Effects of total replacement of corn silage with sorghum silage on milk yield, composition, and quality

BACKGROUND: In the last years, difficulties occurring in corn cultivation (i.e., groundwater shortages, mycotoxin contamination) have been forcing dairy farmers to consider alternative silages. Some experiments conducted on lactating cows have proven that the total replacement of corn silage with sorghum silage did not reduce milk yield. However, this kind of substitution involves supplementing sorghum-based diets with grains, to compensate for the lower starch content of sorghum silage compared to corn silage. Change of silage type and inclusion of starch sources in the diet would influence rumen fermentations, with possible effects on milk composition (i.e., fatty acid profile) and coagulation properties. A worsening of milk coagulation properties would have a negative economic impact in Italy, where most of the milk produced is processed into cheese. This study was designed to compare milk composition and quality, with emphasis on fatty acid profile and coagulation properties, in dairy cows fed two diets based on corn or sorghum silage. RESULTS: The sorghum diet reduced milk yield (P = 0.043) but not 4% fat corrected milk (P = 0.85). Feeding sorghum silage did not influence milk contents of protein (P = 0.07) and lactose (P = 0.65), and increased fat content (P = 0.024). No differences emerged for milk concentrations of saturated (P = 0.61) and monounsaturated fatty acids (P = 0.50), whereas polyunsaturated fatty acids were lower (P < 0.001) for the sorghum diet. Concentrations of n-6 (P < 0.001) and n-3 fatty acids (P = 0.017) were lower in milk of cows fed the sorghum diet. Milk coagulation properties did not differ between the two diets, except the “a30” (the curd firmness, expressed in mm, 30 min after rennet addition), that was lower (P = 0.042) for the sorghum diet. CONCLUSIONS: Feeding a forage sorghum silage, properly supplemented with corn meal, as total replacement of corn silage maintained milk composition and did not influence negatively milk coagulation properties, which have a great economic relevance for the Italian dairy industry. Thus, silages obtained from forage sorghums could have a potential as substitute of corn silages in dairy cow diets

Passive techniques for the enhancement of convective heat transfer in single phase duct flow

This review presents the main results of the experimental campaign on passive techniques for the enhancement of forced convective single phase heat transfer in ducts, performed in the last years at the Laboratory of the Industrial Engineering Department of the University of Parma by the Applied Physics research group. The research was mainly focused on two passive techniques, widely adopted for the thermal processing of medium and high viscosity fluids, based on wall corrugation and on wall curvature . The innovative compound heat transfer enhancement technique that couples together the effect of wall curvature and of wall corrugation has been investigated as well. The research has been mainly focused on understanding the causal relationship between the heat transfer surface modification and the convection enhancement phenomenon, by accounting the effect of the fluid Prandtl number. The pressure loss penalties were also evaluated. The principal results are presented and discussed

Production of Water from the Air: The Environmental Sustainability of Air-conditioning Systems through a More Intelligent Use of Resources. The Advantages of an Integrated System

Abstract The possibility of extracting water from air is an activity that has been studied recently, especially with the purpose of producing it for emergencies or exceptional events, when drinking water is not temporarily available. Several mobile/transportable equipment have been designed in order to producing water from the air: they can be placed, if necessary, in appropriate locations where water is needed. Water extraction can be done with different technologies, one of which is represented by cooling water below the dew point, to cause condensation of the vapour content of the air. The system efficiency, normally calculated in standard conditions, should be tested in the climatic conditions in which it will be used, because water production varies significantly with temperature and air water vapour content. An interesting solution may be an equipment for water extraction that contemporarily uses the cooled air for refrigeration, which consists in a combined HVAC system for the dual purpose of water production and air-conditioning. A case study represented by this kind of HVAC system, for a hotel in a sub-tropical arid climate, is proposed in this paper, to demonstrate the advantages of this solution. To this aim, the comparison is made between a typical HVAC system and an integrated air conditioning system, optimized for water production from air, in order to highlight advantages and capabilities of the second one

PARAMETER ESTIMATION APPLIED TO THE HEAT TRANSFER CHARACTERISATION OF SCRAPED SURFACE HEAT EXCHANGERS FOR FOOD APPLICATIONS

A parameter estimation approach was applied to characterise the heat transfer of Scraped Surface Heat Exchangers (SSHEs) specifically designed for the food industry. It is difficult to apply the data available in the literature to SSHEs, due to the specificity of each product, thermal treatment and geometrical configuration, making the thermal design of these apparatuses critical. Therefore, it appears to be more useful to assess the methodology used to derive a proper heat transfer correlation than to assess the form of the heat transfer correlation itself, as the correlation often cannot be transferred to other heat exchangers, even those that belong to the same class. This study enabled successful and robust estimation of the heat transfer correlation for the product side Nusselt number and the external side heat transfer coefficient; this approach differs from Wilson plot methods, as no assumption is made regarding the functional dependence of the external side heat transfer coefficient. The procedure was validated through application to both synthetic data and experimental data acquired from a coaxial SSHE pilot plant for the treatment of highly viscous fluid foods. The procedure was optimised with the aid of sensitivity and uncertainty analysis, which provided considerable insight into the problem. The application to synthetic data demonstrated that under typical operating conditions, areas of insensitivity to certain parameters are present. The application to the experimental data acquired under both heating and cooling conditions confirmed that the measured values of the overall heat transfer coefficient can be used to estimate the secondary fluid heat transfer coefficient, as well as the power law dependence of the internal fluid Nusselt number on the rotational Reynolds number and the Prandtl number together with the multiplicative constant. The uncertainty analysis provided the confidence intervals associated with each estimated parameter, thereby enabling the quality and robustness of the resulting heat transfer correlations to be determined

Heat transfer delay method for the fluid velocity evaluation in a multi-turn pulsating heat pipe

A multi-turn closed loop pulsating heat pipe made of aluminium is tested in vertical bottom heated mode and different condenser temperatures with the aim of providing quantitative information regarding its flow dynamics through a novel post-processing technique on the local wall-to-fluid heat flux, evaluated within the adiabatic section. The studied device is made of an annealed aluminium tube (inner/outer diameter: 3/5 mm), folded in 14 turns and partially filled with methanol (volumetric filling ratio: 50%). The aluminium channels are coated with a high-emissivity opaque paint, thus allowing thermographic measurements on the outer wall by means of a high-resolution medium wave infrared camera. The proposed method, named Heat Transfer Delay Method, is validated by means of a dedicated experimental approach. Then, the acquired time-space temperature maps are used as input data for the inverse heat conduction problem resolution approach to estimate the local convective heat flux locally exchanged at the inner wall-fluid interface. The resulting wall-to-fluid heat fluxes are then post- processed by applying the Heat Transfer Delay Method to the oscillatory and circulatory flow modes. The average fluid velocity is assessed at varying working conditions during the circulatory flow, finding values up to 0.77 m/s and 0.3 m/s for condenser temperature equal to 20 ◦C and 10 ◦ C, respectivel

Thermal Performance Analysis of Triple Heat Exchangers via the Application of an Innovative Simplified Methodology

Despite the double tube heat exchangers, in the triple tube heat exchangers, there are three fluids, and the methodology based on the assessment of the logarithmic mean temperature difference is no longer applicable. Moreover, in triple tube heat exchangers, there are two overall heat transfer coefficients dependent on each other. As such, it is necessary to solve them simultaneously, thus making the evaluation of the thermal performance of triple tube heat exchangers more complex compared to double tube heat exchangers. Among the proposed approaches in the literature to solve this issue, one of the most powerful and commonly adopted in several engineering applications is the parameter estimation procedure. Nevertheless, for the specific implementation examined in our analysis, a thorough numerical model of the triple tube heat exchanger was required to apply the inverse procedure properly. Furthermore, it is mandatory to measure the temperature of the three fluids at the inlet and outlet sections. In so doing, the inverse procedure can be successfully applied to the characterisation of triple tube heat exchangers tested in well-equipped research labs; however, its application to heat transfer devices operating in industrial facilities can be difficult. In order to overcome this limitation, an innovative parameter estimation technique that enables the evaluation of the thermal performance of this type of heat transfer devices is presented. The suggested methodology is based on a simple model of the triple tube heat exchanger in which an equivalent double tube heat exchanger is considered, thus requiring only four temperature measurements. The results obtained by applying this simplified methodology are numerically validated and compared to those obtained using a comprehensive mode

Recovery of n-3 polyunsaturated fatty acids and conjugated linoleic acids in ripened cheese obtained from milk of cows fed different levels of extruded flaxseed

Abstract The aim of the study was to investigate whether the addition of extruded flaxseed (EF) in dairy cow diets had an effect on milk fat and individual fatty acids (FA) recovery in cheese after 90 d of ripening. Eighteen Holstein-Friesian cows, divided into 3 experimental groups (6 cows/group), were fed 3 isonitrogenous and isoenergetic diets with 0 (CTR), 500 (EF500), or 1,000g/d (EF1000) of EF in 3 subsequent periods (2 wk/each), following a 3×3 Latin square design. Dry matter intake (DMI) and milk yield were recorded daily. Individual milk samples were collected on d 7 and 13 of each period to determine proximate and FA composition. Eighteen cheese-making sessions (2 for each group and period) were carried out, using a representative pooled milk sample obtained from the 6 cows of each group (10L). At 90 d of ripening, cheeses were analyzed for proximate and FA composition. Cheese yield was computed as the ratio between the weights of ripened cheese and processed milk. Recoveries of fat, individual FA, and grouped FA were computed as the ratio between the corresponding weights in cheese and in milk. Inclusion of EF did not affect DMI, milk yield, or milk composition. Compared with CTR, the 2 diets containing EF increased the proportion of C18:3n-3 and total n-3 FA, in both milk and cheese. Cheese yield and cheese fat percentage did not differ among diets. Likewise, milk fat recovery in cheese was comparable in the 3 treatments and averaged 0.85. The recoveries of individual FA were, for the most part, not dissimilar from fat recovery, except for short-chain saturated FA (from 0.38 for C4:0 to 0.80 for C13:0), some long-chain saturated FA (0.56 and 0.62 for C20:0 and C21:0, respectively), and for C18:3n-6 (1.65). The recovery of saturated FA was lower than that of monounsaturated FA, whereas recovery of polyunsaturated FA was intermediate. Compared with medium- and long-chain FA, short-chain FA were recovered to a smaller extent in cheese. No differences in recovery were found between n-6 and n-3 FA. In conclusion, FA have different recoveries during cheese-making, with lower values for the short-chain compared with long-chain FA, and for saturated FA compared with unsaturated FA. The addition of EF in dairy cow diets did not influence cheese yield or fat recovery in cheese, irrespective of the inclusion level. The experiment confirmed that feeding cows with EF represents a successful strategy for improving the FA profile of dairy products, through an increase of n-3 FA

Elliptical double corrugated tubes for enhanced heat transfer

The thermal performance at constant pumping power conditions was numerically investigated in ellipse and super ellipse-based double corrugated tubes. A significant increase in thermal efficiency in double corrugated tubes is accompanied with a reasonable penalty in flow reduction for the cases modelled. An ellipse and a super ellipse-based double corrugated tubes were modelled at laminar fully hydraulically developed incompressible flow. Each base geometry was analysed holding either hydraulic diameter constant or the cross-sectional area constant. The pressure drop was normalized to the length of each modelled tube in order to maintain the pumping power. Thermal analysis was conducted under constant wall temperature boundary condition. The governing equations for non-isothermal flow were solved using the finite element method, and the results of the simulations were normalized to an equivalent straight tube. Numerical results predict a thermal efficiency enhanced by 400% maintaining 4.2 times lower volumetric flow rate in double corrugated tubes at the same pressure drop. The global performance evaluation criterion increases up to 14% for the double corrugated tubes with an ellipse-base and up to 11% for the tubes with super ellipse-base

Experimental analysis of the evaporation of a thin liquid film deposited on a capillary heated tube: estimation of the local heat transfer coefficient

The aim of this work is to estimate the local heat flux and heat transfer coefficient for the case of evaporation of thin liquid film deposited on capillary heated channel: it plays a fundamental role in the two-phase heat transfer processes inside mini-channels. In the present analysis it is investigated a semi-infinite slug flow (one liquid slug followed by one single vapour bubble) in a heated capillary copper tube. The estimation procedure here adopted is based on the solution of the inverse heat conduction problem within the wall domain adopting, as input data, the temperature field on the external tube wall acquired by means of infrared thermography

Fermat's principle and variational analysis of an optical model for light propagation exhibiting a critical radius

Fermat's principle and variational analysis is used to analyze the trajectories of light propagating in a radially inhomogeneous medium with a singularity in the center. It is found that the light trajectories are similar to those around a black hole, in the sense that there exists a critical radius within which the light cannot escape, but spirals into the singularity.Comment: 5 pages from tex file + 3 figures (eps files