I am trying to construct a portable personal cooling device. I am considering using tygon tubing and propylene glycol/water mixture as the coolant in the tubing circulating it through an ice water bath. The tubing would be connected to copper pipes, that would run into the bag containing the ice water to facilitate a better transferance of heat from the tubing into the water/ice mixture. Now my question is how do I calculate the diameter of the tubing, the flow rate of the mixture, and material of tubing be to facilitate maximum heat transfer from a warm body lets say 100 °F into the cooling mixture? Lets assume the bath temp the copper tubing is imersed into is 32°F.