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Small scale hermetic compressors with built-in frequency converters for compressor speed adjustment are an emerging technology on the commercial market. These compressor technologies offer the ability to impose innovative compressor control strategies, such as variable speed drive or adaptive energy optimization, for small scale commercial refrigeration systems. These strategies may both reduce power consumption and increase the temperature stability of the stored goods. Both of which are a necessity for the refrigerators to abide EU regulations 2015/1095 and 2015/1094 of 5 May 2015 and thus pass the test described in EN 16825. The influence of the applied compressor control strategy was investigated in combination with improvements to the cabinet envelope and improvements to the condenser and evaporator design. The investigation was performed using a validated dynamic model of a refrigerated counter using R290 and R600a, under the EN 16825 test conditions. Both variable speed drive and adaptive energy optimization yield significant reductions in power consumption compared to the conventional On-Off control. A more constant product temperature was achieved by variable speed drive, while the product temperature fluctuated slightly more when applying adaptive energy optimization.

Replacement of fossil fuel-fired boilers for generation of high-temperature water and steam is of paramount importance for reaching a fossil-free economy. Heat pumps could be possible substitutes, but the presently marketed solutions are mainly limited to low-temperature applications. This paper compares the thermodynamic performance of various High-Temperature Heat Pumps (HTHP) based on the vapor compression cycle with natural gas boilers for assessing their technical feasibility and competitiveness as future replacements. Different cycle configurations and natural refrigerants were compared based on the coefficient of system performance and exergetic efficiency. Moreover, the technical feasibility of the most interesting cycles was discussed based on current technologies. The results showed that HTHP are promising substitutes for gas boilers for heat production of temperatures up to 180 °C. In particular, ammonia cycles were preferable for source and sink temperatures lower than 60 °C and 110 °C, respectively, while water was a better-working fluid at higher temperatures. The complete exergy analysis showed different behaviors for various natural refrigerants in the working domain but confirmed the results identified by the energy analysis. In any case, the technological analysis showed that further improvement of compressor technologies is required for making these solutions competitive.

The use of zeotropic mixtures in heat pumps in well-designed cycles enables considerable performance improvements beyond the limitations of conventional systems. A beneficial working fluid choice enables matching the temperature profiles of the working fluid and the secondary media. The reduced temperature differences in the heat exchangers decrease the exergy destruction and yield higher cycle performance. Further improvements may be obtained from installing internal heat exchangers and reducing the superheating inside the evaporator.Conducting an advanced exergy analysis for the evaluation of different cycle layouts and working fluids yields varying amounts of unavoidable exergy destruction depending on the scenario. These differences in unavoidable exergy destruction may be considered as the performance improvement potential obtainable by an optimization of the working fluid and the cycle layout. This study therefore suggests splitting the exergy destruction into two contributions, of which one is associated with the heat exchanger operating with an ideal fluid and the other with the fluid being non-ideal. Furthermore, the exergy destruction was related to deviations from the Lorenz cycle in terms of COP.The suggested concept was demonstrated by the case of a heat pump with different mixtures of propane/butane at different cycle layouts. The results were found to be a suitable measure of the potential performance improvement obtainable by working fluid and cycle layout optimization. Furthermore, relating the exergy destruction to changes in COP enabled an intuitive interpretation of the results.

This paper presents a dynamic numerical model of an R134a-based Exhaust Air Heat Recovery Ventilation Heat Pump in domestic hot water production configuration. The model was validated against data collected during an experimental study. The comparison between calculated and tested results showed that the dynamic model could simulate a complete heating-up phase of the system with an error lower than 10 %. The model was used to predict the energy performance of the heatpump and the distribution of the refrigerant charge during the mentioned operation. We found that when the stored water was heated from 12 °C to 50 °C, the average accumulated heating Coefficient of Performance (COP) was 3.28. The assessment of the refrigerant charge distribution showed that most of the refrigerant charge was located in the condenser coil wrapped around the water tank and the lowest quantity in the evaporator.

Energy, exergy and advanced exergy methods were used to analyse a milk powder production facility. While a conventional energy analysis is used to map the energy flows and to suggest possibilities for process integration through pinch analysis, an exergy analysis identifies the locations and magnitudes of thermodynamic irreversibilities. The advanced exergy analysis determines the real potential for thermodynamic improvements by dividing the exergy destruction into its avoidable and unavoidable parts, which relate to technological limitations, and into its endogenous and exogenous parts, which present the interactions between the different sub-systems. This analysis was based on factory data with which the complete production line (milk treatment, evaporators and dryers) and the utility systems were modelled. The results show the potential for optimisation and a comparison of the applicability of the different methods to the dairy industry. The pinch analysis and energy mapping showed that the potential for heat integration was small. The exergy analysis revealed the gas burner and spray dryer caused most exergy destruction, while the heaters had low exergy efficiencies. The advanced exergy analysis found the evaporators to have a high share of avoidable exergy destruction. However not all results from the advanced exergy analysis were practical.

This paper presents a derivation of design guidelines for plate heat exchangers used for evaporation of zeotropic mixtures in heat pumps. A mapping of combined heat exchanger and cycle calculations for different combinations of geometrical parameters and working fluids allowed estimating the trade-off between heat transfer area and pressure drops on the thermodynamic and economic performance indicators of the cycle. Compressor running costs constituted the largest cost share, and increased due to a steep decrease of the heat pump coefficient of performance at high refrigerant pressure drops. It was found that the pressure drop limit leading to infeasible designs was dependent on the working fluid, thereby making it impossible to define a guideline based on maximum allowable pressure drops. It was found that economically feasible designs could be obtained by correlating the vapour Reynolds number and the Bond number at the evaporator inlet as Re V − 0.42 Bd 0.26 ≈ 0.040 . The use of the proposed guideline was illustrated for the mixture Propane/Iso-Pentane (0.5/0.5), leading to evaporator designs with net present values deviating maximum −4.4% from the best value found in the mapping. The presented methodology can be applied in different scenarios to develop similar guidelines, thereby decreasing the cost of combined cycle and component optimizations.

The present study demonstrates the optimization of a heat pump for an application with a large temperature glide on the sink side and a smaller temperature glide on the source side. The study includes a numerical simulation of a heat pump cycle for binary mixtures based on a list of 14 natural refrigerants. This approach enables a match of the temperature glide of sink and source with the temperature of the working fluid during phase change and thus, a reduction of the exergy destruction due to heat transfer. The model was evaluated for four different boundary conditions. The exergy destruction due to heat transfer, which is solely caused by the fluid having a non-ideal temperature profile was quantified and an indicator describing the glide match was defined to analyze its influence on the performance. The results indicated, that a good glide match can contribute to an increased performance. The increase in performance was dependent on the boundary conditions and reached up to 20% for a simple cycle and up to 27% if the superheating can be avoided. The temperature glide match in the source was identified to have a higher influence on the performance than in the sink.

This paper compares estimation of the coefficient of performance (COP) of a large-scale heat pump (HP) for district heating based on four methods to the COP obtained using a detailed thermodynamic HP model. Four heat sources and varying district heating supply temperatures were considered. The COP estimation methods are based on constant COP, Lorenz efficiency, exergy efficiency and a method presented by Jensen et al. (2018). They were implemented in an energy planning tool and further analysed. The planning tool was used to assess HP implementation in a new district in Copenhagen, Denmark. The change in seasonal COP of the HPs, the economic results and optimal HP capacities were compared. The results show that the Jensen et al. (2018) method provides good approximations and that the planning tool identifies a similar solution compared to the use of the thermodynamic HP model. Assuming a constant Lorenz efficiency, exergy efficiency or COP over the year resulted in large deviations in COP, especially for operations very different from the design conditions. Consequently, other heat sources were found for the most economical solution. The accuracy of the three methods decreased when the initial assumptions of constant COP and efficiencies differed from the ones at design conditions.

A method for vector velocity volume flow estimation is presented, along with an investigation of its sources of error and correction of actual volume flow measurements. Volume flow errors are quantified theoretically by numerical modeling, through flow phantom measurements, and studied in vivo. This paper investigates errors from estimating volumetric flow using a commercial ultrasound scanner and the common assumptions made in the literature. The theoretical model shows, e.g. that volume flow is underestimated by 15%, when the scan plane is off-axis with the vessel center by 28% of the vessel radius. The error sources were also studied in vivo under realistic clinical conditions, and the theoretical results were applied for correcting the volume flow errors. Twenty dialysis patients with arteriovenous fistulas were scanned to obtain vector flow maps of fistulas. When fitting an ellipsis to cross-sectional scans of the fistulas, the major axis was on average 10.2mm, which is 8.6% larger than the minor axis. The ultrasound beam was on average 1.5mm from the vessel center, corresponding to 28% of the semi-major axis in an average fistula. Estimating volume flow with an elliptical, rather than circular, vessel area and correcting the ultrasound beam for being off-axis, gave a significant (p=0.008) reduction in error from 31.2% to 24.3%. The error is relative to the Ultrasound Dilution Technique, which is considered the gold standard for volume flow estimation for dialysis patients. The study shows the importance of correcting for volume flow errors, which are often made in clinical practice.

The study analyzes approaches for the selection of working fluids for the design of heat pump cycles based on numerical modeling. Different approaches for defining economically reasonable assumptions for the heat exchanger dimensioning were compared with respect to the identification of thermodynamically and economically promising working fluids. It was revealed that comparisons based on fixed heat exchanger investment do not exploit the performance of potentially high performing fluids. The approach of defining the pinch point temperature differences in the heat exchangers was found to provide results that were closest to the economic optimum, while being readily applicable in screening procedures. The method was demonstrated by two examples using excess heat from data centers for district heating supply. For the two cases, zeotropic mixtures were identified that could improve the thermodynamic performance by 30%–35% while achieving a reduction of levelized cost of heat of 8% to 10%.

Heat transfer correlations for pool and flow boiling are indispensable for boiler design. The correlations for predicting in-tube flow boiling heat transfer of ammonia–water mixtures are not well established in the open literature and there is a lack of experimental measurements for the full range of composition, vapor qualities, fluid conditions, etc. This paper presents a comparison of several flow boiling heat transfer prediction methods (correlations) for ammonia–water mixtures. First, these methods are reviewed and compared at various fluid conditions. The methods include: (1) the ammonia–water specific flow boiling correlations from the open literature, (2) the ammonia–water specific pool boiling correlations from the open literature extended to flow boiling by using the pure fluid correlation by Gungor and Winterton, and (3) the classical wide-boiling correlations. Second, their influence on the required heat exchanger size (surface area) is investigated during numerical design. For this purpose, two case studies related to the use of the Kalina cycle are considered: a flue gas based heat recovery boiler for a combined cycle power plant and a hot oil based boiler for a solar thermal power plant. The results indicate that the nucleate boiling contribution to flow boiling is small compared to the flow boiling contribution for the investigated conditions. Furthermore, the use of the different flow boiling correlation methods resulted in evaporator size differences within 6% for the heat recovery boiler and 28% for the oil based boiler.

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.

Transport properties of fluids are indispensable for heat exchanger design. The methods for estimating the transport properties of ammonia–water mixtures are not well established in the literature. The few existent methods are developed from none or limited, sometimes inconsistent experimental datasets, conducted for the liquid phase only. These datasets are usually confined to low concentrations and temperatures, which are much less than those occurring in Kalina cycle boilers. This paper presents a comparison of various methods used to estimate the viscosity and the thermal conductivity of ammonia–water mixtures. Firstly, the different methods are introduced and compared at various temperatures and pressures. Secondly, their individual influence on the required heat exchanger size (surface area) is investigated. For this purpose, two case studies related to the use of the Kalina cycle are considered: a flue-gas-based heat recovery boiler for a combined cycle power plant and a hot-oil-based boiler for a solar thermal power plant. The different transport property methods resulted in larger differences at high pressures and temperatures, and a possible discontinuous first derivative, when using the interpolative methods in contrast to the corresponding state methods. Nevertheless, all possible mixture transport property combinations used herein resulted in a heat exchanger size within 4.3 % difference for the flue-gas heat recovery boiler, and within 12.3 % difference for the oil-based boiler.

PZFlex is a commercial FEA software that has been optimized for the ultrasound industry and is commonly used to design piezoelectric ultrasound transducers. However, PZFlex is not commonly used within the CMUT research field. Nevertheless, it has an explicit modeling approach allowing large structures like CMUT arrays to be modeled and its transient analysis intrinsically supplies non-linear and broadband results from a single run. A 3-D model of a CMUT array is developed with multiple cells in each element and one active element surrounded by N passive elements. It is demonstrated that the electro-mechanics can precisely be predicted, within 3%, including the pull-in voltage and the spring softening effect. The transmit impulse response is simulated by deconvolving the extrapolated pressure with the excitation pulse, and it is in excellent agreement with the measured. It is shown that the impulse response can directly be used in Field II to assess the image quality of the transducer using the lateral, axial and cystic resolution for two different CMUT designs.

In this study, a comparison between velocity fields for a plane wave 2-D vector flow imaging (VFI) method and a computational fluid dynamics (CFD) simulation is made. VFI estimates are obtained from the scan of a flow phantom, which mimics the complex flow conditions in the carotid artery. Furthermore, the precision of the VFI method is investigated under laminar and complex flow conditions in vivo. The carotid bifurcation of a healthy volunteer was scanned using both fast plane wave ultrasound and magnetic resonance imaging (MRI). The acquired MRI geometry of the bifurcation was used for fabricating an anthropomorphic flow phantom, which was also ultrasound scanned. The same geometry was used in a CFD simulation to calculate the velocity field. Results showed that similar flow patterns and vortices were estimated using CFD and VFI in the phantom. Velocity magnitudes were estimated with a mean difference within 15 %, however, it was 23 % in the external branch. For the in vivo scan, the precision in terms of mean standard deviation (SD) of estimates aligned to the cardiac cycle was highest in the center of the common carotid artery (SD 4.7° for angles) and lowest in the external branch and close to the vessel wall (SD 15.0° for angles).

The objective of the study described here was to investigate the accuracy and precision of a plane wave 2-D vector flow imaging (VFI) method in laminar and complex blood flow conditions in the healthy carotid artery. The approach was to study (i) the accuracy for complex flow by comparing the velocity field from a computational fluid dynamics (CFD) simulation to VFI estimates obtained from the scan of an anthropomorphic flow phantom and from an in vivo scan; (ii) the accuracy for laminar unidirectional flow in vivo by comparing peak systolic velocities from VFI with magnetic resonance angiography (MRA); (iii) the precision of VFI estimation in vivo at several evaluation points in the vessels. The carotid artery at the bifurcation was scanned using both fast plane wave ultrasound and MRA in 10 healthy volunteers. The MRA geometry acquired from one of the volunteers was used to fabricate an anthropomorphic flow phantom, which was also scanned using the fast plane wave sequence. The same geometry was used in a CFD simulation to calculate the velocity field. Results indicated that similar flow patterns and vortices were estimated with CFD and VFI in the phantom for the carotid bifurcation. The root-mean-square difference between CFD and VFI was within 0.12 m/s for velocity estimates in the common carotid artery and the internal branch. The root-mean-square difference was 0.17 m/s in the external branch. For the 10 volunteers, the mean difference between VFI and MRA was −0.17 m/s for peak systolic velocities of laminar flow in vivo. The precision in vivo was calculated as the mean standard deviation (SD) of estimates aligned to the heart cycle and was highest in the center of the common carotid artery (SD = 3.6% for velocity magnitudes and 4.5° for angles) and lowest in the external branch and for vortices (SD = 10.2% for velocity magnitudes and 39° for angles). The results indicate that plane wave VFI measures flow precisely and that estimates are in good agreement with a CFD simulation and MRA.

The present study demonstrates the optimization of a heat pump for an application with a large temperature glide on the sink and a smaller temperature glide on the source side. The study includes a simulation of a heat pump cycle for all possible binary mixtures from a list of 14 natural refrigerants, which enables a match of the temperature glide of sink and source with the temperature of the working fluid during phase change and thus, a reduction of the exergy destruction due to heat transfer. The model was evaluated for four different boundary conditions. For a separated evaluation of the irreversibility solely caused by the fluid properties, the exergy destruction in the heat exchangers has been distinguished accordingly and an indicator quantifying the glide match has been defined to analyse the influence on the performance. It was observed that a good glide match can contribute to an increased performance. Dependent on the boundary conditions a performance increase of 20.0 % for a simple cycle was observed and 26.9 % increase if the required superheating can be avoided. The temperature glide match in the source was identified to have a higher influence on the performance than in the sink.

To obtain accurate blood flow velocity estimates it is important to remove the clutter signal originating from tissue. Conventionally, the clutter signal has been separated from the blood signal based on the difference of their spectral frequencies. However, this approach is not enough for obtaining vector flow measurements, since the spectra overlaps at high beam-to-flow angles. In this work a distinct approach is proposed, where the energy of the velocity spectrum is used to differentiate among the two signals. The energy based method is applied by limiting the amplitude of the velocity spectrum function to a predetermined threshold. The effect of the clutter filtering is evaluated on a plane wave (PW) scan sequence in combination with transverse oscillation (TO) and directional beamforming (DB) for velocity estimation. The performance of the filter is assessed by comparison of the velocity estimates of the proposed filter against a conventional moving average clutter filter. The effect of tissue motion is investigated using a Field II simulation of a straight vessel with moving wall, while the direct effect of the filter on the velocity estimates is evaluated on a CFD model of a carotid bifurcation with a fixed vessel wall. The results show that the proposed filter outperformed the moving average during moving vessel wall conditions, where standard deviations from the velocity magnitudes and angles were kept consistently below 6% and 6◦compared to 63% and 48◦ on the moving average filter. The results on the CFD showed that on non-moving conditions the velocity estimates had minor statistical differences with errors on the magnitude of -7.95±10.1% and angles of 0.15±6.65◦ for the proposed filter compared to -5.83±9.08% and -0.12±4.48◦.

The design of two heat pumps (HP), connected in series, was investigated for operation in the district heating (DH) network of the Greater Copenhagen area, Denmark. The installation was dimensioned to supply 7.2 MW of heat at a temperature of 85 °C. The heat pumps utilise a geothermal heat source at 73 °C. Both heat source and sink experience a large temperature change, which may lead to decreased performance for single vapour compression HP. The performance may be increased by using HPs connected in series and by applying HPs with zeotropic mixtures. First a generic study with a simple representation of the HP was applied to investigate optimal system configurations. It was shown that using two heat pumps in series with direct heat exchange in parallel with the first heat pump could increase the performance compared to the HP performance. Detailed thermodynamic models of a zeotropic mixture HP predicted that an exergetic efficiency of the units between 50% and 65% is possible. The technical feasibility as well as the economic viability of this installation was investigated for a range of optimal configurations. The analysis recommends a heat pump configuration with a system exergetic efficiency of 63%.

This paper presents a method for optimizing parameters affecting the image quality in plane wave imaging. More specifically, the number of emissions and steering angles is optimized to attain the best images with the highest frame rate possible. The method is applied to a specific problem, where image quality for a $\lambda $ -pitch transducer is compared with a $\lambda $ /2-pitch transducer. Grating lobe artifacts for $\lambda $ -pitch transducers degrade the contrast in plane wave images, and the impact on frame rate is studied. Field II simulations of plane wave images are made for all combinations of the parameters, and the optimal setup is selected based on Pareto optimality. The optimal setup for a simulated 4.1-MHz $\lambda $ -pitch transducer uses 61 emissions and a maximum steering angle of 20° for depths from 0 to 60 mm. The achieved lateral full-width at half-maximum (FWHM) is $1.5\lambda $ and the contrast is −29 dB for a scatterer at 9 mm ( $24\lambda $ ). Using a $\lambda $ /2-pitch transducer and only 21 emissions within the same angle range, the image quality is improved in terms of contrast, which is −37 dB. For imaging in regions deeper than 25 mm ( $66\lambda $ ), only 21 emissions are optimal for both the transducers, resulting in a −36 dB contrast at 34 mm ( $90\lambda $ ). Measurements are performed using the experimental SARUS scanner connected to a $\lambda $ -pitch and $\lambda $ /2-pitch transducer. A wire phantom and a tissue mimicking phantom containing anechoic cysts are scanned and show the performance using the optimized sequences for the transducers. FWHM is $1.6\lambda $ and contrast is −25 dB for a wire at 9 mm using the $\lambda $ -pitch transducer. For the $\lambda $ /2-pitch transducer, contrast is −29 dB. In vivo scans of the carotid artery of a healthy volunteer show improved contrast and present fewer artifacts, when using the $\lambda $ /2-pitch transducer compared with the $\lambda $ -pitch. It is demonstrated with a frame rate, which is three times higher for the $\lambda $ /2-pitch transducer.

Directional beamforming (DB) estimates blood flow velocities accurately when the flow angle is known. However, for automatically finding the flow angle a computationally expensive approach is used. This work presents a method for estimating the flow angle using a combination of inexpensive transverse oscillation (TO) estimators and only 3 directional beamformed lines. The suggested DB vector flow estimator is employed with steered plane wave transmissions for high frame rate imaging. Two distinct plane wave sequences are used: a short sequence (3 angles) for fast flow and an interleaved long sequence (21 angles) for both slow flow and B-mode. Parabolic flow with a peak velocity of 0.5 m/s is measured at beam-to-flow angles of 60° and 90°. The DB method estimates the angle with a bias and standard deviation (STD) less than 2°, and the STD of the velocity magnitude is 2.5 %. This is 7 – 8.5 % when using TO. The long sequence has a higher sensitivity, and when used for estimation of slow flow with a peak velocity of 0.04 m/s, the SD is 2.5 % and bias is 0.1 %. This is a factor of 4 better than if the short sequence is used. The carotid bifurcation was scanned on a healthy volunteer, and the short sequence was used with TO and DB to estimate velocity vectors. The STD of the velocity profile over a cardiac cycle was 6.1 % for TO and 4.9 % for DB.

PurposeTo investigate if ultrasound vector-flow imaging (VFI) is equal to the reference method ultrasound dilution technique (UDT) in estimating volume flow and changes over time in arteriovenous fistulas (AVFs) for hemodialysis.Materials and methodsFrom January 2014 to January 2015, patients with end-stage renal disease and matured functional AVFs were consecutively solicited to participate in this prospective study. All patients were included after written informed consent and approval by the National Committee on Biomedical Research Ethics and the local Ethics Committee (journal no. H-4-2014-FSP). VFI and UDT measurements were performed monthly over a six-month period. Nineteen patients were included in the study. VFI measurements were performed before dialysis, and UDT measurements after. Statistical analyses were performed with Bland-Altman plot, Student's t-test, four-quadrant plot, and regression analysis. Repeated measurements and precision analysis were used for reproducibility determination.ResultsPrecision measurements for UDT and VFI were 32% and 20%, respectively (p = 0.33). Average volume flow measured with UDT and VFI were 1161 mL/min (±778 mL/min) and 1213 mL/min (±980 mL/(min), respectively (p = 0.3). The mean difference was -51 mL/min (CI: -150 mL/min to 46 mL/min) with limits of agreement from -35% to 54%, with a strong correlation (r2= 0.87). A large change in volume flow between dialysis sessions detected by UDT was confirmed by VFI (p = 0.0001), but the concordance rate was poor (0.72).ConclusionsVFI is an acceptable method for volume flow estimation and volume flow changes over time in AVFs.

Synthetic Aperture (SA) imaging produces high-quality images and velocity estimates of both slow and fast flow at high frame rates. However, grating lobe artifacts can appear both in transmission and reception. These affect the image quality and the frame rate. Therefore optimization of parameters effecting the image quality of SA is of great importance, and this paper proposes an advanced procedure for optimizing the parameters essential for acquiring an optimal image quality, while generating high resolution SA images. Optimization of the image quality is mainly performed based on measures such as F-number, number of emissions and the aperture size. They are considered to be the most contributing acquisition factors in the quality of the high resolution images in SA. Therefore, the performance of image quality is quantified in terms of full-width at half maximum (FWHM) and the cystic resolution (CTR). The results of the study showed that SA imaging with only 32 emissions and maximum sweep angle of 22 degrees yields a very good image quality compared with using 256 emissions and the full aperture size. Therefore the number of emissions and the maximum sweep angle in the SA can be optimized to reach a reasonably good performance, and to increase the frame rate by lowering the required number of emissions. All the measurements are performed using the experimental SARUS scanner connected to a λ/2-pitch transducer. A wire phantom and a tissue mimicking phantom containing anechoic cysts are scanned using the optimized parameters for the transducer. Measurements coincide with simulations.

District heating (DH) can reduce the primary energy consumption in urban areas with significant heat demands. The design of a serially connected ammonia-water hybrid absorption-compression heat pump system was investigated for operation in the Greater Copenhagen DH network in Denmark, in order to supply 7.2 MW heat at 85 °C utilizing a geothermal heat source at 73 °C. Both the heat source and heat sink experience a large temperature change over the heat transfer process, of which a significant part may be achieved by direct heat exchange. First a generic study with a simple representation of the heat pump was used to investigate optimal system configurations. It was shown that using two heat pumps in series with direct heat exchange in parallel with the first heat pump could increase the performance compared to a base case using direct heat exchange and a single heat pump, under the assumption that the exergetic efficiencies of the heat pumps are similar. Next, ammonia-water hybrid absorption-compression heat pumps were selected as heat pump technology, since these may increase the performance due the non-isothermal phase change. Detailed thermodynamic models predict that an exergetic efficiency of the system of 0.5 to 0.65 is possible. The technical feasibility as well as the economic viability of this installation was investigated for a range of preferred solutions. The analysis recommends a heat pump configuration with an exergetic efficiency of 0.63 which was within 2 % of the theoretical economic optimum.

Clinical applications of plane wave imaging necessitate the creation of high-quality images with the highest possible frame rate for improved blood flow tracking and anatomical imaging. However, linear array transducers create grating lobe artefacts, which degrade the image quality especially in the near field for λ-pitch transducers. Artefacts can only partly be suppressed by increasing the number of emissions, and this paper demonstrates how the frame rate can be increased without loss of image quality by using λ/2-pitch transducers. The number of emissions and steering angles are optimized in a simulation study to get the best images with as high a frame rate as possible. The optimal setup for a simulated 4.1 MHz λ-pitch transducer is 73 emissions and a maximum steering of 22◦ . The achieved FWHM is 1.3λ and the cystic resolution is -25 dB for a scatter at 9 mm. Only 37 emissions are necessary within the same angle range when using a λ/2-pitch transducer, and the cystic resolution is reduced to -56 dB. Measurements are performed with the experimental SARUS scanner connected to a λ-pitch and λ/2-pitch transducer. A wire phantom and a tissue mimicking phantom containing anechoic cysts are scanned and show the performance using the optimized sequences for the transducers. Measurements confirm results from simulations, and the λ-pitch transducer show artefacts at undesirable strengths of -25 dB for a low number of emissions.

This paper presents a method for estimating 2-D vector velocities using plane waves and transverse oscillation. The approach uses emission of a low number of steered plane waves, which result in a high frame rate and continuous acquisition of data for the whole image. A transverse oscillating field is obtained by filtering the beamformed RF images in the Fourier domain using a Gaussian filter centered at a desired oscillation frequency. Performance of the method is quantified through measurements with the experimental scanner SARUS and the BK 2L8 linear array transducer. Constant parabolic flow in a flow rig phantom is scanned at beam-to-flow angles of 90, 75, and 60◦ . The relative bias is between -1.4 % and -5.8 % and the relative std. between 5 % and 8.2 % for the lateral velocity component at the measured beam-to-flow angles. The estimated flow angle is 73.4◦± 3.6◦ for the measurement at 75◦ . Measurement of pulsatile flow through a constricted vessel demonstrate the application of the method in a realistic flow environment with large spatial and temporal flow gradients.

Spray-drying facilities are among the most energy intensive industrial processes. Using a heat pump to recover waste heat and replace gas combustion has the potential to attain both economic and emissions savings. In the case examined a drying gas of ambient air is heated to 200 °C yielding a heat load of 6.1 MW. The exhaust air from the drying process is 80 °C. The implementation of an ammonia–water hybrid absorption–compression heat pump to partly cover the heat load is investigated. A thermodynamic analysis is applied to determine optimal circulation ratios for a number of ammonia mass fractions and heat pump loads. An exergoeconomic optimization is applied to minimize the lifetime cost of the system. Technological limitations are imposed to constrain the solution to commercial components. The best possible implementation is identified in terms of heat load, ammonia mass fraction and circulation ratio. The best possible implementation is a 895 kW heat pump with an ammonia mass fraction of 0.82 and a circulation ratio of 0.43. This results in economic savings with a present value of 146,000 € and a yearly CO2 emissions reduction of 227 ton.

The investigated hypothesis is that quantization of the transmit delay profiles degrades the image quality in plane wave ultrasound imaging. Simulated point spread functions show that transmit delay profile quantization gives rise to artefacts behind the point target. The axial and lateral 6 dB resolution is unaffected, but contrast is reduced. This is quantified by a 20 dB cystic resolution of 1.23 mm compared to 0.53 mm for the ideal (non-quantized) case at 10 mm depth. It is also shown that providing individually phase-shifted excitation waveforms to each element restores the image quality, as seen by the 20 dB cystic resolution being restored to 0.53 mm. The impact on high-quality imaging is discussed.

A comparison of synthetic aperture imaging using spherical and plane waves with low number of emission events is presented. For both wave types, a 90 degree sector is insonified using 15 emission events giving a frame rate of 200 frames per second. Field II simulations of point targets show similar resolution of approximately one wavelength radially and one degree angularly for both wave types. The use of spherical waves is found to have higher signal strength and better cystic resolution than plane waves. Measurements on wires in water yield similar results to simulations with similar resolution between the two wave types but better cystic resolution for spherical waves. Mea- surements on tissue mimicking phantoms show that both wave types penetrate down to 11 cm. Intensity measurements show an I spta: 3 of 18.4 mW/cm 2 for spherical waves and 22.7 mW/cm 2 for plane waves. The derated MI is 0.43 for spherical and 0.70 for plane waves. All measures are well within FDA limits for cardiac imaging. In-vivo images of the heart of a healthy 28-year old volunteer are shown.

This paper investigates sources of error for a vector velocity volume flow estimator. Quantification of the estima tor’s accuracy is performed theoretically and investigated in vivo . Womersley’s model for pulsatile flow is used to simulate velo city profiles and calculate volume flow errors in cases of elliptic al vessels and not placing the transducer at the vessel center. Simulations show, i.e., that volume flow is underestimated w ith 5 %, when the transducer is placed 15 % from the vessel center. Twenty patients with arteriovenous fistulas for hemodialys is are scanned in a clinical study. A BK Medical UltraView 800 ultrasound scanner with a 9 MHz linear array transducer is used to obtain Vector Flow Imaging sequences of a superficial part of the fistulas. Cross-sectional diameters of each fistu la are measured on B-mode images by rotating the scan plane 90 degrees. The major axis of the fistulas was on average 8.6 % larger than the minor axis, so elliptic dimensions should be taken into account in volume flow estimation. The ultrasound beam w as on average 1.5 ± 0.8 mm off-axis, corresponding to 28.5 ± 11.3 % of the major semi-axis of a fistula, and this could result in 15 % underestimated volume flow according to the simulation. Volume flow estimates were corrected for the beam being off- axis, but was not able to significantly decrease the error rel ative to measurements with the reference method.

Gaseous hydrogen as an automotive fuel is reaching the point of commercial introduction. Development of hydrogen fuelling stations considering an acceptable fuelling time by cooling the hydrogen to −40 °C has started. This paper presents a design study of coaxial tube ammonia evaporators for three different concepts of hydrogen cooling, one one-stage and two two-stage processes. An exergoeconomic optimization is imposed to all three concepts to minimize the total cost. A numerical heat transfer model is developed in Engineer Equation Solver, using heat transfer and pressure drop correlations from the open literature. With this model the optimal choice of tube sizes and circuit numbers are found for all three concepts. The results show that cooling with a two-stage evaporator after the pressure reduction valve yields the lowest total cost, 45% lower than the highest, which is with a one-stage evaporator. The main contribution to the total cost was the cost associated with exergy destruction, the capital investment cost contributed with 5–14%. The main contribution to the exergy destruction was found to be thermally driven. The pressure driven exergy destruction accounted for 3–9%.

Synthetic Aperture Sequential Beamforming (SASB) is a technique with low complexity and the ability to yield a more uniform lateral resolution with range. However, the presence of speckle artifacts in ultrasound images degrades the contrast. In conventional imaging speckle is reduced by using spatial compounding at the cost of a reduced frame rate. The objective is to apply spatial compounding to SASB and evaluate if the images have a reduced speckle appearance and thereby an improved image quality in terms of contrast compared to ordinary SASB. Using the simulation software Field II, RF data are acquired for a phantom with cysts at different sizes and scattering levels. 192 scanlines are recorded for five steering angles (0, ±2, ±4 degrees) using a 192 element linear array transducer. SASB is performed for each angle using a rectangular grid in the second stage beamformation. After envelope detection the five second stage images are added to form the compounded image. Using a ProFocus scanner and the 8804 linear array transducer (BK Medical, Herlev, Denmark) measurements of a phantom containing water filled cysts are obtained to validate the simulation results. The setup is the same as in the simulations and SASB second stage beamformation data are processed offline for each of the five angles. Contrast-to-noise ratio (CNR) and speckle-to-noise ratio (SNR) are extracted for the compounded image and the reference image (ordinary SASB). CNR was calculated for the simulated cysts at depths of 40, 50, 60, 70 and 80 mm. On average the CNR was improved by 33.2% compared to the values obtained from the reference image. For regions of increasing depth SNR was on average increased by 9.3%. Results from the simulation were confirmed by calculations on the measured data. CNR of cysts at depths from 18 to 78 mm with a separation of 10 mm was on average improved by 45.9%. On average an improvement of 16.6% in SNR was obtained. The calculations along with visual inspection revealed larger improvements in deeper regions, and the compounded image for the measured phantom showed a 3 mm diameter cyst not detectable in the reference image. Compounding applied to SASB improves CNR and SNR results in images with a reduced speckle appearance. This was shown for simulations and confirmed on measured data.

Energy planning tools often consider a constant coefficient of performance (COP) for large-scale heat pumps (HPs) over the entire year, even though the optimization is usually performed on hourly basis. Because the HP performance is highly dependent on ambient conditions, the constant COP may not represent real implementation well. Ambient temperature levels can be included by assuming simple representations of COP based on a Carnot or a Lorenz cycle. These simple representations of COPs are used, because implementing a thermodynamic HP model in the energy planning software may be complicated or would result in values limited to a specific HP application. Other options of estimating the COP are the use of more advanced COP estimation methods. This paper compares COP estimations based on four different methods to the COP obtained using a thermodynamic HP model. Four different heat sources and varying district heating supply temperatures were considered. Furthermore, the results of implementing the different COP estimations in an energy planning tool were analysed. As a case, the planning tool was used to assess HP implementation in a new development district in Copenhagen, Denmark. The change in seasonal COP of the HPs as well as the economic results and optimal HP capacities were compared. The results show that the Jensen COP estimation method for design conditions provide good approximations compared to a thermodynamic HP model. The results indicate that this method is suitable for the use in energy planning tools. Assuming a constant Lorenz efficiency, constant exergy efficiency or constant COP over the year resulted in very large deviations in COP, especially when the operating conditions differ considerably from the design conditions. Consequently, different heat sources were found for the most economical optimum. The accuracy of the three methods was highly dependent on the initial guesses of constant COP and efficiencies.

A large amount of operational and economic constraints limit the applicability of heat pumps operated with natural working fluids. The limitations are highly dependent on the integration of heat source and sink streams. An evaluation of feasible operating conditions is carried out considering the constraints of available refrigeration equipment and a requirement of a positive Net Present Value of the investment. The considered sink outlet temperature range is from 40 °C to 140 °C, but for the heat pumps considered in this paper, the upper limit is 100 °C. Five heat pumps are studied. For each set of heat sink and source temperatures the optimal solution is determined. At low sink temperature glide R717 heat pumps show best performance, while at higher sink glide transcritical R744 may become important. In a second paper, the results of the VCHP are compared to a similar study considering the ammonia-water absorption-compression heat pump.

Energy, exergy and advanced exergy methods are used in this study to analyse a milk processing facility which is one of the largest energy consumers within the food industry in Denmark. While a conventional energy analysis maps the energy flows of the system and suggests opportunities for process integration, an exergy analysis pinpoints the locations, causes and magnitudes of thermodynamic losses. The advanced exergy analysis further identifies the real potential for thermodynamic improvements of the system by splitting exergy destruction into its avoidable and unavoidable parts, which are related to technological limitations, and into its endogenous and exogenous parts, which illustrate the interactions between the different sub-systems. This analysis is based on actual factory data from one of Europe’s largest dairy producers: the complete production line is modelled, and includes the production of milk, cream and milk powder. The results show the optimisation potential based on 1st and 2nd law analyses. An evaluation and comparison of the applicability of exergy methods, including advanced exergy methods, to the dairy industry is made. The comparison includes typical energy mappings conducted onsite, and discusses the benefits and challenges of applying advanced thermodynamic methods to industrial processes.

Spray drying facilities are among the most energy intensive industrial processes. Using a heat pump to recover waste heat and replace gas combustion has the potential to attain both economic and emissions savings. In the case examined a drying gas of ambient air is heated to 200 XC. The inlet flow rate is 100,000 m3/h which yields a heat load of 6.1 MW. The exhaust air from the drying process is 80 XC. The implementation of an ammonia-water hybrid absorption-compression heat pump to partly cover the heat load is investigated. A thermodynamic analysis is applied to determine optimal circulation ratios for a number of ammonia mass fractions and heat pump loads. An exergoeconomic optimization is applied to minimize the lifetime cost of the system. Technological limitations are applied to constrain the solution to commercial components. The best possible implementation is identified in terms of heat load, ammonia mass fraction and circulation ratio. The best possible implementation is a 865 kW heat pump with an ammonia mass fraction of 0.81 and a circulation ratio of 0.45. This results in economic savings with a present value of 177.000 C and a yearly CO2 emissions reduction of 210 ton.

The energy footprint of spray dryers is the highest among the process operations of milk powder plants. This is mostly due to heating of air up to ~240 °C from ambient temperature, which results in significant use of energy, conventionally supplied by combustion of fossil fuels. Numerous efforts have been invested in investigating opportunities for increasing the energy efficiency of spray dryers, such as heat recovery and heat pumping from the exhaust air. However, these solutions are not state-of-the-art for heating the air above ~80 °C, resulting in a low penetration of renewable energy sources in these processes. In this study, we investigate the possibility to fully electrified spray dryers by integrating a high-temperature heat pump heating the main drying airstream to a design temperature of 236 °C. The solution makes use of a novel spindle compressor. A design is performed including direct heat recovery from the exhaust air above its dew point and heat pumping of heat from the exhaust air below its dew point. Three heat pumps using natural refrigerants are integrated into the process to supply heat at different temperature levels. According to process modelling, pinch analysis, and techno-economic analysis, the trade-off between energy savings and capital cost is investigated. An energy-saving ratio between 0.55 and 0.58 is obtained, while the levelized cost of heat falls between 35.1 and 36.2 €/MWh depending on the heat exchanger temperature approach.

Design optimization of absorber and desorber in hybrid absorption compression heat pumps (HACHPs) is of paramount importance to reduce the installation costs of these systems. This paper presents a simulation framework to optimize the design of plate heat exchangers (PHEs) to be used as absorption and desorption units in HACHPs. A case study of a single-stage HACHP was chosen as an example to utilize the framework. A PHE design model was coupled with a cycle design tool, and the trade-o between heat transfer area and pressure drop in both absorber and desorber was established by estimating the impact of pressure drops on the heat pump thermodynamic performance. Corrugation geometry, plate size and count were selected as design variables for the optimization procedure, in order to obtain a diversied range of optimal solutions. It was found that the desorber pressure drop entails a higher degradation of the thermodynamic performance compared to the absorber,and the two limits of maximum allowable pressure drops of 15 kPa and 35 kPa were selected. The design optimization showed that it is preferred to choose corrugation geometry parameters, such as chevron angle, corrugation pitch and height, with the aim of enhancing the heat transfer at the expense of pressure drop. On the other hand, a diverse range of plate size and count was obtained as output of optimization.The results demonstrate how to select optimal congurations of PHE absorber and desorber for HACHPs.

The ammonia-water hybrid absorption-compression heat pump (HACHP) is a technology suitable for industrial scale heat pumps in the process industry. A helpful tool in the design of cost effective and low environmental impact energy conversion systems, such as the HACHP, is the application of an advanced exergy-based analysis, comprised of both an advanced exergy, exergoeconomic and exergoenvironmental analysis. Recent studies have presented both the advanced exergy and advanced exergoeconmic analysis of the HACHP. Anexergoenvironmental analysis combines exergy analysis with life cycle assessment to allocate the initial and operational environmental impact to the system components, thus revealing the main sources of environmental impact. The application of the advanced exergoenvironmental analysis improves the level of detail attained.This is achieved by accounting for technological and economic constraints as well as component interdependencies.The advanced exergoenvironmental analysis shows that the highest avoidable environmental impact stems from the compressor, followed by the absorber. Further, it is found that the initial environmental impactof the HACHP is negligible compared to the operational environmental impact.

Plate heat exchangers are often applied as evaporators in industrial refrigeration and heat pump systems. In the design and modelling of such heat exchangers the flow and liquid/vapour distribution is often assumed to be ideal. However, maldistribution may occur and will cause each channel to behave differently due to the variation of the mass flux and vapour quality. To evaluate the effect of maldistribution on the performance of plate heat exchangers, a numerical model is developed in which the mass, momentum and energy balances are applied individually to each channel, including suitable correlations for heat transfer and pressure drop. The flow distribution on both the refrigerant and secondary side is determined based on equal pressure drop while the liquid/vapour distribution is imposed to the model. Results show that maldistribution may cause up to a 25 % reduction of the overall heat transfer coefficient, compared to a lumped model with uniform distribution.

Industrial processes are highly dependent on large amounts of energy in the form of heat. This is traditionally delivered by steam or hot water heated in boilers using natural gas, oil, or biomass. High-temperature heat pumps (HTHPs) are a key technology in the transition towards sustainable energy systems. They may provide highly efficient electricity-based process heat contributing to the de-carbonization of the process industry. The implementation of HTHPs in industrial applications is limited by various operational, technological, and thermodynamic constraints. In contrast to boilers, the efficiency of HTHPs greatly increases when lowering the supply temperature. This yields potential economic savings by lowering the utility temperature of industrial processes. This paper aimed at quantifying the decrease in the levelized cost of heat when lowering the supply temperature of HTHPs. The main boiler was replaced by a HTHP, and the steam temperature was lowered. The changes in Coefficient of Performance (COP), Total Capital Investment (TCI) were observed for several HP cascade cycles, with natural working fluids, including water, hydrocarbons, and ammonia. The results showed that the price ratio between natural gas and electricity and the COP of the HTHP were the main factors for determining financial viability when comparing to a natural gas boiler. The operational cost of a HTHP used for hot utility decreases when lowering the utility temperature. Improved performance was observed for all HTHP configurations, however, it was highly sensitive to the COP and electricity price. A cascade HTHP using R-717 and R-718 as refrigerants delivered 160 ◦C steam at a levelized cost of heat (LCOH) of 46EUR/MWh with 30 ◦C as a source temperature. Varying the delivery temperature with 10 ◦C resulted in a change of 1EUR/MWh to 4EUR/MWh in LCOH depending on the technology and reference point. This indicated the significance of correct design temperatures for process heat supply.

By operating heat pumps (HPs) in series, it is possible to obtain closer match between working fluid and sink- and source streams, resulting in higher coefficient of performance (COP). For industrial HPs, it was found that serial connection of either two or three units results in an increase in COP and a decrease in net present value (NPV), due to the effects of economy of scale. However, connecting HPs in series may reduce the discharge temperature, which is of particular interest when assessing R717 HPs. Another possibility from serial connection is to mix different types of HP units, in order obtain specific characteristics. The technical and economical working domains were calculated for two serial connections. Both configurations result in an increased working domain for the investigated dual unit serial connections.

The hybrid absorption/compression heat pump (HACHP) using ammonia-water as working fluid is a promising technology for development of a high temperature industrial heat pump. This is due to two properties inherent to the use of zeotropic mixtures: non-isothermal phase change and reduced vapour pressures. Using standard refrigeration components (28 bar) HACHP up to 100 °C are commercially available. Components developed for high pressure NH3 (52 bar) and transcritical CO2 (140 bar) increase the limiting allowable pressures. It is therefore relevant to evaluate the feasible supply temperatures using these components. A technically and economically feasible solution is defined as one that satisfies constraints on the coefficient of performance (COP), low and high pressure, compressor discharge temperature and volumetric heat capacity. The ammonia mass fraction of the rich solution and the liquid circulation ratio both influence these constraints. The paper investigates feasible combinations of these parameters. A numerical HACHP model is developed in Engineering Equation Solver (EES). The constrained parameters are evaluated for a range of combinations for systems with supply temperatures of 100 °C, 125 °C, 150 °C and 175 °C. Results show that standard components are applicable up to 100 °C, equipment for high pressure NH3 up to 125 °C, and equipment for transcritical CO2 up to 175 °C.