A Virtual EXV Mass Flow Sensor for Applications With Two-Phase Flow Inlet Conditions

In conventional vapor compression systems, electronic expansion valves (EXVs) are used for refrigerant flow control. Subcooled refrigerant enters the expansion device and is expanded to the evaporation pressure while the valve opening is modified to achieve the desired mass flowrate. The relationship between the inlet and outlet conditions, the opening, and the mass flowrate has been extensively studied, e.g. by Park et al. (2007) and appropriate empirical correlations have been developed. However, for certain operating conditions (e.g. low refrigerant charge) or applications that generally have two-phase inlet conditions (e.g. balancing valves used in a hybrid control scheme as proposed by Kim et al. (2008)), these correlations are not applicable, since even low inlet vapor fractions lead to a significant reduction of the valve mass flowrate at a given opening. This paper proposes a continuous correlation that can be used for both two-phase and subcooled valve inlet conditions. The benefit of the continuity is that there is a smooth transition between subcooled and two-phase inlet conditions, which is essential for control and simulation purposes. The new correlation employs the Buckingham-Pi theorem as proposed by Buckingham (1914). The selected dimensionless Pi-groups describe opening of the valve, subcooling, inlet and outlet pressures, driving pressure difference across the valve, inlet density, surface tension, and viscosity. The data that was used to determine the coefficients of the correlation was taken on a dedicated valve test stand, which was sized for the per-circuit capacity of a typical 5-ton R410A heat pump and a 3-ton R404A large room cooling system. The purpose of these tests was mainly to map the valves for the low pressure drops, high inlet qualities and large valve openings that occur when they are used as balancing valves in a hybrid control approach. Two commercially available valves of different rated capacity were tested. Due to the much higher valve capacity for subcooled inlet conditions, valve openings of less than 5% occurred in that case. This led to an accuracy of the correlation for these points that is less than what typically can be found for correlations with subcooled inlet conditions in the open literature. However, for two-phase flow inlet conditions, the resulting RMS of 1.0 g/s for the 8-PI correlation is sufficiently small to use the approach for estimating the refrigerant mass flow and using the EXV as a virtual flow sensor. The limitations of this approach in practical applications, as well as possible applications in fault detection and diagnostics are shown for application as balancing valves within a 5-ton R410A heat pump and a 3-ton R404A large room cooling system

The Difficult Diagnosis of Ischaemic Papillary Muscle Rupture : Case report from an urban emergency department

We present a rare case of severe ischaemic papillary muscle rupture in a 67-year-old male patient who was admitted to the Emergency Department of the University Hospital Bern, Switzerland, in November 2013 with acute chest pain. On admission, the patient’s blood pressure was 60/40 mm/Hg, his pulse was 110 beats per minute and his respiratory rate was 20 breaths per minute. An electrocardiogram was normal and focused assessment with sonography in trauma was negative. Transthoracic echocardiography showed possible thickening of the mitral valve leaflet with no indications of severe mitral insufficiency or wall motion abnormalities. Triple-ruleout computed tomography angiography revealed no pulmonary emboli or aortic dissection, although coronary atherosclerosis was present. Finally, severe insufficiency of the mitral valve with rupture of the papillary muscle, likely due to ischaemia, was observed via transoesophageal echocardiography. The patient underwent a successful surgical intervention and was discharged 10 days later in stable condition

Interleaved Circuitry And Hybrid Control As Means To Reduce The Effects Of Flow Maldistribution.

Flow maldistribution in evaporators can lead to significant degradation of capacity and efficiency of vapor compression equipment. A significant amount of work has previously been done to mend these issues. For variable air flow maldistribution, refrigerant compensation was proposed to reduce the performance degradation. For fixed air side maldistribution, refrigerant circuitry modifications were proposed to significantly reduce the effects of the maldistribution. However, no work has been found on modifying the refrigerant circuitry to make it less vulnerable to varying air side maldistribution. The purpose of this paper is to fill this gap in open literature. The performance of the new, interleaved circuitry approach and an active refrigerant flow control is compared to the standard circuitry for different cases of maldistribution. The results show that the interleaved circuitry recovers less of the performance losses than equalization of the exit superheats. However, the implementation cost in an actual system is expected to be significantly lower and the long term reliability is expected to be much better than for an active control approach

Effects of Vapor Injected Compression, Hybrid Evaporator Flow Control, and Other Parameters on Seasonal Energy Efficiency.

A companion paper (Bach et al. 2014) experimentally investigated the effects of vapor injected compression and hybrid evaporator flow control on capacity and COP. The goal of this paper is to provide insight into the effects of these technologies on heating seasonal performance (HSPF). HSPF was calculated using a modified version of the ANSI/AHRI 210/240 method, and parametric studies were performed to better understand the seasonal performance with a focus on comparing vapor injected and single stage system configuration. It was found that part load degradation and reduced capacity at low ambient temperature are factors that can degrade the seasonal performance. The increase in heat pump COP for the vapor injected configuration leads to only a small benefit - the main contributor to the increased HSPF of the vapor injected system configuration is its increased capacity towards low ambient temperatures. References: Bach C. K., Vetsch, B., Groll, E. A., Braun, J. E., and Horton, W. T, (2014), Experimental Investigation of Vapor Injected Compression for Cold Climate Heat Pumps and its Effects on their Performance, 15th International Refrigeration and Air Conditioning Conference at Purdue, West Lafayette

Management of proximal femur fractures in the elderly: current concepts and treatment options

As one of the leading causes of elderly patients' hospitalisation, proximal femur fractures (PFFs) will present an increasing socioeconomic problem in the near future. This is a result of the demographic change that is expressed by the increasing proportion of elderly people in society. Peri-operative management must be handled attentively to avoid complications and decrease mortality rates. To deal with the exceptional needs of the elderly, the development of orthogeriatric centres to support orthogeriatric co-management is mandatory. Adequate pain medication, balanced fluid management, delirium prevention and the operative treatment choice based on comorbidities, individual demands and biological rather than chronological age, all deserve particular attention to improve patients' outcomes. The operative management of intertrochanteric and subtrochanteric fractures favours intramedullary nailing. For femoral neck fractures, the Garden classification is used to differentiate between non-displaced and displaced fractures. Osteosynthesis is suitable for biologically young patients with non-dislocated fractures, whereas total hip arthroplasty and hemiarthroplasty are the main options for biologically old patients and displaced fractures. In bedridden patients, osteosynthesis might be an option to establish transferability from bed to chair and the restroom. Postoperatively, the patients benefit from early mobilisation and early geriatric care. During the COVID-19 pandemic, prolonged time until surgery and thus an increased rate of complications took a toll on frail patients with PFFs. This review aims to offer surgical guidelines for the treatment of PFFs in the elderly with a focus on pitfalls and challenges particularly relevant to frail patients

Experimental Investigation of Vapor Injected Compression for Cold Climate Heat Pumps

Building heating requirements increase with decreasing ambient temperature, while the coefficient of performance of air-source heat pumps (ASHPs) shows the opposite trend. Additionally, heating capacity decreases with ambient temperature, which leads to the utilization of inefficient electric reheat below the design point. Increasing the capacity and COP at lower ambient temperatures is important for improving the market penetration of heat pumps in climates having significant operating time at low ambient temperature. Simulation studies previously showed that compressor vapor injection leads to an increase of COP under exactly those conditions. Furthermore, reduced capacity degradation towards smaller ambient temperatures was predicted. The work presented in this paper shows experimental results obtained from a commercially available 5-ton heat pump that was retrofitted with a two-port vapor injected scroll compressor. The injection ports within the two compression pathways are located in the fixed scroll with different distance from the suction chamber. The vapor for the two injection pressure levels was generated using two vapor separators in a cascade configuration. This configuration made it necessary to not only control the superheat but also the liquid levels in the separators and subcooling of the refrigerant leaving the condenser. Baseline performance data of the heat pump without vapor injection was obtained and compared with that for the vapor injection and other system configurations. For the baseline, the injection lines to the compression pockets were plugged within the fixed scroll to reduce dead volume and re-expansion losses. Also, the vapor-separator section was shut off and bypassed. In the second step, the plugs were removed and a staged expansion process was performed using the separator section. The generated vapor from each separator was injected into the respective compressor port causing an intercooling effect on the compression process. With identical compressor speed, a 28% improvement in capacity was achieved at the 8.33°C (47 F) design point, when compared to the baseline without vapor injection. When the baseline and vapor injected system capacity were matched by adjusting compressor speed, the COP increased by up to 6% at -8.33°C (17 F). Preliminary results of a bin-type analysis of the experimental data predicts an improvement in HSPF of 6% for Minneapolis and nearly 7% for AHRI climate region 5. The benefit is mainly caused by a reduction of the auxiliary electric heater’s runtime

Dooring-Fahrradunfälle mit schweren Verletzungsmustern: 10-Jahres-Studie eines Level-1-Traumazentrums

Dooring Bicycle Accidents with Severe Injury Patterns: 10-Year Study of a Level 1 Trauma Cente

Stridulation of the clear-wing meadow katydid <i>Xiphelimum amplipennis</i>, adaptive bandwidth

Rubbed wings, analysed calls and peculiar sound generator structure in males of a conocephaline katydid, Xiphelimum amplipennis, give insight into the making of broadband spectra. High shear forces are indicated by a robust forewing morphology. Intensity is high for frequencies in a 20-60 kHz ultrasonic band. Besides a typical katydid sound-radiating mirror and harp, this insect has a long costal series of semitransparent specular sound radiators. These wing cells are loaded behind by an enlarged and partitioned subwing air space. Calls repeat steadily with five different time-domain sound elements. Distinctive spectra are associated with two of these, giving stepwise frequency modulation that combines to create the exceptionally wide spectral breadth. Broadcast sound levels at 10 cm dorsal, right and left, are near 100 dB. Costal wing-cell sound radiation was explored by loading the costal ‘speculae’ with wax. This produced almost no decrease in lateral sound levels, but did alter spectral content. Apparently this insect’s costal region both baffles and radiates. The species lives at high densities in cluttered vegetation and sound signal attenuation should code via spectral shape for distance ranging.Facultad de Ciencias Naturales y Muse

Application Of Oil Flooded Compression With Regeneration To A Packaged Heat Pump System

Heating capacity and coefficient of performance (COP) of conventional air-source heat pumps decreases towards lower ambient temperatures. In addition, high discharge temperature cutout at the compressor outlet might limit the operation of the heat pump at very low ambient temperatures. Oil injected into the compression chamber absorbs part of the heat generated during the compression process, which can result in significant reduction of the compressor discharge temperature. Discharge temperature therefore decreases with increasing injected oil mass fraction, especially at low ambient temperatures. Therefore, oil injection allows the application of air-source heat pumps in regions with very low ambient temperature in winter. Additionally, oil injection decreases the compressor power consumption by providing better sealing and lower friction during the compression process. Furthermore, if oil injection is combined with a regenerative heat exchanger, the system performance of a vapor compression system can be improved significantly. The work presented on this paper shows the experimental results of a 5-ton (17.6 kW) R410A packaged heat pump which was retrofitted with an oil injected compressor and regenerator. The effect of different oil mass fractions on the system performance was investigated under standard AHRI 210/240 heating test conditions. According to the results, more than 7% system COP improvement was observed compared to the baseline system

Transcatheter Aortic Valve Implantation in Dialysis Patients

Background/Aims: Transcatheter aortic valve implantation (TAVI) has emerged as a new therapeutic option for high-risk patients. However, dialysis patients were excluded from all previous studies. The aim of this study is to compare the outcomes of TAVI for dialysis patients with those for patients with chronic kidney disease (CKD) stages 3 and 4 and to compare TAVI with open surgery in dialysis patients. Methods: Part I: comparison of 10 patients on chronic hemodialysis with 116 patients with non-dialysis-dependent CKD undergoing TAVI. Part II: comparison of transcatheter (n = 15) with open surgical (n = 24) aortic valve replacement in dialysis patients. Results: Part I: dialysis patients were significantly younger (72.3 vs. 82.0 years; p < 0.01). Hospital stay was significantly longer in dialysis patients (21.8 vs. 12.1 days; p = 0.01). Overall 30-day mortality was 3.17%, with no deaths among dialysis patients. Six-month survival rates were similar (log-rank p = 0.935). Part II: patient age was comparable (66.5 vs. 69.5 years; p = 0.42). Patients in the surgical group tended to stay longer in hospital than TAVI patients (29.5 vs. 22.5 days; p = 0.35). Conclusion: TAVI is a safe procedure in patients on chronic hemodialysis. Until new data become available, we find no compelling reason to refuse these patients TAVI. Copyright (C) 2012 S. Karger AG, Base