Mechanical draught

It had been known for centuries that the output of a blacksmith’s forge could be increased by the use of a bellows. Later small centrifugal fans were substituted as a labour saving device. As pressures were relatively high for the flowrate, narrow designs were developed incorporating cast iron casings. That produced by Beck and Henkel of Cassel, Germany is shown in Figure 1.35 and is an early example of a unit used not only for forge blowing but also cupolas producing cast iron. The complexity of the design must be admired as a high example of the iron founder’s art, and creates a sense of envy for what we cannot do today — the cost would be enormous.

Another German fan of considerable interest is the Geneste­Herscher design (Figure 1.36) which gained first prize at the Paris Exhibition of 1900. We can see that, although of the for­ward curved bladed centrifugal type, considerable attention was paid to the form of the inlets whilst the volute had a rectan­gular cross section uniformly increasing to the outlet.

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Figure 1.36 The Geneste-Herscher centrifugal fan design

подпись: figure 1.36 the geneste-herscher centrifugal fan design Mechanical draught

Mechanical draught

Figure 1.35 The Beck and Henckel centrifugal fan

We now come to another giant of the fan world, James Howden. Starting in 1854 as a consultant to the flourishing shipbuilding and engineering industry around Glasgow, he soon appreci­ated the need for improvements to engines and boilers. By 1881 he had developed and sold a range whose efficiency and output exceeded anything available.

During this period the concept of supplying air to a boiler under pressure from a fan so that it could also pass through a pre-heat section, to extract heat from the flue gases, emerged. Trials were carried out in the winter of 1882/3 and by the following year had been demonstrated on a refitted ship. Until then, trans-Atlantic steamers had to augment their driving force with sails, as with Brunei’s Great Eastern, or had to proceed via Ice­land and/or Newfoundland for refuelling. Now the resultant im­provement in fuel efficiency and power enabled them to reach New York non-stop.

From this stage his company developed and the forced draught business increased to such an extent that it dominated all its ac­tivities. Boiler making eventually ceased in favour of fans for their marine forced draught system. By 1926 the system had been developed to the extent that land-based water tube boil­ers incorporating air pre-heaters, with forced and induced draught fans were operating with complete success.

James Keith’s company had also manufactured boilers and naturally followed Howden’s example in marine usage. A modi­fied design of the patented impeller was applied to the forced ventilation of engine rooms. That for the Lusitania was manu­factured in 1912 and is shown in Figure 1.37. Is it still at the bot­tom of the sea?

1.2.1 Air conditioning, heating and ventilation

There is considerable evidence that prehistoric man used fire to produce heat for his comfort. Native Americans also used open

Mechanical draught

Figure 1.37 James Keith’s patented impeller

Fires within their wigwams and allowed the products of combus­tion to escape through the hole at the apex, at the same time inducing fresh air.

Medieval Europeans developed fireplaces so that the smoke could be guided up a chimney, resulting in a stack effect which improved combustion and provided room ventilation. Of course, the Romans had done much better 1500 years before by constructing flues within the walls of their buildings to give the first central heating.

Public buildings were some of the first to employ a mechanical system of ventilation. Perhaps as a consequence of the large amounts of hot air produced, the Houses of Parliament in Lon­don were provided with a supply and extract system of ventila­tion as early as 1836. In the unlikely event of heating being nec­essary, air was drawn through steam coils adjacent to the fan. The air was also washed with water sprays and cooling could be achieved by the use of ice.

The more humble beginnings of building ventilation, however, started with the propeller fan which is believed to have origi­nated in the United States. Perhaps times were hard, or the English considered gullible, for Lucius Fisher, Walter Burnham and James Morgan Blackman, all of Illinois, moved to the United Kingdom and formed the Blackman Air Propeller Venti­lating Co. Ltd on 10th September 1883.

A number of propeller fan designs were produced in those early years, each having completely different blades, apparently conceived on the basis of “try anything once”. All were de­signed for belt drive, usually from overhead line shafting. By 1891, however, an electrical direct drive version was available. A prototype produced at the time when the Tottenham factory closed is shown in Figure 1.38.

Perhaps even more interesting was the patented version pro­duced by Blackman’s engineer Mr Water, which had no sepa­rate motor either coupled to the spindle or belted to a pulley. The fan was its own motor, its periphery being the armature, its frame the field magnets and the commutator occupying the place of the pulley. Was this the first inside-out motor driven fan, albeit in a DC form?

This fan was stated to work at “a moderate speed consistent with sound and economical practice… and all noise and risk of vibration is reduced to a minimum”. By 1896 Electrical Review

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Figure 1.38 The Blackman propeller fan prototype

Was waxing lyrical in its description. The long extract that

Follows, is interesting for its language, if nothing else:

Fresh air by electricity

Of the many beneficent purposes to which electricity is ap­plied, none can be more conducive to the comfort and health of the community than its use for driving ventilating fans; and it is with pleasure that we observe the rapidly in­creasing number of electrically driven fans that are being in­stalled for the removal of all kinds of disagreeable fumes, such as the appetising(?) odours that arise from the kitchen, and the unhealthy products of gas burners [incandescent and otherwise]. Enquiries made at the London office of the Blackman Ventilating Company, (the name had soon been shortened) and an inspection of some of the installations of their well-known fans, has convinced us that a wide field is being opened up, and one that will form a valuable addition to the central load.

Not only in the larger public buildings such as the Houses of Parliament, the Stock Exchange, Hotels Cecil, Metronome, Holborn Restaurant, etc. are electric Blackmans (note the use of a name — just like Hoover) freely used for ventilating the dining and smoking rooms, kitchens, and billiard rooms, but many leading club-houses, hotels and private resi­dences are thus fitted.

The wood cut (Figure 1.39) shows the electric Blackman with peripheral motor, as fixed to the upper part of a window. A considerable number of these latter are at work, some of them on windows of the most highly finished rooms in Lon­don, and the effect is in every way satisfactory.

The stuffiness which was once a characteristic of the apart­ments on board ship is in many cases a thing of the past — electric fans are fixed in the dining saloons, drawing fresh air through them and forcing it away when practicable through the cooks’ galleys, thus preventing the odours of cooking from penetrating various parts of the vessel, and preventing many an attack of mal de mer, the sleeping apartments are also ventilated.

It is interesting to note that Messrs Siemens Brothers have six Blackman fans, direct coupled to Siemens motors, on board their cable ship The Faraday, and on its late trip up the Amazon, although the voyage was a most trying one, yet not a single case of yellow fever occurred, and the crew were able to take their meals in the dining saloons, and sleep in their berths, while on previous similar occasions they were driven to eat and sleep on deck.

Speaking of ship ventilation reminds us that the Czar of Russia has followed the example of Her Majesty the Queen by having his magnificent yacht ventilated in this way.

Early development of heating, ventilation and air conditioning

Was held back by the lack of authentic design data. Not only

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Figure 1.39 The electric Blackman with peripheral motor

Was it impossible to calculate the heating or cooling load, but lit­tle was known of equipment capacity, so that they could not be matched.

To proceed beyond the empirical methods, closely guarded by the few companies in the trade, it was necessary to develop the scientific principles involved. Thus was born the American So­ciety of Heating and Ventilating Engineers which had its first an­nual meeting in 1895. It was followed by the Institution of Heat­ing and Ventilating Engineers (UK) in 1897. In 1904 the American Society of Refrigerating Engineers was founded whilst the Swedish Heating, Ventilating and Sanitary Engineers Association commenced operations in 1909. All these organi­zations were active from the start in producing performance standards and in publishing records of research and applicational experience.

The expression “air conditioning” is believed to have been first used by S. W. Cramer who presented a paper on humidity con­trol of textile mills to the National Cotton Manufacturers Associ­ation (USA) in 1907. The measurement and control of the mois­ture content of textiles was known as “conditioning” in the trade, so that the means of circulating humid air to achieve the desired textile moisture content was a natural extension.

Air conditioning was recognised as a branch of engineering in 1911 when Dr Willis H. Carrier presented his two papers Ratio­nal Psychometric Formulae and Air Conditioning Apparatus to the American Society of Mechanical Engineers. From thereon the use of fans for the air conditioning and ventilation of build­ings was rapid. Until that time very large buildings had to have a “light well” at their centre so that not only could all rooms have access to natural light, but they could also be ventilated by opening the windows.

Now architects were released from this consideration. It is tempting to think that skyscrapers could not have reached their present size without fans. By the mid 1920s there were many centrifugal fan manufacturers producing standardized ranges of forward and backward curved types. Selection by multi-rat­ing tables was common but it was H F Hagen of the B F Sturtevant Co. of Massachusetts who was the first to devise an ingenious graphical method under US Patent No. 1358107.

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Figure 1.42 An Aerex axial flow fan

Figure 1.40 The Stork aerofoil backward bladed centrifugal impeller

подпись: 
figure 1.40 the stork aerofoil backward bladed centrifugal impeller

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