From introduction: "The tube arrangement covered in this report was proposed in June, 1950, as a means of halving the weight and volume required for the heat exchanger. Ideally, the pressure drop across this arrangement should be little more than that required to overcome the skin friction on the tube surfaces. If the pressure drop across the tube spacers and in the cross-flow regions can be kept low, this ideal can be approached. much of the test work covered in this report was devoted to this phase of the problem."