A freezing vessel for a freeze drying system that forms freeze dried product in powder form, comprising: an inner circumferential wall defining a freezing chamber; a top wall including at least one nozzle having a nozzle outlet end that sprays fluid product drops that flow downward into the freezing chamber; an outer circumferential wall spaced apart from the inner circumferential wall to form a cavity between the inner and outer walls wherein a lower end of the inner wall defines a freezing chamber outlet; a cavity outlet that extends from the outer wall, wherein the cavity outlet is in fluid communication with the cavity; a cavity inlet that extends from a location on the outer wall that is lower than a location of the cavity outlet, wherein the cavity inlet is in fluid communication with the cavity and wherein a cooling fluid enters the cavity through the cavity inlet and flows through the cavity at a first flow rate and is discharged from the cavity through the cavity outlet to form a freezing zone having a freezing zone temperature between the cavity inlet and the cavity outlet wherein the fluid product drops freeze in the freezing zone andform frozen product particles that exit the freezing chamber outlet; the freezing vessel being characterized by further comprising: a temperature sensor that detects an outlet temperature of the cooling fluid discharged at the cavity outlet, wherein the outlet temperature is indicative of the freezing zone temperature and wherein the freezing vessel is configured to adjust the first flow rate of the cooling fluid to increase or decrease the freezing zone temperature to obtain a setpoint temperature detected by the temperature sensor to maintain a freezing zone temperature suitable for forming the frozen product particles. an inner circumferential wall defining a freezing chamber; a top wall including at least one nozzle having a nozzle outlet end that sprays fluid product drops that flow downward into the freezing chamber; an outer circumferential wall spaced apart from the inner circumferential wall to form a cavity between the inner and outer walls wherein a lower end of the inner wall defines a freezing chamber outlet; a cavity outlet that extends from the outer wall, wherein the cavity outlet is in fluid communication with the cavity; a cavity inlet that extends from a location on the outer wall that is lower than a location of the cavity outlet, wherein the cavity inlet is in fluid communication with the cavity and wherein a cooling fluid enters the cavity through the cavity inlet and flows through the cavity at a first flow rate and is discharged from the cavity through the cavity outlet to form a freezing zone having a freezing zone temperature between the cavity inlet and the cavity outlet wherein the fluid product drops freeze in the freezing zone andform frozen product particles that exit the freezing chamber outlet; the freezing vessel being characterized by further comprising: a temperature sensor that detects an outlet temperature of the cooling fluid discharged at the cavity outlet, wherein the outlet temperature is indicative of the freezing zone temperature and wherein the freezing vessel is configured to adjust the first flow rate of the cooling fluid to increase or decrease the freezing zone temperature to obtain a setpoint temperature detected by the temperature sensor to maintain a freezing zone temperature suitable for forming the frozen product particles.