
What is natural convection? How does it differ from forced convection? What force causes natural convection currents?

The meaning of natural convection, the difference between the natural and forced convections and the force causing natural convection currents.
Explanation of Solution
Introduction:
There are three modes of heat transfer:
- Conduction
- Convection
- Radiation
The convection heat transfer is associated to heat transfer in fluids (liquid and gases) in which there is physical movement of fluid particles. On the basis offorce responsible for the physical movement of fluid particles, the convection is classified as natural and forced convection.
Natural Convection: The convection heat transfer process in which the bulk movement of fluid particles is observed due to density variations arising out of temperature difference is called the natural convection. The difference in temperature causes variation in different fluid layers, and this density variation facilitates movement of fluid particles without any aid of external force. There is no external force involved for the fluid motion.That is why it is referred as natural convection.
Forced Convection: When the movement of fluid particles is assisted by some external media such as fan, blower, pump, suction device, the heat transfer occurring in fluid is termed as forced convection. The forced convection results in better mixing and hence is faster and more efficient. The mild forces like buoyancy and gravity do not play any role in forced convection and the heat transfer process is dominated by the external force.
Forced convection caused by fan
The main difference between the natural and forced convection is the presence of external force. If the external force is present in heat transfer process, it is termed as forced convection, otherwise the convection heat transfer process is natural convection.
The force which play role in natural convection are buoyancy and gravity. The gravity becomes dominant in liquids which helps in producing the natural currents of heat transfer. The heated particles become less dense, they tend to move upward, and cold heavy particles move downward due to gravity, resulting in formation of natural currents. These natural currents are responsible for natural convection.
Want to see more full solutions like this?
Chapter 9 Solutions
Heat and Mass Transfer: Fundamentals and Applications
Additional Engineering Textbook Solutions
Starting Out with Python (4th Edition)
Experiencing MIS
SURVEY OF OPERATING SYSTEMS
Thermodynamics: An Engineering Approach
Automotive Technology: Principles, Diagnosis, And Service (6th Edition) (halderman Automotive Series)
Vector Mechanics for Engineers: Statics and Dynamics
- Calculate the forces in all members of the truss shown using either the method of joints or the method of sectionsarrow_forward20-4-2025 Exam-2-Tribology Q1: What are the assumptions of hydrodynamic lubrication theory: Q2: Explain with sketch the cycle or process of engine lubrication system-pressurized lubrication system Q3: A short bearing is designed to operate with an eccentricity ratio = 0. 7. The journal diameter is 60 mm, and its speed is 1300 r.p.m. The journal is supported by a short hydrodynamic bearing of length L/D = 0. 5, and clearance ratio C/R = 103. The radial load on the bearing is 9800 N. a. Find the Sommerfeld number. b. Find the minimum viscosity of the lubricant for operating at ε = 0.7 c. Select a lubricant if the average bearing operating temperature is 70°c Q4: Two parallel circular disks of 100 mm diameter have a clearance of Imm between them. Under load, the downward velocity of the upper disk is 2 m/s. At the same time, the lower disk is stationary. The clearance is full of SAE 40 oil at a temperature of 60°c. a. Find the load on the upper disk that results in the instantaneous…arrow_forwardTribobolgy 15/2022 Monthly Exam. Automobile Eng. Dert 2nd Semster/3rd class Max. Mark: 100% 7. Viscosity of multi-grade oils (a) Reduces with temperature (c) is less sensitive to temperature (b) Increases with temperature (d) None of the above 8. In a hydrodynamic journal bearing if eccentricity ratio = 1, it means (a) Journal/shaft is subjected to no load and the rotational speed is very high. (b) Journal is subjected to no load and the rotational speed is moderate (c) Journal is subjected to very light load and the rotational speed is very high. (d) Journal is subjected to very high load and the rotational speed is negligible. Q4/ The journal speed of a 100mm diameter journal is 2500 rpm. The journal is supported by a short hydrodynamic bearing of length L=0.6D, eccentricity ratio = 0.75 and a clearance ratio C/R=0.001. The radial load on the bearing is 10 kN. The lubricant is SAE 30, and the operating temperature of the lubricant in the bearing is 700C. 1- Assume…arrow_forward
- 1 of 2 Monthly Exam. Automobile Eng. Dert 2nd Semster/3rd class Max. Mark: 100% Q1/A/ Compare between the long and short journal bearings B/ With the help of Stribeck's curve, discuss different regimes of lubrication. C/ Explain the importance of Tribology in the design of different machine elements Q2 /A/ According to the SAE viscosity grading system all engine oils are divided into two classes: monograde and multi-grade. Compare between them? B/What are the differences between grease and Synthetic oils C/ Explain the effect of eccentricity ratio & with respect to hydrodynamic journal bearing. Q3/A/ What are the major factors which affect the selection of lubricants? B/What are the criteria to classify sliding bearings? C/ Answer of the following: 1. According to the SAE viscosity classification, the oil (SAE 40) is lower viscosity than the oil (SAE 20) at the same temperature. (True or False) 2. For a slow speed-highly loaded bearing, used oils of high viscosity; while for high-speed…arrow_forwardThe uniform rods have a mass per unit length of 10kg/m . (Figure 1)If the dashpot has a damping coefficient of c=50N⋅s/m , and the spring has a stiffness of k=600N/m , show that the system is underdamped, and then find the pendulum's period of oscillation.arrow_forward10-50. The principal plane stresses and associated strains in a plane at a point are σ₁ = 30 ksi, σ₂ = -10 ksi, e₁ = 1.14(10-3), €2=-0.655(103). Determine the modulus of elasticity and Poisson's ratio. emps to plum... Wednesday FI a וח 2 Q Search 48 F5 - F6 4+ F7 FB F9 FIO FII F12 & * S 6 7 8 9 ㅁ F2 # *F3 3 $ 4 F4 % W E R T Y ப S ALT D F G H X C V B N J Σ H L ว { P [ ] ALT " DELETE BACKSPACE NUM LOCK T 7 HOME ENTER 4 PAUSE SHIFT CTRL Earrow_forward
- 10−9. The state of strain at the point has components of ϵx = −100(10−6), ϵy = −200(10−6), and γxy=100(10−6). Use the strain transformation equations to determine (a) the in-plane principal strains and (b) the maximum in-plane shear strain and average normal strain. In each case specify the orientation of the element and show how the strains deform the element within the x−y plane.arrow_forwardThe strain gage is placed on the surface of the steel boiler as shown. If it is 0.5 in. long, determine the pressure in the boiler when the gage elongates 0.2(10−3) in. The boiler has a thickness of 0.5 in. and inner diameter of 60 in. Also, determine the maximum x, y in-plane shear strain in the material. Take Est=29(103)ksi, vst=0.3.arrow_forward(read image, answer given)arrow_forward
- 6/86 The connecting rod AB of a certain internal-combustion engine weighs 1.2 lb with mass center at G and has a radius of gyration about G of 1.12 in. The piston and piston pin A together weigh 1.80 lb. The engine is running at a constant speed of 3000 rev/min, so that the angular velocity of the crank is 3000(2)/60 = 100л rad/sec. Neglect the weights of the components and the force exerted by the gas in the cylinder compared with the dynamic forces generated and calculate the magnitude of the force on the piston pin A for the crank angle 0 = 90°. (Suggestion: Use the alternative moment relation, Eq. 6/3, with B as the moment center.) Answer A = 347 lb 3" 1.3" B 1.7" PROBLEM 6/86arrow_forward6/85 In a study of head injury against the instrument panel of a car during sudden or crash stops where lap belts without shoulder straps or airbags are used, the segmented human model shown in the figure is analyzed. The hip joint O is assumed to remain fixed relative to the car, and the torso above the hip is treated as a rigid body of mass m freely pivoted at O. The center of mass of the torso is at G with the initial position of OG taken as vertical. The radius of gyration of the torso about O is ko. If the car is brought to a sudden stop with a constant deceleration a, determine the speed v relative to the car with which the model's head strikes the instrument panel. Substitute the values m = 50 kg, 7 = 450 mm, r = 800 mm, ko = 550 mm, 0 = 45°, and a = 10g and compute v. Answer v = 11.73 m/s PROBLEM 6/85arrow_forwardUsing AutoCADarrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY





