Eroding ribbon thermocouples: impulse response and transient heat flux analysis

We have investigated a particular type of fast-response surface thermocouple to determine if it is appropriate to use a one dimensional transient heat conduction model to derive the transient surface heat flux from the measurements of surface temperature. With these sensors, low thermal inertia thermocouple junctions are formed near the surface by abrasive wear. Using laser excitation, we obtained the impulse response of these commercially available devices. The response of particular sensors can vary if new junctions are created by abrasive wear. Furthermore, the response of these sensors was found to deviate substantially from the one dimensional model and varied from sensor to sensor. The impulse response was simulated with greater fidelity using a two dimensional finite element model, but three dimensional effects also appear to be significant. The impact of these variations on the derived heat flux is assessed for the case of measurements in an internal combustion engine. When the measured impulse response is used to derive the surface heat flux, the apparent reversal of heat flux during the expansion stroke does not occur

Optimal Prandtl number for heat transfer in rotating Rayleigh-Benard convection

Numerical data for the heat transfer as a function of the Prandtl (Pr) and Rossby (Ro) numbers in turbulent rotating Rayleigh-Benard convection are presented for Rayleigh number Ra = 10^8. When Ro is fixed the heat transfer enhancement with respect to the non-rotating value shows a maximum as function of Pr. This maximum is due to the reduced efficiency of Ekman pumping when Pr becomes too small or too large. When Pr becomes small, i.e. for large thermal diffusivity, the heat that is carried by the vertical vortices spreads out in the middle of the cell, and Ekman pumping thus becomes less efficient. For higher Pr the thermal boundary layers (BLs) are thinner than the kinetic BLs and therefore the Ekman vortices do not reach the thermal BL. This means that the fluid that is sucked into the vertical vortices is colder than for lower Pr which limits the efficiency of the upwards heat transfer.Comment: 5 pages, 6 figure

The rise of aquaculture by-products: Increasing food production, value, and sustainability through strategic utilisation

Since 2000, the use of wild fish inputs in the production of farm raised fish outputs, also known as the Fish In: Fish Out (FI:FO) ratio, has been a primary concern of the sustainability dialogue surrounding aquaculture production. Far less attention has been placed on the sustainability of downstream processing, including how by-products are managed. This paper contributes new information on the current utilisation of aquaculture by-products in a case study on the Scottish Atlantic salmon industry. The findings show that there is considerable potential to increase the sustainability of the industry through maximising human edible yield by strategically managing by-products. Supporting the movement towards the full utilisation of by-products, this paper goes a step further by emphasising the need to maximise their use in human consumption and select animal feeds, highlighting the economic, food security, and environmental benefits of doing so. Through exploratory scenarios based on the case study, the paper identifies that Scotland could increase food production from fish farming by over 60%, increase by-product revenue by 803%, and increase the industry bottom-line by over 5%, all without having to put any new cages in the water, or use any more marine resources. As the aquaculture industry moves into a new era of production and processing, where a diverse range of products can be produced from a single species, sustainability will be sought throughout the value chain. It is hoped that the ideas raised within this paper will encourage further discussion and collaboration on this topic going forward

Coupled wake boundary layer model of wind-farms

We present and test the coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a wind-farm. The model couples the traditional, industry-standard wake model approach with a "top-down" model for the overall wind-farm boundary layer structure. This wake model captures the effect of turbine positioning, while the "top-down" portion of the model adds the interactions between the wind-turbine wakes and the atmospheric boundary layer. Each portion of the model requires specification of a parameter that is not known a-priori. For the wake model, the wake expansion coefficient is required, while the "top-down" model requires an effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion coefficient is obtained by matching the predicted mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing depends on turbine positioning and thus can be determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We illustrate the performance of the model by applying it to both developing wind-farms including entrance effects and to fully developed (deep-array) conditions. Comparisons of the CWBL model predictions with results from a suite of large eddy simulations (LES) shows that the model closely represents the results obtained in these high-fidelity numerical simulations. A comparison with measured power degradation at the Horns Rev and Nysted wind-farms shows that the model can also be successfully applied to real wind-farms.Comment: 25 pages, 21 figures, submitted to Journal of Renewable and Sustainable Energy on July 18, 201

Boundary layer structure in turbulent thermal convection and its consequences for the required numerical resolution

Results on the Prandtl-Blasius type kinetic and thermal boundary layer thicknesses in turbulent Rayleigh-B\'enard convection in a broad range of Prandtl numbers are presented. By solving the laminar Prandtl-Blasius boundary layer equations, we calculate the ratio of the thermal and kinetic boundary layer thicknesses, which depends on the Prandtl number Pr only. It is approximated as $0.588Pr^{-1/2}$ for $Pr\ll Pr^*$ and as $0.982 Pr^{-1/3}$ for $Pr^*\ll\Pr$, with $Pr^*= 0.046$. Comparison of the Prandtl--Blasius velocity boundary layer thickness with that evaluated in the direct numerical simulations by Stevens, Verzicco, and Lohse (J. Fluid Mech. 643, 495 (2010)) gives very good agreement. Based on the Prandtl--Blasius type considerations, we derive a lower-bound estimate for the minimum number of the computational mesh nodes, required to conduct accurate numerical simulations of moderately high (boundary layer dominated) turbulent Rayleigh-B\'enard convection, in the thermal and kinetic boundary layers close to bottom and top plates. It is shown that the number of required nodes within each boundary layer depends on Nu and Pr and grows with the Rayleigh number Ra not slower than \sim\Ra^{0.15}. This estimate agrees excellently with empirical results, which were based on the convergence of the Nusselt number in numerical simulations

Temporal structure of aggregate power fluctuations in large-eddy simulations of extended wind-farms

Fluctuations represent a major challenge for the incorporation of electric power from large wind-farms into power grids. Wind farm power output fluctuates strongly in time, over various time scales. Understanding these fluctuations, especially their spatio-temporal characteristics, is particularly important for the design of backup power systems that must be readily available in conjunction with wind-farms. In this work we analyze the power fluctuations associated with the wind-input variability at scales between minutes to several hours, using large eddy simulations (LES) of extended wind-parks, interacting with the atmospheric boundary layer. LES studies enable careful control of parameters and availability of wind-velocities simultaneously across the entire wind-farm. The present study focuses on neutral atmospheric conditions and flat terrain, using actuator-disk representations of the individual wind-turbines. We consider power from various aggregates of wind-turbines such as the total average power signal, or signals from sub-averages within the wind-farm. Non-trivial correlations are observed due to the complex interactions between turbines placed downstream of each other, and they lead to noticeable spectral peaks at frequencies associated with the inter-turbine spacings when the wind-direction is completely fixed. In that case we observe that the frequency spectra of the total wind-farm output show a decay that follows approximately a $-5/3$ power-law scaling regime, qualitatively consistent with some observations made in field-scale operational wind-parks (Apt, 2007). We find that these features are still observed when the wind-speed varies in magnitude. However, significant changes in the wind-direction over time tend to smooth out the observed spectral peak and reduce the extent of the observed $-5/3$ power-law.Comment: 20 pages, 15 figure

Navigating and properly documenting the procurement process

This project focuses on the development of a uniform procurement manual template that will provide the necessary tools for the new generation of procurement officials who are unaware of what is necessary and required by law to do their jobs

Testing the impact of an educational intervention designed to promote ocular health among people with age-related macular degeneration

Research has shown that individuals affected by age-related macular degeneration (AMD) do not always consume foods or supplements known to be beneficial for ocular health. This study tested the effectiveness of an educational intervention designed to promote healthy eating and nutritional supplementation in this group. A total of 100 individuals with AMD completed baseline measures of several variables: confidence that diet affects AMD, motivation to engage in health-protective behaviours, knowledge about which nutrients are beneficial, and intake of kale, spinach, and eggs. Participants were allocated to either intervention or control conditions. Intervention participants received a leaflet and prompt card that contained advice regarding dietary modification and supplementation. Control participants received a leaflet created by the Royal College of Optometrists. A follow-up questionnaire, measuring the same variables assessed at baseline, was administered 2 weeks later. At follow-up, significant condition × time interactions were found for confidence that diet affects AMD (F(1, 92) = 4.54, p < .05), motivation to talk to an eye professional about supplementation (F(1, 92) = 4.53, p = .036), motivation to eat eggs (F(1, 92) = 12.67, p = .001), and egg intake (F(1, 92) = 11.97, p = .001). In each case, intervention participants scored higher than control participants. Receiving an educational intervention increased participants’ confidence that diet affects AMD, motivation to engage in health-protective behaviours, and egg intake. This intervention could be easily incorporated into current clinical practice delivered by either optometrists or ophthalmologists