Can heat energy be converted back into useful energy?

Question

In chemical reactions, energy can neither be created or destroyed but it can be converterd. In some instances like the burning of gas, most energy is converted to useless heat.

Answer 1

It can be, but not very easily efficiently. How easily it can be converted depends on how much of a temperature differential you can produce; the hotter it is compared to the environment, the easier it is to get useful energy out of it.

The efficiency of the conversion depends on how you do it. Odds are, you'd be wanting to convert the heat into electricity or motion using a heat engine. Depending on the engine you use, your efficiency will vary.

And you'll never get 100% efficiency; you can't recover all the heat as useful work. Just some of it.

For example, with a burning gas - that's how automobile engines work. They use the heat to generate motion.

Answer 2

It all depends how much heat is produced, and what the temperature difference is between the heat source and heat sink.
For example, the burning of fuel in a steam boiler produces heat. The higher the temperature produced and the amount of fuel used, the higher the temperature and amount of steam produced. A higher steam temperature and pressure, combined with a colder condenser in which the steam is turned back into water, makes a more efficient energy conversion.
Internal combustion engines are a different matter. There are various ways; such as 2-stroke operation, design factors, and operation at proper load ratings, that make all IC engines operate at peak efficiency.
But yes, almost all heat produced in chemical reactions is recoverable and usable in some form, if the recovery/heat exchange system is properly designed and built.

Answer 3

Hydrogen from natural gas is passed over an anode (negative electrode) made of nickel and yttria-stabilized zirconia (YSZ). The hydrogen atoms break apart into positively charged ions and electrons. The electrons travel through an external circuit to a cathode (positive electrode) made of the rare-earth oxide lanthanum strontium manganate (LaSrMnO3).

Oxygen from the air or carbon monoxide is collected at the cathode where the gas accepts electrons to form negatively charged oxygen ions, which are passed through a YSZ electrolyte separating the anode and cathode. The electrolyte is heated to 600 to 1000°C by an electric heater to start the electrochemical reaction. On arrival at the anode, each oxygen ion is discharged by reacting with two hydrogen ions to form water. The heat from the electrochemical reaction maintains the cell temperature, allowing the electric heater to be turned off.

The end product is the captured and recirculated. Similar projects are used in model homes as a heat source. You may want to check out Siemens-Westinghouse who has designed a solid-oxide fuel cell that is 60% efficient and a hybrid fuel cell–microturbine plant in which waste heat from the fuel cell is used to drive the microturbine. This combined-cycle power plant is 70% efficient.

Answer 4

What makes you believe heat is useless energy? It is after all the only reason for burning natural gas or coal.