Heat Transfer to Arrays of Impinging Jets in a Crossflow

Abstract

Convective heat transfer measurements are reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was constrained by skirts to exit at one end of the test section, thus establishing a crossflow. Geometric variables included the jet hole diameter d, the streamwise spacing X and spanwise spacing Y between jet holes, and the standoff distance Z between the orifice plate and the target plate. Three patterns of holes, all having d = 3.5 mm, were tested. Their (X, Y) were (4d, 4d), (4d, 8d), and (8d, 4d). Values of the standoff were Z = d, 2d, and 3d; and tests were run for 4, 6, and 8 rows of holes. The airflow was varied to achieve a range of mean jet Reynolds number from 2500 to 25,000. Microfoil heat flux sensors were used to determine streamwise variations in (spanwise-averaged) heat transfer. Excellent resolution was obtained by employing a sensor whose streamwise dimension is considerably less than one hole diameter d. Heat transfer profiles were periodic, with a peak corresponding to each spanwise row of holes. Such peaks were displaced in the steamwise direction by the crossflow, and those nearest the exhaust end of the channel exhibited the largest deflections. Array-averaged heat transfer coefficients were obtained by numerically averaging the local measurements; values agree well with the results of other experiments on similar impingement-with-crossflow systems.

Invisibly at Risk: Low-Income Students in a Middle- and Upper-Class World

“…feet Dh=4. *LEArea/LEperim C********************************************** Write (7,101) , 460., 560., 660., 760., 860., 960., 1060., & 1160., 1260., 1360., 1460., 1560., 1660., 1760., 1860., & 1960., 2060., 2160., 2260., 2360., 2460., 2560., 2660., & 2760., 2860., 2960., 3160., 3360., 3560., 3760., 3960 & 0.1045,0.1075,0.1101,0.1110,0.1170,0.1200,0.1230,0.1265, & 0.1300,0.1330,0.1360,0.1420,0.1480,0.1535,0.1595,0.1655/ data pr/ 0.7710,0.7590, & 0.7390,0.7180,0.7030,0.6940,0.6860,0.6820,0.6790,0.6788, & 0.6793,0.6811,0.6865,0.6880,0.6882,0.6885,0.6887,0.6890, & 0.6891,0.6893,0.6895,0.6897,0.6899,0.6900,0.6902,0.6905, & 0.6907,0.6909,0.6910,0.6913,0.6917,0.6921,0.6925,0.6929/ data cp/ 0.247, 0.242, & 0.241, 0.240, 0.241, 0.242, 0.244, 0.246, 0.248, 0.251, & 0.254, 0.257, 0.260, 0.264, 0.267, 0.270, 0.272, 0.275, & 0.277, 0.279, 0.282, 0.284, 0.286, 0.288, 0.291, 0.293, & 0.296, 0.298, 0.300, 0.305, 0.311, 0.318, 0.326, 0.338/ c c if(t.lt.tab(1)) print 510,t,tab(1) 510 format(" in airprop ---temp=",f8.1," is less than min temp", &" of ",f8.1) if(t.gt.tab(nent)) print 520, t,tab(nent) 520 format(" in airprop ---temp=",f8.1," is greater than max", &" temp of ",f8.1) if(t-tab (1) (6,35)i,v1/a1,v2/a2,v3/a3,v4/a4,v5/a5,v6/a6 write (2,35)i,v1/a1,v2/a2,v3/a3,v4/a4,v5/a5,v6 …”

“…In an investigation by Hollworth and Cole (1987) [7], convective heat transfer measurements were reported for staggered arrays of round turbulent air jets impinging upon a heated flat surface. Spent air was arranged to form a crossflow.…”

Local Heat Transfer Coefficient and Adiabatic Wall Temperature Measurement Beneath Arrays of Staggered and Inline Impinging Jets

“…These authors used a steady state experimental method to produce row resolved Nusselt numbers. The same technique but with narrower heaters was used by Sand et al (1980) and Hollworth et al (1987). The spatial resolution achieved by these workers was sufficient to measure the peak in spanwise average h which occurs beneath the jets and to observe the downstream shift in peak h as local crossflow increases.…”

Full Coverage Impingement Heat Transfer at High Temperatures

“…The data of Chance (1974) Kercher and Tabakoff (1970) and Florschuetz et al (1981) used their correlations for the upstream part of the test section to derive values for an X/D of 5 and Z/D of 3. For Hollworth and Cole (1987) the actual experimental data for an X/D of 4 and Z/D of 3 were used. This data was surface averaged, as in the present work.…”