Considere o enunciado a seguir para responder às questões de n os 26 e 27.
O sistema de transmissão mostrado na Figura abaixo é constituído de dois pares de engrenagens e um eixo. As engrenagens 1 e 3 possuem raios idênticos de 8 cm, e as engrenagens 2 e 4 possuem raios idênticos de 12 cm.
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A equação de Navier Stokes para um escoamento na direção x do sistema cartesiano é dada por:
Água a 5o C, com viscosidade cinemática de 1,5 x 10 -6 m 2 /s, escoa a 0,6 m/s, em um tubo com diâmetro de 0,1 m.
Qual velocidade de escoamento, em m/s, precisa ter um óleo a 20 o C, com viscosidade cinemática de 1,0 x 10 -4 m 2 /s, em um tubo com diâmetro 0,5 m, para que os escoamentos possam ser dinamicamente similares?
O sistema de transmissão de potência transfere o movimento da máquina motora para a bomba.
A transmissão direta é realizada por
Um sistema mecânico com dois graus de liberdade, sujeito a vibrações, possui duas frequências naturais e dois modos de vibração.
Cada modo de vibrar representa a forma do movimento do sistema em vibração
Ao serem determinadas as três frequências naturais de um sistema mecânico com três graus de liberdade, obteve-se, para uma das frequências naturais, o valor nulo. Esse resultado indica que o
Texto associado
Se a engrenagem 1 transmite um torque de 200 N.m à engrenagem 2, o torque de saída na engrenagem 4, em N.m, será de
Em um determinado processo de soldagem, a eficiência de transmissão de calor é de aproximadamente 80%, a potência dispendida pela fonte de calor na soldagem é 1000 W (watts), e a velocidade de avanço é de 0,6 m/min (metros/minutos).
Então, o valor do aporte térmico nessas condições, em kJ/mm, é
Um gás ideal é aquecido de 127°C a 727°C, sendo que seu calor específico a pressão constante, em base molar, é regido pela equação abaixo:
R ˉ C ˉ p = α + β T
Sendo α = 3,5, β = –1,5 × 10 -3 e R ˉ ≅ 8 kJ/kmol.K, a variação de entalpia, em kJ/kg, para um gás de massa molecular igual a 30 kg/kmol é
Em uma fábrica existem três máquinas (M1, M2 e M3) que produzem chips. As máquinas são responsáveis pela produção de 20%, 30% e 50% dos chips, respectivamente. Os percentuais de chips defeituosos produzidos pelas máquinas M1, M2 e M3 são 5%, 4% e 2%, respectivamente.
Ao se retirar aleatoriamente um chip, constata-se que ele é defeituoso; então, a probabilidade de ele ter sido produzido pela máquina M1 é de, aproximadamente:
Texto associado
The key energy questions for 2018
..
The renewables industry has had a great year.
How fast can it grow now?
...
What are the issues that will shape the global
energy market in 2018? What will be the energy
mix, trade patterns and price trends? Every country
is different and local factors, including politics, are
5 important. But at the global level there are four key
questions, and each of which answers is highly
uncertain.
The first question is whether Saudi Arabia is
stable. The kingdom’s oil exports now mostly go to
10 Asia but the volumes involved mean that any volatility
will destabilise a market where speculation is rife.
The risk is that an open conflict, which Iran and
Saudi have traditionally avoided despite all their
differences, would spread and hit oil production and
15 trade. It is worth remembering that the Gulf states
account for a quarter of global production and over
40 per cent of all the oil traded globally. The threat to
stability is all the greater given that Iran is likely to win
any such clash and to treat the result as a licence to
20 reassert its influence in the region.
The second question is how rapidly production
of oil from shale rock will grow in the US — 2017 has
seen an increase of 600,000 barrels a day to over 6m.
The increase in global prices over the past six months
25 has made output from almost all America’s producing
areas commercially viable and drilling activity is rising.
A comparable increase in 2018 would offset most of
the current OPEC production cuts and either force
another quota reduction or push prices down.
30 ---- The third question concerns China. For the
last three years the country has managed to deliver
economic growth with only minimal increases in
energy consumption. Growth was probably lower than
the claimed numbers — the Chinese do not like to
35 admit that they, too, are subject to economic cycles
and recessions — but even so the achievement
is considerable. The question is whether the trend
can be continued. If it can, the result will limit global
demand growth for oil, gas and coal.
40 - --- China, which accounts for a quarter of the world’s
daily energy use, is the swing consumer. If energy
efficiency gains continue, CO2 emissions will remain
flat or even fall. The country’s economy is changing
and moving away from heavy industry fuelled largely
45 by coal to a more service-based one, with a more
varied fuel mix. But the pace of that shift is uncertain
and some recent data suggests that as economic
growth has picked up, so has consumption of oil and
coal. Beijing has high ambitions for a much cleaner
50 energy economy, driven not least by the levels of air
pollution in many of the major cities; 2018 will show
how much progress they are making.
The fourth question is, if anything, the most
important. How fast can renewables grow? The last
55 few years have seen dramatic reductions in costs
and strong increase in supply. The industry has had
a great year, with bids from offshore wind for capacity
auctions in the UK and elsewhere at record low levels.
Wind is approaching grid parity — the moment
60 when it can compete without subsidies. Solar is also
thriving: according to the International Energy Agency,
costs have fallen by 70 per cent since 2010 not least
because of advances in China, which now accounts
for 60 per cent of total solar cell manufacturing
65 capacity. The question is how rapidly all those gains
can be translated into electric supply.
Renewables, including hydro, accounted for just
5 per cent of global daily energy supply according
to the IEA’s latest data. That is increasing — solar
70 photovoltaic capacity grew by 50 per cent in 2016
— but to make a real difference the industry needs
a period of expansion comparable in scale to the
growth of personal computing and mobile phones in
the 1990s and 2000s.
75 - --- The problem is that the industry remains
fragmented. Most renewable companies are small
and local, and in many cases undercapitalised; some
are built to collect subsidies. A radical change will be
necessary to make the industry global and capable
80 of competing on the scale necessary to displace
coal and natural gas. The coming year will show us
whether it is ready for that challenge.
In many ways, the energy business is at a
moment of change and transition. Every reader will
85 have their own view on each of the four questions. To
me, the prospect is of supply continuing to outpace
demand. If that is right, the surge in oil prices over
the past two months is a temporary and unsustainable
phenomenon. It would take another Middle East war
90 to change the equation. Unfortunately, that is all too
possible.
...
Available at: . Retrieved on: Feb 18, 2018. Adapted.
..
The renewables industry has had a great year.
How fast can it grow now?
...
What are the issues that will shape the global
energy market in 2018? What will be the energy
mix, trade patterns and price trends? Every country
is different and local factors, including politics, are
5 important. But at the global level there are four key
questions, and each of which answers is highly
uncertain.
The first question is whether Saudi Arabia is
stable. The kingdom’s oil exports now mostly go to
10 Asia but the volumes involved mean that any volatility
will destabilise a market where speculation is rife.
The risk is that an open conflict, which Iran and
Saudi have traditionally avoided despite all their
differences, would spread and hit oil production and
15 trade. It is worth remembering that the Gulf states
account for a quarter of global production and over
40 per cent of all the oil traded globally. The threat to
stability is all the greater given that Iran is likely to win
any such clash and to treat the result as a licence to
20 reassert its influence in the region.
The second question is how rapidly production
of oil from shale rock will grow in the US — 2017 has
seen an increase of 600,000 barrels a day to over 6m.
The increase in global prices over the past six months
25 has made output from almost all America’s producing
areas commercially viable and drilling activity is rising.
A comparable increase in 2018 would offset most of
the current OPEC production cuts and either force
another quota reduction or push prices down.
30 ---- The third question concerns China. For the
last three years the country has managed to deliver
economic growth with only minimal increases in
energy consumption. Growth was probably lower than
the claimed numbers — the Chinese do not like to
35 admit that they, too, are subject to economic cycles
and recessions — but even so the achievement
is considerable. The question is whether the trend
can be continued. If it can, the result will limit global
demand growth for oil, gas and coal.
40 - --- China, which accounts for a quarter of the world’s
daily energy use, is the swing consumer. If energy
efficiency gains continue, CO2 emissions will remain
flat or even fall. The country’s economy is changing
and moving away from heavy industry fuelled largely
45 by coal to a more service-based one, with a more
varied fuel mix. But the pace of that shift is uncertain
and some recent data suggests that as economic
growth has picked up, so has consumption of oil and
coal. Beijing has high ambitions for a much cleaner
50 energy economy, driven not least by the levels of air
pollution in many of the major cities; 2018 will show
how much progress they are making.
The fourth question is, if anything, the most
important. How fast can renewables grow? The last
55 few years have seen dramatic reductions in costs
and strong increase in supply. The industry has had
a great year, with bids from offshore wind for capacity
auctions in the UK and elsewhere at record low levels.
Wind is approaching grid parity — the moment
60 when it can compete without subsidies. Solar is also
thriving: according to the International Energy Agency,
costs have fallen by 70 per cent since 2010 not least
because of advances in China, which now accounts
for 60 per cent of total solar cell manufacturing
65 capacity. The question is how rapidly all those gains
can be translated into electric supply.
Renewables, including hydro, accounted for just
5 per cent of global daily energy supply according
to the IEA’s latest data. That is increasing — solar
70 photovoltaic capacity grew by 50 per cent in 2016
— but to make a real difference the industry needs
a period of expansion comparable in scale to the
growth of personal computing and mobile phones in
the 1990s and 2000s.
75 - --- The problem is that the industry remains
fragmented. Most renewable companies are small
and local, and in many cases undercapitalised; some
are built to collect subsidies. A radical change will be
necessary to make the industry global and capable
80 of competing on the scale necessary to displace
coal and natural gas. The coming year will show us
whether it is ready for that challenge.
In many ways, the energy business is at a
moment of change and transition. Every reader will
85 have their own view on each of the four questions. To
me, the prospect is of supply continuing to outpace
demand. If that is right, the surge in oil prices over
the past two months is a temporary and unsustainable
phenomenon. It would take another Middle East war
90 to change the equation. Unfortunately, that is all too
possible.
...
Available at: . Retrieved on: Feb 18, 2018. Adapted.
