Question 251. Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.

Question 252. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m².s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m²/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

Question 253. In pipe flow, heat is transferred from hot wall to the liquid by

Question 254. Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by

Question 255. In a cooling tower, water becomes cool by

Question 256. Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m²°C.

Question 257. LMTD for counterflow and prallel flow heat exchanger will be the same, when the

Question 258. In a shell and tube heat exchanger, floating head is used for

Question 259. What is the steam economy in case of a single effect evaporator system?

Question 260. Graetz number is given by