Hi
I need to decide between using a 5uF capacitor and two 2.5uF capacitors in parallel. In which case will size and heat loss be larger. I'm using aluminium electrolytics.
it depends on the type of capacitors that you use. Regarding size the 5uF is probably a better choice but the two 2.2uF give you more flexibility in terms of PCB design. For heat loss check the capacitors datasheet sometimes smaller caps have lower esr (if it is paralleled) and better high frequency characteristics. If the esr of the 2.2uF is more than twice the esr of the 5uF use the latter if it is less use the parallel combination.
You never said how much current, and the operating frecuency.
Please let us know how much currente will flow to the capacitor. Some times when current is big at the start the transition in the capacitor generates a peak of current and if the internal resistance is small the capacitor will blow up. If the current isn't big you must not have any problem in any case.