Surface Tension Devices Research Articles

Review Heat Exchanger: Research Development of Self-rotating Inserts in Heat Exchanger Tubes

Heat exchangers are widely used in power engineering and industrial applications. Many techniques such as coiled tube, surface tension devices, rough surfaces and extended surfaces have been investigated to enhancetherma l performance and minimize the cost and size of the heat exchanger equipment. One of the most important techniques is tube insert. In general,tube inserts can be classified into two broad categories: stationary inserts and self-rotating inserts.Compared with stationary inserts, the self-rotating inserts can rotate in the tube by fluid and the comprehensive performance of selfrotating inserts is improved significantly.This paper mainly focuses on reviewing the large number of experimental and numerical works taken by researchers on self-rotating inserts such as twisted tapes,miniature hydraulic turbine,turbine-type swirl generators, etc. To improve the thermal efficiency of heat exchanger and serviceable to designers implemention of passive enhancement techniques in heat exchanger are required. The authors found that self-rotating inserts can streng then the heat transfer efficiency, meanwhile achieve on-line automatic anti-scaling and descaling effect. When the fluid velocity is more than 0.2m/s, most of self-rotating inserts can be applied.The heat transfer performance and frictional loss have been discussed to get the optimal configuration of self-rotating inserts. The convective heat transfer correlations have also been discussed. Determining how to find the optimal self-rotating insert is the main objective of this paper..

Mission concepts for the Superconducting Gravity Gradiometer

The Superconducting Gravity Gradiometer (SGG), which can measure gravitational field fluctuations to unprecedented precisions, is currently being evaluated for use in an Earth-orbiting platform. Two missions are planned: a Shuttle-based demonstration flight and a dedicated gravity surveying mission. The Shuttle mission will feature a fully functional, self-contained instrument with an intrinsic noise level of 10 −3 E Hz −1 2 , where E is defined at 10 −9m s −2 m −1. Calibration hardware, residual error correction techniques, and surface tension devices which control liquid helium motion in the dewar will be tested. For a dedicated free-flier gravity mission, two concepts have been studied. Both have been formulated to achieve low cost while maintaining an instrument sensitivity of 10 −3 E Hz −1 2 . One concept uses the spacecraft developed for the Sub-millimeter Wave Astronomical Satellite (SWAS), and would be in a polar orbit, decaying from an initial altitude of 380 km. A mission lifetime of 6–9 months is planned. The other concept is based on a re-usable SPARTAN 400 carrier which would be deployed from, and retrieved by, the Shuttle. The carrier can be periodically reboosted and would maintain an altitude between 275 and 350 km. The mission lifetime is restricted to about 3 months, and the orbit inclination is limited to 57 °, the maximum the Shuttle can reach. Since the carrier is retrieved, the instrument could be periodially reflown. The free-flier missions, including experiment and spacecraft design, are described.

Pressurant effects on cryogenic liquid acquisition devices

On-orbit storage and resupply faculties for cryogenic liquids will likely require surface-tension liquid acquisi- tion devices (LADs) in the storage tanks to provide reliable extraction and transfer of vapor-free liquid. The investigation reported in this paper comprised experiments with a screened-channel LAD in liquid hydrogen to measure the performance of the channel as a function of the type and temperature of the pressurant gas used to expel liquid from the test tank through the LAD. With cold pressurant (near the saturation temperature of hydrogen), vapor penetration of the LAD screen occurred at near the predicted pressure difference across the screen for both helium and hydrogen pressurant, although helium provided better results. With warm helium pressurant, there was no observable degradation in screen performance. With warm hydrogen there was a substantial degradation, and if the LAD outflow was interrupted, allowing the liquid in the LAD to stagnate, vapor penetrated the screen at very low differential pressures. ANAGING liquid propellants and other fluids in mi- crogravity will be an essential element of the on-orbit facilities infrastructure needed to support future operations in space. Space transfer vehicles, Space Station Freedom, space- based defense systems, and serviceable satellites, for example, will require on-orbit servicing to replenish liquid propellants, fuels, coolants, commercial stocks, or life support fluids. Much of the technology required for storing and transferring significant amounts of these fluids in microgravity remains under development and is yet to be demonstrated. This is especially true regarding cryogenic liquids: For liquid hydro- gen, oxygen, and nitrogen—which are important for in-space propulsion and life support systems—data describing the ther- mal and dynamic phenomena involved in storage and transfer in space are quite limited. One important aspect of in-space fluid transfer is acquisi- tion of vapor-free liquid from a storage tank. In the absence of gravity or acceleration forces to settle the liquid contents of a tank over the outlet, special devices must be used to transfer the liquid out of the tank. Bellows, bladders, and capillary (surface-tension) devices have been used effectively with non- cryogenic liquids. With cryogens, surface-tension devices (e.g., screen-covered channels) appear to be the best approach because heat conduction may form unwanted vapor bubbles within bellows and bladders. Further development followed by an in-space demonstration is necessary, however, for cryo- genic applications. Liquid hydrogen in particular imposes po- tentially troublesome design constraints because of its low surface tension and ease of vaporization. A liquid acquisition device (LAD) employing fine-mesh screen would usually be designed to serve either as a total communication LAD for withdrawing liquid from one tank for transfer into another or as a start basket in a propellant tank in an upper stage booster for providing vapor-free pro- pellant during engine startup until the thrust settles all of the propellant. In either application, wherever vapor contacts the wetted screen, the surface tension at the liquid-vapor interface within the small pores in the screen inhibits the passage of

Liquid/vapour phase separation in 4He using electric fields

In space, a replacement must be found for gravity to physically control and, in certain instances, contain cryogenic liquids. A programme has been started at the Jet Propulsion Laboratory to study the use of electric field generated forces to establish the required orienting effects. We present measurements which show that it is possible to apply strong enough electric fields to a liquid/vapour interface of 4He to obtain an orienting force comparable to gravity. Our measurements span the temperature range 1.7–4.2 K and demonstrate the applicability of Pashen's law for maximum attainable field before breakdown occurs. Some advantages of the electric field separator as opposed to passive surface tension devices are identified.

A survey of current developments in surface tension devices for propellant acquisition

T task of a propellant expulsion system is to supply gas-free propellant on demand to spacecraft thrusters for the duration of the mission. For orbital spacecraft, which may experience periods of adverse or near zero-gf accelerations, the expulsion system must assure that all or portions of the propellants are in contact with the tank outlet; that gas is prevented from entering the tank outlet during thruster startup; that pressurization gas entrained in the settling propellant bulk does not enter the tank outlet; and that propellant vortexing, gas pull-through, and propellant slosh do not significantly reduce the system expulsion efficiency. Many types of positive propellant expulsion systems have been developed for orbital spacecraft, each with advantages and problems, as summarized in Table 1. Development of these devices usually centers on. mechanical testing in simulated prototype environments. Although performance of these devices has been good, the reliability concern of the mission planner increases when very long missions are considered because there are no established accelerated life testing techniques. Recent experience with capillary systems has shown that they satisfy expulsion system requirements as well as the desire for passive simplicity. Indeed, the question of long-

Dynamics Control for Operational Spacecraft

Present U.S. operational spacecraft fall into one of three categories: communications, meteorological, or navigational. With the exception of the earth-synchronous communications mission, dynamics control for these satellites has consisted only of attitude control. It is the purpose of this paper to extend dynamics control for the latter two categories of operational spacecraft to include orbit adjustment. In addition, the requirements and performance of a dynamics control system for the Earth Resources Observation Mission (a new category) are described. The need for orbit-adjustment capability for operational satellites is established, not only on the basis of future mission requirements, but also as a solution to the ground data-handling problems occasioned by many low-altitude satellites orbiting at the same time.The passive and semi-passive, or hybrid, attitude-control systems utilized in the TIROS series of meteorological satellites, and in the Transit navigation satellites, will continue to be used in the future for operational satellites. Their inherent simplicity and resultant reliability make such systems obvious selections for long-lived applications. However, the use of these techniques introduces unique propulsion-system requirements. In particular, it is shown that dual thrust levels are necessary to first cancel the booster injection errors and acquire station and, subsequently, to provide station keeping. A system configuration is described using hydrazine in a monopropellant thruster directly for high thrust and then the decomposition products in a resistojet for low thrust. The predicted performance of such a system and the dynamic response of the vehicle are analyzed.Another requirement for future operational satellites using orbit-adjustment systems is that propellant management must be accomplished in a zero-g field. A potential solution is presented using surface-tension devices. Current work in this area is reviewed.