Question

Heat flow between two solid objects not touching each other is due to what mechanism?

Answer 1

When you bring two objects of different temperature together, energy will always be transferred from the hotter to the cooler object.  The objects will exchange thermal energy, until thermal equilibrium is reached, i.e. until their temperatures are equal.  We say that heat flows from the hotter to the cooler object.  Heat is energy on the move.  
Units of heat are units of energy.  The SI unit of energy is Joule.  Other often encountered units of energy are 1 Cal = 1 kcal = 4186 J, 1 cal = 4.186 J, 1 Btu = 1054 J.

Without an external agent doing work, heat will always flow from a hotter to a cooler object.  Two objects of different temperature always interact.  There are three different ways for heat to flow from one object to another.  They areconduction, convection, and radiation.

 i hope this helps u