Conventional DH Research Articles

A framework for techno-economic assessment of demand-side power-to-heat solutions in low-temperature district heating

In this paper, technical and economic assessment of power-to-heat (P2H) solutions installed at the building side is presented. A framework solution including different control algorithms, network and operational parameters, is proposed to conduct techno-economic assessment for P2H technologies in low-temperature district heating (LTDH) from an integrated energy system perspective. The framework facilitates the transition from conventional DH to LTDH solution with demand-side P2H technologies. An electric heat booster (EHB), as a typical demand side P2H solution, is modelled with different control algorithms and tank sizes and applied to a 23 single-family test energy system. Steady state combined heat and power flow is studied to investigate the impact on networks. Moreover, minimum differential pressure and supply temperature control of critical nodes are applied to ensure reliable DH operation. The results show the effectiveness of fuel shift control, where the ratio of DH loss is decreased by lowering supply temperature to 50°C. Furthermore, the minimum voltage magnitude is improved to be closer to 1 p.u., meanwhile, the power loss on electricity networks is increased. For the test energy system, the 51L EHBs contribute to lower energy cost of the system compared to the 92L ones, and can provide the lowest levelized cost solution with the supply temperature of 50°C.

2D resolution improvement via 1D scanning Space-Time Digital Holography (STDH) in Optofluidics

Space-Time Digital Holography (STDH) exploits the object motion to record the hologram in a hybrid space-time domain. This representation adds new capabilities to conventional DH, such as unlimited extension of the Field of View (FoV) and tunable phase shifting. Here we show that STDH is able to improve the spatial resolution as well. Differently from other super-resolution approaches, stitching between holograms or their spectra is no longer required. Moreover, we introduce a new STDH modality to record and process hybrid space-time representations. This allows improving resolution with one single object scan, paving the way to the use of STDH for super resolution imaging onboard Lab on a Chip devices.

Resolution gain in space-time digital holography by self-assembling of the object frequencies.

Space-time digital holography (STDH) exploits the object motion to record the hologram in a hybrid ST domain. This representation adds new capabilities to conventional DH, e.g.,unlimited field of view and variable phase shifting. This is the best candidate for imaging biological samples flowing in microfluidic channels. Here, we show that STDH is able to improve the spatial resolution as well. Different from other super-resolution approaches, stitching between holograms or their spectra is no longer required. Moreover, we introduce a new oblique STDH modality to record and process hybrid ST representations. This allows improving resolution in 2D with one single object scan, paving the way to the use of STDH for super-resolution imaging onboard microfluidic devices.

Adaptation of Translated Frame-Based Approach for Forward Kinematics in a Radiosurgical Snake-Like Robot.

Snake-like robots are a typical serial-link manipulator newly adopted to assist human experts during medical procedures. Of the several prototypes that have been proposed for surgical repair of abdominal organs and delivery of radiation doses, only a very few attained FDA clearance and commercialization for clinical usage. This can be ascribed to complexities inherent with teleoperation of the redundant robots when controlled via single-ports or interactions with other organs both along the surgical path and the operation area. In this study, translated frame-based approach is adapted for forward kinematics of snake-like robots that have orthogonal joints. This is realized by modifying the conventional standard DH approach commonly used for frame translation in serial robots. The adapted method is validated with model of a newly proposed radiosurgical snake-like robot. Validation results show that adapted method requires reduced execution times for both workspace generation and inverse kinematics of the snake robot.

Assessing the techno-economic impact of low-temperature subnets in conventional district heating networks

The 4th generation Low-Temperature District Heating (LTDH) is envisioned as a more efficient and environmentally friendly solution to provide heating services to the building stock. Specifically, in countries already with a large share of well-established DH systems, conventional DH and LTDH technologies will be operating simultaneously in the near future. Newly built or refurbished buildings have lower heat demands, which in combination with LTDH brings potential savings compared to conventional DH. This work explores the advantages in DH operation by connecting these loads via LTDH subnets to a conventional DH system, supplied by a Combined Heat and Power (CHP) plant. A techno-economic analysis was performed, through modelling and simulation, by estimating the annual DH operating costs and revenues achieved by the reduction in return temperatures that LTDH would bring. The savings are related to: (1) the reduction in distribution heat losses in the return pipe; and (2) lower pumping power demand. Likewise, additional revenues are assessed from: (3) improved Power-to-Heat ratio for electricity production; and (4) enhanced heat recovery through Flue Gas Condensation (FGC). The annual savings per kWh of delivered heat are estimated as a function of the penetration percentage of ‘energy efficient’ loads over the conventional DH network. Key outcomes show the trade-offs between the potential savings in operating costs and the reduction in heat demand: relative losses in this scenario are maintained at 13.1% compared to 15.3% expected with conventional DH; and relative pumping power demand decreased as well. In other words, the costs of supplying heat decrease, even though the total heat supplied is less.

Evaluation of pore size distribution in boundary region of micropore and mesopore using gas adsorption method

This paper discusses an accurate method of pore size distribution evaluation in boundary regions of micropores and mesopores using the gas adsorption process on the basis of the capillary condensation theory, which is liable to be underestimated with the existing BJH and DH methods. A typical nitrogen adsorption isotherm for highly ordered mesoporous silica, which has cylindrical pores with diameter smaller than 4 nm, is considered to be type IV and it is well known for the steep increase of the amount adsorbed through capillary condensation in the region of the relative pressure P/ P 0 smaller than 0.4. In calculating the distribution of the pore size from the change of the amount adsorbed due to capillary condensation, it is important to accurately predict both the multilayer thickness t of the adsorbed nitrogen molecules and the critical radius r c where capillary condensation occurs. It is necessary to consider the curvature of the adsorption layer–gas phase interface when predicting the multilayer thickness t of nitrogen adsorbed within the pore of highly ordered mesoporous silica. Revision of the Kelvin equation is also required when r c is to be predicted. While the predicted value of t based on the Broekhoff and de Boer theory is matched well with the value of t which is actually measured using highly ordered mesoporous silica, and the predicted value of r c based on the GTKB–Kelvin–cylindrical equation that has been revised considering the effect of the interfacial curvature on the interfacial tension of the adsorption layer–gas phase interface is matched with the value of r c which is actually measured using highly ordered mesoporous silica. A combination method of the Broekhoff and de Boer equation and the GTKB–Kelvin–cylindrical equation is proposed as a means of accurately evaluating, from the nitrogen adsorption isotherm, the pore size distribution in the highly ordered mesoporous silica in boundary region of micropore and mesopore. The proposed new method of pore size evaluation features high accuracy and offers the convenience of obtaining the pore size distribution without repeated calculations by employing the same algorithm as DH method. The pore size predicted by the Halsey equation and the Kelvin equation of the conventional DH method is about 20% smaller than the pore size predicted by the newly proposed evaluation method.

Highly stable operation of AlGaInP/GaInP strained multiquantum well visible laser diodes

The long-term reliability of AlGalnP/GaInP strained multiquantum well (SMQW) lasers has been investigated. Highly stable operation with low operation current for more than 5500 h has been achieved under 50°C, 3mW test conditions, without sudden or rapid failures due to strain induced defects. The estimated mean time to failure (MTTF) is 10900h, which is comparable to that of the conventional DH laser and long enough for practical use.

Dynamic behaviour of a GaAs-AlGaAs MQW laser diode

A comparative study is given on the dynamic properties existing between a GaAs-AlGaAs multi-quantum-well (MQW) laser diode fabricated from an MBE-grown wafer and a conventional double-heterostructure laser diode. Spectral broadening and wavelength shift associated with deep injection current modulation were found to be much smaller in MQW laser diodes than in conventional DH laser diodes.

Optical Properties of Semiconductor Superlattices Grown by MBE

GaAs-AlAs superlattices were grown by molecular beam epitaxy with various widths of the GaAs quantum well. A non-destructive X-ray diffraction technique was shown to be a practical method to measure the GaAs quantum well width Lz with an accuracy of 10%. Photoluminescence measurements showed the main carrier recombination process to be from the n=1 electron quantum level to the n=1 heavy hole level. Optical absorption spectra exhibited the sharply peaked structure assocated with excitons at room temperature. MQW laser diodes with GaAs-Asx Ga1-xAs superlattice active layers had lower threshold current density than in conventional DH laser diodes. This illustrated the good optical quality of the superlattices.

Bistability and Differential Gain in Semiconductor Lasers

Bistable operation and differential gain characteristic have been achieved in the current-light output characteristics for stripe geometry InGaAsP/InP DH lasers with an inhomogeneous excitation. This device has an advantage in that the characteristics can be chosen merely by varying the stripe geometry and tuning the device temperature. Under the operating condition of bistability, switching between the two states was accomplished by applying an electrical pulse of 2.5 mA or less to the device. Switch-on time was less than 0.5 ns and switch-off time was about 1 ns. Bistable operation by optical injection is also reported. An incident optical beam, generated by a conventional DH semiconductor laser, was injected into the bistable laser. Bistability has been achieved in incident beam intensity-optical output intensity curves. The bistable laser also acted as an optical limiter.

Bistable operation of semiconductor lasers by optical injection

Bistable operation in InP/InGaAsP DH lasers by optical injection is reported for the first time. An incident optical beam, generated by a conventional DH semiconductor laser, was injected into the semiconductor laser with inhomogeneous excitation. Bistability has been achieved in the relation between input intensity of the incident beam and the optical output intensity of the inhomogeneously excited laser. The bistable laser also acts as an optical limiter, i.e. the optical output completely saturates above the laser threshold level.

The growth of Al x Ga1−x As-GaAs heterostructure lasers by metalorganic chemical vapor deposition

Al x Ga1−x As-GaAs double-heterostructure lasers have been grown by the metalorganic chemical vapor deposition process. Conventional DH lasers have exhibited excellent performance characteristics that are equal to or better than comparable devices grown by liquid-phase epitaxy. Other unique laser structures have been grown that demonstrate the flexibility of the metalorganic chemical vapor deposition materials technology. This paper will describe the preparation and properties of Ga1−x AlxAs-GaAs lasers grown by this process.

Temperature dependence of threshold current for quantum-well AlxGa1−xAs-GaAs heterostructure laser diodes

Data are presented showing that the threshold current density Jth(T) of quantum-well AlxGa1−xAs-GaAs heterostructure laser diodes, grown by MO-CVD, is less temperature dependent than that of conventional DH lasers. T0 in the usual expression Jth∝exp(T/T0) can be high as 437 °C. This behavior is explained in terms of the steplike density of states and the disturbed electron and phonon distribution functions of the quantum-well active region.

Recombination enhanced annealing effect in AlGaAs/GaAs remote junction heterostructure lasers

New structure lasers, the remote junction heterostructure (RJH) lasers, are made to obtain information about slow degradation of AlGaAs/GaAs DH lasers. The RJH laser is characterized by the presence of a thin clad layer between the active layer and the p-n junction. During the LD and LED mode aging process, the RJH lasers showed a marked reduction of threshold current. This reduction was accompanied by increased spontaneous lifetime and pileup of defects at the p-n junction. From these observations, a model was proposed in which point defect generation in the active layer and defect motion toward the p-n junction during the aging are assumed. The rate equation was derived for concentration of the point defect, and the solution of this equation was compared with the experimental results with reasonable agreement. The parameters relating to the slow degradation were determined, and the ultimate life of conventional DH lasers was discussed using these parameters.

Measurement of spontaneous-emission factor of AlGaAs double-heterostructure semiconductor lasers

In this paper, experimental determination of the spontaneous-emission factor of an injection laser is presented. For a lot of conventional AlGaAs DH stripe lasers, spontaneous-emission factors of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> were obtained from the measurement of the light intensity of a lasing mode versus the injected current. These values are in good agreement with the theoretical prediction based upon the classical wave theory. Brief discussion of the magnitude of the spontaneous-emission factor is given relating to the direct modulation characteristics of a semiconductor laser, which shows that the damping oscillation can be decreased in a laser consisting of very small active region.