Our friends over at Electro Labs have a  DIY Adjustable Electrical Load project posted. There are lots of adjustable load projects out there, they can come in handy when developing your next project so you should consider building one. The heart of this one is a IRF3710 MOSFET, it simply dumps the required energy into the large board mounted heatsink.
“Since the MOSFET works as a resistive element, it dissipates heat depending on the current flowing through it. The simple equation P = VI gives us the amount of heat which will be generated on the MOSFET. To extend the power range of the load, we need to attach a heatsink to the MOSFET case.”