Thermal Resistance

blurb

R is thermal resistance in C/watt
L is the length in meters (m)
K is the Thermal Conductivity of the material in watts/meter C
A is the cross sectional area in meters squared (m²).

Time Required to Cool (or heat) an Object [or, Q required to cool or heat an object within a specific time]

The following image graphically shows Heating and Cooling as Q (heat) being added or removed from an object.

The following formula is shown in two different ways.  The first solves for time t and the second solves for Q.

Where;

Q is the heat added (or being removed) from the object in watts.
m is the mass (weight) of the object in Kg.
C_p is the Specific heat of the object material in J/Kg C.
t is the time required to cool down (or heat up) the object in seconds.
T_s is the starting temperature in C.
T_f is the final temperature in C.

Heat Gain (or loss) - through the walls of an insulated container

Where;

Q is the heat lost or gained in watts 
L is the thickness of insulation in meters (m)
K is the Thermal Conductivity of the insulation material in watts/meter K (or C)
A is the outside surface area of the container in meters squared (m²).
h is the Heat Transfer Coefficient of the surface material in watts/meter² C
T_a is the Outside ambient air temperature in C 
T_I is the Inside temperature in C

Natural or Free Convection is essentially still to slightly stirred air with h values ranging from 1 to 25.
Forced Convection is air moved by a fan or other active method. h values range from 25 to 100.

Heat Loss (or gain) - by Convection

Where;

Q is the heat lost (or gained) in watts 
h is the Heat Transfer Coefficient of the surface material in watts/meter² C
A is the exposed surface area in meters squared (m²).
T_s is the surface temperature in C 
T_a is the ambient air temperature in C

Natural or Free Convection is essentially still to slightly stirred air with h values ranging from 1 to 25.
Forced Convection is air moved by a fan or other active method. h values range from 10 to 100.

Heat is "gained" or added to a surface when the ambient air (T_a) is higher than the surface temperature (T_s).