Cold Streams Research Articles

A novel intercooled series expansion refrigeration/liquefaction cycle using pinch technology

This paper introduces pinch technology into the analysis of large-scale cryogenic processes. This study develops temperature-enthalpy diagrams for different cryogenic cycles based on pinch technology. This enables a better understanding of the development of cryogenic systems to analyze the matching relationships among different components. It is found that the expander has the other functions that parallel or cascade expanders can influence the temperature matched characteristics of the cold and hot streams as well as the irreversibility of heat transfer in cryogenic systems. Based on an analysis of pinch technology, a novel intercooled series expansion refrigeration/liquefaction cycle is proposed and analyzed. In the intercooled series expansion refrigerator/liquefier, the expander and heat exchanger are connected in serial. This paper provides an analysis and design ideas for large-scale cryogenic systems.

Improvement of grinding technology with vortex cooling of steels that are liable to crack propagation

Abstract Complexity of grinding process and phenomena entailing it not always allow reaching required technological results, especially while machining surfaces of parts made of tough-to-machine steels, which are liable to crack propagation. Cracks can occur in these parts during grinding due to considerable temperature difference along the section, which can cause formation of high temporary internal tensile stress. Application of cooled air in grinding process exerts considerable influence over temperature decrease in cutting area. In addition, it depends not only on heat exchange, but also on properties of cold air flow. The greatest effect of temperature decrease can be reached by injection of cold air flow in cutting area with implementation of vortex effect, which occurs in swirl flow of compressed air originating in vortex tube. The study of heat generation during machining by tools with discontinuous cutting surface and vortex air cooling was carried out. Obtained thermophysical parameters of vortex air cooling (increase in speed of stream flowing, expansion degree, share of cold stream and decrease in humidity of air stream) allow reducing heat density due to growth of cooling effect in grinding zone. On the base of experimental studies we developed recommendations for choice of optimal grinding modes by tool with discontinuous cutting surface and vortex air cooling of flat parts made of steels being liable to cracking.

3D design and optimization of heat exchanger network for solid oxide fuel cell-gas turbine in hybrid electric vehicles

The development of electric vehicles is considered as one of the sustainable way in the automotive industry to reduce greenhouse gases emissions and to allow transportation sector to comply with environmental targets required in present and future years. Due to the limited range of autonomy of the electric vehicles and the induced cost and environmental impacts of large capacity batteries, hybrid electric vehicles have been deeply investigated and developed over the last years. In this study, a Solid Oxide Fuel Cell combined with Gas Turbines (SOFC-GT) is used as a range extender in hybrid electric vehicle. The SOFC-GT system increases the autonomy of the electric vehicle and has high electric efficiency of 77%. In this work, the Heat Exchanger Network (HEN) to recover thermal energy in the SOFC-GT system has been studied. The HEN has to meet the targets of limited volume and mass to be compatible with the installation on the hybrid vehicle. This study is basically divided into three steps. In the first step, the HEN synthesis is performed with a mathematical model developed in AMPL, stating the optimal matches between hot and cold streams. In the second step, a model is developed to size the heat exchangers with the LMTD method. In the final step, an optimization problem is solved to minimize the volume or mass of the HEN, by sizing the heat exchangers with a global view of HEN, considering their assembly in a limited space and defining the paths of flow streams. Finally, some heat exchangers have been printed using plastic with a SLA 3D printer, with presentation purpose.

The impact of magnetic fields on cold streams feeding galaxies

ABSTRACT High-redshift, massive haloes are observed to have sustained high star formation rates, which require that the amount of cold gas in the halo is continuously replenished. The cooling time-scale for the hot virialized halo gas is too long to provide the source of cold gas. Supersonic, cold streams have been invoked as a mechanism for feeding massive haloes at high redshift and delivering the cold gas required for continued star formation at the rates observed. This mechanism for replenishing the cold gas reservoir is motivated by some cosmological simulations. However, the cold streams are likely to be subject to the supersonic version of the Kelvin–Helmholtz instability (KHI), which eventually leads to stream disruption. Cosmological simulations have yet to obtain the spatial resolution required for understanding the detailed stability properties of cold streams. In this paper, we consider instead an idealized model of magnetized cold streams that we spatially resolve. Using linear theory, we show how magnetic fields with dynamically important field strengths do not inhibit the KHI but rather enhance its growth rate. We perform non-linear simulations of magnetized stream disruption and find that magnetic fields can nevertheless increase stream survival times by suppressing the mixing rate of cold gas with the circumgalactic medium. We find that magnetic fields can allow streams to survive ∼2–8 times longer and, consequently, that streams ∼2–8 times thinner can reach the central galaxy if the magnetic field strength is $\sim 0.3\rm {-}0.8 \, \mu$G.

A comparison of gas stream cooling and plunge cooling of macromolecular crystals.

Cryocooling for macromolecular crystallography is usually performed via plunging the crystal into a liquid cryogen or placing the crystal in a cold gas stream. These two approaches are compared here for the case of nitro-gen cooling. The results show that gas stream cooling, which typically cools the crystal more slowly, yields lower mosaicity and, in some cases, a stronger anomalous signal relative to rapid plunge cooling. During plunging, moving the crystal slowly through the cold gas layer above the liquid surface can produce mosaicity similar to gas stream cooling. Annealing plunge cooled crystals by warming and recooling in the gas stream allows the mosaicity and anomalous signal to recover. For tetragonal thermolysin, the observed effects are less pronounced when the cryosolvent has smaller thermal contraction, under which conditions the protein structures from plunge cooled and gas stream cooled crystals are very similar. Finally, this work also demonstrates that the resolution dependence of the reflecting range is correlated with the cooling method, suggesting it may be a useful tool for discerning whether crystals are cooled too rapidly. The results support previous studies suggesting that slower cooling methods are less deleterious to crystal order, as long as ice formation is prevented and dehydration is limited.

Hydrodynamic Shielding and the Survival of Cold Streams

Abstract Cold clouds in hot media are quickly crushed, shredded, and then accelerated as a result of their interaction with the background gas. The persistence of cold clouds moving at substantial velocities in harsh environments is a common yet puzzling feature of many astrophysical systems, from quasar absorption lines probing galactic halos to clouds of dust passing near Sgr A *. Here we run a set of idealized numerical experiments, subjecting a line of cold clouds at a series of mutual separations to a hot background wind. We find that this stream of clouds is able to shield itself from hydrodynamic destruction by accelerating the hot background material, creating a protective layer of co-moving gas. We write down a simple diffusion equation that reproduces the behavior of the simulations, and we discuss the implications for cosmological gas accretion and the putative galactic center dust cloud G2.

A young galaxy cluster in the old Universe

ABSTRACT Galaxies evolve from a blue star-forming phase into a red quiescent one by quenching their star formation activity. In high-density environments, this galaxy evolution proceeds earlier and more efficiently. Therefore, local galaxy clusters are dominated by well-evolved red elliptical galaxies. The fraction of blue galaxies in clusters monotonically declines with decreasing redshift, i.e. the Butcher–Oemler effect. In the local Universe, observed blue fractions of massive clusters are as small as ≲0.2. Here we report a discovery of a ‘blue cluster’ that is a local galaxy cluster with an unprecedentedly high fraction of blue star-forming galaxies yet hosted by a massive dark matter halo. The blue fraction is 0.57, which is 4.0σ higher than those of the other comparison clusters under the same selection and identification criteria. The velocity dispersion of the member galaxies is 510 km s−1, which corresponds to a dark matter halo mass of 2.0$^{+1.9}_{-1.0}\times 10^{14}$ M⊙. The blue fraction of the cluster is more than 4.7σ beyond the standard theoretical predictions including semi-analytic models of galaxy formation. The probability to find such a high blue fraction in an individual cluster is only 0.003 per cent, which challenges the current standard frameworks of the galaxy formation and evolution in the ΛCDM universe. The spatial distribution of galaxies around the blue cluster suggests that filamentary cold gas streams can exist in massive haloes even in the local Universe. However these cold streams have already disappeared in the theoretically simulated local universes.

Experimental parametric study of membrane distillation unit using solar energy

Solar distillation is a promising method for the supply of freshwater to rural communities because water is a vital factor for the survival of humans. Therefore potable water demand is increasing continuously because of the industrial, population and, fast agricultural applications. Nowadays, different techniques for water purification have been created to provide freshwater from salty and polluted water such as solar distillation method to distill brackish/saline water. This work presents an experimental study of the solar membrane distillation unit which is coupled with direct contact membrane (DCMD) which located at Kairouan University. The system is installed as part of a cooperation project research and development between Tunisian Electromechanical Systems Laboratory and German Institute for Solar Energy Systems entitled: Solar driven membrane distillation for resource efficient desalination in remote areas. For the heating of the hot feed water stream, a heat exchanger is included which can be operated with any external heat supply between 60 and 80 °C. For the cooling of the cold feed water stream, no heat exchanger is included. The cooling can be provided over the intake of cold feed water. The effect of solar irradiation and all temperature on the journal productivity of the unit has been presented.

Isotope (δD, δ18O, 3H, δ13C, 14C) and chemical (B, Cl) Constrains on water origin, mixing, water-rock interaction and age of low-temperature geothermal water

The isotope (δD, δ18O, 3H, δ13C, 14C) and chemical (B, Cl) compositions of cold (streams, rivers, soil- and groundwater) and low-temperature geothermal water from northern Iceland were investigated in order to delineate the origin, mixing, water-rock interaction and the age of the waters. The waters showed a large range in temperature (0–104 °C) and chemical composition (TDS 7–954 ppm). Based on the δD (−54.9 to −125‰), δ18O (−7.8 to −16.7‰), B (0.001–1.57 ppm), Cl (0.3–500 ppm) content the waters were of meteoric origin that have been modified by primary rock leaching corresponding to rock to water ratio (ξ) of ∼0.001–0.1 kg of basalt dissolved per kg of water. At temperatures above ∼50 °C close to saturation was observed between the waters and common secondary minerals like clays, zeolites and oxides indicating these reactions control the concentrations of reactive elements. At lower temperatures deviation from equilibrium saturation was evident. The water age was constrained by 3H and 14C, the latter corrected for rock carbon using B, Cl and δ13CDIC relations. Most waters displayed modern age. Exceptions were 1) some waters at high ground having lower tritium content and older radiocarbon age; the trend considered to result from mixing between old glacial melt water and modern meteoric water, and 2) some low-temperature geothermal waters in lowland areas considered to be a mixture of old ʽice-ageʼ water, originating from last glacial times >12,000 years ago and modern and/or few decades old meteoric water. Thus, the chemical and isotope composition of cold and low-temperature geothermal waters in the region display a complex story, with waters originating from different conditions and of different age and later mixed and affected by water-rock interaction. These processes need to be considered and understood in order to develop a hydrogeological model of a groundwater system.

An improved design method for retrofitting industrial heat exchanger networks based on Pinch Analysis

Energy integration relies on matching process hot streams with process cold streams, and utilities are only introduced to balance the deficit in energy consumption. A systematic but simple Pinch Analysis (PA)-based retrofit approach is proposed to lessen the utility consumption of any industrial heat exchanger network (HEN) under new minimum temperature approach (ΔTms) at the cost of minor capital investment. This work is an extended and improved version of our previous work (Li and Chang, 2010). Elaborate visualized tool of T–H diagram for identification of cross-pinch heat load is proposed to fully address the case that phases change in the cross-pinch heat exchanger. Main characters of industrial HENs which are large scale, varied heat capacity flow rate and multiple pinches are fully addressed. Specifically, each cross-pinch exchanger or match is identified and those matches with large cross-pinch loads are disconnected first, and then their heat loads on the hot and cold stream side are split according to pinch temperatures. Next, at either side of or between the pinches, the divided heat loads on each stream are combined and matched according to a systematic Pinch Analysis (PA) based procedure. Retrofit modifications are focused on those cross-pinch matches and utility exchangers, so the retrofit procedure of an industrial HEN is obviously simplified. An industrial case of Crude oil preheat train (COPT) is retrofitted to demonstrate the effectiveness of the proposed approach.

Air-gap diffusion distillation: Theory and experiment

A novel Air-Gap Diffusion Distillation (AGDD) technology operated at normal atmospheric pressure was proposed in this paper. In this plant, cold and hot streams flow counter-currently and the strong hydrophilic porous medium is employed as the hot stream channel to control its flow. The operation characteristics of AGDD were investigated and analyzed theoretically and experimentally. Influences of structure and operation parameters on the performances were discussed deeply. The results showed the water productive flux and Gained Output Ratio (GOR) for the AGDD with one air-gap combination were 0.7244 kg·m−2·h−1 and 1.16 respectively when the thickness and height of air-gap, inlet temperatures of cold and hot streams, mass flow rate of cold stream were 5 mm, 0.9 m, 25 °C, 65 °C and 4 kg·h−1 respectively. When the air-gap height was enlarged to 1.8 m and the mass flow rate of cold stream reduced to 2 kg·h−1, the water productive flux and GOR were 0.5255 kg·m−2·h−1 and 5.01 respectively. The results also indicated that the thermal resistance of heat transfer in the AGDD mainly sourced from the air-gap. The variations of structure or operation parameters did not influence on the desalination rate of AGDD which was higher than 99.8% during experiments.

Polygeneration of power, cooling and desalinated water by concentrated solar energy plants equipped with ©GICE engine

Polygeneration of electric power, cooling and fresh water from seawater and brackish water by using solar energy is discussed in this paper. The best plant component arrangement has been selected for a 400–600 square meter Solar Dish surface. The engine is made of turbomachinery derived from the Internal Combustion Engine Turbocharger Technology for reliability and economy reasons. The Micro Gas Turbine has been selected taking the ©GICE complex arrangement concept into account. Such an arrangement is capable of concurrent production of power and of a cold stream by the expansion in the Power Turbine. Such a cold stream is used for ©CryoDesalination of seawater and cooling. An example has been presented, it demonstrates the potential of large solar dish technology used to feed solar energy in an integrated system made of a ©GICE engine, ©CryoDesalination group and a collector of the cold streams for cooling purposes. Two options have been explored and compared.

Insightful heat exchanger network retrofit design using Monte Carlo simulation

The aim of this paper is to use Monte Carlo simulation (MCS) to analyse the effect of stream data variation on the performance of retrofitted heat exchanger networks. MCS offers a stochastic approach to retrofit design analysis by using historical stream data to model how a retrofitted network would perform over time. The method is demonstrated with two case studies. The first is an illustrative example that showcases the features of the proposed method, while the second is a real-life case study using historical data from a section of a Kraft mill's heat exchanger network. The results show how MCS can be used as a comparison tool between exchangers and networks, differentiating between designs with similar steady-state performance, and offering insights into the reliability of the heat exchangers. For example, in the case study, the MCS results show that an estimated 62% of the time, a cold stream will exceed its target temperature under one of the retrofit proposals (which could have serious process operation and safety issues). MCS also offers another way of conducting an economic analysis which has so far tended to be less optimistic than the steady-state analysis and offers greater confidence in the profitability estimates.

Integrated design for direct and indirect solar thermal utilization in low temperature industrial operations

This work presents a flowsheet superstructure and integration possibilities for simultaneous optimization of the maximum share of attainable direct and indirect solar utilization through heat storage in industrial operations. Multi-period Mixed Integer Non-Linear Programming (MINLP) models were developed for this purpose and account for the dynamics in the profile of heat supply and demand using discrete time intervals/periods. The resulting models are applied to an industrial case study of a dairy plant for the two distinct integration alternatives of targeting one and multiple (two) cold stream utility requirements. The design and optimization of the integrated system is implemented and solved in GAMS. The results show good prospect for solar thermal utilization in industries with low temperature applications. Sensitivity analysis shows linear increase in the average attainable heat load up to certain collector area (on case-by-case basis), after which a break point is obtained where it is observed that additional increase in collector area does not result to much increase in the obtained heat load. For the selected case study of a dairy plant, average solar output of about 75 W/m2 of collector is obtained.

A multi-scale conjugate heat transfer modelling approach for corrugated heat exchangers

The paper compares two serrated plate-fin Heat Exchanger (HE) corrugation modelling methods using Computational Fluid Dynamics (CFD). The first method follows closely recent literature studies and models a finite length single channel of a corrugation layer inside the HE core. The second method utilises the conjugate heat transfer methodology and models a section of the HE core with both cold and hot fluid streams separated by a solid conducting wall (HE corrugation). The results of latter model are then extrapolated for the full dimensions of a HE core layer to obtain flow and heat transfer characteristics. The conjugate heat transfer analysis methodology presented is novel and eliminates the need for analytical/empirical modelling currently widely used within industry. Furthermore, it provides more detailed information about the flow and heat transfer inside the HE core enabling potential for more efficient HE designs. Predictions at the corrugation level were carried out at 88⩽Recorrug⩽2957 with mesh independence studies completed for all the computational domains. The results obtained in the HE corrugation predictions were then implemented to the multi-scale HE unit model where the flow inside the HE core was modelled using two porous media simplifications whilst the heat transfer was simplified using the effectiveness source term. The HE unit predictions were validated against industrial experimental data with good agreement found between the numerical and experimental results. All the simulations were completed using the open-source CFD package OpenFOAM.

Application and limits of a constant effectiveness model for predicting the pressure of steam condensers at off-design loads and cooling fluid temperatures

The main steam condenser is an essential part of every steam power plant. It governs the exhaust pressure of the low pressure turbines and defines the minimum cycle temperature. The heat that is extracted from the cycle steam by the condenser is transferred to a cold stream such as air or water and discarded to atmosphere using a cooling device. The effectiveness of the condenser is key in determining steam temperature, and hence the turbine back pressure response at various operating conditions. Several methods have been proposed in literature to predict the change in backpressure due to load changes. This work examines the validity of a constant condenser effectiveness assumption method, for predicting the back pressure response at various loads, and/or for different cooling inlet temperature conditions. It also shows how the effectiveness of a condenser can be evaluated without detailed knowledge of the condenser internal design. The results of the model were validated against data from 2 Air Cooled Condensers and 1 Wet Cooled Condenser. The results indicate that the constant effectiveness assumption is valid for all heat load conditions, and for cooling inlet temperatures within a close range to the design cooling fluid inlet temperature. To further improve on the accuracy, a simple linear adjustment can be added if one extra low load condition is known, resulting in pressure prediction errors below 4% for the full operating range.

Unravelling the origin of the counter-rotating core in IC 1459 with KMOS and MUSE

ABSTRACTThe massive early-type galaxy IC 1459 is a slowly rotating galaxy that exhibits a rapidly counter-rotating kinematically decoupled core (KDC, RKDC ≈ 5 arcsec ≈ 0.1Re). To investigate the origin of its KDC, we coupled large data mosaics from the near-infrared and optical integral field unit instruments K-band Multi-Object Spectrograph (KMOS) and Multi-Unit Spectroscopic Explorer (MUSE), respectively. We studied IC 1459’s stellar populations and, for the first time for a KDC, the spatially resolved initial mass function (IMF). We used full-spectral-fitting to fit the stellar populations and IMF simultaneously, and an alternative spectral-fitting method that does not assume a star formation history (SFH; although does not constrain the IMF) for comparison. When no SFH is assumed, we derived a negative metallicity gradient for IC 1459 that could be driven by a distinct metal-poor population in the outer regions of the galaxy, and a radially constant old stellar age. We found a radially constant bottom-heavy IMF out to ${\sim }\frac {1}{3}R_{\rm e}$. The radially flat IMF and age extend beyond the counter-rotating core. We detected high-velocity dispersion along the galaxy’s major axis. Our results potentially add weight to findings from orbital modelling of other KDCs that the core is not a distinct population of stars but in fact two smooth co-spatial counter-rotating populations. No clear picture of formation explains the observational results of IC 1459, but we propose it could have included a gas-rich intense period of star formation at early times, perhaps with counter-rotating accreting cold streams, followed by dry and gas-rich mergers through to the present day.

The dominant origin of diffuse Lyα halos around Lyα emitters explored by spectral energy distribution fitting and clustering analysis

AbstractThe physical origin of diffuse Lyα halos (LAHs) around star-forming galaxies is still a matter of debate. We present the dependence of LAH luminosity [L(Lyα)H] on the stellar mass (M⋆), star formation rate, color excess [E(B − V)⋆], and dark matter halo mass (Mh) of the parent galaxy for ∼900 Lyα emitters (LAEs) at z ∼ 2 divided into ten subsamples. We calculate L(Lyα)H using the stacked observational relation between L(Lyα)H and central Lyα luminosity of Momose et al. (2016, MNRAS, 457, 2318), which we find agrees with the average trend of VLT/MUSE-detected individual LAEs. We find that our LAEs have relatively high L(Lyα)H despite low M⋆ and Mh, and that L(Lyα)H remains almost unchanged with M⋆ and perhaps with Mh. These results are incompatible with the cold stream (cooling radiation) scenario and the satellite-galaxy star-formation scenario, because the former predicts fainter L(Lyα)H and both predict steeper L(Lyα)H vs. M⋆ slopes. We argue that LAHs are mainly caused by Lyα photons escaping from the main body and then scattering in the circum-galactic medium. This argument is supported by LAH observations of Hα emitters (HAEs). When LAHs are taken into account, the Lyα escape fractions of our LAEs are about ten times higher than those of HAEs with similar M⋆ or E(B − V)⋆, which may partly arise from lower H i gas masses implied from lower Mh at fixed M⋆, or from another Lyα source in the central part.

Customised retrofit of heat exchanger network combining area distribution and targeted investment

Heat exchanger network (HEN) retrofit plays a major role in solving environmental issues and improving plants’ performance. Development of HEN retrofit graphical tools has recently focused on detailed representation of existing HEN to facilitate retrofit problem-solving. This work presents a new customised approach for HEN retrofit that uses a combination of individual stream temperature versus enthalpy plot (STEP) to map hot and cold streams, a heat exchanger area versus enthalpy (A vs H) plot to minimise the required overall heat exchanger area and graphical cost screening tool and strategies to steer and customise a retrofit design toward a desired investment payback period. Application of the new retrofit methodology on a sunflower oil production plant shows comparable energy savings and 20% shorter payback period as compared other established retrofit methodologies.

Taxonomic notes on the genus Chaetocladius (laminatus-group) (Diptera: Chironomidae, Orthocladiinae) II. Descriptions of C. bitusiki sp. n. and C. mantetensis sp. n., two relict species inhabiting cold alpine springs and streams

Two new species of the genus Chaetocladius s. str. (C. bitusiki sp. n. and C. mantetensis sp. n.) are diagnosed and described based on material collected in some cold springs and small streams located at high altitude (1940–2300 m) in the High Tatra Mountains (Slovakia) and Eastern Pyrenees (France). The first one is described as male adult and pupal exuviae, while the second is described as male and female adults and pupal exuviae. Both C. bitusiki sp. n. and C. mantetensis sp. n. key to the laminatus-group for known Chaetocladius species on the basis of some characters found in the male adult: virga composed of three typical parts, inferior volsella sub-triangular to sub-circular, narrow to broad lobe, bearing or lacking a posterior marsupial-like pouch and an apical contrasting protuberance; gonostylus triangular, projecting posteriorly as a pointed or rounded apex. Taxonomic remarks on related Chaetocladius species, key to known male adults of the laminatus-group from Europe with comments on the ecology and geographical distribution of the new species are given. The two new species can be regarded as typical relict representatives of cold springs and streams at high altitudes. Such species could be used as relevant biological indicators of the global warming and local climate change.