rallabandi ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Rib Roughened

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+).

Heat Transfer in a Rotating, Blade-Shaped Serpentine Cooling Passage With Discrete Ribbed Walls at High Reynolds Numbers

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Lesley M. Wright ◽  
Shang-Feng Yang ◽  
Hao-Wei Wu ◽  
Je-Chin Han ◽  
Ching-Pang Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
First Passage ◽  
Heat Transfer Coefficients ◽  
The Third ◽  
High Reynolds Numbers ◽  
High Reynolds

Abstract This paper experimentally investigates the effect of rotation on heat transfer in a typical turbine blade, three-pass, serpentine coolant channel with discrete ribbed walls at high Reynolds numbers. To achieve the high Reynolds number (Re → 190,000) and low rotation number conditions, pressurized Freon R-134a vapor is utilized as the working fluid. Cooling flow in the first passage is radial outward; after the 180 deg tip turn, the flow is radial inward through the second passage; and after the 180 deg hub turn, the flow is radial outward in the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers as low as 0.07 and Reynolds numbers from 85,000 to 187,000 (based on the first passage geometry and flow conditions). Heat transfer coefficients were measured using thermocouples embedded in copper plates to provide regionally averaged heat transfer coefficients. Heat transfer enhancement due to rotation is observed on the first passage, pressure-side with radially outward flow and the second passage, suction-side with radially inward flow, but a reduction in heat transfer is observed on the third passage pressure-side with radially outward flow. In addition, results from the discrete, broken ribs are compared with those from the same serpentine coolant passage with conventional, angled ribbed walls. A significant increase in the heat transfer due to the discrete ribs is observed in the first passage. These results can be useful for understanding real rotor blade coolant passage heat transfer under high Reynolds number and low rotation number conditions.

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.

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.

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