Singly connected ducts

J. C., Irreversibility phenomena associated with heat transfer and fluid friction in laminar flows through singly connected ducts, Int. J. Heat Mass Transfer 40 (1997) 905-914. 

The fluid flow and heat transfer characteristics for 14 types of singly connected ducts are described in this section. 

For the fully developed friction factors for laminar flow in unusual singly connected ducts, interested readers are encouraged to consult Shah and Bhatti [2]. 

Problems can arise if several cupboards, each with its own fan, are connected to a single common duct and discharge stack. If a fume cupboard was switched off or a fan failed, flow through the cupboard could be reversed causing contaminants to be discharged into the room. The collecting duct should be kept at a lower pressure by its own fan to reduce this risk. 

The preceding boundary conditions are applicable to both singly connected and doubly connected ducts. Detailed descriptions of the various boundary conditions are available in Shah... 

Chapter 4 is devoted to single-phase heat transfer. Data on heat transfer in circular micro-tubes and in rectangular, trapezoidal and triangular ducts are presented. Attention is drawn to the effect of energy dissipation, axial conduction and wall roughness on the thermal characteristics of flow. Specific problems connected with electro-osmotic heat transfer in micro-channels, three-dimensional heat transfer in micro-channel heat sinks and optimization of micro-heat exchangers are also discussed. 

An iron foundry has four workstations that are connected to a single duct. Each workstation has a hood that transports 3000 acfin of air flow. The duct length is 400 ft, and the pressure loss at the hood entrance is 0.5 in. of water. There is also a cyclone air cleaner that creates 3.5 in. H2O pressure drop. Determine the diameter of the duct to ensure adequate transport of the dust. Also determine the power required for a combined blower/motor efficiency of 40%. 

Hepatocytes are the commonest cell type found in the liver, constituting about 70% of the total liver mass. The plasma membranes of these cells have three functional domains the sinusoidal domain, an intercellular domain with gap junctions that is the contact area between hepatocytes, and the canalicular domain, where many of the hepatic secretory functions are performed. The hepatocytes are arranged in single cell layers around sinusoids, which are vascular capillary vessels connected to the hepatic portal vein and hepatic artery the perisinusoidal space of Disse separates the endothelial cell from the hepatocytes. Fenestrations (or windows) in the cells lining the sinusoids allow the formation of hepatic lymph fluid and the movement of proteins into the space of Disse. The lymph leaves the liver through the lymphatic vessels, the lymph nodes, and the thoracic duct, although a small proportion leaves the liver through lymph vessels associated with the hepatic vein. 

In Canada, where parks of CANDU tube reactors have been built (up to eight 600 MWe reactors on the same site), vacuum building containment has also been used which consists in building, for each park of reactors, a central empty containment, connected with the containments of any single reactor by a duct provided with a rupture disc or similar device. In the event of a LOCA accident in one of the reactors, the corresponding rupture disc opens and the air-steam mixture under pressure has the whole volume of the vacuum building in which to expand. In this way, the containment of each reactor can be rather small with overall economic advantages. 

When constrained duct or conduit space precludes the use of multiple sheaths, a splice should be used to consolidate the sheaths into one higher fiber count sheath. Combine as many cables as possible at a single splice point, since the incremental cost per additional fiber splice is less than the cost for splicing at different locations. It is important to analyze the entire system when planning splice points. For example, if a planned cross connect is near a manhole that is being considered for a splice point, it might make more sense to route the cables to the cross connect, so that the splice point is combined with the termination point. This can result in substantial labor cost savings (Fig. 9.102). 

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