Leakage Model of Axial Clearance and Test of Scroll Compressors

Leakage clearance plays an important role in guaranteeing high efficiency of scroll compressors.In view of the shortcomings of the existing leakage models of axial clearance of scroll compressors,a modified Fano flow model and a turbulence model are presented based on the flow characteristics of fluid in the leakage passage under actual working conditions.Firstly,according to the Fano flow energy equation and the turbulence theory,two kinds of leakage models,Fano flow model and turbulence model,of axial clearance are established.Then,the established models are verified through an experimental platform established to measure the axial clearance leakage in the working process of a scroll compressor,and the measured values are compared with the values obtained from the two theoretical models.Finally,the effect of such factors as pressure difference,clearance amount,spindle speed on the axial clearance leakage is analyzed.Results show that the two established models can precisely reflect the variation law of axial clearance leakage of scroll compressor under different working conditions.In particular,the Fano flow model is more suitable for predicting the clearance leakage when the spindle speed is low(less than 3500 r/min)and the clearance is small(less than 0.025 mm),whereas the turbulence model is suitable for high spindle speed(more than 3500 r/min)and large clearance(more than 0.025 mm).

Current experimental models, assessment and dietary modulations of intestinal permeability in broiler chickens

Maintaining and optimising the intestinal barrier(IB)function in poultry has important implications for the health and performance of the birds.As a key aspect of the IB,intestinal permeability(IP)is mainly controlled by complex junctional proteins called tight junction proteins(TJ)that link enterocytes together.The disruption of TJ is associated with increased gut leakage with possible subsequent impli-cations for bacterial translocation,intestinal inflammation,compromised health and performance of the birds.Despite considerable data being available for other species,research on IP in broiler chickens and in general avian species is still an understudied topic.This paper reviews the available literature with a specific focus on IP in broiler chickens with consideration given to practical factors affecting the IP,current assessment methods,markers and nutritional modulation of IP.Several experimental models to induce gut leakage are discussed including pathogens,rye-based diets,feed deprivation and stress-inducing agents such as exogenous glucocorticoids and heat stress.Although various markers including fluorescein isothiocyanate dextran,expression of TJ and bacterial translocation have been widely utilized to study IP,recent studies have identified a number of excreta biomarkers to evaluate intestinal integrity,in particular non-invasive IP.Although the research on various nutrients and feed additives to potentially modulate IP is still at an early stage,the most promising outcomes are anticipated for probiotics,prebiotics,amino acids and those feed ingredients,nutrients and additives with anti-inflammatory properties.Considerable research gaps are identified for the mechanistic mode of action of various nutrients to influence IP under different experimental models.The modulation of IP through various strategies(i.e.nutritional manipulation of diet)may be regarded as a new frontier for disease prevention and improving the health and performance of poultry particularly in an antibiotic-free production system.