Single-pass Device Research Articles

Optimizing Device Performance of Multi-Pass Flat-Plate Solar Air Heaters on Various Recycling Configurations

Various external-recycle configurations of multi-pass flat-plate solar air collectors were studied theoretically to examine the optimal thermal performance under the same working dimension and operation conditions. An absorber plate and insulation sheet were implemented horizontally and vertically, respectively, into an open rectangular conduit to conduct a recycling four-pass operation, which the device lengthens the air flow channel and increases the air mass flow rate within the collector, and thus, a more heat transfer efficiency is obtained. Four recycling types with different external-recycle patterns were introduced and expected to augment the heat transfer rate due to the turbulent convective intensity through four subchannels in the present study. Coupling energy balances into one-dimensional modeling equations were derived by making the energy-flow diagram within a finite element, which the longitudinal temperature distributions for each subchannel were obtained. The theoretical predictions show that the improved four-pass device is accomplished due to the multiple heating pathways over and under the absorber plate, from which the turbulence intensity augmentation results in the heat transfer rate as compared to that in the device without inserting the absorber plate and insulation sheet (say a downward-type single-pass solar air collector). The theoretical results also show that the external-recycle configuration (say Type C in the present study) acts as an optimal collector thermal efficiency and leading to a beneficial design in multi-pass solar air collectors for improving heat-transfer rate and increasing resident time under the same operation conditions. Theoretical predictions show a higher heat-transfer efficiency for the present recycling configurations up to a maximum 115% device enhancement in comparison to that of a single-pass device. Examination of implementing the absorber plate and insulation sheet on the heat-transfer efficiency enhancement as well as the hydraulic dissipated power increment were also delineated, and deliberated the suitable external-recycle configuration with respect to an economic consideration.

Efficient second harmonic generation in nanophotonic GaAs-on-insulator waveguides.

Nonlinear frequency conversion plays a crucial role in advancing the functionality of next-generation optical systems. Portable metrology references and quantum networks will demand highly efficient second-order nonlinear devices, and the intense nonlinear interactions of nanophotonic waveguides can be leveraged to meet these requirements. Here we demonstrate second harmonic generation (SHG) in GaAs-on-insulator waveguides with unprecedented efficiency of 40 W-1 for a single-pass device. This result is achieved by minimizing the propagation loss and optimizing phase-matching. We investigate surface-state absorption and design the waveguide geometry for modal phase-matching with tolerance to fabrication variation. A 2.0 µm pump is converted to a 1.0 µm signal in a length of 2.9 mm with a wide signal bandwidth of 148 GHz. Tunable and efficient operation is demonstrated over a temperature range of 45 °C with a slope of 0.24 nm/°C. Wafer-bonding between GaAs and SiO2 is optimized to minimize waveguide loss, and the devices are fabricated on 76 mm wafers with high uniformity. We expect this device to enable fully integrated self-referenced frequency combs and high-rate entangled photon pair generation.

Cascaded downconversion interface to convert single-photon-level signals at 650 nm to the telecom band.

We present a device designed for two-step downconversion of single-photon-level signals at 650nm to the 1.5-μm band with low excess noise and low required pump power as a quantum interface between matter-qubit-based nodes and low-loss photonic channels for quantum communication networks. The required pump power for this interface is around 60% of that for a comparable conventional single-pass device, which reduces the demand on the pump laser and yields a corresponding reduction in dark counts due to inelastic pump scattering. The single-photon-level signal at 649.7nm is downconverted to the telecom band using a fiber-coupled reverse proton exchange periodically poled lithium niobate waveguide and a 2.19-μm pump laser. By testing the device in the linear regime with a classical input, we achieved 99% depletion efficiency for each stage, corresponding to an internal quantum efficiency of 63% at the optimum pump power for the complete cascaded process.

Improvement in Device Performance of Power-Law Fluids in Double-Pass Concentric Circular Heat Exchangers

The mathematical formulation of a heat transfer flow problem was developed assuming a laminar velocity distribution in both inner and annular channels with ignoring axial conduction, and the analytical solution was obtained using an orthogonal expansion technique in terms of power series. Qualitative agreement was achieved between the analytical solutions and the experimental results. Comparisons made between the results from the double-pass concentric circular heat exchanger and those in a single-pass device (open conduit) are presented graphically. A considerable improvement in heat transfer is obtainable by employing double-pass devices instead of single-pass.

Single‐Stage Tympanosotomy Tube Insertion: Design Issues on a New Surgical Approach

Objectives: Multiple efforts are under way to develop methodologies to allow tympanostomy tube (TT) placement in young children under conscious sedation where there can be significant head motion. This practice modification would provide an option for TT placement without the risk of general anesthesia and the potential for procedures being performed in an office. Methods: Investigators evaluated a tool designed to perform a quick, single pass tube delivery across the tympanic membrane with a downward force of motion in a moving child under conscious sedation. Training required bench evaluation and the use of general anesthesia before performing conscious sedation cases. Results: A total of 176 TTs were performed in 89 children at 3 institutions. Ninety-one TTs in 46 children used general anesthesia, and 85 TTs in 43 children used conscious sedation. Conscious sedation included nitrous oxide in 35 children and midazolam plus nitrous oxide in 8 patients. All cases used phenol as a topical anesthetic. Twelve children were converted to general anesthesia for over-insertions, design challenges, anatomy, or movement. The major complication encountered was delivery of the TT into the middle ear space. Multiple tubes were used, but a beveled medial flange tube with a lateral visualization tab to provide depth feedback proved most effective for attenuating patient movement without TT over-insertion (64 children). Conclusions: Early results show that TT placement in children may be done safely under conscious sedation. Additional clinical experience is required to optimize the tool and the training to prevent complications of TT placement with a single-pass device.

Heat transfer modeling of conjugated Graetz problems in double-pass parallel-plate heat exchangers under asymmetric wall temperatures

The heat transfer of a Graetz problem is investigated theoretically. The problem involves an improvement to the design of a parallel-plate heat exchanger using an inserted plate which forms a double-pass device with recycle operation. The parallel plates are at different temperatures. The theoretical mathematical model is solved analytically using the separation of variables, superposition principle, and an orthogonal expansion technique in extended power series. Significant heat transfer improvement can be realized by the design compared to a single-pass device. The improvement is greater for a larger Graetz number system. For a small Graetz number system, the single-pass design is preferred. The optimal location of the inserted plate is when the two subchannels are at the same height.

FemCerv – Single Pass Device for Targeted Endo-Cervical – In-Office Sampling

Demonstrate use of the FemCerv Endocervical Sampler (FemCerv) prototype as a single-pass 360 degree alternative to the multi- pass Kevorkian device. Evaluate adequacy of sample size for pathological evaluation and tissue type specificity. Design Feasitility Study. Extirpated Uterus in Operating Room under institutional IRB approval. Undergoing hysterectomy for benign disease. The FemCerv single use device (Femasys Inc.) is placed transvaginally into the cervical canal utilizing its self-dilating tapered tip is advanced to the placement marker for targeted sampling of the endocervix. The device collection chamber which measures 2.0 cm is opened only within the endo-cervical canal. With the chamber open, it is rotated clockwise 360 degrees and then counter-clockwise to its original position. During the rotation process the laser cut edges gather tissue into the chamber. It is then closed while in the endo-cervix avoiding ecto-cervical sample contamination during device removal. Sample submitted was 1cm in aggregate dimension and upon histopathological evaluation found to contain only endo-cervical tissue. A single pass endo-cervical sampling device that provides an adequate site specific specimen for pathologic evaluation should reduce false positive findings and in turn decrease the number of unnecessary LEEP and Cone-Biospy procedures. With its ease of use and anticipated decreased patient discomfort, health care providers might be less reluctant to sample the endo-cervix and thus with increased use may improve the early detection of high grade lesions. The device's encouraging initial results warrants a more robust extirpated study leading to an in-office evaluation used to assess its applicability in clinical practice.

Effect of External Recycle on Mass Transfer in Countercurrent Double-Pass Cross-Flow Rectangular Dialyzers

A study on mass transfer in countercurrent cross-flow rectangular dialyzers with external recycle was investigated. Theoretical analysis of mass transfer in cross-flow dialyzers is analogous to heat transfer in cross-flow heat exchangers. In contrast to a single-pass cross-flow device without recycle, improvement in mass transfer of about 30% is achievable if a double-pass device of the same size with external recycle is employed, which provides the increase of fluid velocity, resulting in increase of mass-transfer coefficient. Higher effectiveness may be expected when dialysis is operated for the system in which the mass-transfer resistances in the liquid films are comparable with that in the membrane.

Dialysis in double-pass cross-flow rectangular membrane modules with external recycle for improved performance

The predicting equations for mass transfer rate in cross-flow rectangular dialyzers with double flow and recycle, have been derived by mass balances. The recycling operation has two conflicting effects. One is the desirable effect of the increase in fluid velocity, resulting in an increased mass transfer coefficient. The other is the undesirable effect of the reduction in concentration difference due to remixing, resulting in decreased mass-transfer driving force. In contrast a single-pass device without recycling, considerable improvement in mass transfer is achieved if the cross-flow rectangular dialyzer of same size is operated with double pass and external recycling. It is concluded that recycle can enhance mass transfer, especially for larger reflux ratio.

EXTERNAL RECYCLE ON UPWARD-TYPE DOUBLE-PASS SOLAR AIR HEATERS

The external recycle effect on collector efficiency in an upward-type double-pass flat-plate solar air heater is investigated theoretically. Application of recycle to a solar air heater has two conflicting effects: the desirable effect of increasing the heat transfer coefficient and the undesirable effect of decreasing the heat transfer driving force (temperature difference). The theoretical predictions show that more than 150% improvement in collector efficiency is obtainable if external recycling is carried out in a way that the advantage effect compensates for the disadvantage effect. The collector performance improvement increases with increasing recycling ratio, especially when operating at a lower airflow rate with higher inlet air temperature. The collector efficiency obtained with a double-pass device with recycling improves the efficiency obtained with a single-pass device of the same size with recycling.

Numerical analysis of mass transfer in double-pass parallel-plate dialyzers with external recycle

The effect of external recycle on the performance of dialysis in double-pass rectangular membrane modules was investigated. Theoretical analysis of mass transfer in parallel-flow dialyzers is analogous to heat transfer in parallel-flow heat exchangers. In contrast to a single-pass device without recycle, improvement in mass transfer of about 30% is achievable if parallel-flow dialysis is operated in a double-pass device of same size with external recycle which provides the increase of fluid velocity, resulting in reduction of mass-transfer resistance.

Recycle effect on heat-transfer efficiency improvement in a double-pass parallel-plate heat exchanger under uniform wall fluxes

The recycle concept was applied to a double-pass parallel-plate heat exchanger under uniform wall fluxes to enhance the device performance improvement. The mathematical statement of the conjugated Graetz problem was developed theoretically and the analytical solution was obtained by using an eigenfunction expansion in terms of power series for the homogeneous part and an asymptotic solution for the inhomogeneous part. The theoretical predictions of wall temperature and average Nusselt numbers are represented graphically with Graetz number and impermeable-sheet location as parameters. A substantial heat-transfer efficiency improvement is achieved by employing such a recyclic device with suitable adjustments of the impermeable-sheet position and recycle ratio, instead of using the single-pass device. The results indicate that the recyclic operation can effectively enhance the heat transfer efficiency, especially when the recyclic device was operated in large Graetz number.

Heat-transfer efficiency improvement of double-pass concentric circular heat exchangers under uniform wall fluxes

The new design of the double-pass operation with external recycle is proposed to apply to enhance the heat-transfer efficiency of concentric circular heat exchangers under uniform wall fluxes. The mathematical formulation was developed theoretically and the analytical solutions were achieved by using the orthogonal expansion technique with the eigenfunctions expanding in terms of an extended power series. The theoretical predictions were represented graphically and compared with those obtained from the single-pass device without external recycle and the previous work [C.D. Ho, S.C. Yeh, Improvement in device performance on laminar counterflow concentric circular heat exchangers with uniform wall flux, International Journal of Heat and Mass Transfer 49 (2006) 202–2032] under the different flow pattern. The results show that a considerable heat-transfer efficiency improvement was obtained with a suitable adjustment of the subchannel thickness ratio and recycle ratio. The power consumption increment due to the device with external recycle was also discussed in this study.

Improvement on device performance in multi-pass heat transfer through a parallel-plate channel with external recycle

A new external-recycle device of multi-pass heat exchangers with uniform wall temperature, resulting in a considerable heat-transfer efficiency improvement, has been designed and studied theoretically. The theoretical analysis on the temperature profile and heat-transfer efficiency improvement has been developed by using an eigenfunction expansion in power series. The analytical predictions are represented graphically and compared with that in single-pass devices and the previous work [C.D. Ho, H.M. Yeh, Y.C. Tsai, Improvement in performance of multi-pass laminar counterflow heat exchangers with external refluxes, Int. J. Heat Mass Transfer 45 (2002) 3529–3547]. A substantial heat-transfer efficiency improvement is obtained by employing such a new recycle type with a suitable adjustment of the impermeable-sheet position and recycle ratio, instead of using the single-pass device without external recycle for Gz > 10 and the recycle type of the previous study for Gz > 30 .

MASS TRANSFER ENHANCEMENT OF CONJUGATED GRAETZ PROBLEMS IN MULTI-PASS PARALLEL-PLATE MASS EXCHANGERS WITH EXTERNAL RECYCLE

A new external recycle design at the ends of multi-pass parallel plate mass exchangers with uniform wall concentration is theoretically investigated in this study. The analytical solutions were obtained using the orthogonal expansion technique and the eigenfunction expanding in power series. The results are graphically represented. The influences of the recycle ratio, mass-transfer Graetz number, channel thickness ratio, and characteristic parameter of the permeable barrier on the mass transfer rate are presented in this study. Compared to the single-pass device, considerable mass transfer improvement is obtainable by employing the new external recycle design at both ends.

Multimilliwatt ultrashort pulses continuously tunable in the visible from a compact fiber source

We report on a single-pass device that efficiently converts the broadband near-infrared output from a femtosecond fiber laser into a narrow spectrum in the visible. With fan-out poled MgO:LiNbO3 we obtain sub-picosecond, continuously tunable pulses in the 520-700 nm range. Conversion efficiencies as high as 30% are observed at typical pump power levels of 30 mW, corresponding to average output powers up to 9.5 mW. The specifications of our device are ideal for applications in confocal microscopy and frequency metrology.

The recycle effect on the collector efficiency improvement of double-pass sheet-and-tube solar water heaters with external recycle

The paper presents a theoretical prediction of the performance of a double-pass sheet-and-tube solar water heater with external recycle and comparison with that of a conventional type collector. Analytical results show that the recycle effect can effectively enhance the collector efficiency compared with that in a single-pass device with the same flow rate. The desirable effect of increasing convective transfer rate and the undesirable effect of reducing heat-transfer driving force are the two conflict effects produced by the recycle operation. It was found that the increment of convective transfer rate by increasing the recycle ratio could generally compensate for the decrement of the temperature difference, leading to improved performance, especially for low flow rate. Also, the collector efficiency increases with increasing collector aspect ratio (i.e. either increasing the tube length or decreasing the number of tube pairs) for a specified collector area and the distance between tubes.

THE INFLUENCE OF RECYCLE ON MULTI-PASS LAMINAR COUNTERFLOW HEATERS OR COOLERS

A multi-pass laminar counterflow cooler or heater is an open duct divided into four subchannels with uniform wall temperature by inserting three impermeable sheets. Only the temperature of the flow stream varies along the subchannels. Improvements in heat transfer efficiency were investigated analytically with the use of eigenfunction expansions in the power series. The enhancement results in heat-transfer efficiency for two multi-pass devices (flow pattern A and flow pattern B) are represented graphically and compared with those in a single-pass device (without three impermeable sheets inserted) and those in a double-pass device (only one impermeable sheet inserted). Analytical results show that suitable impermeable-sheet position adjustments can effectively enhance heat transfer efficiencies for two multi-pass devices (flow pattern A and flow pattern B) compared with the efficiencies of single and double-pass devices.

Multiple-Pass Flow Mass Transfer in a Parallel-Plate Channel by Inserting Permeable Barriers for Improved Device Performance

A multi-pass laminar counterflow mass exchange device is an open conduit divided into four subchannels with uniform wall concentration, by inserting three permeable barriers. Only the composition of the flow stream varies along the channels. The Sherwood numbers as well as the improvement of mass transfer efficiency have been investigated analytically by using an Eigenfunction power series expansion.The device performance results in multi-pass operations are represented graphically and compared with those in a single-pass device (without permeable barriers inserted). Analytical results show that there exists a best permeable-barrier position when both the mass transfer improvement and the increment of power consumption are considered and thus can effectively enhance the mass transfer efficiency compared with that of single-pass operations.

An Analytical Study of Concentric Circular Heat Exchangers with an Impermeable Sheet Inserted for Double-Pass Operations

A design of inserting a concentric tube with negligible thickness to divide a circular conduit into two subchannels for double-pass flow and recyclic operations, resulting in substantially improved the heat transfer, has been designed and investigated. The results are represented graphically and compared with those in a single-pass device (without an inserting concentric tube and recycle). Heat transfer improvement IS considerably obtainable by employing such a double-pass recyclic device, instead of using the single-pass one. The effect of concentric tube location on the heat transfer efficiency enhancement as well as on the power consumption increment, has been also discussed.