Tetra-n-butyl ammonium bromide clathrate hydrate slurry (CHS) is very promising for cold storage and energy saving in air-conditioning applications because of its appropriate phase-change temperature range of 0-12 degrees C, reasonably large latent heat, and good fluidity. In this study, we experimentally investigate the flow and heat transfer characteristics during CHS generation in both an in-house-made annular channel heat exchanger and a commercial double-tube heat exchanger. Meanwhile, the visualization of the growth of the hydrate crystals is also carried out and the thickness of the crystal layer is estimated from the visualization results. It is concluded from the experimental results that the pressure drop and heat transfer coefficient play very important roles in CHS generation and the commercial double-tube heat exchanger is more effective for CHS generation.