Gene T. Colwell

MATHEMATICAL MODELING OF THE TRANSIENT OPERATING CHARACTERISTICS OF A LOW-TEMPERATURE HEAT PIPE

A computational model has been developed based on finite-difference approximations for predicting the transient operating characteristics of low-temperature heat pipes. To stimulate startup from the supercritical state, a simplified cooldown is modeled using bulk liquid flow through the capillary structure with phase change at the liquid front. Variations of thermal properties are considered using cubic spline interpolation, and nodal temperatures are calculated by an alternating direction implicit method. A fluid gap in the wick and a variety of thermal couplings have been incorporated in the model. Comparisons between predicted and experimental values were made on a refrigerant 11 heat pipe, and agreement is good for normal operation. For cooldown from the supercritical state, the present model predicts operating trends of the device and correct final steady-state performance.

Measurements of the transient behavior of a capillary structure under heavy thermal loading

Abstract The transient operating characteristics of a slab type capillary structure in a refrigerant 11 heat pipe have been studied under conditions which cause partial or complete drying and rewetting to occur. Detailed changes with time in internal liquid and vapor temperature distributions, internal pressure, and heat transport capability are presented. It was found that the device will, under some conditions, approach steady operation with a portion of the capillary structure dried and that rewetting can be quickly accomplished. However, when the entire structure is dried, rewetting is much more difficult to accomplish.

Heat pipe and surface mass transfer cooling of hypersonic vehicle structures

The problem of determining the feasibility of cooling hypersonic vehicle leading-edge structures exposed to severe aerodynamic surface heating using heat pipe and mass transfer cooling techniques is addressed. A description is presented of a numerical finite-difference-based hypersonic leading-edge cooling model incorporating poststartup liquid metal heat pipe cooling with surface transpiration and film cooling to predict the transient structural temperature distributions and maximum surface temperatures of hypersonic vehicle leading edge. An application of this model to the transient cooling of a typical aerospace plane wing leading-edge section. The results of this application indicated that liquid metal heat pipe cooling alone is insufficient to maintain surface temperatures below an assumed maximum level of 1800 K for about one-third of a typical aerospace plane ascent trajectory through the earths atmosphere.

Surface cooling of scramjet engine inlets using heat pipe, transpiration, and film cooling

This article reports the results of applying a finite-difference-based computational technique to the problem of predicting the transient thermal behavior of a scramjet engine inlet exposed to a typical hypersonic flight aerodynamic surface heating environment, including type IV shock interference heating. The leading-edge cooling model utilized incorporates liquid metal heat pipe cooling with surface transpiration and film cooling. Results include transient structural temperature distributions, aerodynamic heat inputs, and surface coolant distributions. It seems that these cooling techniques may be used to hold maximum skin temperatures to near acceptable values during the severe aerodynamic and type IV shock interference heating effects expected on the leading edge of a hypersonic aerospace vehicle scramjet engine. 15 refs.

THERMAL PERFORMANCE OF HEAT PIPE ARRAYS IN SOIL

Arrays of heat pipes placed in soil may be used to good advantage for cooling or heating equipment. This paper gives results of a study that included the coupling of heat pipe thermal characteristics with soil thermal characteristics for such applications. A transient mathematical model was developed for the combination that accounted for thermal capacitance and resistance of the individual heat pipes, the number and arrangement of heat pipes in the soil, and soil properties. The model was verified by comparing it with published experimental and analytical results. Parametric studies were then performed, and the results were used to develop some correlation equations that may be used to predict the thermal performance of arrays of heat pipes in soil. The dependence of spacing, type of array, heat pipe properties, and soil properties is included in the simple correlation equations.

Evaluation of Space Station thermal control techniques

A procedure is developed for evaluating various candidates for thermal control in the orbiting Space Station. Candidates for acquisition, transport and rejection are considered. For example, thermal rejection candidates include heat pipe radiators, high capacity heat pipe radiators and liquid droplet radiators. A computer program has been developed which computes subsystem and total system weights, volumes, powers and costs for a system consisting of selected acquisition, transport and rejection candidates. The program user is also able to select mission parameters such as duration, resupply interval, thermal loads, transport distance, acquisition temperature and rejection temperature. Simulation models are included in the program which allow the user to change candidate designs. For example, for a high capacity heat pipe radiator the user may change working fluid, materials, radiator temperature, radiator geometry, surface emissivity and surface absorptivity. The program also allows the selection of several different acquisitions of thermal energy at different temperatures using different acquisition candidates.

Laminar viscous flow fields in moving curved channels

Abstract The laminar steady flow of air through moving narrow deep circumferential grooves on a rotor is studied. Fluid enters the moving grooves from a stationary inlet nozzle with uniform velocity and exits into a stationary diffuser after approximately 150 degrees of rotation. Three dimensional developing velocity profiles and pressure distributions are presented for a variety of operating conditions. Computed overall head-flow characteristics are found to be in relatively close agreement with a simple Poiseuille model where both walls are taken to be moving at the same rate and in the same direction at a velocity different from the entrance velocity.

Parametric Relations for Ordinary and Confluent Turbulent Boundary-Layer Flows

Theme T paper presents the results of an investigation of parameters associated with the confluent boundary layer shown schematically in Fig. 1. It is shown that with a suitable choice of parameters, velocity profiles in both jet and wake layers become similar, with the same similarity function obtained for different pressure gradients. Moreover, local dynamic similarity allows suitable functional representation of shear stress at the loci of maximum and minimum velocity. Measured eddy viscosity distributions for the confluent boundary layer is presented for one velocity ratio at slot exit. An analytical solution for the conventional flat plate turbulent boundary layer is shown for comparison purposes.