# Physics - Geothermal Energy as an Alternative Energy source. Involves reasonably low level thermodynamics. Tom Schipke.

Essay by TumusHigh School, 11th gradeB+, October 2004

Tom Schipke 11J

Physics - Alternative Energy

Flash-steam Geothermal Plants.

Laws

The three laws involved in Geothermal plants - Three of the four laws of thermodynamics.

1. The 0th law - Temperature: if system A is in thermal equilibrium with another system C, and a thermodynamic system B is also in thermal equilibrium with C, then A and B are in thermal equilibrium. This applies even if A and B are separated by an adiabatic barrier (one through which NO heat can flow)

2. The 1st law - Energy is conserved. It can't be created or destroyed, only transformed into different types of energy.

3. The 2nd law - heat does not of itself flow from a cold object to a hot object.

Basic Intro

A geothermal plant is a plant that sits on top of a hot water reservoir (at least 182ÃÂº Celsius) with an injection and production well, as seen in this diagram.

(from http://www.eere.energy.gov). It produces electricity by powering massive turbines that are connected to electrical generators.

The complex stuff

Deep under the earth's surface, in the mantle, there is water that is heated by the pressure and heat near the earth's core. Although the core can reach temperatures around 5000ÃÂº Celsius, the water under the Earth's crust is anywhere between 50ÃÂº and 350ÃÂº. In reservoirs where the temperature is at or above 182ÃÂº, geothermal plants are often in place to produce electricity, with "steam flash" techniques.

As the heated water is extracted from the earth it is extracted into much cooler temperatures and lower pressure. In the high pressure underneath the ground, the water can be up to 300ÃÂº, yet doesn't evaporate into steam? Why? Because when the water is underground, the pressure from the surrounding environment stops the bubbles of molecules from separating into...