Effects of surface roughness on the average heat transfer of an impinging air jet

Journal Article · Sat Jan 01 04:00:00 EST 2000 · International Communications in Heat and Mass Transfer

DOI:https://doi.org/10.1016/S0735-1933(00)00079-8· OSTI ID:20015631

Beitelmal, A H; Saad, M A; Patel, C D

Localized cooling by impinging flow has been used in many industrial applications such as in cooling of gas turbine blades and drying processes. Here, effect of surface roughness of a uniformly heated plate on the average heat transfer characteristics of an impinging air jet was experimentally investigated. Two aluminum plates, one with a flat surface and the second with some roughness added to the surface were fabricated. The roughness took the shape of a circular array of protrusions of 0.5mm base and 0.5mm height. A circular Kapton heater of the same diameter as the plates (70mm) supplied the necessary power. The surfaces of the plates were polished to reduce radiation heat losses and the back and sides insulated to reduce conduction heat losses. temperatures were measured over a Reynolds number ranging from 9,600 to 38,500 based on flow rate through a 6.85mm diameter nozzle. The temperature measurements were repeated for nozzle exit-to-plate spacing, z/d, ranging from 1 to 10. The average Nusselt number for both cases was plotted versus the Reynolds number and their functional correlation was determined. The results indicate an increase of up to 6.0% of the average Nusselt number due to surface roughness. This modest increase provides evidence to encourage further investigation and characterization of the surface roughness as a parameter for enhancing heat transfer.

• Research Organization: Santa Clara Univ., CA (US)
• OSTI ID: 20015631
• Journal Information: International Communications in Heat and Mass Transfer, Journal Name: International Communications in Heat and Mass Transfer Journal Issue: 1 Vol. 27; ISSN 0735-1933; ISSN IHMTDL
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
HEAT LOSSES
HEAT TRANSFER
IMPINGEMENT
JETS
NOZZLES
NUSSELT NUMBER
ROUGHNESS
USES