Development of an Adjustable Spiral-shaped Evaporator

The cooling of high heat flux is becoming increasingly important in technical applications. This is on the one hand due to the fact that the available installation space is becoming smaller and smaller due to progressive miniaturization, on the other hand to the ever-increasing performance, which has to be taken away in technically demanding processes such as Inconel machining. In order to meet this challenge, a new type of evaporator, the swirl evaporator, was developed. The swirl evaporator is a screw-shaped cylindrical evaporator with an internal diameter between 1 – 3 mm, which is inserted as a blind hole in components with high heat generation. The refrigerant is fed into the blind hole via a concentrically oriented capillary, deflected by 180° in the drilling base and flows out of the evaporator again in a helical way (twist flow) against the inflow direction. The evaporator\u27s design allows a compact size to be achieved, making it suitable for a wide range of technical applications. To enable a design for industrial needs, a 1-D simulation of the process had been conducted. The simulations showed ideal results for a hydraulic diameter of 2.05 mm and an evaporator length of 15 – 20 mm. According to the simulations an improvement of the energy efficiency of up to 19 % is possible when the mass flow is kept constant for R32. Based on the results of these simulations a design of the test-rig had been developed which allows different screw inserts to be tested with a variable length. Former experimental studies with R404A show that the average critical heat flux density of spot evaporators with a twist geometry increases by up to 33 % compared with spot evaporators without twist generation. The spot evaporators with swirl flow generation have a distinct, stable overheating zone with high heat flux (Humpfer, 2013)

Experimental Analysis Of Twisted Shaped Spot Evaporators At High Heat Fluxes

Devices for cooling high heat fluxes within small available spaces are called spot evaporators. Areas of application are for example the cooling of molds, power electronics or electrical mobility. The functionality of the spot evaporator bases on its geometry and is a combination of spray-cooling and pipe flow. Spray-cooling or jet impingement cooling is able to achieve high heat fluxes even at overcritical wall temperatures. To reach the same effects within the pipe-flow part of the spot evaporator, this part has to be twisted shaped. The paper focuses on the experimental analysis of the twisted shaped spot evaporator by varying fundamental parameters corresponding to the Model of Yagov. Two methods of generating the twist have been developed and compared to each other. The experimental results will be discussed. They show that the averaged critical heat flux can be raised up to 30 % compared to spot evaporators without twisted flow. As refrigerant R404A has been used

Hydraulic Characterization of a Adjustable Spiral-shaped Evaporator

To ensure reliability in miniaturized devices or processes with increased heat fluxes, decreasing available cooling surfaces have to be met by novel cooling methods. In order to meet this challenge, a new type of evaporator, the swirl evaporator, was developed. The swirl evaporator is a screw-shaped cylindrical evaporator with an internal diameter between 1 – 3 mm, which is inserted as a blind hole in components with high heat generation. The refrigerant is fed into the blind hole via a capillary, deflected by 180° in the drilling base and flows out of the evaporator again in a helical way (twist flow) against the inflow direction. The refrigerant is pressed against the hot wall by centrifugal forces. This results in an increased critical heat flux. The evaporator\u27s design allows a compact size, making it suitable for a wide range of technical applications. To enable its design for industrial needs, a test stand has been developed. The hydraulic characterization was performed by varying the evaporator length. First experimental results show a linear relationship between swirl evaporator length and pressure loss

Comparison of an automatic analysis and a manual analysis of conjunctival microcirculation in a sheep model of haemorrhagic shock

Life-threatening diseases of critically ill patients are known to derange microcirculation. Automatic analysis of microcirculation would provide a bedside diagnostic tool for microcirculatory disorders and allow immediate therapeutic decisions based upon microcirculation analysis

Comparison of first-line and second-line terlipressin versus sole norepinephrine in fulminant ovine septic shock

The Surviving Sepsis Guidelines suggest the use of vasopressin in case of catecholamine-refractory septic shock. Terlipressin (TP) as a V-1-selective AVP analogue is a potential alternative, though data regarding the first-line administration in septic shock are scarce. The present study explored and compared the effects of first-line vs. second-line infusion of TP or sole norepinephrine regarding organ function, fluid and norepinephrine requirements and survival in fulminant ovine septic shock. Peritoneal sepsis was induced in 23 ewes after laparotomy and faecal withdrawal from the caecum. After onset of shock, causal and supportive sepsis therapy (antibiotics, peritoneal lavage, fluids and open-label norepinephrine) was performed in all animals. Concurrently, animals were randomized to receive 0.9% sodium chloride (control group) or TP (2 mu g.kg(-1).h(-1), first-line group) after shock onset. In the second-line TP group, TP (2 mu g.kg(-1).h(-1)) was started once norepinephrine requirements exceeded 0.5 mu g.kg(-1).min(-1). No significant differences were found between groups regarding survival, haemodynamics as well as fluid-and catecholamine-requirements. Kidney function and electron microscopic kidney injury were comparable between groups. In the present model of fulminant ovine septic shock, first-line TP infusion had no significant effect on fluid and norepinephrine requirements or organ dysfunction as compared to second-line TP infusion or placebo

A new complimentary web-based tool for manual analysis of microcirculation videos: validation of the capillary mapper against the current gold standard AVA 3.2

OBJECTIVE: The aim of the current study was to compare a newly developed web-based freely accessible software program for manual analysis of the microcirculation, the Capillary Mapper (CM), with AVA 3.2 software (AVA; MicroVision Medical B.V., Amsterdam, The Netherlands), which is the current gold standard for analysis of microcirculation videos. METHODS: A web-based software program was developed, which enables manual analysis of videos of the microcirculation to be carried out according to recommendations of the 2018 consensus conference. A set of 50 high quality microcirculation videos was analyzed with AVA and CM with respect to total vessel density, perfused vessel density, proportion of perfused vessels, and the microvascular flow index. RESULTS: Comparison of the mean values derived from manual analysis with CM and AVA revealed no significant differences in microcirculatory variables. Analysis according to Bland and Altman revealed an acceptable bias between manual analysis with the CM and AVA for all variables tested with sufficient limits of agreement. The analysis of intraclass correlation showed "excellent" agreement for all microcirculatory variables analyzed. CONCLUSIONS: The newly developed CM was successfully validated for manual analyses of microcirculation videos against the current gold standard, the software AVA 3.2

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Energy Efficiency of Refrigeration Systems

Energy efficiency plays an important role in the development and operation of refrigeration systems. The method of the VDMA 24247-2 2 “Energy efficiency of refrigeration systems – Requirements for the system design and the components” were recently published. The method will be described within this paper, with the focus on the graphical interpretation

Forced Bulk Boiling At High Heat Fluxes

The influence of very high heat fluxes (105 to 106 W/m²) on the boiling behavior of R404A are investigated. By using a new evaporator design it is possible to change the evaporating effects even at these high heat fluxes to bulk boiling. This paper focusses on the experimental analysis of the new evaporator by varying the parameters geometry, mass flux, subcooling and fluid velocity. The results are compared with experimental works and mathematical models at lower heat fluxes. The results show, that fluid velocity, mass flux and geometry have high influence on the transferred heat flow, while the subcooling of the liquid phase has only a small effect