Noise Effects In Capillary Tubes Caused By Refrigerant Flow

The preferred cooling process for household refrigeration appliances is a vapor compression refrigeration process with a capillary tube as expansion device. The vapor compression refrigeration system requires a phase change of the refrigerant inside the condenser and evaporator. Through a direct connection of condenser outlet and capillary tube inlet, which is commonly practiced for household refrigeration cycles, the condenser outlet defines directly the refrigerant state at the capillary tube inlet. Due to unsteady operation conditions the refrigerant state can change from subcooled liquid to saturated liquid with partially a vapor phase at the capillary tube inlet. The refrigerant flow inside the capillary tube is either adiabatic or non-adiabatic (by utilizing internal heat exchange). In both cases the refrigerants state changes during the expansion with an increase of vapor quality towards the capillary tube outlet. A variable vapor quality at the capillary tube inlet causes different flow patterns, especially at the capillary tube outlet. These flow patterns change periodically depending on the refrigerant state at the capillary tube inlet. Associated with the periodical changing flow patterns the occurrence of noise effects with the same periodicity and remarkable variations of the sound pressure level can be observed at the capillary tube outlet. Â This paper presents the experimental investigations on the simultaneous occurrence of refrigerant flow patterns and corresponding noise effects at the outlet of a capillary tube installed in a refrigeration test cycle. The discussion of the experimental results leads to an explanation of causal relation between distinguishable flow patterns and corresponding noise effects

Electrical resistivity tomography methods for archaeological prospection

Two advanced applications of electrical resistivity methods in archaeological prospecting are presented. The approach is based on new inversion techniques, which enable the modelling of the resistivity distribution below any arbitrary topography. The results of 2D and 3D electrical resistivity measurements on Tell Jenderes in Northern Syria show images of subsurface resistivity structures, which were not detectable by geomagnetics or GPR methods. The interpreted resistivity structures are related to different settlement phases from the Bronze Age to the Hellenistic period. The new 3D-inversion technique is also useful for data sets of complex resistivity. An example, from a slag heap in Morocco, presents the parameter distribution of a 3D-complex resistivity model deriving from Induced Polarisation (IP) measurements

Surface Tension Of Low-viscous Lubricants In High Pressure Carbon Dioxide Atmospheres

The optimization of refrigeration systems can be achieved by increasing the isentropic efficiency of the compressor. One possible way is the reduction of the friction and leakage losses which occur at the piston rings. The viscosity and the surface tension of the lubricant must be known for this purpose. From the literature only a small amount of measured values for the surface tension of commonly used lubricants are known. Additionally natural refrigerants like R-744 are more common according to the latest (European) environmental regulation. The thermophysical properties of lubricant-refrigerant-mixtures can currently only be calculated by generalized calculation methods. For specific mixtures, these equations need to be confirmed by measurements. In this paper the measurement results of the surface tension of different low-viscous lubricants are shown. A test bench was designed to measure the surface tension of different liquids especially under high pressure atmospheres. The investigation was performed by using the pendant drop method and analyzing the results with new algorithms for the solution of the Young-Laplace equation. Effects of the geometry of the used capillaries are discussed which leads to possible optimizations of this measurement method. Dilution effects of the surface tension of the lubricants in carbon dioxide atmospheres are shown and discussed. The effect of higher pressures and different temperatures on the surface tension is shown as well as a comparison of the measurements with generalized methods

Energy Saving Potential of a Temperature Test Chamber by implementing a Heat-Pump

Energy savings become more and more important – also for the rather small industry sector of environmental simulation. So far the technical focus was mainly to realize challenging test cycles which are often gives as temperature profiles. The energy efficiency of the test devices are not specified by any standard. Nevertheless, especially test cycles with intermittent cooling and heating over a wide temperature range need a substantial electrical energy input. As state-of-the-art technology for cooling a vapor compression cycle and for heating an electrical heater is used. In this work a standard temperature test chamber with a specified temperature range from -75 °C to 180 °C using a cascade cooling system and an electric heater is investigated. As a first step the baseline chamber was investigated experimentally and the energy consumption quantified. In the next step the refrigeration cycle was modified with a heat pump capability as well as further cycle modification that indicated energy saving potential in preliminary studies. A comparison to the baseline chamber is carried and reveals substantial energy saving potential

An Investigation Into The Dynamics Of Self-Acting Compressor Valves

In principle, a reciprocating compressor stage consists of a cylinder, the working volume which varies periodically due to a piston moving inside a liner. Latter is sealed by two sets of valves. On the one hand the suction valve for admitting the gas to be compressed and on the other the discharge valve for allowing the high pressure gas to be delivered to the downstream process. The typical type of valves used within compressors for refrigeration plants are reed valves. The key feature of these mentioned valves - simultaneously affecting both their sealing performance as well as the reliability - is that they are not actuated. They are held close by elastic forces and they open and close automatically, in accordance to the balance of gas pressure forces as well as the previously mentioned elastic ones. The former is primarily characterized by the static pressure difference across the closed valve and the aerodynamic drag brought about by the gas flow impinging onto the sealing reed in a partially or fully open valve. Evidently, a high degree of coupling between the gas flow and the sealing element motion, today referred to as fluid-structure interaction (FSI), can be expected. The reed and the absence of a reliable guide that would provide for the plan-parallel motion give rise to non-parallel impacts with other parts of the valve assembly, leading to dynamic stress effects. This not only complicates the prediction of the reed valve dynamics, it also causes premature sealing element fracture, decreases the compressor efficiency and ultimately leads to unscheduled maintenance shutdowns. Consequently pursuing the optimization of the reed valve movement is a necessity. The measurements of reed valve dynamics as well as their movement in compressors can be performed by commercial proximity sensors, strain gauges or in house developed sensors. Although timing and lift information is available through these methods, other modes of fluttering such as torsional movement are more difficult to be observed. This work tries to address these aspects by providing real operation data obtained in a test rig. An in-depth comparative analysis of three measurement methodologies, represented by an optical, resistive as well as an eddy current sensor system will be carried out regarding their possible adoption in a state-of-the-art refrigeration compressor. Furthermore, the acquired data will be evaluated with respect to its potential application for collecting mentioned torsional movements. In the end a comparison against a numerical approach shall be conducted