Homework, Quizzes, Simulation Examples — Convection

Simulation Examples

Several simulation examples are provided here. Each of them comes with a description file, video instruction, and Ansys simulation file. All of the simulations are conducted using Ansys software. Download the student version of Ansys simulation software here.

(1) Laptop With a Heat Sink

To avoid overheating of a laptop, engineers need to appropriately design for heat absorption and heat dissipation to the open air. A heat sink helps to achieve these goals. In this simulation, we use a simplified laptop geometry to study the effects of a heat sink in cooling down a laptop. Download the zip file and extract the contents. Go through the Readme file. Follow along with the provided How To video file.

(2) Water-Cooled Heat Sink

Water-cooled heat sinks are preferred because of their high efficiency, low electricity consumption and quiet operation. In this problem, a type of thermal–fluid coupled element is used to simulate the fluid convection effect for a heat sink. Such elements are applied to line geometries with assigned cross-sections. The mass flow rate is needed to define the velocity of the liquid. For convection between a fluid body and a solid body, the bulk temperature is not a parameter that engineers input — it is calculated based on the fluid flow. In this homework example, you should:

(a) Learn how the thermal—fluid coupled element is defined for this conduction—based solver. Try different mass flow rates to see the difference in the results.

(b) Learn how the convection between a fluid and a solid body is defined and understand why it works as it does.

(c) Two geometry files are provided. One is a heat sink with a water pipe, the other is  the same heat sink without the water pipe. Complete both analyses and compare the results.

Download the zip file and extract the contents. Go through the Readme file. Follow along with the provided How To video file.

Homework

(1) Cooling of a Gingerbread Cookie

When we bake cookies, we generally have to wait a few minutes for the cookies to cool down before we can enjoy them. The cookies lose heat to the surrounding air through convection. In this example, we try out two methods of cooling a cookie and see which is faster.

In the first method, we place the cookies on a cooling rack and put them in the fridge. The temperature inside the fridge is generally maintained at 4°C. Since the convection inside the fridge is natural convection, we assume a film coefficient of 2 W/m² °C. In the second method, the cookies are kept on the kitchen table, but a fan is used to cool them. Assume that the film coefficient for forced convection of air is 20 W/m² °C and that the room temperature is 25°C. Let's say the density of the cookies is 50 kg/m³, its thermal conductivity is 0.3 W/m °C, its specific heat is 2000 J/kg °C and the temperature of the cookies is 230 °C (uniform) when the cookies are taken out of the oven.

To simplify the problem, let's neglect the conduction between the cookie and the cooling rack (since a meshed cooling rack has a very small area in contact with the cookie as compared to the area of the cookie where convection occurs). Also, assume that the convection is the same on the top and bottom faces of the cookie. If the cookies taste best at 30°C, which of the two methods will allow us to enjoy the cookies earlier?

Download the zip file and extract the contents. Go through the Readme file. Follow along with the provided How To video file.