Subcooling Temperature Research Articles

Three-dimensional numerical simulation of the interaction between high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth metal

The rupture accident of the steam generator heat transfer tube of the lead-bismuth cooled fast reactor causes a high-pressure sub-cooled water jet impacting high-temperature liquid lead-bismuth, and the interaction mechanism between water and liquid lead-bismuth needs to be studied clearly. In this paper, based on the volume of fluid method, the LES turbulence model and the Lee phase transition model, a three-dimensional numerical model is developed to study the multiphase flow and heat transfer mechanism of water and lead-bismuth interaction. The effects of sub-cooled water temperature, inlet pressure, and nozzle diameter on the distribution of phase state, pressure, temperature, and generated steam volume are studied in detail. The results indicate that the water jet can be divided into the jet water zone, the water-steam mixed zone, and the multiphase flow zone, respectively. Among them, the appearance of water-steam mixed zone depends on the internal boiling of the jet, and this zone tends to appear under the condition of low inlet pressure, small nozzle diameter and high sub-cooled water temperature. For multiphase flow zone, the temperature increases with sub-cooled water temperature, decreases with nozzle diameter and is almost not influenced by inlet pressure; The pressure increases with sub-cooled water temperature, inlet pressure and nozzle diameter. When nozzle diameter is large enough, however, it no longer has any effect on the temperature and pressure distribution within the jet. The volume of steam generated by water boiling is positively correlated with all three factors. Overall, the steam migrates upward through the outer side of the jet, absorbing heat and expanding during the migration process, and forming a high-temperature area at the top of the jet.

Multiple slot nano-jet impingement cooling of a sinusoidal hot surface by using active rotating cylinders under magnetic field

In this study, cooling performance of a multi-slot jet impingement system for a wavy surface are explored under the triple combined effects of using magnetic field (MG-F), double active rotating cylinders and nanofluid. Double rotating cylinders which provide additional cooling are used while Galerkin weighed residual finite element method is used for the solution of the governing equations. Effects of Rew (rotational Reynolds number, between −1000 and 1000), Ha (MG-F strength between 0 and 30), MG-F inclination (between 0 and 90) and sub-cooling temperature of the active cylinders (dT between 0 and 10) on the cooling performance are assessed. Rotations of the double cylinders generally provide higher Nusselt number (Nu) while 41% and 18.9% increment in the Nu is obtained when using pure fluid and nanofluid. The average Nu behavior is different when using MG-F depending upon the rotations are active or not. Average Nu is sharply reduced by about 25.1% without rotations but it rises by about 89% at Ha = 10 by using rotations. The impacts of sub-cooling is very effective when rotations are active while up to 37.9% rise of Nu is obtained at Rew = −1000. When no cylinders are used, using MG-F reduced the average Nu by about 15.4%. The best cooling performance case in the absence of MG-F with cylinders is obtained at Rew = −1000 and dT = 10.

Dropwise Condensate Comb for Enhanced Heat Transfer.

Dropwise condensation on superhydrophobic surfaces could potentially enhance heat transfer by droplet spontaneous departure via coalescence-induced jumping. However, an uncontrolled droplet size could lead to a significant reduction of heat transfer by condensation, due to large droplets that resulted in a flooding phenomenon on the surface. Here, we introduced a dropwise condensate comb, which consisted of U-shaped protruding hydrophilic stripes and hierarchical micro-nanostructured superhydrophobic background, for a better control of condensation droplet size and departure processes. The dropwise condensate comb with a wettability-contrast surface structure induced droplet removal by flank contact rather than three-phase line contact. We showed that dropwise condensation in this structure could be controlled by designing the width of the superhydrophobic region and height of the protruding hydrophilic stripes. In comparison with a superhydrophobic surface, the average droplet radius was decreased to 12 μm, and the maximum droplet departure radius was decreased to 189 μm by a dropwise condensate comb with 500 μm width of a superhydrophobic region and 258 μm height of a protruding hydrophilic stripe. By controlling the droplet size and departure on hierarchical micro-nanostructured superhydrophobic surfaces, it was experimentally demonstrated that both the heat transfer coefficient and heat flux could be enhanced significantly. Moreover, the dropwise condensate comb showed a maximum heat transfer coefficient of 379 kW m-2 K-1 at a low subcooling temperature, which was 85% higher than that of a superhydrophobic surface, and it showed 113% improvement of high heat flux or heat transfer coefficient when it was compared with that of the hierarchical micro-nanostructured superhydrophobic surface at a high subcooling temperature of ∼10.6 K. This work could potentially transform the design and fabrication space for high-performance heat transfer devices by spatial control of condensation droplet size and departure processes.

Crystal Structure Analysis of Different Flame Retardant Copolymers

In this paper, through the DSC rising and cooling scanning and non-isothermal crystallization tests of different flame retardant copolymers, the crystallization process of four types of copolymers formed by adding different flame retardants such as CEPPA, DDP, Carbon-dots (gCDs), and MOF materials was studied. Also, the crystallization kinetics and crystal structure were explored. The results showed that the flame retardant effect of the flame retardant copolymer was improved after adding gCDs. The subcooling temperature (ΔTmc) values of MOF material and CEPPA were both higher than those of the DDP flame retardant copolymer after the addition of carbon dots, indicating that the introduction of the carbon-dots material made crystallisation easier. With the increase of carbon dot content, the value first increases and then decreases, indicating that the crystallization is the easiest when the content is 1%, and 1% gCDs+8% DDP has a higher crystallization ability. Pure DDP has the highest mc values, which also shows good spinnability. Also, the cooling rate strongly influences the crystallisation process, with crystallisation being more rapid when the crystallisation rate is higher. Also, the cooling rate strongly influence the crystallisation process, with crystallisation being more rapid when the crystallisation rate is higher.

Thermal Performance Analysis of Micro Pin Fin Heat Sinks under Different Flow Conditions

Due to microscale effects, the segmented microchannels or micro pin fin heat sinks emerged as a high thermal management solution. In this context, the present work analyzes the influence of different heights of square micro pin fins with an aligned array and investigates their influence on pressure drop and heat transfer behavior. The HFE-7100 is used as the working fluid, and the pressure drop and surface temperature behavior are analyzed for different mass fluxes and inlet subcooling. The single-phase flow was analyzed numerically using the computational fluid dynamics (CFD) software ANSYS FLUENT® for comparing the simulation results with the experimental data, showing that the highest micro pin fins configuration provides a more uniform and lowest wall temperature distribution compared to the lowest configuration. There is a good agreement between the experimental results and the numerical analysis, with a mean absolute error of 6% for all the considered parameters. For the two-phase flow condition, experimental tests were performed, and for the highest subcooling, an increase in mass flux causes an enhancement in the heat transfer for low heat flux; by increasing heat flux, there is a gradual predominance of boiling heat transfer over convection as the heat transfer mechanism. The pressure drop drastically increases with the vapor amount flowing into the system, regardless of the pin fin height; the boiling curves for the higher fin height show a much smaller slope and a smaller wall superheat than the fin with the smallest height, and consequently, a high heat transfer performance. A larger region of the heat sink is filled with vapor for lower inlet subcooling temperatures, degrading the heat transfer performance compared to higher inlet subcooling temperatures.

Thermal contraction of the boundary layer from progressive cooling and its possible use as active flow control technique

In this work, consideration is given to thermal contraction of the boundary layer from the progressive cooling of the airfoil and its possible technological use as an active flow control technique. Here, it is thought that if the airfoil is progressively cooled from the leading-edge toward the trailing-edge the increase in density will translate into a progressive contraction of the boundary layer which eventually could be used as technique for either re-attachment or delay detachment of the boundary layer. Utilizing the von Karman momentum integral an analytical expression for the reduction of the thickness of the boundary layer by thermal contraction was derived which predicts contractions around 10 percent for temperatures drops around 50° K. Experimental measurements made on a heated flat plate with controlled thermal gradient agree with the theoretical prediction within a ± 10 per cent. The possibility of prompt contraction of the boundary layer by condensation (of the air or its moisture content) if the temperature drops below the subcooling temperature, is an open question which should be addressed in future research.

Sustainable freshwater recovery from radioactive wastewater by gas hydrate formation

Freshwater production from radioactive wastewater is a key issue not only to minimize environmental contamination by nuclear power plants but also to develop new types of nuclear technology such as small modular reactors. Here, we present a sustainable hydrate-based desalination (HBD) technology for freshwater recovery from radioactive wastewater, specifically from Cs, Sr, and I-containing wastewater. CHClF2 and SF6 were selected as a hydrate former for HBD processes, which can be operated under relatively mild conditions. X-ray diffraction and Raman spectroscopy measurements indicated that the crystal structure of the CHClF2 and SF6 hydrates formed with radioactive chemicals was identical to that of pure CHClF2 and SF6 hydrates, respectively. Formation kinetics experiments were performed to investigate the inhibition effect of Cs+, Sr2+, and I− on CHClF2 and SF6 hydrates, indicating that the apparent rate constant, initial reaction rate, and pressure drop caused by the formation of gas hydrate significantly depend on the sub-cooling temperature and concentrations of the radioactive chemicals. A close examination using scanning electron microscopy with energy dispersive X-ray spectroscopy and in situ temperature-dependent solid-state NMR spectroscopy found evidence of the exclusion of radioactive chemicals from solid gas hydrates, signaling the potential of HBD technology for use in freshwater production from radioactive wastewater. More importantly, the proposed HBD process is applicable to wastewater in the very large concentration ranges of Cs+, Sr2+, and I− covering from the percent to hundreds of parts per million (ppm) and even the sub-ppm ranges, revealing equivalent recovery and separation efficiency rates for all wastewater solutions. We conclusively present a clear-cut picture of the dual-functional HBD process of freshwater recovery and radioactive chemical separation from wastewater.

Experimental investigation on flow boiling of HFE-7100 in a microchannel with pin fin array

An experimental investigation on flow boiling heat transfer and pressure drop characteristics in a microchannel with an array of in-line circular pin fins was carried out. The tests with HFE-7100 as a working fluid were conducted at mass fluxes from 189 to 374 kg/m2∙s, inlet subcooling temperatures from 20.4 to 34.4 °C and effective heat fluxes from 17.4 to 239.3 kW/m2 near atmospheric pressure. The effects of mass flux, inlet subcooling temperature, heat flux and vapor quality were examined and analyzed. Flow visualization was also obtained during the experiments to explain the heat transfer mechanism. The boiling hysteresis was observed, which may be attributed to the low surface tension of HFE-7100. The experimental data were compared with various published data of dielectric fluorinated fluids, and many well-known correlations of pressure drop and two-phase heat transfer coefficient for pin–fin microchannels. The improved correlations of pressure drop and two-phase heat transfer were proposed, which demonstrated good predictions for both experimental data of the present and previous studies.

Experimental study on condensation and acoustic characteristics of steam underwater injection

Introduction: Bubbling deaeration is widely applied in marine steam power system, and direct contact condensation (DCC) of steam injected into water under low sub-cooled water is the thermodynamic foundation of this technology. The deaeration process involves complex thermal and hydraulic behaviors, such as violent turbulence, interfacial mass transfer, and multiphase flow etc., which induce significant pressure fluctuation and radiated noise. In this paper, the two-phase flow regimes and acoustic characteristics of DCC of steam injected into water were studied for sub-cooled temperature ranging from 3℃ to 17℃.Methods: Using high-speed camera to capture the dynamic plume shape, four typical plumes are found: external chug with encapsulating bubble, oscillating bubble jet, conical and cylindrical jet and cap jet; The underwater acoustic signal is measured synchronously, and the acoustic spectrum is obtained by Fast Fourier transform (FFT).Results and Discussion: Combined with the plume image, the component sources of the acoustic signal are analyzed. It is found that the first dominant frequency and the second dominant frequency of the acoustic are caused by the evolution of the jet main steam zone and the downstream large steam column respectively; By analyzing the influence of injection parameters on acoustic signal, it is found that steam flow and sub-cooled temperatures have a great influence on acoustic root mean square value and spectrum characteristics. With the decrease of sub-cooled temperature, the main frequency of injection noise signal gradually moves to low frequency. Low frequency noise dominates the radiated noise when the flow field approaches the saturation temperature.

Condensation heat transfer on slippery lubricant-impregnated nanohole-arrayed stainless-steel surface

The condensation heat transfer performance of lubricant-impregnated surfaces has a competitive advantage owing to the improved mobility of droplets and self-healing characteristics. In this study, we fabricated the lubricant-impregnated surfaces featured with Teflon-coated anodized nanoporous oxide layer on stainless steel infused with Krytox GPL103 oil. The characterization shows that the droplet state on the surface changes from the pinning to slippery states (sliding angle α of 1.8 ± 0.3°) enabled by the presence of the lubricant oil. The condensation heat transfer performances of the lubricant-impregnated Teflon-coated anodized stainless-steel surface (L-T-AS) are investigated from the aspects of the surface wettability and droplet mobility, compared to that of Teflon-coated stainless-steel surface (T-S) and Teflon-coated anodized stainless-steel surface (T-AS). Whereas coalescence-induced droplet shedding and droplet sweeping are found on the T-S and T-AS, the shedding of discrete droplets and their sweeping without further coalescence are noticed on the L-T-AS. The heat transfer coefficient of the L-T-AS is 398.4% higher than that of the T-AS at the low subcooling temperature of 0.2 K. The heat transfer performance of the dropwise condensation of the L-T-AS has further been elucidated by the theoretical model considering the heat transfer rate through a single droplet associated with the density distribution function of the droplet.

Simultaneous inhibition of natural gas hydrate formation and CO2/H2S corrosion for flow assurance inside the oil and gas pipelines

Compatibility problems are observed during the co-injection of corrosion and gas hydrate inhibitors inside oil and gas pipelines, which reduces their performance. In this study, the newly synthesized dual-purpose inhibitors (DPIs) were developed to overcome the compatibility challenge between the inhibitors. A detailed experimental and computational study was performed to investigate the inhibition activity of DPIs. The results of constant cooling experiments showed that the inhibitors significantly prevented natural gas hydrate formation. DPI2 with a propyl pendant group was the best sample by providing a subcooling temperature of 18.1 °C at 5000 ppm. DPI1 and DPI3 decreased gas consumption by 2.6 and 2.4 times, respectively, compared to pure water. In addition, molecular dynamics simulation revealed that the transportation of gas molecules to the growing hydrate cages was disrupted due to DPI2 adsorption on the surface of the hydrate, which partially covered it and acted as a mass transfer barrier. Furthermore, the interaction of the anion part of the inhibitor with the nearest neighbor water molecules lowered the water activity to form the hydrogen-bonding networks for the hydrate formation. According to corrosion measurements, DPIs suppressed the corrosion rate of mild steel in H2S–CO2 saturated oilfield-produced water, and a maximum inhibition efficiency of 96.3% was obtained by adding 1000 ppm of DPI2. Moreover, the estimated adsorption energy of DPI2 were relatively high and matched with experimental data, implying that the inhibitor has a high degree of adsorption on the metal for forming a protective layer on the mild steel surface. These findings signified that DPIs provide a potential hybrid inhibition of corrosion and gas hydrate formation for flow assurance applications and reduce the operation costs.

Conjugate Heat Transfer Analysis for Cooling of a Conductive Panel by Combined Utilization of Nanoimpinging Jets and Double Rotating Cylinders.

In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 °C. When increasing the cylinder sizes, temperature drops become 7 °C, while they are only 1.75 °C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 °C and 10 °C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input.

Heat Transfer Deterioration by the Copper Oxide Layer on Horizontal Subcooled Flow Boiling

Water–copper is one of the most common combinations of working fluid and heating surface in high-performance cooling systems. Copper is usually selected for its high thermal conductivity and water for its high heat transfer coefficient, especially in the two-phase regime. However, copper tends to suffer oxidation in the presence of water and thus the heat flux performance is affected. In this research, an experimental investigation was conducted using a cooper bare surface as a heating surface under a constant mass flux of 600 kg·m−2·s−1 of deionized water at a subcooled inlet temperature ΔTsub of 70 K under atmospheric pressure conditions on a closed-loop. To confirm the heat transfer deterioration, the experiment was repeated thirteen times. On the flow boiling region after thirteen experiments, the results show an increase in the wall superheat ΔTsat of approximately 26% and a reduction in the heat flux of approximately 200 kW·m−2. On the other hand, the effect of oxidation on the single phase is almost marginal.

Experimental study on the competition between carbon dioxide hydrate and ice below the freezing point

As climate change and industrial requirements intensify, the potential of CO2 hydrates for carbon storage has attracted increasing attention. However, despite continuous progress, the subzero phase behavior of the CO2-H2O system is not well understood and merits further research. To investigate the competing and coexisting growth mechanisms of CO2 gas hydrate and ice below the quadruple point, we conducted experiments at both the micrometer-scale and mesoscale scales. The growth morphology of hydrate and ice at large and small subcooling temperatures was observed in situ in a high-pressure optical cell, and the thermodynamic behavior of the competitive process after hydrate formation was investigated in a high-pressure reactor with sands. When hydrates and ice are formed together at small subcooling temperatures, preferential hydrate formation leads to ice dissolution or even disappearance. At large subcooling temperatures, ice forms first, and the hydrate mainly forms a fibrous envelope. A small decrease in the subzero temperature after hydrate formation partially decomposes the hydrates owing to ice formation, followed by more rapid hydrate production. This study provides a thorough and expanded understanding of the competition between ice and hydrates by connecting the evolution of crystal frameworks with the thermodynamic features of the process.

Experimental study on improving the performance of vapor compression cycle by using loop-type heat pipe

In this study, an experimental study was carried out on a heat pipe, whose evaporator is located between the compressor outlet and the condenser inlet of an industrial cooler on a vapor compression cycle (VCC). It absorbs heat from the new generation refrigerant fluid of 515B and transfers it to the outdoor air. The heat pipe is a looped thermosiphon-type heat pipe. R134a refrigerant is used as a working fluid in the heat pipe. By changing the condenser air inlet temperatures, the contribution of the heat pipe to the cooling cycle has been determined experimentally. While the evaporation pressure of the refrigeration cycle with the heat pipe remains approximately constant, the condensation pressure decreases, and the sub-cool temperature increases. For condenser air inlet temperatures of 30, 40, and 50°C, the COP of the cooler with heat pipe increases by 1.8%, 2.6%, and 2.76%, respectively. As the air temperature at the condenser inlet increases, the ratio of heat pipe power to the cooling capacity of the cycle also increases. In addition, the compressor outlet temperature is reduced by 1.5%–2.8% using of the heat pipe.

MORPHOLOGICAL EVOLUTION OF Al2O3 AND CNT NANOFLUID DROPLETS DURING SOLIDIFICATION

Nanofluid is an emerging heat transfer fluid with good heat transfer and thermal conductivity properties. It is important to investigate the phase change properties and morphological evolution during the freezing of nanofluid droplets to understand their practical applications. The effect of dynamic wettability on the deformation of a single droplet of aluminum trioxide (Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O) and graphene (CNT-H<sub>2</sub>O) nanofluids at different mass concentrations and substrate temperatures was investigated by visualizing the droplet freezing. The formation of solid-like and freezing front motions inside the droplet during the freezing process of these droplets was investigated. The solidification process was strongly influenced by the temperature gradient perpendicular to the cold surface and the change in the solid–liquid interface wettability during the phase change, resulting in volume redistribution at the top of the droplet. The freezing shape of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O nanodroplets resembled a "moon crater," and the influence of wettability decreased with increasing concentration, leading to a relative increase in the aperture of the top platform. The fully frozen state of the nanofluid droplet had an increasingly pointed tip, with a strong relationship between the substrate temperature and solidification time when the CNT-H<sub>2</sub>O concentration was 5 times higher and showed no change in the freezing droplet deformation rate under the experimental conditions. The contact angle of the two nanofluid droplets did not fluctuate significantly with increasing concentration, while that of the 1% nanofluid droplets remained at an average value of 85° during freezing. Under different freezing conditions, the freezing shape of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O droplets tended to increase in diameter as the subcooling temperature decreased, with the final deformation rate of 1% Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O being twice that at 5% concentration, while the contact angle of the same mass concentration of Al<sub>2</sub>O<sub>3</sub>-H<sub>2</sub>O decreased by 1° as the subcooling temperature dropped. The CNT-H<sub>2</sub>O droplet became sharper at the tip as the subcooling temperature increased, and its contact angle did not change with temperature.

Experimental investigation on vibration characteristics of subcooled and saturated pool boiling

• Subcooled and saturated boiling induced vibration were measured by LDV. • The turbulence mainly excites the first natural frequency of ∼ 45 Hz. • The bubble collapse excites the second natural frequency ∼ 1120 Hz. • The dominant excitation changed with the decreasing of the subcooling value. To investigate the characteristics and the mechanisms of boiling-induced vibration, pool boiling experiments are carried out with deionized water partially filled in a glass vessel under atmospheric pressure. A Laser Doppler Vibrometer (LDV) is employed to acquire the vibration velocity under different heat fluxes (0.30 ∼ 0.65 MW/m 2 ) and subcooled temperatures (0 ∼ 55 °C). Two mechanisms leading to the vibration have been observed: the turbulence and the bubble collapse due to condensation. The turbulence mainly excites the first natural frequency (∼ 45 Hz) of the tested vessel while the bubble collapse mainly excites the second natural frequency (∼ 1120 Hz). For the turbulence induced vibration, the peak amplitude of the first natural frequency increases gradually with the increase of heat flux and the decrease of subcooling degree. For the bubble collapse induced vibration, the pressure pulses are determined by the number of the bubbles and the bulk subcooled temperature (or condensation process). Thus, under the certain bulk subcooled temperature, the corresponding peak amplitude of the second natural frequency increases with the increase of the heat flux when the bulk subcooled temperature is greater than 10 °C, and tends to be stable for the lower bulk subcooled temperatures as the number of bubbles keep constant; while under the certain heat flux, the peak amplitude will increase first and then decrease with the decreasing of the bulk subcooled temperature. The dominant mechanism changes from the bubble collapse to the turbulence with the decreasing of the bulk subcooled temperature for a certain heat flux, and the transition point for all the tested cases is between 10 ∼ 15 °C. In addition, corresponding to the maximal root-mean square (RMS) value of vibration velocity, the bulk subcooled temperature increases with the increase of the heat flux.

Development of Highly Efficient Dual-Purpose Gas Hydrate and Corrosion Inhibitors for Flow Assurance Application: An Experimental and Computational Study

Gas hydrate and corrosion inhibitors are widely used to ensure successful and economic hydrocarbon stream flow inside the oil and gas pipelines. However, compatibility problems are observed during their co-injection into the flowlines as they have different molecular chemistry. Modifying effective gas hydrate inhibitors, such as polyvinylcaprolactam (PVCap), with some active functional groups in corrosion inhibition, can overcome compatibility issues. In this study, maleic anhydride was used as a cheap monomer to synthesize ionic N-vinyl caprolactam/maleic-based copolymers (P(VCap-co-MA)) as potential dual-purpose gas hydrate and corrosion inhibitors. The gas hydrate experiments showed that the inhibitors effectively inhibited natural gas hydrate formation and a maximum subcooling temperature of 14.6 °C achieved in a solution containing 2500 ppm P(VCap-co-MA)-3. The molecular dynamics simulation revealed that P(VCap-co-MA)-3 reduced the gas concentration in the liquid phase and occupied its adsorption sites on the hydrate surface to form a steric hindrance effect, inhibiting the gas hydrate formation. Electrochemical measurements indicated that P(VCap-co-MA)s significantly suppressed steel corrosion in oilfield-produced water saturated with H2S and CO2. P(VCap-co-MA)-3 and P(VCap-co-MA)-5 provided the highest protection of 96.9 and 96.1% in H2S and CO2 media, respectively. Moreover, simulation studies demonstrated that the inhibitors are strongly adsorbed on the steel surface to form a barrier layer on the surface, protecting against corrosive electrolytes. These findings suggest that the modification of a gas hydrate inhibitor improves not only its corrosion and gas hydrate inhibition performance but also decreases the operation costs for flow assurance in the oil and gas pipelines.

Simulasi Termodinamika Pengaruh Temperatur Subcooling di Kondensor Terhadap Kinerja Cold Storage

The subcooling temperature in the condenser can affect the overall performance of the refrigeration system. One of the refrigeration systems that plays an important role in the cold chain of fishery products is cold storage. This paper discusses thermodynamic study of the effect of condenser subcooling temperatures on the performance of cold storage that operates based on a vapor compression refrigeration cycle based on the CoolPack software. The subcooling temperatures varied was 5 – 10 Kelvin and the system performance parameters analyzed were refrigerant mass flow rate, heat rejected in the condenser, compressor power and coefficient of performance. The results of this study indicate that as the subcooling temperature increases, the refrigerant mass flow rate decreases so that the compressor power and the rate of heat release in the condenser also decrease. Thus, the performance coefficient of cold storage will increase as the subcooling temperature increases.

Performance simulation of expander-compressor boosted subcooling refrigeration system

Many applications have made extensive use of refrigeration systems, which have a high energy requirement. Any improvement on the refrigeration systems can reduce the need for energy demand. A common method to improve the system performance is to subcool the condenser exit temperature and known as subcooling. An expander-compressor booster enhanced subcooling vapor compression cycle is proposed as an addition to the subcooling systems described in the literature. The refrigerant is split into two parts at the condenser exit: one portion expands in the expansion device to reach the necessary subcooling temperature, while the other part goes straight into a separate heat exchanger. Later, this additional refrigerant flows into the other expansion valve, the evaporator, and a booster expander-compressor to increase inlet pressure of compressor. As working fluids, six distinct refrigerants including low global warming potential (GWP) are used (namely R134a, R1234yf, R32, R290, R1270, and R600a) in simulations. The coefficient of performance (COP) and increment in COP values for each refrigerant are computed and graphically displayed for various evaporation temperatures between -10 °C and 5 °C. Furthermore, the heat exchanger analysis of subcooling heat exchanger is performed to compare heat transfer surface area and pressure drop for each refrigerant. Results indicate that R1234yf achieves the greatest performance with an increase in COP by 16.7, 19.1 and 21.8% depending on the mechanical efficiencies of the expander and compressors and as well as isentropic efficiency of the expander. By utilizing an expander-compressor with higher or lower mechanical and isentropic efficiencies, these enhancements can be raised or lowered. Heat exchanger analyses show that the pressure drop in the exchanger does not significantly affect the performance of the system.