A Foster

Measurement and prediction of air movement through doorways in refrigerated rooms

Reducing the amount of air infiltration through the doorways of food storage rooms would improve temperature control and the overall economics of food storage. In the UK a joint government/industry supported LINK project has been set up to look at methods of reducing air infiltration. The project is combining direct experimental measurement with computational fluid dynamics (CFD) modelling. A CFD model of air movement through a doorway has been developed and verified against conventional and laser Doppler anemometry (LDA) measurements. The CFD model has been shown to be generally accurate, however, there are areas where the accuracy is less than perfect. For example the CFD model predicted the shape of the vertical profile accurately, although it under-predicted the maximum velocity by 0.1 m s−1 and it predicted the height at which the airflow changed direction to be 40 mm lower than was measured by the LDA.

Experimental verification of analytical and CFD predictions of infiltration through cold store entrances

Measurements of infiltration through different size entrances of a cold store at two different cold store temperatures were taken and compared against established analytical models and computational fluid dynamics (CFD) models. The analytical and CFD models generally tended to over predict the infiltration. The analytical model developed by Gosney et al. [Proc. Inst. Refrig. 72 (1975) 31] provided the closest comparison with the various experiments. The CFD models were more accurate than the fundamental analytical models but less accurate than those based on a semi-empirical approach. For the experimental configurations examined, CFD offered no real advantage over these empirical analytical models. If the conditions were such that the infiltration rate changed with time or if door protection devices (e.g. air curtains) were used, CFD would become much more advantageous in predicting infiltration.

Modelling the pasteurisation of prepared meals with microwaves at 896 MHz

Abstract Microwave heating of prepared meals in sealed retail containers can be used to extend their shelf life. A numerical model to predict food temperatures after heating was developed and tested for use in the design of microwave cavities and foods. The model uses a finite difference scheme to predict temperatures by solving Maxwells equations for electromagnetic fields and the heat conduction equation. Complex-shaped trays containing mashed potato were heated in a microwave tunnel operating at 2.3 kW for 60 s. The temperature distribution in the food was then measured over a 120 s period, during which the food partially cooled. The heat capacity and dielectric properties of the potato, and the power dissipated in the food during heating, were measured. Intricate temperature profiles, with large temperature gradients, were measured and predicted. The model predicted the positions of regions of highest and lowest temperature but large differences of up to 30 °C were found between measurements and predictions. The differences were largest near to regions where the finite difference mesh, which consisted of 4 mm cubes, was least able to simulate accurately the shape of the tray. Predictions carried out on a high performance workstation required 43 h of cpu. Further studies using a finer mesh on a more powerful computer, along with experiments using simple regular shapes of food, are required to test the model further.

Modelling of liquid air energy storage applied to refrigerated cold stores

Liquid Air Energy Storage (LAES) is a promising technology for dealing with the variability in production of various concurrent Renewable Energy Sources (RES). In this context, the work presented forms part of the CryoHub project. CryoHub is an H2020 Innovation Action project to investigate and demonstrate the feasibility of using LAES in conjunction with refrigerated warehouses cooling. In this paper, multiple different configurations that could achieve the project goals have been modelled and ranked against Round Trip Efficiency (RTE). A configuration currently being deployed is presented and its merits are discussed. The effect of multiple process parameters on the RTE are assessed and discussed.

Carbon reduction opportunities for supermarkets

Refrigeration is the largest load in a supermarket, accounting for 50-60% of the electricity consumption. Supermarket refrigeration systems also generate greenhouse gas emissions directly through refrigerant leakage. Technologies that can save direct and indirect emissions in a typical baseline UK supermarket were examined and the application timescales and cost per tonne of CO2abated were calculated using a model of the supermarket. Using the model, the technologies that could save the most carbon were identified. The work examined 81 different technologies and their potential to save direct and indirect emissions in supermarkets. Results from the work have shown that most technologies either save CO2eemissions from reduction in energy or from reduction in refrigerant leakage only a few technologies demonstrated savings from both.