Experimental Investigation of Rotational Effects on Heat Transfer Enhancement Due to Crossflow-Induced Swirl Using Transient Liquid Crystal Thermography

2018 ◽  
Vol 10 (3) ◽  
Author(s):  
Li Yang ◽  
Prashant Singh ◽  
Kartikeya Tyagi ◽  
Jaideep Pandit ◽  
Srinath V. Ekkad ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Liquid Crystal ◽  
Rotation Number ◽  
Swirling Flow ◽  
Transfer Enhancement ◽  
Liquid Crystal Thermography ◽  
Local Reduction ◽  
Channel Velocity ◽  
Pass Through

Rotational effects lead to significant nonuniformity in heat transfer (HT) enhancement and this effect is directly proportional to the rotation number (Ro=ΩD/V). Hence, the development of cooling designs, which have less dependence on rotation, is imperative. This paper studied the effect of rotation on crossflow-induced swirl configuration with the goal of demonstrating a new design that has lesser response toward rotational effects. The new design passes coolant from one pass to the second pass through a set of angled holes to induce impingement and swirling flow to generate higher HT coefficients than typical ribbed channels with 180-deg bend between the two passages. Detailed HT coefficients are presented for stationary and rotating conditions using transient liquid crystal (TLC) thermography. The channel Reynolds number based on the channel hydraulic diameter and channel velocity at inlet/outlet ranged from 25,000 to 100,000. The rotation number ranged from 0 to 0.14. Results show that rotation reduced the HT on both sides of the impingement due to the Coriolis force. The maximum local reduction of HT in the present study was about 30%. Rotation significantly enhanced the HT near the closed end because of the centrifugal force and the “pumping” effect, which caused local HT enhancements up to 100%. Compared to U-bend two pass channels, impingement channels had advantages in the upstream channel and the end region, but HT performance was not beneficial on the leading side of the downstream channel.

Effects of Rotation on Heat Transfer for a Single Row Jet Impingement Array With Crossflow

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Justin A. Lamont ◽  
Srinath V. Ekkad ◽  
Mary Anne Alvin
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Rotation Number ◽  
Coriolis Force ◽  
Room Temperature ◽  
Turbine Blades ◽  
Target Surface ◽  
Channel Height ◽  
Potential Core ◽  
Single Row

The effects of the Coriolis force are investigated in rotating internal serpentine coolant channels in turbine blades. For complex flow in rotating channels, detailed measurements of the heat transfer over the channel surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed more effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer in a rotating, radially outward channel with impingement jets. A simple case with a single row of constant pitch impinging jets with the crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geometry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number, Roj, and jet orifice-to-target surface distance (H/dj = 1,2, and 3). Colder air, below room temperature, is passed through a room temperature test section to cause a color change in the liquid crystals. This ensures that buoyancy is acting in a similar direction as in actual turbine blades where walls are hotter than the coolant fluid. Three parameters were controlled in the testing: jet coolant-to-wall temperature ratio, average jet Reynolds number, Rej, and average jet Rotation number, Roj. Results show, such as serpentine channels, the trailing side experiences an increase in heat transfer and the leading side experiences a decrease for all jet channel height-to-jet diameter ratios (H/dj). At a jet channel height-to-jet diameter ratio of 1, the crossflow from upstream spent jets greatly affects impingement heat transfer behavior in the channel. For H/dj = 2 and 3, the effects of the crossflow are not as prevalent as H/dj = 1: however, it still plays a detrimental role. The stationary case shows that heat transfer increases with higher H/dj values, so that H/dj = 3 has the highest results of the three examined. However, during rotation the H/dj = 2 case shows the highest heat transfer values for both the leading and trailing sides. The Coriolis force may have a considerable effect on the developing length of the potential core, affecting the resulting heat transfer on the target surface.

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