Exhaust Port Challenge
Exhaust Port Challenge
Part A
Conjugate Heat Transfer
The term conjugate heat transfer is used to describe processes which involve variations of temperature within solids and fluids, due to thermal interaction between the solids and fluids. A typical example is the heating or cooling of a solid object by the flow of air in which it is immersed.
Benefits:
CHT analysis is beneficial in accurately predicting the surface temperature and heat exchanging capabilities of the engineering devices. Through the analysis engineers can optimize thermal the thermal characteristics for their chosen product design.
It can be used for following reasons-
- Measurement of heat transfer through conduction in solid regions.
- Identification of fluid flow parameter around the solid domain.
- To understand heat transfer capabilities of the products.
- Design and improve the quality of heat transfer rate and cooling capacity.
APPLICATION-
1. Effective Heat Transfer
Efficiently combining heat transfer in fluids and solids is the key to designing effective coolers, heaters, or heat exchangers.
The fluid usually plays the role of energy carrier on large distances. Forced convection is the most common way to achieve high heat transfer rate. In some applications, the performances are further improved by combining convection with phase change (for example liquid water to vapor phase change).
Even so, solids are also needed, in particular to separate fluids in a heat exchanger so that fluids exchange energy without being mixed.
2. Energy Savings
Heat transfer in fluids and solids can also be combined to minimize heat losses in various devices. Because most gases (especially at low pressure) have small thermal conductivities, they can be used as thermal insulators… provided they are not in motion. In many situations, gas is preferred to other material due to its low weight. In any case, it is important to limit the heat transfer by convection, in particular by reducing the natural convection effects. Judicious positioning of walls and use of small cavities helps to control the natural convection. Applied at the micro scale, the principle leads to the insulation foam concept where tiny cavities of air (bubbles) are trapped in the foam material (e.g. polyurethane), which combines high insulation performances with light weight.
3. Fluid and Solid Interactions
The temperature field and the heat flux are continuous at the fluid/solid interface. However, the temperature field can rapidly vary in a fluid in motion: close to the solid, the fluid temperature is close to the solid temperature, and far from the interface, the fluid temperature is close to the inlet or ambient fluid temperature. The distance where the fluid temperature varies from the solid temperature to the fluid bulk temperature is called the thermal boundary layer.
Natural Convection
The natural convection regime corresponds to configurations where the flow is driven by buoyancy effects. Depending on the expected thermal performance, the natural convection can be beneficial (e.g. cooling application) or negative (e.g. natural convection in insulation layer).
Part B
CHT ANALYSIS ON EXHAUST PORT
CASE-1
Baseline Mesh
- Node- 27371
- Element-137236
- Size Element-150 mm
Result-
Temperature contour
Velocity Streamline
Velocity at throat
Wall Heat transfer coefficient
Case 2-
Refined mesh with inflation layers
Node-169602
Element-478988
Mesh picture
Result
Temperature contour
Velocity Streamline
Velocity at throat
Wall Heat transfer coefficient
From table we observe that finer mesh accurate the value due more element interpolation and velocity increase the higher the Reynold number which in turn increase heat transfer coefficient.
PART C
Verification of Result-
Result can be verification by calculating Nusselts number and heat transfer coefficient and compare with simulated plots.
Factors affecting-
- Number of meshes elements- as above table suggested finer the mesh better the result
- Inflation layer-it provide a body fit condition which provide more accurate result.