Question

1. Over 14 million units of red blood cells are transfused per year in the US. The vast majority of these blood units are stored in a refrigerated state, which yields a shelf life of 6 weeks. The requirement for refrigeration and the short shelf life of blood in the refrigerated state makes it difficult to maintain an adequate blood supply. An alternative that is currently being investigated is room temperature storage in the dry state. Your task is to design a spray dryer for bringing a red blood cell suspension to the dry state. For effective preservation, the dried sample must contain no more than 5% moisture by mass. The blood being fed to the spray drier contains 30% solids by mass and the density of blood is 1.06 kg/L. The blood is fed at 100 ml/min and air is fed at 110°C and an absolute humidity of 0.01 kg/kg dry air. You may assume that the air and the dried solids are at equilibrium at the outlet and that a moisture content of 5% in the solids corresponds with a relative humidity of 20%. The process may be assumed to operate adiabatically. Hint: Perry's Chemical Engineers Handbook has psychrometric charts over a wider range of dry bulb temperatures than your textbook. a. What is the temperature at the outlet of the drier? b. What mass flow rate of dry air must be fed to the drier? c. If it takes 30 seconds for the liquid droplets to achieve adequate drying, what volume should be used for the drying chamber?

Answer 1