Question

Grape juice at a rate of 3 kg/s is concentrated in a single effect evaporator from 18% to 23% solids content. calculate a) the product flow rate, b) the evaporation rate, c) the steam consumption, d) the steam economy, and e) the required heat transfer area of the evaporator if the juice enters the evaporator at 50 ºc, the juice boils in the evaporator at 50 ºc, saturated steam at 100 ºc is used as heating medium, the condensate exits at 100 ºc, the heat capacity of the juice is 3.7 kj/kg ºc and 3.6 kj/kg ºc at the inlet and the outlet of the evaporator respectively, and the overall heat transfer coefficient is 1500 w/m2ºc.

Answer 1

To calculate the product flow rate, evaporation rate, steam consumption, steam economy, and the required heat transfer area in an evaporator concentrating grape juice, one needs to establish mass and heat balances and apply energy equations considering the properties of the juice and steam.

Step-by-step explanation:

Calculations for the Evaporation of Grape Juice

To calculate the various aspects of the evaporator's operation when grape juice is concentrated from 18% to 23% solids content, several steps need to be followed:

1. Product Flow Rate: First, we need to establish the mass balance around the evaporator. Since the solids are conserved in the process, we can equate the mass of solids entering and leaving the system.
2. Evaporation Rate: This is computed based on the mass balance of water in the system, which involves the original and final mass concentrations of the juice.
3. Steam Consumption and Steam Economy: These can be determined by considering the heat balance across the system and the latent heat of evaporation for steam.
4. Required Heat Transfer Area: This is calculated using the overall heat transfer coefficient and requires an energy balance equation to find out the amount of heat that needs to be transferred to evaporate the water.

Note: The specific calculations are not provided here due to the lack of complete information, such as the latent heat of evaporation for the juice and the heat of vaporization for the steam.