Pressure-drop reduction and heat-transfer deterioration of slush nitrogen in horizontal pipe flow

► Pressure drop reduction during heat transfer for slush nitrogen is investigated. ► Differing pipe diameter leads to differing pressure-drop reduction onset-velocity. ► Correlations between pressure drop and heat transfer deterioration are obtained. ► Flow patterns and solid particles are observed using a high-speed video camera. ► Movement of solid particles to the pipe center causes pressure drop reduction.