Direct Contact Heat Exchanger Research Articles

Electrically Induced Shape Oscillation of Drops as a Means of Direct-Contact Heat Transfer Enhancement: Part 1—Drop Dynamics

The shape oscillation of liquid drops passing through an immiscible liquid medium subject to a low-frequency (1 ∼ 16 Hz) alternating electric field having a sinusoidal waveform has been studied experimentally with the intention of investigating the enhancement of the direct-contact heat exchange between the two liquids. We have found that the field can induce, depending on its frequency, not only the resonant oscillation of the second mode of the drops, but also another peculiar oscillation that is related to the resonant oscillation of the third mode superposed on the second-mode oscillation.

Measurement of the surface tensions and the interfacial tensions of n-pentane-water and R 113-water systems

The surface and the interfacial tensions of mutually immiscible liquid systems were experimentally studied. The measured systems are n-pentane-water and R 113-water, which are proposed as heat transfer fluids for a direct-contact heat exchanger to be used for geothermal and waste heat recovery plants. The experimental apparatus was constructed based on the principle of the pendant drop method. Measurements were performed in the temperature range from 20 to 150°C. Based on the correlation of the surface and the interfacial tensions, the temperature dependences of the spreading coefficient, the film pressure, and the work of adhesion in each system were calculated.

Direct-contact heat exchange, shale production, and slag processing as examples of new efficient technologies for power generation

Novel concepts for direct-contact gas-water heat exchangers (DCHX), in which the energy in combustion exhaust gases is recovered as 70–80 °C hot water, are described; such hot water is a considerably more valuable energy stream (e.g. for industrial process heat or district heating) than the water, at best at 50–55 °C, which emerges from a conventional DCHX, where the wet-bulb temperature of the combustion gases is the upper limit of the hot-water temperature. Escape from this constraint is achieved by one of two methods: (1) the use of a high-boiling-point liquid (an aqueous solution of lithium bromide) in the first of two coupled DCHX; or (2) the deliberate introduction of additional water into the combustion exhaust stream to raise its wetbulb temperature. Both technologies have been demonstrated at the Mary Power Plant in Turkmenia, which burns natural gas. The processing of fine shales is assessed, with a quantitative investigation of the value of the principal products and by-products: shale oil and semicoke gas for power generation, chemicals (phenols), and ash useful for the deacidification of soil to increase crops. Finally, the results of an analysis of a new technology for the production of ferrosilicates during the combustion of coal are presented.

Numerical study on the operational performance of spray column direct contact heat exchangers

Spray columns have received considerable attention as direct contact heat exchangers due to their potential high throughput, as well as their near perfect counterflow operations if one-dimensional flow is obtainable. In practice, the degree of success in obtaining one-dimensional flow has depended on the design of the injectors for the disperse and continuous phases. In the past, the design of the injectors have been a trial and error procedure not sufficiently backed up by analyses. In this paper, theoretical analyses are carried out and several designs are evaluated. The influence of proper inlet conditions for the continuous phase to assure near one-dimensional flow is illustrated.

HEAT TRANSFER IN AXIALLY DISPERSED TWO-PHASE FLOW SYSTEMS

A direct-contact heat transfer process in a two-phase (gas-liquid) flow is formulated, and the solution of the two-point boundary-value problem (with Danckwerts-type initial condition) is given. Simulations are performed for a low Peclet number flow and high-pressure coal liquefaction preheater. The simulations show that direct-contact heat exchangers can be considered as an alternative to conventional heat exchangers.

Operating behaviour and crystallization mechanism of a sodium sulphate sodium phosphate mixture in a heat storage system

AbstractThe operating behaviour of a new salt hydrate mixture in a pilot heat storage unit using direct contact heat exchange has been investigated. The new storage medium is based on diluted Glauber's salt in which the excess water has been replaced by Na2HPO4 ṁ 12H2O as an active participant in the storage process.Improved heat storage properties have been found with the new salt mixture. Sampling of the salt solution and deposited crystals during operation indicated that alternate independent crystallization of Glauber's salt and of the phosphate salt occurs. Simulations of the crystallization behaviour based on this assumed mechanism are described.

Heat Transfer in Axially Dispersed Two-Phase Flow Systems

A direct-contact heat transfer process in a two-phase (gas-liquid) flow is formulated, and the solution of the two-point boundary-value problem (with Danckwerts-type initial condition) is given. Simulations are performed for a low Peclet number flow and high-pressure coal liquefaction preheater. The simulations show that direct-contact heat exchangers can be considered as an alternative to conventional heat exchangers.

Developments in geothermal energy in Mexico—Part two: Heat transfer studies in relation to the utilization of geothermal brines

Geothermal fluids withdrawn from wells are normally saturated with dissolved solids such as carbonates and silica. Conventional heat transfer equipment used to recover the geothermal heat is subject to heavy scaling. The overall heat transfer coefficient of a shell and tube exchanger was reduced to one sixth of its original value in 50 days in a typical geothermal field. Chemical methods have been used to inhibit scale formation. However, tests have shown that the most effective solution is to use fluidized bed heat exchangers which work on the principle of controlled precipitation. Experimental studies are underway at IIE on small scale equipment using a range of particle and tube sizes. In addition a low cost fluidized bed exchanger is under development on a geothermal field. A laboratory scale direct contact heat exchanger is also under construction at IIE.

On the temperature jump in liquid-liquid direct-contact heat exchangers

Experimental results on the flow mechanism of the dispersed phase during drop formation and release in a liquid-liquid system are presented. The strong circulation patterns during the formation and release process, the possible turbulent flow conditions and the mixing in the rest drop encountered in the experiments provide a qualitative explanation for the high heat and mass transfer rates which have been consistently found in experimental investigations. On the other hand, the large variety of possible flow fields experienced during drop formation and release account for the difficulty in predicting transfer processes during this process.

Air Molten Salt Direct-Contact Heat Exchange

Volumetric heat transfer coefficients for direct-contact heat exchange between air and molten nitrate salt have been measured as a function of air and salt flow rates at 350° C salt inlet temperature. Using these heat transfer data for a packed column-type heat exchanger, an economic analysis was used to compare direct-contact heat exchange with conventional finned-tube heat exchangers. High volumetric rates of heat transfer (2000–3000 W/m3 °C) and flexibility in choice of materials of construction allow one to realize significant economic benefits by using direct-contact heat exchange in this application.

Experimental and numerical study of direct contact heat exchangers

This paper is a study of a direct contact heat exchanger with a liquid-solid transition. The experiments were carried out on two systems at different working temperatures: Hitec/oil (at 140°C) paradichlorobenzene/water (at 50°C). The particle size distribution at the exchanger column outlet is a function of dispersed-phase and continuous-phase temperatures as well as of the relative velocity of the two fluids at the nozzle. We have established a model based on the heat transfer characteristic times: There is a correlation between the heat exchanger efficiency to the characteristic Peclet number of this type of heat exchangers. We established another model of the heat transfer inside the two-phase flow, giving the temperature profile of the continuous phase along the exchange column and the efficiency of the heat exchange. The results of this model were compared to those obtained experimentally.

Continuous duty solar coal gasification system using molten slag and direct-contact heat exchange

A new, very high temperature solar energy conversion technique which offers the potential of increasing the throughput and decreasing the cost of solar thermal coal gasification is described. Feedgas (CO 2 or steam) is heated to very high temperatures in a direct-contact droplet heat exchanger using slag droplets melted in a solar central receiver. The heated feedgas is then reacted with coal in conventional reaction vessels. Thermal storage at the full thermodynamic potential of the solar receiver is an integral feature of this approach and permits operation of the gasifier at full capacity during periods of no sun.

High-temperature Solar Thermal Energy Storage

The mislocation of solar energy production facilities and points of demand and the temporal mismatch of solar energy availability and energy demand make transport and storage of solar energy essential. Research at the Solar Energy Research Institute has focused on high-temperature, diurnal storage because of the frequency of use and the potential for conservation of premium fossil fuels. Also, high-temperature thermal energy storage can reduce the cost of hydrogen production, electricity and heat produced by cogeneration, and methane reforming. SERI research is concentrating on containment techniques (including materials corrosion, internal insulation, and storage medium for high-temperature molten salts) and direct-contact heat exchange (including cost-effective heat exchanger design and heat transfer of various materials). After initial screening tests we selected carbonates for further study. We are now constructing test equipment that will allow heat transfer experiments with molten carbonate to 700°C

Direct-contact closed-loop heat exchanger: Gregory F Berry, Vladimir Minkov, Michael Petrick assigned to The United States of America as represented by the United States Department of Energy

Direct-contact closed-loop heat exchanger: Gregory F Berry, Vladimir Minkov, Michael Petrick assigned to The United States of America as represented by the United States Department of Energy

Solar storage systems using salt hydrate latent heat and direct contact heat exchange—II Characteristics of pilot system operating with sodium sulphate solution

The operating characteristics of Glauber's salt as a heat storage medium were studied in a pilot heat storage system using direct phase contact heat exchange. The effect of several variables was studied over many complete cycles of the unit, including variable HTF flow rate and inlet temperature, wall insulation, internals to redisperse the HTF and prolonged shutdown of the system. Thermal efficiencies generally exceeded 85 per cent and were often greater than 90 per cent. These values are higher than those reported for smaller heat storage vessels. Volumetric heat transfer coefficients were also determined and correlated with the HTF superficial velocity.

Solar storage systems using salt hydrate latent heat and direct contact heat exchange—III. Operating characteristics of a sodium sulphate-sodium phosphate mixture

Resultats d'etude des caracteristiques de fonctionnement d'un accumulateur de chaleur pilote utilisant soit Na 2 SO 4 .12H 2 O soit un melange de Na 2 SO 4 et Na 2 HPO 4

Analysis of a Liquid/Gas Direct Contact Heat Exchanger Concept

Analyse, a l'aide d'un modele de simulation sur ordinateur, des performances d'un echangeur de chaleur a ecoulement a contrecourant a contact direct direct entre l'air et des goutelettes d'eau de dimensions uniformes

A Calcium Carbonate Scale Inhibitor for Direct-Contact Binary Geothermal Service

Auerbach, Michael H.; Pfizer Central Research Pfizer Central Research Reimer, Robert A.; Pfizer Central Research Pfizer Central Research Olander, Robert G.; Barber-Nichols Engineering Co. Rapier, Pascal M.; Lawrence Livermore Natl. Laboratory Summary A 500-kW direct-contact binary-cycle pilot geothermal power plant was constructed and successfully operated power plant was constructed and successfully operated free of scale at the U.S. DOE East Mesa geothermal test facility. The pilot plant used an Elgin tower direct-contact heat exchanger (DCHX) with isobutane as the working fluid. Initial tests with the untreated 340 deg. F (170 deg. C) geothermal brine gave heavy calcium carbonate fouling of the brine boost pump, flow monitors, and flow-control valves within 20 to 50 hours of startup. Use of 2 ppm high-temperature polymeric scale inhibitor in the feed brine enabled plant operation for more than 700 hours without formation of detrimental scale. The antiscalant was not extracted into the working fluid and did not emulsify the hydrocarbon/brine interface. On the basis of dosage and flow, the additive cost was calculated to be about 0.06 cents per net kW-hr of power generated. Introduction Electrical power is generated from liquid-dominated geothermal resources either bydirect flash of the hot brine to produce steam that drives a turbine ortransfer of sensible heat from the brine to a more volatile working fluid in an organic Rankine cycle loop without brine flash. The vaporized working fluid, usually a low-boiling-point hydrocarbon, drives the power turbine in this binary-cycle process. Heat is transferred from the geothermal brine to the binary-cycle working fluid in either a surface-type tube-and-shell heat exchanger or a DCHX, where the brine and working fluid mix together. The higher effective surface areas and heat-transfer coefficients obtainable with direct contact greatly reduce the capital cost for a given heat flux. However, extraction of steam and noncondensible gases into the working fluid increases turbine backpressure and reduces power output and working fluid recovery, making the DCHX process more complex to operate economically. The direct-flash process is generally more efficient for resources above 392 deg. F (200 deg. C); the binary-cycle process is favored below this temperature. Both processes process is favored below this temperature. Both processes can he completely interrupted or severely restricted by heavy mineral scaling, which fouls or plugs surface piping, pump impellers, and reinjection wellbores. The piping, pump impellers, and reinjection wellbores. The scaling minerals most often found are silica, heavy metal sulfides, and calcium carbonate, depending on the temperature and total dissolved salt content of the particular brine. Scale-control strategy thus depends on the particular brine. Scale-control strategy thus depends on the type of scale, its seventy, and the details of the plant process. process. In 1978 the U.S. DOE commissioned Lawrence Berkeley Laboratory to build and demonstrate a 500-kW direct-contact binary-cycle geothermal pilot plant. Design, construction, and operation of the plant were subcontracted to Barber-Nichols Engineering Co. The plant was built and tested at the U.S. DOE East Mesa plant was built and tested at the U.S. DOE East Mesa geothermal test facility in the Imperial Valley, Holtville, CA, during 1979–81. Extended operation of this plant was severly hampered by CaCO3 scaling. JPT P. 1546

Heat transfer phenomenon in the region of dispersed phase injection in a direct-contact liquid-liquid heat exchanger

A novel temperature measurement technique integrated with a high-speed data acquisition system allowed temperature distributions to be obtained in droplets rising in a liquid-liquid, direct-contact heat exchanger. Heat transfer results were computed from the temperature data and were correlated in terms of dimensionless parameters. A significant amount of the total heat transfer in the column occurred in the region near the dispersed phase inlet nozzle where droplet formation and release effects predominated. Heat transfer results are presented and the related droplet hydrodynamics are discussed.

Instability of horizontal fluid interface in a perpendicular electric field: Observational study

In order to obtain some insight into the potential applicability of electrohydrodynamic augmentation to the direct-contact heat or mass exchange between stratified fluids, observations were made of the phenomena related to the field-induced instabilities at stationary interfaces between air and slightly-conducting oil, slightly-conducting oil and conducting aqueous solution, and two slightly-conducting oils. Established theories assuming the interface conducting or charge-free failed to predict the onset of instability under d.c. or a.c. fields in the last fluid system of the three. The geometries and fluid motions at disturbed interfaces are described laying stress on those, found in the last fluid system, which are very peculiar and have not been reported so far.