Effect of natural convection on laminar flow heat transfer in horizontal circular tubes.

Abstract

The temperature distribution was measured in a horizontal circular tube with a high uniform wall temperature in the case where gas flowed through the tube in the laminar flow range. The temperature in the upper portion of the cross section was higher than that in the lower portion. The isothermal lines estimated from the measured temperature distribution in the cross section were symmetrical to the vertical centerline of the cross section. The heat transfer coefficient from the tube wall is affected by tube diameter, distance from tube inlet, wall temperature and Reynolds number. The empirical equation for the heat transfer coefficient from the tube wall is obtained. To analyze the heat transfer in the tube the fundamental equations are derived under suitable assumptions based upon observation of the flow pattern in the tube and are solved numerically. The calculated temperature distribution and the calculated heat transfer coefficient from the tube wall agree approximately with the experimental findings.