??? Phyiscs?

Question

Identify one place in the technology where percent efficiency of an energy transfer or transformation will be a low value.

Answer 1

If you are purely talking energy transfer efficiency, the lowest one I can think of are the tiles on the space shuttle. The effeciency of the heat transfer from the outside of the spacecraft to the inside of the spacecraft is VERY low. This would be the case in most insulators.

Answer 2

Internal combustion engines aren't very good at converting gasoline to torque and rev/min. Regular compression ratios (8 - 9) with 2 valves per cylinder run at about 10% OR LESS. If you do the chemistry on the enthalpy of a gallon of gas, you only get 1/10th of that at the wheels (or worse). Diesel is better becuase of the higher compression ratios and a thermodynamic concept known as "availability" which is too darn complicated for me to remember right now.

Solar cells convert photon streams to electric current flow and I have heard efficiencies of about 4%. That sucks. If you calculate the available energy delivered by the sun to a one square meter plate in clear weather, you only get 4% of the energy as converted by a solar cell.

One interesting heat transfer efficiency is the steam turbine cycle. If you look at the efficiency of just steam power (not the heat generating the steam) you get efficiencies starting at 50%, which compared to other modes of heat to mechanical energy, STEAM ROCKS. It packs a far bigger punch than any hot air engine (all internal combustion engines are hot air engines because the working fluid is air.) The Nitrox in the atmosphere has such a low specific heat, the availability to do work isn't very good. Superheated steam, however, has the molar heat of fusion AND a strong specific heat which can really move energy from one place to another.

The last steam research had made miniature boilers running at 850F with a water recirculation loop, giving very high efficiencies to reciprocating engines on the vehicle. It is too bad Abner Doble's boilers didn't get the bugs worked out in time before historical momentum and internal combustion engines took over.

Answer 3

in automobiles, the conversion of chemical energy to mechanical energy is relatively low, I believe around 20-30%. Typically in a cycle, the closer the low operating temperature is to the high operating temperature, the lower the cycle efficiency will be, based on the carnot cycle.

Answer 4

That is subjective - but - how 'bout electricity through a wire? Losses are difined as I^2 R - or hysterisis losses. Comparatively speaking they are high efficiency - compared to lets say generation of the electricity in the first place.

Answer 5

Physics, get it right