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

Experimental and numerical analyses of full-span floors and component level subassemblies for robust design of CLT floors

Tall mass timber structures are becoming increasingly prevalent and, with some now rising as tall as 81m (Abrahamsen, 2017) it is vital to consider design for structural robustness and disproportionate and progressive collapse prevention under accidental actions (Starossek & Haberland, 2012). The Eurocode 1-7 approach (European Committee for Standardization, 2006) focuses on material independent objective-based design. An inherent robustness through alternative load paths (ALPs), primarily catenary action, is targeted through introduction of vertical and horizontal ties. This is a prescriptive approach without the necessary physical basis when introducing novel construction methods

Experimental and numerical investigations on full-scale adhesively bonded timber trusses

Timber architecture, taking advantage of modern production techniques, is increasingly moving towards free forms; however, traditional joining techniques are not yet adapted to echo the new expression at the level of the details. This paper reports on adhesively bonded joints as a way to help architects fully unleash their creative potential. For this purpose, experimental and numerical investigations on full-scale adhesively bonded timber trusses were performed, in which adhesive bonds were compared to traditional doweled connections. The adhesively bonded trusses achieved significantly higher failure load and stiffness. Tests on small clear specimens were conducted to determine input parameters for finite element analyses. The sole timber connection was characterised, giving valuable insights into the mechanical behaviour of this truss component. At this end, the influence of the embedded length of the applied sleet plates was experimentally determined, delivering data to benchmark the subsequent dimensioning method. The trusses were then modeled and excellent agreement was found between numerical and experimental results. Finally, a dimensioning method, based on a realistic multi-axial failure criterion coupled with size effects was implemented and yielded very good agreement when with experimental results. The reported investigation demonstrates the high potential of adhesive bonding in timber structure

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

Structural performance of rounded dovetail connections: experimental and numerical investigations

Rounded Dovetail Connections (RDC) are a relatively new wood-to-wood connection concept that, despite the lack of design guidance in standards, has become popular in timber construction due to the widespread of modern milling machinery. Because of the anisotropic nature of wood and the complex stress-strain state in RDC, the question of their dimensioning is very complex. Experimental and numerical investigations were carried out on full scale RDC used to connect two timber members as joist to beam connections subjected to quasi-static shear loading. The influence of two geometric parameters was investigated: the dovetail height (varied between 109 and 189mm) and the flange angle (varied between 5 and 20°). Both, serviceability and ultimate limit states were studied using analysis of variance. It was found that the joint capacity (i) depends on the dovetail height, with an optimum of approximately 2/3 of the beam height and (ii) can be considered almost independent of the flange angle. The development and implementation of a numerical model for the design process of RDC was examined and good agreement between experimental and numerical load deformation curves validated the model, thus making it suitable for developing a method to predict RDC capacity. The paper proposes a probabilistic method to predict the capacity of RDC taking into account the scale sensitivity of the material strength, which is modelled using Weibull statistics, and considers not only the magnitude of the stress fields, but also the volume over which these stress peaks act. The proposed method has immediate actionable application for the improvement of RDC desig

RILEM TC: reinforcement of timber elements in existing structures

The paper reports on the activities of the RILEM technical committee “Reinforcement of Timber Elements in Existing Structures”. The main objective of the committee is to coordinate the efforts to improve the reinforcement practice of timber structural elements. Recent developments related to structural reinforcements can be grouped into three categories: (i) addition of new structural systems to support the existing structure; (ii) configuration of a composite system; and (iii) incorporation of elements to increase strength and stiffness. The paper specifically deals with research carried out at the Bern University of Applied Sciences Switzerland (BFH), the University of Minho Portugal (UniMinho), and the University of Trento Italy (UNITN). Research at BFH was devoted to improve the structural performance of rounded dovetail joints by means of different reinforcement methods: i) self-tapping screws, ii) adhesive layer, and iii) a combination of selftapping screws and adhesive layer. Research at UNITN targeted the use of “dry” connections for timber-to-timber composites, specifically reversible reinforcement techniques aimed at increasing the load-bearing capacity and the bending stiffness of existing timber floors. At UniMinho, double span continuous glulam slabs were strengthened with fibre-reinforced-polymers. All three examples demonstrate the improved structural performance of timber elements after reinforcing them.The research on RDJ was funded by BFH and supported by the staff at the BFH " tech-park" Huesser Holzbau AG and ArundaR. The research at UNITN was carried out by the Timber Research Group (in particular by M. Piazza, R. Tomasi, I. Giongo) within the framework of the RELUIS Project 2011-2013, which is financed by the Italian Emergency Management Agency (Dipartimento della Protezione Civile) and supported by Rothoblaas srl

Capacity prediction of welded timber joints

Linear vibration welding of timber structural elements provides new opportunities to potentially achieve structural joints. This paper investigates to which extent welded joints can be considered for load-bearing structural joints. On the basis of a series of experimental and numerical investigations on a series of welded single-lap joints, failure modes were identified, and the associated failure criterion was quantified. A probabilistic method subsequently allowed accurately predicting the capacity of the tested wood welded joints exclusively based on objective input data, including an estimate of the scattering due to the material's inherent variabilit

STR-930: CROSS LAMINATED TIMBER WALLS WITH OPENINGS: IN-PLANE STIFFNESS PREDICTION AND SENSITIVITY ANALYSIS

Cross-laminated timber (CLT) is gaining popularity in residential and non-residential applications in the North American construction market. An accurate quantification of in-plane stiffness of the CLT walls with openings is required to design a CLT structure subjected to lateral loads. Nevertheless, till today, no general approach is available for the design of CLT-members loaded in plane and there are no standardized methods for determining the stiffness of CLT shearwalls in the respective material design standards: the CSA O86 in Canada, and the NDS in the US. This study aims to quantify the stiffness of CLT walls with openings under in-plane loading. A finite element (FE) model of CLT walls was developed modelling wood as orthotropic elastic material and the glue-lines between layers using non-linear contact elements. The FE model was verified from test results of CLT panels under in-plane loading. A parametric study was performed to evaluate the change in stiffness of CLT walls with the variation of opening size and shape. A simplified equation to predict the in-plane stiffness of CLT walls with openings was proposed. Subsequently, a sensitivity analysis was performed using Meta-model of Optimal Prognosis (MOP) to evaluate the contribution of each parameter on the model response

STR-931: TIMBER I-JOISTS WITH WEB OPENINGS: REINFORCEMENT, CAPACITY PREDICTION AND SENSITIVITY ANALYSIS

Timber I-joists are a popular product in light-frame wood construction in North America. The design with timber I-joists, however, has not yet achieved the same level of refinement compared to reinforced concrete or steel structures. One of the reasons is that timber I-joists have higher variability in their material properties than more homogeneous building materials. Additionally, although very commonly applied in practice, engineers and practitioners have limited knowledge and guidance for I-joists with web opening. As a result, in many cases the design of timber I-joists based on manufacturer’s specifications lead to very conservative solutions. The present research predicts the capacity of unreinforced and reinforced timber I-joists with openings from experimental results. A total of 100 unreinforced and 100 reinforced I-joists with opening were tested under four point loading. The capacity of the I-joists with opening was predicted from regression analysis. A sensitivity analysis was performed for the predicted equations using Meta-model of Optimal Prognosis (MOP) to evaluate the contribution of each parameter on the model responses. The research demonstrates that the reinforcement technique was efficient for I-joists with openings and the proposed equations were very accurate to predict the I-joists capacity