Direct Contact Heat Exchanger Research Articles

Performance analysis of heat storage of direct-contact heat exchanger with phase-change material

This paper describes the improvement of the heat-storage performance of a direct-contact heat exchanger using the phase-change material (PCM) erythritol (melting point: 391 K) and a heat transfer oil (HTO). A vertical cylinder with 200-mm inner diameter and 1400-mm height was used as the heat-storage unit (HSU). A nozzle pointing vertically downwards was placed on the bottom of the HSU. We examined the effect of the height of the PCM in HSU on heat storage, using two characteristic parameters: temperature effectiveness and the rate of heat storage. According to the results, both of these parameters increase during the increase in latent heat storage with the height of PCM, due to the increase in the residence time with the height of PCM.

Experimental study on latent heat storage characteristics of W/O emulsion -Supercooling rate of dispersed water drops by direct contact heat exchange-

Recently, much attention has been paid to investigate the latent heat storage system. Using of ice heat storage system brings an equalization of electric power demand, because it will solved the electric -power-demand-concentration on day-time of summer by the air conditioning. The flowable latent heat storage material, Oil/Water type emulsion, microencapsulated latent heat material-water mixture or ice slurry, etc., is enable to transport the latent heat in a pipe. The flowable latent heat storage material can realize the pipe size reduction and system efficiency improvement. Supercooling phenomenon of the dispersed latent heat storage material in continuous phase brings the obstruction of latent heat storage. The latent heat storage rates of dispersed water drops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The water drops in emulsion has the diameter within 3 ~ 25μm, the averaged water drop diameter is 7.3μm and the standard deviation is 2.9μm. The direct contact heat exchange method is chosen as the phase change rate evaluation of water drops in W/O emulsion. The supercooled temperature and the cooling rate are set as parameters of this study. The evaluation is performed by comparison between the results of this study and the past research. The obtained experimental result is shown that the 35K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It was clarified that the supercooling rate of dispersed water particles in emulsion shows the larger value than that of the bulk water.

Analytical Modelling of a Spray Column Three-Phase Direct Contact Heat Exchanger

An analytical model for the temperature distribution of a spray column, three-phase direct contact heat exchanger is developed. So far there were only numerical models available for this process; however to understand the dynamic behaviour of these systems, characteristic models are required. In this work, using cell model configuration and irrotational potential flow approximation characteristic models has been developed for the relative velocity and the drag coefficient of the evaporation swarm of drops in an immiscible liquid, using a convective heat transfer coefficient of those drops included the drop interaction effect, which derived by authors already. Moreover, one-dimensional energy equation was formulated involving the direct contact heat transfer coefficient, the holdup ratio, the drop radius, the relative velocity, and the physical phases properties. In addition, time-dependent drops sizes were taken into account as a function of vaporization ratio inside the drops, while a constant holdup ratio along the column was assumed. Furthermore, the model correlated well against experimental data.

An Experimental Investigation of a Cold Thermal Energy Storage System

This research work investigates the heat transfer characteristics of a direct contact heat exchanger. A cold two phase refrigerant R134a is injected into water stored in an evaporator to exchange directly heat with the water and form clathrates during the charging mode of the operation. The clathrate is used later for obtaining chilled water for air-conditioning purposes. It was found that the performance of the system depends on the refrigerant, its ratio to water, compressor speed and the mass flow rate of the refrigerant.

Experimental Study on Latent Heat Storage Characteristics of W/O Emulsion by Ultrasonic Wave Impression

The flowable latent heat storage material like Oil/Water type emulsion, microencapsulated latent heat material-water mixture or ice slurry, etc., is enabled to transport the latent heat in a pipe. Supercooling phenomenon of the dispersed latent heat storage material in continuous phase is obstructed by a latent heat storage. The latent heat storage rates of dispersed waterdrops in W/O (Water/Oil) emulsion are investigated experimentally in this study. The waterdrops in emulsion have the diameter within 3 - 25 μm, the averaged diameter of waterdrops is 7.3 μm and the standard deviation is 2.9 μm. Supercooling release of waterdrops in emulsion is examined by short time impressing of the ultrasonic. The direct contact heat exchange method is chosen as the phase change rate evaluation of waterdrops in W/O emulsion. The supercooled temperature is set as parameters of this study. The previous obtained experimental result, as the condition without impressing ultrasonic wave, showed that the 35 K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It is clarified that it is possible to reduce 20 K of supercooling degree by impressing the ultrasonic.

D141 直接接触熱交換法によるW/Oエマルションの潜熱蓄熱量評価(OS-11:凝固・融解を伴う伝熱現象とその応用(3))

The latent heat storage rates of dispersed water drops in W/O (Water/Oil) emulsion are investigated experimentally on this study. The water drops in emulsion has the diameter within 3〜25μm, the averaged water drops diameter is 7.3μm and the standard deviation is 2.9μm. The direct contact heat exchange method is chosen as the phase change rate evaluation of water drops in W/O emulsion. The supercooled temperature and the cooling rate are set as parameters of this study. The evaluation is performed by comparison between the results of this study and the past research. The obtained experimental result is shown that the 35K or more degree from melting point brings 100% latent heat storage rate of W/O emulsion. It was clarified that the supercooling rate of dispersed water particles in emulsion shows the larger value than that of the bulk water.

Analysis of condensation cooling of gases in a hollow counterflow jet scrubber at an initial gas temperature above the dew point

Valdberg and Savitskaya [1] have proposed a method for analysis of the condensation cooling of gases, which is based on values of the efficiency coefficient obtained as a result of experimental investigations for a number of direct-contact heat exchangers. To confirm the feasibility of this computational method for the case of the cooling of gases with an initial temperature significantly higher than the dew point in a hollow jet counterflow scrubber, we compared it with the method normally employed in practice and consisting of separation of the cooling process that occurs in the vessel into two stages: initial ‐ convective (up to the dew point), and subsequent ‐ condensation with water vapor separated from the gases. The analyses were performed on an example of a hollow jet counterflow scrubber intended for the cooling of pyrolysis gases with an initial gas temperature t g ′ = 400°C to a temperature t g ″′ = 35°C. The mass flow rate of dry gases at the inlet to the vessel G g = 2349 kg/h (0.65 kg/sec), the initial moisture content d′ = 0.364 kg/kg of the dry gases (dew point t dp = 60°C), and water with a temperature t l ′ = 20°C and wet-bulb temperature t wb = 85.4°C was delivered for irrigation. For a separate scheme of analysis of the gas-cooling process, the temperature of the liquid at the outlet from the vessel, which can be assumed equal to the temperature of the wet-bulb thermometer t wb , can be described by two heat-balance equations. The first equation (for the lower section of the scrubber):

G061043 混合潜熱蓄熱材を充填した直接接触蓄熱槽の凝固・融解特性([G061-04]熱工学部門,一般セッション(4) : 固液相変化)

The present paper is suggested using waste heat of middle temperature region (100℃〜250℃) as heat source from factories. The purpose of this paper is comparing the melting and solidification characteristics of the mixture of mannitol and erythritol (C_M=70mass%, mannitol[70mass%]: erythritol[30mass%]) and mannitol as phase change materials (PCMs) in a direct-contact heat exchange type vessel. The experimental results show that the solidification behavior of the mixture of C_M=70mass% has a small porous area and the lower part of the porous solidification layer solidifies rapidly compared with mannitol. Furthermore as flow quantity of oil as a heat transfer medium increases, average heat release speed grows up.

Modeling Energy Flow in an Integrated Pollutant Removal (IPR) System with CO2 Capture Integrated with Oxy-fuel Combustion

Oxy-coal combustion is one of the technical solutions for mitigating CO2 in thermal power plants. Many processes have been evolved in past the decade to capture CO2 from process industries. Researchers at the National Energy Technology Laboratory (NETL) have patented a process, integrated pollutant removal (IPR), that uses off the shelf technology to produce a sequestration-ready CO2 stream from an oxy-combustion power plant. The IPR process as it is realized at the Jupiter Oxygen Burner Test Facility is a spray tower (direct-contact heat exchanger) followed by four stages of compression with intercooling. To study the energy flows of the oxy-combustion process, a 15 MWth oxy-combustion pulverized-coal-fired plant integrated with the IPR system was simulated and analyzed using ASPEN Plus and ASPEN energy analyzer. This paper discusses flue-gas recycle, energy flow, recovery, and optimization of IPR systems. ASPEN models of heat- and mass-transfer processes in a flue-gas-condensing heat-exchanger system were developed to predict the heat transferred from flue gas to cooling water. The flue-gas exit temperature, cooling water outlet temperature, and energy flows of IPR streams were computed using ASPEN models. Pinch principles are deployed for targeting design and operation-guiding purposes and balancing the heat and mass transfer in the IPR system. The results are expected to support sophistication of the IPR system design, improving its application in a variety of settings. They open the door for valuable IPR efficiency improvements and generalization of methodology for simultaneous management of energy resources.

Heat storage in direct-contact heat exchanger with phase change material

This paper describes the development and performance of a direct-contact heat exchanger using erythritol (melting point: 391 K) as a phase change material (PCM) and a heat transfer oil (HTO) for accelerating heat storage. A vertical cylinder with 200-mm inner diameter and 1000-mm height was used as the heat storage unit (HSU). A nozzle facing vertically downward was placed at the bottom of the HSU. We examined the effects of flowrate and inlet temperature of the HTO using three characteristic parameters of heat storage – difference between inlet and outlet HTO temperatures, temperature effectiveness, and heat storage rate. The temperature history of latent heat storage (LHS) showed three stages: sensible heat of solid PCM, latent heat of PCM, and sensible heat of liquid PCM. Further, the operating mechanism of the DCHEX was proposed to explain the results. The average heat storage rate during LHS was proportional to the increase in flowrate and inlet temperature of HTO. Thus, latent heat can be rapidly stored under large HTO flowrate and high inlet temperature in the DCHEX.

J133 ゼオライトヒートポンプに用いるニードルフィン付熱交換器の性能の検討(一般講演(3))

Aiming at solution of the problem that the heat exchange speed of zeolite heat pump is slow, the time which 1 cycle takes is long, direct contact type particle packed bed's performance were examined focusing zeolite particle layer height. The findings by as a result making zeolite particle layer height high of there having been without time influence to saturation adsorption temperature, having more influence on the quantity of heat used for desorption per unit mass of the zeolite in a test section downstream site was acquired. As a result ,we found out that the direct contact heat exchanger had the advantage of making a particle layer thin.

Review of Recent Patents on Ice Slurry Generation

Ice slurry can be employed with advantages in many fields, including refrigeration, air conditioning, supermarket display, food process and mine cooling and so on. The most important issue concerning the ice slurry application is still its generation method, relating to the efficiency and reliability of water or aqueous solution converting to ice crystals or ice slurry. Though the ice slurry generation methods have been widely investigated, patented and employed, recent patents of ice slurry generation methods after the year of 2000 are reviewed in this article, which is mainly focused on the generation efficiency and reliability. The novel promotions on the already disclosed methods, including the scraped surface generator, the supercooling method, the direct contact generation, the vacuum ice slurry generator are introduced, expecting to provide more inspirations for the designers. Keywords: Ice slurry, generation methods, refrigeration system, scraped surface generator, blade, auger, supercooling method, supercooling release, direct contact heat exchange, primary refrigerant, secondary refrigerant, vacuum ice slurry generator, absorption, slurry generator combined with storage, recent patent, mine cooling, fraction

Implementation and experimental validation of a modeling tool for humid air turbine saturators

This work presents the re-engineering of the TRANSAT 1.0 code which was developed to perform off-design and transient condition analysis of Saturators and Direct Contact Heat Exchangers. This model, now available in the 2.0 release, was originally implemented in FORTRAN language, has been updated to C language, fully coded into MATLAB/Simulink® environment and validated using the extensive set of data available from the MOSAT project, carried out by the Thermochemical Power Group of the University of Genoa. The rig consists of a fully instrumented modular vertical saturator, which is controlled and monitored with a LABVIEW® computer interface. The simulation software showed fair stability in computation and in response to step variation of the main parameters driving the thermodynamic evolution of the air and water flows. Overall the model proved to be reliable and accurate for energy systems simulations.

ICONE19-43422 EXPERIMENTAL STUDY ON THERMAL INTERACTION OF ETHANOL JETS IN HIGH TEMPERATURE FLUORINERT

As a fundamental study for the direct contact heat exchange which was employed for in-vessel heat exchange in Pb-Bi cooled direct contact boiling water small fast reactor (PBWFR) or Steam Generator Tube Rupture (SGTR) accident in lead alloy-cooled fast reactor (LFR), ethanol jet was injected into high temperature fluorinert (FC-3283) in order to investigate the jet boiling phenomena just after volatile water contacting with the high temperature continuous lead alloy liquid. Two series of tests (no-boiling and boiling) were initiated to evaluate ethanol vapor volume which generated around the ethanol jet. With synchronized temperature measurement around ethanol jet, the overview of the boiling behavior showed that jet boiling occurred at bottom part of jet firstly and developed to the upper part within very narrow area around jet.

Vapor compression CuCl heat pump integrated with a thermochemical water splitting cycle

In this paper, the feasibility of using cuprous chloride (CuCl) as a working fluid in a new high temperature heat pump with vapor compression is analyzed. The heat pump is integrated with a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for internal heat recovery, temperature upgrades and hydrogen production. The minimum temperature of heat supply necessary for driving the water splitting cycle can be lowered because the heat pump increases the working fluid temperature from 755 K up to ∼950 K, at a high COP of ∼6.5. Based on measured data available in past literature, the authors have determined the T– s diagram of CuCl, which is then used for the thermodynamic modeling of the cycle. In the heat pump cycle, molten CuCl is flashed in a vacuum where the vapor quality reaches ∼2.5%, and then it is boiled to produce saturated vapor. The vapor is then compressed in stages (with inter-cooling and heat recovery), and condensed in a direct contact heat exchanger to transfer heat at a higher temperature. The heat pump is then integrated with a copper–chlorine water splitting plant. The heat pump evaporator is connected thermally with the hydrogen production reactor of the water splitting plant, which performs an exothermic reaction that generates heat at 760 K. Additional source heat is obtained from heat recovery from the hot reaction products of the oxy-decomposer. The heat pump transfers heat at ∼950 K to the oxy-decomposer to drive its endothermic chemical reaction. It is shown that the heat required at the heat pump source can be obtained completely from internal heat recovery within the plant. First and second law analyses and a parametric study are performed for the proposed system to study the influence of the compressor's isentropic efficiency and temperature levels on the heat pump's COP. Two new indicators are presented: one represents the heat recovery ratio (the ratio between the thermal energy obtained by internal heat recovery, and the energy needed at the heat pump evaporator), and the other is the specific heat pump work per mole of hydrogen produced. This new heat pump with CuCl as a working fluid can be attractive in other industrial contexts where high temperature heat is needed. One may replace a common heating technology (combustion or electric heating) with the present sustainable method that uses heat recovery and high efficiency temperature upgrading for heating applications.

Experimental study of jet structure and pressurisation upon liquid nitrogen injection into water

The rapid phase change and heat transfer obtained by direct contact heat exchange between a cryogen and water can generate high rates of pressurisation, which is of interest to a number of applications. A visualization study of liquid nitrogen injection into water is conducted in this work, with synchronized pressure and temperature measurement, to obtain insight into this complex phenomenon. High speed imaging reveals a four-stage evolution of liquid nitrogen jet structure upon injection into water, with a thick vapour blanket forming around a liquid nitrogen core and break-up brought on predominantly through impact with the vessel wall. Maximum pressurisation rate occurs in the third stage of injection due to a combination of heat and mass transfer. Pressurisation rates in excess of 350 bar/s are recorded and found to vary proportionally with injection pressure. The scenario of gaseous nitrogen injection is also investigated, and compared with liquid nitrogen injection. A clear advantage of liquid nitrogen injection is elucidated from the point of heat transfer and pressurisation, and implications for use in a cryogenic engine are discussed.

Numerical Simulation of Direct-contact Condensation from a Supersonic Steam Jet in Subcooled Water

The phenomenon of direct-contact condensation, used in steam driven jet injectors, nuclear reactor emergency core cooling systems and direct-contact heat exchangers, was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water. The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter. The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics (CFD) simulations were compared with the published experimental data and fairly good agreement was observed between the two, thus validating the condensation model. The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33, while the condensation heat transfer coefficient varies from 0.75-0.917 MW·(m 2·K) −1 for water temperature in the range of 293-343 K.

ENERGY EFFECTIVENESS OF SIMULTANEOUS HEAT AND MASS EXCHANGE DEVICES

Simultaneous heat and mass exchange devices such as cooling towers, humidifiers and dehumidifiers are widely used in the power generation, desalination, air conditioning, and refrigeration industries. For design and rating of these components it is useful to define their performance by an effectiveness. In this paper, several different effectiveness definitions that have been used in literature are critically reviewed and an energy based effectiveness which can be applied to all types of heat and mass exchangers is defined. The validity and the limitations of the various effectiveness definitions are demonstrated by way of several examples including direct and indirect contact, parallel and counterflow heat and mass exchangers. The limiting case of a simple heat exchanger is also discussed. The importance of thermal balancing in minimizing entropy production and its implications for optimization and design of these devices is dealt with in detail. The application of the energy effectiveness to heat-exchanger-like -NTU correlations is also examined using a detailed numerical model.

Convective heat transfer from molten salt droplets in a direct contact heat exchanger

This paper presents a new predictive model of droplet flow and heat transfer from molten salt droplets in a direct contact heat exchanger. The process is designed to recover heat from molten CuCl in a thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. This heat recovery occurs through the physical interaction between high temperature CuCl droplets and air. Convective heat transfer between droplets and air is analyzed in a counter-current spray flow heat exchanger. Numerical results for the variations of temperature, velocity and heat transfer rate are presented for two cases of CuCl flow. The optimal dimensions of the heat exchanger are found to be a diameter of 0.13 m, with a height of 0.6 and 0.8 m, for 1 and 0.5 mm droplet diameters, respectively. Additional results are presented and discussed for the heat transfer effectiveness and droplet solidification during heat recovery from the molten CuCl droplets.

Turbulent direct-contact heat transfer between two immiscible fluids

Heat transfer between two immiscible liquid phases in turbulent flow is of great interest in improving the residence time, compactness, and energy cost of cooling and heating processes. The high-efficiency vortex (HEV) device used here as a direct-contact heat exchanger (DCHE) is a generic multifunctional exchanger/reactor in which wall tabs generate longitudinal vortices responsible for convective radial transfer that enhance macro-mixing, phase dispersion and fast temperature homogenization in the flow. The experiments reported here concern a continuous flow of water in which an immiscible mineral oil is injected. The inlet water temperature ranges from 11 to 13 °C, and the inlet oil temperature from 40 to 48 °C; the flow Reynolds number varies between 7500 and 15 000. An algebraic one-dimensional thermal model accounting for the axial evolution of the phase temperatures coupled with drop breakup is developed and validated by the experimental thermal results in the DCHE. This model requires knowledge of the turbulent field in single-phase conditions; it can be adapted to other flow geometries and can be used as a sizing tool for engineering design. Despite the phase separation at the outlet, the DCHE is more efficient than a double-jacketed heat exchanger in terms of global Nusselt number. In addition, the HEV heat exchanger is energetically less costly than the other DCHE for the same heat-transfer capacity.