You May Know it.

Rickshaws in a street of Dhaka, Bangladesh.

Rickshaws (or rickshas) are a mode of human-powered transport: a runner draws a two-wheeled cart which seats one or two persons. The word rickshaw came from Asia where they were mainly used as means of transportation for the social elite. However, in more recent times rickshaws have been outlawed in many countries in Asia due to numerous accidents.

Runner pulled rickshaws have mainly been replaced in Asia by bicycle rickshaws. They are also common in Western cities like New York City. In London they are known as pedicabs, and in San Diego they are called bike taxis. The term "rickshaw" is today commonly used for those vehicles as well, but this article deals exclusively with runner-pulled rickshaws.

The word "rickshaw" originates from the Japanese word jinrikisha ( jin = human, riki = power or force, sha = vehicle), which literally means "human-powered vehicle".

Rickshaw and Bangladesh

Rickshaws (riksha) in Bangladesh are cycle-powered, and are available for hire throughout the country; Bangladesh's capital is sometimes called the "City of Rickshaw". However, increasing traffic congestion and the resulting collisions have led to the banning of cycle rickshaws on many major streets in the city. Still, in many parts of Old Dhaka, rickshaws are the only kind of vehicle that can travel through the narrow streets. Rickshaw-pullers are known as rikshawala in Bangla.

Bangladeshi rickshaw pullers are mostly from the district of Rongpur. Because of the recent famine and less job opportunities, people from there migrate to Dhaka, Sylhet and Chittagong to pull rickshaws.

Rickshaw man Omar Ali is Bangla's music star winner in the television "Pop Idol"-style talent show .

GEOTHERMAL POWER

Enhanced Geothermal System

Geothermal power (from the Greek roots geo, meaning earth, and thermos, meaning heat) is power extracted from heat stored in the earth. This geothermal energy originates from the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface. It has been used for space heating and bathing since ancient roman times, but is now better known for generating electricity. About 10 GW of geothermal electric capacity is installed around the world as of 2007, generating 0.3% of global electricity demand. An additional 28 GW of direct geothermal heating capacity is installed for district heating, space heating, spas, industrial processes, desalination and agricultural applications.

Geothermal power is cost effective, reliable, and environmentally friendly, but has previously been geographically limited to areas near tectonic plate boundaries. Recent technological advances have dramatically expanded the range and size of viable resources, especially for direct applications such as home heating. Geothermal wells tend to release greenhouse gases trapped deep within the earth, but these emissions are much lower than those of conventional fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed instead of fossil fuels.

Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in Italy. The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States. As of 2004, five countries (El Salvador, Kenya, the Philippines, Iceland, and Costa Rica) generate more than 15% of their electricity from geothermal sources.


Twenty-four countries generated a total of 56,786 GWh (204 PJ) of electricity from geothermal power in 2005, accounting for 0.3% of worldwide electricity consumption. This output is growing by 3% annually, thanks to a growing number of plants as well as improvements in their capacity factors. Because a geothermal power station does not rely on transient sources of energy, unlike, for example, wind turbines or solar panels, its capacity factor can be quite large; up to 90% has been demonstrated. Their global average was 73% in 2005. The global capacity was 10 GW in 2007.


Geothermal electric power plants have been limited to the edges of tectonic plates until recently.Geothermal electric plants have until recently been built exclusively on the edges of tectonic plates where high temperature geothermal resources are available near the surface. The development of binary cycle power plants and improvements in drilling and extraction technology has opened the hope that enhanced geothermal systems might be viable over a much greater geographical range. A demonstration project has recently been completed in Landau-Pfalz, Germany, and others are under construction in Soultz-sous-Forêts, France and Cooper Basin, Australia.

Steam Trap

A steam trap is a device used to discharge condensate and non condensable gases while not permitting the escape of live steam. Nearly all steam traps are nothing more than automatic valves. They open, close or modulate automatically.

The three important functions of steam traps are: 1) To discharge condensate as soon as it is formed. 2) Not to allow steam to escape. 3) To be capable of discharging air and other incondensible gases.

Basic Operation

The earliest and simplest form of steam trap is the orifice trap. It consists of simply a disc or short solid pipe nipple with a small hole drilled through it installed at the lowest point of the equipment. Since steam condensate will collect at the lowest point and this hot liquid is about 1200 times smaller in volume and denser than live steam, condensate is effectively removed and steam is blocked.

The three important functions of steam traps are: 1) To discharge condensate as soon as it is formed. 2) Not to allow steam to escape. 3) To be capable of discharging air and other incondensible gases.


Issues

The problem with orifice traps is the fact that they do not compensate for varying loads and pressures. If the condensate load increases, liquid will back up in the equipment. If the load is light, then there is little condensate present and live steam will escape through the orifice. Orifice traps will not handle or remove non-condensable gases successfully. These basic inabilities have spawned a multitude of steam trap designs and configurations to meet a whole spectrum of applications. No single steam trap design is ideal for each and every application. This makes understanding each design's abilities and limitations important in selecting the right trap for the right job.


Types

Steam traps can be split into three major types:

1.Mechanical traps. They have a float that rises and falls in relation to condensate level and this usually has a mechanical linkage attached that opens and closes the valve. Mechanical traps operate in direct relationship to condensate levels present in the body of the steam trap. Inverted bucket and float traps are examples of mechanical traps.

2.Temperature traps. They have a valve that is driven on / off the seat by either expansion / contraction caused by temperature change. They differ from mechanical traps in that their design requires them to hold back some condensate waiting for it to cool sufficiently to allow the valve to open. In most circumstances this is not desirable as condensate needs to be removed as soon as it is formed. Thermostatic traps and bimetallic traps are examples of temperature operated traps.

3.Thermodynamic (TD) traps. Thermodynamic traps work on the difference in dynamic response to velocity change in flow of compressible and incompressible fluids. As steam enters, static pressure above the disk forces the disk against the valve seat. The static pressure over a large area overcomes the high inlet pressure of the steam. As the steam starts to condense, the pressure against the disk lessens and the trap cycles. This essentially makes a TD trap a "time cycle" device: it will open even if there is only steam present, this can cause premature wear. If non condensable gas is trapped on top of the disc, it can cause the trap to be locked shut.