Capillary Configuration Research Articles

A two-capillary viscometer for temperatures up to 473 K and pressures up to 100 MPa—operation and verification at low pressure

In this paper, we described the design and construction of a new two-capillary viscometer with several novel technical solutions for viscosity and density measurements. Our design, which is based on the low-pressure principle, featured numerous improvements in hardware and procedure that allowed the greatly extended range of pressure. The new design adopted a (2 × 2) capillary configuration, utilizing different combinations of four capillaries to enable viscosity measurements with a wide range of flow rates, temperatures, and pressures. The design temperature range is 213 K–473 K, and the pressure range is up to 100 MPa. The viscometer was specifically designed for measuring the viscosity of pure CO2 and CO2-rich mixtures, addressing the scarcity of data in conditions relevant to carbon capture, transport, and storage. Our facility is capable of viscosity measurements in different thermodynamic states; gaseous, liquid, supercritical, and critical regions. A commercial densimeter is integrated to measure density under the same temperatures and pressures. We aimed for a total uncertainty target of better than 0.03%. The performance of the viscometer was validated by measurements with pure CO2 at 298.15 K and zero density. We observed a deviation of less than 0.03% between the reference viscosity of CO2 of this work and accurately calculated data using ab initio quantum mechanics with a standard uncertainty of 0.2%. Our primary focus in this paper was to provide a detailed description of the design and construction of the apparatus, emphasizing improvements and introducing new solutions to other research groups in constructing similar instruments suitable for low- and high-pressure viscosity measurements with high accuracy.

Balanced Fast-SpaciMS capillary configurations provide practically noninvasive channel-average measurements in catalytic monoliths

Spatially resolved capillary-inlet mass spectrometry (SpaciMS) provides a detailed picture of the spatiotemporal evolution of reaction network in catalytic monoliths. In the present work, we combine the SpaciMS experiments with a newly developed non-isothermal 3D CFD model for heterogeneously catalyzed reactive flows, including diffusion and permeation through the coated catalyst and channel wall. We explore how the capillary size and sampling rate can be balanced to minimize the impact on probed-channel conversions and provide species concentration measurements representative of the free channel average. In all studied configurations, the balanced sampling-rate fraction is noticeably higher than the corresponding capillary occlusion fraction. For a typical 350-micron capillary that occupies 11% of the channel cross- section, the balanced sampling rate represents 43% of the channel flow. The present work shows that together, a balanced SpaciMS configuration and numerical simulation provide accurate channel-averaged information of a monolithic catalyst under realistic operation conditions.

Lung tissue phantom mimicking pulmonary optical properties, relative humidity, and temperature: a tool to analyze the changes in oxygen gas absorption for different inflated volumes

.SignificanceGas in scattering media absorption spectroscopy (GASMAS) enables noninvasive gas sensing in the body. It is developing as a tool for diagnosis and monitoring of respiratory conditions in neonates. Phantom models with relevant features to the clinical translation of GASMAS technology are necessary to understand technical challenges and potential applications of this technique. State-of-the-art phantoms designed for this purpose have focused on the optical properties and anthropomorphic geometry of the thorax, contributing to the source–detector placement, design, and optimization. Lung phantom mimicking the alveolar anatomy has not been included in the existent models due to the inherent complexity of the tissue. We present a simplified model that recreates inflated alveoli embedded in lung phantom.AimThe goal of this study was to build a lung model with air-filled structures mimicking inflated alveoli surrounded by optical phantom with accurate optical properties ( and ) and physiological parameters [37°C and 100% relative humidity (RH)], and to control the air volume within the phantom to demonstrate the feasibility of GASMAS in sensing changes in pulmonary air volume.ApproachThe lung model was built using a capillary structure with analogous size to alveolar units. Part of the capillaries were filled with liquid lung optical phantom to recreate scattering and absorption, whereas empty capillaries mimicked air filled alveoli. The capillary array was placed inside a custom-made chamber that maintained pulmonary temperature and RH. The geometry of the chamber permitted the placement of the laser head and detector of a GASMAS bench top system (MicroLab Dual ), to test the changes in volume of the lung model in transmittance geometry.ResultsThe lung tissue model with air volume range from to was built. Two measurement sets, with 10 different capillary configurations each, were arranged to increase or decrease progressively (in steps of ) the air volume in the lung model. The respective GASMAS data acquisition was performed for both data sets. The maximum absorption signal was obtained for configurations with the highest number of air-filled capillaries and decreased progressively when the air spaces were replaced by capillaries filled with liquid optical phantom. Further studies are necessary to define the minimum and maximum volume of air that can be measured with GASMAS-based devices for different source–detector geometries.ConclusionsThe optical properties and the structure of tissue from the respiratory zone have been modeled using a simplified capillary array immersed in a controlled environment chamber at pulmonary temperature and RH. The feasibility of measuring volume changes with GASMAS technique has been proven, stating a new possible application of GASMAS technology in respiratory treatment and diagnostics.

Atmospheric Pressure Mass Spectrometry Imaging Using Laser Ablation, Followed by Dielectric Barrier Discharge Ionization.

Mass spectrometry imaging (MSI) has become a powerful tool in diverse fields, for example, life science, biomaterials, and catalysis, for its ability of in situ and real-time visualization of the location of chemical compounds in samples. Although laser ablation (LA) achieves high spatial resolution in MSI, the ion yield can be very low. We therefore combined an LA system with an ambient ion source for post-ionization and an atmospheric pressure (AP) inlet mass spectrometer to construct a novel AP-MSI platform. A dielectric barrier discharge ionization (DBDI) source is operated in the "active sampling capillary" configuration, can be coupled to any mass spectrometer with an AP interface, and possesses high ion transmission efficiency. This study presents some application examples based on LA-DBDI, a low-cost and flexible strategy for AP-MSI, which does not require any sample pretreatment, and we show MS imaging of endogenous species in a traditional Chinese herbal medicine and of a drug molecule in zebra fish tissue, with a lateral resolution of ≈20 μm.

Advances and applications of in-tube solid-phase microextraction for analysis of proteins

In-tube solid-phase microextraction (IT-SPME) with capillary column as extraction device is a well-established green extraction technique with a lot of applications in the fields of biomedicine, food and environment. This article reviews the research contributions of IT-SPME for analysis of proteins. The paper first briefly describes the history of IT-SPME. Then, the development and principle of IT-SPME for analysis of proteins are introduced, in which capillary column configurations of IT-SPME and instruments for quantitative analysis of proteins are summarized. Subsequently, the synthesis strategy and recognition principle of different recognition units, including antibodies, aptamers, molecularly imprinted polymers, and boronate affinity materials, are discussed in detail. This part also introduces several rare recognition units, including lectins, restricted access materials, lysine modified with β-cyclodextrin and cell membrane. The development trend and possible future direction of IT-SPME for analysis of proteins are mentioned.

Differential reperfusion patterns in retinal vascular plexuses following increase in intraocular pressure an OCT angiography study

To describe patterns of reperfusion in the superficial vascular plexus (SVP), deep capillary plexus (DCP) and choriocapillaris (CC) as detected on optical coherence tomography (OCTA) in cynomogulus macaque monkey model following increase in intraocular pressure by an intravitreal injection. Animal imaging study. Two cynomogulus macaque monkeys. A 100 µL intravitreal injection (IVI) of saline was given in one eye of each monkey. Serial OCTA using a Zeiss Plex Elite 9000 was used to evaluate reperfusion patterns within the SCP, DCP, and CC. OCTA evidence of perfusion. Pulsation of the central retinal artery was detected after the intraocular pressure was elevated to 98 and ≥ 99 mmHg from IVI. Episodic flow within the SVP arterioles and venules and poor visualization of flow in capillaries was noted during the initial phase of elevated pressure. As the pressure declined, the flow signal within the DCP appeared initially as dots, which progressed laterally to loops which form capillary vortex configuration. Recovery of flow within the SVP and CC appeared sooner than in the DCP. At 40 min after the injection, well after the intraocular pressure normalized, the retinal and choriocapillaris vascular perfusion showed focal defects in every layer. Compared with pre-injection images, vessel density in the DCP was 68.8% and 78.6% of baseline in monkey 1 and monkey 2, respectively. In contrast vessel density in the SVP recovered to 84.2% and 88.9% of baseline. Increases in intraocular pressure from IVI have the potential to affect every layer of blood flow in the fundus. After nominal return of intraocular pressure, focal defects in flow persisted, which may result in longer term damage to the retina.

Metal Probe Microextraction Coupled to Dielectric Barrier Discharge Ionization-Mass Spectrometry for Detecting Drug Residues in Organisms.

In this study, a novel method for the direct coupling of metal probe microextraction (MPME) and a dielectric barrier discharge ionization (DBDI) source with mass spectrometry (MS) is reported. Analytes adsorbed on a tungsten needle were directly transferred to the DBDI source via rapid thermal desorption, which resulted in a limit of detection as low as 8 pg/mL. This is in part due to the "active capillary" configuration of the plasma ion source, where the efficiency of ion transfer to the MS is ∼100%. Specialty gases to maintain the plasma and carry analytes to the MS are not required. In contrast to direct one-step ionization of molecular adsorbates, the complete separation of the analyte desorption from the probe and the ionization event in our experimental setup greatly enhanced the sensitivity and detection reproducibility (RSD of 8.3%). We show detection of pyrimethamine, a first-line drug for the treatment and prevention of Plasmodium falciparum malaria all over the world, by this MPME/DBDI/MS method. The detection of drug residues in live fish and paramecium was achieved without the need for any sample pretreatment. The relative concentration of the drug in different organs of the fish was determined. This simple and convenient method has the potential for the analysis of chemicals even in single-cell organisms.

Electrochemically Modulated Liquid Chromatography in Fused Silica Capillary Columns.

Electrochemically modulated liquid chromatography (EMLC) uses electrical potentials, applied to a conductive chromatographic stationary phase (e.g., porous graphitic carbon [PGC]), to manipulate analyte retention. This paper reports the design of a capillary EMLC column with a smaller internal diameter (ID; 250 μm) than that of the standard bore predecessor (3.3 mm ID). The new capillary EMLC columns are configured so that the PGC stationary phase serves as the working electrode in a two-electrode electrochemical cell and simplifies electrode placement by obviating the need for a counter electrode. This configuration also eliminates the internal Nafion sleeve that is critical to operation for the standard bore columns, thereby avoiding Nafion deformation as a source of chromatographic band broadening and rupturing as a mode of column failure. Indeed, values for chromatographic efficiency obtained on the capillary columns meet or exceed those measured for the standard columns (20 000-40 000 vs 14 000 plates/m, respectively) with near symmetric elution bands (asymmetry factors of 1.1-1.4 for well-packed capillaries) that surpass band symmetries observed in all prior studies. A test suite of aromatic sulfonates was used to characterize the chromatographic performance of the capillary EMLC columns. Separations of this test mixture showed that retention factors for individual analytes could be manipulated by as much as 21× by changing the applied potential at the PGC stationary phase. Changes in retention behavior at different potential ranges, hypothesized to result from differences in adsorption orientation, were also observed and are consistent with past work. Collectively, the retention behavior unique to EMLC is operative in this new capillary configuration and promises to open new avenues in tuning LC separations.

Mixture theory modeling for characterizing solute transport in breast tumor tissues

BackgroundTumor numerical models have been used to quantify solute transport with a single capillary embedded in an infinite tumor expanse, but measurements from different mammalian tumors suggest that a tissue containing a single capillary with an infinite intercapillary distance assumption is not physiological. The present study aims to investigate the limits of the intercapillary distance within which nanoparticle transport resembles solute extravasation in a breast tumor model as a function of the solute size, the intercapillary separation, and the flow direction in microvessels.MethodsSolute transport is modeled in a breast tumor for different vascular configurations using mixture theory. A comparison of a single capillary configuration (SBC) with two parallel cylindrical blood vessels (2 BC) and a lymph vessel parallel to a blood vessel (BC_LC) embedded in the tissue cylinder is performed for five solute molecular weights between 0.1 kDa and 70 kDa. The effects of counter flow (CN) versus co-current flow (CO) on the solute accumulation were also investigated and the scaling of solute accumulation-decay time and concentration was explored.ResultsWe found that the presence of a second capillary reduces the extravascular concentration compared to a single capillary and this reduction is enhanced by the presence of a lymph vessel. Varying the intercapillary distance with respect to vessel diameter shows a deviation of 10–30% concentration for 2 BC and 45–60% concentration for BC_LC configuration compared to the reference SBC configuration. Finally, we introduce a non-dimensional time scale that captures the concentration as a function of the transport and geometric parameters. We find that the peak solute concentration in the tissue space occurs at a non-dimensional time, {T}_{peak}^{ast } = 0.027 ± 0.018, irrespective of the solute size, tissue architecture, and microvessel flow direction.ConclusionsThis work suggests that the knowledge of such a unique non-dimensional time would allow estimation of the time window at which solute concentration in tissue peaks. Hence this can aid in the design of future therapeutic efficacy studies as an example for triggering drug release or laser excitation in the case of photothermal therapies.

A comparative analysis of flat sheet and capillary membranes for membrane distillation applications

Performance of two commercial membranes, in flat sheet (FS) and capillary (Cap) configurations, has been analyzed for desalination through membrane distillation (MD). The performance of the membranes for large scale applications has been compared in terms of flux, pressure drop, pore size requirements and specific thermal and electric energy consumption. The calculations demonstrate that the FS membrane, characterized by relatively (~11 times) lower thickness, larger (33%) pore size and high (~20%) overall porosity compared to the Cap membrane, performs better in terms of trans-membrane flux and specific thermal energy consumption (maximum 36% less specific thermal energy consumption compared to the Cap membrane). However, the electric energy consumption associated with pumping the fluid inside the flow channels for FS membrane was nearly two orders of magnitudes higher than the Cap membrane. Furthermore, when pore size and contact angle for membranes in the two configurations are the same, the FS membranes are more prone to wetting than the Cap membrane when operating under the same conditions. The study also demonstrates that for a given module size and operating conditions, there exists an optimum freshwater recovery factor at which specific thermal energy consumption is the minimum.

Direct contact membrane distillation for the treatment of wastewater for a cooling tower in the power industry

Abstract Water abstraction for cooling requirements in energy production accounts for more than 40% of the total gross abstraction in the European Union, thus driving the interest in using alternative water resources. The current study presents the application of direct contact membrane distillation for the treatment of wastewater from a flue gas desulphurization (FGD) plant for potential applications in cooling towers. Membrane distillation (MD) performance of two commercial lab-scale membrane modules (in capillary and flat configuration) was compared in terms of flux, specific energy consumption (SEC), and rejection towards non-volatiles present in wastewater samples, pretreated according to various protocols. For the flat module, two commercial membranes were tested. In all cases, a good quality permeate was produced, with stable flux over experimental time. SEC of MD for wastewater treatment, calculated experimentally, varied from 946 to 2,830 kWh/m3 for the various applied membranes operating under different conditions. MD allows extracting more than 80% freshwater from FGD wastewater stream while maintaining high (>99.60%) rejection towards electrical conductivity.

Investigation of a Simple Pickup Method for Doping Molecules into Water Clusters

A capillary pickup method was investigated for doping molecules into water clusters, which were produced by supersonic expansion, and underwent a sticking collision with a crossed beam from the capillary. This method was applied to H2O clusters in a beam with pickup of DCl, CH3OH, NH3, CO2 and D2O molecules, however, we found only molecule of DCl can be picked up by water clusters with the capillary configuration in those tested dopants. Meanwhile, two different distances between the capillary to the nozzle were investigated based on the collected mass spectra, and we found that the smaller distance can obtain the stronger mixed cluster intensity.

Droplet-based liquid–liquid extraction inside a porous capillary

Microfluidic operation of liquid–liquid extraction presents the advantage of very short molecular diffusion distances. This enables improved mass transfer under very controlled conditions. For a successful application of an extraction process in a microfluidic environment three operation steps are required: (I) creation of the interface between both liquids in the form of droplets or slugs, (II) the extraction itself, and (III) the efficient separation of both phases for further downstream processing. The last step still poses a challenge since gravity is ineffective as driving force for phase separation in the sub-millimeter scale. Here we present a novel continuous approach that combines all these stages in a new capillary membrane configuration. The porous membrane is split into two compartments for (a) droplet formation based on hollow-fiber emulsification and (b) phase separation by forced coalescence. The method is demonstrated for the extraction of acetic acid from paraffin oil to water as model system. We also show that it is even possible to invert the phases at the phase separation step by using a second membrane with opposite wetting properties. Finally, the possibility of scale-up by parallelization is proved with a three-fiber device that yields comparable results to the single fiber device. This method establishes a new continuous microscale liquid–liquid extraction in an inexpensive and very simple device design.

Dual Enzymatic Detection by Bulk Electrogenerated Chemiluminescence.

The combination of enzymes, as recognition elements for specific analytes, and of electrogenerated chemiluminescence (ECL) as a readout method has proven to be a valuable strategy for sensitive and specific analytical detection. However, ECL is intrinsically a 2D process which could potentially limit the analysis of inhomogeneous samples. Here, we show how a bulk ECL signal, generated by thousands of carbon microbeads remotely addressed via bipolar electrochemistry, are implemented as a powerful tool for the concomitant ECL sensing and imaging of two enzymatic substrates. We selected two enzymes (glucose dehydrogenase and choline oxidase) that react with their respective model substrates and produce in situ chemical species (β-nicotinamide adenine dinucleotide (NADH) and H2O2) acting as coreactants for the ECL emission of different luminophores ([Ru(bpy)3](2+) at λ = 620 nm and luminol at λ = 425 nm, respectively). Both enzymes are spatially separated in the same capillary. We demonstrate thus the simultaneous quantitative determination of both glucose and choline over a wide concentration range. The originality of this remote approach is to provide a global chemical view through one single ECL image of inhomogeneous samples such as a biochemical concentration gradient in a capillary configuration. Finally, we report the first proof-of-concept of dual biosensing based on this bulk ECL method for the simultaneous imaging of both enzymatic analytes at distinct wavelengths.

Computation of Three-Phase Capillary Pressure Curves and Fluid Configurations at Mixed-Wet Conditions in 2D Rock Images

Summary In this study, we present a three-phase, mixed-wet capillary bundle model with cross sections obtained from a segmented 2D rock image, and apply it to simulate gas-invasion processes directly on images of Bentheim sandstone after two-phase saturation histories consisting of primary drainage, wettability alteration, and imbibition. We calculate three-phase capillary pressure curves, corresponding fluid configurations, and saturation paths for the gas-invasion processes and study the effects of mixed wettability and saturation history by varying the initial water saturation after primary drainage and simulating gas invasion from different water saturations after imbibition. In this model, geometrically allowed gas/oil, oil/water, and gas/water interfaces are determined in the pore cross sections by moving two circles in opposite directions along the pore/solid boundary for each of the three fluid pairs separately. These circles form the contact angle with the pore walls at their front arcs. For each fluid pair, circle intersections determine the geometrically allowed interfaces. The physically valid three-phase fluid configurations are determined by combining these interfaces systematically in all permissible ways, and then the three-phase capillary entry pressures for each valid interface combination are calculated consistently on the basis of free-energy minimization. The valid configuration change is given by the displacement with the most favorable (the smallest) gas/oil capillary entry pressure. The simulation results show that three-phase oil/water and gas/oil capillary pressure curves are functions of two saturations at mixed wettability conditions. We also find that oil layers exist in a larger gas/oil capillary pressure range for mixed-wet conditions than for water-wet conditions, even though a nonspreading oil is considered. Simulation results obtained in sandstone rock sample images show that gas-invasion paths may cross each other at mixed-wet conditions. This is possible because the pores have different and highly complex, irregular shapes, in which simultaneous bulk-gas and oil-layer invasion into water-filled pores occur frequently. The initial water saturation at the end of primary drainage has a significant effect on the gas-invasion processes after imbibition. Small initial water saturations yield more-oil-wet behavior, whereas large initial water saturations show more-water-wet behavior. However, in both cases, the three-phase capillary pressure curves must be described by a function of two saturations. For mixed-wet conditions, in which some pores are water-wet and other pores are oil-wet, the gas/oil capillary pressure curves can be grouped into two curve bundles that represent the two wetting states. Finally, the results obtained in this work demonstrate that it is important to describe the pore geometry accurately when computing the three-phase capillary pressure and related saturation paths in mixed-wet rock.

Experimental and simulation investigation of ion transfer in different sampling capillaries.

Atmospheric pressure interfaces were a fundamental structure for transferring air generated ions into the vacuum manifold of a mass spectrometer. This work is devoted to the characterization of ion transfer in metal capillaries through both experimental and simulated investigations. The impact of capillary configurations on ion transmission efficiency was evaluated using an electrospray mass spectrometer with various bent capillaries as the transfer devices. In addition, a numerical model has been set up by coupling the SIMION 8.0 and the computational flow dynamics for simulation study of ion migration in the complex atmospheric system. The transfer efficiency was found to be highly affected by the variation in electric field and the capillary geometry, revealing that the hydrodynamic and electric force were both dominant and interactional during the transmission process. The consistency of the results from the experimental analysis and simulation modeling proved the validity of the model, which was helpful for understanding ion activity in transfer capillaries.

Programmable digital droplet microfluidics using a multibarrel capillary bundle

The integration of multibarrel glass capillaries into a microfluidic co-flow configuration is demonstrated for parallel production of nanoliter scale droplets. The multibarrel system supports the generation of a continuous stream of single-phase or dual-phase droplets with digital control over droplet content, enabling the formation of dynamically-programmable and tunable emulsions. The multibarrel capillary method allows simultaneous generation of multiple droplets from parallel droplet generators, with controlled switching between selected dispersed phase or continuous phase compositions. Individual phases emerging from each capillary outlet may be selected to yield merged droplets combining continuous phase emitted from one or more neighboring droplet generators. Because the capillary emitters are configured in a two dimensional array, the multibarrel system provides greater flexibility toward producing controlled interactions between multiple solutions and phases than conventional planar microfluidic droplet generators. Using a 7-barrel capillary configuration, the ability to regulate droplet composition and particle size of individual as well as combined single and merged water-in-oil droplets is explored, together with the use of two-dimensional spatial control within the multibarrel array to generate higher order emulsions.

Generation of dc pin-hole discharges in liquids: comparison of discharge breakdown in diaphragm and capillary configuration

Electrical discharges in liquids can be generated in several electrode configurations; one of them is called as a pin-hole. The discharge is created inside a small orifice in the dielectric barrier connecting two chambers filled by any conductive solution. Each chamber contains one electrode. Based on the orifice length/diameter ratio, the discharge is called as a capillary or diaphragm discharge. The present paper gives the first detailed observation of the dependence of discharge creation on the orifice shape for selected NaCl solution conductivities (250−1000 µ Sc m �1 ). As a dielectric barrier, ceramic discs with thickness varying from 0.3 to 1.5 mm were used. Diameter of one central pin-hole was in the range of 0.25−1.00 mm. The non-pulsing dc high voltage up to 2 kV with power up to 500 W was used for the presented study. The bubble theory of the discharge generation was confirmed at the set conditions.

Computational Simulations of Flow and Oxygen/Drug Delivery in a Three-Dimensional Capillary Network

A computational fluid dynamics (CFD) model is developed to simulate the flow and delivery of oxygen and other substances in a capillary network. A three-dimensional capillary network has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model of blood and the oxygen transport model including in-stream oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study delivery of drugs and other materials in the capillary streams. The model is first run to compute the volumetric flow rates from the velocity profiles in the segments and compared with Secomb’s work with good agreement. Effects of abnormal pressure and stenosis conditions, as well as those arising from different capillary configurations, on the flow and oxygen delivery are investigated, along with a brief look at the unsteady effects and drug dispersion in the capillary network. The current approach allows for inclusion of oxygen and other material transports, including drugs, nutrients, or contaminants based on the flow simulations. Also, three-dimensional models of complex circulatory systems ranging in scale from macro- to microvascular vessels, in principle, can be constructed and analyzed in detail using the current method.

An experimental study of the Effect of capillary tube diameter and configuration on the performance of a simple vapour compression refrigeration system

The study of the expansion device in the simple vapour compression refrigeration system is necessary in order to understand the parameters which can enhance the overall performance of the system. The experimental study was done on the capillary tubes of 31 gauge, 36 gauge and 40 gauge and each test section was studied with three distinct configurations i.e. helical coiled, straight coiled and serpentine coiled configuration. The effect of the configuration and the capillary tube diameter on the overall performance of the system was studied. The findings of the experimental study revealed that the mass flow rate is maximum for the straight configuration and is least for the helical coiled configuration. The refrigeration effect was found to be maximum for the helical coiled configuration and was found to be least for straight coiled configuration. The compressor work was found to reduce as the load was increased on the system. Decreasing the capillary tube diameter increased the mass flow rate in the system and decreased the refrigeration effect produced.