The main idea that I would like you to get from this set of notes is that convection currents are a swirling motion of a fluid that needs a heat source and a cold source to work. The rest of the notes will deal with supporting this idea and giving some examples of convections currents here on earth.

Once the earth collects enough material it will start to get so heavy that it compresses inward toward the center of gravity a lot. This smashing of the atoms of rock causes them to get really hot. Radioactive atoms are also giving of energy. The combination of the two heat sources made the earth so hot that it turned into a molten ball of rock. The fact that everything turned into a liquid allowed the heaviest material to sink to the center of the earth. This forces lighter material out of the way, eventually placing it on the outside edge of the earth and heaviest material on the inside of the earth. The fact that these layers have been created is actually what allows convection currents to form in the first place.

The layers cause specific material, radioactive material, to be concentrated in the center of the earth. This is important because a concentrated heat source is needed to get convection currents to work. If the heat were spread out all over the place, there would be no place for the heated magma to go. When the core gives off the heat energy from radioactive decay and compression, it excites the electrons of the magma nearby. The atoms of magma will push away from each other as the electrons jump to new energy levels. This makes the magma near the core much more spread out and lighter than the rest of the magma around it. Gravity pulls on the denser magma harder than the lighter magma. So the denser goes down towards the core and forces the lighter magma out of the way so that it goes up towards the surface of the earth. However, if the earth were not layered there wouldn't be a...

...of warm water is placed on top of the cold water, the more dense cold water stays in the bottom bottle and the less dense warm water is confined to the top bottle. However, when the cold water bottle rests on top of the warm water, the less dense warm water rises to the top bottle and the cold water sinks. The movement of water is clearly seen as the yellow and blue food coloring mix, creating a green liquid. Likewise, when the water mixes in the Split Demo Tank, the less dense, cold water stays on the bottom of the tank, and the more dense, warm water moves to the top.
The movement of warm and cold water inside the bottles (or tank) is referred to as the convectioncurrent. In our daily life, warm currents can occur in oceans, like the warm Gulf Stream moving up north along the American Eastern Seaboard. Convectioncurrents in the atmosphere are responsible for the formation of thunderstorms as the warm and cold air masses collide.
Although the bottles whose colored liquids mix are more interesting to watch, the other set of warm and cold water bottles helps to illustrate another important phenomenon that occurs in the atmosphere during the winter months. During daylight hours, the sun heats the surface of the earth and the layer of air closest to the earth. This warm air rises and mixes with other atmospheric gases. When the sun goes down, the less dense warm air high up in the atmosphere often...

...3rd Year Thermodynamics Lab Report
Mechanical Engineering Science 10
Forced Convection (in a cross flow heat exchanger)
Summary
The aim of this lab is to determine the average convective heat transfer coefficient for forced convection of a fluid (air) past a copper tube, which is used as a heat transfer model.
Introduction
The general definition for convection may be summarized to this definition "energy transfer between the surface and fluid due to temperature difference" and this energy transfer by either forced (external, internal flow) or natural convection.
Heat transfer by forced convection generally makes use of a fan, blower, or pump to provide high velocity fluid (gas or liquid). The high-velocity fluid results in a decreased thermal resistance across the boundary layer from the fluid to the heated surface. This, in turn, increases the amount of heat that is carried away by the fluid. [1]
Theory Background [2]
Considering the heat lost by forced convection form the test rod. The amount of heat transferred is given by
(1)
Where
= rate of heat transfer, unknown value.
= film heat transfer coefficient, this is what we need to found out.
A = area for heat transfer, this is the area of the cross section area of test section.
T = temperature of the copper rod, the temperature after heating.
Ta = temperature of...

...Forced Convection Heat Transfer
I. Introduction
This laboratory deals with forced convection, forced convection can be considered as a staple of heat transfer. That is to say that forced convection can be found in almost any heat transfer problem, and thus understanding its importance and how it affects a given problem is one of the more important learning objectives/outcomes of heat transfer.
When dealing with forcedconvection the most important section, after understanding how convection works, is the convection heat transfer coefficient. The heat transfer coefficient for convection is denoted by (h) and is measured in w/m^2*K, this lab delves into the application of convection heat transfer and how it correlates to temperature, velocity, ect of the fluid in question.
II. Objectives
The objectives for this laboratory include; determining the convective heat transfer coefficient and friction factor of the air flowing through a copper pipe, as well as evaluation of the Reynolds analogy and taking measurements of the radial velocity and temp profile in an internal pipe flow.
III. Procedure and Apparatus
-Apparatus
A fan forces air through a long pipe with an orifice plate along the way. Before the test section there is a reduction in diametrical area which will cause an increase in velocity and a decrease in pressure. It...

...Experiment 8 - Free & Forced ConvectionConvection Heat Transfer.doc
EXPERIMENT ON FREE AND FORCED CONVECTION HEAT TRANSFER 8.1 OBJECTIVES To study experimental data for heat transfer in order to evaluate the overall heat transfer coefficients and heat balances for the following cases of heat transfer in a .shell and tube heat exchanger. (a) Natural convection and (b) Forced convection. 8.2 THEORY A basic diagram of a shell and tube heat exchanger is shown in Figure 8.1. Here steam at a temperature of Tv is sent to the shell side at the port A at a rate of W kg/s. The steam transfers heat to a fluid at the tube side .The steam condenses during this process and leaves the shell side at the port B at a temperature Ts. The tube side fluid enters the heat exchanger at C with a flow rate of M kg/s at a temperature Ti and leaves at D at a temperature To. The heat loss QH from the steam can be expressed as QH = W(λ + CpH.(Tv-Ts)) Similarly, the heat gained by the tube side fluid QC can be expressed as QC= M.CpT. (Ti-To) The heat transfer coefficient for the shell side and tube side hH and hc can be estimated using QH = hH .ΔTM and QC = hC. ΔTM .
Page 1 of 15
Experiment 8 - Free & Forced ConvectionConvection Heat Transfer.doc
STEAM AT TV ENTER AT PORT A
TUBE SIDE FLUID ENTERS AT Ti
TUBE SIDE FLUID LEAVES AT To
CONDENSED STEAM LEAVES PORT B AT TEMPERATURE TS...

...experiment is to analyse the rate of heat transfer losses through convection and radiation separately from a cylindrical glass rod suspended in a pressure vessel. The variation of the dimensionless quantities; Nusselt number, Prandtl number and Grashof Number, with Pressure are to be analysed graphically as well. The experimental graph of log10(Nu) vs log10(Gr.Pr) should be plotted and analysed against the graph of the empirical equations.
2. Introduction:
2.1 Theoretical Background Information:
Heat can be transferred via three different methods: conduction in solids, convection of fluids (liquid or gases) and radiation (IPAC Caltec ). The method used to transfer heat is usually the one that is the most efficient. If there is a temperature difference in a system, heat will always move down the temperature gradient (i.e. from higher to lower temperatures).
Conduction is the movement of heat through a substance by the collision of molecules. At the place where the two object touch, the faster-moving molecules of the warmer object collide with the slower moving molecules of the cooler object. As they collide, the faster molecules give up some of their energy to the slower molecules. The slower molecules gain more thermal energy and collide with other molecules in the cooler object. This process continues until heat energy from the warmer object spreads throughout the cooler object. (IPAC Caltec )
Convection occurs when...

...Journal of HVAC&R Research, Vol. 9, No. 3, July 2003. This article may not be copied nor distributed in either paper or digital form without ASHRAE's permission.
VOL. 9, NO. 3
HVAC&R RESEARCH
JULY 2003
Impact of Mixed Convection on Ceiling Radiant Cooling Panel Capacity
Jae-Weon Jeong
Student Member ASHRAE
Stanley A. Mumma, Ph.D., P.E.
Fellow ASHRAE
The main thrust of the research described in this paper was to develop a simplified method of accurately estimating the impact of mixed convection on the cooling capacity of a ceiling radiant panel in mechanically ventilated spaces. The simplified correlation for mixed convection heat transfer was derived from established mixed and natural convection correlations. It was found that the total capacity of ceiling radiant cooling panels can be enhanced in mixed convection situations by 5% to 35% under normal operating temperatures.
INTRODUCTION
Currently, most ceiling radiant cooling panel (CRCP) performance estimates are based on natural convection only. This is reflected in ASHRAE (2000) literature, where the analysis is based upon the natural convection heat transfer work of Min et al. (1956), and the European CRCP capacity rating standard, DIN 4715 (1997), which uses natural convection as the test condition. However, Kochendörfer (1996) found that in real buildings, cooling outputs of CRCPs...

...FREESTUDY
HEAT TRANSFER
TUTORIAL 2
CONVECTION AND RADIATION
This is the second tutorial in the series on basic heat transfer theory plus some elements of advanced
theory. The tutorials are designed to bring the student to a level where he or she can solve problems
ranging from basic level to dealing with practical heat exchangers.
On completion of this tutorial the student should be able to do the following.
•
•
Explain the use of the surface heat transfer coefficient.
•
Explain the use of the overall heat transfer coefficient.
•
Combine convection and conduction theory to solve problems involving
flat, cylindrical and spherical surfaces.
•
Explain the basic theory behind radiated heat transfer.
•
Explain the affect of the emissivity and shape of the surface.
•
Calculate effective surface heat transfer coefficient.
•
(c) D. J. Dunn
Explain natural and forced convection.
Solve basic problems involving convection and radiation.
1
CONVECTIONConvection is the study of heat transfer between a fluid and a solid body. Natural convection occurs
when there is no forced flow of the fluid. Forced convection occurs when the fluid is forced to flow
over the object.
Consider a hot vertical surface placed in a cool fluid. The
molecules in contact with the surface will receive heat transfer
through the...

...External Forced Convection
4.1 Introduction to Laminar Boundary Layers 4.1.1 Introduction
Chapters 1 through 3 consider conduction heat transfer in a stationary medium. Energy transport within the material of interest occurs entirely by conduction and is governed by Fourier’s law. Convection is considered only as a boundary condition for the relatively simple ordinary or partial differential equations that govern conduction problems. Convection is the transfer of energy in a moving medium, most often a liquid or gas ﬂowing through a duct or over an object. The transfer of energy in a ﬂowing ﬂuid is not only due to conduction (i.e., the interactions between micro-scale energy carriers) but also due to the enthalpy carried by the macro-scale ﬂow. Enthalpy is the sum of the internal energy of the ﬂuid and the product of its pressure and volume. The pressure-volume product is related to the work required to move the ﬂuid across a boundary. You were likely introduced to this term in a thermodynamics course in the context of an energy balance on a system that includes ﬂow across its boundary. The additional terms in the energy balance related to the ﬂuid ﬂow complicate convection problems substantially and link the heat transfer problem with an underlying ﬂuid dynamics problem. The complete solution to many convection problems therefore requires sophisticated computational ﬂuid dynamic (CFD) tools that are...