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A versatile meteorological index for predicting heat stress in dairy cattle remains elusive. Despite numerous attempts at developing such indices and widespread use of some, there is growing skepticism about the accuracy and adequacy of the existing indices as well as the general statistical approach used to develop them. At the same time, precision farming of high-yielding animals in a drastically changing climate calls for more effective prediction and alleviation of heat stress. The present paper revisits classical work on human biometeorology, particularly the apparent temperature scale, to draw inspiration for advancing research on heat stress in dairy cattle. The importance of a detailed, mechanistic understanding of heat transfer and thermoregulation is demonstrated and reiterated. A model from the literature is used to construct a framework for identifying and characterizing conditions of potential heat stress. New parameters are proposed to translate the heat flux calculations based on heat-balance models into more tangible and more useful meteorological indices, including an apparent temperature for cattle and a thermoregulatory exhaustion index. A validation gap in the literature is identified as the main hindrance to the further development and deployment of heat-balance models. Recommendations are presented for systematically addressing this gap in particular and continuing research within the proposed framework in general. [ABSTRACT FROM AUTHOR]

Preventing and alleviating heat stress remain an enormous challenge in dairy farming. Although enhanced air distribution techniques have been developed and deployed in many barns, ventilation alone is no longer sufficient even in regions with historically mild climates. There is an increasing need for cooling of the intake fresh air. Evaporative cooling is a cost-effective sustainable technique used in many applications, including livestock farming. This paper presents a graphical method for preliminary evaluation of evaporative cooling as a viable and effective solution. Thermodynamic principles are combined with models for heat transfer in dairy cattle to develop a set of criteria on the psychrometric chart. The proposed method is demonstrated for a naturally ventilated dairy barn located in the continental central European climate and in two locations with hot climates, a semi-arid/Mediterranean and a humid subtropical climate. • Thermoregulation models combined with thermodynamic principles. • Limits for effectiveness of evaporative cooling derived. • Developed criteria mapped onto psychrometric chart. • A graphical method to assess effectiveness of evaporative cooling proposed. • Proposed method demonstrated for sample barn in Europe. [ABSTRACT FROM AUTHOR]

Laminar free convection in a vertical channel with isothermal walls is a classical heat transfer problem. In general, the channel walls may be at different temperatures, leading to a difference in the rate of heat transfer at the walls. Although numerical and experimental results are often presented in terms of average wall Nusselt numbers, separate correlations for heat transfer at each wall are rarely available. The few existing relations are complex in form due to the extra parameters introduced to facilitate the correlation of results. Moreover, the existing correlations do not reflect the physics of the problem in full. In this work, the three-temperature problem of laminar-free convection of air in a tall vertical channel with isothermal walls is studied in a new theoretical framework, namely the extended Newton formulation. This formulation eliminates the need for an effective temperature difference, hence simplifying the presentation and correlation of the results. The dQdT technique was utilized along with computational fluid dynamics to calculate the average paired Nusselt numbers that characterize the extended Newton formulation of the problem. The dQdT results were then used to derive heat transfer correlations which are both simpler in form and more accurate than the existing correlations. The proposed correlations are applicable to cases of both channel walls hotter or both colder than the ambient air. [ABSTRACT FROM AUTHOR]