The effects of orientations have been studied for excessive heat dissipation as the vapor and liquid dispersion varies due to drastic variation in density. The heat transfer coefficient and pressure fluctuations are investigated with water as a working fluid at atmospheric pressure in flow boiling for horizontal, vertical up, and vertical down orientations for different mass flux and heat flux. A test-section made up of stainless steel (SS304) of 11.7 mm inner diameter and 0.5 mm thickness having 1.5 m length is used. The Froude number at the test-section outlet is varied from 0.078 to 0.6. The thermal imaging technique is used to visualize and plot the contours of the distribution of wall temperature. The centreline local and average heat transfer coefficient is comparatively higher for horizontal flow than vertical downflow and vertical upflow for the same mass flux and heat flux in flow boiling. However, the heat transfer is asymmetric for horizontal flow while symmetric for vertical up and downflow. For horizontal flow, the wall temperature is asymmetric for the Froude number less than 0.22 and vapor quality greater than 0.03. The pressure fluctuates more in horizontal orientation than the vertical orientation for two-phase flow. © 2021 Elsevier Ltd