Exercise 1. Heating a fermentation medium. A fermentation liquid with a temperature of 30 °C is pumped at a speed of 2000 kg/h through a heating unit where the liquid is heated to 70 °C under pressure. The fermentation liquid is partially heated by waste water passing through the unit. The waste water enters at a temperature of 95 °C and exits at a temperature of 85 °C. The average heat capacity for the fermentation liquid is 4.06 kJ kg-1K-1. The waste water used for heating has a heat capacity of 4.21 kJ kg-1K-1. Fermentation liquid and the water are separated by a metal surface where heat is transferred, but the liquids are not in physical contact with each other. Set up an energy balance for the system. Calculate the flow rate of water and the amount of heat supplied to the fermentation liquid. Assume that no heat loss occurs in the process. (Answer: 7715 kg/h; 90.25 kW)
Exercise 1. Heating a fermentation medium.
A fermentation liquid with a temperature of 30 °C is pumped at a speed of 2000 kg/h through a heating unit where the liquid is heated to 70 °C under pressure. The fermentation liquid is partially heated by waste water passing through the unit. The waste water enters at a temperature of 95 °C and exits at a temperature of 85 °C. The average heat capacity for the fermentation liquid is 4.06 kJ kg-1K-1. The waste water used for heating has a heat capacity of 4.21 kJ kg-1K-1. Fermentation liquid and the water are separated by a metal surface where heat is transferred, but the liquids are not in physical contact with each other. Set up an energy balance for the system. Calculate the flow rate of water and the amount of heat supplied to the fermentation liquid. Assume that no heat loss occurs in the process.
(Answer: 7715 kg/h; 90.25 kW)
Original text (norwegian):
Oppgave 1. Oppvarming av et fermenteringsmedium.
En fermenteringsvæske med temperatur 30 °C pumpes med hastighet 2000 kg/h gjennom en oppvarmingsenhet der væsken varmes til 70 °C under trykk. Fermenteringsvæsken varmes delvis ved avløpsvann som går gjennom enheten. Avløpsvannet går inn med temperatur 95 °C og ut med temperatur 85 °C. Gjennomsnittlig varmekapasitet for fermenteringsvæsken er 4,06 kJ kg-1K-1. Avløpsvannet som brukes til oppvarming har varmekapasitet 4,21 kJ kg-1K-1. Fermenteringsvæske og vannet er separert med en metalloverflate der det overføres varme, men væskene er ikke i fysisk kontakt med hverandre. Sett opp en energibalanse for systemet. Beregn strømningshastigheten for vann og varmemengden som tilføres fermenteringsvæsken. Anta at det ikke skjer noe varmetap i prosessen.
(Svar: 7715 kg/h; 90,25 kW)
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