Recent content by jt316

Yeah, that would probably work but I think I can I use the lumped method to determine just the time it takes for the center of the (non flowing) water to reach the freezing temperature. Which would be my t_c (time to cool the water to its freezing temp). I think the lumped method would...

So you're saying that I should probably not use the same heat rate in the freezing time as I used in the cooling time because of the smaller delta T?... makes sense. I'll try that. I'm sure that will make the freezing time longer because of the smaller heat rate. Isn't the change in...

Ah... so you think this is a homework problem? I was wondering why no one was responding to the problem... I am a mechanical engineer and this is actually a design related problem. We are in the design phase of a project that requires the installation of a cooling tower and 18 inch water...

I don't think that can use the lumped capacitance method when dealing with a phase change so I've tried another approach... Is this the correct method? I calculated the surface heat transfer coefficient (h) by h=\frac{N_u * k_f}{D_o}, where k_f= thermal conductivity of air Then I...

I don't think that can use the lumped capacitance method when dealing with a phase change so I've tried another approach... Is this the correct method? I calculated the surface heat transfer coefficient (h) by h=\frac{N_u * k_f}{D_o}, where k_f= thermal conductivity of air Then I...

I've attached an ASHRAE example where they are calculating the time to freeze orange juice in a 1ft diameter container. I used a similar calculation but with using the properties of water. Now that I look at their result for the orange juice it is ~17hrs... and the thermal conductiviy and heat...

I did the calc. again and took into consideration the conduction through the pipe wall and found a new "overall" heat transfer value of around ~11.2 \frac{W}{m^2 K} So it went from around ~10.5 \frac{W}{m^2 K} to ~11.2 \frac{W}{m^2 K} and the new time is 8.2 hrs... Any idea if this is the...

I posted this in another section and haven't receive any feedback so I thought I might have it in the wrong section. Thanks in advance for any help. I'm at little rusty on my heat transfer and could use some help. I'm trying to calculate the approximate time to freeze standing water in a...

I'm at little rusty on my heat transfer and could use some help. I'm trying to calculate the approximate time to freeze standing water in a 18inch steel pipe. I have some parameters and made some assumptions and they are: The pipe is 18inch carbon steel The standing water is initially...

I'll try to find that book. Thanks again for the help.

I see what I'm doing wrong. I was trying to put the boundry conditions into y(x) and y'(x) instead of puting those two into the boundry conditions. B= 1/cos(1) Thanks for the help oh yeah [I hope it's the last question :) ] but how did you find the general solution to y''(x) + y(x)=0...

I see where I was messing up. I found y(1),y(-1),y'(1) & y'(-1) but I was trying to plug the boundry conditions into these equations instead of pluging these into my boundry conditions. Thanks for the insight.

If y(x) = Acos(x) + Bsin(x) y'(x) = Bcos(x) - Asin(x) y''(x) = -Acos(x) - Bsin(x) y(1)= - y(-1) y'(1) = 2-y'(-1) but I'm still not sure about this type of boundry condition...

am not sure how to apply this type of boundry condition

I don't think that the solution I am looking for has the integral expression in it. I think that we can find a solution from only: y''(x) +y(x)=0 with BC's of: y(1)+y(-1)=0 y'(1)+y'(-1)=2 I just don't know exactly how to do that.. I can tell that you have a great...