Thermodynamic aspects of heat pipe operation

Richter, R.

doi:10.2514/6.1990-1772

Cited by 12 publications

(10 citation statements)

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“…We begin by addressing the heat transfer limit that results from the capillarity phenomena active in heat pipes. ________________________________________________________________________ Unfortunately, the standard capillary limit model for even a simple cylindrical system has struggled to predict experimental data [104], [105], [106]. The need for an improved model became apparent as a model-based leading edge design methodology was devised.…”

Section: Discussionmentioning

confidence: 99%

“…Of the few studies which have attempted to experimentally validate the Chi design model, most find that the experimentally determined limit lies well below the predicted values [104], [105], [106]. The model is therefore not ________________________________________________________________________ conservative: its use could lead to unexpected failure under thermal conditions for which a heat pipe design was anticipated to successfully operate.…”

Section: Shortcomings Of the Chi Modelmentioning

confidence: 99%

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Thermal Management at Hypersonic Leading Edges

Kasen

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The intense heat flux incident upon the leading edges of hypersonic vehicles traveling through the low earth atmosphere at speeds of Mach 5 and above requires creative thermal management strategies to prevent damage to leading edge components. Conventional thermal protection systems (TPSs) include the ablative coatings of NASA's Mercury, Gemini, and Apollo vehicles and the reusable reinforced carbon-carbon (RCC) system of the Space Shuttle Orbiter. The ablative approach absorbs heat by endothermic transformation (phase and/or chemical change to the polymeric coating). The heat is dissipated from the vehicle as the single-use coating eventually vaporizes. The RCC approach manages the intense heat by operating at high temperatures and radiating heat to its surroundings. The effectiveness of both approaches is predicated on keeping the heat flux that impinges upon the susceptible aluminum airframe below a critical level.ii ________________________________________________________________________ This dissertation has explored an alternative metallic TPS concept which seeks to redistribute the heat from the leading edge, thereby eliminating local hot spots. It makes use of high thermal conductance heat pipes coupled to the leading edge so that the thermal load may be redistributed from a high heat flux location (at the stagnation point) to regions where it can be effectively radiated from the vehicle. The sealed system concept is based upon the evaporation of a fluid near the heat source that sets up a region of elevated vapor pressure inside the pipe. The latent heat is transported down the resulting pressure gradient by the vapor stream where it condenses at cooler regions, releasing the heat for removal.Replenishment of the condensed working fluid to the evaporator region is accomplished through the capillary pumping action of a porous wick which lines the interior surface of the pipe.A design methodology for a wedge-shaped heat pipe is presented which uses a coupled flow-wall temperature model to construct design maps which relate design parameters of the leading edge system (overall length, wall thickness, and alloy) to its operating conditions (isothermal temperature, maximum temperature, maximum thermal stress). Potential bounds on heat transport due to physical phenomena linked to the sound speed within a chamber (sonic limit), capillarity, and boiling nucleation are considered by extending models developed for tube designs to the wedge geometry. A new heat flux limit is proposed which, should it be exceeded, subjects the leading edge to thermally-induced plastic deformation of the TPS. iii ________________________________________________________________________To investigate the validity of the design approach and thermal spreading effectiveness of the proposed concept, a low temperature wedge-shaped leading edge was designed and constructed using stainless steel as the case material and water as the working fluid. Under localized tip heating, the maximum temperatures were significantly reduced compa...

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Section: Discussionmentioning

confidence: 99%

Section: Shortcomings Of the Chi Modelmentioning

confidence: 99%

Thermal Management at Hypersonic Leading Edges

Kasen

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“…These investigations range in complexity from simple state-to-state thermodynamic analyses (Khalkhali et al 1999;Richter and Gottschlich 1994;Zuo and Faghri 1997) to transient, multidimensional computational models of the fluid flow and heat transfer in the liquid and vapor phases (Cao and Chang 1997;Cao and Faghri 1991;Cao and Faghri 1993;Tournier and El-Genk 1994;Tournier and El-Genk 1996;Tournier and El-Genk 2003).…”

Section: 1modeling Of Stationary Heat Pipesmentioning

confidence: 99%

Numerical and Experimental Investigations of a Rotating Heat Pipe

Jankowski

2007

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“…[47]; the effect of pumping in bringing down the temperature at dry out is illustrated. Fig.15 Basic thermodynamic cycle of heat pipe operation on a temperature-entropy diagram [48]. Fig.16 Experimental and predicted friction factors in a countercurrent air-water heat pipe for various channel angles [56].…”

Section: Closurementioning

confidence: 99%