Impingement heating

Percent excess oxygen needed to maintain a required hot mix temperature when burning natural gas or distillate fuel oil using nonpreheated air. 

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FIGURE 18.18 Effect of the Reynolds number on local heat transfer parameter Nu/Pr042 for jet impingement heating with nozzle-to-surface parameter Hid (a) Hid=5.0, and (b) Hid = 1.0 (after Klammer and Schupe [88]). 

Jet-induced crossflow has been found to have an important effect on impingement heat transfer [82, 92, 93]. In order to delineate its influence on average convective coefficients more clearly, Obot and Trabold have identified three crossflow schemes, referred to minimum, intermediate, and maximum, and correlated their experimental data. The best heat transfer performance was obtained with the minimum crossflow scheme. Intermediate and complete crossflow was associated with varying degrees of degradation. The average Nusselt numbers for air were represented by the equation... 

N. T. Obot and T. A. Trabold, Impingement Heat Transfer Within Arrays of Circular Air Jets. Part I. Effects of Minimum, Intermediate and Complete Crossflow for Small and Large Spacings, J Heat Transfer, 107, pp. 872-879,1987. 

S. Faggiani and W. Grassi, Round Liquid Jet Impingement Heat Transfer Local Nusselt Numbers in the Region with Non-Zero Pressure Gradient, in G. Hestroni (ed.) Proceedings of the 9th International Heat Transfer Conference, 4, pp. 197-202, Hemisphere, New York, 1990. 

Thermocouple installation is important to ensure the proper temperature will be measured. Figure 5.3 shows a thermocouple located at the top of the radiant section in a process heater used to measure the temperature of fhe heater. As will be discussed later, this type of fhermocouple measurement needs to be corrected to get the actual temperature. The location of this thermocouple is important because if it is located too close to the wall, then the temperature will be lower due to the lower temperature tubes that are cooled by process fluid. That lower temperature would not be representative of the average heater temperature. Figure 5.4 shows a photo of the thermocouples used to measure the water outlet temperatures from calorimeters in a flame impingement heating study [17]. The thermocouples were positioned so that water would have to flow over the junctions, regardless of the flow rate. If the thermocouples were positioned, for example, perpendicular to a vertically downward flow of water, there is a good chance the junction would not... 

Example of measuring the outlet temperature from calorimeters used to measure the heat flux in flame impingement heating. (From Baukal, C. E., Heat Transfer from Flame Impingement Normal to a Plane Surface, Saarbriicken, Germany VDM Verlag, 2009.)... 

Hargrave, G. K., Fairweather, M., and Kilham, J. K. "Forced Convective Heat Transfer from Premixed Flames—Part 2 Impingement Heat Transfer." International Journal of Heat and Fluid Flow 8, no. 2 (1987) 132-38. 

Schulte, E. M. "Impingement Heat Transfer Rates from Torch Flames." Journal of Heat Transfer 94 (1972) 231-33. 

Baukal, G. E., and Gebhart, B. "Surface Condition Effects on Flame Impingement Heat Transfer." Thermal and Fluid Science 15 (1997) 323-35. 

Flame impingement normal to a cooled target. (From Baukal, C. E., Farmer, L. K., Gebhart, B., and Chan, I., "Heat Transfer Mechanisms in Flame Impingement Heating," In 1995 International Gas Research Conference, Vol. II, edited by D. A. Dolenc, 2277-87, Rockville, MD Government Institutes, 1996.)... 

Examples of different target materials used in flame impingement tests (a) copper, (b) brass, and (c) stainless steel. (From Baukal, C. E., and Gebhart, B., "Surface Condition Effects on Flame Impingement Heat Transfer," Experimental Thermal Fluid Science 15 (1997) 323-35.)... 

V. G., Viskanta, R., and Fedorov, A. G. "Direct Flame Impingement Heating for Rapid Thermal Materials Processing." International Journal of Heat and Mass Transfer 44 (2001) 1751-58. 

Viskanta, R. "Convective and Radiative Flame Jet Impingement Heat Transfer." International Journal of Transport Phenomena 1 (1998) 1-15. 

Viskanta, R. "Overview of Flame Impingement Heat Transfer Fundamentals and Applications." Proceedings of the Fourth Baltic Heat Transfer Conference, August 25-27,... 

Chander, S., and Ray, A. "Flame Impingement Heat Transfer A Review." Energy Conversion and Management 46 (2005) 2803-37. 

Dong, L. L., Cheung, C. S., and Leung, C. W. "Heat Transfer Characteristics of an Impinging Inversion Diffusion Flame Jet. Part II Impinging Flame Structure and Impingement Heat Transfer." International Journal of Heat and Mass Transfer 50 (2007) 5124-38. 

Rigby, J. R., and Webb, B. W. "An Experimental Investigation of Diffusion Flame Jet Impingement Heat Transfer." Proceedings of the ASME/JSME Thermal Engineering Conference, Vol. 3,117-26. New York ASME, 1995. 

Tariq, A. S. "Impingement Heat Transfer From Turbulent and Laminar Flames." PhD thesis, Portsmouth Polytechnic, Hampshire, UK, 1982. 

Fig. 4.15. Barrel furnaces for impingement heating of skelp edges—for welding into seamed pipe or tube, left, side view of three barrels right, end view. Not shown, but necessary, are slag cleanout access doors in all sections.

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