Research Projects

The number of cases of cancer has increased significantly in recent times. The surgeons are forced to find an alternative of the conventional treatment modalities because of their inability to treat the disease effectively. This has given birth to modern day cryotherapy. Cryotherapy deals with treating superficial cancers (like skin cancer) or cancers occurring in the inner organs (like prostate, liver, kidney etc.). Cryospray is a method of destructing cancerous lesions occurring on the skin. In this process, cryogen is sprayed on the affected area using a cryogun and ablation is achieved through rapid freezing of the cell. It should be mentioned here that the spread (ice front) on the skin surface can easily be figured out by visual inspection but the penetration depth and the necrotic zone below the skin surface can not be measured, rather it is assessed by the surgeons based on their experience. This makes the process more surgeon’s oriented rather than making it a comprehensive method. Therefore, understanding each and every aspect of the cryospray process becomes extremely important. The amount of cooling (spread and penetration depth) produced by cryogen during the cryospray depends on its interaction with the surrounding and the tissue. Cryogen sprays are different from liquid sprays in which mechanical forces cause the atomization of liquid. The saturation temperature of cryogens are much lower than the ambient temperature, therefore flashing occurs in the cryogen as they interact with the surrounding. Flashing causes primary atomization of the droplets. A secondary break up occurs due to surface tension of the droplets and the velocity difference between the two phases. Thus, during its (cryogen) flight from nozzle exit to cooling surface, cryogen exchanges heat and mass with the surrounding. Further downstream, the liquid nitrogen droplets interact with the tissue initiating a change of phase from water to ice where necrosis occurs. The fate of the cancerous cell will be decided by the cooling provided by the liquid nitrogen droplets. In comparison to the spray interacting with a solid, the cryospray process is quite complex. The problem involves multi-phase fluids with phase changes from liquid to vapour and liquid to solid. Also, the presence of atomization with phase change makes this process more complicated. Till now, none of the researchers have addressed this issue. Therefore, following points will be explored in this project: • Characterization of liquid nitrogen spray interacting with the surrounding during cryospray process • Numerical study of interaction of liquid nitrogen droplets with the surrounding during cryospray process • Studying heat transfer characteristics of liquid nitrogen interacting with the tissue mimicking gel (a phase change material) • Studying effect of customized multihole nozzle (developed by the investigator) on the spray characteristics and the cryospray outcomes