Experimental Study of a Light Commercial Refrigeration System Operating Under Frosting Conditions

Investigation the effect of frost formation on a light commercial refrigeration syste

Advanced spreadsheet based methodology for the dynamic thermal modelling of buildings

Thermal analysis of buildings was carried out using simplified design tools, prior to the widespread use of computers. Since the early 1980's, the rapid growth of computational power has lead to the introduction of many building dynamic thermal simulation software programs. The accurate performance of many of these programs has lead to the view that manual calculation methods should only be used as indicative design tools. The CIBSE admittance method is based on the fundamentals of building heat transfer, its calculations procedures being simplified for use on hand held calculators. Manual calculation methods must be developed for use on more powerful calculators, if greater accuracy is required. Such calculators are available in the form of computer spreadsheet programs. The computational power of the computer spreadsheet program, combined with suitable mathematical thermal modelling techniques, has thus far, remained unexploited. This thesis describes the development of a powerful manual thermal design method, for application on a computer spreadsheet program. All the modes of building heat transfer are accurately modelled. Free-running or plant-controlled spaces can be simulated. In the case of a single zone, the accuracy of the new manual dynamic thermal model is comparable with commercially available software programs. The level of mathematical modelling complexity is limited only by computer power and user ability. The Iterative Frequency Domain Method (IFDM) and the Adiabatic Iterative Frequency Domain Method (AIFDM) are alternative mathematical simulation techniques developed to form the core of the Thermal Analysis Design Method. In the IFDM and AIFDM, the frequency domain and numerical iteration techniques have been integrated to produce a thermal simulation method that can model all non-linear heat transfer processes. A more accurate formulation of sol-air temperature, a window sol-air temperature and an accurate reduced internal long-wave radiant exchange model is a sample of further innovations in the thesis. Many of the developments described in the thesis, although designed for the computer spreadsheet environment, may also be employed to enhance the performance of some of the current dynamic thermal models of buildings.EThOS - Electronic Theses Online ServiceDublin Institute of TechnologyGBUnited Kingdo

Integration of CO2 refrigeration and tri-generation systems for supermarket Applications

The environmental impact of supermarkets is significant not only because of the indirect effect from CO2 emissions at the power stations but also due to the direct effect arising from refrigerant leakage to the atmosphere. One approach through which the overall energy efficiency can be increased and the environmental impacts reduced, is through the integration of CO2 refrigeration and trigeneration systems where the refrigeration generated by the trigeneration system is used to condense the CO2 refrigerant in a cascade arrangement. Such a system is being investigated by Brunel University and a number of commercial organisations in the UK. This paper presents results of simulation studies that investigate the seasonal energy and environmental performance of such a system in a medium size supermarket

Performance optimization of a secondary refrigerant display cabinet using tests and CFD modelling

In this paper a computational investigation to address some of the design parameters that have significant effects on the performance of a secondary refrigerant refrigerated display cabinet is presented. The investigated design parameters include air curtain velocity, width, discharge angle and positioning of the air curtain outlet from the front edge of the display cabinet’s top shelf. In addition the effect of using honeycomb on the flow path at the air curtain outlet was also investigated. A 3D CFD model was constructed to assess the effect of the side flow on the performance of the vertical display cabinet. The suitability of using 2D CFD to carry out the display cabinet design optimization was investigated and it was concluded that for the length of the cabinet considered, the flow could be assumed to be two-dimensional for most of the cabinet length. The results also indicated that the optimum air curtain mass flow rate constituted approximately a third of the total air mass flow rate. For the geometry considered with respect to air curtain discharge and top shelf outer edge position it was found that shaping the honeycomb to produce more uniform flow and reduce recirculation at the inner edge of the air curtain outlet improved the air curtain performance and led to a 4% reduction in the cabinet load

Investigation of the performance characteristics of an ammonia-water absorption chiller in a tri-generation system arrangement

Trigeneration systems have been used in a number of applications including commercial buildings and industrial facilities. Most of these have been for space cooling applications with a smaller number for refrigeration applications in the food processing industry which requires temperatures below 0oC. This paper is concerned with the investigation and development of modular trigeneration systems for food industry applications based on the integration of microturbines and ammonia water absorption refrigeration systems. Specifically, the paper presents results of experimental investigations on the performance of a 12 kW capacity ammonia-water absorption refrigeration system driven by thermal energy recovered from the exhaust gases of a microturbine in a trigeneration arrangement. The heat transfer between the microturbine exhaust heat exchanger and the generator of the absorption refrigeration system is performed by a heat transfer fluid in a closed heat transfer loop. Tests were performed at different brine temperatures and heat transfer fluid temperatures. The performance of the unit was evaluated and found to compare favourably with the performance of a directly gas fired absorption chiller. In addition, the overall efficiency of the trigeneration system was also evaluated

Investigation of the performance characteristics of an ammonia-water absorption chiller in a tri-generation system arrangement

Trigeneration systems have been used in a number of applications including commercial buildings and industrial facilities. Most of these have been for space cooling applications with a smaller number for refrigeration applications in the food processing industry which requires temperatures below 0oC. This paper is concerned with the investigation and development of modular trigeneration systems for food industry applications based on the integration of microturbines and ammonia water absorption refrigeration systems. Specifically, the paper presents results of experimental investigations on the performance of a 12 kW capacity ammonia-water absorption refrigeration system driven by thermal energy recovered from the exhaust gases of a microturbine in a trigeneration arrangement. The heat transfer between the microturbine exhaust heat exchanger and the generator of the absorption refrigeration system is performed by a heat transfer fluid in a closed heat transfer loop. Tests were performed at different brine temperatures and heat transfer fluid temperatures. The performance of the unit was evaluated and found to compare favourably with the performance of a directly gas fired absorption chiller. In addition, the overall efficiency of the trigeneration system was also evaluated

Numerical methodology and CFD simulations of a rotary vane energy recovery device for seawater reverse osmosis desalination systems

Energy recovery devices in Seawater Reverse Osmosis Systems (SWRO) reduce energy consumption and may facilitate the large-scale deployment of desalination systems. In this paper, a Rotary Vane Energy Recovery Device (RVERD) is analysed and optimised by aiming at weakening cavitation and improving the volumetric performance of the machine. An innovative analytical methodology based on user defined nodal displacement is proposed to address the need to discretise the rotating and deforming computational domain of double-acting vane machines. The generated grids are interfaced with the ANSYS FLUENT solver for multi-phase computational fluid dynamics simulations. The flow topology is analysed to reveal the flow and cavitation features especially in the blade tip regions. A port optimisation is then carried out followed by a sensitivity analysis on the design parameters to improve RVERD performance. The results show that delaying the discharge angle at the high-pressure outlet port by 3° and an optimal port to stator length ratio of 70% helped to prevent backflows and eliminate torque peaks. The sensitivity analysis has identified the rotational speed and the blade tip clearance as the two most influential factors affecting cavitation and, in turn, the volumetric efficiency of the machine. With respect to the baseline design configuration, at the optimal rotational speed of 1000 RPM and with a tip clearance gap of 50 μm, the volume-averaged vapour volume fraction in the core decreased from 20.6 × 10−3 to 0.6 × 10−3 while the volumetric efficiency increased from 85.7% to 91.6%. The axial clearance gap of 70 μm contributed to 2.9% of the volumetric losses

Analytical grid generation and numerical assessment of tip leakage flows in sliding vane rotary machines

The research presents a new analytical grid generation methodology for computational fluid dynamics studies in positive displacement sliding vane rotary machines based on the user defined nodal displacement approach. This method is more inclusive than state of the art ones since it enables the investigation of a broader range of design configurations, such as single, double and multiple-acting vane machines with non-circular housing, slanted blade and asymmetric blade tip profiles. Node number and radial divisions of blade tip are the parameters that affect most the mesh quality. The method was validated against indicated pressure measurements on a rotary vane expander resulting in a confidence interval within 4.31%. The benchmark analysis showed that the proposed method is as accurate as the manual ANSYS ICEM one but more than 1500 times faster (111s instead of 48h to generate 360 grids). The paper further proposes a novel method to track the leakage flows at the blade tip gaps of vane machines through a post-processing routine in ANSYS CFD-Post based on rotating monitoring planes. The leakage assessment on the vane expander case study showed that a 10 μm gap between blade tip and the 76 mm stator led to a 0.06 unit increase of the expander filling factor