Post Time: 20 April 2018
It is well known that the water content of most of fruits and vegetables is higher than 80%; it is perishable quickly. Dehydrate fruits and vegetables instead of fresh material cold storage are alternative method to extend their shelf-life and are more popular as suppling nutritional value of vitamins, minerals, fiber and low fat.
In the process of drying, heat is required to evaporate moisture from the product and a flow of air to carry away the evaporated moisture, making drying a high energy consuming operation ((FAO, 1994).
Heat pump drying has the ability to recover the latent and sensible heat by condensing moisture from the drying air (Jangam & Mujumdar, 2010). The recovered heat is recycled back to the dryer through heating of the dehumidified drying air hence the energy efficiency is increased substantially as a result of heat recovery which otherwise is lost to the atmosphere in conventional dryers (Current Concerns 2009). This enables drying at lower temperatures, lower cost and operation even under humid ambient conditions.
One improvement that heat pump has over other heat sources for drying is that it can be applied to any kind of dryer. Any dryer that uses convection as the primary mode of heat input can be fitted with a suitably designed heat pump but dryers that require large amounts of drying air e.g. flash or spray dryers are not suited for HP operation (Jangam & Mujumdar, 2010).
A heat pump is attractive because it can deliver more energy as heat than the electrical energy it consumes. Also it can use modified atmospheres to dry sensitive materials like fruits and vegetables.