http://us.lge.com/products/model/det...WM3431HW.jhtml
That is not the exact one I have but it works the same way. Instead of a vent, it uses a compressor (like the ones used in air conditioners) to compress a gas (commonly chlorodifluoromethane, also known as R-22), getting it hot. The hot gas flows through a radiator (condenser) that allows it to give up heat to the air stream that dries the clothes. In the process, the gas loses so much heat that it condenses into a liquid. A control valve (TXV) lets some of that liquid flow into another radiator (evaporator). As the pressure drops, the liquid boils and takes in heat from the air stream leaving the clothes, causing the moisture to condense for removal. The air is recirculated through the condenser for reheating, and the gas from the liquid boiling off is returned to the compressor.