A vertical tubular condenser is to be used to condense 2,100 kg/h of ethyl alcohol. which enters at atmospheric pressure. Cooling water is to flow through the tubes at an average temperature of 30°C. The tubes are 31-mm OD and 27-mm ID. The water-side coefficient is 2,800 W/m²·°C. Fouling factors and the resistance of the tube wall may be neglected. If the available tubes are 3 m long, how many tubes will be needed? Data are as follows: 

Boiling point of alcohol:         T_h = 78.4°C

Heat of vaporization:              λ = 856 J/g

Density of liquid:                     ρ_ƒ = 769 kg/m³