## Convection Currents Essay

Convection Currents Essay.

There are many different reasons why the earth’s crust is moving. Some for example are the friction between two plates causing major earthquakes. Sometimes when this plates are pushed together they form fold mountains or ridges. Today we know that the continents are gradually moving apart. Therefore the there is new rocks created in between those areas. New volcanoes are created and new rocks are formed.

Plate tectonics allow scientists to know about the earth’s centre. The oceanic plate slides under the continental plate because it is heavier.

Once it goes under the continental plate it melts into the asthenosphere. The Richter scale is a scale that scientists use to measure the magnitude of an earthquake. It can tell us how much the earth’s crust has moved (how hard; effecting the surface). A shift along a fault on the continental crust could also cause earthquakes.

Teacher copy The earth’s crust I s made up of sections called plates.

These sections ‘float’ on the liquid mantle and slowly move around. The movement of the plates is caused by convection currents. A convection current is how a liquid moves when it is heated. Hot liquid rises up and pushes the cooler liquid out of the way. In the mantle, this is happening all the time. As the liquid rock moves, it can push the continents on the plates In this diagram you can see the convection currents in the mantle and the direction

In the middle of the ocean, new rock is formed when hot rock from the mantle rises up. At the edges of ocean, old crust is destroyed when it stinks down under the continent an melts again. In this diagram, you can see new crust forming at the mid-ocean ridge and pushing the old crust towards the continent.

Convection Currents Essay ## Forced Convection (in a cross flow heat exchanger) Essay

Forced Convection (in a cross flow heat exchanger) Essay.

The aim of this lab is to determine the average convective heat transfer coefficient for forced convection of a fluid (air) past a copper tube, which is used as a heat transfer model. Introduction The general definition for convection may be summarized to this definition “energy transfer between the surface and fluid due to temperature difference” and this energy transfer by either forced (external, internal flow) or natural convection. Heat transfer by forced convection generally makes use of a fan, blower, or pump to provide high velocity fluid (gas or liquid).

The high-velocity fluid results in a decreased thermal resistance across the boundary layer from the fluid to the heated surface. This, in turn, increases the amount of heat that is carried away by the fluid.  Theory Background  Considering the heat lost by forced convection form the test rod. The amount of heat transferred is given by (1) Where = rate of heat transfer, unknown value. ?= film heat transfer coefficient, this is what we need to found out.

A= area for heat transfer, this is the area of the cross section area of test section. T= temperature of the copper rod, the temperature after heating.

Ta= temperature of air, surrounding temperature. So, in any period of time, dt, then the fall in temperature, dT, will be given as: (2) Where m= mass of copper rod, cp= specific heat of the copper rod, J/kgK Eliminating Q from (1) and (2) then Since Ta is constant, dT=d(T-Ta) Integrating gives: At t = 0, T=To, hence C1 = ln(T-To), hence: Or Therefore a plot of ln((T-Ta)/(Tmax-Ta))) against t should give a straight line of gradient from which the heat transfer coefficient, ? , can be found. To find the velocity of air passing the rod, first the velocity upstream must be found.

Forced Convection (in a cross flow heat exchanger) Essay 