Heat Exchangers & Overall Heat Transfer This quiz covers concepts like LMTD, NTU, effectiveness, and overall heat transfer coefficient, helping you understand the working principles of parallel flow, counter flow, and shell-and-tube heat exchangers. Ideal for students preparing for thermal engineering exams and real-world applications. 1 / 20 In a double-pipe heat exchanger, heat transfer is mainly by Conduction and convection Only conduction Only radiation Convection and radiation Heat passes through pipe walls by conduction and by convection in fluids. 2 / 20 The effectiveness of a parallel flow heat exchanger is always Zero Equal to counter flow More than counter flow Less than counter flow Counter flow allows larger temperature difference and higher effectiveness. 3 / 20 Increasing flow velocity in a heat exchanger Has no effect Increases fouling Increases heat transfer coefficient Decreases heat transfer coefficient Higher velocity improves turbulence, enhancing convection. 4 / 20 The ratio of actual heat transfer to maximum possible heat transfer is Effectiveness Efficiency Conductivity Capacity ratio It measures actual exchanger performance relative to ideal. 5 / 20 Fouling in a heat exchanger Decreases heat transfer Increases heat transfer Has no effect Reduces flow resistance Deposits form thermal resistance, lowering efficiency. 6 / 20 For two fluids with equal mass flow rate and specific heat, the temperature change will be Equal Zero Double for cold fluid Half for hot fluid Equal capacities result in equal temperature changes. 7 / 20 Fins are used in heat exchangers to Reduce turbulence Increase thermal resistance Increase heat transfer area Decrease heat transfer rate Fins enlarge the area for better convection heat transfer. 8 / 20 A regenerative heat exchanger works by Changing phase Storing heat temporarily Using cooling water Mixing both fluids It stores heat from hot fluid and releases it to cold fluid alternately 9 / 20 The value of overall heat transfer coefficient is highest for Free convection Radiation Condensation Convection Condensation offers very high film coefficients leading to large U values. 10 / 20 In a shell-and-tube heat exchanger, baffles are used to Support the tubes only Reduce heat transfer Guide fluid in straight path Increase turbulence and heat transfer Baffles improve fluid mixing and enhance heat transfer rates 11 / 20 The overall heat transfer coefficient depends on Individual film coefficients and wall resistance Flow rate only Temperature only Density of fluids U is influenced by convection, conduction, and fouling resistances. 12 / 20 NTU stands for Normal Thermal Unit Number of Transfer Units Nominal Transfer Utility Net Transfer Usage NTU indicates the size and performance capability of a heat exchanger. 13 / 20 The effectiveness of a heat exchanger depends on NTU and capacity ratio Only mass flow rate Only temperature Only material Effectiveness increases with NTU and depends on heat capacity rates of fluids. 14 / 20 In a counter flow heat exchanger, LMTD is Zero Equal to parallel flow Less than parallel flow Greater than parallel flow Counter flow arrangement has higher temperature difference, improving efficiency. 15 / 20 The unit of overall heat transfer coefficient (U) is W/m²·K W/m·K W/m³·K J/m²·s It represents total heat transfer per unit area per unit temperature difference. 16 / 20 The Log Mean Temperature Difference (LMTD) is used to calculate Velocity of fluid Rate of heat transfer Mass flow rate Fluid pressure LMTD represents the average driving temperature difference across the exchanger. 17 / 20 The performance of a heat exchanger is usually measured by Effectiveness Pressure drop Temperature difference Flow velocity Effectiveness shows how well a heat exchanger transfers heat. 18 / 20 In a counter flow heat exchanger, the fluids move In circular paths In opposite directions In the same direction Perpendicular to each other Counter flow gives maximum temperature difference and efficiency. 19 / 20 In a parallel flow heat exchanger, both fluids Flow in opposite directions Remain stationary Flow perpendicular Flow in the same direction In parallel flow, hot and cold fluids move parallel and in the same direction. 20 / 20 The main function of a heat exchanger is to Transfer heat between two fluids Store heat energy Increase pressure of fluid Reduce fluid friction A heat exchanger allows thermal energy transfer without mixing fluids. Your score isThe average score is 0% 0% Restart quiz
